Effect of initial ammonium concentration on a one-stage partial nitrification/anammox biofilm system: Nitrogen removal performance and the microbial community

One-stage partial nitrification coupled with anammox (PN/A) technology effectively reduces the energy consumption of a biological nitrogen removal system. Inhibiting nitrite-oxidizing bacteria (NOB) is essential for this technology to maintain efficient nitrogen removal performance. Initial ammonium concentration (IAC) affects the degree of inhibited NOB. In this study, the effect of the IAC on a PN/A biofilm was investigated in a moving bed biofilm reactor. The results showed that nitrogen removal efficiency decreased from 82.49% ± 1.90% to 64.57% ± 3.96% after the IAC was reduced from 60 to 20 mg N/L, while the nitrate production ratio increased from 13.87% ± 0.90% to 26.50% ± 3.76%. NOB activity increased to 1,133.86 mg N/m2/day after the IAC decreased, approximately 4-fold, indicating that the IAC plays an important inhibitory role in NOB. The rate-limiting step in the mature biofilm of the PN/A system is the nitritation process and is not shifted by the IAC. The analysis of the microbial community structure in the biofilm indicates that the IAC was the dominant factor in changes in community structure. Ca. Brocadia and Ca. Jettenia were the main anammox bacteria, and Nitrosomonas and Nitrospira were the main AOB and NOB, respectively. IAC did not affect the difference in growth between Ca. Brocadia and Ca. Jettenia. Thus, modulating the IAC promoted the PN/A process with efficient nitrogen removal performance at medium to low ammonium concentrations.

Constructing porous ZnFC-PA/PSF composite spheres for highly efficient Cs+ removal

Radioisotope leaking from nuclear waste has become an intractable problem due to its gamma radiation and strong water solubility. In this work, a novel porous ZnFC-PA/PSF composite sphere was fabricated by immobilization of ferrocyanides modified zinc phytate into polysulfone (PSF) substrate for the treatment of Cs-contaminated water. The maximum adsorption capacity of ZnFC-PA/PSF was 305.38 mg/g, and the removal efficiency of Cs+ was reached 94.27% within 2 hr. The ZnFC-PA/PSF presented favorable stability with negligible dissolution loss of Zn2+ and Fe2+ (< 2%). The ZnFC-PA/PSF achieved high-selectivity towards Cs+ (Kd = 2.24×104 mL/g) even in actual geothermal water. The adsorption mechanism was inferred to be the ion-exchange between Cs+ and K+. What's more, ZnFC-PA/PSF worked well in the fixed-bed adsorption (E = 91.92%), indicating the application potential for the hazardous Cs+ removal from wastewater.

Antibiotic ciprofloxacin removal from aqueous solutions by electrochemically activated persulfate process: Optimization, degradation pathways, and toxicology assessment

Ciprofloxacin (CIP) is a commonly used antibiotic in the fluoroquinolone group and is widely used in medical and veterinary medicine disciplines to treat bacterial infections. When CIP is discharged into the sewage system, it cannot be removed by a conventional wastewater treatment plant because of its recalcitrant characteristics. In this study, boron-doped diamond anode and persulfate were used to degrade CIP in an aquatic solution by creating an electrochemically activated persulfate (EAP) process. Iron was added to the system as a coactivator and the process was called EAP+Fe. The effects of independent variables, including pH, Fe2+, persulfate concentration, and electrolysis time on the system were optimized using the response surface methodology. The results showed that the EAP+Fe process removed 94% of CIP under the following optimum conditions: A pH of 3, persulfate/Fe2+ concentration of 0.4 mmol/L, initial CIP concentration 30 mg/L, and electrolysis time of 12.64 min. CIP removal efficiency was increased from 65.10% to 94.35% by adding Fe2+ as a transition metal. CIP degradation products, 7 pathways, and 78 intermediates of CIP were studied, and three of those intermediates (m/z 298, 498, and 505) were reported. The toxicological analysis based on toxicity estimation software results indicated that some degradation products of CIP were toxic to targeted animals, including fathead minnow, Daphnia magna, Tetrahymena pyriformis, and rats. The optimum operation costs were similar in EAP and EAP+Fe processes, approximately 0.54 €/m3.

Screening and identification of functional bacterial attachment genes in aerobic granular sludge

The screening and identification of attachment genes is important to exploring the formation mechanism of biofilms at the gene level. It is helpful to the development of key culture technologies for aerobic granular sludge (AGS). In this study, genome-wide sequencing and gene editing were employed for the first time to investigate the effects and functions of attachment genes in AGS. With the help of whole-genome analysis, ten attachment genes were screened from thirteen genes, and the efficiency of gene screening was greatly improved. Then, two attachment genes were selected as examples to further confirm the gene functions by constructing gene-knockout recombinant mutants of Stenotrophomonas maltophilia; when the two attachment genes were knocked out, the attachment potential was reduced by 50.67% and 43.93%, respectively. The results provide a new theoretical principle and efficient method for the development of AGS from the perspective of attachment genes.

Removal of antibiotics, bacterial toxicity, and occurrence of antibiotic resistance genes in secondary hospital effluents treated with granular activated carbon and the impact of preceding chlorination

This comprehensive investigation highlighted the complex adsorption behaviors of antibiotics onto granular activated carbon (GAC), the effectiveness of this adsorption in reducing bacterial toxicity, and the reduction of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in hospital wastewater (HWW) effluents. Six GACs were characterized for their physicochemical properties, and their ability to adsorb six antibiotics in the background matrix of actual HWW was evaluated. Coconut shell-derived GAC (Co-U), which had the highest hydrophobicity and lowest content of oxygen-containing acidic functional groups, demonstrated the highest adsorption capacities for the tested antibiotics. Bacterial toxicity tests revealed that GACs could eliminate the bacterial toxicity from antibiotic intermediates present in chlorinated HWW. By contrast, the bacterial toxicity could not be removed by GACs in non-chlorinated HWW due to the greater presence of intermediate components identified by LC-MS/MS. The intraparticle diffusion coefficient of antibiotics adsorbed onto Co-U could be calculated by adsorption kinetics derived from the linear driving force model and the homogenous intraparticle diffusion model associated with the linear adsorption isotherms (0-150 μg/L). Meropenem and sulfamethoxazole exhibited the highest adsorption capacities in a single-solute solution compared to penicillin G, ampicillin, cetazidime, and ciprofloxacin. However, the greater adsorption capacities of meropenem and sulfamethoxazole disappeared in mixed-solute solutions, indicating the lowest adsorption competition. GAC can eliminate most ARGs while also promoting the growth of some ARB. Chlorination (free chlorine residues at 0.5 mg Cl2/L) did not significantly affect the overall composition of ARGs and ARB in HWW. However, the accumulation of ARGs and ARB on GAC in fixed bed columns was lower in chlorinated HWW than in non-chlorinated HWW due to an increase in the adsorption of intermediates.

A critical review of characteristics of domestic wastewater and key treatment techniques in Chinese villages

As of 2022, China's rural sewage treatment rate is only approximately 31 %. Rapid rural development has led to higher demand. However, China's rural areas are complex and face many problems, such as uneven economic development, population distribution, and water availability. Long-lasting and low-cost wastewater treatment measures are needed for application in rural areas. The quantity and quality of rural domestic wastewater in China were characterized first. Next, the hot topic of domestic wastewater in Chinese villages was confirmed via bibliometric analysis using CiteSpace, and the treatment technologies for rural domestic wastewater were compared. Specifically, the technical status and challenges of the most common technology in rural domestic wastewater treatment, constructed wetlands, were summarized.

Greenhouse gases emissions and carbon budget estimation in horizontal subsurface flow constructed wetlands with different plant species

Constructed wetlands (CWs) are pivotal for wastewater treatment due to their high efficiency and numerous advantages. The impact of plant species and diversity on greenhouse gas (GHG) emissions from CWs requires a more comprehensive evaluation. Moreover, controversial perspectives persist about whether CWs function as carbon sinks or sources. In this study, horizontal subsurface flow (HSSF) CWs vegetated with Cyperus alternifolius, Typhae latifolia, Acorus calamus, and the mixture of these three species were constructed to evaluate pollutant removal efficiencies and GHG emissions, and estimate carbon budgets. Polyculture CWs can stably remove COD (86.79 %), NH4+-N (97.41 %), NO3--N (98.55 %), and TP (98.48 %). They also mitigated global warming potential (GWP) by suppressing N2O emissions compared with monoculture CWs. The highest abundance of the Pseudogulbenkiania genus, crucial for denitrification, was observed in polyculture CWs, indicating that denitrification dominated in nitrogen removal. While the highest nosZ copy numbers were observed in CWs vegetated with Cyperus alternifolius, suggesting its facilitation of denitrification-related microbes. Selecting Cyperus alternifolius to increase species diversity is proposed for simultaneously maintaining the water purification capacity and reducing GHG emissions. Carbon budget estimations revealed that all four types of HSSF CWs were carbon sinks after six months of operation, with carbon accumulation capacity of 4.90 ± 1.50 (Cyperus alternifolius), 3.31 ± 2.01 (Typhae latifola), 1.78 ± 1.30 (Acorus calamus), and 2.12 ± 0.88 (polyculture) kg C/m2/yr. This study implies that under these operation conditions, CWs function as carbon sinks rather than sources, aligning with carbon peak and neutrality objectives and presenting significant potential for carbon reduction efforts.

Enhanced Sb(V) removal of sulfate-rich wastewater by anaerobic granular sludge assisted with Fe/C amendment

Antimony (Sb) and sulfate are two common pollutants in Sb mine drainage and Sb-containing textile wastewater. In this paper, it was found that iron‑carbon (Fe/C) enhanced Sb(V) removal from sulfate-rich wastewater by anaerobic granular sludge (AnGS). Sulfate inhibited Sb(V) removal (S + Sb, k = 0.101), while Fe/C alleviated the inhibition and increased Sb(V) removal rate by 2.3 times (Fe/C + S + Sb, k = 0.236). Fe/C could promote the removal of Sb(III), and Sb(III) content decreased significantly after 8 h. Meanwhile, Fe/C enhanced the removal of sulfate. The 3D-EEM spectrum of supernatant in Fe/C + S + Sb group (at 24 h) showed that Fe/C stimulated the production of soluble microbial products (SMP) in wastewater. SMP alleviated the inhibition of sulfate, promoting AnGS to reduce Sb(V). Sb(V) could be reduced to Sb(III) both by AnGS and sulfides produced from sulfate reduction. Further analysis of extracellular polymeric substances (EPS) and AnGS showed that Fe/C increased the adsorbed Sb(V) in EPS and the c-type cytochrome content in AnGS, which may be beneficial for Sb(V) removal. Sb(V) reduction in Fe/C + S + Sb group may be related to the genus Acinetobacter, while in Sb group, several bacteria may be involved in Sb(V) reduction, such as Acinetobacter, Pseudomonas and Corynebacterium. This study provided insights into Fe/C-enhanced Sb(V) removal from sulfate-rich wastewater.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

Unveiling the influence of microaeration and sludge recirculation on enhancement of pharmaceutical removal and microbial community change of the novel anaerobic baffled biofilm - membrane bioreactor in treating building wastewater

This research aims to conduct a comparative investigation of the role played by microaeration and sludge recirculation in the novel anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) for enhancing pharmaceutical removal from building wastewater. Three AnBB-MBRs - R1: AnBB-MBR, R2: AnBB-MBR with microaeration and R3: AnBB-MBR with microaeration and sludge recirculation - were operated simultaneously to remove Ciprofloxacin (CIP), Caffeine (CAF), Sulfamethoxazole (SMX) and Diclofenac (DCF) from real building wastewater at the hydraulic retention time (HRT) of 30 h for 115 days. From the removal profiles of the targeted pharmaceuticals in the AnBB-MBRs, it was found that the fixed-film compartment (C1) could significantly reduce the targeted pharmaceuticals. The remaining pharmaceuticals were further removed with the microaeration compartment. R2 exhibited the utmost removal efficiency for CIP (78.0 %) and DCF (40.8 %), while SMX was removed most successfully by R3 (microaeration with sludge recirculation) at 91.3 %, followed by microaeration in R2 (88.5 %). For CAF, it was easily removed by all AnBB-MBR systems (>90 %). The removal mechanisms indicate that the microaeration in R2 facilitated the adsorption of CIP onto microaerobic biomass, while the enhanced biodegradation of CAF, SMX and DCF was confirmed by batch biotransformation kinetics and the adsorption isotherms of the targeted pharmaceuticals. The microbial groups involved in biodegradation of the targeted compounds under microaeration were identified as nitrogen removal microbials (Nitrosomonas, Nitrospira, Thiobacillus, and Denitratisoma) and methanotrophs (Methylosarcina, Methylocaldum, and Methylocystis). Overall, explication of the integration of AnBB-MBR with microaeration (R2) confirmed it as a prospective technology for pharmaceutical removal from building wastewater due to its energy-efficient approach characterized by minimal aeration supply.

Harmony in detoxification: Microalgae unleashing the potential of lignocellulosic pretreatment wastewater for resource utilization

Lignocellulosic biomass is a pivotal renewable resource in biorefinery process, requiring pretreatment, primarily chemical pretreatment, for effective depolymerization and subsequent transformation. This process yields solid residue for saccharification and lignocellulosic pretreatment wastewater (LPW), which comprises sugars and inhibitors such as phenols and furans. This study explored the microalgal capacity to treat LPW, focusing on two key hydrolysate inhibitors: furfural and vanillin, which impact the growth of six green microalgae. Chlorella sorokiniana exhibited higher tolerance to furfural and vanillin. However, both inhibitors hindered the growth of C. sorokiniana and disrupted algal photosynthetic system, with vanillin displaying superior inhibition. A synergistic inhibitory effect (Q < 0.85) was observed with furfural and vanillin on algal growth. Furfural transformation to low-toxic furfuryl alcohol was rapid, yet the addition of vanillin hindered this process. Vanillin stimulated carbohydrate accumulation, with 50.48 % observed in the 0.1 g/L furfural + 0.1 g/L vanillin group. Additionally, vanillin enhanced the accumulation of C16: 0 and C18: 2, reaching 21.71 % and 40.36 %, respectively, with 0.1 g/L vanillin. This study proposed a microalgae-based detoxification and resource utilization approach for LPW, enhancing the comprehensive utilization of lignocellulosic components. The observed biomass modifications also suggested potential applications for biofuel production, contributing to the evolving landscape of sustainable biorefinery processes.

An overview of quorum sensing in shaping activated sludge forms: Mechanisms, applications and challenges

Activated sludge method is an effective method for the wastewater treatment and has been widely applied. Activated sludge usually exists in various forms such as activated sludge floc, biofilm and granule. Due to the different character and function for each sludge type, the role and mechanism in the wastewater treatment process are also different, but all were crucial. The quorum sensing (QS) /quorum quenching (QQ) have been demonstrated and proved to regulate the group behavior by secreting signaling molecules among microorganisms and thus affect the manifestation of sludge. However, the complex mechanisms and regulatory strategies of QS/QQ in sludge forms have not been systematically summarized. This review provided an overview on the mechanism of QS/QQ shaping sludge forms from macro to micro (Explore it through signaling molecules, extracellular polymeric substances and microorganisms). In addition, the application and challenges of QS/QQ regulating sludge forms in various wastewater treatment processes including biofilm batch reactor, granule sludge and membrane bioreactor were discussed. Finally, some suggestions for further research and development of effective and economical QS/QQ strategies are put forward.

Multifunctional polyaniline modified calcium alginate aerogel membrane with antibacterial, oil-water separation, dye and heavy metal ions removal properties for complex water purification

With the rapid development of urbanization, the discharge of industrial wastewater has led to increasingly critical water pollution issues. Additionally, heavy metals, organic dyes, microorganisms and oil pollution often coexist and have persistence and harmfulness. Developing materials that can treat these complex pollutants simultaneously has important practical significance. In this study, a calcium alginate-based aerogel membrane (PANI@CA membrane) was prepared by spraying, polymerization, Ca2+ cross-linking and freeze-drying using aniline and sodium alginate as raw materials. Oil-water emulsion can be separated by PANI@CA membrane only under gravity, and the separation efficiency was as high as 99 %. At the same time, the membrane can effectively intercept or adsorb organic dyes and heavy metal ions. The removal rates of methylene blue and Congo red were above 92 % and 63 % respectively even after ten times of cyclic filtration. The removal rate of Pb2+ was up to 95 %. In addition, PANI@CA membrane shows excellent photothermal conversion ability, and it can effectively kill Staphylococcus aureus under 808 nm laser irradiation. PANI@CA membrane has the advantages of low cost, simple preparation, good stability and high recycling ability, and has potential application prospects in wastewater treatment.

Trace metal transfer to passerines inhabiting wastewater treatment wetlands

Wastewater treatment wetlands are cost-effective strategies for remediating trace metals in industrial effluent. However, biogeochemical exchange between wastewater treatment wetlands and adjacent environments provides opportunities for trace metals to cycle in surrounding ecosystems. The transfer of trace metals to wildlife inhabiting treatment wetlands must be considered when evaluating wetland success. Using passerine birds as bioindicators, we conducted a multi-tissue analysis to investigate the mobilization of zinc, copper, and lead derived from wastewater to terrestrial wildlife in treatment wetlands and surrounding habitat. In addition, we evaluate the strength of relationships between metal concentrations in non-lethal (blood and feathers) and lethal (muscle and liver) sample types for estimation of toxicity risk. From July 2020 to August 2021, 177 passerines of seven species were captured at two wetlands constructed to treat industrial wastewater and two reference wetlands in the coastal plain of South Carolina. Feather, blood, liver, and muscle samples from each bird were analyzed for fourteen metals using inductively coupled plasma mass spectrometry and direct mercury analysis. Passerines inhabiting wastewater treatment wetlands accumulated higher concentrations of zinc in liver, copper in blood, and lead in feathers than passerines in reference wetlands, but neither blood nor feather concentrations were correlated with internal tissue concentrations. Of all the detected metals, only mercury in the blood showed a strong predictive relationship with mercury in internal tissues. This study indicates that trace metals derived from wastewater are bioavailable and exported to terrestrial wildlife and that passerine biomonitoring is a valuable tool for assessing metal transfer from treatment wetlands. Regular blood sampling can reveal proximate trace metal exposure but cannot predict internal body burdens for most metals.

Influence of vegetation and substrate type on removal of emerging organic contaminants and microbial dynamics in horizontal subsurface constructed wetlands

Constructed wetlands (CWs) offer an efficient alternative technology for removing emerging organic contaminants (EOCs) from wastewater. Optimizing CW performance requires understanding the impact of CW configuration on EOC removal and microbial community dynamics. This study investigated EOC removal and microbial communities in horizontal subsurface flow (HSSF) CWs over a 26-month operational period. Comparison between tuff-filled and gravel-filled CWs highlighted the superior EOC removal in tuff-filled CWs during extended operation, likely caused by the larger surface area of the tuff substrate fostering microbial growth, sorption, and biodegradation. Removal of partially positively charged EOCs, like atenolol (29-98 %) and fexofenadine (21-87 %), remained constant in the different CWs, and was mainly attributed to sorption. In contrast, removal rates for polar non-sorbing compounds, including diclofenac (3-64 %), acyclovir (9-85 %), and artificial sweeteners acesulfame (5-60 %) and saccharin (1-48 %), seemed to increase over time due to enhanced biodegradation. The presence of vegetation and different planting methods (single vs. mixed plantation) had a limited impact, underscoring the dominance of substrate type in the CW performance. Microbial community analysis identified two stages: a startup phase (1-7 months) and a maturation phase (19-26 months). During this transition, highly diverse communities dominated by specific species in the early stages gave way to more evenly distributed and relatively stable communities. Proteobacteria and Bacteroidetes remained dominant throughout. Alphaproteobacteria, Acidobacteria, Planctomycetes, Salinimicrobium, and Sphingomonas were enriched during the maturation phase, potentially serving as bioindicators for EOC removal. In conclusion, this study emphasizes the pivotal role of substrate type and maturation in the removal of EOCs in HSSF CW, considering the complex interplay with EOC physicochemical properties. Insights into microbial community dynamics underscore the importance of taxonomic and functional diversity in assessing CW effectiveness. This knowledge aids in optimizing HSSF CWs for sustainable wastewater treatment, EOC removal, and ecological risk assessment, ultimately contributing to environmental protection.

Supercritical fluid technology as a sustainable alternative method for textile dyeing: An approach on waste, energy, and CO2 emission reduction

The clothing industry is considered one of the most polluting industries on the planet due to the high consumption of water, energy, chemicals/dyes, and high generation of solid waste and effluents. Faced with environmental concerns, the textile ennoblement sector is the most critical of the textile production chain, especially the traditional dyeing processes. As an alternative to current problems, dyeing with supercritical CO2 (scCO2) has been presented as a clean and efficient process for a sustainable textile future. Supercritical fluid dyeing (SFD) has shown a growing interest due to its significant impact on environmental preservation and social, economic, and financial gains. The main SFD benefits include economy and reuse of non-adsorbed dyes; reduction of process time and energy expenditure; capture of atmospheric CO2 (greenhouse gas); use and recycling of CO2 in SFD; generation of carbon credits; water-free process; effluent-free process; reduction of CO2 emission and auxiliary chemicals. Despite being still a non-scalable and evolving technology, SFD is the future of dyeing. This review presented a comprehensive overview of the environmental impacts caused by traditional processes and confronted the advantages of SFD. The SFD technique was introduced, along with its latest advances and future perspectives. Financial and environmental gains were also discussed.

Rapid start-up and operational characteristics of partial denitrification coupled with anammox driven by innovative strategies

The Partial Denitrification-Anammox (PD/A) process established a low-consumption, efficient and sustainable pathway for complete nitrogen removal, which is of great interest to the industry. Rapid initiation and stable operation of the PD/A systems were the main issues limiting its engineering application in wastewater nitrogen removal. A PD/A system was initiated in a continuous stirred-tank reactors (CSTRs) in the presence of low concentration of organic matter, and the effects of organic matter types and COD/NO3--N ratios on the performance of the PD/A system, and microbial community characteristics were explored. The results showed that low concentrations of organic matter could promote the rapid initiation of the Anammox process and then the strategy of gradually replacing NO2--N with NO3--N could successfully initiate the PD/A system at 70 days. The type of organic matter had a significant effect on the initiation of the Anammox and the establishment of the PD/A system. Compared to glucose, sodium acetate was more favorable for rapid start-up and the synergy among microorganisms, and organic matter was lower, with an optimal COD/NO3--N ratio of 3.0. Microorganisms differed in their sensitivity to environmental factors. The relative abundance of Planctomycetota and Proteobacteria in R2 was 51 %, with the presence of three typical anammox bacteria, Candidatus_Brocadia, Candidatus_Kuenenia, and Candidatus_Jettenia in the system. This study provides a new strategy for the rapid initiation and stable operation of the PD/A process.

Inadvertently enriched cyanobacteria prompted bacterial phosphorus uptake without aeration in a conventional anaerobic/oxic reactor

The enhanced biological phosphorus removal (EBPR) process requires alternate anaerobic and aerobic conditions, which are regulated respectively by aeration off and on. Recently, in an ordinary EBPR reactor, an abnormal orthophosphate concentration (PO43--P) decline in the anaerobic stage (namely non-aerated phosphorus uptake) aroused attention. It was not occasionally but occurred in each cycle and lasted for 101 d and shared about 16.63 % in the total P uptake amount. After excluding bio-mineralization and surface re-aeration, indoor light conditions (180 to 260 lx) inducing non-aerated P uptake were confirmed. High-throughput sequencing analysis revealed that cyanobacteria could produce oxygen via photosynthesis and were inhabited inside wall biofilm. The cyanobacteria (Pantalinema and Leptolyngbya ANT.L52.2) were incubated in a feeding transparent silicone hose, entered the reactor along with influent, and outcompeted Chlorophyta, which existed in the inoculum. Eventually, this work deciphered the reason for non-aerated phosphorus uptake and indicated its potential application in reducing CO2 emissions and energy consumption via the cooperation of microalgal-bacterial and biofilm-sludge.

A data-driven approach for revealing the linkages between differences in electrochemical properties of biochar during anaerobic digestion using automated machine learning

Biochar is commonly used to enhance the anaerobic digestion of organic waste solids and wastewater, due to its electrochemical properties, which intensify the electron transfer of microorganisms attached to its large surface area. However, it is difficult to create biochar with both high conductivity and high capacitance, which makes selecting the right biochar for engineering applications challenging. To address this issue, two Auto algorithms (TPOT and H2O) were applied to model the effects of different biochar properties on anaerobic digestion processes. The results showed that the gradient boosting machine had the highest predictive accuracy (R2 = 0.96). Feature importance analysis showed that feedstock concentration, digestion time, capacitance, and conductivity of biochar were the main factors affecting methane yield. According to the two-dimensional (2D) partial dependence plots, high-capacitance biochar (0.27-0.29 V·mA) is favorable for substrates with low-solid content (< 19.6 TS%), while the high-conductivity biochar (80.82-170.58 mS/cm) is suitable for high-solids substrates (> 20.1 TS%). The software, based on the optimal model, can be used to obtain the ideal range of biochar for AD trials, aiding researchers in practical applications prior to implementation.

A review of emerging membrane-based microalgal-bacterial processes for wastewater treatment: Process configurations, biological and membrane performance, and perspectives

Microalgal-bacterial (MB) consortia create an excellent eco-system for simultaneous COD/BOD and nutrients (N and P) removals in a single step with significant reduction in or complete elimination of aeration and carbonation in the biological wastewater treatment processes. The integration of membrane separation technology with the MB processes has created a new paradigm for research and development. This paper focuses on a comprehensive and critical literature review of recent advances in these emerging processes. Novel membrane process configurations and process conditions affecting the biological performance of these novel systems have been systematically reviewed and discussed. Membrane fouling issues and control of MB biofilm formation and thickness associated with these emerging suspended growth or immobilized biofilm processes are addressed and discussed. The research gaps, challenges, outlooks of these emerging processes are identified and discussed in-depth. The findings from the literature suggest that the membrane-based MB processes are advanced biotechnologies with a significant reduction in energy consumption and process simplification and high process efficiency that are not achievable with current technologies in wastewater treatment. There are endless opportunities for research and development of these novel and emerging membrane-based MB processes.

Isolation and characterization of novel 3,3'-iminodipropionitrile biodegrading Paracoccus communis, from an industrial wastewater treatment bioreactor

Until now, bacteria able to degrade, 3,3'-iminodipropionitrile (IDPN), a neurotoxin that destroys vestibular hair cells, causing ototoxicity, culminating in irreversible movement disorders, had never been isolated. The aim of this study was to isolate a novel IDPN-biodegrading microorganism and characterize its metabolic pathway. Enrichment was performed by inoculating activated sludge from a wastewater treatment bioreactor that treated IDPN-contaminated wastewater in M9 salt medium, with IDPN as the sole carbon source. A bacterial strain with a spherical morphology that could grow at high concentrations was isolated on a solid medium. Growth of the isolated strain followed the Monod kinetic model. Based on the 16S rRNA gene, the isolate was Paracoccus communis. Whole-genome sequencing revealed that the isolated P. communis possessed the expected full metabolic pathway for IDPN biodegradation. Transcriptome analyses confirmed the overexpression of the gene encoding hydantoinase/oxoprolinase during the exponential growth phase under IDPN-fed conditions, suggesting that the enzyme involved in cleaving the imine bond of IDPN may promote IDPN biodegradation. Additionally, the newly discovered P. communis isolate seems to metabolize IDPN through cleavage of the imine bond in IDPN via nitrilase, nitrile hydratase, and amidase reactions. Overall, this study lays the foundation for the application of IDPN-metabolizing bacteria in the remediation of IDPN-contaminated environments.

Decoding the influence of low temperature on biofilm development: The hidden roles of c-di-GMP

Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.

Biochar from recovered cellulose as new admixture in constructed wetlands for micropollutant removal: A circular approach

This study aimed to evaluate the suitability of biochar produced by pyrolysis from recovered wastewater cellulose and activated biologically as an admixture in Constructed Wetlands (CWs) when applied as a post-treatment step to remove micropollutants (MPs) from municipal wastewater effluent. Two planted vertical flow mesocosm CWs with cellulose-based admixtures of different origins (plant residue and recovered toilet paper) were fed with a municipal wastewater effluent representative for rural catchments. The results showed an average MPs elimination of 89.1 % for the activated biochar produced from recovered cellulose when 15 relevant compounds are considered and a reduction of the risk from compounds cocktail below the maximum acceptable level having diclofenac, carbamazepine, PFOS, ciprofloxacin and clarithromycin as main risk drivers (Risk Quotient > 1). The implementation of a circular approach to reduce MPs was finally conducted for the Blies catchment (Saarland region in Germany) characterized by low population density and small, sensitive water bodies. This approach demonstrates the feasibility of combining cellulose recovery with a fine sieve in large wastewater treatment plants (WWTPs) and providing biochar produced from recovered cellulose as an admixture to small WWTP where CW is an affordable solution for MP mitigation.

Towards zero excess sludge discharge with built-in ozonation for wastewater biological treatment

In this study, a biological treatment process, which used a built-in ozonation bypass to achieve sludge reduction, was built to treat the industrial antifreeze production wastewater (mainly composed of ethylene glycol). The results indicated there is a positive correlation between ozone dosage and sludge reduction. At the laboratory level, the MLSS in the system can be stably controlled at around 3400 mg MLSS L-1 under the dosage of 0.18 g O3 g-1 MLSS. Ozonation can increase the compactness of sludge flocs (fractal dimension increased from 1.89 to 1.92). Ozone destroys microbial cell membranes and alters the structure of sludge flocs through direct oxidation through electrophilic reactions. It leads to the release of intracellular polysaccharides, proteins, and other biological macromolecules in microorganisms, thereby promoting the implicit growth of microbial populations. Some bacteria such as g_Pseudomonas, g_Gemmobacter, etc. have strong ethylene glycol degradation ability and tolerance to ozonation. The removal of ethylene glycol includes the glyoxylate cycle, glycine serine carbon cycle, and the glutamate-cysteine ligase pathway of assimilation. Gene KatG and gpx may be key factors in improving microbial tolerance to ozonation. The comprehensive evaluation from the perspectives of cost and carbon emission shows that choosing ozone cracking-implicit growth in wastewater treatment systems has significant cost advantages and application value.

Toxicity removal from contaminated water by constructed wetlands assessed using multiple biomarkers in human stem cell assays

Constructed wetlands (CWs) have been developed rapidly as a sustainable water treatment technique. However, the capability of CWs for remediating the contaminated water based on toxicity assessment remains largely unknown. Four surface flow CWs and two integrated surface-subsurface flow CWs, from five cities in central and eastern region of China were evaluated, concerning the adverse effects of effluents and the toxicity reduction efficiency. Human bone marrow mesenchymal stem cells (hBMSCs) were employed as a human relevant in vitro model. The influent extractions caused cytotoxicity in a dose-dependent manner. The non-cytotoxic dilutions of the influents enhanced the genotoxicity marker γ-H2AX and reactive oxygen species levels. In addition, the influent repressed the osteogenic and neurogenic differentiation, and stimulated the adipogenic differentiation. Cytotoxicity of the contaminated water was reduced by 54 %-86 % after treatment with CWs. CWs were effective to remove part of the sub-lethal effects, with lower reduction than cytotoxicity. The integrated biomarker response (IBR) value of the effluents from the six CWs is lower than that of four secondary and one tertiary wastewater treatment plants. The IBR of the six CWs influents were in the range of 8.6-10.6, with a reduction of 15-50 % after the pollution restoration in CWs. The two integrated surface-subsurface flow CWs achieved higher IBR removal than the four surface flow CWs, possibly due to improved treatment effects by the combined systems. Cytotoxic and genotoxic effects of polar fractions in the CW effluents were stronger than the medium-polar and the non-polar fractions. Besides, PPARγ agonists present in the effluents played crucial roles and ERα agonists may make modest contributions. The present study enhances understanding of the role of CWs in achieving safe wastewater reclamation and provides evidence for further improving toxicity reduction in CWs performance.

Thermal hydrolysis alleviates polyethylene microplastic-induced stress in anaerobic digestion of waste activated sludge

Microplastics are known to negatively affect anaerobic digestion (AD) of waste activated sludge. However, whether thermal hydrolysis (TH) pretreatment alters the impact of microplastics on sludge AD remains unknown. Herein, the effect of TH on the impact of polyethylene (PE) microplastics in sludge AD was investigated. The results showed that the inhibition of methane production by PE at 100 particles/g total solids (TS) was reduced by 31.4% from 12.1% to 8.3% after TH at 170 °C for 30 min. Mechanism analysis indicated TH reduced the potential for reactive oxygen species production induced by PE, resulting in a 29.1 ± 5.5% reduction in cell viability loss. In addition, additive leaching increased as a result of rapid aging of PE microplastics by TH. Acetyl tri-n-butyl citrate (ATBC) release from PE with 10 and 100 particles/g TS increased 11.5-fold and 8.6-fold after TH to 68.2 ± 5.5 μg/L and 124.0 ± 5.1 μg/L, respectively. ATBC at 124.0 μg/L increased methane production by 21.4%. The released ATBC enriched SBR1031 and Euryarchaeota, which facilitate the degradation of proteins and promote methane production. This study reveals the overestimated impact of PE microplastics in sludge AD and provides new insights into the PE microplastics-induced impact in practical sludge treatment and anaerobic biological processes.

Synergistic algal/bacterial interaction in membrane bioreactor for detoxification of 1,2-dichloroethane-rich petroleum wastewater

The study addressed the challenge of treating petroleum industry wastewater with high concentrations of 1,2-dichloroethane (1,2-DCA) ranging from 384 to 1654 mg/L, which poses a challenge for bacterial biodegradation and algal photodegradation. To overcome this, a collaborative approach using membrane bioreactors (MBRs) that combine algae and bacteria was employed. This synergistic method effectively mitigated the toxicity of 1,2-DCA and curbed MBR fouling. Two types of MBRs were tested: one (B-MBR) used bacterial cultures and the other (AB-MBR) incorporated a mix of algal and bacterial cultures. The AB-MBR significantly contributed to 1,2-DCA removal, with algae accounting for over 20% and bacteria for approximately 49.5% of the dechlorination process. 1,2-DCA metabolites, including 2-chloroethanol, 2-chloro-acetaldehyde, 2-chloroacetic acid, and acetic acid, were partially consumed as carbon sources by algae. Operational efficiency peaked at a 12-hour hydraulic retention time (HRT) in AB-MBR, enhancing enzyme activities crucial for 1,2-DCA degradation such as dehydrogenase (DH), alcohol dehydrogenase (ADH), and acetaldehyde dehydrogenase (ALDH). The microbial diversity in AB-MBR surpassed that in B-MBR, with a notable increase in Proteobacteria, Bacteroidota, Planctomycetota, and Verrucomicrobiota. Furthermore, AB-MBR showed a significant rise in the dominance of 1,2-DCA-degrading genus such as Pseudomonas and Acinetobacter. Additionally, algal-degrading phyla (e.g., Nematoda, Rotifera, and Streptophyta) were more prevalent in AB-MBR, substantially reducing the issue of membrane fouling.

Using UV/peracetic acid as pretreatment for subsequent bio-treatment of antibiotic-containing wastewater treatment: Mitigating microbial inhibition and antibiotic resistance genes proliferation

UV/peracetic acid (PAA) treatment presents a promising approach for antibiotic removal, but its effects on microbial community and proliferation of antibiotic resistance genes (ARGs) during the subsequent bio-treatment remain unclear. Thus, we evaluated the effects of the UV/PAA on tetracycline (TTC) degradation, followed by introduction of the treated wastewater into the bio-treatment system to monitor changes in ARG expression and biodegradability. Results demonstrated effective TTC elimination by the UV/PAA system, with carbon-centered radicals playing a significant role. Crucially, the UV/PAA system not only eliminated antibacterial activity but also inhibited potential ARG host growth, thereby minimizing the emergence and dissemination of ARGs during subsequent bio-treatment. Additionally, the UV/PAA system efficiently removed multi-antibiotic resistant bacteria and ARGs from the bio-treatment effluent, preventing ARGs from being released into the environment. Hence, we propose a multi-barrier strategy for treating antibiotic-containing wastewater, integrating UV/PAA pre-treatment and post-disinfection with bio-treatment. The inhibition of ARGs transmission by the integrated system was verified through actual soil testing, confirming its effectiveness in preventing ARGs dissemination in the surrounding natural ecosystem. Overall, the UV/PAA treatment system offers a promising solution for tackling ARGs challenges by controlling ARGs proliferation at the source and minimizing their release at the end of the treatment process.

Biomineralization of phosphorus during anaerobic treatment of distillery wastewaters

This study addresses the pressing environmental concerns associated with the rapidly growing distillery industry, which is a significant contributor to wastewater generation. By focusing on the treatment of distillery wastewater using anaerobic digestion, this research explores the potential to convert organic materials into biofuels (methane). Moreover, the study aims to recover both methane and phosphorus from distillery wastewater in a single anaerobic reactor, which represents a novel and unexplored approach. Laboratory-scale experiments were conducted using mesophilic and thermophilic upflow anaerobic sludge blanket reactors. A key aspect of the study involved the implementation of a unique strategy: the mixing of centrate and spent caustic wastewater streams. This approach was intended to enhance treatment performance, manipulate the microbial community structure, and thereby optimizing the overall treatment performance. The integration of the centrate and spent caustic streams yielded remarkable co-benefits, resulting in significant biomethane production and efficient phosphorus precipitation. The study demonstrated a phosphorus removal efficiency of ∼60 % throughout the 130-140 days operation period. The recovery of phosphorus via the reactor sludge offers exciting opportunities for its utilization as a fertilizer or as a raw material within the phosphorus refinery industry. The biomethane produced during the treatment exhibits significant energy potential, estimated at 0.5 GJ/(m3 distillery wastewater).

Sustained oxidation of Tea-Fe(III)/H2O2 simultaneously achieves sludge reduction and carbamazepine removal: The crucial role of EPS regulation

Establishing an economic and sustained Fenton oxidation system to enhance sludge dewaterability and carbamazepine (CBZ) removal rate is a crucial path to simultaneously achieve sludge reduction and harmless. Leveraging the principles akin to "tea making", we harnessed tea waste to continually release tea polyphenols (TP), thus effectively maintaining high level of oxidation efficiency through the sustained Fenton reaction. The results illustrated that the incorporation of tea waste yielded more favorable outcomes in terms of water content reduction and CBZ removal compared to direct TP addition within the Fe(III)/hydrogen peroxide (H2O2) system. Concomitantly, this process mainly generated hydroxyl radical (•OH) via three oxidation pathways, effectively altering the properties of extracellular polymeric substances (EPS) and promoting the degradation of CBZ from the sludge mixture. The interval addition of Fe(III) and H2O2 heightened extracellular oxidation efficacy, promoting the desorption and removal of CBZ. The degradation of EPS prompted the transformation of bound water to free water, while the formation of larger channels drove the discharge of water. This work achieved the concept of treating waste with waste through using tea waste to treat sludge, meanwhile, can provide ideas for subsequent sludge harmless disposal.

Occurrence and fate of pharmaceuticals and personal care products in a wastewater treatment plant with Bacillus bio-reactor treatment

Pharmaceuticals and personal care products (PPCPs) have attracted wide attention due to their environmental impacts and health risks. PPCPs released through wastewater treatment plants (WWTPs) are estimated to be 80 %. Nevertheless, the occurrence of PPCPs in the WWTPs equipped with Bacillus spec.-based bioreactors (BBR) treatment system remains unclear. In this study, sludge and waste water samples were collected during separate winter and summer sampling campaigns from a typical BBR treatment system. The results indicate that out of 58 target PPCPs, 27 compounds were detected in the waste water (0.06-1900 ng/L), and 23 were found in the sludge (0.6-7755 ng/g dw). Paraxanthine was the chemical of the highest abundance in the influent due to the high consumption of the parent compounds caffeine and theobromine. The profile for PPCPs in the wastewater and sludge exhibited no seasonal variation. Overall, the removal of target PPCPs in summer is more effective than the winter. In the BBR bio-reactor, it was found that selected PPCPs (at ng/L level) can be completely removed. The efficiency for individual PPCP removal was increased from 1.0 % to 50 % in this unit, after target specific adjustments of the process. The effective removal of selected PPCPs by the BBR treatment system is explained by combined sorption and biodegradation processing. The re-occurrence of PPCPs in the wastewater was monitored. Negative removal efficiency was explained by the cleavage of Phase II metabolites after the biotransformation process, and the lack of equilibrium for PPCPs in the sludge of the second clarifier. A compound specific risk quotient (RQ) was calculated and applied for studying the potential environmental risks. Diphenhydramine is found with the highest environmental risk in wastewater, and 15 other PPCPs show negligible risks in sewage sludge.

[Effect of Thermal Hydrolysis Pretreatment Time on Microbial Community Structure in Sludge Anaerobic Digestion System]

To evaluate the effect of thermal hydrolysis pretreatment time on the sludge anaerobic digestion system of wastewater treatment plants (WWTPs) in Daxing district, Beijing, the structure and diversity of microbial communities in primary sludge and an activated sludge anaerobic digestion system with different thermal hydrolysis pretreatment times (15 min, 30 min, and 45 min) were analyzed using Illumina MiSeq high-throughput sequencing. The results showed that the dominant groups of digested sludge were mainly distributed in Firmicutes, Cloacimonadota, Chloroflexi, and Synergistota, with W5 being the most common genus. The sum of relative abundance of the dominant phylum was greater than 60%, and W5 accounted for 20.8%-54.5%, showing a high abundance of a few dominant species. During the anaerobic digestion of thermo-hydrolyzed sludge, the relative abundance of acetogenic methanogens decreased due to high levels of volatile fatty acids (VFAs) and ammonia nitrogen (NH4+-N) concentrations, which suggested that the hydrogenophilic methanogenic pathway was more than that of the acetogenic methanogenic pathway. Correlation analysis showed that the soluble protein and pH of thermo-hydrolyzed sludge, NH4+-N of digested sludge, and thermal hydrolysis pretreatment time were the four main environmental factors affecting microbial community structure, and NH4+-N of digested sludge had the largest negative correlation with methanogens. The thermal hydrolysis pretreatment time was negatively correlated with both the Chao index and Shannon index, so longer thermal hydrolysis pretreatment time was not conducive to microbial flora during anaerobic digestion.

From "resistance genes expression" to "horizontal migration" as well as over secretion of Extracellular Polymeric Substances: Sludge microorganism's response to the increasing of long-term disinfectant stress

Glutaraldehyde-Didecyldimethylammonium bromides (GDs) has been frequently and widely employed in livestock and poultry breeding farms to avoid epidemics such as African swine fever, but its long-term effect on the active sludge microorganisms of the receiving wastewater treatment plant was keep unclear. Four simulation systems were built here to explore the performance of aerobic activated sludge with the long-term exposure of GDs and its mechanism by analyzing water qualities, resistance genes, extracellular polymeric substances and microbial community structure. The results showed that the removal rates of CODCr and ammonia nitrogen decreased with the exposure concentration of GDs increasing. It is worth noting that long-term exposure to GDs can induce the horizontal transfer and coordinated expression of a large number of resistance genes, such as qacE, sul1, tetx, and int1, in drug-resistant microorganisms. Additionally, it promotes the secretion of more extracellular proteins, including arginine, forming a "barrier-like" protection. Therefore, long-term exposure to disinfectants can alter the treatment capacity of activated sludge receiving systems, and the abundance of resistance genes generated through horizontal transfer and coordinated expression by drug-resistant microorganisms does pose a significant threat to ecosystems and health. It is recommended to develop effective pretreatment methods to eliminate disinfectants.

Sludge dewaterability improvement with microbial fuel cell powered electro-Fenton system (MFCⓅEFs): Performance and mechanisms

Throughout the entire process of sludge treatment and disposal, it is crucial to explore stable and efficient techniques to improve sludge dewaterability, which can facilitate subsequent resource utilization and space and cost savings. Traditional Fenton oxidation has been widely researched to enhance the performance of sludge dewaterability, which was limited by the additional energy input and the instabilities of Fe2+ and H2O2. To reduce the consumption of energy and chemicals and further break the rate-limiting step of the iron cycle, a novel and feasible method that constructed microbial fuel cell powered electro-Fenton systems (MFCⓅEFs) with ferrite and biochar electrode (MgFe2O4@BC/CF) was successfully demonstrated. The MFCⓅEFs with MgFe2O4@BC/CF electrode achieved specific resistance filtration and sludge cake water content of 2.52 × 1012 m/kg and 66.54 %. Cellular structure and extracellular polymeric substances (EPS) were disrupted, releasing partially bound water and destroying hydrophilic structures to facilitate sludge flocs aggregation, which was attributed to the oxidation of hydroxyl radicals. The consistent electron supply supplied by MFCⓅEFs and catalytically active sites on the surface of the multifunctional functional group electrode was responsible for producing more hydroxyl radicals and possessing a better oxidizing ability. The study provided an innovative process for sludge dewaterability improvement with high efficiency and low energy consumption, which presented new insights into the green treatment of sludge.

Insight into performance of nitrogen removal enhanced by adding lactic acid-rich food waste fermentation liquid as carbon source in municipal wastewater treatment

Lactic acid-rich fermentation liquid (LAFL) of food waste is found to act as a promising alternative carbon source for nitrogen removal in wastewater treatment. Here, LAFL was employed to investigate its impacts on nitrogen removal during raw municipal wastewater treatment with a comparison to sodium acetate (NaAc). Results indicated that nitrogen removals were comparable when incorporated with LAFL and NaAc (92.89 % v.s. 91.23 %). Unlike the utilization of NaAc, using LAFL could avoid suppressing the relative abundance of the nitrification genes and thus pose a negative risk to nitrogen removal during prolonged operation. The introduction of LAFL increased the stability and robustness of the functional microbial community and effectively reduced excess activated sludge (AS) generation by 109 % compared to NaAc addition, consequently enhancing nitrogen removal but diminishing the treatment cost. In general, LAFL exhibits prospective engineering application potentials and economic advantages in improving nitrogen removal by AS process.

Assessment of hybrid fixed and moving bed biofilm applications for wastewater treatment capacity increase - In situ tests in El-Gouna WWTP, Egypt

This paper provides a procedure for comparing the performance of different biofilm carrier medias and their surrounding suspended biomass through oxygen uptake rate (OUR) tests. For in situ (oxygen uptake rate (OUR) measurements, three identical lab scale biofilm reactors were set up at the El Gouna wastewater treatment plant (WWTP). In this setup, two options of media for moving-bed biofilm reactors (MBBR) and one media for fixed-bed biofilm reactors (FBBR) were compared. The WWTP also used the same carrier in a real scale hybrid application to analyze how the interactions between the carrier type and the suspended biomass influences the overall performance. The in situ OUR approach is recommended to measure the contribution of the biofilm fixed biomass under site specific conditions. Specifically, settleability and diffusion limitations are the two opposite poles that cannot be predicted adequately for mild climate conditions based on the literature. A biofilm carrier application can add but actually can also reduce the capacity in a hybrid activated sludge system: The added MBBR-media was able to grind down the sludge flocs forming a poorly settleable suspended biomass. The added FBBR-media can lead to extracellular polymeric substances (EPS) rich biofilms that contribute very little as substrate and oxygen are unavailable for the microorganisms present in the biofilm. In this application of the comparison procedure, Kaldnes K1 like MBBR media was compared with a recycling MBBR carrier option (poly propylene bottle caps) and Jäger Envirotech "BioCurlz™" FBBR media. The study showed higher average rates for the MBBR but decreased settleability. The FBBR showed higher peak rates when flushed to break up the biofilm and well settleable sludge. The determination of OUR per g of volatile solids (SOUR) showed comparable results for all the carriers and in warm conditions, only the capacity to accommodate biomass determines the contribution of the carrier.

Concurrent removal of carbon and nutrients in a one-stage dual internal circulation airlift A2O bioreactor from milk processing industrial wastewater: Process optimization, sludge characteristics and operating cost evaluation

In this work, a one-stage dual internal circulation airlift anaerobic/anoxic/aerobic (DCAL-A2O) bioreactor was continuously operated for concurrent removal of nutrients and organics from milk processing wastewater (MPW). Special configuration of the airlift A2O bioreactor created possibility of the formation of desired anaerobic, anoxic and aerobic zones in a single unit. The process functionality of the bioreactor was examined under three influential operating variables i.e. hydraulic retention time (HRT; 7-15 h), air flow rate (AFR; 1-3 L/min) and aerobic volume ratio (AVR; 0.324-0.464). The optimum region was identified at HRT of 13h, AFR of 2L/min and AVR of 0.437, leading to TCOD, TN and TP removal efficiency of 94.5 %, 59.6 %, and 62.2 %, respectively, and effluent turbidity of 8 NTU. The impact of feed biodegradability on the process performance of the bioreactor treating the MPW, soft drink wastewater (SDW) and soybean oil plant wastewater (SOW) was also assessed. From the results, the feed characteristics affected significantly the nutrients removal. Moreover, the feeding location played an effective role in the nutrient removal while treating the MPW at optimum operating conditions. In this study, the change in residual organic matters as soluble microbial products (SMP) was monitored at various operating conditions. In addition, the impact of SMP extracted from sludge, extracellular polymeric substances (EPS) comprising of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) was analyzed on sludge characteristics as bio-flocculation and settleability properties. According to the obtained data, the increase in operating variables led to the reduction in contents of effluent SMP, sludge SMP, LB-EPS, turbidity, and SVI, thereby, the enhancement in the sludge characteristics. Meanwhile, analysis of microbial communities verified the presence of various functional bacterial species. The cost operating evaluation confirmed the cost effectiveness of the airlift A2O bioreactor in reduction of energy consumption for the MPW treatment.

Phytoremediation of an integrated poultry and aquaculture wastewater using sub-surface constructed wetland planted with Phragmites karka and Typha latifolia

This study focused on assessing the effectiveness of vertical subsurface constructed wetlands (VSFCW) in purifying integrated poultry and aquaculture wastewater (PAW) in a tropical region. This evaluation encompassed the treatment of physico-chemical, heavy metal, and microbiological pollutants across three distinct climatic seasons and hydraulic retention time (HRT: 21 days). Parameters such as BOD (29.50 mg/L), COD (56.67 mg/L), Zn (2.97 mg/L), Cr (0.24 mg/L), Cu (1.78 mg/L), Pb (0.21 mg/L), total fecal coliform (866.67 cfu/mL), total coliform (1666.67 cfu/mL), E. coli (1133.33 cfu/mL), and Salmonella/Shigella (700 cfu/mL) exceeded the discharge limits for wastewater into nearby surface water bodies. Significant removal efficiencies were observed for all parameters tested in the CW planted with both Phragmites karka and Typha latifolia. The macrophytes showed similar removal efficiencies for all tested parameters, and there was no significant difference in the initial concentrations of the parameters based on the experimental season, except for microbial properties. This suggests that weather conditions did not significantly impact the concentration of physical and chemical properties in the wastewater. Consequently, this study successfully demonstrates the potential of using a VSFCW for effective treatment of PAW.

Electrocoagulation in treatment of municipal wastewater- life cycle impact assessment

The purpose of this study is investigation of electrocoagulation (EC) as a treatment of municipal wastewater, integrating life cycle impact assessment (LCIA) for assessing its environmental performance of investigated treatment. The study evaluated the effectiveness of EC in removing physico-chemical and microbial parameters using aluminum (Al) and iron (Fe) electrodes in monopolar and bipolar modes. Bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes achieved the highest removals: 70% COD, 72% BOD5 followed by complete elimination of total phosphorous, turbidity and microbial parameters. This treatment was subject to investigation of the influence of reaction time (t = 10-60 min) on removals at higher current density (CD = 3.33 mA/cm2). In order to reduce energy consumption, the same reaction time range was used with a reduced CD = 2.33 mA/cm2. Following removal efficiencies obtained: 47-72% COD (higher CD) and 53-78% (lower CD); 69-75% BOD5 (higher CD) and 55-74% CD (lower CD); 12-21% NH4- (higher CD) and 7-22% NH4- (lower CD). Total P, NO3- and NO2- compounds showed the same removals regardless the CD. Decrease in current density did not influence removals of total suspended matter, turbidity, salinity as well as microbial parameters. The bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes, assuming a lower CD = 2.33 mA/cm2 and t = 30 min, was assessed with the Recipe 2016Midpoint (H) and USEtox v.2 LCIA methods to explore the environmental justification of using EC for wastewater treatment. The LCIA results revealed that the EC process significantly reduces water eutrophication and toxicity for freshwater and marine ecosystems, but has higher impacts in global warming, fossil fuel consumption, human toxicity, acidification, and terrestrial ecotoxicity due to high energy consumption. This can be mainly explained by the assumption in the study that the EC precipitate is dispersed to agricultural soil without any pre-treatment and material recovery, along with relatively high energy consumption during the process.

Mechanistic insights into different illumination positions control algae production in anaerobic dynamic membrane filtration (AnDM) during decentralized wastewater treatment

Sunlight illumination has the potential to control the stability and sustainability of dynamic membrane (DM) systems. In this study, an up-flow anaerobic sludge blanket (UASB) reactor was combined with DM under different illumination positions (direct, indirect and no illumination) to treat wastewater. Results indicated that the UASB achieved a COD removal up to 87.05 % with an average methane production of 0.28 L/d. Following treatment by the UASB, it was found that under illumination, the removal of organic substances by DM exhibited poor performance due to algal proliferation. However, the DM systems demonstrated efficient removal of ammonia nitrogen, ranging from 96.21 % to 97.67 % after stabilization. Total phosphorus removal was 45.72 %, and membrane flux remained stable when directly illuminated. Conversely, the DM system subjected to indirect illumination showed unstable membrane flux and severe fouling resistance. These findings offer valuable insights into optimizing illumination positions in DM systems under anaerobic conditions.

Formation/characterization of humin-mediated anaerobic granular sludge and enhanced methanogenic performance

This study presents a novel method for accelerating the granulation of methanogenic anaerobic granular sludge (AnGS) in an upflow anaerobic sludge blanket (UASB) reactor using solid-phase humin (HM). The results demonstrated that HM-mediated AnGS (HM-AnGS) formed rapidly within 50 days. The increase in particle size, settling velocity and mechanical strength was attributed to the rapid granulation of the HM-AnGS. The maximum methane yield of the HM-AnGS was 5-fold higher than that of the control group. This is consistent with the findings, which showed that HM-AnGS had 3.2-3.4 times more methyl-coenzyme M reductase (Mcr) activity and 2.4-2.9 times more adenosine triphosphate (ATP) than control groups. Molecular analyses indicate that HM most likely accelerated interspecies electron transfer (IET) in HM-AnGS (e.g., from Enterococcus to Methanosaeta). Furthermore, the HM-AnGS was effective in recovering energy from actual slaughterhouse wastewater.

The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization

Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields. To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Yobs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10-60 %) with the increase of the AET (7.9-13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Yobs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Yobs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=-0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process.

Purification of the secondary treatment tail water for wastewater reclamation by integrated subsurface-constructed wetlands

A whole-year investigation of full-scale integrated subsurface-constructed wetlands (ISCWs) was carried out to purify the tail water from a wastewater treatment plant (WWTP) for wastewater reclamation under four plant species, four hydraulic loading rates (HLRs), and four seasons. The results showed that ISCWs were effective for the purification of WWTP discharge, with the average removal efficiencies of COD, NH4+-N, TN, and TP being 48%, 49%, 9%, and 30%, respectively. Typical pollutant concentrations in the treated effluent of ISCWs were 8.19 mg/L COD, 1.76 mg/L NH4+-N, 11.57 mg/L TN, and 0.36 mg/L TP, which met most of the water quality standards for reusing recycling water. Emergent plants with well-developed root systems may be capable of promoting the decontamination of ISCWs. Seasonal change played an important role in the treatment process: the removal of phosphorus by plant uptake and microbial utilization was more active in the warm season and the co-occurrence of organic degradation and nitrification, whereas the cold season is conducive to exothermic adsorption process of pollutants to substrates. Properly increasing the HLRs may improve the availability of ISCWs according to the requirement of effluent quality. Furthermore, the C/N ratio might be the key factor for the purification effect of ISCWs, because the COD level of WWTP discharge may change the process of NH4+-N biotransformation.

Mesoporous activated carbon derived from fruit by-product by pyrolysis induced chemical activation: optimization and mechanism for fuchsin basic dye removal

In this study, pineapple crown (PC) feedstock residues were utilized as a potential precursor toward producing activated carbon (PCAC) via pyrolysis induced with ZnCl2 activation. The PCAC has a surface area (457.8 m2/g) and a mesoporous structure with an average pore diameter of 3.35 nm, according to the Brunauer-Emmett-Teller estimate. The removal of cationic dye (Fuchsin basic; FB) was used for investigating the adsorption parameters of PCAC. The optimization of significant adsorption variables (A: PCAC dose (0.02-0.1 g/100 mL); B: pH (4-10); C: time (10-90); and D: initial FB concentration (10-50 mg/L) was conducted using the Box-Behnken design (BBD). The pseudo-second-order (PSO) model characterized the dye adsorption kinetic profile, whereas the Freundlich model reflected the equilibrium adsorption profile. The maximum adsorption capacity (qmax) of PCAC for FB dye was determined to be 171.5 mg/g. Numerous factors contribute to the FB dye adsorption mechanism onto the surface of PCAC, which include electrostatic attraction, H-bonding, pore diffusion, and π-π stacking. This study illustrates the utilization of PC biomass feedstock for the fabrication of PCAC and its successful application in wastewater remediation.

PHA and EPS production from industrial wastewater by conventional activated sludge, membrane bioreactor and aerobic granular sludge technologies: A comprehensive comparison

The present study has focused on the mainstream integration of polyhydroxyalkanoate (PHA) production with industrial wastewater treatment by exploiting three different technologies all operating in sequencing batch reactors (SBR): conventional activated sludge (AS-SBR), membrane bioreactor (AS-MBR) and aerobic granular sludge (AGS). A full aerobic feast/famine strategy was adopted to obtain enrichment of biomass with PHA-storing bacteria. All the systems were operated at different organic loading (OLR) rate equal to 1-2-3 kgCOD/m3∙d in three respective experimental periods. The AS-MBR showed the better and stable carbon removal performance, whereas the effluent quality of the AS-SBR and AGS deteriorated at high OLR. Biomass enrichment with PHA-storing bacteria was successfully obtained in all the systems. The AS-MBR improved the PHA productivity with increasing OLR (max 35% w/w), whereas the AS-SBR reduced the PHA content (max 20% w/w) above an OLR threshold of 2 kgCOD/m3∙d. In contrast, in the AGS the increase of OLR resulted in a significant decrease in PHA productivity (max 14% w/w) and a concomitant increase of extracellular polymers (EPS) production (max 75% w/w). Results demonstrated that organic carbon was mainly driven towards the intracellular storage pathway in the AS-SBR (max yield 51%) and MBR (max yield 61%), whereas additional stressors in AGS (e.g., hydraulic selection pressure, shear forces) induced bacteria to channel the COD into extracellular storage compounds (max yield 50%) necessary to maintain the granule's structure. The results of the present study indicated that full-aerobic feast/famine strategy was more suitable for flocculent sludge-based technologies, although biofilm-like systems could open new scenarios for other biopolymers recovery (e.g., EPS). Moreover, the AS-MBR resulted the most suitable technology for the integration of PHA production in a mainstream industrial wastewater treatment plant, considering the greater process stability and the potential reclamation of the treated wastewater.

New insights on destruction mechanisms of waste activated sludge during simultaneous thickening and digestion process via forward osmosis membrane

This study delved into the efficacy of sludge digestion and the mechanisms involved in sludge destruction during the implementation of forward osmosis process for sludge thickening and digestion (FO-MSTD). Utilizing a lab-scale FO membrane reactor for the thickening and digestion of waste activated sludge (WAS), the investigation explored the effects of sludge thickening and digestion in FO-MSTD processes using draw solutions of varying concentrations. The findings underscored the significance of hydraulic retention time (HRT) as a pivotal parameter influencing the swift thickening or profound digestion of sludge. Consequently, tailoring the HRT to specific processing objectives emerged as a key strategy for achieving desired treatment outcomes. In the investigation, the use of a 1 M NaCl draw solution in the FO-MSTD process showcased enhanced thickening and digestion capabilities. This specific setup raised the concentration of mixed liquor suspended solids (MLSS) to over 30 g/L and achieved a 42.7% digestion efficiency of mixed liquor volatile suspended solids (MLVSS) within an operational timeframe of 18 days. Furthermore, the research unveiled distinct stages in the sludge digestion process of the FO-MSTD system, characterized by fully aerobic digestion and aerobic-local anaerobic co-existing digestion. In the fully aerobic digestion stage, the sludge digestion rate exhibited a steady increase, leading to the breakdown of sludge floc structures and the release of a substantial amount of nutrients into the sludge supernatant. The predominant microorganisms during this stage were typical functional microorganisms found in wastewater treatment systems. Transitioning into the aerobic-local anaerobic co-existing digestion stage, both MLSS concentration and MLVSS digestion efficiency continued to rise, accompanied by a decreasing dissolved oxygen (DO) concentration. More organic matter was released into the supernatant, and sludge microbial flocs tended to reaggregate. The localized anaerobic environment within the FO-MSTD reactor fostered an increase in the relative abundance of bacteria with nitrogen and phosphorus removal functions, thereby positively impacting the mitigation of total nitrogen (TN) and total phosphorus (TP) concentrations in the sludge supernatant. The results of this research enhance comprehension of the advanced FO-MSTD technology in the treatment of WAS.

Demonstrating scale-up of a novel water treatment process using super-bridging agents

Fiber-based materials have emerged as a promising option to increase the efficiency of water treatment plants while reducing their environmental impacts, notably by reducing the use of unsustainable chemicals and the size of the settling tank. Cellulose fiber-based super-bridging agents are sustainable, reusable, and versatile materials that considerably improve floc separation in conventional settling tanks or via alternative screening separation methods. In this study, the effectiveness of fiber-based materials for wastewater treatment was evaluated at lab-scale (0.25 L) and at pilot-scale (20 L) for two separation methods, namely settling and screening. For the fiber-based method, the performance of floc separation during settling was slightly affected by an 80x upscaling factor. A small decrease in turbidity removal from 93 and 86 % was observed for the jar and pilot tests, respectively. By contrast, the turbidity removal of the conventional treatment, i.e., no fibers with a settling separation, was largely affected by the upscaling with turbidity removals of 84 and 49 % for jar and pilot tests, respectively. Therefore, results are suggesting that fiber-based super-bridging agents could be implemented in full-scale water treatment plants. Moreover, the tested fibers increase the robustness of treatment by providing better floc removal than conventional treatment under several challenging conditions such as low settling time and screening with coarse screen mesh size. Furthermore, at both lab-scale and pilot-scale, the use of fiber-based materials reduced the demand for coagulant and flocculant, potentially lowering the operational costs of water treatment plants and reducing the accumulation of metal-based coagulants and synthetic polymers in sludge. Acute toxicity tests using the model organism Daphnia magna show that the cellulose fibers introduce insignificant toxicity at the optimized fiber concentration. Although dedicated mechanistic studies are required at various scales to understand in detail the influence of fibers on water treatment (coagulation/flocculation time, floc formation, floc size distribution velocity gradient, etc.), the efficacy and scalability of the fiber-based approach, along with its minimal environmental impact, position it as a viable and sustainable option for existing and future wastewater treatment plants.

Visualization of water transfer channel in sludge dewatering conditioned with skeleton builders by X-ray micro-computed tomography

Skeleton builders were normally deemed to improve the high porosity and newly-generated permeability of sludge cakes by building water transfer channel during high pressure filtration, thus enhancing sludge dewaterability. However, currently a direct visualization proof of water transfer channel was still lacking. This study provided the direct proof for visualizing water transfer channel in dewatered sludge cakes conditioned with a typical skeleton builder (i.e., phosphogypsum (PG)) by X-ray micro-computed tomography (micro-CT) for the first time. After the addition of PG, the pixel value and image luminance increased significantly, indicating the presence of high density substances from both two-dimensional (2D) cross section and three-dimensional (3D) reconstruction CT images. Moreover, the CT numbers showed strong and negative correlations with specific resistance to filtration (SRF) (R = - 0.99, p < 0.05), capillary suction time (CST) (regression coefficient (R) = - 0.87, probability (p) < 0.05), and water content of the dewatered sludge cake (R = - 0.99, p < 0.05), respectively. These results indicated that the X-ray micro-CT could be a potential technique for analyzing the water distribution in sludge samples conditioned with skeleton builders.

Advanced nitrogen and phosphorus removal in pilot-scale anaerobic/aerobic/anoxic system for municipal wastewater in Northern China

Removing nitrogen and phosphorus from low ratio of chemical oxygen demand to total nitrogen and temperature municipal wastewater stays a challenge. In this study, a pilot-scale anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A-SBR) system first treated 15 m3/d actual municipal wastewater at 8.1-26.4 °C for 224 days. At the temperature of 15.7 °C, total nitrogen in influent and effluent were 45.5 and 10.9 mg/L, and phosphorus in influent and effluent were 3.9 and 0.1 mg/L. 16 s RNA sequencing results showed the relative abundance of Competibacter and Tetrasphaera raised to 1.25 % and 1.52 %. The strategy of excessive, no and normal sludge discharge enriched and balanced the functional bacteria, achieving an endogenous denitrification ratio more than 43.3 %. Sludge reduction and short aerobic time were beneficial to energy saving contrast with a Beijing municipal wastewater treatment. This study has significant implications for the practical application of the AOA-SBR process.

Biological feasibility of discharge a local WTTP sludge to sewer network and centralized WWTP; a case study: Tehran, Iran

Over the recent years, ever-increasing population growth and higher wastewater production has been a challenge for decentralized wastewater treatment plants (WWTPs). In addition, sludge treatment due to high cost for equipment and place make authorities to find a sustainable approach in both of economical and technical perspectives. One of the proposed solutions is transferring the sludge produced from decentralized WWTP to centralized WWTP. However, the appropriate proportional ratio of raw sludge to raw sewage is a challenge, otherwise, it make anaerobic conditions and sewage rotting along the sewer network based on permissible limit of dihydrogen sulfide (H2S) gas (5 ppm). In the present study, seven reactors with different ratios of sludge to raw sewage (0, 15, 20, 25, 50, 75, 100) were used to stimulate the feasibility of transferring Shahrake Gharb WWTP sludge along the wastewater transfer pipe to the centralized sewage treatment south Tehran WWTP plant in Tehran, Iran. The septic situation and H2S emission of different reactors within 7 h (Time to reach the compound in the south treatment plant) was analyzed by gas meter. The results indicated that the optimum ratio of sludge to raw sewage was 15% without H2S production during 7 h. In addition, due to the high volume of sludge produced by the Shahrake Gharb WWTP, the optimal ratio of lime to total solids (TS) in sludge (gr/gr) (0.6) increased the sludge loading rate from 15 to 30% without any H2S emission during the stimulation study period. Therefore, the lime stabilization and transfer of sludge from a decentralized WWTP to a centralized WWTP is a feasible way to manage the sludge and enhance the treatment capacity in local WWTP.