Nutrient removal from domestic wastewater: A comprehensive review on conventional and advanced technologies

Higher order volatile fatty acid metabolism and atypical polyhydroxyalkanoate production in fermentation-enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is an established wastewater treatment process, but its wider implementation has been limited by factors like high temperature and low carbon availability. Fermentation-enhanced EBPR (F-EBPR) processes have shown promise in addressing these limitations, but the underlying mechanisms are not fully understood. This study investigates the metabolism of higher order (C4-5) volatile fatty acids (VFAs) in F-EBPR systems using a combination of carbon isotope labelling and shotgun metagenomic sequencing analyses. Results show that butyrate (HBu) uptake leads to the formation of both typical (C4-5) and atypical (C6+) polyhydroxyalkanoates (PHAs) through a combination ofβ-oxidation and standard condensation pathways, while the putative role of HBu oxidisers were identified relative to substrate composition in F-EBPR processes. Metagenomic analysis reveals the presence of genes required for higher order VFA metabolism in both polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). This study also highlights the limitations of current models in describing F-EBPR processes and emphasises the need for improved models that account for higher order VFA metabolism and microbial community dynamics.

High-efficiency nitrogen and phosphorus removal for low C/N rural wastewater using a full-scale multi-stage A2O biofilm reactor combined with horizontal-vertical flow constructed wetlands system

Rural wastewater treatment faces significant challenges in achieving stable effluent quality due to factors such as temperature fluctuations, variations in water quality and quantity, and low carbon-to-nitrogen (C/N) ratios. This study developed a full-scale, non-membrane, multi-stage anaerobic-anoxic-oxic (MSA2O) biofilm reactor integrated with horizontal-vertical flow constructed wetlands (HVCWs), which was operated continuously for approximately 320 days with an average flow of 11.9 m3/d in a rural area of northern China. Key parameters were optimized: hydraulic retention time (HRT) of 21-32 h, aeration rate of 4.0 m3/h, carbon source dosing at 1.25 L/h, PAC dosing at 0.55 L/h, and mixed liquor reflux ratio at 200 %. The system demonstrated high removal efficiencies for COD (74.2 %), NH4+-N (93.4 %), TN (90.6 %), and TP (86.3 %), consistently meeting the class 1A of GB18918-2002, China (COD ≤50 mg/L, NH4+-N ≤ 5 mg/L, TN ≤ 15 mg/L, TP ≤ 0.5 mg/L), even under challenging conditions such as low C/N (3.3) and rainy seasons. More than 70 % of nitrogen and phosphorus were removed in the MSA2O system. Microbial analysis revealed the enrichment of many functional bacteria. Proteobacteria play a key role in denitrification and phosphorus removal. Actinomycetes, Acidobacteria, and Firmicutes to nitrogen fixation and organic matter degradation. Nitrosomonas dominated ammonia oxidation, while Dechloromonas and Accumulibacter significantly contributed to phosphorus uptake. Seasonal variations in microbial diversity enabled consistent and highly efficient nutrient removal. The HVCWs system contributed 16.3 % of total phosphorus removal through selected plant species and phosphorus-absorbing modified ceramsite, ensuring effluent polishing and stability. With low operational costs ($0.12/m3), the integrated system provides an effective and scalable solution for rural wastewater treatment, delivering high-quality effluent with minimal energy consumption.

Nutrient removal performance and microbial composition analysis in hybrid membrane bioreactor for municipal wastewater treatment

The removal of nutrients from wastewater to reduce the toxicity of these compounds to the environment requires more space in wastewater treatment plants to establish anaerobic, anoxic and aerobic treatment stages. To address this limitation, researchers have developed practical, intensive hybrid treatment systems that enhance nutrient removal performance while requiring less space. However, the implementation of hybrid systems within a reactor introduces the interaction between the attached and suspended growth that can influence the microbial community structure and the performance of the system, so it is crucial to understand the composition of the microbial communities involved in hybrid growth to optimize control strategies in these systems. This study investigated the microbial community structure of the integrated moving bed membrane bioreactor (IMBMBR) system and its impact on nutrient removal in municipal wastewater. The findings demonstrated that the effluent quality was improved with the IMBMBR. The efficiency of removing COD, BOD5,NH 4 + -N andPO 4 3 - -P in the IMBMBR were 91 ± 4.0%, 95 ± 4.0%, 99 ± 0.2% and 24 ± 3.0%, respectively. The IMBMBR had better nitrite oxidation and complete nitrification by increasing the diversity and abundance of effective bacteria. The abundance of Proteobacteria, Bacteroidetes and Nitrospira was enhanced in IMBMBR. Coexistence of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in IMBMBR led to increased nutrient removal. The study results suggest that IMBMBR can be an effective process for nutrient removal, achieving quality standards that comply with legal requirements for wastewater in municipal and industries with limited space for establishing treatment facilities. Additionally, this process can be quickly implemented as an upgrade to existing wastewater treatment plants, avoiding the need to develop an entirely new system.

Wastewater as a resource for carbon capture: A comprehensive overview and perspective

As two important but energy-intense processes, carbon capture and wastewater treatment always attract wide research interests to improve their operational efficiency and technological feasibility. Consequently, utilizing wastewater for carbon capture or integrating carbon capture plants into wastewater treatment facilities has become a promising concept drawing great attention to investigate and demonstrate its feasibility and efficiency. In this study, recent research progress and concept validation studies of utilizing wastewater for carbon capture were briefly reviewed and summarized with the status and main challenges of this concept provided accordingly. Three integration strategies for combining carbon capture with wastewater treatment-utilization of wastewater as the absorbent to capture CO2, biological pathway for simultaneous carbon capture and wastewater treatment, and electrochemical approach to integrate wastewater purification with carbon capture-were primarily reviewed and discussed in this study. Meanwhile, the perspectives of these integrated technology strategies were also discussed providing guidance for future investigations and development of carbon capture with wastewater treatment. Based on our study, the integrated wastewater treatment and carbon capture shows promising prospects in terms of reducing energy consumption and cost of carbon capture and wastewater treatment. However, more relevant studies and demonstrations are still necessary to improve efficiency and reduce possible carbon emissions. As a promising technology contributing to achieving net-zero emission and mitigating global warming, the integration of wastewater treatment and carbon capture will attract more attention in the future.

Assessment of Garbage Enzyme as a Bioremediation Method for the Wastewater Treatment

This study evaluates the efficacy of garbage enzyme (GE) in bioremediation to reduce pollutants in sewage drains that discharge into the natural streams and rivers. Garbage enzyme is prepared with help of brown sugar, fruit, vegetable wastes, and water in the proportion 1:3:10 (by weight), which is then applied to the samples collected from various drainage sites in Jaunpur district, Uttar Pradesh, India. Different concentrations of GE (ranging from 0% to 20%) are mixed with sewage to assess pollution reduction. Different parameters, that is, pH, dissolved oxygen (DO), total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and CD have been measured on 3rd, 5th, 7th, 10th, 15th, and 20th days. It has been observed in the study that significant percentage reduction in BOD, COD, TSS, and TDS of 80.6%, 62.9%, 74.29%, and 43.9%, respectively, while an increase in DO is 67.8% on 20th day of experiment with 20% GE addition. The result of the study reveals that there is highest reduction occurring on the 20th day with a 20% GE concentration. It has been observed that the GE possesses protease, amylase, and lipase activity. Meaning GE contains microorganisms that breakdown carbohydrates, fats, and proteins and it hydrolyzes these complex organic molecules into simpler compounds, making them more readily biodegradable and that is the reason for substantial reduction in the pollutants. Moreover, in this study it has been observed that there is a notable decrease in foul odor emanating from the samples. Time-dependent fluctuations in pH, TDS, DO, BOD, COD, and temperature are documented, with their correlations examined. This investigation underscores GE's potential in pollution mitigation, particularly in sewage systems, and offers valuable insights for sustainable environmental management practices aimed at conserving natural water bodies. Further tests are required to check the efficiency of treatment with GE dosage higher than 20%.

The fate of atenolol in wastewater treatment plants of representative densely urban agglomerations in China

Atenolol (ATL) that can decrease heart rate and reduce renin release is extensively used in the treatment of hypertension, angina, and other diseases. ATL's popularity has therefore drawn attention to its environmental behavior and potential impacts. Wastewater treatment plants (WWTPs) are the main collection point for ATL entering the water environment, highlighting the necessity of studying its fate in the environment. In this study, five WWTPs with different processes in China's representative densely urban agglomerations (Pearl River Delta [PRD] region) were selected as certain representative sampling sites to investigate the fate of ATL in the WWTPs over four seasons. Results showed that ATL concentration in the influent of these WWTPs was 146.5-918.6 ng/L and the corresponding concentration in the effluent was 43.0-534.1 ng/L, achieving a certain degree of removal. The seasonal ATL removal performance varied greatly among these WWTPs, Liede, Tai Po, and Sha Tin WWTPs showed better removal stability. Meanwhile, the average ATL removal rates in Tai Po (83.36%) and Sha Tin (81.67%) were higher than those in the Futian (71.24%), Liede (55.44%), and Stonecutters Island WWTPs (44.96%). The primary treatment capacity of Futian WWTP was better than that of Tai Po and Sha Tin WWTPs in removing ATL, while the performance of secondary treatment was opposite. Moreover, Zahn-Wellens test demonstrated that ATL could be almost completely degraded after 30 days and some protonated molecules (e.g., m/z 145 and m/z 190) metabolites were formed, indicating that degradation may play a role in ATL removal in WWTPs.

Engineered crystalline polymers for effective contaminant removal from water

Herein, we discuss the structure-function of biomimetic imidazole-quartet substrates (I-quartets) obtained through the adaptive self-assembly of octyl-ureido-polyol structures in polyamide membranes designed as adsorbents. Molecular dynamics (MD) and well-tempered metadynamics simulations are utilized to examine ion contaminants' adsorption process and dynamic behaviors onto alkylureido-ethylimidazoles with well-defined supramolecular structures. Moreover, the atoms-in-molecules (AIM) analysis identified multiple types of atomic interactions between the contaminant molecules and the substrates. The results demonstrate that I-quartets with hydrophobic tails significantly enhance the adsorption of contaminant species in the aquatic environment. Descriptors involving interaction energies mean square displacement, radial distribution function, root-mean-square deviation, the number of hydrogen bonds, and solvent-accessible surface area are estimated from the simulation trajectories to study this process. The system containing PO43- exhibited notable stability, as indicated by data analysis. Electrostatic interactions primarily govern the adsorption process; however, the interaction between the active sites of alkylureido-ethylimidazole-based channels, such as N = C and O = C, and the investigated contaminant species (PO43-, NO3-, NO2-, and HNO3) can enhance adsorption due to these interactions. In addition, the free energy values for the adsorption process of PO43-, NO3-, NO2-, and HNO3 contaminants in water are - 604.77, - 532.63, - 461.24, and - 348.62 kJ mol-1, respectively. The obtained results confirm that alkylureido-ethylimidazoles are prominent adsorbents for removing pollutant ions from wastewater, thus contributing to the development of more efficient materials for water purification.

Simultaneous nitrification and denitrification framework for decentralized systems: Long-term study utilizing rope-type biofilm media under field conditions

This research introduces a novel approach to achieve simultaneous nitrification-denitrification (SND) under dynamic load conditions using a cost-effective rope-type biofilm technology. The approach represents a significant advancement in wastewater treatment, particularly beneficial for remote and decentralized communities. The biofilm-based SND process was developed using a pilot-scale flow-through reactor by implementing upstream carbon management with constant-timer-based aeration control versus dynamic-sensor-based aeration control strategies. The findings indicate that adding an upstream anaerobic pretreatment process to handle excess carbon plays a substantial role in achieving a sustainable SND process under a dynamic load environment using simple aeration on-off control. The most optimal nitrification performance of 0.32 g NH3-N/m2/d (89 % removal) was achieved under a 1-hour ON/30-minute OFF aeration. The process sustained an average bulk liquid DO of 5.16 mg/L and 3.80 mg/L during the aeration ON and OFF periods, respectively, facilitating a 0.13 g N/m2/d (41 %) total inorganic nitrogen (TIN) removal, notably, implementing advanced aeration strategies driven by DO, NH3, and NO3 sensors enhanced TIN removal efficiency to 72 %. The nitrification performance remained comparable (89 % removal), resulting in 3 and 10 mg N/L effluent ammonia and TIN concentration, respectively. Additionally, utilizing two multivariate approaches accounting for 82 % and 64 % of the variance, this study discerned patterns in monitored variables and performance. Additionally, the analysis underscored the difference of bulk liquid DO levels in the biofilm versus suspended systems inhibiting the SND process. Distinct bacterial communities were established in biofilms under aerobic, anaerobic, and SND conditions, with the SND reactor showing a hierarchy of functional group and enzymes, enriched sequentially from heterotrophs to denitrifiers, nitrifiers, and anammox bacteria. These innovations underline the potential of tailored control strategies to enhance a passive biofilm-based SND process efficiency under dynamic conditions, providing scalable solutions for diverse target water quality demands in remote communities and decentralized systems.

Spatial variability of bacterial biofilm communities in a wastewater effluent-impacted suburban stream ecosystem

Wastewater discharge is a global threat to freshwater resources. Streams, in particular, are receiving waterbodies that are directly impacted chemically and biologically due to effluent discharge. However, it is largely unknown how wastewater serves as a subsidy or a stressor to aquatic biodiversity, particularly microbiota, over space. Nutrient-diffusing substrata (NDS) were deployed; NDS release nutrients through diffusion into the water column into a wastewater-dependent stream across three reaches. We used N, P, and N + P treatments for the measurement of single nutrient and co-nutrient limitation, and a no-nutrient control. Both algal and total biofilm biomass was measured and the 16S ribosomal RNA genes via targeted amplicon sequencing was used to assess bacterial/archaeal community diversity. Data indicated that total organic matter in biofilms differs spatially with the greatest organic matter (OM) concentrations in the confluence downstream of wastewater inputs. Biofilm OM concentrations were greatest in P and N + P treatments in the confluence site relative to control or N-only treatments. This indicates heterotrophic microbial communities-likely bacteria that dominate stream biofilms-are P-limited in this ecosystem even with upstream wastewater inputs. In conjunction, bacteria/archaeal communities differed the greatest among nutrient treatments versus spatially and had several indicator taxa belonging to Flavobacterium spp. in N treatments relative to controls. Collectively with historical water quality data, we conclude that this wastewater-fed stream is primarily N-enriched but potentially P-limited, which results in significant shifts in biofilm bacterial communities and likely their overall biomass in this urban watershed.

IMPORTANCE

Streams in arid and semi-arid biomes are often dependent on their flow from municipal sources, such as wastewater effluent. However, wastewater has been shown to contain high concentrations of nutrients and chemical pollutants that can potentially harm aquatic ecosystems and their biota. Understanding if and the type of microorganisms that respond to pollution sources, specifically effluent from wastewater treatment facilities, in regions where flow is predominantly from treatment facilities, is critical for developing a predictive monitoring approach for eutrophication or other ecological degradation states for freshwaters.

Short-term effect of reclaimed water irrigation on soil health, plant growth and the composition of soil microbial communities

The scarcity of freshwater poses significant challenges to agriculture, often necessitating the use of alternative water sources such as reclaimed water. While reclaimed water offers a viable solution by providing water and nutrients to crops, its potential impacts on soil microbial communities remain a subject of investigation. In this investigation, we conducted a field experiment cultivating Maize (Zea mays) and Lavender (Lavandula angustifolia), employing irrigation with reclaimed water originating from domestic wastewater, while control samples were irrigated using freshwater. Utilizing high-throughput sequencing, we assessed the effect of reclaimed water on soil bacteria and fungi. Plant biomass exhibited a significant response to treated wastewater. Alpha diversity metrics of soil microbial communities did not reveal significant changes in soils irrigated with reclaimed water compared to control samples. Reclaimed water, however, demonstrated a selective influence on microorganisms associated with nutrient cycling. Co-occurrence network analysis unveiled that reclaimed water may alter soil microbial community structure and stability. Although our work presents overall positive outcomes, further investigation into the long-term implications of reclaimed water irrigation is warranted.

Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for household wastewater treatment: simultaneous pollutant removal and hydrogen production

The septic tank is the most commonly used decentralized wastewater treatment systems for household wastewater treatment in on-site applications. The removal rate of various pollutants is lower in different septic tank configurations. The integration of a microbial electrolysis cells (MEC) into septic tank or biofilm-based reactors can be a green and sustainable technology for household wastewater treatment and energy production. In this study, a 50-L septic tank was converted into a 50-L MEC coupled with biofilm-based reactor for simultaneous household wastewater treatment and hydrogen production. The biofilm-based reactor was integrated by an anaerobic packed-bed biofilm reactor (APBBR) and an aerobic moving bed biofilm reactor (aeMBBR). The MEC/APBBR/aeMBBR was evaluated at different organic loading rates (OLRs) by applying voltage of 0.7 and 1.0 V. Result showed that the increase of OLRs from 0.2 to 0.44 kg COD/m3 d did not affect organic matter removals. Nutrient and solids removal decreased with increasing OLR up to 0.44 kg COD/m3 d. Global removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), ammoniacal nitrogen (NH4+), total phosphorus (TP) and total suspended solids (TSS) removal ranged from 81 to 84%, 84 to 85%, 53 to 68%, 88 to 98%, 11 to 30% and 76 to 88% respectively, was obtained in this study. The current density generated in the MEC from 0 to 0.41 A/m2 contributed to an increase in hydrogen production and pollutants removal. The maximum volumetric hydrogen production rate obtained in the MEC was 0.007 L/L.d (0.072 L/d). The integration of the MEC into biofilm-based reactors applying a voltage of 1.0 V generated different bioelectrochemical nitrogen and phosphorus transformations within the MEC, allowing a simultaneous denitrification-nitrification process with phosphorus removal.

Identifying leverage points using material flow analysis to circularise resources from urban wastewater and organic waste

Anthropogenic systems are synonymous with linear economies that cause widespread resource waste and environmental degradation. Urban areas are hotspots for this behaviour due to their high population density and resource consumption. Changing this situation is limited by the lack of a holistic but sufficiently detailed understanding of system units where resource waste occurs. The objectives of this study were: (1) to develop and apply a model of the material and substance (nitrogen, phosphorus, and carbon) flows of organic waste and wastewater systems at a local scale, taking Christchurch, New Zealand, as a study case, and (2) to identify leverage points within the system to achieve resource circularisation. Results show that groundwater, infiltrated water, and industrial wastewater are the predominant material flows into the system. Nitrogen and phosphorus inputs predominantly come from food products, detergents, green waste, and industrial wastewater. The Christchurch wastewater system is a prime example of a linear economy, where ∼66 % of the nitrogen and ∼63 % of the phosphorus entering the wastewater system is discharged to the ocean. Leakage from the water supply system reduces water resource efficiency, while water infiltration into the wastewater network inflates the quantity of wastewater treated at the centralised treatment plant, limiting nutrient recovery. In the compost facility, 86 % of the waste is composted, with 33% of the nitrogen and all the phosphorus exiting as compost, while ∼66 % of the nitrogen treated exits through volatilisation. The remaining 14 % of the organic waste entering the treatment plant is deemed unsuitable for composting and is landfilled. The material and substance flow analysis allowed the identification of flows with leverage points in the system where there are opportunities to reduce, reuse, or recover materials and substances to encourage circularisation. These flows include food products, detergents, unsuitable materials for composting, domestic water supply leakages, wastewater network infiltration, and wastewater treatment plant's nutrient recovery.

Enhanced pollution removal from canal water by coupling aeration to floating treatment wetlands

Floating treatment wetlands (FTWs) are natural solutions for purifying polluted water, providing a green surface area and improving city landscape. This study investigated if the efficiency of FTWs can be improved by aeration for treating contaminated canal water. The three used plant species were Canna generalis, Phragmites australis, and Cyperus alternifolius. The experiment was carried out in three FTWs with aeration and three without aeration to compare the removal for COD, NH4+-N, E. coli, PO43--P, and Fe. In the aerated FTWs, air blowers were installed to run at two different air flow rates of 2.5 L min-1 (Batch 1) and 1.0 L min-1 (Batch 2). Aeration increased the dissolved oxygen concentrations in each tank, which came over 6.5 mg L-1 in both batches. This study sheds light on the positive impact of aeration has on COD and NH4+-N removal: these are nearly three-fold higher compared to non-aeration conditions and reached approximately 99% (1.7-log reduction) for E. coli removal. Additionally, the plant growth rate in the aerated FTWs was higher than in the non-aerated ones. The average shoot growth rate of Phragmites australis was 0.76 cm d-1 for the aerated FTW which was two-fold higher compared to the non-aerated one.

Establishing mainstream partial nitrification in the membrane aerated biofilm reactor by limiting the oxygen concentration in the biofilm

The proliferation of nitrite oxidizing bacteria (NOB) still remains as a major challenge for nitrogen removal in mainstream wastewater treatment process based on partial nitrification (PN). This study investigated different operational conditions to establish mainstream PN for the fast start-up of membrane aerated biofilm reactor (MABR) systems. Different oxygen controlling strategies were adopted by employing different influent NH4+-N loads and oxygen supply strategies to inhibit NOB. We indicated the essential for NOB suppression was to reduce the oxygen concentration of the inner biofilm and the thickness of aerobic biofilm. A higher NH4+-N load (7.4 g-N/(m2·d)) induced higher oxygen utilization rate (14.4 g-O2/(m2·d)) and steeper gradient of oxygen concentration, which reduced the thickness of aerobic biofilm. Employing closed-end oxygen supply mode exhibited the minimum concentration of oxygen to realize PN, which was over 46% reduction of the normal open-end oxygen mode. Under the conditions of high NH4+-N load and closed-end oxygen supply mode, the microbial community exhibited a comparative advantage of ammonium oxidizing bacteria over NOB in the aerobic biofilm, with a relative abundance of Nitrosomonas of 30-40% and no detection of Nitrospira. The optimal fast start-up strategy was proposed with open-end aeration mode in the first 10 days and closed-end mode subsequently under high NH4+-N load. The results revealed the mechanism of NOB inhibition on the biofilm and provided strategies for a quick start-up and stable mainstream PN simultaneously, which poses great significance for the future application of MABR.

Optimizing wastewater treatment through artificial intelligence: recent advances and future prospects

Artificial intelligence (AI) is increasingly being applied to wastewater treatment to enhance efficiency, improve processes, and optimize resource utilization. This review focuses on objectives, advantages, outputs, and major findings of various AI models in the three key aspects: the prediction of removal efficiency for both organic and inorganic pollutants, real-time monitoring of essential water quality parameters (such as pH, COD, BOD, turbidity, TDS, and conductivity), and fault detection in the processes and equipment integral to wastewater treatment. The prediction accuracy (R2 value) of AI technologies for pollutant removal has been reported to vary between 0.64 and 1.00. A critical aspect explored in this review is the cost-effectiveness of implementing AI systems in wastewater treatment. Numerous countries and municipalities are actively engaging in pilot projects and demonstrations to assess the feasibility and effectiveness of AI applications in wastewater treatment. Notably, the review highlights successful outcomes from these initiatives across diverse geographical contexts, showcasing the adaptability and positive impact of AI in revolutionizing wastewater treatment on a global scale. Further, insights on the ethical considerations and potential future directions for the use of AI in wastewater treatment plants have also been provided.

Levels of Potentially Toxic and Essential Elements in Water and Estimation of Human Health Risks in a River Located at the Interface of Brazilian Savanna and Amazon Biomes (Tocantins River)

The Tocantins-Araguaia basin is one of South America's largest river systems, across three Brazilian states (Maranhão, Tocantins, and Pará), within the Legal Amazon region. Despite draining extensive Cerrado savanna and rainforest ecosystems, it has suffered significant degradation, notably in the past 40 years. Human activities, including agricultural expansion, deforestation, and the introduction of non-native species, have worsened the environmental damage, which is alarming since many residents and villages along the middle Tocantins River rely on it for water supply, recreation, and fishing. This study assessed the concentration of potentially toxic and essential elements in water samples from four sampling sites distributed along the middle Tocantins River. The monitoring occurred throughout 2023, involving the measurement of parameters both on-site and in the laboratory. Water quality and its health implications were evaluated using the Weighted Arithmetic Water Quality Index (WAWQI), the Water Quality Index (WQI), and the health risk assessment index. The levels of aluminum, copper, iron, magnesium, and selenium exceeded legal standards. Seasonal fluctuations indicate a complex dynamic influenced by climatic or seasonal factors, with February showing the highest values. Site P1, located in urban areas, exhibited elevated mean concentrations for conductivity, total dissolved solids (TDS), and chlorophyll, indicating the need for continuous monitoring. The nitrogen concentrations at P1 raise concerns regarding drinking water quality, which is a concern for the region's residents who use untreated river water. Despite seasonal variations in element concentrations, the overall WAWQI categorized all sections as "Excellent," and the WQI rated as "Good." Human health risk assessments detected no risks, but continuous monitoring and interventions are crucial for sustained water quality improvement.

Modeling greenhouse gas emissions from biological wastewater treatment process with experimental verification: A case study of paper mill

Wastewater treatment plants (WWTPs) have been regarded as the main sources of greenhouse gas (GHG) emissions. This study compares the influent characteristics of industrial wastewater represented by the WWTP of paper mill and that of domestic sewage represented by the Benchmark Simulation Model No. 1 (BSM1) under stormy weather. The various sources of GHG emissions from the two processes are calculated, and the contribution of each source to the total GHG emissions is assessed. Firstly, based on the mass balance analysis and the recognized emission factors, a GHG emission calculation model was established for the on-site and off-site GHG emission sources from the WWTP of paper mill. Simultaneously, a GHG emission experimental model was established by determining the dissolved concentrations of carbon dioxide (CO2) and nitrous oxide (N2O) in the papermaking wastewater, to verify the accuracy of the developed GHG calculation model. Subsequently, an optimum aeration rate for the paper mill was investigated to comply with the discharging norms. Under the optimum aeration rate of 10 h-1, the obtained calculation accuracies of CO2 and N2O emissions were 94.6 % and 91.1 %, respectively. The mean total GHG emission in the WWTP of paper mill was 550 kg CO2-eq·h-1, of which 44.6 % came from the on-site emission sources and 55.4 % from the off-site emission sources. It was also uncovered that the electrical consumption for aeration was the largest contributor to the total GHG emissions with a proportion of 25.2 %, revealing that the control strategy of the aeration rate is highly significant in reducing GHG emissions in WWTP of paper mills.

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.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Engineered algal systems for the treatment of anaerobic digestate: A meta-analysis

The objective of this review was to provide quantitative insights into algal growth and nutrient removal in anaerobic digestate. To synthesize the relevant literature, a meta-analysis was conducted using data from 58 articles to elucidate key factors that impact algal biomass productivity and nutrient removal from anaerobic digestate. On average, algal biomass productivity in anaerobic digestate was significantly lower than that in synthetic control media (p < 0.05) but large variation in productivity was observed. A mixed-effects multiple regression model across study revealed that biological or chemical pretreatment of digestate significantly increase productivity (p < 0.001). In contrast, the commonly used practice of digestate dilution was not a significant factor in the model. High initial total ammonia nitrogen suppressed algal growth (p = 0.036) whereas initial total phosphorus concentration, digestate sterilization, CO2 supplementation, and temperature were not statistically significant factors. Higher growth corresponded with significantly higher NH4-N and phosphorus removal with a linear relationship of 6.4 mg NH4-N and 0.73 mg P removed per 100 mg of algal biomass growth (p < 0.001). The literature suggests that suboptimal algal growth in anaerobic digestate could be due to factors such as turbidity, high free ammonia, and residual organic compounds. This analysis shows that non-dilution approaches, such as biological or chemical pretreatment, for alleviating algal inhibition are recommended for algal digestate treatment systems.

Health risk assessment of heavy metals in saffron (Crocus sativus L.) cultivated in domestic wastewater and lake water irrigated soils

Irrigation of crops with domestic wastewater (DW) is a common practice in developing countries like India. However, domestic wastewater irrigation poses a risk of migration of toxic heavy metals to edible parts of crops, which requires serious measures to prevent their uptake. In this study, the effect of DW irrigation in comparison with Sarbal Lake water (SLW) and borewell water (BW) on soil characteristics and cultivated saffron (Crocus sativus L.) was investigated. For this purpose, samples of water, soil, and saffron (corm, petal, and stigma) were collected from the suburban area of Pampore, Srinagar district, Jammu and Kashmir, India. The results showed that DW irrigation had the maximum significant (p < 0.05) influence on the physico-chemical and nutrient characteristics of the soil, followed by SLW and BW irrigation, respectively. The growth and yield parameters of saffron were also significantly (p < 0.05) increased in the case of DW irrigation as compared to SLW and BW. The quality ranking of the cultivated saffron was found to be in accordance with the ISO standard (III: BW and II: DW and SLW). On the other hand, DW irrigation showed a significant increase in heavy metal contents (mg/kg) of saffron plant parts such as As (0.21-0.40), Cd (0.04-0.09), Cr (0.16-0.41), Cu (7.31-14. 75), Fe (142.38-303.15), Pb (0.18-0.31), Mn (15.26-22.81), Hg (0.18-0.25), Ni (0.74-1.18), Se (0.13-0.22), and Zn (3.44-4.59), followed by SLW and BW. However, the levels of heavy metals did not exceed the FAO/WHO safe limits. Bioaccumulation factor (BAF), dietary intake modeling (DIM<0.006496), health risk assessment (HRI<0.028571), and target hazard quotient (THQ<1) analyses showed no potential health hazard associated with the consumption of saffron irrigated with DW and SLW. Therefore, the results of this study provide valuable insights into the optimization of irrigation sources for saffron cultivation.

A critical review of the mechanisms, factors, and performance of pervious concrete to remove contaminants from stormwater runoff

Stormwater can carry pollutants accumulated on impervious surfaces in urban areas into natural water bodies in absence of stormwater quality improvement devices. Pervious concrete (PC) pavement is one of the low-impact development practices introduced for urban flooding prevention and stormwater pollution reduction. PC removes various types of water contaminants. Mechanisms contributing to the water pollution removal capacity of PC can be categorized into three groups: physical, chemical, and biological. Properties of PC such as permeability, porosity, thickness, and adsorption capacity influence removal of all contaminants, although their impact might differ depending on the pollutant properties. Chemical mechanisms include precipitation, co-precipitation, ion and ligand exchange, complexation, diffusion, and sorption. Bulk organics and nutrients are removed primarily by biodegradation. Physical filtration is the primary mechanism to retain suspended solids, although biological activities may have a minor contribution. Release of calcium (Ca2+) and hydroxide (OH-) from hardened cement elevates the effluent pH, which is an environmental concern. However, the pH elevation is also the prime contributor to heavy metals and nutrients removal through precipitation. Specific cementitious materials (e.g., Pozzolans and nanoparticles) and carbonation curing approach are recommended to control effluent pH elevation. Complexation, diffusion, ion solubility, and stability constants are other mechanisms and parameters that influence heavy metal removal. Organic matter availability, electrostatic attraction, temperature, pH, contact time, specific surface area, and roughness of PC pores contribute to the pathogen removal process. Although PC has been found promising in removing various water pollutants, limited salinity removal can be achieved due to the inherent release of Ca2+and OH- from PC.

A multi-criteria decision framework for circular wastewater systems in emerging megacities of the Global South

Lima faces increasing water stress due to demographic growth, climate change and outdated water management infrastructure. Moreover, its highly centralized wastewater management system is currently unable to recover water or other resources. Hence, the primary aim of this study is to identify suitable wastewater treatment alternatives for both eutrophication mitigation and indirect potable reuse (IPR). For eutrophication mitigation, we examined MLE, Bardenpho, Step-feed, HF-MBR, and FS-MBR. For IPR, we considered secondary treatment+UF + RO + AOP or MBR + RO + AOP. These alternatives form part of a WWTP network at a district level, aiding Lima's pursuit of a circular economy approach. This perspective allows reducing environmental impacts through resource recovery, making the system more resilient to disasters and future water shortages. The methods used to assess these scenarios were Life Cycle Assessment for the environmental dimension; Life Cycle Costing for the economic perspective; and Multi-Criteria Decision Analysis to integrate both the quantitative tools aforementioned and qualitative criteria for social and techno-operational dimensions, which combined, strengthen the decision-making process. The decision-making steered towards Bardenpho for eutrophication abatement when environmental and economic criteria were prioritized or when the four criteria were equally weighted, while HF-MBR was the preferred option when techno-operational and social aspects were emphasized. In this scenario, global warming (GW) impacts ranged from 0.23 to 0.27 kg CO2eq, eutrophication mitigation varied from 6.44 to 7.29 g PO4- equivalent, and costs ranged between 0.12 and 0.17 €/m3. Conversely, HF-MBR + RO + AOP showed the best performance when IPR was sought from the outset. In the IPR scenario, GW impacts were significantly higher, at 0.46-0.51 kg CO2eq, eutrophication abatement was above 98 % and costs increased to ca. 0.44 €/m3.

A hybrid deep learning approach to improve real-time effluent quality prediction in wastewater treatment plant

Wastewater treatment plant (WWTP) operation is usually intricate due to large variations in influent characteristics and nonlinear sewage treatment processes. Effective modeling of WWTP effluent water quality can provide valuable decision-making support to facilitate their operations and management. In this study, we developed a novel hybrid deep learning model by combining the temporal convolutional network (TCN) model with the long short-term memory (LSTM) network model to improve the simulation of hourly total nitrogen (TN) concentration in WWTP effluent. The developed model was tested in a WWTP in Jiangsu Province, China, where the prediction results of the hybrid TCN-LSTM model were compared with those of single deep learning models (TCN and LSTM) and traditional machine learning model (feedforward neural network, FFNN). The hybrid TCN-LSTM model could achieve 33.1 % higher accuracy as compared to the single TCN or LSTM model, and its performance could improve by 63.6 % comparing to the traditional FFNN model. The developed hybrid model also exhibited a higher power prediction of WWTP effluent TN for the next multiple time steps within eight hours, as compared to the standalone TCN, LSTM, and FFNN models. Finally, employing model interpretation approach of Shapley additive explanation to identify the key parameters influencing the behavior of WWTP effluent water quality, it was found that removing variables that did not contribute to the model output could further improve modeling efficiency while optimizing monitoring and management strategies.

Experimental investigation on sludge conditioning and dewatering using an agricultural biomass coupled with resource recovery

In this study, the effect of modified areca husk fibre biochar (MAFB-AlCl3) on dairy sludge conditioning and dewatering along with raw and modified coconut shell biochar (MCSB-FeCl3) was investigated. Further, MgO impregnated biochars of areca husk fibre and coconut shells was carried out to evaluate the performance on phosphate recovery from the diary sludge. The enhancement in sludge dewatering with MAFB-AlCl3 were evaluated experimentally and significant reduction of capillary suction time (CST) (51.6 %), moisture content (18%), zeta potential (1.3 mV) and increased settleability (32.7%) were observed. The sludge conditioning parameters namely dosage (% of dry solids (DS)), rapid mixing time (RMT), slow mixing time (SMT) were optimized by response surface methodology for the modified biochars. Optimum CST (31.51 s) was obtained at dosage (50 % of DS), RMT (9.89 min) and SMT (17.23 min). Results of batch study for phosphate recovery by MgO impregnated biochars (MgB) was found to be 96.6 % and 100 % by MgB of areca husk fibre (MgAFB) and coconut shells (MgCSB) respectively. The morphological characteristics and elemental distribution using field emission scanning electron microscopy (FE-SEM) & energy dispersive X-ray spectroscopy (EDS) reveals the structural change in the sludge particles for the modified biochars as well as for sludge. Hence MAFB-AlCl3, MgAFB and MgCSB is proved to be suitable and an effective candidate for sludge conditioning and dewatering coupled with phosphate recovery in handling the diary sludge.

A pilot-scale study of a novel system for simultaneous nitrogen and carbon removal: technological advancement of a structured bed reactor with intermittent aeration (SBRIA) in real domestic sewage treatment

This study outlines the development of an effective pilot-scale simultaneous denitrification and nitrification (SDN) system using intermittent aeration for the removal of carbon and nitrogen from real domestic sewage. Given the limited research in this area, the main objective was to evaluate the overall performance of the SBRIA system on a pilot scale and show its benefits in domestic wastewater treatment. The structured bed reactor with intermittent aeration (SBRIA) notably achieved 57% efficiency in removing total nitrogen without requiring external carbon sources. It also demonstrated impressive removal rates of 56% for total chemical oxygen demand (CODT) and 82% for biochemical oxygen demand (BOD5), indicating its effectiveness in degrading organic matter. In addition, the SBRIA showed high pH control and managed the consumption of alkalinity without the need for an alkalizer, maintaining consistent mean values of 7.7 ± 0.8 for pH and 166.8 ± 79.8 mg·L-1 for alkalinity. The system also proved resilient against toxic shocks caused by significant variations in influent characteristics. This study offers valuable insights and compelling results into a cost-effective and efficient treatment approach using an innovative technology not previously applied at the pilot scale. Its potential to remediate polluted water is substantial.

Effect of antibiotics addition on nutrient removal stability and microbial community change of the solar-powered oxidation ditch-membrane bioreactor in treating building wastewater

The solar-powered oxidation ditch-membrane bioreactors (SOD-MBR) system was developed and operated with long solid retention times (SRTs) of 80 and 160 days. The aim was to investigate the effects of using a long SRT and antibiotics in building wastewater on the stability of nutrient removal, as well as membrane fouling. An increase in the SRT from 80 days to 160 days did not significantly affect the performance of the SOD-MBR system. Ciprofloxacin and Sulfamethoxazole removal efficiencies were 94.47 ± 1.54% and 87.54 ± 24.7%. However, the presence of antibiotics resulted in lower removal efficiencies for NH4+-nitrogen and phosphorus and stimulated the production of extracellular polymeric substances (EPS), particularly proteins in L-EPS and T-EPS of the foulant. FTIR and FEEM analysis revealed that the microbial sludge primarily consisted of proteins, carbohydrates, and lipids. Furthermore, the relative abundance analysis of microbial communities identified bacteria associated with nitrogen removal in the SOD-MBR system, including Anammox, AOB (ammonia oxidizing bacteria), DNB (denitrifying bacteria), and NOB (nitrite oxidizing bacteria), with a total of 25 genera. The majority of these bacteria were stimulated by the presence of antibiotics, resulting in higher relative abundance. Finally, the SOD-MBR system achieved energy savings of 97.38% by utilizing photovoltaic (PV) technology.

Is nitrification inhibition the bottleneck of integrating hydrothermal liquefaction in wastewater treatment plants?

Sewage sludge management poses challenges due to its environmental impact, varying composition, and stringent regulatory requirements. In this scenario, hydrothermal liquefaction (HTL) is a promising technology for producing biofuel and extracting phosphorus from sewage sludge. However, the toxic nature of the resulting process water (HTL-PW) raises concerns about integrating HTL into conventional wastewater treatment processes. This study investigated the inhibitory effects of HTL-PW on the activity of the main microbial functions in conventional activated sludge. Upon recirculation of the HTL-PW from the excess sludge into the wastewater treatment plant, the level of COD in the influent is expected to increase by 157 mgO2⋅L-1, resulting in 44% nitrification inhibition (IC50 of 197 mg⋅L-1). However, sorption of inhibitory compounds on particles can reduce nitrification inhibition to 27% (IC50 of 253 mg⋅L-1). HTL-PW is a viable carbon source for denitrification, showing nearly as high denitrification rates as acetate and only 17% inhibition at 157 mgO2⋅L-1 COD. Under aerobic conditions, heterotrophic organic nitrogen and organic matter conversion remains unaffected up to 223 mgO2⋅L-1 COD, with COD removal higher than 94%. This study is the first to explore the full integration of HTL in wastewater treatment plants for biofuel production from the excess activated sludge. Potential nitrification inhibition is concerning, and further long-term studies are needed to fully investigate the impacts.

Effects of microaeration and sludge recirculation on VFA and nitrogen removal, membrane fouling reduction and microbial community of the anaerobic baffled biofilm-membrane bioreactor in treating building wastewater

A novel anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) with microaeration of 0.62 LO2/LFeed was developed to improve VFA and nitrogen removal from building wastewater. Three different membrane bioreactor systems - R1: AnBB-MBR (without microaeration); R2: AnBB-MBR with microaeration; and R3: AnBB-MBR with integrated microaeration and sludge recirculation - were operated in parallel at the same hydraulic retention time of 20 h and sludge retention time of 100 d. The microaeration promoted greater microbial richness and diversity, which could significantly enhance the removal of acetic acid and dissolved methane in the R2 and R3 systems. Moreover, the partial nitrification and the ability of anammox (Candidatus Brocadia) to thrive in R2 enabled NH4+-N removal to be enhanced by up to 57.8 %. The worst membrane fouling was found in R1 due to high amount of protein as well as fine particles (0.5-5.0 μm) acting as foulants that contributed to pore blocking. While the integration of sludge recirculation with microaeration in R3 was able to improve the membrane permeate flux slightly as compared to R2. Therefore, the AnBB-MBR integrated with a microaeration system (R2) can be considered as promising technology for building wastewater treatment when considering VFA and nutrient removal and an energy-saving approach with low aeration intensity.

Effect of different types of volatile fatty acids on the performance and bacterial population in a batch reactor performing biological nutrient removal

Different ratios of four volatile fatty acids (VFAs) were used as the primary feed to a laboratory scale biological nutrient reactor during four operational stages. The reactor performed efficiently over 500 days of operation with over 90% dissolved phosphorus and over 98% ammonium-nitrogen (NH4+-N) removal. Through in the first experimental phase, acetate and propionate were present in a significant proportion as carbon sources, the relative abundance of Candidatus Accumulibacter, a potential polyphosphate accumulating organism, increased from 10% to 57% and the Defluviicoccus genus, a known glycogen accumulating organism (GAO), decreased from 41% to 5%. Further tests indicated the presence of denitrifying phosphorus accumulating organisms (DPAO) belonging to Clade IIC, that could use nitrite as the electron acceptor during P-uptake. In general, VFAs favored the increase of the genus Defluviicoccus and Candidatus Accumulibacter. High relative abundance of Defluviicoccus did not affect the stability and the performance of the BNR process.

Microbial fuel cell: Interplay of energy production, wastewater treatment, toxicity assessment with hydraulic retention time

Microbial fuel cell (MFC) operation under similar conditions to conventional methods will support the use of this technology in large-scale wastewater treatment. The operation of scaled-up air-cathode MFC (2 L) fed with synthetic wastewater (similar to domestic) in a continuous flow was evaluated using three different hydraulic retention times (HRT), 12, 8, and 4 h. We found that electricity generation and wastewater treatment could be enhanced under an HRT of 12 h. Additionally, the longer HRT led to greater coulombic efficiency (5.44%) than MFC operating under 8 h and 4 h, 2.23 and 1.12%, respectively. However, due to the anaerobic condition, the MFC was unable to remove nutrients. Furthermore, an acute toxicity test with Lactuca sativa revealed that MFC could reduce wastewater toxicity. These outcomes demonstrated that scaled-up MFC could be operated as a primary effluent treatment and transform a wastewater treatment plant (WWTP) into a renewable energy producer.

Landfill leachate treatment with a full-scale membrane bioreactor: impact of leachate characteristics on filamentous bacteria

Bulking and foaming are extreme filamentous bacterial growths that present serious challenges for the biological leachate treatment process. The current study evaluates the performance of long-term full-scale membrane bioreactor (MBR) treating landfill leachate, specifically focusing on filamentous bacteria overgrowth in the bioreactors. The influence of the variation in leachate structure and operational conditions on floc morphology and filamentous bacteria overgrowth were analyzed for 11 months of operation of the full-scale MBR system. The average chemical oxygen demand (COD) and NH4-N removal efficiencies of the system were 87.8 ± 4% and 99.5 ± 0.7%. However, incomplete denitrification was observed when the F/M ratio was low. The high C/N ratio was observed to enhance the frequency of small flocs. Furthermore, a poor to medium diversity of the microbial community was observed. Haliscomenobacter hydrossis, Microthrix parvicella, and Type 021N were found as the most numerous filamentous organisms. Paramecium spp., Euplotes spp., and Aspidisca spp. were found in small quantities. The limited concentration of PO4-P in the leachate compared to high COD and NH4-N concentrations most probably caused phosphate deprivation and increased abundance of identified filamentous microorganisms. This work is the first study in Türkiye that investigates the bulking and foaming problem in full-scale MBR that treats landfill leachate. Hence, it may provide some pioneering perspectives into landfill leachate remediation by monitoring the hybrid biological system.

Examining current trends and future outlook of bio-electrochemical systems (BES) for nutrient conversion and recovery: an overview

Nutrient-rich waste streams from domestic and industrial sources and the increasing application of synthetic fertilizers have resulted in a huge-scale influx of reactive nitrogen and phosphorus in the environment. The higher concentrations of these pollutants induce eutrophication and foster degradation of aquatic biodiversity. Besides, phosphorus being non-renewable resource is under the risk of rapid depletion. Hence, recovery and reuse of the phosphorus and nitrogen are necessary. Over the years, nutrient recovery, low-carbon energy, and sustainable bioremediation of wastewater have received significant interest. The conventional wastewater treatment technologies have higher energy demand and nutrient removal entails a major cost in the treatment process. For these issues, bio-electrochemical system (BES) has been considered as sustainable and environment friendly wastewater treatment technologies that utilize the energy contained in the wastewater so as to recovery nutrients and purify wastewater. Therefore, this article comprehensively focuses and critically analyzes the potential sources of nutrients, working mechanism of BES, and different nutrient recovery strategies to unlock the upscaling opportunities. Also, economic analysis was done to understand the technical feasibility and potential market value of recovered nutrients. Hence, this review article will be useful in establishing waste management policies and framework along with development of advanced configurations with major emphasis on nutrient recovery rather than removal from the waste stream.

Bio-fabricated bismuth-based materials for removal of emerging environmental contaminants from wastewater

Although rapid industrialization has made life easier for humans, several associated issues are emerging and harming the environment. Wastewater is regarded as one of the key problems of the 21st century due to its massive production every year and requires immediate attention from all stakeholders to protect the environment. Since the introduction of nanotechnology, bismuth-based nanomaterials have been used in variety of applications. Various techniques, such as hydrothermal, solvo-thermal and biosynthesis, have been reported for synthesizing these materials, etc. Among these, biosynthesis is eco-friendly, cost-effective, and less toxic than conventional chemical methods. The prime focuses of this review are to elaborate biosynthesis of bismuth-based nanomaterials via bio-synthetic agents such as plant, bacteria and fungi and their application in wastewater treatment as anti-pathogen/photocatalyst for pollutant degradation. Besides this, future perspectives have been presented for the upcoming research in this field, along with concluding remarks.

Insights into roles of triclosan in microalgal-bacterial symbiosis system treating wastewater

Triclosan (TCS) is an antimicrobial agent and frequently detected in wastewater or water body. This study investigated the role of TCS in microalgal-bacterial symbiosis (MABS) system treating wastewater. The results showed that the removal efficiencies of NH₄⁺-N, total nitrogen, and total phosphorus decreased under increased TCS stress, with decrease ratios of 32.0%, 28.9%, and 46.1%. The activities of microalgae were more affected than that of bacteria. The secretion of extracellular polymeric substances (EPSs) and activity of superoxide dismutase firstly increased and then decreased with aggravated TCS stress, while the accumulation of malondialdehyde increased, leading to increased permeability of cytomembrane and bioaccumulation of TCS. In addition, the aggregation properties of microalgae and bacteria were enhanced with TCS loading increasing, and the migration of TCS was affected by enhanced EPSs secretions and MABS aggregates. This work may provide some new insights into the roles of TCS in MABS system.

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

Electrodialysis Metathesis (EDM) Desalination for the Effective Removal of Chloride and Nitrate from Tobacco Extract: The Effect of Membrane Type

Electrodialysis Metathesis (EDM) desalination was investigated using a squad of three ion-exchange membranes (ACS, TW-A, and A3) and simulated tobacco extract liquid for selective ions removal. We have studied various factors affecting EDM desalination efficiency using a complete experimental design. First, diffusion dialysis (DD) was conducted to determine the permeation rate of different anions in tobacco liquor with different membrane materials. We conclude that A3 had the fastest permeation rate of anions. However, ACS has the lowest permeation rate for different salts. The investigation of the EDM process showed the excellent ion permeation ability of A3 by detecting the current, conductivity, and ion concentration of the target tobacco liquor in the metathesis chamber of the EDM process. The EDM had shown the most excellent chloride ion removal ability. We found that A3 was the best membrane for the EDM process of tobacco liquor.

Macro-nutrients recovery from liquid waste as a sustainable resource for production of recovered mineral fertilizer: Uncovering alternative options to sustain global food security cost-effectively

Global food security, which has emerged as one of the sustainability challenges, impacts every country. As food cannot be generated without involving nutrients, research has intensified recently to recover unused nutrients from waste streams. As a finite resource, phosphorus (P) is largely wasted. This work critically reviews the technical applicability of various water technologies to recover macro-nutrients such as P, N, and K from wastewater. Struvite precipitation, adsorption, ion exchange, and membrane filtration are applied for nutrient recovery. Technological strengths and drawbacks in their applications are evaluated and compared. Their operational conditions such as pH, dose required, initial nutrient concentration, and treatment performance are presented. Cost-effectiveness of the technologies for P or N recovery is also elaborated. It is evident from a literature survey of 310 published studies (1985-2022) that no single technique can effectively and universally recover target macro-nutrients from liquid waste. Struvite precipitation is commonly used to recover over 95 % of P from sludge digestate with its concentration ranging from 200 to 4000 mg/L. The recovered precipitate can be reused as a fertilizer due to its high content of P and N. Phosphate removal of higher than 80 % can be achieved by struvite precipitation when the molar ratio of Mg²⁺/PO₄^3- ranges between 1.1 and 1.3. The applications of artificial intelligence (AI) to collect data on critical parameters control optimization, improve treatment effectiveness, and facilitate water utilities to upscale water treatment plants. Such infrastructure in the plants could enable the recovered materials to be reused to sustain food security. As nutrient recovery is crucial in wastewater treatment, water treatment plant operators need to consider (1) the costs of nutrient recovery techniques; (2) their applicability; (3) their benefits and implications. It is essential to note that the treatment cost of P and/or N-laden wastewater depends on the process applied and local conditions.

A new hybrid ensemble approach for the prediction of effluent total nitrogen from a full-scale wastewater treatment plant using a combined trickling filter-activated sludge system

In this study, different K-nearest neighbors (KNN), support vector regression (SVR), decision tree (DT), and random forest (RF) algorithms integrated with the Bayesian optimization algorithm (BOP) have been applied as novel hybrid modeling/optimization tools to predict the total nitrogen in treated wastewater of Southern Tehran Wastewater Treatment Plant (STWWTP). In order to enhance the outcomes of hybrid models, the chosen sub-models (the best and least correlated hybrid models) were used to generate voting average and stacked regression ensemble models. Throughout the preprocessing step, two alternative scenarios were used to handle missing values from the samples, including elimination versus estimation via linear interpolation. The results of this research demonstrated that ensemble models were better than individual hybrid models, although not all ensemble models were superior to single models. The results also revealed that the stacking regression ensemble model using KNN-BOP and SVR-BOP as sub-models was the most superior model among the developed models, with the coefficient of determination (R²) = 0.640, root mean squared error (RMSE) = 2.378, and mean absolute error (MAE) = 1.838 on the test data. The best hybrid ensemble model that can accurately predict the concentration of total nitrogen (TN) in the effluent can give people a heads-up about water pollution caused by eutrophication before it gets bad.

Technological advancements in valorisation of industrial effluents employing hydrothermal liquefaction of biomass: Strategic innovations, barriers and perspectives

Hydrothermal liquefaction (HTL) is identified as a promising thermochemical technique to recover biofuels and bioenergy from waste biomass containing low energy and high moisture content. The wastewater generated during the HTL process (HTWW) are rich in nutrients and organics. The release of the nutrients and organics enriched HTWW would not only contaminate the water bodies but also lead to the loss of valued bioenergy sources, especially in the present time of the energy crisis. Thus, biotechnological as well as physicochemical treatment of HTWW for simultaneous extraction of valuable resources along with reduction in polluting substances has gained significant attention in recent times. Therefore, the treatment of wastewater generated during the HTL of biomass for reduced environmental emission and possible bioenergy recovery is highlighted in this paper. Various technologies for treatment and valorisation of HTWW are reviewed, including anaerobic digestion, microbial fuel cells (MFC), microbial electrolysis cell (MEC), and supercritical water gasification (SCWG). This review paper illustrates that the characteristics of biomass play a pivotal role in the selection process of appropriate technology for the treatment of HTWW. Several HTWW treatment technologies are weighed in terms of their benefits and drawbacks and are thoroughly examined. The integration of these technologies is also discussed. Overall, this study suggests that integrating different methods, techno-economic analysis, and nutrient recovery approaches would be advantageous to researchers in finding way for maximising HTWW valorisation along with reduced environmental pollution.

Water Harvesting Strategies through Solar Steam Generator Systems

Solar steam generator (SSG) systems have attracted increasing attention, owing to its simple manufacturing, material abundance, cost-effectiveness, and environmentally friendly freshwater production. This system relies on photothermic materials and water absorbing substrates for a clean continuous distillation process. To optimize this process, there are factors that are needed to be considered such as selection of solar absorber and water absorbent materials, followed by micro/macro-structural system design for efficient water evaporation, floating, and filtration capability. In this contribution, we highlight the general interfacial SSG concept, review and compare recent progresses of different SSG systems, as well as discuss important factors on performance optimization. Furthermore, unaddressed challenges such as SSG's cost to performance ratio, filtration of untreatable micropollutants/microorganisms, and the need of standardization testing will be discussed to further advance future SSG studies.

Microalgae Harvesting after Tertiary Wastewater Treatment with White-Rot Fungi

Tertiary wastewater treatment with microalgae incorporates environmental sustainability with future technologies and high exploitation costs. Despite the apparent ecological benefits of microalgae-assisted wastewater treatment/biomass-based resource production, technological improvements are still essential to compete with other technologies. Bio-flocculation instead of mechanical harvesting has been demonstrated as an alternative cost-effective approach. So far, mostly filamentous fungi of genus Aspergillus have been used for this purpose. Within this study, we demonstrate a novel approach of using white-rot fungi, with especially high potential of algae-Irpex lacteus complex that demonstrates efficiency with various microalgae species at a broad range of temperatures (5-20 °C) and various pH levels. Harvesting of microalgae from primary and secondary wastewater resulted in 73-93% removal efficiencies within the first 24 h and up to 95% after 48 h. The apparent reuse potential of the algae-I. lacteus pellets further complements the reduced operating costs and environmental sustainability of bio-flocculation technology.

Portable Colorimetric Hydrogel Test Kits and On-Mobile Digital Image Colorimetry for On-Site Determination of Nutrients in Water

Portable colorimetric hydrogel test kits are newly developed for the on-site detection of nitrite, nitrate, and phosphate in water. Griess-doped hydrogel was prepared at the bottom of a 1.5 mL plastic tube for nitrite detection, a nitrate reduction film based on zinc powder was placed on the inner lid of a second 1.5 mL plastic tube for use in conjunction with the Griess-doped hydrogel for nitrate detection, and a molybdenum blue-based reagent was entrapped within a poly(vinyl alcohol) hydrogel matrix placed at the bottom of a third 1.5 mL plastic tube to detect phosphate. These test kits are usable with on-mobile digital image colorimetry (DIC) for the on-site determination of nutrients with good analytical performance. The detection limits were 0.02, 0.04, and 0.14 mg L−1 for nitrite, nitrate, and phosphate, respectively, with good accuracy (<4.8% relative error) and precision (<1.85% relative standard deviation). These test kits and on-mobile DIC were used for the on-site determination of nutrients in the Pak Bang and Bang Yai canals, the main canals in Phuket, Thailand. The concentrations of nitrite, nitrate, and phosphate were undetectable to 0.60 mg L−1, undetectable to 2.98 mg L−1, and undetectable to 0.52 mg L−1, respectively.

Efficient phosphorus recovery as struvite by microbial electrolysis cell with stainless steel cathode: Struvite purity and experimental factors

Phosphorus (P) recovery from waste streams is an essential choice due to the coming global P crisis. One promising solution is to recover P by microbial electrolysis cell (MEC). Both the P recovery effectiveness and product quality are of critical importance for application. In this study, a two-chamber MEC was constructed and the effects of applied voltage, NaAc concentration, Mg/P molar ratio, N/P molar ratio, and initial P concentration on P recovery and product purity were explored. The maximum P recovery efficiency of 99.64 % and crystal accumulation rate over 106.49 g/m³-d were achieved. Struvite (MAP) was confirmed as the final recovered product and the purity obtained could reach up to 99.95 %. Besides, higher applied voltage, N/P molar ratio and initial P concentration could promote P recovery efficiency, while the purity of MAP showed correlation with applied voltage, Mg/P molar ratio, N/P molar ratio and initial P concentration. The correlation between NaAc concentration and both of the above was not very significant. A lower energy consumption of 4.1 kWh/kg P was observed at the maximum P recovery efficiency. In addition, the efficiency of P recovery from real wastewater also could reach nearly 88.25 %. These results highlight the promising potential of efficient phosphorus recovery from P-rich wastewater by MEC.

Recovery of phosphorus from wastewater: A review based on current phosphorous removal technologies

Phosphorus (P) as an essential nutrient for life sustains the productivity of food systems; yet misdirected P often accumulates in wastewater and triggers water eutrophication if not properly treated. Although technologies have been developed to remove P, little attention has been paid to the recovery of P from wastewater. This work provides a comprehensive review of the state-of-the-art P removal technologies in the science of wastewater treatment. Our analyses focus on the mechanisms, removal efficiencies, and recovery potential of four typical water and wastewater treatment processes including precipitation, biological treatment, membrane separation, and adsorption. The design principles, feasibility, operation parameters, and pros & cons of these technologies are analyzed and compared. Perspectives and future research of P removal and recovery are also proposed in the context of paradigm shift to sustainable water treatment technology.

A Review of the Role of Extracellular Polymeric Substances (EPS) in Wastewater Treatment Systems

A review of the characterization and functions of extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems is presented in this paper. EPS represent the complex high-molecular-weight mixture of polymers excreted by microorganisms generated from cell lysis as well as adsorbed inorganic and organic matter from wastewater. EPS exhibit a three-dimensional, gel-like, highly hydrated matrix that facilitates microbial attachment, embedding, and immobilization. EPS play multiple roles in containments removal, and the main components of EPS crucially influence the properties of microbial aggregates, such as adsorption ability, stability, and formation capacity. Moreover, EPS are important to sludge bioflocculation, settleability, and dewatering properties and could be used as carbon and energy sources in wastewater treatment. However, due to the complex structure of EPS, related knowledge is incomplete, and further research is necessary to understand fully the precise roles in biological treatment processes.