A novel comparative study of modified carriers in moving bed biofilm reactor for the treatment of wastewater: Process optimization and kinetic study

Wastewater treatment using moving bed biofilm reactor technology: a case study of ceramic industry

Biological approaches and coagulation are frequently used to reduce the chemical oxygen demand (COD) for treatment of ceramic effluent water. The technology known as the moving bed biofilm reactor (MBBR) can accomplish this goal. Further, the process of emulsification-aided innovative MBBR using biosurfactants can be proposed for ceramic effluent treatment. In a step-by-step upgrading scheme, biosurfactants and a consortia of halophilic and halotolerant microbial culture was utilized for the treatment of the effluent water. Over the course of 21 days, a progressive decrease in COD of up to 95.79% was achieved. Over the next 48 h period, the biochemical oxygen demand (BOD) was reduced by 98.3%, while total suspended solids (TSS) decreased by 79.41%. With the use of this innovative MBBR technology, biofilm formation accelerated, lowering the COD, BOD, and TSS levels. This allows treated water to be used for further research on recycling it back into the ceramics sector and repurposing it for agricultural purposes. PRACTITIONER POINTS: Implementation of modified MBBR technology for the treatment of effluent water. Biosurfactants could reduce in the organic and inorganic loads. Increase in MLSS values with COD removal observed. The plant operations without the use of chemical coagulants was effective with biosurfactants. Biofilm formation on carriers was scraped and the presence of surfactin and rhamnolipid was confirmed.

Alkali-thermal activated persulfate treatment of tetrabromobisphenol A in soil: Parameter optimization, mechanism, degradation pathway and toxicity evaluation

The continued accumulation of halogenated organic pollutants in soil posed a potential threat to ecosystems and human health. In this study, tetrabromobisphenol A (TBBPA) was used as a typical representative of halogenated organic pollutants in soil, for alkali-thermal activated persulfate (PS) treatment. The results of response surface methodology (RSM) showed a optimal debromination efficiency of TBBPA was 88.99 % under the optimum reaction conditions. Quenching experiments and electron paramagnetic resonance (EPR) confirmed that SO4-•, HO•, O2-• and 1O2 existed simultaneously in the oxidation process. SO4-• played a major role in the initial stage of the reaction, and O2-• played a major role in the the last stage. Based on density functional theory (DFT) and intermediate products, two degradation pathways were proposed, including debromination reaction and β bond scission. Moreover, the basic physical and chemical properties of the soil were affected to a certain extent, while the soil surface structure, elements and functional group composition rarely changed. In addition, the T.E.S.T. analysis and biotoxicity tests proved that alkali-thermal activated PS can effectively reduce the toxicity of TBBPA-contaminated soil, which is conducive to the subsequent safe secondary utilization of soil.

Characterization of the microbial community and prediction of metabolic functions in an anaerobic/oxic system with magnetic micropolystyrene as a biocarrier

Polystyrene (PS) and magnetic polystyrene (MPS) materials have been used extensively in wastewater treatment. In this research, a 55-day anaerobic/oxic process was carried out to evaluate the effects of PS and MPS on microorganisms under aerobic and anaerobic conditions. Scanning electron microscopy results revealed differences in the entanglement state of the sludge with the biocarrier due to differences in surface morphology. High-throughput sequencing analysis showed that the microbial communities differed considerably in the presence of PS and MPS addition under both aerobic and anaerobic conditions. The highest abundance and diversity were observed in the PS reactor, with 929 observed species and a PD_whole_tree index of 91.58 under anaerobic conditions. MPS promoted the enrichment of bacteria related to nitrogen recycling such as Nitrospirota which increased from 1.13% in the seeding sludge to 3.48% and 10.07% in the aerobic reactors with PS and MPS, respectively. Moreover, advanced analysis showed that PS inhibited many microbial functions (e.g., protein export, nitrogen metabolism), and MPS alleviated this inhibition. This study provides significant insights into the microbial effects of PS and MPS and may shed light on biocarrier selection in future studies.

A mini-review on indigenous microbial biofilm from various wastewater for heavy-metal removal - new trends

Biofilm, as a form of the microbial community in nature, represents an evolutionary adaptation to the influence of various environmental conditions. In nature, the largest number of microorganisms occur in the form of multispecies biofilms. The ability of microorganisms to form a biofilm is one of the reasons for antibiotic resistance. The creation of biofilms resistant to various contaminants, on the other hand, improves the biological treatment process in wastewater treatment plants. Heavy metals cannot be degraded, but they can be transformed into non-reactive and less toxic forms. In this process, microorganisms are irreplaceable as they interact with the metals in a variety of ways. The environment polluted by heavy metals, such as wastewater, is also a source of undiscovered microbial diversity and specific microbial strains. Numerous studies show that biofilm is an irreplaceable strategy for heavy metal removal. In this review, we systematize recent findings regarding the bioremediation potential of biofilm-forming microbial species isolated from diverse wastewaters for heavy metal removal. In addition, we include some mechanisms of action, application possibilities, practical issues, and future prospects.

Biodegradation of Congo Red Dye Using Lysinibacillus Species in a Moving Bed Biofilm Reactor: Continuous Study and Kinetic Evaluation

The objective of this work was to develop a low-cost and efficient biocarrier for biodegradation of azo dye (i.e., Congo red (CR) dye). The potential bacterial species, i.e., Lysinibacillus fusiformis KLM1 and Lysinibacillus macrolides KLM2, were isolated from the dye-contaminated site. These bacterial species were immobilized onto the polypropylene-polyurethane foam (PP-PUF) and employed in a moving bed biofilm reactor (MBBR) for the treatment of CR dye. The effectiveness of the MBBR was investigated by operating the bioreactor in a continuous mode at various initial CR dye concentrations (50-250 mg/L) for 113 days. The removal efficiency was found in the range of 88.4-64.6% when the initial dye concentration was varied from 50 to 250 mg/L. The maximum elimination capacity (EC) of 213.18 mg/L.d was found at 250 mg/L of CR dye concentration. In addition, the CR dye utilization rate in the MBBR was studied by using two kinetics, namely, first-order and second-order (Grau) models. The high regression coefficients (R2 > 0.97) and the satisfactory root mean square (RMSE) values (0.00096-0.02610) indicated the reasonable prediction of CR dye degradation rate by the Grau model.

Kinetic Study for Startup of Aerobic Moving Bed Biofilm Reactor in Treatment of Textile Dye Wastewater

Due to high augmentation in population and low availability of land, the quantum of wastewater production has surged resulting in advancements in wastewater treatment systems. To cope under such stressful circumstances, moving bed biofilm reactor (MBBR) proves to be an upgraded treatment technology for industrial and municipal wastewater treatment. The present startup study has been carried out using a laboratory-scale aerobic MBBR with working volume of 25L for textile dye wastewater treatment having AnoxKaldnes K3 media at filling percentage of 50%. In order to acclimatize the microorganisms on textile dye wastewater, the startup of the reactor was carried out using lactose as readily degradable co-substrate with textile dye wastewater in different ratios at hydraulic retention time (HRT) of 24 h. The biofilm on the media was developed in 63 days duration and the reactor attained pseudo-steady state (PSS) in 185 days period. During PSS condition of the MBBR, the maximum chemical oxygen demand (COD) removal efficiency of 92% with mixed liquor suspended solids (MLSS) concentration of 4224 ± 22 mg/L has been achieved. The kinetic study for biodegradation of textile dye wastewater has also been carried out using the Monod growth kinetics. The values of bio-kinetic coefficients of yield of heterotrophic biomass (Y) and endogenous decay coefficient for heterotrophic biomass (Kd) recorded are 0.394 mgVSS/mgCOD.d and 0.087 day-1, respectively. The values of specific substrate removal rate (k), Monod half saturation constant (Ks), and maximum specific growth rate for heterotrophic biomass (µmax) are 0.024 mgCOD/mgVSS.d, 53.203 mg/L, and 0.0095 day-1, respectively, demonstrating the suitability and healthy performance of MBBR for textile dye wastewater treatment.

Controllable synthesis of Co-Al layered double hydroxides with different anionic intercalation layers for the efficient removal of methyl orange

In order to investigate the effect of the types of interlayer anions on the adsorption performance of LDHs, herein, we synthesized three cobalt-aluminum layered double hydroxides (CoAl-LDHs) with different interlayer anions (NO3-/Cl-/CO32-). The experimental results demonstrate that the CoAl-LDH (Cl-) exhibited high adsorption capacity of 1372.1 mg/g at room temperature and the fastest adsorption rate on methyl orange (MO), mainly attributed to the excellent ion exchange capacity and high specific surface area and pore volume. Furthermore, the ion exchange driven by electrostatic interaction, hydrogen bonding, and surface complexation might be the main mechanisms for MO adsorption on CoAl-LDH (Cl-) and CoAl-LDH (NO3-). However, the MO adsorption on CoAl-LDH (CO32-) was strongly pH-dependent and the optimal pH value was about 3.5. Additionally, the supramolecular structure of CoAl-LDHs-MO was formed through electrostatic interaction, hydrogen bonding, and surface complexation between the host hydroxide layers and the guest MO- after adsorption equilibrium. An in-depth understanding of the differences in the adsorption performance of three anion-intercalated CoAl-LDHs will provide opportunities for further improvement of the adsorption capacity and exhibit a bright future for the design and optimization of efficient nano-adsorbents shortly.

Construction and performance assessment of Recirculating packed bed biofilm reactor (RPBBR) for effective biodegradation of p-cresol from wastewater

Wastewater containing excess phenolic compounds is considered a major environmental concern due to its adverse impacts on the ecosystem. In this work, an effort has been given to treat the p-cresol from wastewater using Recirculating Packed Bed Biofilm Reactor (RPBBR). The process parameters, namely inoculum dose, pH, and NaCl (w/v) concentration were optimized to enhance the specific growth and obtained to be 14 ml, 7.0, and 1% NaCl (w/100 ml), respectively. Maximum p-cresol removal efficiency of 99.36±0.2% was achieved at 100 mg L^-1 of p-cresol. First-order rate constants were found to be 0.70 day^-1 and 0.96 day^-1 for batch and continuous mode, respectively. The intermediates were analysed using FT-IR and GC-MS analysis. Pseudomonas fluorescens was used to assess bacterial toxicity and observed that the toxicity was reduced in case of treated wastewater. Finally, the performance of continuous RPBBR was better than the batch mode.

Composite carrier enhanced bacterial adhesion and nitrogen removal in partial nitrification/anammox process

The rapid start-up and stable operation of one-stage (Partial nitrification/anammox) PN/A process for low-ammonium wastewater are difficult to be achieved, and many carriers are designed to solve this problem. Here, a composite carrier was developed, in which sepiolite and non-woven fabrics were assembled in polypropylene spherical shells. At the start-up phase, P_A reactor using the composite carriers reached a higher nitrogen removal rate of 134.50 ± 19.60 mg·N·L^-1d^-1, in contrast to that of 48.85 ± 19.64 mg·N·L^-1d^-1 in the P_B reactor without sepiolite carriers. When the final influent ammonium concentration of PN/A process is 100 mg/L, the total nitrogen removal efficiency can reach 72 ± 0.03 %. High biomass immobilization ability of composite carrier was evidenced by the greater adsorption trend between sludge and sepiolite than that between sludge and non-woven fabrics, where hydrophobic interaction and Van der Waals interaction played a major role. Extracellular protein (PN) content and the ratio of PN and extracellular polysaccharide of samples in P_A were significantly higher than those in P_B, verifying higher biofilm formation ability on the composite carrier. The composite carrier also increased the abundance of dominant bacteria in PN/A process, especially AOB, the relative abundance of which reached 46.11 %. And it increased the abundance of essential functional genes for nitrogen conversion as their perfect acid neutralizing effects. This study is of great significance in improving the start-up speed and stable operation of this process.

Treatment capacity of a novel flexible fibre biofilm bioreactor treating high-strength milk processing wastewater

This study was focused on the capacity investigation of a novel multistage flexible fibre biofilm reactor (MS-FFBR) to treat milk processing wastewater (MPW) with high organic loading (OLR). The MS-FFBR performance was evaluated at four intermediate stages separately, and also the final effluent quality of the overall system with an influent chemical oxygen demand (COD_in) ranged from 1500 ± 20 to 6000 ± 50 mg/L and hydraulic retention times (HRTs) of 8, 12, and 16 h. By comparting the bioreactors into the four stages effectively enhanced the bioreactor's performance. The maximum TCOD removal efficiency was achieved at the first stage, which was about 89 ± 20, 82 ± 20, and 78 ± 20% at HRTs of 16, 12, 8 h, and low COD_in of 1600 ± 20, 1590 ± 20, and 1673 ± 20 mg/L, respectively. However, the first stage had less contribution to TCOD removal at high COD_in concentrations, reported to be about 42 ± 4%, 46 ± 4%, and 25 ± 4% at COD_in of 5960 ± 40, 5830 ± 40, and 5870 ± 40 mg/L, respectively. Furthermore, the MS-FFBR was effective in removing total suspended solids (TSS) and turbidity. The bioreactor has reduced the effluent turbidity to 9.0 ± 0.2, 20.0 ± 0.6, and 16.1 ± 0.5 NTU at low COD_in concentrations of 1600 ± 20, 1590 ± 20, and 1670 ± 20 mg/L and HRTs of 16, 12, and 8 h, respectively. The bioreactor revealed a high COD removal rate increased from 2.3 ± 0.1 to 12.2 ± 0.4 kg TCOD/m³d by increasing the OLR from 2.4 ± 0.1 to 17.6 ± 0.4 kg TCOD/m³d, confirming high reactor capacity for treatment of high-strength wastewater. Kinetic studies confirmed that the biomass yield was low at various HRTs ranging from 0.1 to 0.2 gVSS/gCOD.

A novel bioscrubber for the treatment of high loads of ammonia from polluted gas

This work presents a novel bioscrubber configuration for the treatment of high ammonia loads at short contact times. The biological reactor was designed to work as a moving-bed biofilm rector (MBBR) increasing biomass retention time. This configuration is still unexplored for the treatment of waste gases. Long-term operation of a lab-scale bioscrubber under different inlet concentrations of ammonia (60-570 ppm_v) and a gas contact time of 4 s was performed to study the system operational limits during 250 days. The effect of the dissolved oxygen concentration on the nitrification rate was also evaluated. Under these conditions, a critical elimination capacity (EC) of 250 NH₃·m^-3·h^-1 and a maximum EC of 300 g NH₃·m^-3·h^-1 were obtained. The maximum nitrification rate obtained was 0.5 kg N·m^-3·day^-1. However, this nitrification rate only was possible to be achieved under partial nitrification. For complete nitrification, the critical nitrification rate was 0.3 kg N·m^-3·day^-1. These results confirm that bioscrubber coupled to a MBBR is a good alternative to treat high ammonia loads with remarkable advantages, such as the retention of properly biomass concentration without auxiliary equipment.

Influence of MBBR carrier geometrical properties and biofilm thickness restraint on biofilm properties, effluent particle size distribution, settling velocity distribution, and settling behaviour

The relatively poor settling characteristics of particles produced in moving bed biofilm reactor (MBBR) outline the importance of developing a fundamental understanding of the characterization and settleability of MBBR-produced solids. The influence of carrier geometric properties and different levels of biofilm thickness on biofilm characteristics, solids production, particle size distribution (PSD), and particle settling velocity distribution (PSVD) is evaluated in this study. The analytical ViCAs method is applied to the MBBR effluent to assess the distribution of particle settling velocities. This method is combined with microscopy imaging to relate particle size distribution to settling velocity. Three conventionally loaded MBBR systems are studied at a similar loading rate of 6.0 g/(m² •day) and with different carrier types. The AnoxK™ K5 carrier, a commonly used carrier, is compared to so-called thickness-restraint carriers, AnoxK™ Z-carriers that are newly designed carriers to limit the biofilm thickness. Moreover, two levels of biofilm thickness, 200 μm and 400 μm, are studied using AnoxK™ Z-200 and Z-400 carriers. Statistical analysis confirms that K5 carriers demonstrated a significantly different biofilm mass, thickness, and density, in addition to distinct trends in PSD and PSVD in comparison with Z-carriers. However, in comparison of thickness-restraint carriers, Z-200 carrier results did not vary significantly compared to the Z-400 carrier. The K5 carriers showed the lowest production of suspended solids (0.7 ± 0.3 g-TSS/day), thickest biofilm (281.1 ± 8.7 µm) and lowest biofilm density (65.0 ± 1.5 kg/m³). The K5 effluent solids also showed enhanced settling behaviour, consisting of larger particles with faster settling velocities.

A kinetic study on the nitrification process in the upflow submerged biofilter reactor

In extent of this study, ammonium removal from wastewater through biological nitrification process was performed in upflow biofilm reactors. The effects of hydraulic retention time (HRT) and nitrogen loading rate (NLR) on the nitrification process were investigated. For the nitrification process, the optimum HRT and NLR were determined to be 80 hr and 0.044 kg/m³.day, respectively. It is observed that the efficiency increased from 53% to 96% along with the increase in HRT from 22 hr to 80 hr and the decrease in NLR from 0.165 kg/m³.day to 0.044 kg/m³.day.The substrate consumption kinetics were studied in the attached growth reactor, and the Monod kinetic model, first-order kinetic model, modified Stover-Kincannon and Grau second-order kinetic models were examined. For the substrate consumption kinetic study, experimental studies were performed at 125, 150, 175, 200, 225 mg NH₄-N/L substrate concentrations and 62 hr at HRT during the nitrification process. As a result of the considering kinetic studies, it was determined that the kinetic study was suitable for the modified Stover-Kincannon kinetic model that had the highest coefficient of regression by 0.997 and when the effluent NH₄-N concentrations and NH₄-N removal efficiencies calculated using kinetic models were examined, it was observed that the results closest to the experimental results (4.5, 10.1, 19.7, 26.2 and 42.3 mg NH₄-N/L) were obtained through the modified Stover-Kincannon model (4.16, 10.71, 18.92, 28.12 and 39.51 mg NH₄-N/L).

Mn oxides enhanced pyrene removal with both rhizosphere and non-rhizosphere microorganisms in subsurface flow constructed wetlands

The polycyclic aromatic hydrocarbons (PAHs) are substantial wastewater pollutants emitted mostly by petroleum refineries and petrochemical industries, and their environmental fate has been of increasing concern among the public. Consequently, subsurface flow constructed wetlands (SFCWs) filled with Mn oxides (W-CW) or without Mn oxides (K-CW) were established to investigate the performance and mechanisms of pyrene (PYR) removal. The average removal rates of PYR in W-CW and K-CW were 96.00% and 92.33%, respectively. The PYR removal via other pathways (microbial degradation, photolysis, volatilisation, etc.) occupied a sizeable proportion, while the total PYR content in K-CW plant roots was significantly higher than that of W-CW. The microorganisms on the root surface and rhizosphere played an important role in PYR degradation in W-CW and K-CW and were higher in W-CW than that in K-CW in all matrix zones. The microorganisms between the 10-16 cm zone from the bottom of W-CW filled with Mn oxides (W-16) were positively correlated with PYR-degrading microorganisms, aerobic bacteria and facultative anaerobes, whereas K-16 without birnessite-coated sand was negatively correlated with these microorganisms.

Bio-augmentation of the filler-enhanced denitrifying sulfide removal process in expanded granular sludge bed reactors

Sulfur- and nitrogen-containing organic industrial wastewaters, which primarily result from several processes, including pharmaceutical, slaughter, papermaking, and petrochemical processes, are typical examples of refractory wastewaters. To ensure resource utilization, sulfur compounds at high concentrations in such wastewaters can be converted to elemental sulfur through specific methods. Specifically, the denitrifying sulfide removal (DSR) process can be employed to effectively recover elemental sulfur via biological sulfide oxidation, and reportedly, bio-augmentation presents as an effective strategy by which the challenges that limit the application of the DSR process can be overcome. However, the bacterial loss resulting from microorganism activity inhibition owing to toxic effect of high sulfide concentration as well as the complexity of the organic matter (carbon source) in actual wastewater environments reduce the actual elemental sulfur production rate. In this regard, the bio-augmentation effect of adding fillers under complex carbon source conditions was studied. The structure and function of the microbial community on the surface of the fillers were also analysed to reveal the internal factors that contributed to the increased efficiency of elemental sulfur generation. The results obtained showed that relative to the control, elemental sulfur generation increased 1.5- and 2-fold following the addition of fillers and fillers with microbial inoculants, respectively. Further, in the reactor with the added filler, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Azoarcus, while in reactor with added fillers plus microbial inoculates, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Arcobacter. These findings indicated that bio-augmentation promoted the expression of sulfur oxidation functional genes. Furthermore, adding Pseudomonas sp. gs1 for bio-augmentation improved the impact load resistance of the biofilm on the surface of the filler, leading to the rapid restoration of the elemental sulfur generation rate after the impact.

Efficiency of various biofilm carriers and microbial interactions with substrate in moving bed-biofilm reactor for environmental wastewater treatment

In a moving bed-biofilm reactor (MBBR), the fluidization efficiency, immobilization of microbial cells, and treatment efficiency are directly influenced by the shape and pores of biofilm carriers. Moreover, the efficacy of bioremediation mainly depends on their interaction interface with microbes and substrate. This review aims to comprehend the role of different carrier properties such as material shapes, pores, and surface area on bioremediation productivity. A porous biofilm carrier with surface ridges containing spherical pores sizes > 1 mm can be ideal for maximum efficacy. It provides diverse environments for cell cultures, develops uneven biofilms, and retains various cell sizes and biomass. Moreover, the thickness of biofilm and controlled scaling shows a significant impact on MBBR performance. Therefore, the effect of these parameters in MBBR is discussed detailed in this review, through which existing literature and technical strategies that focus on the surface area as the primary factor can be critically assessed.

Bioremediation on a chip: A portable microfluidic device for efficient screening of bacterial biofilm with polycyclic aromatic hydrocarbon removal capacity

Polycyclic aromatic hydrocarbons (PAHs) are pollutants of critical environmental and public health concern and their elimination from contaminated sites is significant for the environment. Biodegradation studies have demonstrated the ability of bacteria in biofilm conformation to enhance the biodegradation of pollutants. In this study, we used our newly developed microfluidic platform to explore biofilm development, properties, and applications of fluid flow, as a new technique for screening PAHs-degrading biofilms. The optimization and evaluation of the flow condition in the microchannels were performed through computational fluid dynamics (CFD). The formation of biofilms by PAHs-degrading bacteria Pseudomonas sp. P26 and Gordonia sp. H19, as pure cultures and co-culture, was obtained in the developed microchips. The removal efficiencies of acenaphthene, fluoranthene and pyrene were determined by HPLC. All the biofilms formed in the microchips removed all tested PAHs, with the higher removal percentages observed with the Pseudomonas sp. P26 biofilm (57.4% of acenaphthene, 40.9% of fluoranthene, and 28.9% of pyrene). Pseudomonas sp. P26 biofilm removed these compounds more efficiently than planktonic cultures. This work proved that the conformation of biofilms enhances the removal rate. It also provided a new tool to rapid and low-cost screen for effective pollutant-degrading biofilms.

Current technologies and future perspectives for the treatment of complex petroleum refinery wastewater: A review

Petroleum refinery wastewater (PRW) is a complex mixture of hydrocarbons, sulphides, ammonia, oils, suspended and dissolved solids, and heavy metals. As these pollutants are toxic and recalcitrant, it is essential to address the above issue with efficient, economical, and eco-friendly technologies. In this review, initially, an overview of the characteristics of wastewater discharged from different petroleum refinery units is discussed. Further, various pre-treatment and post-treatment strategies for complex PRW are introduced. A segregated approach has been proposed to treat the crude desalting, sour, spent caustic, and oily wastewater of petroleum refineries. The combined systems (e.g., ozonation + moving bed biofilm reactor and photocatalysis + packed bed biofilm reactor) for the treatment of low biodegradability index wastewater (BOD₅/COD < 0.2) were discussed to construct a perspective map and implement the proposed system efficiently. The economic, toxicity, and biodegradability aspects are also introduced, along with research gaps and future scope.

Bioremediation of greywater using a novel bacterial-fungal consortium: optimization and validation of the operating parameters in vitro

In the present study, removal of pollutants in greywater was investigated using a novel bacterial-fungal consortium. Response surface methodology was used for the optimization of process variables like pH, temperature, inoculum size, and Carbon/Nitrogen (C/N ratio) for degradation of pollutants. Experiments were based on Box Behnken statistical design and the results show a good fit with the quadratic model, coefficient of determination (R²) value of 0.9499. The reliability of the model was established by various statistical parameters like lack of fit, pure error, and residual sum of squares. The optimized conditions for maximum reduction in chemical oxygen demand, oil & grease and sulphate were found to be 78.7%, 82.6% and 89.7%, respectively after 96 h of incubation of the reaction mixture at pH 7; temperature 35°C; inoculum size 150 µl and C/N ratio of 1:2. Our results clearly demonstrate that the developed novel bacterial-fungal consortium can be a cost-effective, safe, and environment-friendly alternative for remediation of greywater.

Biodegradation of Congo red dye using polyurethane foam-based biocarrier combined with activated carbon and sodium alginate: Batch and continuous study

Dyes are an important class of organic pollutants and are well known for their adverse effects on aquatic life and human beings. In this work, an effort has been made to treat the dye-containing wastewater using modified biocarriers in packed bed bioreactors (PBBRs). Lysinibacillus sp. immobilized polyurethane foam combined with activated carbon and sodium alginate was used for the biodegradation of Congo red dye. The optimum values of process time, glucose concentration, and dye concentration were obtained to be 4.0 days, 2.0 g/L, and 50 mg/L, respectively. The maximum dye removal efficiency (RE) of 92.63 % was obtained at the optimized conditions. The continuous PBBR offered a maximum RE and elimination capacity of 90.73% and 10.89 mg/L. d, respectively, at an inlet loading rate of 12 mg/L. d. Moreover, the growth kinetic of Lysinibacillus sp. was well predicted by the Andrew-Haldane model with a regression coefficient of 0.98.

Degradation of 2-Naphthol in Aqueous Solution by Electro-Fenton System with Cu-Supported Stainless Steel Electrode

For the treatment of 2-naphthol wastewater, the homogeneous electro-Fenton process was considered as an effective method but some disadvantages greatly restrict its application. The three-dimensional electro-Fenton (3D-EF) system using a nano zero-valent iron-supported biochar (NZVIs-BC) particle electrode and a Cu-supported stainless steel electrode (Cu-SSE) was proposed to avoid the disadvantages of the homogeneous electro-Fenton. In this work, the 3D-EF system was developed, which consisted of a Cu-SSE (cathode), a graphite rod (anode) and a NZVIs-BC particle electrode. The effect of the ratio of ferrous sulfate heptahydrate (FS) to rice straw (RS), CuSO4•5H2O amount, initial pH of 2-naphthol wastewater and current intensity (the output current of the power supply) on the removal rate of 2-naphthol were investigated. It is noteworthy that more than 98.36% of the 2-naphthol in aqueous solution was removed by the 3D-EF system, and only about 60.09% of 2-naphthol was removed by the homogeneous electro-Fenton system. Furthermore, naphthalene, benzoic acid, β-naphthoquinone, 1, 2-naphthalenedione, phenol and aromatic hydrocarbon were the main degradation products of 2-naphthol by the 3D-EF system; the toxicity of 2-naphthol wastewater was also greatly reduced.

Metagenomic insights into the effects of various biocarriers on moving bed biofilm reactors for municipal wastewater treatment

Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH₄⁺-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to stronger simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.

Bacterial biofilm and extracellular polymeric substances in the moving bed biofilm reactor for wastewater treatment: A review

Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacteriumsp. andRhodobactersp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH₄⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.

Analysis of nitrifying bacteria growth on two new types of biomass carrier using respirometry and molecular genetic methods

This work addresses the testing of two newly produced biomass carriers (micro- and nanofibers) and one commercially available AnoxKaldnes™ K3 carrier in a laboratory post-nitrification reactor. The carriers were prepared under parameters suitable for high-quality biomass adhesion to their surface, and each was characterized by its specific structures. As part of the evaluation of the biofilms using respirometry and molecular genetic methods, the carriers were assessed in terms of their effectiveness and comparability. The rate of biofilm development was dependent on the structure and surface properties of the individual carriers. The results showed that the biofilm most strongly adhered to nanofiber carriers, where nitrating bacteria's slower but more abundant development occurred. Microfiber carriers were more stable, but a diverse internal structure may be unsuitable in a populated carrier's early stages. The AnoxKaldnes™ K3 carriers showed the slowest growth of biofilm, but the monitored nitrifying bacteria were abundant after an extended time. AOB representatives are likely to prefer an environment with a high amount of biomass and a large active area. Conversely, NOB representatives thrive better in a slowly forming biofilm. The methods used to monitor biofilm are challenging to compare directly, but they do complement each other, which aids in verifying the individual test results. Developing new types of biomass carriers with the potential for high-quality adhesion of microorganisms is a prerequisite for the expansion of highly efficient biotechnological processes, especially for wastewater treatment.

Combining biofilm and membrane flocculation to enhance simultaneous nutrients removal and membrane fouling reduction

The stability and processing capacity of membrane bioreactor can be improved with long sludge retention time. However, phosphorus removal will be markedly reduced under long sludge retention time and membrane fouling will be aggravated. Adding aluminum (Al) salt is a common way to achieve chemical phosphorus removal and membrane fouling reduction. But, accumulated Al will cause the decline of metabolic activity of activated sludge. In this study, biofilm-membrane flocculation reactor was proposed to enhance simultaneous nutrients removal and membrane fouling reduction. It showed that the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) in biofilm-membrane flocculation reactor were 95.7%, 96.7%, 87.4%, and 97.2%, respectively. Compared with the control group, accumulated Al increased extracellular polymeric substances (EPS) secretion by 1.9%-35.4%, biofilm biomass by 12.4%-26.1%, and the activities of ammonia oxidation bacteria (AOB) and nitrite oxidation bacteria (NOB) in the biofilm increased by 42.9% and 65.9%, respectively. The relative abundance of Nitrospira, Dechloromonas, and Terrimonas in the biofilm increased by 1.78%, 3.01%, and 2.88%, respectively, which was conducive to facilitating the nitrification. Therefore, biofilm-membrane flocculation reactor is a promising way for enhancing simultaneous nutrients removal and membrane fouling reduction.

Water recovery and on-site reuse of laundry wastewater by a facile and cost-effective system: Combined biological and advanced oxidation process

Combined biological and physicochemical process was selected for treatment of laundry wastewater. The results show that after microbial adaptation, almost 91% of COD was removed at food to microorganism (F/M) ratio of 0.12 gBOD/gMLSS·d. Dehydrogenase activity of the biomass showed an increasing trend and finally reached 3.8 μgTFgbiomass.d corresponding to the highest process performance. 16SrRNA fragment and phylogenetic analysis identified Pseudomonas pharmacofabricae and Bacillus spp. as the dominant bacteria. The effluent of the biological process was then injected into the UV/O3 process for complete removal of residual COD and detergent. Finally, microfiltration and ultrafiltration were used to remove any remaining suspended solids. The operating cost analysis showed that 0.65 €/m3 treated wastewater is required for treatment of the laundry wastewater. Accordingly, the suggested combination of the biological and physicochemical process could be a promising and highly efficient process for treatment and reuse of laundry wastewater.

Biofilm producing indigenous bacteria isolated from municipal sludge and their nutrient removal ability in moving bed biofilm reactor from the wastewater

In the present study, improved moving bed biofilm reactor (MBBR) was applied to enhance the nutrient removal ability of the municipal wastewater. A total of 18 indigenous bacterial isolates were screened from the sewage sludge sample and nitrate reductase, nitrite reductase and hydroxylamine oxidase was analyzed. The strains Pseudomonas aeruginosa NU1 and Acinetobacter calcoaceticus K12 produced 0.87 ± 0.05 U/mg and 0.52 ± 0.12 U/mg hydroxylamine oxidase, 1.023 ± 0.062 U/mg and 1.29 ± 0.07 U/mg nitrite reductase, and 0.789 ± 0.031 U/mg and 1.07 ± 0.13 U/mg nitrate reductase. Nitrogen and phosphate removal improved by the addition of nutrient sources and achieved > 80% removal rate. pH and temperature of the medium also affected nutrient removal and improved removal was achieved at optimum level (p < 0.05). MBBR was designed with R1 (aerobic), R2 and R3 (anoxic) reactors. MBBR reactors removed acceptable level phosphorus removal properties up to 7.2 ± 3.8%, 42.4 ± 4.6%, and 84.2 ± 13.1% in the R1, R2, R3 and R4 reactors, respectively. Denitrification rate showed linear relationship at increasing concentrations nitrogen content in the reactor and denitrification rate was 1.43 g NO₂-N /m²/day at 1.5 g NO₂-N /m²/day. Dehydrogenase activity was assayed in all reactors and maximum amount was detected in the aerobic biofilm reactor. Based on the present findings, MBBRs and the selected bacterial strains are useful for the degradation domestic wastewater with minimum working area.

Construction of biotreatment platforms for aromatic hydrocarbons and their future perspectives

Aromatic hydrocarbons (AHCs) are one of the major environmental pollutants introduced from both natural and anthropogenic sources. Many AHCs are well known for their toxic, carcinogenic, and mutagenic impact on human health and ecological systems. Biodegradation is an eco-friendly and cost-effective option as microorganisms (e.g., bacteria, fungi, and algae) can efficiently breakdown or transform such pollutants into less harmful and simple metabolites (e.g., carbon dioxide (aerobic), methane (anaerobic), water, and inorganic salts). This paper is organized to offer a state-of-the-art review on the biodegradation of AHCs (monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs)) and associated mechanisms. The recent progress in biological treatment using suspended and attached growth bioreactors for the biodegradation of AHCs is also discussed. In addition, various substrate growth and inhibition models are introduced along with the key factors governing their biodegradation kinetics. The growth and inhibition models have helped gain a better understanding of substrate inhibition in biodegradation. Techno-economic analysis (TEA) and life cycle assessment (LCA) aspects are also described to assess the technical, economical, and environmental impacts of the biological treatment system.

Application of nanofiber carriers for sampling of microbial biomass from contaminated groundwater

Sampling of microbial biomass is crucial for understanding and controlling remediation processes ongoing at contaminated sites in general, particularly when molecular genetic analyses are employed. In this study, fiber-based carriers with a nanofiber layer were developed and tested as a method to sample microbial biomass in groundwater for molecular genetic analysis. Nanofiber carriers, varying in the shape and the linear density of nanofibers, were examined throughout a 27-month monitoring period in groundwater contaminated with benzene, toluene, ethylbenzene and xylene isomers (BTEX), and chlorinated ethenes. The effect of carrier shape and nanofiber layer density on the microbial surface colonization and composition of the microbial biofilm was determined using real-time PCR and next-generation sequencing (NGS) analysis. Differences in microbial community composition between nanofiber carriers, groundwater, and soil samples were also analyzed to assess the applicability of carriers for biomass sampling at contaminated sites. The nanofiber carriers showed their applicability as a sampling tool, particularly because of their easy manipulation that facilitates DNA isolation. The majority of taxa (Proteobacteria, Firmicutes, and Bacteroidetes) present on the carrier surfaces were also detected in the groundwater. Moreover, the microbial community on all nanofiber carriers reflected the changes in the chemical composition of groundwater. Although the carrier characteristics (shape, nanofiber layer) did not substantially influence the microbial community on the carrier surface, the circular and planar carriers with a nanofiber layer displayed faster microbial surface colonization. However, the circular carrier was the most suitable for biomass sampling in groundwater because of its high contact area and because it does not require pre-treatment prior to DNA extraction.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

Biological fixed-film systems

The technical papers published in 2019 regarding wastewater treatment and microbial films were classified into two categories: biofilm and biofilm reactors. The biofilm category includes biofilm formation, biofilm consortia, bacterial signals, biofouling, extracellular polymeric substances, and biofilm membrane bioreactors. The biofilm reactors category provides recent information on rotating biological contactors, fluidized-bed biofilm reactors, integrated fixed-film activated sludge, moving-bed biofilm reactors, packed-bed biofilm reactors, sequencing biofilm batch reactors, and trickling filters.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min^-1 to 0.13 min^-1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min^-1 was only 4.23%, which is higher than 0.13 min^-1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Performance of novel sponge biocarrier in MBBR treating recirculating aquaculture systems wastewater: Microbial community and kinetic study

In this study, a novel sponge biocarriers (SB) in moving bed bioreactor (MBBR) treating recirculating aquaculture systems wastewater was evaluated for the first time. Two lab-scale MBBRs were operated simultaneously for 116 days under various hydraulic retention times (HRTs). The reactors R1 and R2 were filled with K5 plastic carriers and SB, respectively. From the results, at an optimum HRT of 6 h, ammonia removal efficiency and nitrification rate were 86.67 ± 2.4% and 1.43 mg/L.h for the R1 and, 91.65 ± 1.3% and 1.52 mg/L.h for the R2, respectively. The microbial community analysis showed that the predominant genera in the nitrifying community were Nitrosomonas (AOB) and Nitrospira (NOB) in co-existence with heterotrophic genera Hyphomicrobium, Mesorhizobium, Zhizhongheella, and Klebsiella spp. Modified Stover-Kincannon model examined the ammonia removal kinetics, and the values of kinetic parameters obtained were U_max: 0.909 and 1.111 g/L.d and K_B: 0.929 and, 1.108 g/L.d for the R1 and R2, respectively. The correlation coefficients (R²) of the MBBRs were higher than 0.98, indicating that the model adequately described the experimental data. Overall, MBBR, filled with the proposed novel SB operated at 6 h HRT, can achieve the highest nitrification performance and increase the diversity of the functional microbial communities.

Acceleration of biofilm formation in start-up of sequencing batch biofilm reactor using carriers immobilized with Pseudomonas stutzeri strain XL-2

P. stutzeri strain XL-2 initially immobilized on polypropylene carriers accelerated the biofilm formation in start-up of sequencing batch biofilm reactor (SBBR) (denoted R1). The biofilm formation in R1 was approximately completed in 36 days, which was shorter than that of 48 days in an identical SBBR (denoted R2) without strain XL-2. Meanwhile, R1 presented a rapid stabilization of NH₄⁺-N and TN removal to 81.7% and 72.4% respectively. Surface plasmon resonance demonstrated that strain XL-2 enhanced the initial adhesion of carrier surface due to the production of extracellular polymeric substances (EPS), which made it easier for other EPS-producing strains, such as Thauera and Flavobacterium, to adhere to the carriers. PICRUSt revealed that biofilm in R1 presented relatively higher activity of EPS biosynthesis enzymes (glycosyltransferase and asparagine synthase). Thus, high EPS content was obtained due to the application of carriers immobilized with strain XL-2 and finally promoted the biofilm formation.

Performance evaluation of a continuous packed bed bioreactor: Bio-kinetics and external mass transfer study

The biodegradation of naphthalene using low-density polyethylene (LDPE) immobilized Exiguobacterium sp. RKS3 (MG696729) in a packed bed bioreactor (PBBR) was studied. The performance of a continuous PBBR was evaluated at different inlet flow rates (IFRs) (20-100 mL/h) under 64 days of operation. The maximum naphthalene removal efficiency (RE) was found at low IFR, and it further decreased with increasing IFRs. In a continuous PBBR, the external mass transfer (EMT) aspect was analysed at various IFRs, and experimental data were interrelated between Colburn factor (J_D) and Reynolds number (N_Re) as [Formula: see text] . A new correlation [Formula: see text] was obtained to predict the EMT aspect of naphthalene biodegradation. Andrew-Haldane model was used to evaluate the bio-kinetic parameters of naphthalene degradation, and kinetic constant ν_max, J_s, and J_i were found as 0.386 per day, 13.6 mg/L, and 20.54 mg/L, respectively.

Application of Arjuna (Terminalia arjuna) seed biochar in hybrid treatment system for the bioremediation of Congo red dye

In the present study, a hybrid treatment system (biological and ozonation) was developed and used in the decolorization of Congo red (CR) dye. The biological treatment was performed in packed bed bioreactor (PBBR) containing Arjuna (Terminalia Arjuna) seeds biochar immobilized with Providencia stuartii, whereas ozonation was carried out in an ozone reactor. The process variables such as temperature, process time, and inoculum size were optimized and found to be 30 °C, 2 48 h, and 3 × 10⁵ CFU/mL, respectively with 92.0 ± 5.0% of dye decolorization. Furthermore, biologically treated effluent was subject to ozone treatment for the decolorization of the remaining CR dye. The hybrid approach reveals almost complete decolorization of Congo red (CR) dye. The kinetic study of microbial growth was examined by Monod model. In addition, the cost analysis estimation for the removal of CR dye was done, and removal per liter was found to be economic.

Integration of Marine Macroalgae (Chaetomorpha maxima) with a Moving Bed Bioreactor for Nutrient Removal from Maricultural Wastewater

Rather than direct nutrient removal from wastewaters, an alternative approach aimed at nutrient recovery from aquacultural wastewaters could enable sustainable management for aquaculture production. This study demonstrated the feasibility of cultivating marine macroalgae (Chaetomorpha maxima) with a moving bed bioreactor (MBBR-MA), to remove nitrogen and phosphorus in aquaculture wastewater as well as to produce macroalgae biomass. MBBR-MA significantly increased the simultaneous removal of nitrate and phosphate in comparison with only MBBR, resulting in an average total nitrogen (TN) and total phosphorus (TP) removal efficiency of 42.8 ± 5.5% and 83.7 ± 7.7%, respectively, in MBBR-MA while MBBR had no capacity for TN and TP removal. No chemical oxygen demand (COD) removal was detected in both reactors. Phosphorus could be a limiting factor for nitrogen uptake when N : P ratio increased. The recovered nitrogen and phosphorus resulted in a specific growth rate of 3.86%–10.35%/day for C. maxima with an uptake N : P ratio of 6. The presence of macroalgae changed the microbial community in both the biofilter and water by decreasing the relative abundance of Proteobacteria and Nitrospirae and increasing the abundance of Bacteroidetes. These findings indicate that the integration of the macroalgae C. maxima with MBBR could represent an effective wastewater treatment option, especially for marine recirculating aquaculture systems.

Removal of methylene blue dye using rice husk, cow dung and sludge biochar: Characterization, application, and kinetic studies

The present studies aimed for the removal of Methylene blue (MB) dye using the rice husk biochar (RHB), cow dung biochar (CDB) and domestic sludge biochar (SB) synthesized through slow pyrolysis at 500 °C. The biochar was used for the adsorption of synthetic aqueous MB dye. The removal efficiencies of MB by CDB, RHB and SB in a batch experiment were 97.0-99.0; 71.0-99.0 and 73.0-98.9% at conditions, pH (2.0-11.0); Biochar dosage (0.5-6.0 g/100 mL) for 5 days. Adsorption isotherm of Langmuir constant (K_L) were obtained 0.101, 0.583 and 0.128 for RHB, CDB and SB respectively. Further, adsorption kinetics of pseudo first order for RHB, CDB and SB were 0.068, 0.018, and 0.066 while it was 0.031, 0.023 and 0.273 for pseudo second order kinetics. Thus, CDB was more effective adsorbent for the dye removal. The pHz values were 7.8, 6.3 and 6.0 for the CDB, RHB, and SB, respectively.

Treatment of isopropanol wastewater in an anaerobic fluidized bed microbial fuel cell filled with macroporous adsorptive resin as multifunctional biocarrier

The isopropanol (IPA) wastewater was treated in an anaerobic fluidized bed microbial fuel cell (AFB-MFC) filled with macroporous adsorptive resin (MAR) particles as multifunctional biocarrier. MAR was used as a biological carriers and adsorbent. MAR was characterized by scanning electron microscope. The diffusion of isopropanol in MAR was studied by Materials Studio (MS) software, and diffusion coefficients were analyzed and calculated by molecular dynamics simulation. The simulation results were qualitatively consistent with the available experimental data. The diffusivity of IPA in MAR increased firstly, with the increasing IPA weight, and then decreased. The maximum diffusivity was resulted to be 0.3722 Å²/ps. In addition, the response surface methodology (RSM) and Box-Behnken design were used to study the effects of initial IPA concentration, flow rate and external resistance on performance of power output and pollutant degradation. The optimal experimental condition was observed as initial IPA concentration of 483.49 mg/L, a flow rate of 57.70 mL/min, and external resistance of 5225.78 Ω. After 21 h of operation under the optimized conditions, the maximum power density was 135.73 ± 0.17 mW/m² and the COD removal was 68.21 ± 0.24%, which increased by 65.85% and 9.29%, respectively.

Collective removal of phenol and ammonia in a moving bed biofilm reactor using modified bio-carriers: Process optimization and kinetic study

The performance of a moving bed biofilm reactor (MBBR) with bio-carriers made of polypropylene-polyurethane foam (PP-PUF) was evaluated for the collective removal of phenol and ammonia. Three independent variables, including pH (5.0-8.0), retention time (2.0-12.0 h), and airflow rate (0.8-3.5 L/min) were optimized using central composite design (CCD) of response surface methodology (RSM). The maximum removal of phenol and ammonia was obtained to be 92.6, and 91.8%, respectively, in addition to the removal of 72.3% in the chemical oxygen demand (COD) level at optimum conditions. First-order and second-order kinetic models were analyzed to evaluate the pollutants removal kinetics in a MBBR. Finally, a second-order model was found to be appropriate for predicting reaction kinetics. The values of second-order rate constants were obtained to be 2.35, 0.25, and 1.85 L2/gVSS gCOD h for phenol, COD, and ammonia removal, respectively.

Biodegradation of Congo red dye in a moving bed biofilm reactor: Performance evaluation and kinetic modeling

The biodegradation of Congo red dye was performed using polyurethane foam-polypropylene immobilized Bacillus sp. MH587030.1 in a moving bed biofilm reactor (MBBR). The central composite design (CCD) based response surface methodology (RSM) was used to optimize the process parameters; pH, Congo red concentration, and media filling ratio, and optimum conditions were observed to be 7.0, 50 mg/L, and 45%, respectively in batch MBBR. At optimum condition, MBBR was operated in continuous mode at different flow rates (25-100 mL/h) over a period of 564 h. The maximum removal efficiency (RE) and elimination capacity (EC) were obtained as 95.7% and 57.6 mg/L·day, respectively under steady-state. The kinetics of Congo red biodegradation at various flow rates were evaluated by a modified Stover-Kincannon model, and kinetic constants; K_B and U_max were found to be 0.253 g/L·day and 0.263 g/L·day, respectively.

Optimization of nutrient removal of novel electrochemically active carriers by response surface methodology

In order to improve the nutrient removal capacity of the carriers in the integrated fixed-film activated sludge (IFAS) system, a novel electrochemically active carrier was developed in this study. The nutrient removal performance of the carrier under different operating conditions was deeply investigated based on response surface methodology. The higher concentration of mixed liquor suspended solid (MLSS) and lower dissolved oxygen (DO) value inhibited ammonium (NH₄⁺-N) removal performance of the carrier, while promoted total nitrogen (TN) depletion. Lower influent C/N ratio favored denitrification of the carrier. In addition, it was found that the enhanced removal of NH₄⁺-N and TN in IFAS depended not only on the increase of carrier biomass, but also on the electrochemical activity of the novel carrier. Under the most effective conditions, the novel carrier could improve the TN removal efficiency by 19.7% compared with the activated sludge process.