Improving antifouling performance of FO membrane by surface immobilization of silver nanoparticles based on a tannic acid: diethylenetriamine precursor layer for municipal wastewater treatment

In this study, a facile method for multifunctional surface modification on forward osmosis (FO) membrane was constructed by surface immobilization of AgNPs based on tannic acid (TA)/diethylenetriamine (DETA) precursor layer. The cellulose triacetate (CTA) FO membranes modified by TA and DETA with different co-deposition time (6 h, 12 h, 24 h) were investigated. Results indicated that the TA/DETA (24)-Ag CTA membrane with a TA/DETA co-deposition time of 24 h was identified to be optimal, which attained more hydrophilic. And it had the bacterial mortality of Escherichia coli and Staphylococcus aureus reaching 98.23% and 99.83% respectively and possessed excellent physical and chemical binding stability. Meanwhile, the coating layer resulted in the antifouling ability without damaging the membrane intrinsic transport characteristics. As for synthetic municipal wastewater treatment, the water flux of CTA FO membrane decreased approximately 49% of the initial flux after running for 14 days. In contrast, the flux decline rate of TA/DETA (24)-Ag CTA membrane was about 37%. Furthermore, less foulant deposition and higher recovery rate of water flux was observed for TA/DETA (24)-Ag CTA membrane, implying that the modified membrane effectively alleviated membrane fouling and processed a lower flux decline during municipal wastewater treatment. It was attributed to the enhanced surface hydrophilicity and antibacterial property of the coating layer, which improved antifouling property.

Effluent parameters prediction of a biological nutrient removal (BNR) process using different machine learning methods: A case study

This paper proposes a novel targeted blend of machine learning (ML) based approaches for controlling wastewater treatment plant (WWTP) operation by predicting distributions of key effluent parameters of a biological nutrient removal (BNR) process. Two years of data were collected from Plajyolu wastewater treatment plant in Kocaeli, Türkiye and the effluent parameters were predicted using six machine learning algorithms to compare their performances. Based on mean absolute percentage error (MAPE) metric only, support vector regression machine (SVRM) with linear kernel method showed a good agreement for COD and BOD5, with the MAPE values of about 9% and 0.9%, respectively. Random Forest (RF) and EXtreme Gradient Boosting (XGBoost) regression were found to be the best algorithms for TN and TP effluent parameters, with the MAPE values of about 34% and 27%, respectively. Further, when the results were evaluated together according to all the performance metrics, RF, SVRM (with both linear kernel and RBF kernel), and Hybrid Regression algorithms generally made more successful predictions than Light GBM and XGBoost algorithms for all the parameters. Through this case study we demonstrated selective application of ML algorithms can be used to predict different effluent parameters more effectively. Wider implementation of this approach can potentially reduce the resource demands for active monitoring the environmental performance of WWTPs.

A novel carbon emission evaluation model for anaerobic-anoxic-oxic urban sewage treatment

The proposal of the dual carbon goal and the blue economy in China has sparked a keen interest in carbon emissions reduction from sewage treatment. Carbon accounting in urban sewage plants serves as the foundation for carbon emission reduction in sewage treatment. This paper re-evaluated carbon accounting in the operational processes for urban sewage treatment plants to develop a novel carbon emission evaluation model for anaerobic-anoxic-oxic treatment plants. The results show that the carbon emissions generated by non-carbon dioxide gases far exceed the carbon emissions from carbon dioxide alone. Moreover, the recycling of sewage leads to carbon emissions reduction that offsets the carbon emissions generated during the operation of the sewage plant. Also, the carbon emissions generated by sewage treatment plants are lower than those generated by untreated sewage. The findings and insights provided in this paper provide valuable references for carbon accounting and the implementation of low-carbon practices in urban sewage treatment plants.

Development of nature-based sustainable passive technologies for treating and disinfecting municipal wastewater: Experiences from constructed wetlands and slow sand filter

There is an urgent need to develop low-cost technology for effective wastewater treatment and its further disinfection to the level that makes it economically useful. This work has designed and evaluated the various types of constructed wetlands (CWs) followed by a slow sand filter (SSF) for wastewater treatment and disinfection. The studied CWs were, CWs with gravels (CW-G), free water surface-CW (FWS-CWs), and CWs integrated microbial fuel cell (MFC) with granular graphite (CW-MFC-GG) planted with Canna indica plant species. These CWs were operated as secondary wastewater treatment technologies followed by SSF for disinfection purposes. The highest total coliform removal was observed in the combination of CW-MFC-GG-SSF which achieved a final concentration of 172 CFU/100 mL, whereas faecal coliform removal was 100 % with the combinations of CW-G-SSF and CW-MFC-GG-SSF, achieving 0 CFU/100 mL in the effluent. In contrast, FWS-SSF achieved the lowest total and faecal coliform removal attaining a final concentration of 542 CFU/100 mL and 240 CFU/100 mL, respectively. Furthermore, E. coli were detected as negative/absent in CW-G-SSF and CW-MFC-GG-SSF, while it was positive for FWS-SSF. In addition, the highest turbidity removal was achieved in CW-MFC-GG and SSF combination of 92.75 % from the municipal wastewater influent turbidity of 82.8 NTU. Furthermore, in terms of overall treatment performance of CW-G-SSF and CW-MFC-GG-SSF, these systems were able to treat 72.7 ± 5.5 % and 67.0 ± 2.4 % of COD and 92.3 % and 87.6 % of phosphate, respectively. Additionally, CW-MFC-GG also exhibited a power density of 85.71 mA/m3 and a current density of 25.71 mW/m3 with 700 Ω of internal resistance. Thus, CW-G and CW-MFC-GG followed by SSF could be a promising solution for enhanced disinfection and wastewater treatment.

The responding mechanism of indigenous bacteria in municipal wastewater inoculated with different concentrations of exogenous microalgae

Indigenous bacteria popularly exist in real wastewater. Therefore, the potential interaction between bacteria and microalgae is inevitable in microalgae-based wastewater treatment systems. It is likely to affect the performance of systems. Accordingly, the characteristics of indigenous bacteria is worth serious concerning. Here we investigated the response of indigenous bacterial communities to variant inoculum concentrations of Chlorococcum sp. GD in municipal wastewater treatment systems. The removal efficiency of COD, ammonium and total phosphorus were 92.50%-95.55%, 98.00%-98.69%, and 67.80%-84.72%, respectively. The bacterial community responded differently to different microalgal inoculum concentrations, which was mainly affected by microalgal number, ammonium and nitrate. Besides, there were differential co-occurrence patterns and carbon and nitrogen metabolic function of indigenous bacterial communities. All these results indicated that bacterial communities responded significantly to environmental changes caused by the change of microalgal inoculum concentrations. The response of bacterial communities to different microalgal inoculum concentrations was beneficial for forming a stable symbiotic community of both microalgae and bacteria to remove pollutants in wastewater.

Step-feeding food waste fermentation liquid as supplementary carbon source for low C/N municipal wastewater treatment: Bench scale performance and response of microbial community

Municipal wastewater treatment often lacks carbon source, while carbon-rich organics in food waste are deficiently utilized. In this study, the food waste fermentation liquid (FWFL) was step-fed into a bench-scale step-feed three-stage anoxic/aerobic system (SFTS-A/O), to investigate its performance in nutrients removal and the response of microbial community as a supplementary carbon source. The results showed that the total nitrogen (TN) removal rate increased by 21.8-109.3% after step-feeding FWFL. However, the biomass of the SFTS-A/O system was increased by 14.6% and 11.9% in the two phases of the experiment, respectively. Proteobacteria was found to be the dominant functional phyla induced by FWFL, and the increase of its abundance attributed to the enrichment of denitrifying bacteria and carbohydrate-metabolizing bacteria was responsible for the biomass increase. Azospira belonged to Proteobacteria phylum was the dominant denitrifying genera when step-fed with FWFL, its abundance was increased from 2.7% in series 1 (S1) to 18.6% in series 2 (S2) and became the keystone species in the microbial networks. Metagenomics analysis revealed that step-feeding FWFL enhanced the abundance of denitrification and carbohydrates-metabolism genes, which were encode mainly by Proteobacteria. This study constitutes a key step towards the application of FWFL as a supplementary carbon source for low C/N municipal wastewater treatment.

Realizable wastewater treatment process for carbon neutrality and energy sustainability: A review

Despite a quick shift of global goals toward carbon-neutral infrastructure, activated sludge based conventional systems inhibit the Green New Deal. Here, a municipal wastewater treatment plant (MWWTP) for carbon neutrality and energy sustainability is suggested and discussed based on realizable technical aspects. Organics have been recovered using variously enhanced primary treatment techniques, thereby reducing oxygen demand for the oxidation of organics and maximizing biogas production in biological processes. Meanwhile, ammonium in organic-separated wastewater is bio-electrochemically oxidized to N₂ and reduced to H₂ under completely anaerobic conditions, resulting in the minimization of energy requirements and waste sludge production, which are the main problems in activated sludge based conventional processes. The anaerobic digestion process converts concentrated primary sludge to biomethane, and H₂ gas recovered from nitrogen upgrades the biomethane quality by reducing carbon dioxide in biogas. Based on these results, MWWTPs can be simplified and improved with high process and energy efficiencies.

Chemical composition and species identification of microalgal biomass grown at pilot-scale with municipal wastewater and CO2 from flue gases

The production potential of a locally isolated Chlorella vulgaris strain and a local green-algae consortium, used in municipal wastewater treatment combined with CO₂ sequestration from flue gases, was evaluated for the first time by comparing the elemental and biochemical composition and heating value of the biomass produced. The microalgae were grown in outdoor pilot-scale ponds under subarctic summer conditions. The impact of cultivation in a greenhouse climate was also tested for the green-algae consortium; additionally, the variation in species composition over time in the three ponds was investigated. Our results showed that the biomass produced in the consortium/outdoor pond had the greatest potential for bioenergy production because both its carbohydrates and lipids contents were significantly higher than the biomasses from the consortium/greenhouse and C. vulgaris/outdoor ponds. Although greenhouse conditions significantly increased the consortium biomass's monounsaturated fatty acid content, which is ideal for biodiesel production, an undesirable increase in ash and chemical elements, as well as a reduction in heating value, were also observed. Thus, the placement of the pond inside a greenhouse did not improve the production potential of the green-algae consortium biomass in the current study infrastructure and climate conditions.

Auto-floating oxygenic microalgal-bacterial granular sludge

As an emerging green wastewater treatment technology, the microalgal-bacterial granular sludge (MBGS) process has attracted increasing interest under the current situation of global climate change. However, little information is available for its performance in treating municipal wastewater under outdoor conditions. Thus, this study evaluated the behaviors of MBGS for treating simulated and real municipal wastewater under natural diel conditions. The results showed that a significant accumulation of oxygen bubbles during daily operation led to the auto-floating of the conventional settable MBGS. The removal of organics was relatively stable during day-night cycles, while the removals of total nitrogen and total phosphorus were dependent on the saturated oxygen concentration over 10 mg/L in MBGS system. Furthermore, oxygen bubbles generated by photosynthesis of microalgae (Scenedesmaceae and Cyanobacteria) due to microalgae phototaxis were found to be attached onto the surface of granules, causing the auto-flotation of MBGS. The formation process of the auto-floating oxygenic MBGS was clarified and further analysis suggested that the non-aerated settable MBGS would be able to auto-float at an average outdoor light intensity of 140 μ mol/m²/s. Overall, the auto-floating oxygenic MBGS process was demonstrated to be feasible for real municipal wastewater treatment, even under rainy and cloudy days, advancing the knowledge and adding theoretical basis for its further applications.

Formation of vivianite in digested sludge and its controlling factors in municipal wastewater treatment

Engineering solutions to recover phosphorus from municipal wastewater are required to close the anthropogenic phosphorus cycle. After chemical phosphorus elimination by iron, the ferrous iron‑phosphorus mineral vivianite forms in digested sludge, and its separation is being researched at the pilot scale. In this study, sludge samples from 16 wastewater treatment plants (WWTPs) demonstrated that phosphorus bound to biomass and redox-sensitive iron in activated sludge was transformed into other phosphorus binding forms, including vivianite, during digestion. Vivianite quantity was approximated using X-ray diffraction and two sequential extractions. These three independent methods of approximating vivianite quantity were closely related confirming their relationship to the vivianite content in the samples. The digested sludge from three WWTPs exhibited comparatively high levels of vivianite-bound phosphorus approximated between 31 % and 51 % of total phosphorus. The controlling factors of vivianite formation were investigated in order to enhance its formation in digested sludge and increase the amount of phosphorus recoverable as vivianite. They were identified using single and multivariate correlation (MLR), considering the sludge properties, sludge composition, and process parameters within the operating range of the 16 WWTPs. Increasing iron content was verified as the primary predictor of significantly increased vivianite formation (MLR: p < 0.001). In addition, increasing sulphur content was found to be an additional significant factor that decreased vivianite formation (MLR: p < 0.05). Furthermore, a comparison of plants using sulphur-free (FeCl2 and FeCl3) and sulphur-containing (FeSO4 and FeClSO4) precipitants indicated that the latter could increase the sulphur content in digested sludge (one-tailed Welch two-sample t-test: t(14.6) = 2.3, p = 0.02). Thus, by increasing the sulphur content, the use of sulphur-comprising precipitants may counteract vivianite formation, whereas sulphur-free precipitants may facilitate it and, hence, promote vivianite recovery.

Municipal Wastewater Treatment uses Vertical Flow Followed by Horizontal Flow in a Two-Stage Hybrid-Constructed Wetland Planted with Calibanus hookeri and Canna indica (Cannaceae)

The utilization of hybrid-constructed wetland systems has recently expanded due to more rigorous municipal wastewater discharge and also complex wastewaters treated in hybrid-constructed wetlands (HCWs). A lab-scale two-stage experimental setup of vertical flow followed by horizontal flow hybrid-constructed wetland (VFHCW-HFHCW) configuration was built. First-stage vertical flow hybrid-constructed wetland reactor with the surface area was 1963.49 cm² and second-stage horizontal flow hybrid-constructed wetland reactor with the surface area was 2025 cm². The HCW unit was planted with two type plants: Calibanus hookeri and Canna indica (Cannaceae). Influent Municipal wastewater flow rate 112.32 l/day, hydraulic loading rate (HLR) 0.55 m/day, and hydraulic retention time of 1 day. The efficiency was evaluated in municipal wastewater quality improvement and physico-chemical analysis in our laboratory. The removal rate after the second-stage horizontal flow of BOD₃ at 27 °C, COD, TSS, TP, NH₃-N, and NO₃-N reached 92.75%, 89.90%, 85.45%, 88.83%, 99.09%, and 96.05%, respectively. The results shown after both stage hybrid-constructed wetland VFHCW-HFHCW, treated effluent of Municipal wastewater produced high-quality effluent which may be reused in gardening, agriculture, and flushing in toilet purpose according to Bureau of Indian Standards (BIS) code for practices. However, in the future, hybrid-constructed wetlands could be standards design criteria developing and enhancing the performance standards and economic meets both to make more popular technology of the hybrid-constructed wetland (HCW).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-022-05984-0.

A review of enhanced municipal wastewater treatment through energy savings and carbon recovery to reduce discharge and CO2 footprint

Municipal wastewater treatment that mainly performed by conventional activated sludge (CAS) process faces the challenge of intensive aeration-associated energy consumption for oxidation of organics and ammonium, contributing to significant directly/indirectly greenhouse gas (GHG) emissions from energy use, which hinders the achievement of carbon neutral, the top priority mission in the coming decades to cope with the global climate change. Therefore, this article aimed to offer a comprehensive analysis of recently developed biological treatment processes with the focus on reducing discharge and CO2 footprint. The biotechnologies including "Zero Carbon", "Low Carbon", "Carbon Capture and Utilization" are discussed, it suggested that, by integrating these processes with energy-saving and carbon recovery, the challenges faced in current wastewater treatment plants can be overcome, and a carbon-neutral even be possible. Future research should investigate the integration of these methods and improve anammox contribution as well as minimize organics lost under different scales.

Microalgal-bacterial granular sludge for municipal wastewater treatment: From concept to practice

Recently, increasing interest has been placed in microalgal-bacterial granular sludge (MBGS) in the journey towards the energy and carbon neutrality of municipal wastewater treatment. Different from aerobic granular sludge, the performance of MBGS is mainly determined by the mutualism and symbiosis between coexisting microalgae and bacteria. It appears from the literature that most of studies on MBGS were conducted at small benchtop scales under controlled conditions with synthetic wastewater. Therefore, this article attempts to look into the major engineering gaps between the knowledge generated from numerous laboratory research works and the large-scale application of MBGS, including massive production of MBGS, type of bioreactor, effect of alternate photo and dark metabolisms on effluent quality, resource recovery from waste MBGS, etc. It is clearly demonstrated that MBGS is still at its infant stage, and more effort is strongly needed to identify the technological bottlenecks of full-scale applications, while providing corresponding engineering solutions.

Optimal sensor placement method for wastewater treatment plants based on discrete multi-objective state transition algorithm

Parameters monitoring is essential to maintain the stability and efficiency of the wastewater treatment process, which has spurred ubiquitous installation of sensors in wastewater treatment plants (WWTPs). As the rich process data of WWTPs is not effectively transformed into actionable knowledge for system optimization due to improper sensor installation, the sensor placement scheme needs to be optimized. In this paper, a weighted sensor placement optimization model based on sensor cost, information richness and reliability is established to transform the sensor optimization problem to a nonlinear mathematical programming problem. Then a discrete multi-objective state transition algorithm is proposed to find the Pareto optimal solutions. Finally, an evaluation strategy is designed to select the most suitable solution for industrial application. The results of simulation experiments on three different WWTPs demonstrate the validity and superiority of the proposed method, increasing the degree of variable observability and measurement redundancy while keeping the sensor cost at a low level.

Sustainable upgrading of biological municipal wastewater treatment based on anammox: From microbial understanding to engineering application

Anaerobic ammonium oxidation (anammox) has drawn increasing attention as a promising option to energy-neutral wastewater treatment. While anammox process still faces challenges in the low-strength and organics-contained municipal wastewater due to its susceptibility and the technical gaps in substrate supply. Effective strategies for extensive implementation of anammox in municipal wastewater treatment plants (WWTPs) remain poorly summarized. In view of the significance and necessity of introducing anammox into mainstream treatment, the growing understanding not only at level of microbial interactions but also on view of upgrading municipal WWTPs with anammox-based processes need to be considered urgently. In this review, the critical view and comprehensive analysis were offered from the perspective of microbial interactions within partial nitrification- and partial denitrification-based anammox processes. To minimize the microbial competition and enhance the cooperation among anammox bacteria and other functional bacteria, targeted control strategies were systematically evaluated. Based on the comprehensive overview of recent advances, the combination of flexible regulation of input organic carbon with anaerobic/oxic/anoxic process and the integration of sludge fermentation with anoxic biofilms in anaerobic/anoxic/oxic process were proposed as promising solutions to upgrade municipal WWTPs with anammox technology. Furthermore, a new perspective of coupling anammox with denitrifying dephosphatation was proposed as a promising method for in-depth nutrients removal from carbon-limit municipal wastewater in this study. This review provides the critical and comprehensive viewpoints on anammox engineering in municipal wastewater and paves the way for the anammox-based upgrading of municipal WWTPs.

Anaerobic membrane bioreactors (AnMBRs) for municipal wastewater treatment- potential benefits, constraints, and future perspectives: An updated review

The application of Anaerobic Membrane Bioreactors (AnMBRs) for municipal wastewater treatment has been made sufficiently sustainable for practical implementations. The potential benefits are significant as AnMBRs effectively remove a broad range of contaminants from wastewater for water reuse, degrade organics in wastewater to yield methane-rich biogas for resultant energy production, and concentrate nutrients for subsequent recovery for fertilizer production. However, there still exist some concerns requiring vigilant considerations to make AnMBRs economically and technically viable. This review paper briefly describes process fundamentals and the basic AnMBR configurations and highlights six major factors which obstruct the way to AnMBRs installations affecting their performance for municipal wastewater treatment: (i) organic strength, (ii) membrane fouling, (iii) salinity build-up, (iv) inhibitory substances, (v) temperature, and (vi) membrane stability. This review also covers the energy utilization and energy potential in AnMBRs aiming energy neutrality or positivity of the systems which entails the requirement to further determine the economics of AnMBRs. The implications and related discussions have also been made on future perspectives of the concurrent challenges being faced in AnMBRs operation.

Chemical oxygen demand and nitrogen transformation in a large pilot-scale plant with a combined submerged anaerobic membrane bioreactor and one-stage partial nitritation-anammox for treating mainstream wastewater at 25 °C

A novel municipal wastewater treatment process towards energy neutrality and reduced carbon emissions was established by combining a submerged anaerobic membrane bioreactor (SAnMBR) with a one-stage partial nitritation-anammox (PN/A), and was demonstrated at pilot-scale at 25 °C. The overall COD and BOD₅ removal efficiencies were 95.1% and 96.4%, respectively, with 20.3 mg L^-1 COD and 5.2 mg L^-1 BOD₅ remaining in the final effluent. The total nitrogen (TN) removal efficiency was 81.7%, resulting 7.3 mg L^-1 TN was discharged from the system. The biogas yield was 0.222 NL g^-1 COD _removed with a methane content range of 78-81%. Approximately 90% of influent COD was removed in the SAnMBR, and 70% of influent nitrogen was removed in the PN/A. The denitrification which occurred in the PN/A enhanced overall COD and nitrogen removal. The successful operation of this pilot-scale plant indicates the SAnMBR-PN/A process is suitable for treating real municipal wastewater.

Reuse-focused selection of appropriate technologies for municipal wastewater treatment: a multi-criteria approach

Wastewater treatment technologies (WWTTs) are employed across the world, and the selection is mainly based on 'past experiences' aimed at 'pollution prevention' in the receiving water bodies. This paper aims to develop a methodology for the selection of an appropriate wastewater treatment chain that produces effluent suitable for the defined reuse. Adopting the least weighted cost approach, four decision criteria: Capital cost, Operation and Maintenance cost, Land requirement, and Energy requirement, have been used and the Full Consistency Method (FUCOM) has been employed for obtaining weights. Quality expectations for 14 reuses have been enlisted, and 25 WWTTs have been evaluated in a total of 360 combinations. In Kanpur city, for water reuse in industrial cooling under restricted land and challenging influent quality conditions, a combination of Membrane Bioreactor (MBR) with Wuhrmann process (WP) is obtained as the most preferred suggestion. For non-potable domestic reuse, Anaerobic Anoxic Oxic (A2O) with Ultrafiltration (UF) and Reverse Osmosis (RO) is the most preferred combination. In Varanasi city, for vehicular washing operations and for flow augmentation (inland surface water), under energy-constraint scenario, high-rate activated sludge-based biological filtration and oxygenated reactor (BIOFOR-F) is suggested. For technology supplementation to existing ASP-based STPs in the city to obtain effluent for inland surface water augmentation, WP in combination with microfiltration (MF) and reverse osmosis (RO) is suggested. Thus, the developed model may be used as a decision-making tool for planning a reuse-focused water reclamation program or for upgradation of existing STPs as per resource availability and target reuse objectives.

Recent advances in partial denitrification-anaerobic ammonium oxidation process for mainstream municipal wastewater treatment

To solve the bottleneck of the unstable accumulation of nitrite in the partial nitrification (PN)-anammox (AMX) in municipal wastewater treatment, a novel process called partial denitrification (PD)-AMX has been developed. PD-AMX, which is known for cost-efficiency and environmental friendliness, has currently exhibited a promising potential for the removal of biological nitrogen from municipal wastewater and has attracted much research interest regarding its process mechanisms, as well as its practical applications. Here, we review the recent advances in the PD process and its coupling to the anammox process, including the development, basic principles, main characteristics, and critical process parameters of the stable operation of the PD-AMX process. We also explore the microbial community and its characteristics in the system and summarize the knowledge of the dominant bacteria to clarify the key factors affecting PD-AMX. Then, we introduce the engineering feasibility and economic feasibility as well as the potential challenges of the process. The induction and implementation of partial denitrification and maintenance of mainstream anammox are critical issues to be urgently solved. Meanwhile, the implementation of a full mainstream anammox application remains burdensome, while the mechanism of partial denitrification coupled to anammox needs to be further studied. Additionally, stable operation performance and process control¹ methods need to be optimized or developed for the PD-AMX system for better engineering practice. This review can help to accelerate the research and application of the PD-AMX process for municipal wastewater treatment.

Biogas maximization using data-driven modelling with uncertainty analysis and genetic algorithm for municipal wastewater anaerobic digestion

Anaerobic digestion processes create biogases that can be useful sources of energy. The development of data-driven models of anaerobic digestion processes via operating parameters can lead to increased biogas production rates, resulting in greater energy production, through process modification and optimization. This study assessed processed and unprocessed input operating parameter variables for the development of regression models with transparent structures ('white-box' models) to: (1) estimate biogas production rates from municipal wastewater treatment plant (MWTP) anaerobic digestors; (2) compare their performances to artificial neural network (ANN) and adaptive network-based fuzzy inference system (ANFIS) models with opaque structures ('black-box' models) using Monte Carlo Simulation for uncertainty analysis; and (3) integrate the models with a genetic algorithm (GA) to optimize operating parameters for maximization of MWTP biogas production rates. The input variables were anaerobic digestion operating parameters from a MWTP including volatile fatty acids, total/fixed/volatile solids, pH, and inflow rate, which were processed via correlation tests and principal component analysis. Overall, the results indicated that the processed data did not improve regression model performances. Additionally, the developed non-linear regression model with the unprocessed inputs had the best performance based on values including R = 0.81, RMSE = 0.95, and IA = 0.89. However, this model was less accurate, but interestingly had less uncertainty, as compared to ANN and ANFIS models which indicates the compromise between model accuracy and uncertainty. Thus, all three models were coupled with GA optimization with maximum biogas production rate estimates of 22.0, 23.1, and 28.6 m³/min for ANN, ANFIS, and non-linear regression models, respectively.

Dissolved oxygen concentrations affect the function but not the relative abundance of nitrifying bacterial populations in full-scale municipal wastewater treatment bioreactors during cold weather

This study aimed to understand the effect of different dissolved oxygen (DO) concentrations on the abundance and performance of nitrifying bacteria in full-scale wastewater treatment bioreactors, particularly during the winter when nitrifying bacterial activity is often negligible. Biomass samples were collected from three parallel full-scale bioreactors with low DO concentrations (<1.3 mg/ L) and from two full-scale bioreactors with higher DO concentrations (~4.0 and ~2.3 mg/ L). The relative abundance of nitrifying bacteria was determined by sequencing of PCR-amplified 16S rRNA gene fragments. In the three bioreactors with low DO concentrations, effluent ammonia concentrations sharply increased with a decline in temperature below approximately 17 °C, while the bioreactors with high DO concentrations showed stable nitrification regardless of temperature. Even with the decline in nitrification during the winter in the three low DO bioreactors, the relative abundance of ammonia oxidizing bacteria (mostly Nitrosomonas spp.) was curiously maintained. The relative abundance of nitrite oxidizing bacteria was similarly maintained, although there were substantial seasonal fluctuations in the relative abundance values of Nitrospira spp. versus Nitrotoga spp. This research suggests that nitrification activity can be controlled during the winter via DO to produce better effluent quality with high DO concentrations or to reduce aeration costs with a concomitant decline in nitrification activity.

Soluble microbial products from the white-rot fungus Phanerochaete chrysosporium as the bioflocculant for municipal wastewater treatment

Soluble microbial products (SMP), a type of polymers released from microbial metabolism and decay, show great potential for wastewater treatment as bioflocculants; however, biogenic flocculant utilization is currently limited to bacterial SMP. In this study, SMP produced by Phanerochaete chrysosporium BKMF-1767 (SMP-P) was investigated to determine the application potential of fungal SMP. SMP-P exhibited high flocculation activity in kaolin suspension at a dosage range of 0.67-0.84 mg/L with Ca²⁺ assistance, comparable to that of commercial polyacrylamide. The high molecular weight polysaccharides (2.0 × 10⁶-4.7 × 10⁷ Da) in SMP-P, which enabled flocculation via the bridging mechanism and served as the dominant active constituent, were composed of glucose and arabinose at a molar ratio of 1: 0.03, with (1 → 4, 6)-linked glucose as the main backbone and a small proportion of branched structures. They contained hydroxyl and carboxyl, effective functional groups for the flocculation process, and displayed parallel self-orientation behavior in water. Efficient chemical oxygen demand removal was achieved during municipal wastewater treatment using SMP-P as the bioflocculant. This study demonstrates the feasibility of utilizing fugal SMP as bioflocculants and provides guidance for their practical application.

Characterization and modelling of soluble microbial products in activated sludge systems treating municipal wastewater with special emphasis on temperature effect

Soluble microbial products (SMP) classified as utilization-associated products (UAP) and biomass-associated products (BAP) are the predominant foulants determining fouling in tertiary filtration. However, the exact mechanisms of BAP and UAP generation when treating real wastewaters under cold temperatures remain unrevealed. This paper presents the first study linking biological processes and SMP formation when treating real wastewaters through a combination of bioprocess modelling and advanced SMP characterization. Further, the impact of low operating temperatures on SMP production which has received relatively little attention was studied in detail. The use of liquid chromatography-organic carbon detection (LC-OCD) revealed a significant increase in protein and polysaccharide concentrations in the treated effluents as temperature decreased with a more sensitive impact on polysaccharides. The generation of SMP from biomass decay (BAP) and substrate utilization (UAP) was derived from the LC-OCD data on the basis of protein and polysaccharide mass balances. UAP and BAP yields were estimated as the ratios of the observed generation rates to the rates of substrate utilization and endogenous decay respectively, which both declined as temperature increased. A strong correlation was observed between temperature and BAP/UAP yields whereas the generation of BAP was more temperature sensitive than UAP. Such process modelling can be employed to assist with the optimization of the design and operation of membrane processes when treating wastewaters under challenging conditions like low temperature.

Innovative technology of municipal wastewater treatment for rapid sludge sedimentation and enhancing pollutants removal with nano-material

This study aims to develop a novel technology for actual municipal wastewater treatment to achieve rapid sludge sedimentation and high pollutants removal efficiency. The SBRs were modified and operated with periodic addition of 20 μL·L^-1 nanofloc®. Results revealed that NH₄⁺-N and chemical oxygen demand (COD) was efficiently removed in both laboratory- and pilot-scale SBRs, and the average removal efficiency of total nitrogen (TN) and total phosphorus (TP) was as high as 72.43 ± 2.66% and 98.63 ± 0.74%, respectively, with hydraulic retention time (HRT) of 8 h. Besides, the sludge volume index at 30 min (SVI₃₀) was only 40.06 ± 1.99 mL·g^-1, comparable with aerobic granular sludge (AGS). This novel technology could be proposed as a competitive method to upgrade, reconstruct and delay the expansion of municipal wastewater treatment plants (WWTPs) due to its rapid sludge sedimentation and efficient pollutants removal with low HRT.

Microalgal-bacterial granular sludge process: A game changer of future municipal wastewater treatment?

This article is in the hope to open a fundamental discussion on what should future municipal wastewater treatment process be. A paradigm shift of treatment technology from present single functionality of removing to multiple-functionality of synergetic water-resource-energy recovery and carbon neutral for maximizing both environmental and economic sustainability. However, the current treatment technologies could hardly meet such requirements. It is elucidated in this article that a microalgal-bacterial granular sludge process could offer a promising option for achieving the multiple goals of municipal wastewater reclamation including energy generation, resource recovery and carbon reduction.

Application of two anaerobic membrane bioreactors with different pore size membranes for municipal wastewater treatment

Pore size is one of the most important properties in the successful operation of membrane-based bioprocesses for the treatment of municipal wastewater. The characteristics of two anaerobic membrane bioreactors (AnMBRs), one with a hollow fiber membrane of 0.4 μm pore size (AnMBR1), and the other with a membrane of 0.05 μm pore size (AnMBR2) were investigated for the treatment of real municipal wastewater at room temperature (25 °C) under varied hydraulic retention times (HRTs). Process performance was evaluated in terms of organic removal efficiency, biogas production and membrane filtration behaviours during a long-term continuous operation. Both AnMBRs showed good organic removal performance with COD and BOD removal efficiencies of around 89% and 93%, respectively. High energy recovery potential was achieved, with the biogas yield ranging between 0.20 and 0.26 L-gas/g-COD_rem and a methane content of approximately 75%. The differences in the membrane filtration behaviours in the two AnMBRs included different permeate flux and total filtration resistance (R_t). In the AnMBR with a 0.4 μm pore size membrane, an average R_t of 1.08 × 10^12 m^-1 was obtained even when the permeate flux was a high 0.274 m/day, while a higher average R_t of 1.51 × 10^12 m^-1 was observed in the AnMBR with 0.05 μm pore size membrane even when the flux was a low 0.148 m/day. The off-line membrane cleaning strategy used for AnMBR1 indicated that the membrane restoration efficiency was 90.2%.

Steroid hormones and estrogenic activity in the wastewater outfall and receiving waters of the Chascomús chained shallow lakes system (Argentina)

Natural and synthetic steroid hormones, excreted by humans and farmed animals, have been considered as important sources of environmental endocrine disruptors. A suite of estrogens, androgens and progestogens was measured in the wastewater treatment plant outfall (WWTPO) of Chascomús city (Buenos Aires province, Argentina), and receiving waters located downstream and upstream from the WWTPO, using solid phase extraction and high-performance liquid chromatography mass spectrometry. The following natural hormones were measured: 17β-estradiol (E₂), estrone (E₁), estriol (E₃), testosterone (T), 5α-dihydrotestosterone (DHT), progesterone (P), 17-hydroxyprogesterone (17OHP) and the synthetic estrogen 17α-ethinylestradiol (EE₂). Also, in order to complement the analytical method, the estrogenic activity in these surface water samples was evaluated using the in vitro transactivation bioassay that measures the estrogen receptor (ER) activity using mammalian cells. All-natural steroid hormones measured, except 17OHP, were detected in all analyzed water samples. E₃, E₁, EE₂ and DHT were the most abundant and frequently detected. Downstream of the WWTPO, the concentration levels of all compounds decreased reaching low levels at 4500 m from the WWTPO. Upstream, 1500 m from the WWTPO, six out of eight steroid hormones analyzed were detected: DHT, T, P, 17OHP, E₃ and E₂. Moreover, water samples from the WWTPO and 200 m downstream from it showed estrogenic activity exceeding that of the EC₅₀ of the E₂ standard curve. In sum, this work demonstrates the presence of sex steroid hormones and estrogenic activity, as measured by an in vitro assay, in superficial waters of the Pampas region. It also suggests the possibility of an unidentified source upstream of the wastewater outfall.

Harvesting biomass of an oil-rich microalga Parachlorella kessleri TY02 by ferric chloride: Effects on harvesting efficiency, lipid production and municipal wastewater treatment

Inorganic coagulants have been widely used to harvest microalgal biomass. A great deal of attention has been mainly focused on the response of harvesting efficiency, lipid production and feasibility of the reuse of medium to inorganic coagulants. The physiological state of harvested cells and feasibility of wastewater treatment remain unclear. In this context, the effect of ferric chloride as a conventional inorganic coagulant on the harvesting efficiency, physiological state and lipid content of an oil-rich microalga Parachlorella kessleri TY02 was evaluated. Moreover, the performance of harvested cells for municipal wastewater treatment was also evaluated. When the dosage of iron ions was 0.077 mg/mg dry biomass and the sedimentation time was 5 min, the microalga had good harvesting efficiency and cell viability. As the dosage of iron ions was up to 0.15 mg/mg dry biomass, cell viability notably decreased. Cells harvested by 0.077 and 0.15 mg/mg dry biomass of iron ions showed good wastewater treatment efficiency. It was also found that long sedimentation time (40 min) not only did not promote harvesting efficiency, but also reduced cell viability. Iron ions had no notable effect on lipid content of the microalga. Through comprehensive evaluation of harvesting efficiency, lipid production, physiological state and wastewater treatment efficiency, it indicated that 0.077 mg/mg dry biomass of iron ions could be used to harvest biomass of the microalga.

Defensive responses of microalgal-bacterial granules to tetracycline in municipal wastewater treatment

Nowadays, tetracycline has been frequently detected in municipal wastewater, posing a pressing threat for wastewater treatment. This study investigated the defensive responses of microalgal-bacterial granules to tetracycline. It was found that the physical structure of microalgal-bacterial granules tended to shift from individual granules to loosely inter-connected agglomerates. In response to tetracycline, microalgae instead of bacteria in granules were found to produce more low molecular weight polysaccharides in extracellular polymeric substances (EPS), which increased from 0.26 mg C/g VSS in the control to 17.81 and 25.15 mg C/g VSS after being exposed to 1 and 10 mg/L of tetracycline, respectively. It was further revealed that tetracycline could bind to tryptophan in EPS proteins, and this action in turn could help to alleviate the direct toxicity of tetracycline to microorganisms in granules. Moreover, it appeared that the abundance of Pseudomonas-carrying tetracycline resistant genes increased substantially, together with gradual disappearance of Cyanobacteria.

IR microspectroscopic identification of microplastics in municipal wastewater treatment plants

Municipal wastewater treatment plants (WWTPs) have been identified as a key source of microplastics (MPs) release into rivers and oceans. Varied extents of MPs pollution have been observed at different WWTPs with limited information in Thailand. This research aimed to study the occurrence of MPs in municipal WWTPs in Thailand by measuring MPs of three WWTPs which employ different treatment process. The WWTPs were selected to represent MP pollution from urbanized and suburbanized areas with different treatment set-ups, i.e., sequence batch reactor (WWTP-A), oxidation ditch (WWTP-B), and conventional activated sludge (WWTP-C). Water and sludge sampling was performed at the inlet and outlet of primary and secondary treatment units. The results indicate that the average MPs removal efficiency of the WWTPs was ca. 84%, with the aeration tank as the main removal unit by transferring MPs from the water phase to sludge. Primary treatment comprising of screening and grit chambers could not remove MPs effectively. Most of the MPs observed in the WWTPs were fibers (32-57%), mostly made of polyester, polyethylene, polyacrylate, and polypropylene. From these results, it is suggested to implement tertiary treatment options to improve MPs removal efficiency in WWTPs, and to apply post-treatment to the WWTPs' raw sludge to prevent the MPs' release into the environment when the sludge is applied to agricultural land.

Long-term stability of partial nitritation-anammox for treatment of municipal wastewater in a moving bed biofilm reactor pilot system

Nitrogen removal from the mainstream of municipal wastewater with partial nitritation-anammox (PNA) would be highly beneficial with regard to the uses of energy and organic carbon. However, the challenges of process instability, low nitrogen removal rates (NRR) and unwanted aerobic nitrite oxidation need to be solved to reach large-scale implementation. Here, we have operated pilot-scale moving bed biofilm reactors (MBBRs) for mainstream treatment, together with sidestream treatment of sludge liquor from anaerobic digestors, for over 900 days to investigate process stability, reactor performance and microbial community structure at realistic conditions. The MBBR biofilm contained stable and high relative abundances of anammox bacteria (10-32%) consisting of two major Brocadia sp. populations, and several populations of aerobic ammonia-oxidising bacteria (AOB) within Nitrosomonas sp. (0.2-3.1%), as assessed by 16S rDNA amplicon sequencing. In addition, nitrite-oxidising bacteria (NOB) consisting of Nitrospira sp. (0.4-0.8%) and Nitrotoga sp. (up to 0.4%) were present. Nitrogen was removed at a peak rate of 0.66 g N m^-2 d^-1 (0.13 kg N m^-3 d^-1) with a nitrate production over ammonium consumption of 15% by the NOB, at operation with continuous aeration at 15 °C. However, during most periods with continuous aeration, the NRR was lower (≈ 0.45 g N m^-2 d^-1), with larger relative nitrate production (≈40%), presumably due to problems to maintain stable residual ammonium concentrations during wet-weather mainstream flows. Changing reactor operation to intermittent aeration decreased the NRR but did not help in suppressing the NOB. The study shows that with MBBRs, stable mainstream PNA can be attained at realistic NRR, but with need for post-treatment of nitrate, since effective NOB suppression was hard to achieve.

Evaluation of a biological post-treatment after full-scale ozonation at a municipal wastewater treatment plant

To reduce the discharge of trace organic compounds into water bodies associated with potential toxic effects such as endocrine disruption, new advanced treatment methods are being investigated at several wastewater treatment plants (WWTPs). One of the most studied and already implemented technologies is ozonation. However, ozonation only partially oxidizes trace organic compounds (TrOC) and as a result, transformation products (TPs) with unknown properties can be formed. In order to minimise the risk of releasing unknown and potentially toxic TPs into surface water, it is recommended to install a biological post-treatment after ozonation. The aim of this study was to evaluate the efficiency of a moving bed reactor following ozonation in a full-scale plant. Different ozone dosages (z_spec. = 0.3, 0.5, 0.7 mg _O3/mg_DOC) were investigated. To assess the biological activity of the post-treatment, the assimilable organic carbon (AOC) was determined in addition to the formed biomass. Furthermore, selected TrOC were analysed in parallel to monitor the ozonation efficiency at different ozone doses. In addition, estrogenic, androgenic as well as corresponding antagonistic effects were investigated after each treatment step using the A-YES and A-YAS assay. A non-target screening was performed to evaluate a trend analysis of formed TPs as well as their removal by the post-treatment procedure. The results proved the successful design of the biological post-treatment reactor by a constant biofilm development and reduction of the AOC. Endocrine effects were removed below the limit of detection (LOD) of 10 pg EEQ/L already after ozonation for all applied ozone doses. Antagonistic effects were not significantly reduced during ozonation and subsequent biological post-treatment. For this reason, further research is needed to evaluate different post-treatment technologies. The trend analysis from non-target screening data showed a reduction of about 95% of the number of formed TPs by the biological post-treatment. Consequently, an assessment of the biological activity and the elimination capacity of a certain biological post-treatment technique is thus possible by applying the AOC in combination with a non-target screening.

Comparative evaluation of ultrafiltration and dynamic membranes in an aerobic membrane bioreactor for municipal wastewater treatment

This study investigated the applicability of self-forming hollow fiber dynamic membrane (DM) as a low-cost alternative to ultrafiltration (UF) membrane. A hollow fiber polyester fabric was used as a support material to form the DM layer. Submerged DM and UF hollow fiber membrane were placed in the same reactor in order to compare the treatment and filtration performance of each membrane. Morphological analyses were also carried out for DM surface. The system was operated continuously at a flux of 5 L/m² h for 85 days. High COD removal efficiency and total suspended solids (TSS) rejection were achieved by the DM. Transmembrane pressure (TMP) of the DM was higher in comparison to the UF membrane, which was related with the formation of cake layer in DM. DM technology can be used as an alternative to UF membrane for municipal wastewater treatment.

Evaluation of foam-glass media in a high-rate filtration process for the removal of particulate matter containing phosphorus in municipal wastewater

Foam-glass as an effective filter media in a high-rate filtration process was evaluated for the removal of particulate matter containing phosphorus in municipal wastewater. The foam-glass with a low sphericity exhibited a higher porosity (60.2%) and a lower apparent specific gravity (0.50 g/cm³) compared with a conventional sand media (35.1% and 1.19 g/cm³). In particular, the high porosity of the foam-glass increased its surface area for capturing particles with coagulation, leading to a significantly decreasing head loss in the filtration bed column, resulting in a significantly longer filtration duration (more than 2 times) and a slightly higher removal of contaminants (approximately 4.8% for a suspended solid and 2% for the total phosphorus). Additionally, while backwashing of the conventional sand media required about 30% of the bed volume, the low specific gravity of the foam-glass media could be expanded to 100% of the volume due to its lower energy demand. Based on these advantages, it is expected that the foam-glass media will have a vital role as an alternative media in high-rate filtration processes.

Removal and fate of emerging organic micropollutants (EOMs) in municipal wastewater by a pilot-scale membrane bioreactor (MBR) treatment under varying solid retention times

This study investigates the removal and fate of 23 emerging organic micropollutants (EOMs) including a wide range of pharmaceuticals (antibiotics, β-blockers, analgesics, diuretics, psychostimulants, antiepileptics, immunosuppressives, anticoagulants), and steroid hormones detected in municipal wastewater by a pilot-scale membrane bioreactor (MBR) plant at two different solid retention times (SRTs) of 60 and 21 days. Different removal efficiencies of the selected EOMs were observed and explained based on their physicochemical properties (such as distribution coefficient, log D; dissociation constant, pK_a; solid-water distribution coefficients, and K_d) along with process operating parameters. The dominant removal mechanisms of EOMs were biotransformation and sorption onto the sludge, which were confirmed by the mass balance study. Moreover, changes in the sludge properties, as a consequence of different SRTs, were evaluated based on variations in soluble microbial products (SMP), extracellular polymeric substances (EPS), and capillary suction time (CST). Finally, the quality of the MBR effluent was compared with some established guidelines, which confirmed the fulfilment of water quality requirements for reuse purposes.

Efficient fouling control using outer-selective hollow fiber thin-film composite membranes for osmotic membrane bioreactor applications

This paper investigates the efficiency of fouling mitigation methods using a novel outer selective hollow fiber thin-film composite forward osmosis (OSHF TFC FO) membrane for osmosis membrane bioreactor (OMBR) system treating municipal wastewater. Two home-made membrane modules having similar transport properties were used. Two operation regimes with three different fouling mitigation strategies were utilized to test the easiness of membrane for fouling cleaning. These two membrane modules demonstrated high performance with high initial water flux of 14.4 LMH and 14.1 LMH and slow increase rate of mixed liquor's salinity in the bioreactor using 30 g/L NaCl as draw solution. OMBR system showed high removals of total organic carbon and NH4 + -N (>98%). High fouling cleaning efficiency was achieved using OSHF TFC FO membrane with different fouling control methods. These results showed that this membrane is suitable for OMBR applications due to its high performance and its simplicity for fouling mitigation.

Transcriptomics investigation of thyroid hormone disruption in the olfactory system of the Rana [Lithobates] catesbeiana tadpole

Thyroid hormones (THs) regulate vertebrate growth, development, and metabolism. Despite their importance, there is a need for effective detection of TH-disruption by endocrine disrupting chemicals (EDCs). The frog olfactory system substantially remodels during TH-dependent metamorphosis and the objective of the present study is to examine olfactory system gene expression for TH biomarkers that can evaluate the biological effects of complex mixtures such as municipal wastewater. We first examine classic TH-response gene transcripts using reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) in the olfactory epithelium (OE) and olfactory bulb (OB) of premetamorphic Rana (Lithobates) catesbeiana tadpoles after 48 h exposure to biologically-relevant concentrations of the THs, 3,5,3'-triiodothyronine (T3) and L-thyroxine (T4), or 17-beta estradiol (E2); a hormone that can crosstalk with THs. As the OE was particularly sensitive to THs, further RNA-seq analysis found >30,000 TH-responsive contigs. In contrast, E2 affected 267 contigs of which only 57 overlapped with THs suggesting that E2 has limited effect on the OE at this developmental phase. Gene ontology enrichment analyses identified sensory perception and nucleoside diphosphate phosphorylation as the top affected terms for THs and E2, respectively. Using classic and additional RNA-seq-derived TH-response gene transcripts, we queried TH-disrupting activity in municipal wastewater effluent from two different treatment systems: anaerobic membrane bioreactor (AnMBR) and membrane enhanced biological phosphorous removal (MEBPR). While we observed physical EDC removal in both systems, some TH disruption activity was retained in the effluents. This work lays an important foundation for linking TH-dependent gene expression with olfactory system function in amphibians.

Effluent concentration and removal efficiency of nine heavy metals in secondary treatment plants in Shanghai, China

Wastewater treatment plants (WWTPs) are the most common form of industrial and municipal wastewater control. To evaluate the performance of wastewater treatment and the potential risk of treated wastewater to aquatic life and human health, the influent and effluent concentrations of nine toxic metals were determined in 12 full-scale WWTPs in Shanghai, China. The performance was evaluated based on national standards for reclamation and aquatic criteria published by US EPA, and by comparison with other full-scale WWTPs in different countries. Potential sources of heavy metals were recognized using partial correlation analysis, hierarchical clustering, and principal component analysis (PCA). Results indicated significant treatment effect on As, Cd, Cr, Cu, Hg, Mn, Pb, and Zn. The removal efficiencies ranged from 92% (Cr) to 16.7% (Hg). The results indicated potential acute and/or chronic effect of Cu, Ni, Pb, and Zn on aquatic life and potential harmful effect of As and Mn on human health for the consumption of water and/or organism. The results of partial correlation analysis, hierarchical clustering based on cosine distance, and PCA, which were consistent with each other, suggested common source of Cd, Cr, Cu, and Pb and common source of As, Hg, Mn, Ni, and Zn. Hierarchical clustering based on Jaccard similarity suggested common source of Cd, Hg, and Ni, which was statistically proved by Fisher's exact test.

Monitoring of 943 organic micropollutants in wastewater from municipal wastewater treatment plants with secondary and advanced treatment processes

To perform a systematic survey on the occurrence and removal of micropollutants during municipal wastewater treatment, 943 semi-volatile organic chemicals in 32 wastewater samples including influents of secondary treatments, secondary effluents and final effluents (effluents of advanced treatments), which were collected from seven full-scale municipal wastewater treatment plants (MWTPs) in China, were examined by gas chromatography-mass spectrometry (GC-MS) coupled with an automated identification and quantification system with a database (AIQS-DB). In total, 196 and 145 chemicals were detected in secondary and final effluents, respectively. The majority of the total concentrations (average removal efficiency, 87.0%±5.9%) of the micropollutants were removed during secondary treatments. However, advanced treatments achieved different micropollutant removal extents from secondary effluents depending on the different treatment processes employed. Highly variable removal efficiencies of total concentrations (32.7%-99.3%) were observed among the different advanced processes. Among them, ozonation-based processes could remove 70.0%-80.9% of the total concentrations of studied micropollutants. The potentially harmful micropollutants, based on their detection frequency and concentration in secondary and final effluents, were polycyclic aromatic hydrocarbons (PAHs) (2-methylnaphthalene, fluoranthene, pyrene, naphthalene and phenanthrene), phosphorus flame retardants (tributyl phosphate (TBP), tris(2-chloroethyl) phosphate (TCEP) and tris(1,3-dichloro-2-propyl) phosphate (TDCP)), phthalates (bis(2-ethylhexyl)phthalate (DEHP)), benzothiazoles (benzothiazole, 2-(methylthio)-benzothiazol, and 2(3H)-benzothiazolone) and phenol. This study indicated that the presence of considerable amounts of micropollutants in secondary effluent creates the need for suitable advanced treatment before their reuse.

Intuitionistic fuzzy analytical hierarchical processes for selecting the paradigms of mangroves in municipal wastewater treatment

Municipal wastewater discharge is widespread and one of the sources of coastal eutrophication, and is especially uncontrolled in developing and undeveloped coastal regions. Mangrove forests are natural filters of pollutants in wastewater. There are three paradigms of mangroves for municipal wastewater treatment and the selection of the optimal one is a multi-criteria decision-making problem. Combining intuitionistic fuzzy theory, the Fuzzy Delphi Method and the fuzzy analytical hierarchical process (AHP), this study develops an intuitionistic fuzzy AHP (IFAHP) method. For the Fuzzy Delphi Method, the judgments of experts and representatives on criterion weights are made by linguistic variables and quantified by intuitionistic fuzzy theory, which is also used to weight the importance of experts and representatives. This process generates the entropy weights of criteria, which are combined with indices values and weights to rank the alternatives by the fuzzy AHP method. The IFAHP method was used to select the optimal paradigm of mangroves for treating municipal wastewater. The entropy weights were entrained by the valid evaluation of 64 experts and representatives via online survey. Natural mangroves were found to be the optimal paradigm for municipal wastewater treatment. By assigning different weights to the criteria, sensitivity analysis shows that natural mangroves remain to be the optimal paradigm under most scenarios. This study stresses the importance of mangroves for wastewater treatment. Decision-makers need to contemplate mangrove reforestation projects, especially where mangroves are highly deforested but wastewater discharge is uncontrolled. The IFAHP method is expected to be applied in other multi-criteria decision-making cases.

Membrane fouling characteristics and mitigation in a coagulation-assisted microfiltration process for municipal wastewater pretreatment

Maximizing the energy-profitable treatment of municipal wastewater (MW) is of significance to achieve energy-neutral operation for wastewater treatment plant. Direct membrane filtration technology has been considered as an effective way to separate organic carbon from MW for subsequent anaerobic energy-recovering process, but its application is restrained by severe membrane fouling issues. Thus, it is essential to identify the substances in MW that are responsible for membrane fouling and find out efficient anti-fouling methods. In this work, an integrated approach through combining multivariate curve resolution-alternating least squares analysis with infrared attenuated total reflection mapping was adopted to explore the membrane fouling process, and three coagulants, i.e., polyacrylamide, Al₂(SO₄)₃ and FeCl₃, were individually used to mitigate membrane fouling. Results show that the 1-8 μm biopolymer clusters, i.e., humic-like and protein-like substances, were the predominant foulants in MW. In addition, membrane fouling caused by proteins was found to be more severe than that by humic substances. Coagulation pretreatment was demonstrated to be effective in mitigating membrane fouling. Al₂(SO₄)₃ or FeCl₃ had superior anti-fouling performance comparing to that of polyacrylamide. The dosage of polyacrylamide needs to be optimized according to the actual MW characteristics as its overdose would cause a substantial decline of membrane flux. These results provide a deep understanding of the membrane fouling mechanisms for organic carbon separation from MW and are beneficial for developing efficient and cost-effective membrane fouling mitigation strategies.

Increasing phosphorus recovery from dewatering centrate in microbial electrolysis cells

BACKGROUND

Microbial electrolysis cells (MECs) use bioelectrochemical reactions to remove organic contaminants at the bioanode and produce hydrogen gas at the cathode. High local pH conditions near the cathode can also be utilized to produce struvite from nutrient-rich wastewater. This beneficial aspect was investigated using lab-scale MECs fed with dewatering centrate collected at a local wastewater treatment plant. The main objective was to improve phosphorus recovery by examining various cathode configurations and electric current conditions.

RESULTS

The stainless steel mesh (SSM) cathode was relatively inefficient to achieve complete phosphorus recovery because struvite crystals were smaller (a few to tens of micrometers) than the open space between mesh wires (80 µm). As a result, the use of multiple pieces of SSM also showed a limited improvement in the phosphorus recovery up to only 68% with 5 SSM pieces. Readily available organic substrates were not sufficient in the dewatering centrate, resulting in relatively low electric current density (mostly below 0.2 A/m²). The slow electrode reaction did not provide sufficiently high pH conditions near the cathode for complete recovery of phosphorus as struvite. Based on these findings, additional experiments were conducted using stainless steel foil (SSF) as the cathode and acetate (12 mM) as an additional organic substrate for exoelectrogens at the bioanode. With the high electric current (>2 A/m²), a thick layer of struvite crystals was formed on the SSF cathode. The phosphorus recovery increased to 96% with the increasing MEC operation time from 1 to 7 days. With the high phosphorus recovery, estimated energy requirement was relatively low at 13.8 kWh (with acetate) and 0.30 kWh (without acetate) to produce 1 kg struvite from dewatering centrate.

CONCLUSIONS

For efficient phosphorus recovery from real wastewater, a foil-type cathode is recommended to avoid potential losses of small struvite crystals. Also, presence of readily available organic substrates is important to maintain high electric current and establish high local pH conditions near the cathode. Struvite precipitation was relatively slow, requiring 7 days for nearly complete removal (92%) and recovery (96%). Future studies need to focus on shortening the time requirement.

Construction and application of the Synechocystis sp. PCC6803-ftnA in microbial contamination control in a coupled cultivation and wastewater treatment

Inspired by iron fertilization experiments in HNLC (high-nitrate, low-chlorophyll) sea areas, we proposed the use of iron-rich engineered microalgae for microbial contaminant control in iron-free culture media. Based on the genome sequence and natural transformation system of Synechocystis sp. PCC6803, ftnA (encoding ferritin) was selected as our target gene and was cloned into wild-type Synechocystis sp. PCC6803. Tests at the molecular level confirmed the successful construction of the engineered Synechocystis sp. PCC6803-ftnA. After Fe(3+)-EDTA pulsing, the intracellular iron content of Synechocystis sp. PCC6803-ftnA was significantly enhanced, and the algae was used in the microbial contamination control system. In the coupled Synechocystis sp. PCC6803-ftnA production and municipal wastewater (MW, including Scenedesmus obliquus and Bacillus) treatment, Synechocystis sp. PCC6803-ftnA accounted for all of the microbial activity and significantly increased from 70% of the microbial community to 95%. These results revealed that while the stored iron in the Synechocystis sp. PCC6803-ftnA cells was used for growth and reproduction of this microalga in the MW, the growth of other microbes was inhibited because of the iron limitation, and these results provide a new method for microbial contamination control during a coupling process.

Fate of fluorescent core-shell silica nanoparticles during simulated secondary wastewater treatment

Increasing use of silica nanoparticles (SiO2 NPs) in consumer products and industrial processes leads to SiO2 NP discharge into wastewater. Thus, there is a need to understand the fate of SiO2 NPs during wastewater treatment. However, the detection of SiO2 NPs in environmental systems is hindered by the elevated background levels of natural silicon. In this work, laboratory-synthesized fluorescent core-shell SiO2 NPs were used to study the fate of these NPs during secondary wastewater treatment. Fluorescent measurements provided an easy and fast method for SiO2 NP tracking. A laboratory-scale activated sludge system consisting of an aeration tank and a settler was fed with synthetic wastewater containing ca. 7.5 mg L(-1) of fluorescent SiO2 NPs for 30 days. SiO2 NPs were effectively removed from the wastewater (>96%) during the first 6 days, however the concentration of SiO2 NPs in the effluent gradually increased afterwards and the NP discharge was as high as 65% of the input after 30 days of NP dosing. The poor removal of the SiO2 NPs was related to the high colloidal stability of the NPs in the wastewater and their limited propensity to biosorption. Although some degree of NP adsorption on the biomass was observed using fluorescence microscopy, the affinity of SiO2 NPs for the activated sludge was not enough for a sustained and effective removal of the SiO2 NPs from the wastewater.

Bioaugmentation treatment of municipal wastewater with heterotrophic-aerobic nitrogen removal bacteria in a pilot-scale SBR

PCN bacteria capable of heterotrophic-aerobic nitrogen removal was successfully applied for bioaugmented treatment of municipal wastewater in a pilot-scale SBR. At an appropriate COD/N ratio of 8, the bioaugmentation system exhibited stable and excellent carbon and nutrients removal, the averaged effluent concentrations of COD, NH4(+)-N, TN and TP were 20.6, 0.69, 14.1 and 0.40 mg/L, respectively, which could meet the first class requirement of the National Municipal Wastewater Discharge Standards of China (COD<50 mg/L, TN<15 mg/L, TP<0.5 mg/L). Clone library and real-time PCR analysis revealed that the introduced bacteria greatly improved the structure of original microbial community and facilitated their aerobic nutrients removal capacities. The proposed emerging technology was shown to be an alternative technology to establish new wastewater treatment systems and upgrade or retrofit conventional systems from secondary-level to tertiary-level.

Integrated production of polyhydroxyalkanoates (PHAs) with municipal wastewater and sludge treatment at pilot scale

A pilot-scale process was operated over 22 months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55 °C) produced centrate (6-9.4 gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42 °C. Centrate was used to accumulate PHA up to 0.39 gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5 gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities.

Nutrient removal and microbial communities' development in a young unplanted constructed wetland using Bauxsol™ pellets to treat wastewater

Municipal wastewater was treated over a six month period in an unplanted constructed wetland with a lower soil layer and an upper Bauxsol™ pellet layer. The interactions between Bauxsol™ pellets, soil, effluent and microbial communities demonstrated a positive influence on contaminant removal. Bauxsol™ treated effluent showed >95% phosphate removal and ~26% nitrogen removal during the trial. Substantial quantities of nitrate, trace-metals and Colwell P were bound to the pellets, whereas only ammonium was bound to the soil. The structure of microbial communities analysed by denaturing gradient gel electrophoresis (DGGE) showed distinct bacterial communities attached to Bauxsol™ pellets and soil owing to differences in geochemistry and micro-environmental conditions. Polymerase chain reaction (PCR) amplification of specific marker genes (i.e. bacterial and archaeal amoA genes, nosZ gene, and hzo gene) was used to evaluate the presence of microbial communities associated with nitrogen transformation. Data revealed the co-existence of aerobic ammonia-oxidising bacteria, anaerobic ammonia-oxidising bacteria (anammox) and denitrifiers attached to Bauxsol™ pellets and ammonia-oxidising bacteria and archaea attached to soil. This study successfully demonstrates that Bauxsol™ pellets are a suited alternative media for constructed wetland to treat wastewater effectively removing phosphate and serving as biomass support particles for bacterial communities associated with nitrogen-cycling.

Key design factors affecting microbial community composition and pathogenic organism removal in horizontal subsurface flow constructed wetlands

Constructed wetlands constitute an interesting option for wastewater reuse since high concentrations of contaminants and pathogenic microorganisms can be removed with these natural treatment systems. In this work, the role of key design factors which could affect microbial removal and wetland performance, such as granular media, water depth and season effect was evaluated in a pilot system consisting of eight parallel horizontal subsurface flow (HSSF) constructed wetlands treating urban wastewater from Les Franqueses del Vallès (Barcelona, Spain). Gravel biofilm as well as influent and effluent water samples of these systems were taken in order to detect the presence of bacterial indicators such as total coliforms (TC), Escherichia coli, fecal enterococci (FE), Clostridium perfringens, and other microbial groups such as Pseudomonas and Aeromonas. The overall microbial inactivation ratio ranged between 1.4 and 2.9 log-units for heterotrophic plate counts (HPC), from 1.2 to 2.2 log units for total coliforms (TC) and from 1.4 to 2.3 log units for E. coli. The presence of fine granulometry strongly influenced the removal of all the bacterial groups analyzed. This effect was significant for TC (p=0.009), E. coli (p=0.004), and FE (p=0.012). Shallow HSSF constructed wetlands were more effective for removing Clostridium spores (p=0.039), and were also more efficient for removing TC (p=0.011) and E. coli (p=0.013) when fine granulometry was used. On the other hand, changes in the total bacterial community from gravel biofilm were examined by using denaturing gradient gel electrophoresis (DGGE) and sequencing of polymerase chain reaction (PCR)-amplified fragments of the 16S rRNA gene recovered from DGGE bands. Cluster analysis of the DGGE banding pattern from the different wetlands showed that microbial assemblages separated according to water depth, and sequences of different phylogenetic groups, such as Alpha, Beta and Delta-Proteobacteria, Nitrospirae, Bacteroidetes, Acidobacteria, Firmicutes, Synergistetes and Deferribacteres could be retrieved from DGGE bands.

Seasonal variation of diclofenac concentration and its relation with wastewater characteristics at two municipal wastewater treatment plants in Turkey

The pharmaceutically active compound diclofenac has been monitored during one year at separate treatment units of two municipal wastewater treatment plants (WWTPs) to evaluate its seasonal variation and the removal efficiency. Conventional wastewater characterization was also performed to assess the possible relationship between conventional parameters and diclofenac. Diclofenac concentrations in the influent and effluent of both WWTPs were detected in the range of 295-1376 and 119-1012ng/L, respectively. Results indicated that the higher diclofenac removal efficiency was observed in summer season in both WWTPs. Although a consistency in diclofenac removal was observed in WWTP_1, significant fluctuation was observed at WWTP_2 based on seasonal evaluation. The main removal mechanism of diclofenac in the WWTPs was most often biological (55%), followed by UV disinfection (27%). When diclofenac removal was evaluated in terms of the treatment units in WWTPs, a significant increase was achieved at the treatment plant including UV disinfection unit. Based on the statistical analysis, higher correlation was observed between diclofenac and suspended solids concentrations among conventional parameters in the influent whereas the removal of diclofenac was highly correlated with nitrogen removal efficiency.

Performance of the biosorptive activated sludge (BAS) as pre-treatment to UF for decentralized wastewater reuse

A biosorptive activated sludge (BAS) was operated at lab-scale with diluted and concentrated municipal wastewater to study the efficiency of removal of organics (particulate and soluble COD) and recovery of nutrients (TKN, ammonia, phosphorus). The system performed significantly better with concentrated wastewater, where COD removal efficiency was 80% at organic loading rates between 10 and 20kg m(-3)d(-1). Supplementation of ferrous iron at 20mg L(-1), significantly improved both the removal of particulate, soluble COD and phosphorus. The effluent from the BAS was further treated using an ultrafiltration process with backwashing. The average permeate flux (at constant TMP=0.3bar) increased from 23 to 28 and 34L m(-2)h(-1) when raw sewage, BAS without iron, and iron respectively were tested. The proposed technology is compact, efficient and suitable for decentralized water reuse, while the capital and operational expenses were calculated as 0.64 and 0.43€ m(-3), respectively.