Municipal wastewater treatment plants coupled with electrochemical, biological and bio-electrochemical technologies: Opportunities and challenge toward energy self-sufficiency

Promotion of direct electron transfer between Shewanella putrefaciens CN32 and carbon fiber electrodes via in situ growth of α-Fe2O3 nanoarray

The iron transport system plays a crucial role in the extracellular electron transfer process of Shewanella sp. In this study, we fabricated a vertically oriented α-Fe2O3 nanoarray on carbon cloth to enhance interfacial electron transfer in Shewanella putrefaciens CN32 microbial fuel cells. The incorporation of the α-Fe2O3 nanoarray not only resulted in a slight increase in flavin content but also significantly enhanced biofilm loading, leading to an eight-fold higher maximum power density compared to plain carbon cloth. Through expression level analyses of electron transfer-related genes in the outer membrane and core genes in the iron transport system, we propose that the α-Fe2O3 nanoarray can serve as an electron mediator, facilitating direct electron transfer between the bacteria and electrodes. This finding provides important insights into the potential application of iron-containing oxide electrodes in the design of microbial fuel cells and other bioelectrochemical systems, highlighting the role of α-Fe2O3 in promoting direct electron transfer.

Biopolymer-based beads for the adsorptive removal of organic pollutants from wastewater: Current state and future perspectives

Among biopolymer-based adsorbents, composites in the form of beads have shown promising results in terms of high adsorption capacity and ease of separation from the effluents. This review addresses the potential of biopolymer-based beads to remediate wastewaters polluted with emerging organic contaminants, for instance dyes, active pharmaceutical ingredients, pesticides, phenols, oils, polyaromatic hydrocarbons, and polychlorinated biphenyls. High adsorption capacities up to 2541.76 mg g-1 for dyes, 392 mg g-1 for pesticides and phenols, 1890.3 mg g-1 for pharmaceuticals, and 537 g g-1 for oils and organic solvents have been reported. The review also attempted to convey to its readers the significance of wastewater treatment through adsorption by providing an overview on decontamination technologies of organic water contaminants. Various preparation methods of biopolymer-based gel beads and adsorption mechanisms involved in the process of decontamination have been summarized and analyzed. Therefore, we believe there is an urge to discuss the current state of the application of biopolymer-based gel beads for the adsorption of organic pollutants from wastewater and future perspectives in this regard since it is imperative to treat wastewater before releasing into freshwater bodies.

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

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

Prediction of biological nutrients removal in full-scale wastewater treatment plants using H2O automated machine learning and back propagation artificial neural network model: Optimization and comparison

The effective control of total nitrogen (ETN) and total phosphorus (ETP) in effluent is challenging for wastewater treatment plants (WWTPs). In this work, automated machine learning (AutoML) (mean square error = 0.4200 ∼ 3.8245, R2 = 0.5699 ∼ 0.6219) and back propagation artificial neural network (BPANN) model (mean square error = 0.0012 ∼ 6.9067, R2 = 0.4326 ∼ 0.8908) were used to predict and analyze biological nutrients removal in full-scale WWTPs. Interestingly, BPANN model presented high prediction performance and general applicability for WWTPs with different biological treatment units. However, the AutoML candidate models were more interpretable, and the results showed that electricity carbon emission dominated the prediction. Meanwhile, increasing data volume and types of WWTP hardly affected the interpretable results, demonstrating its wide applicability. This study demonstrated the validity and the specific advantages of predicting ETN and ETP using H2O AutoML and BPANN model, which provided guidance on the prediction and improvement of biological nutrients removal in WWTPs.

A walnut shell biochar-nano zero-valent iron composite membrane for the degradation of carbamazepine via persulfate activation

In this study, novel walnut shell biochar-nano zero-valent iron nanocomposites (WSBC-nZVI) were synthesized using a combined pyrolysis/reduction process. WSBC-nZVI displayed a high removal efficiency (86 %) for carbamazepine (CBZ) compared with walnut shell biochar (70 %) and nano zero-valent iron (76 %) in the presence of persulfate (PS) (0.5 g/L catalyst, 10 mg/L CBZ, 1 mM persulfate). Subsequently, WSBC-nZVI was applied for the fabrication of the membrane using a phase inversion method. The membrane demonstrated an excellent removal efficiency of 91 % for CBZ in a dead-end system (2 mg/L CBZ, 1 mM persulfate). In addition, the effect of various operating conditions on the degradation efficiency in the membrane/persulfate system was investigated. The optimum pH was close to neutral, and an increase in CBZ concentration from 1 mg/L to 10 mg/L led to a drop in removal efficiency from 100 % to 24 %. The degradation mechanisms indicated that oxidative species, including 1O2, OH, SO4-, and O2-, all contribute to the degradation of CBZ, while the role of 1O2 is highlighted. The CBZ degradation products were also investigated, and the possible pathways and the predicted toxicity of intermediates were proposed. Furthermore, the practical use of the membrane was validated by the treatment of real wastewater.

Critical analysis on the transformation and upgrading strategy of Chinese municipal wastewater treatment plants: Towards sustainable water remediation and zero carbon emissions

In the light of circular economy aspects, processing of large-scale municipal wastewater treatment plants (WWTPs) needs reconsideration to limit the overuse of energy, implement of non-green technologies and emit abundant greenhouse gas. Along with the huge increase in the worldwide population and agro-industrial activities, global environmental organizations have issued several recent roles to boost scientific and industrial communities towards sustainable development. Over recent years, China has imposed national and regional standards to control and manage the discharged liquid and solid waste, as well as to achieve carbon peaking and carbon neutrality. The aim of this report is to analyze the current state of Chinese WWTPs routing and related issues such as climate change and air pollution. The used strategies in Chinese WWTPs and upgrading trends were critically discussed. Several points were addressed including the performance, environmental impact, and energy demand of bio-enhanced technologies, including hydrolytic acidification pretreatment, efficient (toxic) strain treatment, and anaerobic ammonia oxidation denitrification technology, as well as advanced treatment technologies composed of physical and chemical treatment technologies, biological treatment technology and combined treatment technology. Discussion and critical analysis based on the current data and national policies were provided and employed to develop the future development trend of municipal WWTPs in China from the construction of sustainable and "Zero carbon" WWTPs.

Application of artificial intelligence-based methods in bioelectrochemical systems: Recent progress and future perspectives

Bioelectrochemical Systems (BESs) leverage microbial metabolic processes to either produce electricity by degrading organic matter or consume electricity to assist metabolism, and can be used for various applications such as energy production, wastewater treatment, and bioremediation. Given the intricate mechanisms of BESs, the application of artificial intelligence (AI)-based methods have been proposed to enhance the performance of BESs due to their capability to identify patterns and gain insights through data analysis. This review focuses on the analysis and comparison of AI algorithms commonly used in BESs, including artificial neural network (ANN), genetic programming (GP), fuzzy logic (FL), support vector regression (SVR), and adaptive neural fuzzy inference system (ANFIS). These algorithms have different features, such as ANN's simple network structure, GP's use in the training process, FL's human-like thought process, SVR's high prediction accuracy and robustness, and ANFIS's combination of ANN and FL features. The AI-based methods have been applied in BESs to predict microbial communities, products or substrates, and reactor performance, which can provide valuable information and improve system efficiency. Limitations of AI-based methods for predicting and optimizing BESs and recommendations for future development are also discussed. This review demonstrates the potential of AI-based methods in optimizing BESs and provides valuable information for the future development of this field.

Biodegradation of petroleum wastewater for the production of bioelectricity using activated sludge biomass

Objective

This research is based on the treatment of petroleum wastewater (PWW) with pretreated activated sludge for the production of electricity and removal of chemical oxygen demand (COD) using microbial fuel cell (MFC).

Methods

The application of the MFC system which uses activated sludge biomass (ASB) as a substrate resulted in the reduction of COD by 89.5% of the original value. It generated electricity equivalent to 8.18 mA/m2 which can be reused again. This would solve the majority of environmental crises which we are facing today.

Results

This study discusses the application of ASB to enhance the degradation of PWW for the production of a power density of 1012.95 mW/m2 when a voltage of 0.75 V (voltage) is applied at 30:70% of ASB when MFC is operated in a continuous mode. Microbial biomass growth was catalyzed using activated sludge biomass. The growth of microbes was observed by scanning through an electron microscope. Through oxidation in the MFC system, bioelectricity is generated which is used in the cathode chamber. Furthermore, the MFC operated using ASB in a ratio of 35 with the current density, which decreased to 494.76 mW/m2 at 10% ASB.

Application

Our experiments demonstrate that the efficiency of the MFC system can generate bioelectricity and treat petroleum wastewater by using activated sludge biomass.

Comprehensive understanding of electrochemical treatment systems combined with biological processes for wastewater remediation

The presence of toxic pollutants in wastewater discharge can affect the environment negatively due to presence of the organic and inorganic contaminants. The application of the electrochemical process in wastewater treatment is promising, specifically in treating these harmful pollutants from the aquatic environment. This review focused on recent applications of the electrochemical process for the remediation of such harmful pollutants from aquatic environments. Furthermore, the process conditions that affect the electrochemical process performance are evaluated, and the appropriate treatment processes are suggested according to the presence of organic and inorganic contaminants. Electrocoagulation, electrooxidation, and electro-Fenton applications in wastewater have shown effective performance with high removal rates. The disadvantages of these processes are the formation of toxic intermediate metabolites, high energy consumption, and sludge generation. To overcome such disadvantages combined ecotechnologies can be applied in large-scale wastewater pollutants removal. The combination of electrochemical and biological treatment has gained importance, increased removal performance remarkably, and decreased operational costs. The critical discussion with depth information in this review could be beneficial for wastewater treatment plant operators throughout the world.

Visual analysis of greenhouse gas emissions from sewage treatment plants based on CiteSpace: from the perspective of bibliometrics

With the global reduction actions of greenhouse gas (GHG) emissions, environmental facilities, including sewage treatment plants (STPs), need to reduce pollutants while minimizing GHG emissions. Therefore, more and more publications revealed the formation mechanism of GHGs in STPs and committed to finding better reduction schemes. From the perspective of bibliometrics, this study used CiteSpace to conduct quantitative and visual analysis based on 1,543 publications retrieved from Web of Science between 2000 and 2021 around the world. We have systematically evaluated the structure, development trend, hot spots, and research frontier in the field of GHG emissions from STPs and compared with the contents of top journals to verify the scientificity of the analysis. The results show that the number of publications has increased year by year, and the networks of authors and institutions show a strong correlation. Among them, the clusters of nitrous oxide, anaerobic digestion, and life cycle assessment (LCA) started earlier and received extensive attention, which derived other clusters in the research process. With the development of the field, researchers have gradually changed from single water treatment facilities to multi-carriers that can realize energy regeneration and utilization simultaneously. Accordingly, the GHG reduction of STPs through energy regeneration and resource recovery has become a hot point and frontier direction, which also challenges the breakthroughs in relevant technologies. Furthermore, it provides scientific support for the formulation of relevant incentive policies and economic subsidy systems, so as to alleviate the pressure of global warming and realize the sustainable development of STPs concurrently.

Investigating the Effect of Bi2MoO6/g-C3N4 Ratio on Photocatalytic Degradation of Sulfadiazine under Visible Light

In this study, a series of Bi2MoO6/g-C3N4 composites were prepared through a wet-impregnation method, and their photocatalytic properties were investigated for the degradation of sulfadiazine (SDZ) under visible light irradiation. Physical and chemical characterizations were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), UV-vis diffuse reflectance spectra (UV-vis), and electrochemical impedance spectra (EIS). Compared to pure g-C3N4, the introduction of Bi2MoO6 significantly enhanced the visible light responsive photocatalytic activity, with the 1:32 Bi2MoO6/g-C3N4 composite exhibiting the highest photodegradation efficiency towards SDZ under visible light irradiation with a photocatalytic efficiency of 93.88% after 120 min of visible light irradiation. The improved photocatalytic activity can be attributed to the formation of a heterojunction between Bi2MoO6 and g-C3N4, which promotes the transfer of photogenerated electron-hole pairs, thereby elevating its photocatalytic activity. The results suggest that Bi2MoO6/g-C3N4 composites have potential application for the degradation of sulfonamides in aquatic environments.

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.

Towards Sustainable Wastewater Treatment: Bioindication as a Technique for Supporting Treatment Efficiency Assessment

Constructed wetlands (CWs) are a promising alternative for conventional methods of wastewater treatment. However, the biggest challenge in wastewater treatment is the improvement of the technology used so that it is possible to remove micropollutants without additional costs. The impact of wastewater treatment in CWs on toxicity towards Aliivibrio fischeri, Daphnia magna and Lemna minor was investigated. The effects of feeding regime (wastewater fed in five batches per week at a batch volume of 1 L, or twice per week at a batch volume of 2.5 L) and the presence of pharmaceuticals (diclofenac and sulfamethoxazole), as well as the presence of Miscantus giganteus plants in CW columns (twelve of the 24 columns that were planted) were analyzed. A reduction in toxicity was observed in all experimental setups. The effluents from constructed wetlands were classified as moderately toxic (average TU for A. fischeri, D. magna and L. minor was 0.9, 2.5 and 5.5, respectively). The feeding regime of 5 days of feeding/2 days of resting resulted in a positive impact on the ecotoxicological and chemical parameters of wastewater (removal of TOC, N-NH₄ and pharmaceuticals). Extended exposure of Miscantus giganteus to the wastewater containing pharmaceuticals resulted in elevated activity of antioxidant enzymes (catalase and superoxide dismutase) in leaf material.

Insight into integration of photocatalytic and microbial wastewater treatment technologies for recalcitrant organic pollutants: From sequential to simultaneous reactions

The more and more stringent environmental standards for recalcitrant organic pollutants pushed forward the development of integration of photocatalytic and microbial wastewater treatment technologies. The past studies proposed mainly two typical integration ways: a) Independent sequence of photocatalysis and biodegradation (ISPB) conducting the sequential reactions; b) Intimate coupling of photocatalysis and biodegradation (ICPB) conducting the simultaneous reactions. Although ICPB has received more attraction recently due to its novelty, ISPB gives an edge in certain cases. The article reviews the state-of-the-art ISPB and ICPB studies to comprehensively compare the two systems. The strengths and weaknesses of ISPB and ICPB regarding the treatment efficiency, cost, toxicity endurance and flexibility are contradistinguished. The reactor set-ups, photocatalysts, microbial characteristics of ISPB and ICPB are summarized. The applications for different kinds of recalcitrant compounds are elaborated to give a holistic view of the removal efficiencies and transformation pathways by the two technologies. Currently, in-depth understandings about the interference among mixed pollutants, co-existing components and key parameters in realistic wastewater are urgently needed. The long-term and large-scale application cases of the integration technologies are still rare. Overall, we conclude that both ISPB and ICPB technologies are reaching maturity while challenges still exist for two systems especially regarding the reliability, economy and generalization for realistic wastewater treatment plants. Future research should not only manage to reduce the cost and energy consumption by upgrading reactors and developing novel catalysts, but also attach importance to the cocktail effects of wastewater during the sequential or simultaneous photocatalysis and biodegradation.

Municipal Wastewater Treatment Plants: Gap, Challenges, and Opportunities in Environmental Management

Municipal Wastewater Treatment Plants (MWWTPs) have proven to be sources of adverse environmental impacts; however, integrated management can help improve their efficiency. Therefore, this study aims to evaluate the gap between the current management and another based on an international standard applied to WWTPMs, in order to understand their environmental commitment, and to identify the challenges and opportunities they present for the adoption or certification of an environmental management system (EMS) based on ISO 14001. For this purpose, a descriptive cross-sectional study was carried out in two MWWTPs in southern Mexico. In a first step, an automated checklist was designed based on the requirements of the ISO 14001:2015 standard and based on a modified FMEA (Failure Mode and Effects Analysis) calculation method. In a second step, a diagnosis was carried out at the MWWTPs, followed by a SWOT (Strengths, Weaknesses, Opportunities and Threats) analysis to determine internal and external factors until a series of challenges and opportunities was identified. The findings indicate that the selected MWWTPs have a wide gap that keeps them away from efficient management. Among the challenges, "limited financial resources" were identified followed by "high turnover of managerial staff", while the opportunities with the greatest potential for improvement are related to the factors "candidate for investment" and "environmental policy". The treatment plants show a weak environmental commitment, therefore rigorous action plans should be considered, not only to protect the environment but also the investment, and they should be the main promoters that challenge the private sector.

Decolorization of textile wastewater by electrooxidation process using different anode materials: Statistical optimization

The presence of reactive dyes in textile wastewater is a serious environmental concern due to their associated mutagenic and carcinogenic effects. The present study aims to analyze the effect of different anodic materials on the decolorization of a real textile wastewater effluent. For this purpose, four different anodic materials-TiO2 -coated platine, TiO2 -coated ruthenium dioxide (RuO2 ) (viz., RuO2 ), titanium dioxide (TiO2 ), and graphite-were connected, respectively, to titanium dioxide (TiO2 ) used as a cathode electrode. Color and cost optimization studies were performed using the response surface methodology and the Box-Behnken experimental design (BBD). According to ANOVA results, the R2 values for Pt/TiO2 , RuO2 /TiO2 , TiO2 /TiO2 , and graphite/TiO2 electrode pairs were found to be 97.4%, 93.8%, 92.44%, and 92.2%, respectively, indicating a good compatibility as it is close to one. The results show that color removal efficiencies at the optimal conditions were 86.3%, 90.8%, 91.5%, and 93.6% for Pt/TiO2 , graphite/TiO2 , TiO2 /TiO2 , and RuO2 /TiO2 , respectively. Furthermore, energy consumption cost at the optimum conditions was also evaluated, and the results were as follows: Pt/TiO2 (0.95 €/m3 ), graphite/TiO2 (0.74 €/m3 ), TiO2 /TiO2 (0.31 €/m3 ), and RuO2 /TiO2 (0.26 €/m3 ). Consequently, this research paper shows that all of the tested anodic materials give satisfactory color removal efficiencies higher than 86%. When energy consumption and color removal are considered together, the use of TiO2 /TiO2 and RuO2 /TiO2 pairs would be preferred. PRACTITIONER POINTS: Anodic contribution was investigated for decolorization of textile wastewater by electrooxidation process. Graphite, TiO2 -coated Pt, TiO2 -coated RuO2 , and TiO2 were used as anode materials. Highest color removal with lowest energy consumption was achieved with TiO2 -coated RuO2 anode material (93.6%).

Microbial electrolysis cells for return flow: Simultaneous nitrogen and carbon removal

The concentration of solids in secondary sludge before anaerobic digestion in a wastewater treatment plant, bring about the production of a return flow, which contains high concentrations of all the common pollutant parameters. This return flow could unfavourably affect the performance of the processes and effluent quality of the waterline. Here, we report the utilisation of three similar microbial electrolysis cells reactors that performs simultaneous carbon and nitrogen removal to reduce the impact of the return flow in the plant. The result of the batch-fed (72 h) experiment showed COD and total nitrogen removal efficiencies that reached 90% and 80%, respectively, supporting the premise that return flows are suitable substrates for a bioelectrochemical treatment. The three reactors followed similar trends, showing good replicability and confirming the potential of MECs as a feasible technology for return flow treatment. Furthermore, when cathodic conversion efficiency was higher than 80%, the pure hydrogen production allows to recover the electric energy consumption, indicating that the system could be theoretically energy neutral.

Electro-bioremediation of a mixture of structurally different contaminants of emerging concern: Uncovering electrokinetic contribution

This study analyses the electrokinetic (EK) contribution to the removal from a clay soil of a mixture of 10 different contaminants of emerging concern (CECs; 17β-estradiol, E2; sulfamethoxazole, SMX; bisphenol A, BPA; ibuprofen, IBU; 17α-ethinylestradiol, EE2; oxybenzone, OXY; diclofenac, DCF; triclosan, TCS; caffeine, CAF; carbamazepine, CBZ). After 4 days, the CECs natural attenuation was between 0% (CBZ) and 90% (E2) yet increasing with the application of EK (20 mA, 12 h ON/OFF) to 14% (CBZ) and 100% (E2). When EK was applied, the CECs more recalcitrant to biodegradation (i.e. ≤ 13% biotic decay) mostly underwent electro-chemical induced degradation (OXY, DCF, TCS, CAF, CBZ). Daily irrigation enhanced the rates of the electro-oxidation -osmosis and -migration, increasing the CECs decay. After 8 days of EK treatment, the CECs decay increased, surpassing the decay lag phase of some compounds (OXY, TCS, and CBZ). Yet after 16 days, most CECs showed similar removals with and without EK, with EK only acting positively on SMX, OXY, TCS and CBZ (ca. +10%). Our results support that EK application can improve the removal of CECs from soil, however, under the conditions tested, 16-day treatment lead to pH alterations that decreased the bioremediation efficiency and inhibited electro-degradation near the cathode.

Characterization of a new electrochemically active bacterium phylogenetically related to Alicyclobacillus hesperidum and its electrochemical performance in microbial fuel cell

Extremophilic microorganisms in microbial electrochemical systems have opened new possibilities for waste treatment. Here, a phenomenon of electricity generation under acidophilic condition was found in organic acid fermentation wastewater treatment using microbial fuel cell (MFC). The anodic microbial community analysis showed that the percentage of Firmicutes was 99.03%, which accounted for the vast majority of the microbial community at the late discharge stage with pH 3.0. As the dominant bacterium of Firmicutes, Alicyclobacillus hesperidum EG was isolated and identified. MFC experiments confirmed that Alicyclobacillus hesperidum EG exhibited good electricity generating capability with a maximum power density of 188.1 mW m^-2 at 50 °C and low pH. It is the first time that Alicyclobacillus hesperidum EG was discovered as a newly electrochemically active bacterium. Additionally, the morphological analysis combined with electrochemical experiments demonstrated that no nanowires were found in the anodic biofilm of Alicyclobacillus hesperidum EG, and Alicyclobacillus hesperidum EG may produce soluble redox-active small molecules as electron shuttles to facilitate extracellular electron transfer. Based on unique characteristics such as good acid resistance, high temperature resistance, and high electricity generation ability, Alicyclobacillus hesperidum EG exhibited great potential in wastewater treatment and energy recovery.

Benchmarking environmental and economic indicators of sludge management alternatives aimed at enhanced energy efficiency and nutrient recovery

Wastewater treatment plants (WWTPs) have been developed as multifunctional systems that aim to eliminate pollutants present in wastewater, manage the sludge produced and improve energy efficiency. Specifically, sludge management accounts for the largest share in operational costs. Considering the relevant role of sludge treatment within the overall management scheme, this study aims to evaluate different alternatives and strategies for sludge management and treatment from the perspective of life cycle analysis, with special emphasis on those options that reduce environmental impacts and economic costs. Two pre-treatments (chemical or thermal) and two post-treatments (composting unit followed by land application or incineration) were evaluated to improve the eco-balance of the anaerobic digestion (AD) process in terms of operational (biogas production and digested sludge), environmental and economic indicators. According to the results obtained, both sludge pre-treatment alternatives proved to be an adequate alternative to improve biogas production without negatively affecting environmental and economic impacts. Finally, if the final disposal of the digestate is analysed, its application to the soil as a biofertiliser is recommended, since it presents a better environmental profile than incineration.

Assessment and management of lake eutrophication: A case study in Lake Erhai, China

Some wastewater sources, such as agricultural waste and runoff, and industrial sewage, can degrade water quality. This study summarises the sources and corresponding mechanisms that trigger eutrophication in lakes. Additionally, the trophic status index and water quality index (WQI) which are effective tools for evaluating the degree of eutrophication of lakes, have been discussed. This study also explores the main nutrients (nitrogen and phosphorus) driving transformations in the water body and sediment. Lake Erhai was used as a case study, and it was found to be in a mesotrophic state, with N and P co-limitation before 2006, and only P limitation since 2006. Finally, effective measures to maintain sustainable development in the watershed are proposed, along with a framework for an early warning system adopting the latest technologies (geographic information systems (GIS), remote sensing (RS)) for preventing eutrophication.

Anaerobic-Based Water Resources Recovery Facilities: A Review

The concept of water resources recovery facilities (WRRFs) has gained more attention as a more sustainable substitute for the conventional activated sludge-based wastewater treatment plant (CAS-WWTPs). Anaerobic treatment is advantageous due to its lower energy use, limited sludge production, and higher recovery of the soluble chemical oxygen demand (sCOD) from the received wastewater. In this article, a critical review of the proposed scheme for the anaerobic-based WRRF (An-WRRFs) is presented which is preceded with discussion of CAS-WWTPs limitations. In addition, the evolution of anaerobic treatment from being viewed as wastewater treatment plant (WWTP) to WRRF is demonstrated. It is attained that, even though anaerobic WWTPs (An-WWTPs) have simple and low energy mainline and very limited sludge handling process, its limited removal and recovery capacity have been widely reported, especially in cold weather. On the other hand, in the An-WRRF, higher energy expenditures are employed by using membranes, dissolved methane recovery unit, and primary treatment (extra sludge handling). Yet, energy recovery in the form of biogas is notably increased, as well as the removal efficiency under moderate residence times. The three key challenges to be overcome are the low value of biogas, reducing the energy use associated with membranes, and maintaining high performance in full-scale, especially in cold weather.

Simultaneous wastewater treatment and energy harvesting in microbial fuel cells: an update on the biocatalysts

The development of microbial fuel cell (MFC) makes it possible to generate clean electricity as well as remove pollutants from wastewater. Extensive studies on MFC have focused on structural design and performance optimization, and tremendous advances have been made in these fields. However, there is still a lack of systematic analysis on biocatalysts used in MFCs, especially when it comes to pollutant removal and simultaneous energy recovery. In this review, we aim to provide an update on MFC-based wastewater treatment and energy harvesting research, and analyze various biocatalysts used in MFCs and their underlying mechanisms in pollutant removal as well as energy recovery from wastewater. Lastly, we highlight key future research areas that will further our understanding in improving MFC performance for simultaneous wastewater treatment and sustainable energy harvesting.

Electrochemical treatments of coking wastewater and coal gasification wastewater with Ti/Ti4O7 and Ti/RuO2-IrO2 anodes

Electrochemical treatments of coking wastewater (CW) and coal gasification wastewater (CGW) were conducted with Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes. The performances of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes were investigated by analyzing the effects of five key influencing factors including anodes material, current density, anode-cathode distance, initial pH value, and electrolyte type. The removal efficiencies of total organic carbon (TOC) were analyzed during the processes of CW and CGW electro-oxidation. The removal efficiencies of sixteen polynuclear aromatic hydrocarbons (PAHs) in CW and CGW by electro-oxidation were also explored to further assess the electrochemical activities of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes. The Ti/Ti₄O₇ anode achieved 78.7% COD removal efficiency of CW, 85.8% COD removal efficiency of CGW, 50.3% TOC removal efficiency of CW, and 54.8% TOC removal efficiency of CGW, higher than the Ti/RuO₂-IrO₂ anode (76.7%, 78.1%, 44.8% and 46.8%). The COD removal efficiencies increased with the applied current density, decreased with the increase of the anode-cathode distance, and slightly decreased with the increase of the initial pH value. Meanwhile, the removal efficiencies of sixteen PAHs by the Ti/Ti₄O₇ anode were mostly higher than those by the Ti/RuO₂-IrO₂ anode. By comprehensively analyzing the performances of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes on electrochemical treatments of CW and CGW, this study may supply insights into the application potentials of these anodes to the electrochemical treatments of real wastewater.

Towards the Implementation of Circular Economy in the Wastewater Sector: Challenges and Opportunities

The advancement of science has facilitated increase in the human lifespan, reflected in economic and population growth, which unfortunately leads to increased exploitation of resources. This situation entails not only depletion of resources, but also increases environmental pollution, mainly due to atmospheric emissions, wastewater effluents, and solid wastes. In this scenario, it is compulsory to adopt a paradigm change, as far as the consumption of resources by the population is concerned, to achieve a circular economy. The recovery and reuse of resources are key points, leading to a decrease in the consumption of raw materials, waste reduction, and improvement of energy efficiency. This is the reason why the concept of the circular economy can be applied in any industrial activity, including the wastewater treatment sector. With this in view, this review manuscript focuses on demonstrating the challenges and opportunities in applying a circular economy in the water sector. For example, reclamation and reuse of wastewater to increase water resources, by paying particular attention to the risks for human health, recovery of nutrients, or highly added-value products (e.g., metals and biomolecules among others), valorisation of sewage sludge, and/or recovery of energy. Being aware of this situation, in the European, Union 18 out of 27 countries are already reusing reclaimed wastewater at some level. Moreover, many wastewater treatment plants have reached energy self-sufficiency, producing up to 150% of their energy requirements. Unfortunately, many of the opportunities presented in this work are far from becoming a reality. Still, the first step is always to become aware of the problem and work on optimizing the solution to make it possible.

Reducing energy costs of the wastewater treatment plant by improved scheduling of the periodic influent load

The wastewater treatment plant (WWTP) is a major actor of the water-energy nexus. This study proposes to partially store in available WWTP tank infrastructure the wastewater received during the day-time and schedule the purification of the stored wastewater at night-time. The intended operational approach aims to shift part of the WWTP electrical energy consumption from day-time into the night-time period when the energy has lower prices, also contributing to the balance of the electrical power generation system. This research presents the case study of a Romanian WWTP with Anaerobic-Anoxic-Oxic (A²O) process configuration. A proposed control strategy was implemented and tested on the dynamic calibrated WWTP model, based on the Activated Sludge Model No. 1 and the secondary settler Takács model. Simulations of the proposed scheduling program for the storing and processing time-periods of the influent wastewater, associated to the designed control strategies, demonstrate the reduction of the operational costs and energy savings, while keeping the effluent quality within the requested regulation limits and improving the plant sustainability. In the most favorable case and considering the overall WWTP performance, the operational costs are reduced by 47% and the effluent quality is improved by 25%. To achieve this performance a part of the influent wastewater is stored from 2 p.m. in the available tanks (day-period) while the beginning of the stored wastewater treatment is scheduled at 12 a.m. (night-period). Air flow rate distribution in the nitrification zone and the two water recirculation flow rates are also found by optimization.

Bio-electrochemical power generation in petrochemical wastewater fed microbial fuel cell

The petrochemical wastewater (PCW) from acrylic acid plants possesses a very high chemical oxygen demand (COD) due to the presence of acrylic acid along with other organic acids. The treatment of PCW by conventional aerobic and anaerobic methods is energy intensive. Therefore, the treatment of PCW with concurrent power generation by employing microbial fuel cell (MFC) could be a potential alternative to solve the energy and environmental issues. This study demonstrates the potentiality of PCW from acrylic acid plant with an initial COD of 45,000 mg L^-1 generating maximum power density of 850 mW m^-2 at a current density of 1500 mA m^-2 using acclimatized anaerobic sludge (AS) as biocatalyst. The predominant microbes present in acclimatized AS were identified using Biolog GEN III analysis, which include the electrogenic genera namely Pseudomonas spp. and Bacillus spp. along with methanogenic archea Methanobacterium spp. The mechanism of electron transfer was elucidated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) which clearly demonstrated the natural metabolite-based electron transfer across the electrode/biofilm/solution interface. The abundance of the electron shuttle metabolites was increased with the microbial growth in the bulk solution as well as in the biofilm leading to a high power generation. The COD removal efficiency and the coulombic efficiency (CE) were found to be 40% and 21%, respectively after 11 days of operation using initial COD of 45,000 mg L^-1. The low COD removal efficiency could drastically be increased to 82% when the initial COD of PCW was 5000 mg L^-1 generating a power density of 150 mW m^-2. The current work proves the feasibility of the MFC for the treatment of acrylic acid plant PCW using acclimatized anaerobic sludge (AS) as a biocatalyst.