Bioelectrochemical anaerobic sewage treatment technology for Arctic communities

Potential application of bioelectrochemical systems in cold environments

Globally, more than half of the world's regions and populations inhabit psychrophilic and seasonally cold environments. Lower temperatures can inhibit the metabolic activity of microorganisms, thereby restricting the application of traditional biological treatment technologies. Bioelectrochemical systems (BES), which combine electrochemistry and biocatalysis, can enhance the resistance of microorganisms to unfavorable environments through electrical stimulation, thus showing promising applications in low-temperature environments. In this review, we focus on the potential application of BES in such environments, given the relatively limited research in this area due to temperature limitations. We select microbial fuel cells (MFC), microbial electrolytic cells (MEC), and microbial electrosynthesis cells (MES) as the objects of analysis and compare their operational mechanisms and application fields. MFC mainly utilizes the redox potential of microorganisms during substance metabolism to generate electricity, while MEC and MES promote the degradation of refractory substances by augmenting the electrode potential with an applied voltage. Subsequently, we summarize and discuss the application of these three types of BES in low-temperature environments. MFC can be employed for environmental remediation as well as for biosensors to monitor environmental quality, while MEC and MES are primarily intended for hydrogen and methane production. Additionally, we explore the influencing factors for the application of BES in low-temperature environments, including operational parameters, electrodes and membranes, external voltage, oxygen intervention, and reaction devices. Finally, the technical, economic, and environmental feasibility analyses reveal that the application of BES in low-temperature environments has great potential for development.

Operational parameter prediction of electrocoagulation system in a rural decentralized water treatment plant by interpretable machine learning model

Electrocoagulation (EC) is a promising alternative for decentralized drinking water treatment in rural areas as a chemical-free technology. However, seasonal fluctuations of water quality in influent remain a significant challenge for rural decentralized water supply, which was a potential threat to water safety. The frequent operation was required to ensure the effluent water quality by the experienced technicians, who were in shortage in rural areas. If the operational parameters prediction model based on water quality could be established, it might reduce the dependence on technicians. Therefore, an artificial neural network (ANN) model combined with genetic algorithm (GA) was used to establish a prediction model for unattended intelligent operation. Data on water quality and operational parameters were collected from a practical EC system in a decentralized water treatment plant. Seven water quality parameters (e.g., turbidity, temperature, pH and conductivity) were selected as input variables and the operational current was employed as the output. A non-linear relationship between water quality parameters and the operational current was verified by correlation analysis and principal component analysis (PCA). The mean squared error (MSE) and coefficient of determination (R²) were used as evaluation indexes to optimize the structure of the GA-ANN model. Influent turbidity was identified to be crucial in the GA-ANN model by model interpretation using sensitivity analysis and scenario analysis. The Garson weight of turbidity in the seven input variables achieved 45.4%. The predictive accuracy of the GA-ANN model sharply declined from 90% to 67.1% when influent turbidity data were absent. In addition, it was estimated that energy consumption savings of the GA-ANN method declined by 14.2% in comparison with the gradient control method. This study verifies the feasibility and stability of machine learning strategy for unattended operation in the rural decentralized water treatment plant.

Psychrophilic treatment of municipal wastewater with a combined UASB/ASD system, and perspectives for improving urban WWTP sustainability

According to new paradigms of urban wastewater management, energy savings and resources and energy recovery from sewage will assume an ever-increasing importance. Anaerobic processes, aside from being more energy efficient than conventional aerobic ones, are particularly suited to recover embedded organic energy, improving the overall energy balance of treatment processes, however, their performance is limited by low temperatures and slower kinetics. In this study, a pilot Upflow Anaerobic Sludge Blanket (UASB) reactor was operated to treat municipal wastewater at low temperature regime (16.5-18.5 °C) for 22 weeks, both as standalone process and combined with a sidestream anaerobic sludge digester. Process performance highlighted good system robustness, as proved by stable pH and volatile fatty acid/total alkaline buffer capacity ratio, even though observed methane yield was low. Observed COD and TSS removal efficiencies were in the ranges of 60-69% and 63-73%, respectively. Methane production ranged between 0.106 and 0.132 Nm³_CH4/kg_CODrem. An economic assessment was carried out to evaluate the feasibility and benefits of implementing UASB pre-treatment of municipal wastewater in existing conventional facilities (activated sludge and anaerobic sludge digestion), showing that significant energy demand reduction could be achieved for both biological secondary treatment and sludge management, leading to considerable operational economies, and possible positive economic returns within a short pay-back period (3-4 yrs).

Selenite and selenate removal in a permeable flow-through bioelectrochemical barrier

This study demonstrated the removal of selenite and selenate in flow-through permeable bioelectrochemical barriers (microbial electrolysis cells, MECs). The bioelectrochemical barriers consisted of cathode and anode electrode compartments filled with granular carbon or metallurgical coke. A voltage of 1.4 V was applied to the electrodes to enable the bioelectrochemical removal of selenium species. For comparison, a similarly designed permeable anaerobic biobarrier filled with granular carbon was operated without voltage. All biobarrier setups were fed with water containing up to 5,000 µg L^-1 of either selenite or selenate and 70 mg L^-1 of acetate as a source of organic carbon. Significant removal of selenite and selenate was observed in MEC experimental setups, reaching 99.5-99.8% over the course of the experiment, while in the anaerobic biobarrier the removal efficiency did not exceed 88%. By simultaneously operating several setups and changing operating parameters (selenium species, influent Se and acetate concentrations, etc.) we demonstrated enhanced removal of Se species under bioelectrochemical conditions.

Synthetic Organic Compounds From Paper Industry Wastes: Integrated Biotechnological Interventions

Synthetic organic compounds (SOCs) are reported as xenobiotics compounds contaminating the environment from various sources including waste from the pulp and paper industries: Since the demand and production of paper is growing increasingly, the release of paper and pulp industrial waste consisting of SOCs is also increasing the SOCs' pollution in natural reservoirs to create environmental pollution. In pulp and paper industries, the SOCs viz. phenol compounds, furans, dioxins, benzene compounds etc. are produced during bleaching phase of pulp treatment and they are principal components of industrial discharge. This review gives an overview of various biotechnological interventions for paper mill waste effluent management and elimination strategies. Further, the review also gives the insight overview of various ways to restrict SOCs release in natural reservoirs, its limitations and integrated approaches for SOCs bioremediation using engineered microbial approaches. Furthermore, it gives a brief overview of the sustainable remediation of SOCs via genetically modified biological agents, including bioengineering system innovation at industry level before waste discharge.

Electrode passivation, faradaic efficiency, and performance enhancement strategies in electrocoagulation-a review

Treating water and wastewater is energy-intensive, and traditional methods that require large amounts of chemicals are often still used. Electrocoagulation (EC), an electrochemical treatment technology, has been proposed as a more economically and environmentally sustainable alternative. In EC, sacrificial metal electrodes are used to produce coagulant in-situ, which offers many benefits over conventional chemical coagulation. However, material precipitation on the electrodes during long term operation induces a passivating effect that decreases treatment performance and increases power requirements. Overcoming this problem is considered to be the greatest challenge facing the development of EC. In this critical review, the studies that have examined the nature of electrode passivation, and its effect on treatment performance are considered. A fundamental approach is used to examine the association between passivation and faradaic efficiency, a surrogate for EC performance. In addition, the strategies that have been proposed to remove or avoid passivation are reviewed, including aggressive ion addition, AC current operation, polarity reversal, ultrasonication, and mechanical cleaning of the electrodes. It is concluded that the success of implementing each method is dependent on critical operating parameters, and careful consideration should be taken when designing an EC system based on the phenomena discussed in this article. In conclusion, this review provides insight into passivation mechanisms, delivers guidelines for sustaining high treatment performance, and offers an outlook for the future development of EC.

Real-time monitoring of a microbial electrolysis cell using an electrical equivalent circuit model

Efforts in developing microbial electrolysis cells (MECs) resulted in several novel approaches for wastewater treatment and bioelectrosynthesis. Practical implementation of these approaches necessitates the development of an adequate system for real-time (on-line) monitoring and diagnostics of MEC performance. This study describes a simple MEC equivalent electrical circuit (EEC) model and a parameter estimation procedure, which enable such real-time monitoring. The proposed approach involves MEC voltage and current measurements during its operation with periodic power supply connection/disconnection (on/off operation) followed by parameter estimation using either numerical or analytical solution of the model. The proposed monitoring approach is demonstrated using a membraneless MEC with flow-through porous electrodes. Laboratory tests showed that changes in the influent carbon source concentration and composition significantly affect MEC total internal resistance and capacitance estimated by the model. Fast response of these EEC model parameters to changes in operating conditions enables the development of a model-based approach for real-time monitoring and fault detection.

Long-term performance of a microbial electrolysis cell operated with periodic disconnection of power supply

This study describes a new approach for achieving stable long-term performance and maximizing removal of chemical oxygen demand (COD) in a Microbial Electrolysis Cell (MEC) by periodic disconnection of the MEC power supply.