Four integrated CW-MFC reactors were employed namely R1 (single anode with plants), R′1 (multi-anode with plants), R2 (single anode unplanted), and R′2 (multi-anode unplanted) for real domestic wastewater treatment. Reactors R1, R′1, R2, and R′2 rendered 95.9 %, 97.4 %, 88.1 %, and 91.6 % COD removal. Reactor R′1 showed the highest FC inactivation (log 4.23 ± 0.20) in closed circuit, but the efficiency dropped to log 3.49 ± 0.15 in open circuit operation. Interestingly, not much differences were observed in E. coli inactivation between single and multi-anode reactors in both open and closed-circuit operations. Typha contributed significantly towards increased FC and E. coli removal and power density by increasing the cathode ORP. The application of multi-anode assembly resulted in higher operating voltages as a cumulative of individual anodes compared to single anode reactors. The maximum coulombic efficiency was obtained in R′1 (4.64 %). Inter-electrode gap and organic availability at the anode were the governing factors for the voltage and power density.

In the current study, domestic wastewater was treated in three identical vertical up-flow reactors; R1 (constructed wetland), R2 (CW-MFC), and R3 (unplanted CW-MFC) under different HRTs of 36 h (Phase 1), 24 h (Phase 2), and 18h (Phase 3). Periodic reduction of HRT from Phase 1 to Phase 3 resulted in deteriorated organics and fecal coliform removal by the reactors. R2 showed higher pollutant removal and voltage generation in every phase of the study compared to R1 and R3. R2 exerted 93%, 87%, and 57% mean COD removal during Phase 1, Phase 2, and Phase 3; with maximum open circuit voltage generated as 925 mV, 695 mV, and 429 mV respectively. Linear regression analysis showed that operating voltage and power density had significant effects on the variance of effluent fecal coliform concentration. The regression analysis also revealed that 36 h–24 h HRT was critical where power density influenced the pathogen inactivation considerably. Multiple batch studies revealed the main role of reactor media and plant roots was to support the attached microbial growth for biodegradation of the organics. Radial oxygen loss did not affect the anaerobic environment at the anode after 800 days of reactor operation.

The study is focused on the removal of fecal coliforms from low-strength domestic wastewater using a vertical up-flow microbial fuel cell (MFC) reactor. Raw domestic wastewater was collected from the grit chamber of the sewage treatment plant, which is located inside the campus of the Indian Institute of Technology Guwahati. The MFC reactor was cylindrical with an effective volume of 4.5 L. Stainless steel mesh with graphite rod was used as the anode and graphite rod was used as the cathode in the MFC. The mean COD and fecal coliform of the raw wastewater during the study period were observed to be 177.8 mg/L and log 6.94 per 100 mL respectively. The lab scale MFC was operated with a retention time of 36 h and found to be efficient in COD and coliform removal. Mean COD removal in MFC was 91.34% and mean effluent fecal coliform was log 3.49 units. The MFC was operated in continuous vertical up-flow mode and stable operating voltage was obtained continuously under varying external resistances. Biomass activity study showed higher substrate utilization by reactor microbial population in summer compared to that of winter. Seasonal temperature variation was found to be a significant influencing factor for the removal of total and fecal coliforms inside the MFC reactor. Throughout the study, the first-order inactivation rate for fecal coliform in the MFC reactor was calculated and the seasonal effect on the variation of the rate coefficient was also monitored.

The current study is focused on understanding the operational mechanism of an integrated constructed wetland-microbial fuel cell (CW-MFC) reactor emphasizing fecal coliform (FC) removal. Few studies are available in the literature investigating the inherent mechanisms of pathogen inactivation in a CW-MFC system. Raw domestic wastewater was treated in three vertical reactors, one planted constructed wetland (R1), one planted CW-MFC (R2), and one unplanted CW-MFC (R3). Spatial analysis of treated effluents showed a considerable amount of organics and fecal coliform removal at the vicinity of the anode in R2. Assessment of the microbial population inside all the reactors revealed that EABs (Firmicutes, Bacteroidetes, and Actinobacteria) were more abundant in R2 compared to R1 and R3. During the activity study, biomass obtained from R2 showed a maximum substrate utilization rate of 1.27 mg COD mgVSS−1 d−1. Kinetic batch studies were carried out for FC removal in all the reactors, and the maximum first order FC removal rate was obtained at the anode of R2 as 2.13 d−1 when operated in closed circuit mode. This value was much higher than the natural die-off rate of FCs in raw wastewater which was 1.16 d−1. Simultaneous bioelectricity monitoring inferred that voltage generation can be correlated to faster FC inactivation, which was probably due to EABs outcompeting other exogenous microbes in a preferable anaerobic environment with the presence of an anode. Reactor R2 was found to be functioning as a symbiotic bio-electrochemical mesocosm.

Wastewater treatment with integrated constructed wetland–microbial fuel cell technology has attracted serious attention from researchers. The economic sustainability of any potential technology is the key to its commercialization from laboratory to field application, which is fulfilled through an exhaustive assessment of the related costs and benefits. This article presents a comparative cost-benefit analysis of three reactors: constructed wetland (R1), integrated CW-MFC (R2), and unplanted CW-MFC (R3) for domestic wastewater treatment and economic sustainability assessment. The study was conducted with 36 h and 24 h hydraulic retention times of the reactors and the respective cost-benefit ratio was determined. Results revealed that R2 was the most sustainable option with maximum economic benefits during Phase 1 and Phase 2 without effluent disinfection. With effluent disinfection in place, R1 emerged with the best cost-benefit ratio due to less investment cost and low revenue from electricity production in R2 and R3. Sensitivity analysis with net investment cost, power density, electrode area, effective reactor volume, and hydraulic retention time; showed power density was the most influential parameter affecting the cost-benefit ratio. Revenue from wastewater treatment was found essential for economic sustainability which shows the importance of producing high-quality effluent and greater power density to make CW-MFC technology economically attractive.

Wastewater treatment with energy recovery is a major concern in environmental engineering research nowadays. The current study focuses on the removal of organics and fecal coliforms which are primary source of pollution in domestic wastewater, using three identical reactors. One vertical planted constructed wetland (R1), one planted CW-MFC (R2), and one unplanted CW-MFC (R3). Bioenergy production in R2 and R3 was also monitored. In terms of COD removal, R2 reactor achieved 93.13 ± 4.83% efficiency, and R1 and R3 achieved 87.21 ± 4.56% and 86.31 ± 4.37% efficiencies, respectively. BOD removal efficiency in R1, R2, and R3 reactors were found to be similar around 91.79 ± 3.58% to 92.7 ± 3.3%. The total coliform removal was better in R1 (log 2.95) than in R2 (log 2.93). However, the fecal coliform removal in R2 was much higher (log 3.51) compared to R1 (log 2.94). Coliform and organic removal deteriorated during winter time, though electricity generation remained unaffected. The maximum open-circuit voltage in R2 was 886 mV and in the R3 was 487 mV during the complete study. Plants played a positive role in enhancing the electrical performance of R2 compared to unplanted R3 by increasing the redox potential. Presence of dissolved oxygen in the range of 1.97–2.1 mg/L was also detected near the rhizosphere of the planted reactors. Combined role of plants and electrodes was crucial for COD removal and anaerobic condition near anode with low ORP governed the pathogen removal from domestic wastewater.

Endocrine disrupting pollutants (EDPs) are a group of exogenous chemicals affecting the endocrine function causing adverse health effects such as pubertal changes, neurotoxicity, malfunctioning of the human reproductive system, and carcinoma. EDPs are comprised of pharmaceuticals, personal care products (PCP), antibiotics, surfactants, etc. generally found as a micropollutant in raw and treated effluents from municipal wastewater treatment plants. Apart from photocatalytic degradation, bioremediation techniques like algal bioreactors, constructed wetlands, and aerobic granular sludge are reported to achieve nearly 80% removal efficiency while treating pharmaceuticals, surfactants, or other emerging pollutant containing wastewater loaded with EDPs in approximately 1 ng/L–500 µg/L of range. Since EDPs possess recalcitrant groups like polychlorinated biphenyls or phthalates and identified as trace contaminants in municipal wastewater, slow biodegradation and the requirement of sophisticated detection and remediation methods are the major challenges toward successful bioremediation. This scenario justifies the need of developing efficient, integrated, economic biological treatment strategies along with modification of existing biotechnologies to treat EDPs in municipal wastewater. This chapter provides an insight into the occurrence, classification, hormonal and toxicological characteristics of EDPs along with emerging bioremediation techniques, challenges, and future research prospects.

In the present study, the performance of a circular flow constructed wetland (CFCW) system was assessed for organics and total phosphorus removal from fertilizer plant effluent. The CFCW system has five media compartments containing gravel, slag iron, and a mixture of sand and zeolite as the media substrates. Synthetic fertilizer wastewater having initial COD 520.98 ± 8.27 mg/L, was fed to the wetland, maintaining hydraulic loading rate of 6.945 L/m2-h. Typha angustifolia was used as the wetland vegetation. The Phase 1 of the study included three cycles, with influent phosphorus concentrations 10, 20, and 30 mg/L, respectively without step feeding and effluent recirculation. The Phase 2 of the study included two cycles with influent phosphorus concentrations of 20 and 30 mg/L, and application of step feeding and effluent recirculation strategies. The average phosphorus removal efficiencies of the system in three cycles of Phase 1 were 85.16 %, 88 %, and 81.95 %, respectively, along with average COD removal of 87.48 %, 87.65 %, and 86.84 %, respectively. The average phosphorus removal efficiencies of the system in two cycles of Phase 2 were 89.01 % and 90.22 % respectively, along with average COD removal of 91.6 % and 91.23 %, respectively. The step feeding and effluent recirculation strategies have shown satisfactory improvement in organics and total phosphorus removal performance of the CFCW system. However, future long-term studies are recommended involving an unplanted control system, step feeding and effluent recirculation in varying compartments, and varying combination of media substrates for improving the design and performance of the CFCW systems.