Electricity generation from the treatment of wastewater with a hybrid up-flow microbial fuel cell

Paradigm shift in Nutrient-Energy-Water centered sustainable wastewater treatment system through synergy of bioelectrochemical system and anaerobic digestion

With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost.

Operation adjustments of an electrochemically coupled system for total nitrogen removal and the associated mechanism

A coupled system consisting of sequencing batch reactor and microbial fuel cell (SBR-MFC) was designed to buffer pH drift and purify wastewater. The addition of nitrifying sludge and the adjustment of hydraulic retention time (HRT) were performed to achieve better removal of total nitrogen (TN). When anaerobic/aerobic/anoxic phases in one cycle were 6/4/2 h, the removal efficiency of ammonium was 99.0 ± 1.3%, whereas denitrification was insufficient and the overall removal efficiency of TN was only 29.1 ± 5.8%. When the phases were adjusted to 6/2/4 h, the removal efficiencies of ammonium were 100.0 ± 0.0% in both closed and open circuits, and the overall removal efficiencies of TN were 91.4 ± 0.2% and 71.7 ± 4.2%, respectively, improved by 20% in MFC mode; the maximum voltage (200 Ω) maintained at 0.1 V. Ammonium-oxidizing bacteria (AOB) and Nitrite-oxidizing bacteria (NOB) in the sludge carried out nitrification. The main denitrification pathways in anoxic phase involved polyhydroxyalkanoate (PHA) denitrification by denitrifying glycogen accumulating organisms (GAOs) and electrochemical denitrification by electrochemical active bacteria (EAB). Few polyphosphate accumulating organisms (PAOs) were present, which accounted for poor P removal.

Control of power sourced from a microbial fuel cell reduces its start-up time and increases bioelectrochemical activity

Microbial fuel cell (MFC) performance depends on the selective development of an electrogenic biofilm at an electrode. Controlled biofilm enrichment may reduce start-up time and improve subsequent power performance. The anode potential is known to affect start-up and subsequent performance in electrogenic bio-catalytic consortia. Control strategies varying electrical load through gradient based maximum power point tracking (MPPT) and transient poised anode potential followed by MPPT are compared to static ohmic loading. Three replicate H-type MFCs were used to investigate start-up strategies: (1) application of an MPPT algorithm preceded by poised-potential at the anode (+0.645 V vs Ag/AgCl); (2) MFC connected to MPPT-only; (3) static external load of 1 kΩ and 500 Ω. Active control showed a significant reduction in start-up time from 42 to 22 days, along with 3.5-fold increase in biocatalytic activity after start-up. Such active control may improve applicability by accelerating start-up and enhancing MFC power and bio-catalytic performance.

Submersible microbial fuel cell sensor for monitoring microbial activity and BOD in groundwater: focusing on impact of anodic biofilm on sensor applicability

A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm-colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm-colonized anode showed linear relationship with BOD content, to up to 250 mg/L (∼233 ± 1 mA/m(2)), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine-triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m(2)) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol-ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers.

Integration of a microbial fuel cell with activated sludge process for energy-saving wastewater treatment: taking a sequencing batch reactor as an example

In the research and application of microbial fuel cell (MFC), how to incorporate MFCs into current wastewater infrastructure is an importance issue. Here, we report a novel strategy of integrating an MFC into a sequencing batch reactor (SBR) to test the energy production and the chemical oxygen demand (COD) removal. The membrane-less biocathode MFC is integrated with the SBR to recover energy from the aeration in the form of electricity and thus reduce the SBR operation costs. In a lab-scale integrated SBR-MFC system, the maximum power production of the MFC was 2.34 W/m(3) for one typical cycle and the current density reached up to 14 A/m(3) . As a result, the MFC contributed to the 18.7% COD consumption of the integrated system and also recovered energy from the aeration tank with a volume fraction of only 12% of the SBR. Our strategy provides a feasible and effective energy-saving and -recovering solution to upgrade the existing activated sludge processes.