Coupling mixotrophic denitrification and electroactive anodic nitrification by nitrate addition for promoting current generation and nitrogen removal

Optimized feeding schemes of heterotrophic anodic denitrification coupled with cathodic phosphate recovery from wastewater using a microbial fuel cell

Enhanced water quality standards and increasing resource scarcity have prompted extensive research into low-cost nitrogen removal and phosphate recovery from wastewater. Microbial fuel cells (MFCs) offer a viable solution by simultaneously removing nitrogen, recovering phosphorus, and generating electrical energy. This study employed MFCs to achieve simultaneous nitrogen removal and phosphorus recovery, investigating the impact of different feeding schemes. The experimental results indicated that replacing the entire anode chamber solution and recycling the anode effluent to the cathode chamber effectively prevented the accumulation of nitrifying bacteria while achieving the highest pollutant removal performance. Under closed circuit conditions, the system consistently maintained low nitrite concentrations, achieving an average nitrate removal efficiency of 68.09 ± 1.86 % and phosphate recovery efficiency of 83.46 ± 5.30 %. Furthermore, this feeding scheme facilitated microbial growth and reproduction while also improving operational convenience. The study utilized metagenomics and other technologies to comprehensively analyze the system's operation mechanism and reasons for its excellent performance.

Achieving synchronous nitrogen and phosphorus removal by aerobic enrichment of electrotrophic/heterotrophic bacteria and denitrifying polyphosphate-accumulating organisms in repeatedly oxygen-rich microbial fuel cells

Realizing the enrichment of functional bacteria in microbial fuel cells (MFCs) for wastewater treatment holds substantial research significance. This study explored a novel method of repeatedly oxygen-rich anode environment to enrich electrotrophic/heterotrophic bacteria (EHB) and denitrifying polyphosphate-accumulating organisms (DPAOs) in membrane-less single-chamber air-cathode (AC) MFCs to treat household wastewater. Repeated accumulation of higher dissolved oxygen (DO) was conducive to enhancing the growth of EHB and DPAOs. The systems achieved the maximum removal of 99% of ammonium, 78% of total inorganic nitrogen and 55% of total phosphorus. Repeated oxygen-rich conditions favored the selection of nitrogen-oxidizing bacteria on both electrodes, such as unclassified_f_Xanthomonadaceae, unclassified_p_Bacteroidota, Nitrosomonas and Nitrospira, thereby increasing nitrate availability for DPAOs like Candidatus Contendobacter, unclassified_c_Actinomycetia as well as other denitrifiers such as Anaerolineales, unclassified_p_Chloroflexi, unclassified_o_Rhodospirillales. The genes nxrAB, narGH and nasC, associated with nitrification and denitrification, and the genes gcd, phoD, ugpQ, glpQ, involved in phosphate metabolism, were up-regulated in presence of repeated DO accumulation, thereby enhancing pollutants removal. This study presents a novel approach for the synchronous removal of nitrogen and phosphorus from domestic wastewater through the enrichment of functional bacteria in the repeatedly oxygen-rich ACMFCs.

Revealing the performance of aerotolerant anodes for electroactive nitrification/denitrification and current production under coexistence of oxygen and nitrate conditions

The coexistence of oxygen and/or nitrate at anode usually affects the biofilm activities of traditional anaerobic anode, thereby deteriorating wastewater treatment performance of microbial fuel cells (MFCs). Improving the aerotolerant responses of anode biofilms is a challenge for field application. In this study, we report that using the electroactive nitrifying/denitrifying inoculum and air-cathode expansion could fabricate the aerotolerant anode biofilms (AAB) under affordable nitrate stress (90 ± 5 mg/L). The highest average removal efficiencies were 99% for chemical oxygen demand (COD), NH4+-N and total nitrogen. The highest average current output of 0.69 mA and power density of 290 mW/m2 were obtained. The average current was confirmed to be reduced 10%-78% but the power density remained almost stable except the quart-air-cathodes MFC by increasing dissolved oxygen concentration with expansion of the air-cathode area. The higher oxygen concentration also contributed to oxidation of ammonium through electroactive autotrophic nitrification. The facultative anaerobic bacteria including Thauera, Microsillaceae, Shinella, Blastocatellaceae, Rhodobacter, Comamonadaceae, Caldilineaceae were enriched, which forms the AAB to remove nitrogen and produce current. Therefore, an easy-to-use method to fabricate AAB is evaluated to realize practical applications of MFCs in wastewater treatment.

Deciphering three-dimensional bioanode configuration for augmenting power generation and nitrogen removal in air-cathode microbial fuel cells

In this study, the engineering-oriented three-dimensional (3D) bioanode concept was applied, demonstrating that spiral-stairs-like/rolled carbon felt (SCF/RCF) configurations achieved good performances in air-cathode microbial fuel cells (ACMFCs). With the 3D anodes, ACMFCs generated significantly higher power densities of 1535 mW/m3 (SCF) and 1800 mW/m3 (RCF), compared with that of a traditional flat carbon felt anode (FCF, 315 mW/m3). The coulombic efficiency of 15.39 % at SCF anode and 14.34 % at RCF anode also is higher than the 7.93 % at FCF anode. The 3D anode ACMFCs exhibited favorable removal of chemical oxygen demand (96 % of SCF and RCF) and total nitrogen (97 % of SCF, 99 % of RCF). Further results show that three-dimensional anode structures could enrich more electrode surface biomass and diversify the biofilm microbial communities for promoting bioelectroactivity, denitrification, and nitrification. These results demonstrate that three-dimensional anodes with active biofilm is a promising strategy for creating scalable MFCs-based wastewater treatment system.