Development of a Combined Aerobic–Anoxic and Methane Oxidation Bioreactor System Using Mixed Methanotrophs and Biogas for Wastewater Denitrification

Abstract

We developed a lab-scale aerobic–methane oxidation bioreactor (MOB)–anoxic system, combining a MOB and the aerobic–anoxic denitrification process, and evaluated its potential for advanced nitrogen treatment in wastewater treatment plants (WWTPs). The MOB used biogas generated from a WWTP and secondary-treated wastewater to support mixed methanotroph cultures, which mediated the simultaneous direct denitrification by methanotrophs and methanol production necessary for denitrifying bacteria in the anoxic chamber for denitrification. Compared to the aerobic–anoxic process, the aerobic–MOB–anoxic system with an influent concentration of 4.8 L·day−1 showed a marked increase in the reduction efficiency for total nitrogen (41.9% vs. 85.9%) and PO4−3-P (41.1% vs. 69.5%). However, the integrated actions of high nitrogen and phosphorus consumption are required for methanotroph growth, as well as the production and supply of methanol as a carbon source for denitrification and methane monooxygenase-mediated oxidation of NH3 into N2O by methanotrophs. After three months of continuous operation using actual wastewater, the total nitrogen removal rate was 76.3%, equivalent to the rate observed in a tertiary-advanced WWTP, while the total phosphorus removal rate reached 83.7%.

Simultaneous Denitrification and Bio-Methanol Production for Sustainable Operation of Biogas Plants

“…Furthermore, the nitrogen and phosphorus contents in the methanotroph sludge showed that the TN content in the activated sludge of the wastewater treatment plant was 5.34% on average, but was 8.53% in the methane-oxidizing bacteria sludge. This result suggests that methanotroph growth has a high nitrogen demand [35].…”

“…Furthermore, in the metabolism process of methanotrophs, ammonia was oxidized to N 2 O through NH 3 OH in the same path as that of the ammonia oxidation of ammonia-oxidizing bacteria (AOB) by the methane monooxygenase (MMO), which is a methane-oxidizing enzyme [34,35]. Consequently, the tendency of removing high concentration ammonium and some nitrates in the digested FW leachate by using methanotrophs and biogas was verified.…”

Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter

“…Results of this study illustrated the critical role of pH in CO 2 capture. In future studies on slag filter-upgraded septic tanks, the analysis could be extended to methane release, an important greenhouse gas [29], as methanogenesis could be affected by the pH rise induced by the slag filter, considering an optimum anaerobic digestion pH range of 6.5 to 7.5 [30]. Methanogenesis inhibition by a high pH was achieved in microbial electrolysis cells [31].…”

Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter

“…Results of this study illustrated the critical role of pH in CO2 capture. In future studies on slag filter upgraded septic tanks, the analysis could be extended to methane release, an important greenhouse gas [27], as methanogenesis could be affected by the pH rise induced by the slag filter, considering an optimum anaerobic digestion pH range of 6.5 to 7.5 [28]. As methane produced from small septic tanks is released to the atmosphere, the use of slag filters could reduce greenhouse gas emission by reducing methanogenesis in the septic tank.…”