Membrane-aerated biofilm reactor enabling simultaneous removal of ammonium and sulfide from a simulated anaerobic secondary effluent

Anaerobic secondary treatment is promising for energy-positive operation but creates ammonium- and sulfide-rich effluent. Here, we investigated a lab-scale membrane aerated biofilm reactor (MABR) incorporating silicon tubes as gas permeable membranes for simultaneous removal of ammonium and sulfide from synthetic mainstream anaerobic secondary effluent. At an ammonium loading rate of 2.06 g NH4+-N/m(2)/d and sulfide loading rate of 0.44 g S/m(2)/d, the MABR removed approximately 80 % of influent ammonium and >99 % of influent sulfide. A decrease in the ammonium loading rate to 1.18 g NH4+-N/m(2)/d and a stepwise increase in the sulfide loading rate to 0.88 and 1.77 g S/m(2)/d resulted in an average total nitrogen removal efficiency of 77 %. Sulfide removal efficiency consistently remained >99 %, but sulfate recovery had a wide variation due to elemental sulfur accumulation within biomass. Community analysis from 16s rRNA gene sequencing and mass balance data suggested that ammonium was primarily oxidized to nitrate by Nitrospira and was subsequently removed by denitrification with sulfide (Thiobacillus) or heterotrophically (Rhodocylaceae). We conclude that silicone tubes could be used gas permeable membranes to enable simultaneous ammonia and sulfide removal in anaerobic secondary effluent. More research is needed to maintain optimal biofilm thickness and control elemental sulfur accumulation in the reactor.