Recycling

Biography

Biography: Hyokwan Bae

Abstract

Forward osmosis (FO) and biological nitrification processes were integrated in this study. High strength ammonia wastewater of 2500 mg-N/L was partially nitrified at an ammonia conversion rate of 1.34 ± 0.25 kg-N/m³-day under the limitation of an acidification buffer, i.e., HCO₃^–-C/NH₄⁺-N = 1, as a control factor. To mitigate the membrane fouling, direct contact between the biomass and cellulose triacetate FO membrane was avoided by employing PVA/alginate-immobilized nitrifiers in the bioreactor. The simultaneous FO process concentrated the wastewater at concentration factors (CFs) of up to 2.34 during the partial nitritation (PN) reaction. As a result, the concentration of total dissolved solids (TDS) ranged from 13.6 g/L to 35.7 g/L. It was found that salinity higher than 17 g-TDS/L inhibited the activity of the nitrite-oxidizing bacteria, but not the ammonia-oxidizing bacteria. Then, the nitrogen content of wastewater was further concentrated using direct contact membrane distillation (DCMD). The ratio of transferred ammonia to water (i.e., specific ammonia transfer: SAT) was controlled by operational conditions of membrane materials, pH and temperature. It was identified that free ammonia (FA) concentration has a critical role on SAT values under different total ammoniacal nitrogen concentration and pH. Thus, the acidification pretreatment was essential to minimize the FA concentration in the feed before operating the DCMD system. Taken together, membrane-based dewatering processes were effective to reduce the water contents in the wastewater and the remained nitrogen contents can be utilized as a concentrated fertilizer.