Sustainable ammonia recovery from anaerobic digestion effluent through pretreating the feed by biomass ash

Abstract

Ammonia recovery from anaerobic digestion (AD) effluent by vacuum membrane distillation (VMD) is a sustainable and low-carbon footprint strategy for nitrogen fertilizer production and waste treatment. However, due to the good buffering performance of AD effluent, lots of alkali chemicals are consumed to adjust the pH value, thereby increasing the treatment cost. To reduce the consumption of alkali chemicals, biomass ash (BA) is proposed as the alternative to replace the alkali chemical for pretreating the AD effluent before ammonia recovery in this study. Compared with the case using NaOH for pH adjustment, the ammonia separation factor increases by 40 % for BA addition case. Meanwhile, the 30-h VMD experiment for AD effluent treatment is conducted to testify to the stability. Additionally, the high germination index (GI) value (0.84) illustrates the potential of ammonia-removed AD effluent in agricultural applications. Furthermore, the greenhouse emission of ammonia recovery from AD effluent pretreated with BA is only 2.06 kg-CO2 eq/kg, which decreases by 51 % compared with that of the Haber-Bosch process. Finally, BA addition adopted for AD effluent pretreatment has economic superiority to NaOH addition. Inferably, using BA to pretreat the AD effluent can be acted as a high-efficacy and sustainable candidate strategy for ammonia recovery.