Synergy of phosphate and hyperthermophilic bio-drying reduces pollution of sludge bio-drying: Reducing ammonia emissions and heavy metal migration risk

Abstract

Hyperthermophilic bio-drying has stronger organic matter degradation and drying ability than the conventional bio-drying. However, ammonia emissions during the hyperthermophilic bio-drying are significantly higher than those during the conventional bio-drying process due to the higher temperature and pH value. Phosphate has been reported to reduce ammonia emissions during composting. Meanwhile, both the degradation of organic matter and the addition of phosphate buffer can promote the formation of EPS. EPS exhibits strong passivation and adsorption properties for heavy metals and organic pollutants, thus positively impacting the control of pollution in bio-drying products. Furthermore, the formation of EPS and the risk of the migration of heavy metals during hyperthermophilic bio-drying have not been reported. According to the results, compared to conventional bio-drying, the hyperthermophilic bio-drying significantly increased the yield of EPS and generated more active groups, reducing the migration risk of Cu, Zn, Cr, Pb, Cd, As, and Ni. The comprehensive potential ecological risk was reduced by 29.71%, which was higher than the reduction achieved by conventional bio-drying (13.81%). The addition of phosphate significantly reduced the ammonia emissions from the hyperthermophilic bio-drying and retained more nitrogen. Meanwhile, it promoted the formation of EPS and the enrichment of active groups, further reducing the migration risk of heavy metals. Moreover, the addition of phosphate buffer further reduced the comprehensive potential ecological risk of the products obtained from.