Enhanced Sewage Sludge Composting With Addition Of Chemical Agents

Composting is a biochemical process converting biodegradable organic matters of sewage sludge into relatively stable biosolids.It is an important technology to realize the harmless and stabilization of sludge,which has been regard as a popular method to utilize sludge.Since the slow composting rate and nitrogen loss of sewage sludge composting,in this study,KH₂PO₄-K₂HPO₄ buffer solution was added to enhance composting,and buffer solution was combined with struvite precipitation to reduce nitrogen loss.The main results are as follows:（1）The effects of the dosage of KH₂PO₄-K₂HPO₄ buffer solution on composting were studied.The compost,where 0.1 mol·kg^-1 DM,KH₂PO₄and 0.1 mol·kg^-1 DM,K₂HPO₄ were added,shown the best results.The composting lasted for 17days at high temperature stage and reached sanitary requirements.Its organic matter degradation was up to 36.3%,which increased by 15.6%compared to that of control.pH value was well controlled between 7.5-8.5,which ensured microbial activities.Besides,NH₃-N loss of the compost was reduced by 46.7%compared to that of control.（2）The effects of KH₂PO₄-K₂HPO₄ buffer solution and MgSO₄ on composting were studied.The compost,where 0.2 mol·kg^-1 DM,MgSO₄,0.1 mol·kg^-1 DM,KH₂PO₄ and 0.1 mol·kg^-1 DM,K₂HPO₄ were added,shown the best results.Its organic matter degradation was up to 36.8%,which increased by 23.1%compared to that of control.which ensured microbial activities.The addition of KH₂PO₄-K₂HPO₄ buffer solution could effectively maintain pH in neutral or alkaline condition,which ensured the optimum pH for microbial activities as well as struvite formation.Moreover,NH₃-N loss of the compost was reduced by 62.5%compared to that of control,and total nitrogen loss was reduced by 72.7%compared to that of control.（3）The best proportion of Mg and P salts and the best addition time of buffer solution were analyzed.The compost,where 0.13 mol·kg^-1 DM,MgSO₄ was added on day 0 and 0.1 mol·kg^-1 DM,KH₂PO₄ and 0.1mol·kg^-1 DM,K₂HPO₄ were added on day 5,shown the best results.The composting lasted for 17days at high temperature stage and reached sanitary requirements.Its organic matter degradation was up to 35.5%,which was the highest in all composts and increased by 32.0%compared to that of control.NH₃-N loss of the compost was reduced by 60.0% compared to that of control.（4）XRD confirmed the formation of struvite.The addition of buffer solution helped to maintain pH in neutral or alkaline condition,which ensured microbial activities as well as struvite formation.Mg²⁺and HPO₄^2-reacted to produce MgHPO₄.Then,a large amount of NH₄⁺,which were reserved in the compost through buffer solution,and MgHPO₄ reacted to form struvite（MgNH₄PO₄·6H₂O）.The struvite precipitation effectively reduced nitrogen loss.