Preparation And Application Of External Carbon Source For Denitrification With Excess Sludge

Ammonium is an important substance that causes eutrophication of water body and environmental pollution.More seriously,it can be further converted into nitrite and nitrate that directly threaten the human health.With the rapid improvement of the modern industries and the quality of life,the concentration of ammonium in various wastewaters（e.g.,urban sewage and landfill leachate）has risen remarkably,which brings a problematic challenge,i.e.,an insufficient organic carbon source in denitrification process,for the treatment of wastewater with high ammonium.At the same time,as an inevitable product of the municipal sewage treatment plant,the yield of excess sludge is also increasing over year.The excess sludge contains a large amount of unstable organic matter.The reclamation of these organic matter will no doubt bring practical significance to the reduction and disposal of the excess sludge.Considering the aforementioned two requirements,this study adopted an alkali-hydrolysis method to treat excess sludge to prepare an external organic carbon source for denitrification process,explored the optimal alkali-hydrolysis conditions,and applied the sludge alkali-hydrolysate in treating a practical synthetic ammonia wastewater.Main findings are summarized as follows:This study first investigated the feasibility of using the sludge alkali-hydrolysate as a carbon source for denitrification process.Batch experiments were conducted to compare the nitrogen removal performance of denitrification with different organic carbon sources（i.e.,sludge hydrolysate,methanol,and glucose）.Experimental results showed a residual alkali-hydrolysate in the system under low C/N ratio conditions,which could further serve as carbon sources for the denitrifiers to reduce nitrate.Compared to methanol and glucose,the denitrification rate of the system with the sludge alkali-hydrolysate as a carbon source was improved by 25.3%and 23.7%,respectively.In addition,this system exhibited the lowest accumulation of nitrite,and almost no nitrite could be detected at the end of the experiments.Subsequently,after the feasibility of using the sludge alkali-hydrolysate as an external carbon source for denitrification process was corroborated,a series of batch experiments were carried out to explore the optimal operational parameters for the denitrification process with the sludge alkali-hydrolysate as an organic carbon source.The optimized results were as follows:C/N ratio=5.5,initial p H=8,reaction T=35℃,HRT=5 h.Under the optimal conditions,a complete removal of nitrate without nitrite accumulation could be achieved.Finally,this study established a combined A/O process and adopted the sludge alkali-hydrolysate as an external carbon source to treat a practical synthetic ammonia wastewater with a low C/N ratio.The sludge alkali-hydrolysate was supplemented into the anaerobic reactor with an adjusted C/N ratio of 5.5.The A/O process was operated in continuous mode and the determination results indicated a stable effluent quality with TN<15 mg/L,NH₄⁺-N<5 mg/L and almost no NO_x^--N accumulation.All the nitrogen-related indexes met the national first-level A discharge standard.Moreover,the development of the microbial community of the acclimated sludge revealed that the anaerobic reactor was dominated by several denitrifying bacteria including,JTB255＿marine＿benthic＿group,Truepera,Hydrogenophaga,and SM1A02.This study elaborated the feasibility and effectiveness of using the alkali-hydrolysate of excess sludge as an external carbon source to treat the practical synthetic ammonia wastewater with a low C/N ratio.Based on this study,a strong support for the treatment of such wastewaters and the sludge reclamation could be provided.