Feasibility analysis of excess sludge as carbon source for wastewater denitrification from the perspective of carbon emissions
With the increasing emphasis on carbon neutrality,the exploration of resource utilization for excess sludge has gained prominence.In order to assess the viability of utilizing excess sludge as a carbon source for nitrogen removal in sewage treatment,focusing on the perspective of carbon emissions,a daily sewage treatment volume of 10 000 m3 was taken as the basis for calculation in this study.A comprehensive process route employing excess sludge alkaline hydrolysate as a carbon source for nitrogen removal was established.The proposed process involves alkaline hydrolysis pretreatment of excess sludge with NaOH,recovery of phosphorus through supernatant struvite crystallization,nitrogen removal via partial nitrification and anammox,and utilization of the supernatant from post-nitrogen and phosphorus removal process as the carbon source for nitrogen removal.The feasibility of this process was evaluated based on the different scenarios involving various excess sludge recycle ratios for carbon emissions accounting.Considering that denitrification of alkaline hydrolysis supernatant consumes a portion of COD,the option of denitrification directly after phosphorus recovery from the excess sludge alkaline hydrolysis solution was also investigated.The results indicate that the carbon emissions from the excess sludge alkaline hydrolysis solution are lower than those from an external carbon source,with the operational cost also being less than that of the original wastewater treatment process.Theoretically speaking,the higher the sludge reuse ratio,the smaller the carbon emission in the whole process,with a 100％reuse ratio of excess sludge,the carbon emissions from the excess sludge alkaline hydrolysis solution after phosphorus recovery for wastewater denitrification could reach the lowest value of a 0.309 6 kg·m-3.During this condition,the operational cost savings of 1 222.0～1 261.1 yuan per 10 000 m3 of wastewater treatment compared to the original process.However,considering the accumulation of inert substances in the system,the actual optimal reuse ratio needs to be further studied.The results of this paper show that it is feasible to use the excess sludge as a denitrification carbon source in the sewage treatment process.
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