Experimental Study On Using Residual Sludge Pretreatment Decomposed Liquid As An Additional Carbon Source For Denitrification

In recent years,with the advancement of urbanization in China,the proportion of urban population has been increasing year by year,and the scale of sewage treatment has been increasing year by year.However,how to dispose of residual sludge,a byproduct of wastewater treatment,has always been a thorny problem.Excess sludge not only has a pungent odor,but also contains toxic substances such as heavy metals and pathogens.Improper treatment can easily cause secondary damage to the environment.The traditional disposal methods for excess sludge in China mainly include incineration,burial,etc.However,traditional disposal methods not only increase transportation costs,but also easily pollute underground water sources and cause damage to the ecological environment.A large amount of organic matter in the surplus sludge can be effectively released through pretreatment,which can not only improve the anaerobic digestion rate of the surplus sludge,but also can be used as a carbon source for denitrification to improve the efficiency of denitrification in the sewage treatment system.The study used electrolysis alkaline hydrolysis and the addition of electrolyte Na Cl as a pre-treatment method to investigate the effect of different p H values,temperature,voltage gradients,and Na Cl dosage on sludge cracking.The experiment found that the optimal pre-treatment parameters were p H=12,voltage gradient of 6,Na Cl dosage of 0.075mg/L,and temperature of 50 ℃.Under this parameter,it was found through experiments that the SCOD of the remaining sludge increased from250.58mg/L to 1310.4mg/L under the optimal parameter,an increase of 423%compared to the original sludge,and the COD dissolution rate reached 8%.Polysaccharides and soluble proteins reached 119.3mg/L and 1025.5mg/L,respectively,which increased by 886% and 323.8% compared to the original sludge.The pretreated sludge was used as the carbon source in the denitrification stage for the experimental study of denitrification,and the effects of different C/N,temperature,p H,HRT on the results of denitrification were explored.Batch denitrification single factor control experiment is adopted,that is,each experiment controls one variable,and the next group of variable experiments are conducted under the optimal parameters of this variable.It was found that the optimal denitrification parameters were: C/N=6,T=30 ℃,p H=8,HRT=4h.Under these optimal parameters,the average specific denitrification rate is 4.899 mg(g MLVSS · h),and the denitrification effect is ideal.The SCOD removal rate is 54.9%,and the effluent SCOD concentration is 135.2 mg/L.This study shows that it is feasible to pretreat excess sludge and use its hydrolysate as carbon source in denitrification stage by alkaline hydrolysis electrolysis and adding electrolyte Na Cl,which provides reference and technical support for WWTP to select similar external carbon source.