Optimization Of Acid Production Conditions By Anaerobic Fermentation Of Primary Sludge And Study Of Fermentation Liquid Carbon Source Utilization

Aiming at the shortage of carbon sources in many sewage plants,there are many studies on the use of sludge fermentation as carbon source supplementation.However,the existing researches mainly focused on the fermentation of acid produced by the secondary sludge,while the research on the primary sludge of the higher organic matter was less.At the same time,there are two main difficulties in the research of the primary sludge fermentation:the first is the removal of high concentration of nitrogen and phosphorus in the fermentation process;the other is the improvement of the sludge dewatering performance after fermentation.In view of the above problems,this study proposed a way the the NaOH and Ca?OH?₂ mixed alkali dosing to improve the primary sludge fermentation performance,synergistically improved the sludge dewatering performance and controled phosphorus.Hence,the main parameters of the method were optimized,and then the zeolite enhanced denitrification efficiency was studied.In addition,the carbon source in fermentation liquied was used to investigate its effect on nitrogen and phosphorus removal in multistage AO process.Firstly,the acid production conditions of anaerobic fermentation were optimized by lab-scale test,including the reaction time,temperature and pH,and then optimized the mixing ratio of NaOH and Ca?OH?₂.The results showed that the best comprehensive effect was the reaction time was 6 d,the temperature was 35?and the pH value was 10,and the mixing ratio of NaOH and Ca?OH?₂ was 1:3 with the yield of volatile fatty acids can reach 4538 mg COD/L,the content of PO₄^3--P can be reduced to 2.7 mg/L,and the CST of sludge can be as low as 280 s.Secondly,based on the modification of natural zeolite and the optimization of particle size,the properties of two zeolites to be removed by NH₄⁺-N were investigated by simultaneous addition of modified zeolite to fermented sludge or subsequent fermentation.The results showed that zeolite was soaked in 2 mol/L H₂SO₄ for 8 h,and the optimum particle size was 40⁶0 mesh.Compared with the NH₄⁺-N was removed by the addition of the modified zeolite to the fermentation liquid,the modified zeolite was added to the fermentation sludge to remove NH₄⁺-N method had the advantages of simple process and simultaneous improvement of sludge performance,which was suitable for NH₄⁺-N removal.Under modified zeolite dosage of 200 g/L condition,the fermentation owned the best overall effect.NH₄⁺-N in the fermentation liquid could be controlled at88.8 mg/L,TP can be reduced to 2.8 mg/L,the CST of the sludge can be further reduced to 202 s,and the yield of VFAs can be 4249 mg COD/L.Finally,the effect of fermentation liquied as carbon source for multistage AO process was studied by continuous dynamic test.The results showed that the fermentation liquid was a good carbon source.At raw water TN was 58 mg/L and TP was 5 mg/L,added the fermentation liquid to the raw water of the multi-stage AO process,the ratio of C/N of raw water was increased from 4.3 to 8,the effluent water COD,NH₄⁺-N,TN and TP of respectively were 30 mg/L,0.4 mg/L,8.0 mg/L and 0.5 mg/L,which could reach first level A standard.