Study On The Products Regulation Of Waste Activated Sludge Hydrolytic Acidification Based On Carbon Source Recycling

Products of Waste activated sludge（WAS）hydrolytic acidification such as volatile fatty acids（VFAs）can be used as supplementary carbon sources for treatment of municipal wastewater with a low C/N ratio.However,it is difficult to accumulate sufficient VFAs and other useful carbon source products from WAS hydrolytic acidification due to methanogenesis.In addition,the extremely high nitrogen and phosphorus contents in the recycling liquid from the hydrolytic acidification process further increases the nitrogen and phosphorus load of municipal wastewater treatment plant（WWTP）.Based on the carbon source recycling target,a series of completely stirred tank reactors（CSTR）were employed to regulate the WAS hydrolytic acidification products,exploring the optimum operating conditions for WAS treatmeng process.After different kinds of hot-alkali pretreatment,the effect of WAS hydrolysis acidification showed significant difference.With NaOH and KOH treatment,the SCOD in sludge supernatant were 8.4 and 8.2 times higher than that of the control group.The accumulation of SCOD and VFAs in the process of WAS hydrolysis acidification was significantly higher than that of Ca（OH）₂ and Mg（OH）₂.The addition of BES to WAS alkaline fermentation process can greatly increase the accumulation of SCOD and VFAs,which were56.7%and 56.5%higher than that of the control group,just the percentage of acetic acids mass fractions in VFAs were 66.4%.The addition of CaO₂ could further reduced the concentration of NH₄⁺-N and PO₄^3--P in sludge hydrolyzate,the mass concentrations only were 166.0 mg/L and 9.6 mg/L respectively,which were 66.5%and 68.0%lower than that of the control group.The effect of sludge concentrations on the characteristics of SCOD and nitrogen and phosphorus release were investigated under medium temperature（30℃）and low temperature（15℃）as addition of BES and CaO₂ in batch experiments.The results showed that the sludge concentrations and the dissolution rate of organic matters are linearly correlated under the same temperature,the maximum dissolution of SCOD per unit sludge under medium/low temperature conditions were 979.3 mg/g VSS,717.5 mg/g VSS.When the sludge concentrations were 10 g/L,20 g/L,30 g/L and 40 g/L,under medium temperature,the maximum mass fractions of SCOD were higher 65.8%,56.1%,56.6%and 54.9%than that of low temperature respectively,and the highest were arrived at 6596.7 mg/L For medium temperature,the increase rate of highest mass fractions of VFAs upon to 122.0%,169.2%,215.8%,228.2%respectively than low temperature.Under medium temperature conditions,the acidification rate of organic matters were all above to 20%,and the highest was 23.3%when the sludge concentrations were higher than 20 g/L.At the same temperature,The higher sludge concentrations,the higher release of nitrogen and phosphorus.When the sludge concentrations were 30⁴0 g/L,the highest mass concentrations of NH₄⁺-N and PO₄^3--P were181.9 mg/L and 14.6 mg/L,and the SCOD/N and SCOD/P in sludge hydrolyzate supernatants reached to 35.3³6.3、432.6⁴51.8 respectively under medium temperature.The effects of acid/alkaline startup modes on the WAS hydrolysis acidification and nitrogen and phosphorus release were investigated by CSTR.The results showed that treatment process with acid startup（pH=6.0）mode could more conducive to the dissolution of organic matters in the sludge,the accumulation of SCOD and VFAs in the hydrolytic acidification liquid were higher than that in alkaline startup mode.With acid startup mode,when SRT was 6 d,the highest accumulation of SCOD and VFAs were 6235.8 mg/L and1683.5 mg/L,which were higher 21.4%、35.7%respectively than that of alkaline startup mode,the mass fractions of acetic acids and propionic acids were over 85%,the higest acetic acids mass fractions in VFAs reached 69.4%.The apparent conversion rates of SCOD and VFAs in hydrolytic acidification liquids of WAS were 5.3%and 17.3%higher than alkaline startup mode.When SRT is shortened to 6 d,the reduction of VSS were 35.5%and 10.7%respectively under acid and alkaline startup modes.There was no significant difference in the release of nitrogen and phosphorus.The results showed that addition of BES and CaO₂ can be control the products of WAS alkaline hydrolysis acidification efficiently.With the treatment of WAS by acid startup（pH=6.0）-alkaline hydrolysis acidification（p H=10.0）mode under medium temperature（30℃）,when SRT was 6 d and the sludge concentrations were 30⁴0 g/L,the reduction of sludge can be reached 35.5%after WAS hydrolysis acidification,the SCOD/N and SCOD/P in sludge hydrolyzate supernatants reached to 35.3³6.3、432.6⁴51.8 respectively.Under these conditions,the utilization of WAS could be realized.