Enhancement Of Waste Activated Sludge Anaerobic Fermentation And Stability Of Heavy Metals By Adding Alkaline Residue

Anaerobic fermentation technology is a green and resource utilization method for sludge treatment.Currently,alkali chemical reagents,eg.NaOH and Ca(OH)2 were used to improve the sludge hydrolysis rate in anaerobic fermentation,which resulted in poor dewaterability of WAS and high costs of treatment.Alkaline residue(AR)is the common by-product generated from soad ash plants.Due to the large yield,high moisture content,strong alkaline and hard for treatment,it is urgent to develop an efficiently and innovative utilization approach for alkaline residue.This research studied the effect of alkaline residue on sludge anaerobic fermentation to achieve the reasonable treatment of WAS and alkaline residue.Firstly,we studied that the effect of alkaline residue calcination temperature and dosages on sludge anaerobic fermentation.The results showed that the higer calcination temperature of alkaline residue,the higher initial pH of sludge system that lead to enhanced sludge hydrolysis.When the calcination temperature was 800 ? the highest SCOD and VFAs concentration was 3450 and 1798.6 mg/L,respectively.Then,the total production of VFAs was no longer continue to increase.The sludge dewaterability was only slightly deteriorated under the calcined alkaline residue at 800 ?.It might be the bridging role between the sludge and the presence of Ca.Hence,the optimal calcination temperature of alkaline residue was 800?.When the AR800 dosage was 0.35 g/gVSS,the maximum production of VFAs reached 2177.4 mg/L,but the sludge dewaterability deteriorated slightly.The concentration of PO43-kept at a low level in fermentated liquid,which was conducive to sludge reuse.When the dosage reached 0.75 g/g VSS,the total production of VFAs was no longer continue to increase.However,the TSS of sludge was higher than raw sludge,which was incompatible with the principle of sludge reduction to further treatment.Hence,the optimal dosage as 0.35 g/g VSS.Under the condition of this study,the mechanism of enhancing anaerobic fermentation by adding alkaline residue revealed that the sludge hydrolysis played more significant role than the flocculation under alkaline environment.The study of three-dimensional fluorescence intensity and microbial community structure in anaerobic digestion showed that the readily biodegradable soluble organic substances obviously released,and a large number of hydrolytic cidification bacteria(Firmicutes,Acidobacteria,Planctomycetes)were enriched underr the addition of 800 ?calcined alkaline residue.The effects of alkaline residue on stability of heavy metals(Zn,Cu,Cr and As)was also studied during the sludge anaerobic fermentation process.The results showed that the stabililty of the heavy metals increased after the addition of alkaline residue.The contents of Zn,Cu,Cr and As were the highest in 7 d,which the percentages in stable were 69.25%,94.49%,98.74%and 97.27%,respectively.When the dosage of AR and AR800 were 2%,5%and 8%,the percentages of heavy metal in speciation was no significant difference.Therefore,2%was the optimum dosage.The ratios of unstable and stable contents of Zn,Cu,Cr and As decreased from 2.17,0.35,0.08 and 0.16 to 0.69,0.04,0.02 and 0.05.Hence,it could be effectively reduce the potential heavy metals availability in sludge anaerobic fermentation process.The reason might be the increasing charge of fermentated sludge due to the presence of alkaline substances,which promotes the more stable speciation of heavy metals in anaerobic fermentated process.