Effects Of Polyaluminium Chloride On Acids Production From Sludge Anaerobic Fermentation And Its Improvement

In recent years,the sludge production has increased dramatically with the rapid development of economy and urbanization.There are a large number of harmful substances in sludge such as heavy metals and pathogenic bacteria,sludge will cause harm to the environment and human health if not disposed properly.Among numerous sludge treatment technologies,anaerobic fermentation technology has attracted much attention,which can not only stabilizethe sludge but also realizes the recovery of biogas,in other words,it is a technology that can effectively realize the utilization of sludge biogas.The acid production is the main initial stage of sludge anaerobic fermentation process.In order to explore the affecting factors of the acid production,this paper investigated the effect of polyaluminum chloride(PAC)on the acid production of sludge anaerobic fermentation.As a high performance flocculant,PAC is widely used in wastewater treatment and sludge dewatering processes.Although studies have shown that low concentration of PAC can inhibit sludge anaerobic fermentation for acid production,there is no research to further explore the specific effects and improvement strategies of different levels of PAC on sludge anaerobic fermentation Therefore,this study investigated the effect of the different concentration levels of PAC on the acid production of sludge anaerobic fermentation.The results showed that lower concentration levels of PAC(0.01～0.15 g AL/g TS)reduced the acid production efficiency of sludge anaerobic fermentation,while higher concentration levels of PAC(0.2～1 g AL/g TS)could promote the acid production of sludge anaerobic fermentation.Especially when the concentration of PAC was 1 g AL/g TS,the accumulation of short chain fatty acids(SCFAs)was the largest,reaching 3884.68 mg/L,which was 3 times of the blank group and 5 times of the inhibition group(the PAC concentration of 0.15 g AL/g TS).The mechanistic studies have shown that higher concentrations of PAC increased the concentration of soluble protein,soluble polysaccharide and soluble extracellular polymer(S-EPS)in the fermentation broth,and scanning electron microscopy(SEM)also showed that the morphology was more loose,which promoted the dissolution of organic matter in the sludge,thus improving the anaerobic fermentation efficiency of the sludge.Because the lower concentration of PAC had significant inhibitory effect on the sludge anaerobic fermentation process,and the low carbon-nitrogen ratio in the sludge causes low acid production efficiency of sludge anaerobic fermentation,the study proposed “Sodium citrate deflocculation” and “Highland barley stem tempering” in the sludge anaerobic fermentation process to improve efficiency of produce acid.By investigating the improvement effect of sodium citrate on the sludge anaerobic fermentation by lower concentration PAC,the results showed that when the ratio of sodium citrate to polyaluminum chloride was 2:1,the maximum accumulation of SCFAs was 2891.6 mg/L,which was 2.5 times that of the contemporaneous inhibition group.By adding carbon source highland barley stem,the effect of lower concentration PAC on the acid production of sludge anaerobic fermentation was improved.The research showed that adding a certain proportion of highland barley stem can improve the acid production efficiency of sludge anaerobic fermentation.This process can not only improve the acid production efficiency of anaerobic fermentation,but also realize the utilization of waste resources.