Effect Of Chemical Pretreatment On Sludge Anerobic Fermentation And Microbial Electrolysis Coupling System

Volatile fatty acids (VFAs) is a kind of chemicals with high added-value. It is notonly the important intermediate of waste activated sludge (WAS) anaerobic treatment,but also can be used as carbon source to product synthetic biopolymers, enhancebiological nitrogen and phosphorus removal and so on. The production of VFAs viaanaerobic fermentation is a new promising way of sludge utilization. However, the maincomposition of WAS is the dead microbial cells, because of the cell wall with semi-rigidstructure, it is difficult to be biodegradated and seriously hinder the dissolution of cellcontents and further hydrolyzed. So it is significant to find appropriate pretreatmenttechnologies for promoting the broken of sludge microbial cell wall and improving thehydrolysis rate, then promoting the process of acidification. Currently, many researchersuse a variety of chemical pretreatments for WAS, this work selected commonly usedchemical pretreatments, comparatively analyzed the effect of them on anaerobicfermentation for VFAs production with WAS and investiged the utilization andconversion of WAS fermentation liquid via different chemical pretreatments inmicrobial electrolysis system for hydrogen productionIn order to investigate the effect of different chemical pretreatments on sludgeacidification performance, the work selected five kinds of typical chemicals, includingsodium dodecyl sulfate (SDS), peracetic acid, NaOH, β-cyclodextrin andrhamnolipid.The result showed that sludge particles crushing effect is not obvious viachemical pretreatment. The main way to accelerate hydrolysis rate was to promoting thedegradation of extracellular polymeric substances (EPS), and provided abundantsubstrates for the subsequent acid fermentation. Among them, the rhamnolipid groupreached the highest lysis rate (50.7%), it increased9.3times compared with the controlgroup, β-cyclodextrin could also signifacantly increase the solubility of proteins andcarbohydrates, increased112times and32times respectively, compared with untreatedsludge.The mesophilic anaerobic digestion batch experiments were carried out to studythe effect of chemical pretreatment on sludge acid fermentation process. It reflected thatchemical pretreatment could effectively improve the amount of VFAs and affect itscomposition.Considering the economy and production of VFAs, the work selected72has the best fermentation time, then the concentration of VFAs in each group ordered:β-cyclodextrin group> Rhamnolipid group> SDS group> peracetic acid group> NaOHgroup> control group, were3973142mgCOD/L、345072mgCOD/L、308057mgCOD/L、287511mgCOD/L、221815mgCOD/L and113919mgCOD/L, respectively. The chemical pretreatment could also inhibit methane generation andincreased accumulation of VFAs during fermention process, the Rhamnolipid performedbest while NaOH did not inhibit.The mesophilic anaerobic digestion semi-continuous flow experiments werecarried out to study the stability of acid production in anaerobic digestion via chemicalpretreatment under a certain sludge load (SRT=10d). It resulted that only Rhamnolipid,β-cyclodextrin pretreatment were able to achieve stable production of acid in a certaintime, and the NaOH group and the control performed the worst.WAS fermentation liquid was used as substrates for hydrogen production inmicrobial electrolysis cell (MEC) to achieve its utilization. Study the MEC performanceof hydrogen production focus on the transform from fementation fractions to energy.The result showed that VFAs was the main consumed fraction of fermentation, in whichSDS group, peracetic acid group and NaOH group, reached the highest use of the totalVFAs. In addition acetic acid was the first easily degradable fraction, followed bypropionic acid, n-butyric acid, isobutyric acid, n-valeric acid, isobutyric acid.Comparing energy recovery yield of hydrogen of each test group, and it founds thatthe reacter feeding with fermentation liquid via peracetic acid pretreatment performedthe best in3d-batch experiment, the average hydrogen yield rate was0.310.11m3H2/(m3reactor·d) and energy recovery rate was19545%,1.72and2.67timesthan control. In addition the main factors of hydrogen generation included the use ofVFAs and carbohydrates.