Effects Of Trace Metal Elements On The Production Of Volatile Fatty Acids From Anaerobic Sludge Fermentation

Amounts of organic matter take a large part in Municipal Sludge, which can beused in VFAs production from anaerobic fermentation and that will be a nice way inresource utilization of Municipal Sludge. Compared with the anaerobic methanogenicmore mature status quo, the research of anaerobic VFAs process is difficult to control.But the value that VFAs may bring about is much higher than that of CH4.This study aimed to investigate the effects of six metals(Zn²⁺,Co²⁺,Mo⁷⁺,Cu²⁺,Fe²⁺,Mn²⁺) on volatile fatty acids generation from municipalsludge by anaerobic fermentation. Anaerobic bioreactors containing200mLpretreatment liquid of excess activated sludge mixed with30mL sludge seeding. Zn²⁺,Co²⁺, Mo⁷⁺, Cu²⁺（0,5,20,40,60,100mg/L） and Fe²⁺, Mn²⁺（0,100,200,400,600,1000,1500mg/L） of various does were added to anaerobic bioreactors to examine theiranaerobic fermentation performance. Results showed:①Different trace metals couldinfluence VFAs composition. In the experiments of different concentrations ofZn²⁺,Fe²⁺,Mn²⁺,four kinds of acids（Acetic acid, propionic acid, butyric acid, pentanoicacid） were detected; In the experiments of different concentrations of Cu²⁺,Mo⁷⁺,fivekinds of acids（Acetic acid, propionic acid, butyric acid, pentanoic acid,caproic acid）were detected; In the experiments of different concentrations of Co²⁺,five kinds ofacids（acetic acid, propionic acid, isobutyric acid, butyric acid, pentanoic acid） weredetected;All kinds of VFAs were with acetic acid and butyric acid as the maincomponent.②Comparing with different concentrations of trace elements, Fe²⁺had themost obvious effects on VFAs generation, followed by Co²⁺,respectively increased56.4%and42.4%than contrast.③The sequence of the six metals on volatile fatty acidsgeneration as follow: Fe²⁺> Co²⁺> Mn²⁺> Zn²⁺> Cu²⁺≈Mo⁷⁺.The fermentation conditions of trace metals(Fe²⁺,Co²⁺,Cu²⁺,Zn²⁺,Mn²⁺) onproduction of VFAs from municipal sludge were optimized. Based on single factorexperiments, response surface methology with three variables of Fe²⁺,Co²⁺,Cu²⁺,Zn²⁺and Mn²⁺was employed to optimize the fermentation condition for aceticacidproduction\butyric acid production\total VFAs production. Under optimal conditions, the production of aceticacid was increased by1.62times,while butyric acid increased13.20times and total VFAs increased2.52times. Finally, the consistent results betweenthe prediction and experiments indicated the established model in this study is feasible.The result from EEMs of metabolites of VFAs production process also indicate thatthe dosing of trace metal can affect the biodegration of municipal sludge and promotethe production of metabolites. Under T-RFLP experiments and SRT gene scanning, tracemetal can rerich anaerobic fermentation acid microflora structure, which could also betested through Shannon-Wiener and Simpson diversity index.