Exploration On The Application Of Coupling MEC And Anaerobic Digestion With WAS

In order to enhance the production rate of methane in the process of anaerobicdigestion, considering the microbial electrolysis cell and anaerobic digestion,suggest using the electrochemical as an assistant tool to stimulate the evolution ofmethane in anaerobic digestion process.As cell wall limit the dissolve of organic compound, three differentpretreatment methods including micro-aerobic, alkali and ultrasound+alkali wereutilized to boost the break of the wall and dissolve of organic compound in wastedactivated sludge. SCOD can indicate the effect of dissolve of organic compound,thus, SCOD was determined before and after the pretreatment. Analyze the changeof SCOD, it is obvious that ultrasound+alkali exhibited high performance comparedwith other kinds of pretreatment. The quantity of SCOD with ultrasound+alkali wasclose to6767mg/L and6782mg/L that were13.4times and13.8times than initialconcentration of SCOD that was498mg/L. The accumulation of VFA in wasteactivated sludge increased from480to3049after the ultrasound+alkali pretreatment.Under the sole alkali pretreatment condition, the number of SCOD went up to2667mg/L, which was11.1times than240mg/L of initial sludge. SCOD showed noapparent improvement before or after micro-aerobic pretreatment compared withalkali and ultrasound+alkali pretreatment. Only3333mg/L of SCOD was obtainedwhen the initial SCOD was546mg/L,6.1times was achieved.Considering the significant of pH in the process of hydrogen evolution inmicrobial electrolysis cell, lower or higher value of pH can influence theperformance of anode as predominant bacteria at anode is mainly adjusted to neutralcondition, three different buffer solution were compared in microbial electrolysis cellfeeding with sludge fermentation liquid. As the sludge fermentation liquid not onlycontained NH4+and PO43-but also contained organic compound, therefore, sludgefermentation liquid can be utilized as the carbon source for hydrogen evolution inmicrobial electrolysis cell without buffer solution. Compared with reactors addedPBS or BBS as buffer solution, sludge fermentation liquid as solely substrateexhibited comparable performance, the energy efficiency was108%and the hydrogen yield was0.92mL/mgCOD, which was close to1.04mL/mgCOD withPBS and1.03mL/mgCOD with BBS. Although the energy efficiency of microbialelectrolysis cell with PBS was121%, which was higher than reactor without buffersolution, the recovery of PBS is hard and the emission of it is not friendly toenvironment.Acetoclastic methanogen consumed acetate as substrate for methane productionsolely and it is the predominant bacteria in the process of anaerobic digestion, hence,the C-3or other complex compound except acetate or formate should hydrolysis andferment before methane production. During the process of anaerobic digestion,hydrolysis always limited the methane production rate. Reckon with the bacteria atanode in microbial electrolysis cell can consume complex organic compoundsincluding volatile fatty acid, carbohydrate, protein and so forth, as well as generatehydrogen at cathode, microbial electrolysis cell can combine with anaerobicdigestion for enhancing methane production rate based on hydrogen was easilyconsumed by.After ultrasound+alkali pretreatment, the highest methane productionrate was0.138m3CH4/m3reactor/d in hybrid reactors, while the highest methaneproduction rate of AD reactors was only0.073m3CH4/m3reactor/d. The methaneproduction rate of hybrid reactors was0.067m3CH4/m3reactor/d that was significanthigher than0.041m3CH4/m3reactor/d of AD reactors when use alkali as thepretreatment method solely. Apparently, the methane production rate was enhancedwhen coupled microbial electrolysis cell with anaerobic digestion. The sum of theorymethane production yield and AD was accordant to the hybrid reactors, whichtestified the enhancement in the methane production via microbial electrolysis cell.Compared VSS removal efficiency under different pretreatment, the value of hybridreactor was higher than AD by average18.15%when used ultrasound+alkali aspretreat method, changed the pretreat method to alkali alone, the value decreased to8.7%. It is proved that the enhancement of methane production was supplied viamicrobial electrolysis cell as the VSS removal efficiency indicated that decrease ofbiomass in sludge.