Study On Pretreatment For Corn Straw And Anaerobic Co-digestion Of Corn Straw And Excess Sludge

Anaerobic digestion is one of the most commonly applied technique forutilization of excess sludge and straw. The carbon-to-nitrogen ratio(C/N) of excesssludge is lower and the C/N of crop straw is higher, which reduces the efficiency ofsingle excess sludge or crop straw anaerobic digestion. Pretreatment techniques andanaerobic co-digestion of excess sludge and crop straw are applied to improveanaerobic digestion efficiency and biogas yield. The results of corn straw pretreatedby NaOH, ammonia, water and excess sludge mixed with crop straw after pretreatedfor anaerobic digestion are studied.In the pretreatment experiment, by single factor experiment, the result oforganic(SCOD and dextrose) produced by corn straw pretreated by NaOH liquor andammonia is optimized using response surface methodology, according to theBox-Behnken central composite designs. In the design, corn straw dimension,chemical concentration and pretreatment time are concerned. Anaerobic digestionexperimentation studys the effect of different dilution rate and different excess sludgeto corn straw ratio promoting the biogas yield every day, volatile solid(VS) removerate and biogas yield by remove unit VS.The pretreatment experimentation rerults show that NaOH liquor solution is thebetter effective solution, the optimal medium is as follows: corn straw dimension:30mesh, NaOH liquor concentration: 4%, pretreatment time: 48h. After pretreated, theSCOD and dextrose concentration are 41944mg/L和25.8 mg/L respectively and thefibrin proportion in corn straw increases from 40.4% to 59.4～68.2%, otherwise, thelignin proportion in corn straw decreases from 24.4% to 5.4～16.5%.The results of sequence anaerobic digestion experiment show that When thedilution rate is 4%, 5% and 8%, the result of excess sludge anaerobic digestion mixedwith corn straw prtreated by water (excess sludge to crop straw mass ratio(dry)is 1.2:1)is much better, biogas yield by remove unit VS and VS remove rate are 20～50% and1～7 times than the results of single excessn anaerobic digestion. In the term of 8%dilution rate, the result of excess sludge anaerobic digestion mixed with corn strawprtreated by water is the best compared with the results of 4% and 5% dilution rate,biogas yield by remove unit VS is about 430 ml/gVS and VS remove rate is about60%. Batch anaerobic digestion experimentation also reveals that the result of excesssludge anaerobic digestion mixed with corn straw prtreated by water (excess sludge to crop straw mass ratio(dry)is 1.2:1) is the best. The total biogas cubage is 6557 ml andbiogas yield by unit total solid(TS) reaches 210.2 ml/gTS.Otherwise, the time ofbiogas production persists more than 35d and the methane(CH4) proportion in biogasreaches 60.6%.The results of anaerobic digestion reveal that the C/N ratio can be reasonable foranaerobic co-digestion of pretreated corn straw and excess sludge to produce biogas.Although the biogas yield peak of excess sludge anaerobic digestion mixted with cornstraw pretreated by NaOH liquor is earlier, too high Na+ concentration in anaerobicreactor has a bad impact on anaerobic digestion.