Study On The Effect Of Flocculation Treatment On The Biogas Fermentation Of Corn Stover Hydrolysate

The hydrolysate obtained from the hydrothermal treatment of agricultural straw is rich in sugar compounds,which can be converted into bio-based fuels and chemicals by microorganisms.However,the phenolic compounds contained in the hydrolysate have inhibitory effect on the growth and metabolism of microorganisms.This paper studied the process of removing phenolic compounds in corn stover hydrolysate by flocculation to improve the biogas fermentation performance of hydrolysate,and analyzed the antioxidant activity of flocs obtained after flocculation.Firstly,cationic polyacrylamide（CPAM）,ferric chloride（Fe Cl₃）and polyferric chloride（PFC）were used as flocculants,and the process conditions such as the amount of flocculant,the p H of the flocculation system,the molecular weight of the flocculant,and the initial concentration of the hydrolysate were investigated.Effect on the removal of phenolic compounds from corn stover hydrolysate.The results showed that the removal efficiency of phenols reached the maximum value of 16.62%after flocculation treatment under the conditions of CPAM molecular weight of 8 million,dosage of 0.2 g/L,p H=9.0,and settling time of 3.0 h.Using PFC and Fe Cl₃ as flocculants respectively,under the conditions of flocculant dosage of 2.0 g/L,p H of hydrolysate was 9.0,and flocculation time of 3.0h,the maximum removal rates of phenolic compounds can reach 21.24%and 22.69%,respectively.On this basis,the effect of using CPAM as coagulant on Fe Cl₃ and PFC flocculation to remove phenolic compounds in hydrolysate was investigated.The results showed that the removal rate of phenolic compounds in the hydrolysate can be significantly improved by using CPAM as a coagulant.Under the conditions of 0.1 g/L of coagulant CPAM,2.0 g/L of flocculants Fe Cl₃ and PFC,p H of hydrolysate was 4.0 and settling time was 3.0h,the removal rate of phenolic compounds in hydrolysate reached 27.09%and 30.59%.Studies have shown that the addition of coagulant aid CPAM can enhance the removal effect of phenolic compounds in the hydrolysate under acidic and alkaline conditions.Among them,inorganic flocculants Fe Cl₃ or PFC firstly adsorbed phenolic compounds through charge neutralization or charge neutralization-bridging mechanism under acidic conditions,and then enhanced the removal of phenolic compounds through CPAM charge neutralization and bridging mechanism;under alkaline conditions,Fe Cl₃ or PFC firstly adsorbed phenolic compounds through a roll-sweep mechanism,and then CPAM enhanced the removal of phenolic compounds through a patch and roll-sweep mechanism.Next,the effect of the initial concentration of the hydrolysate on the removal of phenolic compounds was further investigated,and the results showed that diluting the hydrolysate can promote the removal of phenolic compounds.After diluting the hydrolysate by 3 fold,flocculation was carried out under the conditions of inorganic flocculant 2.0 g/L and CPAM0.1 g/L.After treatment with flocculants such as CPAM,Fe Cl₃,PFC,Fe Cl₃-CPAM and PFC-CPAM,the removal rate of phenols in the hydrolysate reached 28.23%,22.16%,26.53%,41.61%and 43.04%respectively.The BOD/COD increased by 29.51%,27.87%,24.59%,42.62%and 39.34%respectively,and the biodegradability was significantly improved.After the hydrolysate obtained after flocculation was inoculated for biogas fermentation under the conditions of inoculation ratio of 0.2 kg VS/kg COD,37±1℃,and alkalinity of 2700 mg/L,the biogas fermentation rate increased by 26.25%,179.14%,56.83%,182.76%,and 33.99%respectively.After CPAM,PFC and PFC-CPAM treatments,the cumulative methane yields increased by 20.00%,16.86%and 18.94%,respectively.The chemical composition of the flocs was analyzed by infrared spectroscopy,and it was confirmed that the organic compounds in the flocs were mainly composed of phenolic compounds.The ABTS⁺·（2,2′-azino-di（3-ethylbenzothiazoline-6-sulfonic acid））free radical scavenging rate experiment confirmed that the flocs have a certain antioxidant activity,and each gram of flocs is equivalent to 3.40～17.23 mg BHT（butylated hydroxytoluene）antioxidants,which can be used as raw materials for further processing to prepare antioxidants,thereby improving the overall economy of the process.