Study On Methane Production By Co-fermentation Of Swine Wastewater And Brewery Wastewater

With the development of intensive pig breeding,the amount of swine wastewater increased rapidly.Utilizing swine wastewater through anaerobic fermentation to produce biogas(such as methane and hydrogen)is an effective way of resource utilization.However,the fermentation of swine wastewater alone has many problems such as low methane production and ammonia accumulation.Therefore,exploring the way to achieve high-efficiency biogas production from swine wastewater is of great significance for the resource recycling and ecological environment protection.In this paper,brewery wastewater was used as a co-fermentation substrate to investigate the single-phase methane production potential and the best biogas production loading rate of the co-fermentation of swine wastewater and brewery wastewater.The effect of adding different additives(zero-valent iron,ferroferric oxide and granular activated carbon)to co-fermentation of two types of wastewater on methane production and the variation of composition and diversity of the microbial community was studied.Based on the above results,a two-phase(ASBR+UASB)fermentation system to produce hydrogen and methane was designed and built.The biogas production potential and optimal biogas output under different organic loading rates of two kinds of wastewater through the two-phase mesophilic anaerobic fermentation was investigated and the biogas production output was compared between single-phase and two-phase processes.Models suitable for hydrogen and methane production in a two-phase system in a semi-continuous mode were established.The final purpose of the this research is to provide a theoretical basis for the resource utilization of swine wastewater and brewery wastewater.The main conclusions of this research are as follows:(1)The addition of brewery wastewater promoted the single-phase methane production of swine wastewater.The effect of different mixing ratios(swine wastewater:brewery wastewater,10:0,9:1,7:3,5:5,3:7,1:9 and 0:10,volume ratio)on methane production was studied.The results showed that the co-fermentation of two kinds of wastewater achieved better methane production than each of them alone.Among those mixing ratios,the best mixing ratio of swine wastewater and brewery wastewater was 5:5.Under this ratio,the highest methane production rate and methane yield were 212 mL/d and 77 mL CH₄/g COD_added,which were 82%and 114%higher than that of swine wastewater fermentation alone,respectively.Based on the best mixing ratio(5:5),the effect of increasing organic load rates(2.6,5.2,6.9,9.2 and 11.5 g COD/L/d)on methane production was investigated.The results showed that with the increment of organic loading rate,volumetric methane production rate and methane yield increased first and then decreased.Among the five organic loading rates,9.2 g COD/L/d was the largest organic loading rate which could maintain the normal fermentation process.Also,under this loading rate,the highest methane yield(0.2 L CH₄/L/g COD_removed)and volumetric methane production rate(1.1 L CH₄/L/d)were acquired with the85%COD removal efficiency and ammonia of 160 mg/L without ammonia accumulation.(2)The effect of adding zero-valent iron and ferroferric oxide in the co-fermentation system of the two kinds of wastewater was researched.It was found that the addition of zero-valent iron could increase the methane production rate,however,with the increment of zero-valent iron additive amount(2.5 g,5 g,7.5 g,10 g),the methane production rate declined.Among the above additive amounts,the 2.5 g zero-valent iron group got the highest methane production rate(294 mL/d),which was 19%higher than control.The addition of ferroferric oxide reduced the methane production rate of the fermentation system.The addition of two kinds of iron could increase the p H value and promote the degradation of propionic acid,butyric acid and soluble chemical oxygen demand.The addition of zero-valent iron could increase the relative abundance of Bacteroides,Smithella,Syntrophomonas and Methanolinea,and the last three could degrade propionic acid and butyric acid through syntrophic interaction,thereby increasing the methane production rate.The addition of ferroferric oxide significantly decreased the relative abundance of Firmicutes,Clostridium?sensu?stricto?1 and Terrisporobacter,thereby reducing the rate of substrate utilization and the methane production.(3)Adding different amounts of granular activated carbon(GAC)(addition of 1,2,4,6,8 g)could increase the methane production rate of co-fermentation of swine wastewater and brewery wastewater.Highest cumulative methane volume(1422 mL)and relatively high methane production rate(282 mL/d)were achieved under the additive amount 2 g,which increased by 28%and 15%respectively compared with the control group.The effect of adding GAC on the composition and diversity of the microbial community was investigated.The results showed that the addition of GAC promoted the degradation of butyric acid,and increased the relative abundance of acidogen of Clostridium?sensu?stricto?1,and thus improved the methane production rate.The addition of GAC had no effect on degradation of acetic acid,propionic acid and soluble chemical oxygen demand.A comprehensive comparison of the effects of the three additives on the single-phase fermentation system of mixed wastewater was conducted.The result showed that GAC was the best additive for the single-phase co-fermentation of swine wastewater and brewery wastewater.(4)A two-phase fermentation system was designed and built based on the characteristics of swine wastewater and brewery wastewater,and was successfully started.The effect of different organic load rates on the co-fermentation of swine wastewater and brewery wastewater was investigated.With the increment of organic load rates(3.4,5.2,6.9,8.6,10.3,12.1 g COD/L/d,respectively),the volumetric hydrogen production rate,hydrogen yield and volumetric methane production rate first inclined and then declined.The organic loading rate of 8.6 g COD/L/d derived the best methane production.Under this loading rate,hydrogen content,volumetric hydrogen production rate,and hydrogen yield were 32%,0.30 L H₂/L/d,and 0.034 L H₂/g COD_added,respectively.The methane content,volumetric methane production rate and methane yield were 83%,0.50 L CH₄/L/d and 0.13 L CH₄/g COD_added,respectively.The biogas production output of two-phase through co-digestion of two kinds of wastewater was better than that of single-phase.(5)Two semi-continuous biogas production models for the two-phase system were established:the double-e model and the continuous modified Gompertz model(CMGM).Both of them could fit the two-phase biogas production results well,and CMGM fitted better than double-e.According to the prediction of CMGM,the volume of hydrogen in the hydrogen-producing phase would reach a peak every 11.7 hours,and the volume of methane in the methane-producing phase would reach a peak every 11.8 hours.