Studies On Gas Dynamic Laws Of Composite Additives In Anaerobic Fermentation

With the rapid development of large-scale animal husbandry,the amount of animal waste produced far exceeds nature's ability to decompose it.Animal waste pollution becomes a serious problem.Anaerobic digestion(AD)not only converts animal waste into harmless resources that can be utilized;it also produces a source of clean energy(biogas),which helps solve another problem;that is,the scarcity of energy sources.This paper presents research on the AD of dairy manure under mesophilic conditions.Separate batches were employed to study the influence of pre-treatments,composite additives,carbon materials,multi-phosphate based composite additives,and transition metal compounds on the dynamic regulation of anaerobic digestion in biogas production.(1)Ultrasonic,microwave,and mechanical pre-treatments were applied to mixtures of dairy manure and accelerants to determine the ways in which these various pre-treatments affect the AD process.Effective pre-treatment processes for AD of dairy manure were determined by comparing biogas production,p H level,and chemical oxygen demand(COD)reduction in separate batches using these three pre-treatment methods.Results showed that all the three pre-treatment methods(especially the mechanical pre-treatment method)could significantly increase biogas production and improve the COD reduction rate.(2)The effects of various quantities and combinations of additives on digestion time,daily biogas production,total biogas production,and COD reduction rate were compared by carrying out AD in different batches.Additives tested included:urea alone;and compounds of two,three,or four additives.They were:(two additives)urea+bentonite,or urea+activated carbon;(three additives)urea+bentonite+plant ash,or urea+activated carbon+plant ash;and(four additives)urea+bentonite+activated carbon+plant ash.Results showed that,over the course of 35 days,composite additives increased cumulative biogas production by 0.54%-50.65%over the comparison group,and improved COD reduction by 13.43%-103.75%.The use of composite additives shortened the AD reaction time,and significantly improved biogas production rates and COD reduction rates.(3)Based on the concept of converting waste into usable resources,corn cobs,cardboard boxes,sawdust,and walnut shells were carbonized using microwave carbonization methods to obtain four types of biochar additives(C_{corn cobs},C_{cardboard boxes},C_sawdust,and C_{walnut shells}).Mesoporous carbon,activated carbon,and waste ink were also studied,for a total of 7 different additives(C_{corn cobs},C_{cardboard boxes},C_sawdust,C_{walnut shells},mesoporous carbon,activated carbon,and waste ink).Their effects upon the AD of cattle manure were compared in terms of daily biogas production,total biogas production,p H value,and COD reduction.The results showed that not only did the various carbon material additives significantly increase total biogas production over the comparison group,but they also shortened the duration of the AD reaction process.Total biogas production increased by 29.25%-70.75%.The addition of waste ink resulted in a 70.75%increase in total biogas production and a 44.31%improvement in COD reduction.(4)With phosphate as a substrate,the effects of composite additives with one to five-element phosphate groups were studied in terms of their dynamic regulation of the anaerobic digestion of dairy manure in biogas production.Results showed that composite additives with single-element phosphates resulted in 3.74%-9.86%more total biogas production than the comparison group.Additives with 2,3,4,and 5-element phosphate groups resulted in 13.27%-26.53%,5.10%-24.15%,8.50%-35.37%,and31.63%more total biogas production than the control group,respectively.Not only did compound additives with phosphate groups increase cumulative biogas production rate,they also shortened the AD reaction time.(5)With urea alone as a baseline for comparison,various transition metal compounds and non-ransition metal compounds were added to the process of AD of dairy manure to study their dynamic regulatory influence in biogas production.The following compounds were tested:Ta O,Ta₂O₅,Hf O₂,Hf C,WO₂,WN,and Si C.Results showed that the addition of transition metal compounds not only improved the AD environment,but also improved the biogas production and COD reduction rates.Cumulative biogas production was improved by 8.50%-35.37%over the comparison batch.Cumulative gas production using Ta O was the highest(506.0 m L/g TS),and cumulative gas production using WN was the lowest(460.0 m L/g TS).