Characteristic Of Anaerobic Co-digestion Of Livestock Manures With Wheat Straw

About700million-tons of crop straw and25million-tons of livestock manure wereproduced in China every year. It will cause very serious environmental problem if not handledproperly. The main component of wheat straw was lignocellulose. When taking wheat strawlonely as fermentable material, lignocellulose was very difficult to be used directly byanaerophyte. Mixed fermentation can improve the biogas production effectively. Co-digestionof livestock manure and wheat straw could avoid the shortcomings of single material andbalance the C/N of fermentable system.To improve the utilization of agricultural wastes and the digestion efficiency, this studyinvestigated the performance of anaerobic co-digestion of three kinds of livestock manuresand wheat straw with different compositions at three different temperatures. Experimentswere conducted by self-manufactured anaerobic fermentable reactor, in sets with livestockmanure/wheat straw ratios of1:9,3:7,5:5,7:3and9:1at15℃,35℃and55℃with totalsolid concentrations of8%in digesters. The pH value, the contents of volatile fatty acid(VFA), total alkalinity and ammonia nitrogen were examined every6days during anaerobicdigestion. The main results obtained in this paper were listed as the followings:(1) Increasing the proportion of livestock manure, changes of cumulative biogas yield ofdifferent co-digestion of manure and wheat straw were different. And changes of indexes inthe fermentable process were as following: The concentration of VFA was reduced, theconcentration of total alkalinity, pH and ammonia nitrogen was increased. But when theproportion of pig manure was increasing, VFA of mixed pig manure and wheat straw at15℃was increased and its pH value was decreased.(2) By the result of variance analysis, it was known that there were significantdifferences among averages of cumulative biogas production of mixed livestock manure andwheat straw at different temperatures (15℃,35℃,55℃). The cumulative biogas productionof cattle manure-wheat straw and sheep manure-wheat straw was increased with thetemperature increasing significantly.(3) To analyz the average cumulative gas production of mixed livestock manure andwheat straw by one-way anova at the same temperature condition, it was known that: there was no significant difference among the co-digestion of three different livestock manure andwheat straw at15℃. The highest average of cumulative biogas production was sheepmanure-wheat straw; At the temperature of35℃, the difference was significant except pigmanure-wheat straw and sheep manure-wheat straw(P=0.515). The highest average ofcumulative biogas production was pig manure-wheat straw; At the temperature of55℃,differences among co-digestion of three sorts of livestock manure and wheat straw weresignificant. The highest average of cumulative biogas production was mixed cattle manureand wheat straw.(4) With the increasing of temperature, changes of VFA, ammonia nitrogen and pHaverage value of mixed livestock manure and wheat straw were different. The change of pHaverage value was opposite with its corresponding change of VFA. Total alkalinity averagevalue was increased while temperature increasing. Analyzed the correlativity among VFA,total alkalinity, pH, ammonia nitrogen and daily biogas production of co-digestion oflivestock manure and wheat straw, it was known that VFA and daily biogas production wasnegative correlation, pH and daily biogas production was correlative, VFA was significantlynegative correlation with pH. And total alkalinity and ammonia nitrogen was positivecorrelation except the co-digestion of pig manure and wheat straw at15℃.(5) At15℃, when the ratio of sheep manure/wheat straw was5.03:1,the maximum totalbiogas production was expected to reach3429.32mL. At35℃，when the ratio of cattlemanure/wheat straw was7.61:1, the maximum total biogas production was expected to reach11880.41mL, when the ratio of sheep manure/wheat straw was5.28:1, the maximum totalbiogas production was expected to reach11241.23mL. At55℃, when the ratio of cattlemanure/wheat straw was4.41:1, the maximum total biogas production was expected to reach16536.52mL, when the ratio of sheep manure/wheat straw was4.47:1, the maximum totalbiogas production was expected to reach16926.97mL.