Two Kinds Of Mineral Additions On Anaerobic Digestion Of Different Substrates

Anaerobic digestion(AD) is an efficient method for reducing waste via biogas production, which can convert wastes into energy sources for life consumption. But the conversion rate of biogas is very low, only 30% ~ 40%. It is pointed out that the use of plant ash, metal element and hydrolase economizes energy and enhances biogas production, but few studies on natural minerals. To optimize biogas yields, batch experiments were conducted under mesophilic conditions(35℃) by using magnetite and ziolite with wheat straw(WS), goat manure(GM) and mixed materials(MM) of both(GM/WS=1:9, 3:7, 5:5, 7:3 and 9:1), and the additive doses of additions are 0g, 1.5g, 3g, 4.5g and 6g. The variations of CH4 production, pH value, TAN concentration, VFA/alkalinity and dehydrogenase activity(DHA) during the anaerobic process were investigated. Furthermore, the best conditions of the AD process by using three types of substrates with additives were optimized by the response optimizer. The ruslts are showen blow:(1) Methane-producing phase can be accelerated and the accumulative methane production can be enhanced by the addition of magnetite in the AD process. The peak of gas-generating is appeared 8 ~10 days early when adding magnetite in AD process of WS, the best accumulative methane yield is 6014 mL when adding 3 g magnetite of WS which is increased by 44.74% compared with control group, and there exist significant differences; for GM, the peak of gas-generating is appeared 3 ~ 4 days early, the the best accumulative methane yield when adding 3 g magnetite is increased by 28.23% than the control; when co-digestion of WS and GM, there is a positive interaction effect of WS/GM ratios and magnetite doses, and the best methane yield is 8875 mL when the GM/WS ratio is 5:5 and the additive dose of magnetite is 3 g which is significant higher than control. By using the response optimizer when the GM proportion is 51%, the best methane yield will obtained with the addition of 3.71 g magnetite.(2) The accumulative methane production can be enhanced by the addition of zeolite too.The best accumulative methane yield is 5365 mL when adding 1.5 g zeolite of WS which is increased by 29.12% than the control; for GM, the the best accumulative methane yield is 6419 mL when adding 4.5 g zeolite which is significant higher than control; for co-digestion of WS and GM, there is a positive interaction effect of WS/GM ratios and zeolite doses, and the best methane yield is 8667 mL when the GM/WS ratio is 5:5 and the additive dose is 1.5 g which is increased by 25.39% compared with control group, and there exist significant differences. By using the response optimizer when the GM proportion is 55%, the best methane yield will obtained with the addition of 1.97 g zeolite.(3) When magnetite and zeolite mix, the best result is obtained by 1.5 g magnetite + 0.75 g zeolite, and the best methane yield of WS, GM and MM respectively is 6821 mL, 5137 mL and 7919 mL which is increased by 53.90%, 4.09% and 16.68%, reaching an remarkable level. By using the response optimizer when the GM proportion is 43%, the best methane yield will obtained with the addition of 1.65 g magnetite + 1.97 g zeolite.(4) The addition of magnetite and zeolite in the AD process helps maintain a good fermentation environment, which includes proper range of pH and VFA/alkalinity, low content of TAN and VFA, and the DHA with is higher than control.