Effects Of Cu, Cd On Microorganisms And Enzyme Activities During Agricultural Waste Fermentation Process

There produce a lot of agricultural waste in China every year. The agricultural wastehave been piled up at will or been burned in the open air, which caused serious pollution tothe environment. To prepare compost and to produce methane is the effective way to achieveresource recycling and harmless treatment of agricultural waste. However, with thedevelopment of industry and the enhancement of the level of breeding dimensions andintensive, the feed additive containing high concentration of heavy metals have beenwidespread used. As a result, the heavy metal pollution of agricultural waste is more andmore serious. On the one hand heavy metal reduce agricultural waste utilization efficiency,on the other hand, it bring risks and limitations during agricultural waste utilization. Theanaerobic fermentation process and aerobic composting process is proceeding under the roleof microbes and enzymes secreted by them. The level of hydrolytic enzyme activities is thespeed limiting factor during anaerobic fermentation process of agricultural waste. Heavymetals produce certain toxic effects to microorganisms and inhibiting effects to enzymeactivities during anaerobic fermentation process and aerobic composting process. Thus thestudy of the effects of heavy metals on microorganisms and enzyme activities duringagricultural waste anaerobic fermentation process and aerobic composting process is of greatsignificance.In this paper,we used wheat straw and pig manure as the experimental materials spikedwith different levels of heavy mental copper and cadmium.The effects of heavy metal copperon hydrolysis enzyme activities and the microbial community during anaerobic fermentationprocess and the influence of cadmium on the microbial community during aerobiccomposting process were studied. The main research results are as follows:1. Effects of Cu on hydrolysis enzyme activities and gas production process duringanaerobic fermentation process(1) The average cellulase activities and sucrase activities in CK treatment(the massfraction of Cu was49.70mg/kg)were significantly higher (p<0.05) than those in H treatment(the mass fraction of Cu was949.70mg/kg)during the whole fermentation process, and theaverage urease activities of CK treatment and L treatment (the mass fraction of Cu was 349.70mg/kg)were significantly higher (p<0.05) than those of M treatment (the mass fractionof Cu was649.70mg/kg) and H treatment. The inhibition effect of high copper concentrationon hydrolysis enzyme activities was observed.(2) In the anaerobic digestion system with pig manure and wheat straw as raw material,high concentration of exogenous Cu showed obvious inhibition effects on gas production rateat initial and middle stage of anaerobic fermentation process. Instead it showed weakstimulative effect in the later period of anaerobic fermentation process.The total gasproduction of CK treatment was2.20%,2.18%,9.44%higher than L, M, H treatment.(3) The pH value of anaerobic digestion system dropped to the lowest through acidproducing process, and then rise to appropriate range for microbial growth.The existence ofCu in anaerobic system has little effect on the pH value.(4) Correlation analyses demonstrated that the activities of hydrolysis enzyme activitiesof the treatment without adding exogenous Cu were significantly related to the biogasproduction rate. While copper could exert comprehensive impacts on rate of gas productionthrough such factors as microbial activities and hydrolytic enzyme activities, Which lead tothe correlation between three kinds of hydrolase activities and gas production rate is poor.2. Effects of Cu on microbial community during anaerobic fermentation process(1) DNA yield of Microbial genomic reveals a tendency of first increasing and thendeclining during anaerobic fermentation process. When the gas production rate is high, theDNA yield was also high. DGGE profiles showed that abundance of H treatment's band islow. Some bands of CK treatment disappeared along with the fermentation.(2) In anaerobic fermentation process, microbial community prefer to use polymerscarbon source, the utilization degree of aromatic compounds is the lowest. Diversity indexand cluster analysis of microbial community carbon source utilization showed that lowconcentrations of Cu produced promoting effect on the metabolic function diversity of themicrobial community, while high density of heavy metal Cu treatment showed depressioneffect on them.3. Effects of Cd on microbial community during aerobic composting process(1) Exogenous Cd reduced the heating rate of windrow, the treatment in lowconcentrations of Cd (the mass fraction of Cd were15mg/kg,30mg/kg,45mg/kg)lengthened high temperature period, raised the compost maturity. High concentrations ofheavy metal Cd (the mass fraction of Cd was60mg/kg) inhibit the compost maturity process,compost pile temperature had not reached50℃all the time.(2) We analyzed the impact of Cd on the microbial community from the four aspects: theAWCD value of the microbial community, diversity index, the utilization rate of the six categories carbon source and principal component analysis from Biolog data. The resultsshowed that Cd reduced the metabolic capability to use the six categories carbon source,which reduced the functional diversity of microbial communities and overall metabolicactivity. The principal component analysis also showed that, under the influence of Cd, thecarbon source types used by microbial were changed.