| The disposition of municipal sludge is becoming a serious environmental problem in recent years. Sludge compost, with a considerable application prospect, is an effective way to make it harmless and recycling. Compost amendments have an important influence on the compost efficiency and product quality. Crop straw has been widely used in sludge compost as compost amendments. However, crop straw consists of cellulose, hemicellulose, and lignin, which is a kind of material that is rather difficult to be decomposed. This is not conducive to the efficiency of composting and its nutrient utilization. Therefore, to solve the problem of sludge compost with straw, we first need to find a way to deal with the problem of cellulose degradation.Microbial degradation of cellulose has always been paid highly attention to in the respects such as the cellulase-producing microbe and the research of cellulase structure and application, whereas most of these cellulose-decomposing microbe were isolated from soil or the compost product of crop straw. They became inefficiency and unsatisfactory when applied into the compost of sewage sludge.Bacteria play a leading role during the composting process, and at least80～90%of the microbial activities are contributed by bacteria.In view of that, we focused on bacteria screening. To provide the original microbe for sludge biological treatment, we obtained highly active strains with cellulose-decomposing ability from the compost product of sludge and straws. In this paper, we carried out the research from the following aspects:(1) We chose dehydrated sludge from Tangwang Sewage Treatment Plant of Yangzhou as the compost substrates and crop straw (with a certain proportion mushroom residue) as amendments in sludge compost. Three treatments (A, B, C) with different proportions of mushroom residue were set in the same ratio of1to0.025for sludge and crop straw. The final compost effects of the three piles were evaluated from7aspects as follows:the variation of temperature, pH, water content, oganic matter, TN, NH4+-N and NO3-N during the composting process.The results showed that Pile C, compared with A and B, had a significant advantage in temperature rise with the shortest time and the highest temperature. Organic matter was fully biodegraded and moisture lost in great quantities, which effectively realized the sludge reduction. Besides that, Pile C had a suitable pH range for compost and a lower loss in nitrogen at the same time. As a result, the compost effect of Pile C was the best and the following cellulase-producing bacteria were isolated from the compost product of this pile.(2) Enrichment culture, using CMC-Na as the main carbon source, was carried out with the collected samples. With the advantage of Congo red differential medium,16strains of bacteria were isolated from the compost product of Pile C during the primary screening. In order to obtain strains with high cellulase activity, secondary screening was further performed with the analysis of CMCase and FPase. Therefore, a relatively highly active cellulose-decomposing bacteria S9, of which CMCase (the activity of carboxymethyl cellulase) and FPase (the activity of filter paper enzyme) reached46.00U/mL and18.21U/mL respectively after4days of fermentation, was screened out.Combined with the results of morphology observation, the analysis of phylogenetic relationships based on16S rDNA gene sequences indicated that strain S9was similar to Devosia sp.DDB001.(3) Single factor experiments were adopted to optimize the cellulase-producing fermentation conditions for strain S9. The optimal conditions were showed as follows, cultivation time of60h, cultivation temperature at30℃, rotation rate at130rpm, inoculation quantity of4%and initial pH of culture medium of7.2～7.5. Under above conditions, FPase and CMCase of strain S9achieved23.10U/mL and54.97U/mL, respectively. |
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