Effects Of Vermicomposting On Nitrogen Mineralization And Related Factors In Sewage Sludge

Vermicomposting is an ecologically sound technologies which are not only cost-effective,but also sustainable in terms of possible recovery of recyclable constituents from municipalsewage sludges as they are rich in nutrients and have higher organic matter content. Based onthe stabilization, reduction and recycling of vermicomposting, the characteristics of nitrogenmineralization in the process of vermicompostin g were studied, included the changes ofmineral N, the cumulative amount of net mineralization, the net rate of mineralization and therate of mineralization in sewage sludge, the effect and influence way of vermicomposting onnitrogen mineralization of swege sludge; the nitrogen transformation and nitrogen losses inthe process of vermicomposting, the effect of vermicomposting on the ability of supplynitrogen of swege sludge and the effect of fertilizerin sludge; the changes of the basicphysical and chemical indicators and protease and urease activity in sewage sludge, thecorrelation between the changes of environment of substrate and nitrogen mineralization,aimed at exploring the influence mechanism and the synergistic mechanism of earthworm andmicroorganism in nitrogen mineralization of swege sludge, at the same time, evaluating theeffect of agricultural fertilizer in sludge after vermicomposting. The results are as follows:1. Earthworm and disposing time and their interaction effect all have significant positiveeffects (p<0.001) on mineral N, the cumulative amount of net mineralization, the net rate ofmineralization and the rate of mineralization in sewage sludge, and the vermicomposting is asynergistic mechanism of earthworm and microorganism, and microorganism are still themain factors affect nitrogen mineralization of sludge, and their synergistic effect hassignificant positive effects on it.2. The process of nitrogen mineralization of sludge included two main phases which areammoniation (1~15day) and nitrification (22~36day), vermicomposting respectivelyaccelerated the rate of ammoniation and nitrification1.12times and1.29times than controlgroup, and after trement, the nitrate nitrogen of sludge reached1576.6mg/kg, which was90times of original sludge, and higher than control group about90%, and vermicomposting hasa more significant positive effects on nitrification.3. Vermicomposting promoted the transformation of other form of nitrogen to mineralnitrogen, and the mineral nitrogen content has a significant increase, at the end of treatmentreached2066.27mg/kg, which was4times of original sludge, and higher than control groupabout30.65%. Vermicomposting optimized the composition of mineral nitrogen structure ofsludge, the propotion of nitrate nitrogen in total mineral nitrogen increased from3%to76%,increased24.3times, while ammonia nitrogen decreased to24%from97%, which wasreduced by75.3%, and nitrate nitrogen become the major component of mineral nitrogen of sludge, and the sludge has stronger ability of supply nitrogen and enhanced the agriculturalvalue of sludge.4. In vermicomposting process the total nitrogen content of sludge decreased, which wasreduced by42.5%, and there are two main reasons that caused nitrogen losses, one form isammonia volatilization, and another is denitrification. The activity of earthworm has positiveeffects on these two aspects, but the impact is not significant.5. In vermicomposting process, TOC, moisture content and pH respectively decreased31%、27%and11%, while EC increased, which was2.6times of original sludge. And theseindicators all have significant or more significant correlation with nitrate nitrogen and mineralN and TN, and except EC, the rest of the indicators are not relevant with ammonium nitrogen.6. In vermicomposting process, the protease and urease activity decreased84.8%and7.8%respectively, have significant difference with control group. The protease and ureaseactivity all have significant (p<0.05) or most significant(p<0.01) correlation with TOC,moisture content, pH, EC and nitrate nitrogen, mineral N and TN, while urease activity andammonium nitrogen has positively significant (p<0.05) correlation.Our research suggests that vermicomposting has significant positive effects on nitrogenmineralization of sludge and enhanced the agricultural value of sludge; vermicomposting is aprocess that earthworm cooperated with microorganism on sludge, but the join of earthwormdidn’t change the nitrogen mineralization process, its main role is in deepening the amount ofmineralization, and increasing the diversity of utilization of substrate, stimulating themineralization reaction, at the end showed the increase in the mineral nitrogen. And the mainway that vermicomposting promote nitrogen mineralization is to promote nitrification, and itmainly based on activities of earthworm on microbial community in sludge and thatearthworm castings are enriched in NO-3and NH+4and shows a high potential for microbialnitrification and denitrification.