Abstract
This study aimed to investigate the effects of temperature on the quality of vermicompost and microbial profiles of dewatered sludge during vermicomposting. To do this, fresh sludge was separately vermicomposted with the earthworm Eisenia fetida under different temperature regimes, specifically, 15 °C, 20 °C, and 25 °C. The results showed that the growth rate of earthworms increased with temperature. Moreover, the lowest organic matter content along with the highest electrical conductivity, ammonia, and nitrate content in sludge were recorded for 25 °C indicating that increasing temperature significantly accelerated decomposition, mineralization, and nitrification. In addition, higher temperature significantly enhanced microbial activity in the first 30 days of vermicomposting, also exhibiting the fastest stabilization at 25 °C. High throughput sequencing results further revealed that the alpha diversity of the bacterial community was enhanced with increasing temperature resulting in distinct bacterial genera in each vermicompost. This study suggests that quality of vermicompost and dominant bacterial community are strongly influenced by the contrasting temperature during vermicomposting of sludge, with the optimal performance at 25 °C.
Highlights
With the development of China in recent years, the government has built thousands of wastewater treatment plants, generating large amounts of dewatered sludge with several pollutants that are difficult to be treated [1,2]
For the Dehydrogenase activity (DHA), the higher activity was observed at 25 ◦ C during the first 30 days, which was earlier compared to the other two treatments. These findings suggest that temperature can enrich microbial activity during the first phase of vermicomposting, which may imply that sludge decomposition mainly occurred in the first 30 days
Amounted to 164, 256, and 340, respectively. These results suggest that high temperature conditions can strongly increase the number of bacterial species, forming a different bacterial community in the final vermicompost
Summary
With the development of China in recent years, the government has built thousands of wastewater treatment plants, generating large amounts of dewatered sludge with several pollutants that are difficult to be treated [1,2]. Vermicomposting is a biochemical method for converting sludge into high-value organic microbial fertilizer by the joint action of earthworms and microorganisms [4,5,6,7]. Plenty of vermicomposting factories for treating sludge have been recently established in China allowing them to profit highly from vermicompost and vermiculture in the process. Both earthworms and microorganisms play important roles in the decomposition and conversion of sludge [8]. Earthworms make a larger contribution to sludge stabilization through gut digestion, mucus production, and casting
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