Biodrying of storage sludge and analysis of the stability and agricultural properties of biodried products

Abstract

Biodrying was first used for treatment storage sludge by adding bulking agents to reduce its moisture content and improve its quality and stability. The influence on the stability and agricultural application of biodried products after adding bulking agents was investigated by analyzing the variation of the AT4 index, organic matter, and heavy metals of biodried products. Two treatments were considered: the addition of straw (trial A) and sawdust (trial B) to storage sludge as bulking agents before biodrying. After 18 d of biodrying, trial A with straw as bulking agent achieved the higher water-removal rate by 19.24% and also had the higher matrix temperature (57°C). Additionally, the content of protein decreased by 38.45%, while the polysaccharide content only decreased by 5.96%. Additionally, the content of humic substances increased by 48.58%. Further investigation showed that most of the heavy metals transformed from acid soluble fraction to oxidizable and residual fractions, the contents of heavy metals increased insignificantly (6.29%–10.81%), and Zn content exceeded the maximum permissible value stipulated for soil in China (GB 4284-1984). Thus, the risk for farm-oriented storage sludge still exists.