Heavy Metal Remediation in Sludge Compost: Recent Progress

The safe and efficient disposal and utilization of sludge are major issues to be solved in solid waste treatment and environmental protection due to the complex characteristics of sludge and the low rate of innocuous treatments.Composting is a process of decomposing organic matter and transformed low-molecular organic acids into high-molecular humus substances under the action of microorganisms.Although land-use after composting has become an important direction for sludge treatment,heavy metal pollution is still the bottleneck problem restrict-ing land use of sludge compost.Adding zeolite,hydroxyapatite,and other conditioning agents to the composting process affects the concentration or form of some heavy metals and effectively reduces the environmental risk.Lime and phosphorus modifiers change heavy metal speciation in samples,playing a role in decreasing biological availability and mobility.In this study,the effects of sludge composting treatment and conditioning agents on the concentrations and forms of heavy metals are reviewed.This review will provide a theoretical basis to treat heavy metals in sludge composting and lay the foundation for the land utilization and waste recycling of sludge.

Feasible strategy for the nitrogen fixation and humification quality improvement by spent mushroom substrate as conditioning agent

There is an overlooked problem which increasing microbial abundance while reducing nitrogen loss during composting.This study investigated the viability of spent mushroom substrate(SMS)as conditioners in the aerobic composting of kitchen waste(KW)with cattle manure(CM).The variation of temperature,pH,C/N,organic matter,cellulose,hemicelluloses,germination index(GI),and microflora structure were explored to evaluate the potential in accelerating maturity and nitrogen fixation by SMS addition.The results showed that the addition of SMS accelerated the heating rate,prolonged the high temperature time,and decreased organic matter,hemicellulose,and cellulose by 17.49%,23.61%,and 18.62%,respectively.The GI reached 105.86%with SMS addition,while 74.17%was found in control treatment after composting.SMS changed the microbial community composition and increased the species abundance.Proteiniclasticum,Clostridium XI and Azomonas were dominant bacteria,which increased the retention of nitrogen,promoted organic matter degradation and reduce compost time.The study can provide a feasible strategy for nitrogen fixation in the field of organic waste recycling.