Contents of heavy metals and available nitrogen in the compost of sewage sludge and rice straw

This study evaluates the changes of physicochemical properties during the compost of sewage sludge and rice straw in different proportion.The changes of NH+4-N and NO-3-N content after composting for sixty days are assessed.The value of the total and EDTA extracted metals including Zn,Cu,Cr,Pb,Cd and Ni is also detected.The final results indicate that the content of NH+4-N is decreased from 33.21% to 47.71% during the composting,and the NO-3-N is increased from 18.23% to 35.12%.The mixture causes a significant increase in total heavy metal concentrations than initial materials and deactivates the heavy metals in rice straw.The increase in Cd content is 21.31%,which is higher than other heavy metals.But the reduction in bioavailability of heavy metals contents in sewage sludge is about 18.42%.The compost effect is better when the mass ratio of sludge and rice straw is 4∶1.