Basic Research On The Sewage Sludge Compost And Its Application In Agriculture

With the increase of municipal wastewater treatment plant (WWTP) in China, thedisposal of the waste sludge has become an urgent environmental problem. This papertried to seek a feasible way to dispose the sewage sludge from the view of agricultureapplying. The sludge from a town WWTP was firstly composted to fertilizer, whichwas used for corn plantation. On the other side, heavy metals were leached from thesludge of another WWTP by biological methods. The conclusions were as the follows:(1) The moisture content of the mixture was decreased from45%to23%duringcomposting process. The total nutrient content of the mature compost was56.15g/kgwhich including total nitrogen (N), total phosphorus (P2O5) and total potassium (K2O).The mortality of worm eggs could reach to100%and the value of the coliform was0.043. The above results indicated that the composted sludge could meet the standardof "Disposal of Agricultural Sludge from Urban Sewage Treatment Plant"(GJ/T309-2009). The index of seed germination was54.9%for the mature compost, and theconcentrations of all heavy metals tested were lower than that in of the "ControlStandards ofAgricultural Sludge Pollutant".(2) The sludge’s physicochemical properties and nutrient contents weresignificantly improved after the composted sludge was used for planted corns. Thecontents of available nitrogen, phosphorus and potassium in the soil with compostedsludge as fertilizer were respectively3.07,1.91and6.36times higher than that in thesoil with the contents in the chemical fertilizer at the end of the test. In addition, thebiological parameters of the soil were also significantly improved when compost wasused as fertilizer. Moreover the compost could promote the growth of the plants, height and stem diameter. However used too much sludge had a bad influence on the corn’sbiomass was affected by the compost sludge, which may be attributed to theaccumulation of heavy metal in the soil.(3) Both the thiobacillus ferrooxidans and thiobacillus thiooxidans had a superability to leach Cu, Zn, Cr and Pb. Compared with thiobacillus thiooxidans to bio-leachheavy metals, thiobacillus ferrooxidans (especially with the inoculation of10%) wasmuch better. The removal order of heavy metals by the two strains from high to lowwas Zn, Cu, Cr and Pb, indicating that both of the two strains could leach heavy metalsbiologically from the waste sludge. For the ferrooxidans thiobacillus, the leachingeffeciency of Zn, Cu, Cr and Pb was respectively82.5%,82.3%,46.9%and23.2%atthe end of the experiment.