Abstract:

In order to study the basic physical and chemical properties, available nutrients, change of heavy metal forms of the compost before and after composting and the influence of zymophyte on composting effects during aerobic composting systematically, the experiment of thermophilic composting for excess sluge from No.3 WWTP was carried out by turning the pile manually. The results showed that throughout the 35 days of composting, organic matter degradation rate of two composts adding zymophyte or not (compost A and B) were 30.38% and 30.32%, respectively, nitrogen loss rate were 24.58% and 23.69%, respectively, available nitrogen, phosphorus and potassium increased to some extent. Germination index reached 59.3% and 55.6%, respectively, the effect of whether adding zymophyte or not was not significant on composting. The heavy metal forms analysis by sequential extraction method indicated that Cu largely existed in the form of X-NaOH and X-HNO3, and Zn, Pb X-EDTA, while X-(KNO3+H2O) fraction of Ni was relatively high. Bioavailability of Cu, Zn, Pb and Ni tended to decrease to some extent after composting, with Ni exceeding 50% which decreased greatest. It was expected that the test results derived from this study might be valuable to utilization of sewage sludge from waste water treatment plants in Xi’an City.