Evaluation of the biosolids compost maturity in south Isfahan wastewater treatment plant

The composting process is a useful method of producing a stabilized material that can be used as a source of nutrients and soil conditioner. Maturity of compost is essential for its optimal use as a soil amendment and a source of plant nutrients as well. Immature composts pose problems of malodors and flies and phytotoxicity and pollution during use. Stability and maturity both are required for compost quality control. Compost maturity tests can be classified into physical, chemical, plant, and microbial activity assays. In this study, several methods of evaluating the stability and maturity of composted biosolids were compared based on chemical and biological properties. The sludge used of windrow composting was obtained from the drying beds of South Isfahan wastewater treatment plant. The results showed that, C/N ratio after 100 days of composting reached to 15/1; NH[4]/NO[3] ratio decreased with increase of the time dewatered sludge compost, which this loss is 57.3%. The content of volatile solids, 28.8% decreased with composting time. The number of fecal coliforms in the initial sewage sludge compost was 17.9 x 10[6] and at the end of composting was 898MPN/g of total solids and the compost process provided class A pathogen criteria. Use of chemical and biological parameters exhibited three phases: rapid decomposition [day 40], stabilization [day 80] and maturation [day 100] in biosolids compost. Thus, the biosolid compost was mature and ready for use as an agricultural substrate after about 100 days of composting

Combined compost and vermicomposting process in the treatment and bioconversion of sludge

Traditional thermophillic composting is commonly for treatment of sludge. A related technique as vermicomposting process, using earthworms to breakdown sludge, is also becoming popular. These two techniques have their inherent advantages and disadvantages. The combined approach suggested in this study to enhance the overall process and improve the products qualities. Two systems,vermicomposting and combined compost vermicomposting processes, have been investigated in this study. The sludge used in this study was obtained from the drying beds of South Isfahan wastewater treatment plant.The sludge mixed with sawdust to provide C/N ratio of 25/1.Eisenia fetida was the species of earthworms used in the vermicomposting processes.The results obtained indicates reduction in the amount of volatile solids,total carbon and C/N ratio with the vermicompost age,which indicates the reduction in the biodegradable organic content and mineralization of sludge. Also increase in phosphorus concentration by the end process because of mineralization of organic matter. The results indicate that, a system that combines the two mentioned processes not only shortens stabilization time, but also improves the products quality. Combining the two systems resulted in a product that was more stable and homogenous; the product could meet the pathogen reduction requirements