Effect Of Co-digested Sludge Application On Infertile Soil Properties And Vegetable Growth

Sewage sludge contains high content of organic matters and plant nutrients, but some potential toxic substances such as heavy metals, organic contaminants and pathogens might impact environmental quality and human health. Anaerobic digestion can reduce sludge amount, stabilize sludge, kill pathogens, and recover energy. The addition of food wastes, and fruit and vegetable wastes can promote the efficiency of co-digestion. Agricultural use of co-digested sludge may be an effective method for the sewage sludge disposal and soil improvement.In this study, co-digested sludge was applied in agricultural use via plot experiments. Two vegetable species, radish (Raphanussativus) and Chinese cabbage(Brassicachinensis), were chosen as test plants. Effect of co-digested sludge application on soil physical properties, soil nutrients, soil heavy metals, and their uptake and accumulation by vegetables were studied, and the soil improvement and application risk were evaluated.The results showed that radish and Chinese cabbage growth was significantly promoted by the co-digested sludge application within the range of675-3760kg/hm2. The radish root biomass for the CDS(108) and COD(150) respectively increased by159%and467%, and the cabbage leaf biomass respectively increased by369%and1050%, compared with the blank. The soil physical properties including bulk density and porosity were little influenced by the co-digested sludge application, and their change were less than1.5%, however, capillary porosity increased6.48%and non-capillary porosity decreased7.17%due to the plant growth. Content of organic matters, hydrolysable nitrogen, total nitrogen, total phosphorus and available phosphorus in soil increased with the co-digested sludge application, and the largest increase of five kinds of nutrients was51%,125%,212%,15%and87%, respectively, compared with that in blank. A linear relationship (R2≥0.790) was observed between the soil nutrient increase and co-digested sludge dosage. The nitrogen and phosphorus uptake by vegetables increased, while the total potassium content in soil and vegetables was little influenced by co-digested sludge application. After co-digested sludge application, Zn, Cu and Cd were accumulated in soil and vegetables, and the largest rises of them were16%,17%and69%, respectively. However, the content of all kinds of heavy metals in the soil was lower than the limits of the secondary standards in environmental quality standard for soils, and Nemerowint index of the soil for each treatment was below0.7. The content of heavy metals in edible part of vegetables was lower than the limits of contaminants in foods. The co-digested sludge has the potential to improve soil productivity as a fertilizer or soil conditioner.