Pyrolytic conversion of sewage sludge to biochar and its application in agriculture is an effective method for management of sludge in an acceptable environmental and economic way. Pyrolysis of sewage sludge could potentially be a method of choice for sludge management, especially in comparison with conventional landfilling methods and its direct application in agriculture. This process, while reducing the volume of solid residues and eliminating pathogens in the sludge, also has positive consequences on soil properties. The aim of this study was to produce biochar from pyrolysis of sewage sludge and to eva‎luate the effects of the biochar on the physical and chemical properties of the soil as well as the growth of wheat plant. In a preliminary experiment, the sewage sludge was pyrolyzed at two temperatures of 250 and 450° C and converted to biochar. Subsequently, the produced biochars were applied as soil amendments in a greenhouse study. Treatments included two types of pyrolyzed biochar at 250 ° C (B250) and 450 ° C (B450) and 4 amounts of biochars along with control and a total of 27 experimental samples in the greenhouse. This factorial study was conducted in a completely randomized design with three replications. The results showed that the addition of biochar to the soil reduced the apparent density of the soil. Soil treated with 4 levels of B250 and 0.5 and 1% of B450 had more hydrophobicity and soil-water contact angle than the control. With increasing field capacity and permanent wilting point in the applied treatments, the available soil moisture in the four levels of B250 and B450 significantly increased. The fitted alpha parameter in Wengnokhten model had a significant increase at different levels of B250 as well as 2% and 4% of B450 and decreased at 0.5 and 1% of B450. The n-parameter decreased in the soils treated with 0.5, 1, 2 and 4% of B250 and B450 compared to the control. Saturation moisture percentage increased in the soils amended with four levels of biochars. The dry weight of wheat plants increased with the addition of 0.5, 1 and 4% of B250 and all the levels of B450 to the soil. The use of 0.5, 2 and 4% of B250 and 0.5, 1, 2 and 4% of B450 increased plant nitrogen uptake. The uptake of iron and zinc by the plant was not statistically significant at the level of 0.5% but the concentration of these elements increased in all treatments. Application of all levels B250 and B450 increased the total soil nitrogen compared to the control sample. Soil bioavailable phosphorus in the soil treated with 2% of B250 and 4% of B450 had a significant increase compared to the control. The effect of biochar on soil available potassium and iron as well as pH and EC was not significant. The amount of available zinc in the soil treated with 4% of B250 and 2% of B450 had a significant increase compared to the control. Addition of biochar also significantly increased the percentage of soil organic carbon. In conclusion, the addition of sewage sludge biochar to the soil as a conditioner improved the physical and chemical properties of the soil and the growth of the wheat plants.

مجيد افيوني، مهران شيرواني

بنفشه خليلي

محمدرضا مصدقي، حميدرضا عشقي زاده