The use of irradiated wastewater sludge cake to increase soil fertility and crop yields, and to preserve the environment

A 4-year field experiment was conducted to compare the effects of ammonium sulphate and irradiated wastewater sludge cake on growth, yields and uptake of N by maize (Zea mays L.). Six crops were grown. Heavy metals were determined in soil and plant. Total coliforms and some soil properties were determined after harvest. Results of experiments showed that wastewater sludge cake from Sripraya wastewater-treatment plant can be used for agricultural application. In the third application of sludge cake (fourth year of the experiment) dry weight and N uptake at the higher rate of sludge-cake application gave better results than did chemical fertilizer. Nitrogen was residual from the sludge cake, but not from chemical fertilizer. Nitrogen derived from sludge cake (Ndfss) was calculated for the whole experiment; %Ndfss values were higher when the frequency of application increased and with higher application rates of sludge cake. Plots receiving higher rates of sludge cake gave higher percent fertilizer-use efficiency (%FUE) values. Comparison of irradiated sludge cake and non-irradiated sludge indicated that the latter gave higher values in terms of maize yields, N uptake, %Ndfss and %FUE. Zinc, Mn, and Ni were detected in maize in the order Zn>Mn>Ni. Copper, Pb, Cr, and Cd were not detected. The concentrations did not increase with higher application of sludge cake. Micro-organisms, yeasts and molds, and coliforms, including Escherichia coli were reduced in number by irradiation. Some pathogens, such as Salmonella, Staphylococcus aureus, Ascaris ova were not found in the wastewater sludge cake. Sludge-cake applications had no influence on soil properties, consistent with lack of treatment effects, in the first 2 years of the experiment. (author)