Efficiency optimisation of sewage sludge usage for soil fertilisation

Abstract

Sewage sludge is forming in the process of treating household and industrial sewage. If sludge is improperly treated or untreated at all this poses danger to the environment. Efficient ways of sludge treatment and usage are sought worldwide. One of the cheapest and economically beneficial ways of sludge application is its usage for soil fertilization. The possibilities of sludge usage are restricted by sludge quality. Its suitability for fertilization is determined by the microbiological-parasitological parameters of sludge and content of heavy metals in it. Quality sewage sludge from a dairying company was used for the experimental research. This sludge was distinguished by low contents of heavy metals and high concentrations of plant nutrients. During the experiment plants were grown in mixtures of soil and sewage sludge mixed up at different proportions. The optimum amounts of sewage sludge and soil were established experimentally. Different versions of sludge and soil mixtures were used during the experiment. Due to an insufficient number of sludge and soil mixture variants efforts were made to determine the optimum sludge and soil ratio by mathematical modelling, which depends on certain parameters. These parameters were selected according to experimental data through the application of the method of least squares. When applying the method of least squares the unknown parameters of this model were determined by minimising the square-error.