Abstract
Sewage sludge is a very complex system, with solids and water. It is generated as waste from wastewater treatment. Sewage sludge is used to fertilize agricultural and forest areas and to rehabilitate devastated areas. It is a good organic fertilizer because it contains significant amounts of nutrients beneficial for plant development and humus-forming substances. The composition of sludge from municipal wastewater treatment plants is similar to soil organic matter, therefore it can be used to improve the physicochemical properties of soil, increasing its sorption capacity. Research material was collected in the Swietokrzyskie and Mazowieckie Voivodships. Sewage sludge was collected from the wastewater treatment plants in Sitkowka Nowiny (Sitkowka) and Kunow, as well as high-quality agricultural soil from Opatowiec and sandy-clay soil from Jastrzebie. Research was carried out on the sorption of heavy metals (Cd, Cr, Cu, Pb, Ni, Zn) by mixtures of sewage sludge with soil. The calculations were made for the concentrations of heavy metals in sewage sludge, soil, and sewage sludge–soil mixtures. The geoaccumulation index (Igeo) and the risk assessment code (RAC) were calculated. Increased sorption capacity was demonstrated in samples with a predominance of sewage sludge. It was shown that heavy metals from sewage sludge, after mixing with soil, changed their form from immobile to mobile.
Highlights
The rapid pace of the development of civilization and industry causes the degradation of the natural environment, and special attention should be paid to large urban agglomerations, areas around industrial plants, and a number of small towns
A favorable solution may be the use of sewage sludge in agriculture, because it is the cheapest method for their disposal and allows for a significant reduction in the consumption of mineral fertilizers
It is assumed that if the content of heavy metals in these sediments is lower than or equal to the permissible value, they lose the features of the sewage sludge and can be used as mineral-organic fertilizer [3,4]
Summary
The rapid pace of the development of civilization and industry causes the degradation of the natural environment, and special attention should be paid to large urban agglomerations, areas around industrial plants, and a number of small towns. Our health is exposed to the influence of polluted air, soil, water, and chemical substances contained in food [1,2]. Soil is a natural resource necessary for the survival of human life, but it accumulates toxic compounds (heavy metals), and there is a high probability of these pollutants getting into groundwater and the trophic chain. A favorable solution may be the use of sewage sludge in agriculture, because it is the cheapest method for their disposal and allows for a significant reduction in the consumption of mineral fertilizers. It is assumed that if the content of heavy metals in these sediments is lower than or equal to the permissible value, they lose the features of the sewage sludge and can be used as mineral-organic fertilizer [3,4]
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