Recovery of Residual Sludge From a Wastewater Treatment Plant. Impact of Sluge-Soil Mixture on the Growth of Tomato Solanum Lycopersicum L.

Abstract

Sewage sludge is used as a fertilizer in agriculture to rehabilitate deteriorated soils and replace artificial fertilizers. Sludge can be utilized to improve soil characteristics, promote microbial life, and increase plant production where it includes the primary nutrients and organic matter. The current study investigated the impact of the treatment of sewage sludge on the physico-chemical characteristics of the soil, and also on the growth of tomato (Solanum lycopersicum). The experiment consists of using a sludge-soil mixture, with different fractions of sewage sludge: soil control (0% sludge) and 20%, 40%, 60%, 100% of sludge. Biometric measurements (height, stem diameter and number of leaves) were performed on the tomato. The results showed good fertilizing properties of a sludge/soil mixture with the 60% sludge fraction. However, the tomato that grew on the 40% fraction had better growth and high foliage compared to the plants on the other fractions. The spreading of sludge provides a soil amendment and an additional supply of nutrients for tomatoes. The use of 40% fraction of sludge spreading for the cultivation of this plant can maintain better soil fertility while reducing the risk of heavy metal accumulation. Indeed, the 40% fraction of sludge has concentrations which are: 86±0.40 mg/kg for copper, 294 ±0.40 mg/kg for zinc and 50±5.9 mg/kg for lead, lower than the limits recommended by the European directives.