Production of Liquid Organic Fertilizer from Sewage Sludge with Reduced Heavy Metal Toxicity via Chemical and Organic Treatments.

The usage of sewage sludge in agriculture has increased the accumulation of some heavy metals (such as cadmium, copper, lead, etc.) in soil and plants, due to the high concentration of these elements. Therefore, this research was conducted to investigate the best method to reduce the toxicity of heavy metals in sewage sludge while causing less environmental pollution. This approach utilized NaOH and HCl, along with humic and fulvic acids, to precipitate heavy metals from sewage sludge complexed with heavy metals in sludge to reduce the concentration of heavy elements and produce liquid organic fertilizer. In this research, the concentration of heavy metals (As, Cd, Cu, Ni, Pb, and Zn) in the sewage sludge, humic, fulvic, and liquid organic fertilizer were measured. Also, the humic, fulvic, and the produced organic fertilizer were tested on corn plants in terms of two treatments (10%, and 20%) and the heavy metals of those were analyzed. All experiments were conducted in three replications. The results showed the values of heavy metals in the humic, fulvic and liquid organic fertilizer were lower than the acceptable contents of EPA. The content of these elements in corn plants treated with humic, fulvic, and liquid organic fertilizers were lower than the EPA standard. Therefore, this liquid organic fertilizer can be used as two concertation (10% and 20%) for plant nutrition and compared to chemical fertilizers, is not only economically cost-effective, but also does not have the pollution caused by the use of chemical fertilizers.