PHYTOTOXICITY EVALUATION AND SANITATION ASSESSMENT OF BIOSOLIDS FOR AGRICULTURAL PURPOSES

Abstract

The use of municipal biosolids for agriculture can be restricted because of the presence of heavy metals in them. This study assessed the ecotoxicity and bioavailability of heavy metals in municipal biosolids while considering metal speciation. Next, biosolids were added to the soil in a pot system at varying ratios to observe the uptake of HMs in wheat grass and their assemblage in the soil. Dewatered biosolids collected from 10 STPs located in Uttar Pradesh, Uttarakhand, and Delhi were characterized. They were then matured for 2 months with periodic turning, during these 2 months phytotoxic evaluation was done by performing seed germination tests at 0, 15, 30, 45 & 60 days. Finally, heavy metal speciation and the total concentration of heavy metals were evaluated. Phytotoxicity of biosolids was evident during the initial 30 days of maturation of biosolids and after that the concentrations of the inhibitors, ammonia, and water-extractable metal, decreased as the process progressed, suggesting that these inhibitors were gradually reduced. Throughout 45 to 60 days of maturation, root elongation, and seed germination could reach 90–106%. By day 45, all of the biosolids in the current study had Gl's more than 80%, indicating that the biosolids had attained their mature condition by 45-60 days. According to the review of the literature, NH4-N was a key inhibitor that causes phytotoxicity in the early stages of maturation. An increase in seed germination and root elongation was accompanied by reduced NH4-N levels. The following heavy metal concentration order was discovered in biosolids: Zn > Cr > Cu > Ni > Pb > Cd > Mo > As > Se. Although land application has emerged as a promising method for recycling sewage sludge's resources and energy, more research needs to be done in India on how applying biosolids affects the concentrations of toxic metals in the soil. In the present study, the bioavailability of heavy metals is examined by taking metal speciation into consideration. The BCR sequential extraction technique was adapted to investigate the metal speciation. Experimental research revealed that the biosolids gathered from the ten sewage facilities were usually rich in organic matter, nitrogen, and phosphorus. After characterization and maturation, the biosolids were applied to agricultural land in three different ratios: 2%, 5%, and 10%. With 10% biosolids applied to the soil as compared to 2% or 5%, wheatgrass attained more length but also contained more heavy metals than 2% & 5%.