Utilization of Banana, Pineapple and Watermelon Wastes-Substrate: As Consortiums to Remediating Cyanide Polluted Soil

Abstract

The act of processing cassava for varied food products has come with unguided and wide-spread contamination of cyanide in the environment. The need for effective reduction in cost to enable remediation of cyanide-contaminated sites from cassava mill factories is the purpose of this investigation. This involves bio-stimulation of organic wastes with indigenous microorganisms to degrade cyanide. The application of organic wastes as a substrate for the removal of cyanide was adopted. Banana, pineapple, and watermelon wastes were selected and bio-stimulated in cyanide contaminated soil. Each set-up containing 100 g of Cassava Mill Effluent (CME) contaminated soil was added with varied percent - 1, 5 and 10% of pineapple, banana, and watermelon waste, respectively. The monitoring of cyanide reduction was studied for 28 days. Periodic collection of soil samples from each set-up was done at four days interval to determine total cyanide concentration, total heterotrophic bacteria, and enzymes activities. Results indicated that after 28 days of applying the 10% watermelon, 5% pineapple and 1% banana waste, the 10% watermelon waste gave a better cyanide reduction compared to pineapple and watermelon waste treatment. The one phase-decay equation of 1% - banana, 5% - pineapple and 10% - watermelon waste treatment gave the shortest disintegration rate. The soil physicochemical properties, agro waste, microbial population, soil enzymes activities, soil microbial respirometric index, the bio-parameters sensitivity, carbon, nitrogen, and phosphorus were determined. The first order kinetics model revealed by the nth order algorithm; pineapple waste treated soil had the highest reduction rate - 0.9098/day of CME with half-life - 6.98 days. The 1% banana and 10% watermelon treated soil samples have the cyanide reduction rates - 0.9315/day and 0.8997/day. The cyanide reduction rate was significantly higher than the untreated contaminated CME (control) soil - 0.8975/day. The microbial counts and the three agrowaste treatment samples increase in day 4-16 (2.20×10⁸ to 6.40×10⁸ CFU/g) for 5% - pineapple; 1% - banana increased from 20×10⁸ to 8.90×10⁸ CFU/g (day 20 - 28) and 10% - banana increased -1.20×10⁸ to 8.70×10⁸ CFU/g (day 4-20); 1% - watermelon increased from 8.40×10⁸ to 8.80×10⁸ CFU/g (day 20-24) and 10% watermelon increased from -8.10×10⁸ to 8.70×10⁸ CFU/g (day 24-28), than the control which showed increase from 3.40×10⁸–7.20×10⁸ CFU/g (day 4-12) during the 28 days of remediation study. Soil organic carbon content gave a positive correlation with microbial biomass, carbon, nitrogen, and phosphorus, as well as microbial population, basal soil respiration and soil enzyme - catalase, lipase, dehydrogenase, urease and phosphatase activity. Soil contamination decreased (p<0.05) catalase, urease and dehydrogenase activities in all the waste treated soil compared to the control set-up. Owing to the use of this agro-waste-banana, pineapple and watermelon has proved to be effective in enhancing soil nutrient, improved soil enzymes activity and removed of cyanide from CME contaminated soil.