Mineralization of Pyrene in Clay Soil Supplemented with Animal Organic Carbon Source

Abstract

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) is a major concern in the environment due to their toxic nature and ubiquitous occurrence. The study aimed to determine the best animal supplement of organic carbon source (cow dung, goat dung, pig dung and poultry (chicken) droppings) and indigenous microbes capable of mineralizing pyrene in clay soil. Clay soil sample was collected from the top surface soil (0 – 15cm) in Ikpoba River and upper Lawani river bank, both in Benin City with the aid of stainless steel trowel and gloved hands and stored in a polyethylene bag. The isolation and identification process was evaluated by staining method, microscopic examination and biochemical tests. The degradation experiment was conducted in bioreactors and supplemented cow dung, pig dung, goat dung and fowl droppings were added in varying amounts of 25 g, 50 g, 75 g and 100 g. The potential effects of animal organic carbon as nutrient supplements to enhance mineralization of pyrene were investigated. The rates of biodegradation of pyrene were studied for a remediation period of 35 days at the room of about 25°C. Results obtained from microbial isolation showed that Bacillus substilis and Aspergillus niger were the most populated in the soil and were therefore selected. The degradation experiment showed that mixed culture of B. substilis and A. niger using 50 g supplement with the dungs and droppings gave the highest percentage degradation with goat dung 97.8%, pig dung 98.1%, cow dung 97.7% and fowl droppings 98.3%. The least degradation was observed in supplement with 100g in a single culture of A. niger with fowl droppings yielded 64.5% degradation, pig dung 63.8%, goat dung 63.7% and cow dung 62.7%. The overall results of the study showed that 50g of animal wastes supplement in the ratio of 1:4 with pyrene contaminated soils are most effective in degradation processes.