Biodegradation of Waste Drilling Mud Using Spent Mushroom Substrate

Abstract

Biodegradation of waste drilling muds (WDM) was carried out with the aim to investigate the efficacy and applicability of spent mushroom substrate (SMS) for enhanced bioremediation of impacted mangrove swamp. Microcosm study was carried over a 60-day period. Microbial population dynamics of waste drilling muds utilizing bacteria/fungi in the mangrove soil sediment (MSS) undergoing bioremediation was investigated. The experiment was done in four Set-ups labelled A to D: Set-up A (WDM + MSS); Set-up B (WDM+ Sterile MSS) as control; Set-up C (WDM+ MSS + Fresh SMS) and Set-up D (WDM+ MSS + Composted SMS). Physicochemical and microbiological parameters were monitored from baseline to the 60th day, following 20 days intervals. Results obtained show that the drilling muds utilizing bacterial count ranged from 0.4X104─2.5X104 cfu/g, while drilling muds utilizing fungal count ranged from 0.2X103 ─1.5X103 cfu/g. The isolated drilling muds utilizing bacteria belong to the genera Bacillus, Corynebacterium, Citrobacter, Klebsiella, Alcaligenes, Micrococcus and Pseudomonas, and the drilling muds utilizing fungi belong to the genera Candida, Cryptococcus, Rhodotorula, Saccharomyces, Trichosporium, Geotrichum, Aspergillus, Penicillium, Mucor, Fusarium, Cladosporium, Cephalosorium, Monosporium, Neurospora, Rhizopus and Microsporium. The values of the pH in Set-ups were within the neutral to slightly alkaline pH range during the study period. The concentrations of nitrate, phosphate, sulphate, potassium and total organic carbon (TOC) of the Set-ups with fresh and composted SMS (treatment Set-ups) decreased significantly during the study period. The concentrations of heavy metals (Fe, Cu, Zn, Ni and Pb) in the SMS amended Set-ups also showed significant reductions. The percentage of total petroleum hydrocarbon (TPH) biodegraded was greater in Set-up D containing composted SMS (71.48%) than in Set-up C containing fresh SMS (67.93%), followed by Set-up A (22.69%)and the least was the control Set-up B with 8.36%. This study showed that both fresh and composted spent mushroom substrates are effective in the biodegradation of waste drilling muds contaminated Niger Delta mangrove soil sediment.