Author: Nwakwegu Amaechi Sampson
Department: Applied Microbiology
Affiliation: Nnamdi Azikiwe University

Comparative evaluation of the use of compost manure, artificial fertilizer (NPK 15:15:15) and natural attenuation in the bioremediation of diesel polluted agricultural soil was carried out in this study. The total culturable microbial counts of the polluted soil over time using spread plate method were also evaluated. The total microbial counts increased progressively between week2 through week4 after an observable growth lag between week zero and week 1. The natural attenuation option showed very slight rate of increase in its microbial growth. All the treatment options demonstrated progressive increase in microbial growth but not at the same rates and counts as higher microbial growth/loads occurred in the compost amended option, followed by N.P.K fertilizer amended option and natural attenuation. Statistical analyses depicted that there was a significant difference at (p<0.05), level for the three conditions (compost, fertilizer, and natural attenuation). It was therefore concluded that the contents of the compost manure played role in rapid microbial multiplication. Relatively alkaline pH was observed in the treatment options with slight acidity among the artificial fertilizer amended option. The total petroleum hydrocarbon (TPH) of the polluted soil decreased with time in the different options as gas chromatographic analyses revealed 19.0 – 78% for natural attenuation, 11.0 – 89% for the N.P.K amended option and 68.0 – 93.0% for the compost amended option. The degradation rate however, was higher in the compost amended option than the other options. Experimental results fitted into second reaction of kinetic orders with preferred results obtained in both r2values and reaction half-life (t1/2). The hydrocarbon utilizers isolated included; Bacillus nealsoni, Micrococcus luteus, Aspergillus awamori, and Fusarium proliferatum as confirmed by sequencing results. In the ecotoxicity assessment, the maize grain germinated in both natural attenuation and N.P.K fertilizer amended options only on the week8 with germination indices of 34.0% and 56.0% respectively whereas germination occurred in week6 through week8 in the compost amended option with germination indices of 38.0%, and 89.0% respectively. This invariably confirmed that effective microbial remediation was established earlier in the compost amended option. The root elongation and shoot length showed no observable differences among the treatment options. The study therefore, showed that use of organic nutrients like compost in the bioremediation of diesel impacted agricultural soil should be encouraged for large scale biorestoration efforts.

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