Comparison of the effects of two forms of organic stimulation on the bioremediation of monocyclic-aromatic hydrocarbon in soils

Authors

  • S. U. Oghoje
  • J. E. Ukpebor
  • E. E. Ukpebor
  • C. Ejeomo

Abstract

The mono-cyclic aromatic hydrocarbons (MAHs) particularly benzene, toluene, ethyl benzene and xylene generally classified as the BTEX are among the persistence organic pollutants (POPs) prevalent in our environment. They are often referred to as recalcitrant compounds due to their resistance to biodegradation thus, their remediation from soils need special and very effective bioremediation techniques. This study was therefore designed to investigate the use of locally generated manure digestates as nutrient supplement for landfarming of BTEX polluted soils in comparison to the conventional use of animal composted manures. The soil samples were spiked with 4% diesel and 1% BTEX and Naphthalene (at 0.2% each) and were treated with 10 or 20% of the two manure forms. The effects of various treatments on the removal of the BTEX from the soil was monitored for 336 days with periodical sampling at day 1, 14, 28, 56, 84, 168 and 336. The concentration of individual BTEX at various sampling periods was evaluated using GC – FID and the bioremediation potentials of the nutrient supplements were also assayed. Results obtained indicated an increase in the concentration of benzene at the early stages of the remediation protocol; with concentration of benzene increased from 1580 mg/kg at day 1 to 1661mg/kg at day 14 in the control samples and for the nutrient stimulated samples; benzene increased from 1501 to 1554mg/kg and from 1471 to 1608  for composted manure (CLM) treatments; 1457 to 1564  and from 1530 to 1638 mg/kg for manure digestates (CLD) treatments at the same period of remediation with 10 and 20% treatments respectively. However, significant percentage removal of benzene was noticed as the remediation period prolongs with values ranging from 0.59 - 20, 0.67 – 41, 2.54 – 36, 12 - 28 and 15 – 42%  in the control (PSC), 10% CLM treatment (CLM10), 20% CLM treatment (CLM20), 10% CLD treatment (CLD10) and 20 % CLD treatment (CLD20) respectively from day 14 or 28 to day 336. For the BTEX, their percentage removal ranged from 1.56 – 36, 1.83 – 58, 1.50 – 57, 2.43 – 56 and 1.75 – 84% in the PSC, CLM10, CLM20, CLD10 and CLD20 in samples respectively. It was observed the CLM had more nutrient (with respect to nitrogen and phosphorus) than the CLD as nutrient supplements but with lesser hydrocarbon utilizing microbes than the CLD. Specifically, the HUB and HUF were  7.0 x 103 and1.2 x 104 respectively (for CLM) and 1.6 x104 and 1.3 x 104 respectively for CLD. The results have revealed that the manures digestates treatment led to highest removal of benzene as well as the BTEX generally, which may be attributed to the population and diversity of hydrocarbons utilizing microbes in them. Consequently, animal manure digestates would be a better nutrient and microbial inoculation enhancement for optimal remediation of benzene and other members of the BTEX family in particular and the hydrocarbon pollutants in general. Key Words: Organic stimulation, Bioremediation, Monocyclic-aromatic Hydrocarbon, Soils

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Published

2020-05-23