Impact of substrate amendment on the polyaromatic hydrocarbon contents of a five month old waste engine oil polluted soil

Abstract

The present study investigated the impact of substrate amendment on the bioremediation of waste engine oil-polluted soil. Top soil was collected randomly from a 50 × 50 m marked plot on a farmland, sun-dried and weighed. Ten kilogram’s of soil each was placed into perforated 25 L buckets. Waste engine oil (WEO) was prepared at 5 different levels of pollution: 0, 1.0, 2.5, 5.0, and 10.0% w/w, and poured into the measured soil, and thoroughly mixed. The entire set up was left under an open shade for 5 months without mechanically disturbing the soil, after which the polluted soil was amended with sawdust and left for a further 9 months. Significant reductions in polyaromatic hydrocarbon (PAH) content of soils over the experimental period were recorded. Total (100%) remediation of some PAH compounds (benzo[a]anthracene, benzo(a)pyrene, benzo[b]fluoranthene, benzo[g,h,i]perylene, benzo[k]fluoranthene, chrysene, dibenzo[a,h]anthracene, fluoranthene, fluorene, and indeno[1,2,3-c,d]pyrene) was recorded. Total PAH ranged from 1.10 to 6.35 mg/L in the substrate-amended treatment compared to a range of 25.45 to 456.99 mg/L in the unamended soil. Toxicity equivalencies (TEQ) in the unamended soils were generally higher than benchmark values, implying that the cleanup levels were not met. In the amended treatments, however, TEQs were presented for only benzo[a]pyrene (0.7284) in the control and indeno[123-c]pyrene (0.0272) in 2.5% w/w oil in soil treatment. TEQ’s of benzo[a]pyrene in the amended 5% w/w oil in soil treatment was 3.1252 mg/L, also higher than the benchmark TEQ of 1.0 mg/L.

Key words: biooremediation, substrate amendment, polyaromatic hydrocarbon.