Bioremediation of Petroleum Hydrocarbon-contaminated Soil Using Activated Sludge Derived from Vitellaria paradoxa Seed Wastewater

Contamination of soil with petroleum hydrocarbons (HCs) is a serious environmental challenge, posing severe immediate and long-term impacts as many of their constituents are potentially toxic, mutagenic and/or carcinogenic. In this study, activated sludge derived from Vitellaria paradoxa nut wastewater was evaluated for its most effective component in bioenhancement of a sandy soil that is low in nutrients and endogenous microbial affinity for HCs (<10% of HC concentrations converted to CO2 in 30 d). Soils contaminated with aviation fuel, kerosene, petrol, diesel and crude oil (1%w/w and 2%w/w) were bioenhanced with (i) HC-adapted mixed-culture degraders derived from activated sludge (bioaugmentation only), (ii) sterilised sludge (biostimulation only), and (iii) activated sludge (combined bioaugmentation and biostimulation). Mineralization, substrate-induced respiration, microbial biomass-C and PAH-degrading Pseudomonas population were monitored in the HC-contaminated soils over 30 d using standard methods. A consortium of HC-adapted degraders (applied at 1.2×106 cfu·gsoil–1) consistently produced significantly (p < 0.05) greatest extents of HC mineralization (362–450 vs. 58–87 mgCO2·10gsoil–1 in non-amended HC-contaminated soils). There was no much difference in the enhancement using sterilised sludge or activated sludge (199–376 vs. 204–312 mgCO2·10gsoil–1 respectively). Increases in PAH-degrading Pseudomonas number from 3.4 × 104 in control soil to x.x–y.y × 106 cfu·gsoil–1 in HC-contaminated soils were observed. Ecophysiological indices (e.g. microbial metabolic quotient qCO2, microbial respiratory efficiency MRE, and microbial respiratory coefficient QR) showed that the augmented degraders were well-adapted to the HC-contaminated soils with strong biodegradability, particularly to heavier HCs diesel and crude oil. This study revealed the use of activated Sludge Derived from Vitellaria paradoxa Seed Wastewater in bioremediation of Petroleum Hydrocarbon-Contaminated Soil could serve as a potent and applicable non-toxic method for degradation of hydrocarbon for contaminated land for resiliency.