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The most common approaches for the in-situ bioremediation of contaminated sites worldwide are bioaugmentation and biostimulation. Biostimulation has often proved more effective for chronically contaminated sites. This study examined the effectiveness of optimized water hyacinth compost in comparison with other organic and inorganic amendments for the remediation of crude oil-polluted soils. Water hyacinth was found to be rich in nutrients necessary to stimulate microbial growth and activity. An organic geochemical analysis revealed that all amendments in this study increased total petroleum hydrocarbon (TPH) biodegradation by ≥75% within 56 days, with the greatest biodegradation (93%) occurring in sterilized soil inoculated with optimized water hyacinth compost. This was followed by polluted soil amended with a combination of spent mushroom and water hyacinth composts (SMC + WH), which recorded a TPH biodegradation of 89%. Soil amendment using the inorganic fertilizer NPK (20:10:10) resulted in 86% TPH biodegradation. On the other hand, control samples (natural attenuation) recorded only 4% degradation. A molecular analysis of residual polycyclic aromatic hydrocarbons (PAHs) showed that the 16 PAHs designated by the US EPA as priority pollutants were either completely or highly degraded in the combined treatment (SMC + WH), indicating the potential of this amendment for the environmental remediation of soils contaminated with recalcitrant organic pollutants.

Aim: To analyse the potential risk of hydrocarbon polluted surficial soil, from a heavy-duty generator plant at Delta Campus, University of Port Harcourt, Nigeria. Study Design: Conceptual site model (CSM). Methodology:  A CSM was designed and applied prior to sample collection in order to screen for heavy metals and other chemicals of concern (COCs) from three different high-risk points. The CSM showed a credible source-pathway-receptor chain at three high-risk points. Risk assessment associated with the heavy metals was significantly reduced based on the Department of Petroleum Resources (DPR) – Environmental Guidelines and Standards for the Petroleum Industry In Nigeria (EGASPIN) values after 28 days of bioremediation study. Results: The hazard quotient of the target (COCs) namely Arsenic, Cadmium, Chromium and Lead was less than one (< 1). This suggests that the study area does not pose significant risk on both Adults and children. Conclusion: The evaluation is essential for the formulation of remedial actions and risk-based management plans geared toward risk reduction. In other words, it is an approach to the determination of imminent risk posed by a pollutant to the environmental proxies. Poor education and sensitization of the public on the causal effect of pollution have been identified as a leading cause of indiscriminate pollution of the environment.

Heavy-duty generators constitute a form of hydrocarbon pollution but enrich microorganisms to having degradative ability of hydrocarbons hence can be used for remediation. In this study a laboratory treatability (biodegradation screening) study was employed to investigate the hydrocarbon degradation competence of bacteria and fungi. Culture-dependent microbiological and physicochemical analyses was conducted on the soil samples obtained from the polluted site. The total aerobic heterotrophic bacterial and fungi counts increased from 5.0-7.5 (Log10 cfu/mL) between day 0-14 then reduced to 6.5 Log10 cfu/mL. The hydrocarbon-utilizing bacteria increased from 4.5-5.2 (Log10 cfu/mL). Percentage degradation hydrocarbons, attributed to fungi bacteria and bacteria/fungi consortia, were 42.3%, 54% and 70% respectively while the control had 6.0%. The total petroleum hydrocarbon (TPH) removal rate (K) was modelled using the first order kinetics:  y=-0.0398x+9.79; K=0.0398d-1. These results, correspond to a degradation efficiency of 70% and t1/2 of 17 days for the bacterial/fungal consortium. The K values for the other setups were 0.019 d-1, 0.0261 d-1 and 0.0022 d-1 with the corresponding degradation efficiencies of 42%, 54% and 6.01% and half-life of 37 days, 27 days and 315 days for fungi, bacteria and control respectively. This result indicates that the use of microbial consortia has high potentials in remediation of hydrocarbons and other pollutants of concern.

Water Hyacinth (Eichhornia crassipes), an aquatic macrophyte, is a resource that has attracted a lot of interest in recent times. The physicochemical constituents of Eichhornia crassipes have been reported in some literature to constitute high carbon, nitrogen, phosphorus, potassium including other important micro and macronutrient like potassium and zinc. These findings by scientists informed its utilization in the assemblage of animal feed, bio-energy generation, pharmaceutical industries, and biofilters. The bioconversions of this problematic plant to various products (compost, biochar, and digestate) are green inexpensive options to be considered for use in the restoration of hydrocarbon polluted sites is reviewed in the paper. In addition to crude oil pollution clean-ups, compost improves soil fertility and also increases its organic matter content. This article also shall review composting, Water Hyacinth compost applications in remediation, remediation monitoring parameters, limitations of remediation by composting technology, and the way forward.