Formulation and Evaluation of Slow-Release Fertilizer from Agricultural and Industrial Wastes for Remediation of Crude Oil-Polluted Soils

Fertilizers are used to enhance the degradation and sequestration of oil-polluted environments, but a decrease in fertilizer efficiency can lead to severe environmental consequences. The aim of this study was, therefore, to formulate a slow release fertilizer using nutrient-rich, ecofriendly and readily available agricultural and industrial wastes. The formulated fertilizer was coated with a renewable, nontoxic and biodegradable material which was then tested against commercial NPK fertilizer for its effect on hydrocarbon degradation rate. Crude oil polluted soil from an artisanal refining site was used to evaluate the efficiency of the fertilizers. Next-generation sequencing technique was used to determine the microbiome of the oil-polluted soil. Metabolic fingerprints were also determined as remediation progressed. Other parameters monitored were pH, extractable total petroleum hydrocarbons (ETPH), NO3- -N, total phosphate and total potassium. Initial ETPH of the polluted soil was 16,388 mg/kg which reduced to 2,250.21 mg/kg after 56 days of remediation. The formulated fertilizer gradually led to an increase in soil pH from being slightly acidic (5.6) to near neutral (6.9), while the commercial NPK fertilizer led to a further decrease in soil pH. Both fertilizers enhanced degradation without significant differences, however, the formulated fertilizer greatly improved microbial diversity. Proteobacteria, Chloroflexi and Acidobacteria dominated the soil microbiome with Acidocella being the leading bacterial genus. Signature metabolites identified included benzenamine, cyclobutanone, octadecane and hexadecane which were all related to hydrocarbon biodegradation. The study revealed that the formulated fertilizer effectively enhanced the restoration of oil-polluted soils as well as microbial diversity and soil fertility. It also shows that acid-loving bacteria are important in the bioremediation of acidic oil-polluted soils.