Crude oil-based fuel products are the primary energy source for households and industries. (Wolicka, Suszek, Borkowski, & Bielecka, 2009; Okoh, Yelebe, Oruabena, Nelson, & Indiamowei, 2020). However, the improper handling of crude oil and its related products has resulted in oil spillage, a severe environmental issue of multiple dimensions. (Jonsson & Haller, 2014). Crude oil spills have had devastating impacts on several localities in the Nigeria oil-rich Niger Delta, affecting the environment, people’s health, and the availability of food, necessitating the restoration of such contaminated environments (Berkes, Colding, & Folke, 2008; Rockström, et al., 2009; Steffen, et al., 2015). Most researchers have used a standardised engineering approach of biostimulation by applying inorganic fertiliser to restore crude oil-contaminated sites. Human excreta are highly generated and valuable, have a high moisture and nitrogen content, are a rich source of nutrients for plant growth, and could be used as a biostimulant for soil bacteria in crude oil-contaminated soil remediation. However, faecal sludge is grossly under-utilised and dumped indiscriminately (Goldstein, 2012; Netting, 1993; Kôrner, et al., 2003.). The unregulated faecal sludge discharged into the environment has affected land, water resources, and human and animal health because of the enteric pathogens in these wastes. Faecal sludge contains exceptionally high concentrations of pathogens responsible for the increased endemic rate of excreta-related diseases (World Health Organization, 2006). A high incidence of helminth eggs occurs when faecal sludge is reused untreated as fertiliser to promote plant development, close the nutrient gap, or dispose of within habitable areas (Monney & Awuah, 2015). According to Cofie et al. (2006) the die-off time of helminth eggs in faecal compost is a function of temperature, dryness and pH of the compost mass, surviving between 10 and 12 months upon excretion under tropical climates (Sanguinetti, et al., 2005).
According to Rose et al. (2015) and Onabanjo et al. (2016), faecal sludge contains approximately 50% carbon (C), 45% N, 23% potassium (K), and 23% P, and when applied untreated to land to maintain soil fertility and increase crop yields (Krounbi, Enders, van Es, Woolf, & von Herzen, 2019). Faecal sludge is being promoted in line with principles of environmental sustainability as interest in resource recycling has revived (Phuc, Konradsen, Phuong, Cam, & Dalsgaard, 2006)
Available literature (Laboy-Nieves, Schaffner, Abdelhadi, & Goosen, 2008; Monney & Awuah, 2015) has shown that pathogen destruction in faeces can be achieved using several technologies, including ammonia treatment, irradiation, and dewatering, or a combination of these technologies. And most of these technologies are known to be efficient in removing enteric pathogens (Strande, Ronteltap, & Brdjanovic, 2014; Monney & Awuah, 2015). Most excreta sanitation studies found in the literature were limited to raw excreta from on-site systems, and nutrient recycling from faecal sludge was never considered. Any sanitation technology employed is expected to remove or minimise the broad spectrum of microbial pathogens in human faeces to prevent potential health and environmental influences (Monney & Awuah, 2015). Opportunities exist within the standardised procedures, which embrace sustainability as a principle of rural empowerment to apply sanitised human faecal sludge to restore contaminated environments. The prospect of co-composted dewatered faecal sludge with kitchen waste as an organic amendment for contaminated soil remediation and use as a plant nutrient in agriculture is high (Winblad & Simpson-Hérbert, 2004; Zbytniewski & Bszewski, 2005; Castaldi, Alberti, Merella, & Melis, 2005). Using sanitised faecal sludge in crude oil-polluted soil remediation will shape the oil-producing area's economy and other communities affected by crude oil spills into their ecosystems. The production of nutrient-rich compost from excreta for agriculture is an old practice (Timmer & Visker, 1998 ; Martin, et al., 2003). Composting is the most preferred method of neutralising dewatered faecal sludge, although it is a complicated process. Co-composting of dewatered faecal sludge with other carbon sources is aimed at killing pathogenic organisms, stabilise the organic matter to maturity, and thoroughly drying the sludge mixture to produce a material that can be used or sold in an environmentally friendly way (Bazrafshan, Zarei, Kord-Mostafapour, Poormollae, & Mahmoodi, 2016). However, studies have shown that human excrement will not compost independently due to high moisture, high wet bulk density, and low C/N ratio. Because of its dense and plastic structure, dewatered faecal sludge or raw excreta are susceptible to compaction (Bazrafshan, Zarei, Kord-Mostafapour, Poormollae, & Mahmoodi, 2016). The faecalsludge’s high moisture content and the structure’s absence result in compressive stress and compaction on a compost bed, triggering reduced air-filled porosity and penetrability (Das & Keener, 1997; Malińska & Richard, 2006). For optimal successful composting of faecal sludge, carbon-based structural materials in a suitable proportion are applied to allow optimal moisture content, balance the C/N ratio and provide the structural support needed to obtain sufficient air-filled porosity in the correct consistency, quantity, and moisture content.
Dewatered faecal sludge and organic kitchen waste were co-composed with sawdust as the structural component to create a sterilised compost that may be used as a biostimulant to repair crude oil-contaminated soils. The sawdust addition to the composting system balanced the water content, eliminated odour, and ensured the proper consistency of the composting materials. The work demonstrates safe resource reuse by sanitising human faeces and food waste to create benefits. The resulting high-nutrient compost can be utilised as a biostimulant for efficiently removing crude oil pollutants in soil or used as a soil conditioner in agriculture (Antizar-Ladislao, Joe, & Beck, 2006 ).