Cattle rumen content, rice husk and cow horn biochars as amendments for enhanced remediation of petroleum-hydrocarbon-contaminated soil: physicochemical characterization and performance evaluation

Petroleum hydrocarbon contamination of soil is a major environmental challenge in crude-oil-producing areas. Agricultural and abattoir wastes are promising low-cost soil amendments but remain greatly underutilized. In this study, cattle rumen content (CRC), rice husk biochar (RHB) and cow horn biochar (CHB) were converted into soil amendments and applied to petroleum-hydrocarbon-contaminated soils. Physicochemical characterization showed that CaO, SiO2 and SO3 were predominant in CRC, RHB and CHB, respectively. Quantitative phase X-ray diffraction gave 65 wt% and 56 wt% graphite in RHB and CHB, respectively, while a chaoite-like phase was tentatively observed in CRC at about 28 wt%. Brunauer--Emmett-Teller surface areas were 356.0, 254.9 and 185.9 m2 g-1 for CHB, RHB and CRC, respectively, with all materials exhibiting mesoporous structures (pore diameters 2.55-2.65 nm). RHB had a higher ash content (50%) than CHB (16%) and CRC (12%). When the amendments were applied to contaminated soil with an initial total petroleum hydrocarbon (TPH) concentration of 1307 mg kg-1 for 60 days, amendment type and application rate affected TPH reduction. RHB and CHB reduced TPH by 94% and 93%, respectively, at a 20% application rate, whereas CRC reduced TPH by 98% at a 10% application rate. Hydrocarbon-utilizing bacteria increased with time, with CRC producing the strongest stimulation. The study highlights the practical value of converting agricultural and abattoir wastes into effective soil remediation amendments for hydrocarbon-impacted areas.