Synergistic amendment strategy for enhanced remediation of hydrocarbon-contaminated soils using optimized biochar and cattle rumen content combinations

Petroleum hydrocarbon contamination of soil poses significant environmental challenges. The high cost and low efficiency of conventional remediation methods necessitate cost-effective and sustainable remediation strategies. This study evaluated synergistic effects of agricultural waste-derived amendments on crude oil-contaminated soil over 60 days. Following a preliminary screening to determine optimal concentrations, eight amendment strategies were compared: control (unamended), three single amendments (rice husk biochar (RHB), cow horn biochar (CHB), cattle rumen content (CRC)), three dual combinations (RHB + CHB, RHB + CRC, CHB + CRC), and one triple combination (RHB + CHB+CRC). Amendments were applied at optimized concentrations (20% w/w for biochars, 10% w/w for CRC) established from initial screening experiments. Amendment performance followed the order: triple amendment > dual amendment > single amendment > control. The triple amendment combination demonstrated superior performance, achieving 72.6% and 91.8% removal at days 30 and 60, respectively. Dual combinations showed intermediate effectiveness (67.4–91.5% removal), single amendments exhibited moderate performance (38.8–82.7%), while natural attenuation (unamended control) accounted for 7.4–27.8%. The dual biochar system (RHB + CHB) achieved 91.5% TPH removal at day 60, significantly exceeding both RHB alone (57.7%, p < 0.01) and CHB alone (71.4%, p < 0.01), indicating positive interactions. Despite the increased TPH removal by RHB (57.7%) and CRC (82.7%), their combination (81.8%) did not exceed CRC alone, suggesting limited additional benefit. These findings demonstrate that optimized agricultural waste amendments can substantially enhance hydrocarbon remediation, offering sustainable and cost-effective alternatives for contaminated soil management.