POLLUTED SOIL

This study evaluated the effects of cassava mill effluent (CME) on the NPK of hydrocarbon polluted soil in Delta State, Nigeria. This has severely degraded soil fertility by depleting essential macronutrients nitrogen (N), phosphorus (P), and potassium (K) and elevating total petroleum hydrocarbon (TPH) levels beyond regulatory limits thereby threatening agricultural productivity and food security for local communities dependent on subsistence farming. This study aimed to evaluate baseline NPK levels in contaminated clay-loam soils from spill-affected sites while investigating the bioremediation potential of cassava mill effluent as a nutrient-rich bio stimulant containing 2–3% N, 0.5% P and 0.3% K, applied at varying frequencies including daily, once, weekly, monthly and control setups. Soil samples were collected from 0–15 cm depths pre treatment and post-treatment over a 12-week period, with analyses conducted using the Kjeldahl method for N via digestion and titration, ascorbic acid spectrophotometry at 710 nm for P, flame photometry at 766.5 nm for K, and gas chromatography-flame ionization detection with n-hexane extraction for TPH, leveraging indigenous microbes like Pseudomonas and Bacillus for bio stimulation in alignment with sustainable waste-to-wealth approaches in cassava-producing regions. Results demonstrated substantial nutrient restoration and TPH reduction following remediation, with pre-treatment values showing low NPK (N: 0.008–0.07%; P: 1,055–5,322 ug/g; K: approximately 0.10 mg/kg) while diminishing TPH to undetectable levels, surpassing the outcomes of single or monthly treatments. These improvements arose from heightened microbial activity and enhanced nutrient cycling, which alleviated toxicity and reinstated bioavailability in the polluted soils. The findings highlight the effectiveness of cassava effluent for affordable soil rehabilitation at near-zero cost, with potential to elevate crop yields by 20–40% and contribute to United Nations Sustainable Development Goals 2 (Zero Hunger) while recommendations advocate for ongoing bio stimulation protocols and regular monitoring to refine remediation efforts in Niger Delta ecosystems, ultimately promoting ecological resilience and supporting community livelihoods.