Enhanced rhizoremediation of crude oil–contaminated mangrove swamp soil using two wetland plants (Phragmites australis and Eichhornia crassipes)

Abstract

Comparative studies of enhanced rhizoremediation with biostimulation and bioaugmentation techniques in remediation of oil-contaminated mangrove environment were investigated. Contaminated soils at 7190 mg/kg of oil were subjected to the following treatments: soil (S), soil + oil (SO), soil + oil + fertilizer (NPK) (SOF), soil + oil + fertilizer + microorganisms (SOFM), soil + oil + fertilizer + microorganisms + solarization (SOFMS) (triplicates): two sets planted with P. australis, E. crassipes, and one unplanted. These were studied comparatively for 120 days for culturable (aerobic, mesophilic) heterotrophic and hydrocarbon-utilizing microbial populations, and soil residual TPH. Results showed culturable heterotrophic and hydrocarbon-utilizing microbial populations and TPH loss in planted soils were consistently higher than those in unplanted receiving corresponding treatments (P ˂ 0.05). There were 44.4, 71.8, 74.7, and 67.5, and 50.5, 71.8, 82.3, and 71.8% reduction in residual TPH in soil planted with P. australis and E. crassipes respectively for treatments PSO, PSOF, PSOFM, and PSOFMS as against 20.0, 62.6, 67.5, and 67.5% losses in SO, SOF, SOFM, and SOFMS. Treatments PSOFM and SFOM recorded the highest TPH loss with daily residual TPH loss in the order as follows: E. crassipes (49.20 mg/kg/day) ˃ P. australis (44.64 mg/kg/day) ˃ unplanted soil (40.32 mg/kg/day). Enhanced rhizoremediation was more effective than biostimulation and bioaugmentation techniques.