Remediation of petroleum contaminated soils through composting and rhizosphere degradation.

Composting along with rhizodegradation was used to remediate petroleum-contaminated soils in the Yellow River Delta, China. The average concentration of total petroleum hydrocarbons (TPH) in these soils was reduced from 7900-17,900 mg kg(-1) to 1400-3700 mg kg(-1) after field composting. The best volume ratio of amendment to contaminated soil was 2/1 and the best C/N ratio was 15/1. After composting, four local dominant plant species, Seepweed, Sealavander, Central Asia Saltbush and Reed, were selected and planted in composted soils for rhizodegradation in the field. After 90 days of cultivation, the highest net TPH degradation rate was over 40% for Seepweed, probably because of strong root system and active microbial community. In addition, Seepweed roots significantly reduced the surface and volume of soil micropores (which are able to sequestrate organic compounds inside), thus increasing the bioavailability of TPH. In sum, composting followed with planting Seepweed was most effective in remediating the contaminated soil in the Yellow River Delta.