Dewatering and remediation of contaminated dredged sediments

Dewatering and remediation of contaminated sediments is a critical issue in the management of dredged sediments because of limited space in confined disposal facilities (CDFs). Many of the contaminants in sediments require an aerobic environment for degradation, presenting a problem for bioremediation as these sediments exist under anaerobic conditions. A three-year study was conducted to test plant species for their ability to dewater sediments and to enhance loss of contaminants. Wetland plants were found to have high transpiration rates and useful to effectively dewater contaminated dredged sediments. Of the plants tested, Salix nigra and Spartina pectinata are recommended for use in dewatering applications because these species were able to dewater the sediments to nearly -1500 kPa without death. The presence of high transpiring plant species impeded the loss of congeners monitored in Arochlor 1260. The presence of these high transpiring species introduced oxygen as the terminal electron acceptor which prevented the formation of highly reducing conditions needed for the reductive dechlorination of these compounds. The presence of high transpiring and high yielding plant species also impeded the progress of PAH loss from the field sediments. Statistically, the sediment moisture content and the nitrogen removed by plant treatments were significant predictors of PAH loss. However, the sediment moisture content rarely reached low enough values to limit microbial activity, so the inhibition of PAH loss by these plant treatments must have been due to something else that correlated with sediment moisture content such as water use or nitrogen uptake. Although the high biomass plant treatments impeded the progress of PAH loss, plant cover is desired to reduce losses of contaminated sediments to wind erosion. This study identified the Lolium multiflorum as a plant species able to provide good cover while not impeding the progress of remediation on these sediments