An Enzyme-Based Treatment Technology for Contaminated Sediment Remediation

Biocatalysts have not been used for sediment remediation in large scale, although they have been tested in a few pilot projects around the world. This paper presents a large scale ex-situ sediment remediation project in Guangzhou, China using an enzyme based technology followed by a solids separation, dewatering and solidification/stabilization. The goals of the project are to remediate two million tons of contaminated sediment dredged from twelve rivers in Guangzhou City, China, and to reuse the dredged materials. In addition, this technology is compared to a Portland cement based technology commonly used for sediment treatment. The system comprises an enzyme based pre-treatment oxidation ditch that processes 8000 tons of 15% solid slurry daily, a hydro-cyclone dewatering unit that takes slurry from the pretreatment and sorts the sediment into sand, silt and clay, followed by a clarifier process that settles the fine clays in a settlement pond, discharging the supernatant to receiving water. The fundamental finding was that that 85% of the solids separated and dewatered by the hydro-cyclone unit meet or exceed both “China’s National Standards about the Disposal of Sludge from Municipal Wastewater Treatment Plant” and “The Control Standards for Pollutants in Sludge from Agricultural Use”. The remaining 15% comprising clay was solidified and stabilized. The data showed that the enzyme addition not only degraded organic pollutants, but also improved sediment dewatering efficiency, with a low 60% moisture content in the dewatered sediment. Compared to the Portland cement-based solidification/stabilization technology, the technology has substantial advantages in terms of area required, volume reduced, odors eliminated and materials reused.