Development of combined system to remediate and recycle contaminated dredged sediments

摘要

The appropriate management of contaminated sediments dredged from harbors and waterways is a concern as they may pose ecological and human health risks. Thus, effective remediation and promotion of the beneficial use of dredged sediments are necessary. A strategic remediation process for dredged sediments, applying both washing and stabilization technologies mainly for heavy metal treatment, is developed in this study. In the early stage, the sediments are separated into two particle sizes. The coarse-grained sediment over 0.075 mm, generally decontaminated with less trouble, follows normal washing steps and is sent for recycling. The fine-grained sediments are separated again at the cyclone and treated in two ways. The advanced washing is applied to the highly contaminated sediment for potential recycling. The relatively less contaminated sediment is stabilized by mixing an appropriate adsorbent. The particle sizes at which second separation occur will be determined based on site specific conditions. The washing system, containing the portable cyclone for the particle separation, and the stabilization technique are under development. The advanced washing process is designed to involve a special metal separation procedure optimized for the particle size and the metal species. For the washing process, the separation apparatus such as the ultra hydrocyclone and the spiral separator particularly for the second separation step are being tested. For stabilization, the preliminary isotherm, Toxicity Characteristic Leaching Procedure (TCLP), and sequential extraction test results show that birnessite and apatite are the most effective stabilizing agents among tested. The collaborated research is ongoing for the beneficial use of stabilized sediments by solidification. The efficacy of the process will be demonstrated at the pilot scale test site. Pilot scale verification will focus on systematic operation of each process incorporated into full scale performance. The suggested strategic approach to remediate contaminated sediments can help promote more secure treatment and the beneficial use of dredged sediments, leading to an effective and economic management for dredged materials.