Remediation of polluted sediment assisted by tidal energy

英国和世界各地的许多河口和河流沉积物受到对生态系统有害的有机污染物的影响。例如，英格兰北部的泰恩河口受到石油碳氢化合物的严重污染，包括多环芳烃(PAHs)，最近的研究表明，对鱼类，如比目鱼和鳗鱼，具有生态毒理作用。欧盟水框架指令将多环芳烃列为水政策领域的优先物质，因为它们具有致癌能力。自然过程，如微生物分解和污染物(如多环芳烃)对某些沉积物成分(如碳质颗粒)的强烈吸附，可以显著降低受污染沉积物的生态毒性。然而，养分和氧气的可获得性有限，微生物分解形成生态毒性产物，自然沉积物中有限的强吸附部位，以及污染物从弱吸附剂向微生物或强吸附剂的缓慢传质，都可能阻碍自然恢复。因此，有人建议设计一种低成本的工程系统，在受控的环境中加强自然过程以恢复沉积物。潮汐能量将被利用来搅动沉积物并为其补充营养和氧气。这将加速微生物对污染中可降解部分的分解。污染和最终分解产物中不稳定但不可降解的部分将被从沉积物中去除，方法是用吸附剂将系统流出的污水渗透到床上。在处理结束时，沉积物中的残留污染将通过向沉积物中添加一剂强的、最好是天然的吸着剂(如煤)来隔离。据推测，这将大大减少沉积物的生态毒性，并长期稳定残留污染。通过利用潮汐能和自然过程，这种处理的成本可以保持在较低水平。该方案可在原地实施，以避免清除沉积物，或在现有构筑物(如废弃的干船坞)内进行异地迁移，以处理常规疏浚作业所产生的沉积物。与处置未经处理的沉积物相比，就地就位或海洋处置经处理的稳定沉积物的风险较小，或者经处理的稳定的沉积物可成为岸上可接受的材料，例如用作填充材料。

Many estuaries and river sediments in the UK and worldwide are impacted by organic pollutants at levels which are harmful to the ecosystem. For instance, the Tyne Estuary in the North of England is heavily polluted with petroleum hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), and recent studies demonstrated ecotoxicological effects in fish, e.g. flounder and eels. The EU water framework directive lists PAHs as priority substances in the field of water policy because of their carcinogenic potency.Natural processes such as the microbial break-down and the strong adsorption of pollutants like PAHs to certain sediment constituents (e.g. carbonaceous particles) can reduce the ecotoxicity of polluted sediment significantly. However, the limited availability of nutrients and oxygen, the formation of ecotoxic products from microbial break-down, a limited number of strong sorption sites in natural sediment, and slow mass transfer of pollutants from weak sorbents to microorganisms or strong sorbents may impede a natural recovery. It is thus proposed to devise a low-cost engineering system in which natural processes leading to a sediment recovery can be enhanced in a controlled setting.Tidal energy will be exploited to agitate the sediment and replenish it with nutrients and oxygen. This will accelerate the microbial break-down of the degradable portion of the pollution. The labile, but non-degradable portion of the pollution and eventual break-down products will be removed from the sediment by infiltrating the effluent from the system across a bed with an adsorbent. The residual pollution in the sediment will be sequestered by adding a dose of a strong, preferably natural sorbent (e.g. coal) to the sediment at the end of the treatment. Presumably this will result in a substantially reduced sediment ecotoxicity and longterm stabilization of the residual pollution.By exploiting tidal energy and natural processes the costs for this treatment can be kept low. The scheme could be implemented in situ to avoid the removal of sediment or ex situ, possibly within existing structures such as abandoned dry docks, to treat sediment from routine dredging operations. The in situ emplacement or ocean disposal of treated, stabilized sediment would implicate less risks than disposal of the untreated sediment, or the treated, stabilized sediment may become an acceptable material for use on shore, e.g. as a filling material.