Constructed wetlands for treating highly alkaline industrial drainage

高度碱性(PH值9-13)的废水可能是钢铁制造、水泥生产和发电等全球重要行业的副产品风化的结果。水域的极端碱性反映了来源残留物的高度碱性，其中包括富含石灰的钢渣和飞灰。这些残留物传统上被填埋或储存，历史上很少或根本没有控制渗滤液的迁移。离开这种处置地点的排水pH值如此之高，以至于它们从大气中吸收二氧化碳，并大量沉淀固体(主要是方解石：CaCO3)，以至于溪流和河流被窒息，以至于水中几乎没有水生生物。此外，金属/类金属(特别是砷、铬、硒和钒)浓度升高和高硫酸盐负载量可能是严重的环境问题，也是遵守欧盟水框架指令中规定的法定水质标准的障碍。已有的碱性渗滤液处理方案，如加酸、活性曝气和/或将渗滤液循环到堆存的残留物上，都非常昂贵。鉴于目前已知的高pH值渗滤液的产生在相关工业操作的运行寿命结束后仍会持续多年，通过这些传统方法进行持续处理的情况很少，而且未经处理的渗滤液可能会造成持续的环境破坏。国家环境研究中心最近的研究强调了天然湿地在降低这些排水水域的pH值和碱度方面的有效性。富含有机物质的湿地基质中的微生物呼吸似乎加速了方解石的沉淀，这是一个降低碱度的过程。这些富含方解石的固体也可以用作一些潜在有毒金属的水槽。这项研究中提出的工作旨在将人工处理湿地作为一种低成本、对环境敏感的被动选择来商业开发，以处理高碱性水。被动式处理系统的特点是初始资本支出较低，但不经常(尽管是定期)维护的运行成本较低。此外，人工湿地创造了宝贵的湿地栖息地，提供了一个可使用的绿色公共空间，并与更广泛的工业后景观生态恢复很好地融合在一起。这项研究将与项目合作伙伴之一环境署联系，开发人工湿地的一些技术组成部分，以确保按照法定环境质量标准进行有效的污染物处理。还将通过量化方解石沉淀率和建立基于水流和化学的分级和成本计算处理系统的关系来评估经济可行性。这将通过在属于项目合作伙伴Corus的场地建设和监测一个试点湿地系统来进行。然而，这项工作的主要重点将是与处理技术的潜在工业终端用户接触，并开发商业开发机会。虽然这项技术不太可能产生任何正式的知识产权，但成功设计这些处理系统的技术诀窍是一笔宝贵的资产。纽卡斯尔大学的HERO小组在商业上利用这一技术为其他工业后污染源设计新型处理系统方面有着良好的记录。最终用户的参与将通过各种途径进行，但主要将由项目合作伙伴矿业研究组织(MIRO)承担，他们的成员包括一系列拥有问题现场的聚合和加工公司。将利用与潜在最终用户举行的讲习班和会议来展示处理湿地的技术能力，并鼓励工业采用这项技术。

Highly alkaline (pH 9-13) drainage waters can result from the weathering of by-products from globally important industries such as steel manufacture, cement production and electricity generation. The extreme alkalinities of the waters reflect the highly basic nature of the source residues which include lime-rich steel slags and fly ashes. These residues have traditionally been landfilled or stockpiled, historically with little or no control of leachate migration. Drainage waters leaving such disposal sites are of such high pH that they absorb carbon dioxide from the atmosphere and precipitate solids (predominantly calcite: CaCO3) so prolifically that streams and rivers are smothered to the point where little or no aquatic life can be sustained in the waters. In addition, elevated concentrations of metals/metalloids (especially arsenic, chromium, selenium and vanadium) and high sulphate loadings can be of significant environmental concern, and a barrier to compliance with statutory water quality standards such as those set out in the EU Water Framework Directive. Established treatment options for alkaline leachates, such as acid dosing, active aeration and/or recirculation of leachates over stockpiled residues, are very expensive. Given that generation of high pH leachates is now known to continue for many years after the operational life of the associated industrial operations, sustained treatment by these traditional methods is rare, and untreated leachates can produce a legacy of persistent environmental damage. Recent NERC research has highlighted the effectiveness of natural wetlands in lowering the pH and alkalinity of these drainage waters. Microbial respiration in the organic-rich wetland substrate appears to accelerate calcite precipitation, a process which lowers alkalinity. These calcite-rich solids can also serve as a sink for some potentially toxic metals. The work proposed in this study aims to commercially develop constructed treatment wetlands as a low-cost, environmentally sensitive passive option for treating highly alkaline waters. Passive treatment systems are characterised by an initial capital outlay but low running costs for infrequent (albeit regular) maintenance. In addition, constructed wetlands create valuable wetland habitat, provide a useable green public space and integrate well with the wider ecological restoration of post-industrial landscapes. This research will develop some of the technical components of constructed wetlands to ensure effective pollutant treatment with regard statutory environmental quality standards, in liaison with one of the project partners: the Environment Agency. Economic feasibility will also be assessed through quantifying calcite precipitation rates and establishing relationships for sizing and costing treatment systems based on water flows and chemistry. This will be carried out through the construction and monitoring of a pilot wetland system at a site belonging to project partner Corus. The principal focus of the work will however be to engage with potential industrial end-users of the treatment technology and develop opportunities for commercial exploitation. While the technology is unlikely to yield any formal intellectual property rights, the technical know-how for successful design of these treatment systems is a valuable asset. The HERO Group at Newcastle University has a strong track record in commercially-exploiting this know-how for the design of novel treatment systems for other post-industrial pollution sources. End-user engagement will come through various avenues, but will be principally undertaken by project partner the Mineral Industry Research Organisation (MIRO) who count in their membership a range of aggregate and process companies who own problem sites. Workshops and meetings convened with potential end-users will be used to demonstrate the technical capabilities of treatment wetlands and encourage industrial uptake of the technology.