Constructed wetlands for treating highly alkaline industrial drainage

高碱性（pH值9-13）的排水可能是全球重要工业（如钢铁制造、水泥生产和发电）副产品风化的结果。水的极端碱度反映了源残留物的高度碱性，其中包括富石灰钢渣和粉煤灰。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。从这些处理场流出的排水的pH值非常高，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可以维持。此外，高浓度的金属/类金属（特别是砷、铬、硒和钒）和高硫酸盐含量可能会引起严重的环境问题，并阻碍遵守法定水质标准，例如欧盟水框架指令中规定的标准。碱性渗滤液的既定处理方案，如加酸、主动曝气和/或在储存的残留物上再循环渗滤液，是非常昂贵的。鉴于高pH值渗滤液的产生在相关工业作业的使用寿命之后仍会持续多年，因此采用这些传统方法进行持续处理是罕见的，而且未经处理的渗滤液可能会产生持续的环境破坏。最近的NERC研究强调了天然湿地在降低这些排水的pH值和碱度方面的有效性。富有机物湿地基质中的微生物呼吸作用似乎加速了方解石的沉淀，这一过程降低了碱度。这些富含方解石的固体也可以作为一些潜在有毒金属的水槽。本研究提出的工作旨在商业化开发人工处理湿地，作为一种低成本、环境敏感的被动选择，用于处理高碱性水。被动处理系统的特点是初始资本支出，但不频繁（尽管定期）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，提供了可用的绿色公共空间，并与后工业景观的更广泛的生态修复相结合。这项研究将与项目伙伴之一环境署联络，开发人工湿地的一些技术组成部分，以确保根据法定环境质量标准有效地处理污染物。经济可行性也将通过量化方解石沉淀率和建立基于水流和化学的处理系统的规模和成本关系来评估。这将通过在属于项目合作伙伴Corus的一个地点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最终用户接触，并开发商业开发的机会。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项宝贵的资产。纽卡斯尔大学的HERO集团在商业上利用这一技术为其他后工业污染源设计新型处理系统方面有着良好的记录。最终用户将通过各种途径参与，但主要由项目合作伙伴矿物工业研究组织（MIRO）承担，该组织的成员包括拥有问题站点的一系列聚合和加工公司。与潜在最终用户召开的讲习班和会议将用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.