Wealth from Waste: A Framework to Evaluate the Beneficial Reuse of By-Products As Substrate in Constructed Wetlands.

Extensive changes in global land use such as urbanisation and intensive agriculture have substantially increased pollutant loads to aquatic environments in many regions.  Effective mitigation of pollutants, particularly excess nutrients, in wastewater is essential for the long-term management of aquatic ecosystems and is pivotal to efficient water reuse.  Conventional wastewater treatment systems are unsuitable in many instances due to on-going requirements for a guaranteed power supply and skilled labour for facility operation and maintenance.  Wetlands and similar engineered structures for passive wastewater treatment are widely recognised as a cost-effective means of attenuating diffuse water pollution.  Locally-sourced mining and industrial by-products may be suitable for beneficial reuse as substrate in constructed wastewater treatment wetlands or in similar engineered structures for the treatment of wastewater previously discarded or treated by less efficient or more costly means.  The present analysis outlines a framework for the evaluation of industrial by-products for potential reuse in constructed wetlands and similar deployments.  A case study involving twelve representative industrial by-products from China is presented, wherein residues from steelmaking, titanium mineral processing, magnesia recycling and water treatment, and carbonized grain husks from energy production, were comprehensively characterised in terms of their mineralogy, geochemistry, and radiochemistry.  The capacity of each by-product to attenuate nutrients and dissolved organic carbon in wastewater was assessed in laboratory column trials and the phosphorus sorption capacity of each by-product was further quantified in batch experiments.  The potential environmental toxicity of leachates from selected residues was assessed using measures of algal growth, cladoceran mobility, and bacterial fluorescence.  The assessment framework devised as part of this study to evaluate locally-sourced industrial by-product suitability for reuse in constructed wetlands can be applied to a wide range of by-products in order to evaluate their potential for beneficial reuse as environmental amendments.