Development of an alum sludge based constructed wetland system for improving organic matter and nutrients removal in high strength wastewater

Final Report for the ERTDI project: 2005-ET-MS-38-M3

Summary: STRIVE Report 57 - Yaqian Zhao

The generation of alum sludge in Ireland is inevitable. Its disposal, however – amidst decreasing available landfill space coupled with escalating costs and public concerns – remains an environmental quagmire. Seeking cost effective and environmentally sustainable disposal alternatives is, as a result, a significant environmental issue. Alum sludge is a by-product of drinking-water treatment processes in Ireland. It is obtained when aluminium (Al) salts are used as a chemical coagulant. Once alum sludge is dewatered, however, aluminium hydroxides become the dominant constituent, making it possible to reuse the sludge as a valuable raw material in wastewater treatment. This is because the ions enhance adsorption and chemical precipitation processes that remove various pollutants, especially phosphorus, from wastewater. Moreover, there is huge potential in Ireland for the application of small wastewater treatment systems, especially constructed wetlands (CWs), because of the unique geographic distribution of Irish residents. Constructed wetlands (commonly known in Europe as ‘treatment reed beds’) are regarded as a low-cost promising technology for wastewater treatment and have been increasingly employed for wastewater treatment since the early 1990s. This project conceptualised and developed a novel CW system integrating alum sludge as its main substrate.

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