title: Key issues to consider when using alum sludge as substrate in constructed wetland.
abstract: Globally, alum sludge is an easily, locally and largely available by-product from water treatment plants where aluminium sulphate is used as the coagulant for raw water purification. Owing to the high content of Al ions (29.7±13.3% dry weight) in alum sludge and the strong affinity of Al ions to adsorb various pollutants especially phosphorus (P), alum sludge (in the form of dewatered cakes) has been investigated in recent years as a low-cost alternative substrate in constructed wetland (CW) systems to enhance the treatment efficiency especially for high strength P-containing wastewater. Long-term trials in different scales have demonstrated that the alum sludge-based CW is a promising technique with a two-pronged feature of using 'waste' for wastewater treatment. Alum sludge cakes in CW can serve as a medium for wetland plant growth, as a carrier for biofilm development and as a porous material for wastewater infiltration. After the intensive studies of the alum sludge-based CW system, this paper aims to address the key issues and concerns pertaining to this kind of CW system. These include: (1) Is alum sludge suitable for reuse in CWs? (2) Is Al released from the sludge a concern? (3) What is the lifespan of the alum sludge in CWs? (4) How can P be recovered from the used alum sludge? (5) Does clogging happen in alum sludge-based CW systems and what is the solution?
authors.affiliation: The Key Laboratory of Water Supply and Drainage, Ministry of Housing and Urban-Rural Development, Chang'an University, Xi'an 710054, China E-mail: yaqian.zhao@ucd.ie; Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhao
authors.affiliation: The Key Laboratory of Water Supply and Drainage, Ministry of Housing and Urban-Rural Development, Chang'an University, Xi'an 710054, China E-mail: yaqian.zhao@ucd.ie; Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland.
authors.forename: Yaqian
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: The Key Laboratory of Water Supply and Drainage, Ministry of Housing and Urban-Rural Development, Chang'an University, Xi'an 710054, China E-mail: yaqian.zhao@ucd.ie.
authors.forename: Wenke
authors.initials: W
authors.lastname: Wang
authors.affiliation: Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland; School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
authors.forename: Yongzhe
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland; Hydro-environmental Research Centre, Cardiff University School of Engineering, Queen's Buildings, The Parade, Cardiff, Wales CF24 3AA, UK.
authors.forename: Akintunde
authors.initials: A
authors.lastname: Babatunde
authors.affiliation: Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland; The R & D Centre of Sustainable Environmental Biotechnology, Beijing University of Civil Engineering and Architecture, 1 Zhan Lan Guan Road, Beijing 100044, China.
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Dooge Centre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin, Newstead, Belfield, Dublin 4, Ireland; Department of Soil Water Land Engineering and Management, Vaugh School of Agricultural Engineering and Technology, Sam Higginbottom Institute of Agriculture, Technology and Sciences, Allahabad, India.
authors.forename: Lordwin
authors.initials: L
authors.lastname: Kumar
mesh_terms: D000327:Adsorption; D000534:Alum Compounds / Q000737:chemistry*; D000535:Aluminum / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D059027:Recycling; D012722:Sewage / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry; D018508:Water Purification / Q000379:methods; D053833:Wetlands
chemical_list: D000534:Alum Compounds; D012722:Sewage; D014874:Water Pollutants, Chemical; D010758:Phosphorus; C041524:aluminum sulfate; D000535:Aluminum