Use of industrial by-products and natural media to adsorb nutrients, metals and organic carbon from drinking water

• The use of waste media in the water sector results in a robust, sustainable option. • Fly ash and Bayer residue successfully adsorb TOC, nutrients and Cu. • Granular blast furnace slag and pyritic fill have good adsorption potential. • pH adjustment is not necessary for optimal adsorption of contaminants. • Kinetic studies show that at least 60% of adsorption had taken place after 8 h. a b s t r a c t a r t i c l e i n f o Filtration technology is well established in the water sector but is limited by inability to remove targeted contaminants, found in surface and groundwater, which can be damaging to human health. This study optimises the design of filters by examining the efficacy of seven media (fly ash, bottom ash, Bayer residue, granular blast furnace slag (GBS), pyritic fill, granular activated carbon (GAC) and zeolite), to adsorb nitrate, ammonium, total organic carbon (TOC), aluminium, copper (Cu) and phosphorus. Each medium and contaminant was modelled to a Langmuir, Freundlich or Temkin adsorption isotherm, and the impact of pH and temperature (ranging from 10°C to 29°C) on their performance was quantified. As retention time within water filters is important in contaminant removal, kinetic studies were carried out to observe the adsorption behaviour over a 24 h period. Fly ash and Bayer residue had good TOC, nutrient and Cu adsorption capacity. Granular blast furnace slag and pyritic fill, previously un-investigated in water treatment, showed adsorption potential for all contaminants. In general, pH or temperature adjustment was not necessary to achieve effective adsorption. Kinetic studies showed that at least 60% of adsorption had occurred after 8 h for all media. These media show potential for use in a multifunctional water treatment unit for the targeted treatment of specific contaminants

Development of filtration technologies for effective, cost-efficient and robust water treatment

The provision of high quality, potable water in a sustainable and effective manner is a key challenge for water engineers, scientists, and policy makers. Urbanisation and industrial development, along with population growth, intensification of agriculture and climate change, has increased the strain on current potable water supplies in the developed world, not only in terms of supply, but also by way of introducing new contaminants into the abstraction waters. Emerging contaminants, alongside increasingly stringent environmental legislation, make the maximum allowable concentrations for various contaminants within potable water more difficult to achieve. Although the situation is improving, over 660 million people worldwide still do not have access to improved water supplies. Sustainable and robust solutions that ensure effective water treatment for a variety of contaminants, while also being low cost and low maintenance, are required. Metals and nutrients continue to enter source water supplies by anthropogenic and natural sources. While metals can be damaging to human health, nutrients can lead to excessive microbial activity. The presence of organic matter in source waters also challenges water treatment plants (WTPs), as disinfectants used post-treatment can trigger a reaction with organic matter to create toxic by-products. These can develop both in the WTP and along the distribution network, and long-term exposure can be detrimental to human health. This is a major problem in Ireland and elsewhere, and to date, no cost-effective and sustainable solution has been found. Various technologies are being developed to target problem contaminants, including coagulation systems, gas transfer systems, oxidation technologies, and membranes. Although these may be effective, they may also require high capital investment, be subject to fouling, and require expert maintenance. In addition, costly treatment systems are not feasible for smaller water treatment facilities and developing countries. Instead, a move towards more traditional contaminant removal and retention mechanisms, such as adsorption and filtration, may be more sustainable. Such technologies, in tandem with the use of alternative filter media, such as waste products and locally sourced material, can improve the sustainability of WTPs while not negatively impacting performance. This study aimed to address the issue of contaminant removal, by designing a filter that could fit into the current model of a WTP, and which could remove a variety of contaminants including metals, nutrients, and disinfection by-product precursors. The technology incorporated the use of waste materials to reduce cost and maintain sustainability, and was comprehensively tested at laboratory-scale and pilot-scale. A number of waste products and local materials were first tested at bench-scale, using a variety of common water contaminants to assess their adsorptive capacities. The media tested included coarse sand, zeolite, granular activated carbon (GAC), pyritic fill, Bayer residue, bottom ash, fly ash, and granular blast furnace slag. Following this, laboratory-scale stratified filters were constructed, comprising some of the most successful media from the bench-scale study: fly ash, Bayer residue, zeolite, sand, and GAC. The filters were evaluated for treatment performance and media clogging potential. The results obtained from the laboratory-scale study led to a re-design for the pilotscale study, which was operated at a WTP that used lake water as its potable water source. The WTP was chosen as it had a history of formation of disinfection byproducts. Two filter configurations were examined under intermittent and constant loading rates, and comprised combinations of sand, Bayer residue, GAC, and pyritic fill. While each of the alternative designs proved more successful than a standard sand filter, a filter configuration comprising sand, GAC, and pyritic fill, proved most effective in dissolved organic carbon removal under a continuous loading regime. These studies show that waste products can be used in filtration technologies, where adsorption is a key mechanism, thereby reducing overall capital and maintenance requirements. Adsorption isotherms are instrumental in the design of bespoke filters, and this study found that it is possible to target the removal of specific contaminants, depending on the constituents of the source water. This study presents a simple, lowmaintenance design to reduce the concentration of key contaminants in potable water, and addresses a major problem for WTPs

Performance of novel media in stratified filters to remove organic carbon from lake water

Disinfection by-products (DBPs) are an ever-increasing occurrence in water networks, particularly those which abstract water from peatland areas. Although much research has been carried out to discover novel methods to remove specific DBPs, the removal of natural organic matter (NOM) from source water may provide a more sustainable solution in many areas. This study focuses on the removal of NOM by novel filters, which could be retrospectively fitted to any conventional water treatment facility. The filters comprised stratified layers of a variety of media, including sand, Bayer residue, granular activated carbon (GAC), and pyritic fill. The filters were operated under two loading regimes, continuous and intermittent, at loading rates similar to recognised design standards. The most successful filter design comprised stratified layers of sand, GAC, and pyritic fill. Over the duration of a 240 day study, these filters obtained average dissolved organic carbon removal rates of 40%, and achieved average specific ultra-violet absorbance reductions from 2.9 to 2.4 L mg-1 m-1. The study demonstrates that these novel filters may be used to reduce NOM levels, thus reducing the potential for DBP formation. Such designs can incorporate the use of waste media, making the overall design more sustainable and robust.peer-reviewed2017-02-1

Performance of novel media in stratified filters to remove organic carbon from lake water

Disinfection by-products (DBPs) are an ever-increasing occurrence in water networks, particularly those which abstract water from peatland areas. Although much research has been carried out to discover novel methods to remove specific DBPs, the removal of natural organic matter (NOM) from source water may provide a more sustainable solution in many areas. This study focuses on the removal of NOM by novel filters, which could be retrospectively fitted to any conventional water treatment facility. The filters comprised stratified layers of a variety of media, including sand, Bayer residue, granular activated carbon (GAC), and pyritic fill. The filters were operated under two loading regimes, continuous and intermittent, at loading rates similar to recognised design standards. The most successful filter design comprised stratified layers of sand, GAC, and pyritic fill. Over the duration of a 240 day study, these filters obtained average dissolved organic carbon removal rates of 40%, and achieved average specific ultra-violet absorbance reductions from 2.9 to 2.4 L mg-1 m-1. The study demonstrates that these novel filters may be used to reduce NOM levels, thus reducing the potential for DBP formation. Such designs can incorporate the use of waste media, making the overall design more sustainable and robust.2017-02-1

The potential for the use of waste products from a variety of sectors in water treatment processes.

Journal articleThis review examines the utilisation of waste products from three sectors (industry, agriculture, and construction and demolition) in filters for the removal of contaminants from water. Sand is commonly used in drinking water filtration in water treatment plants. However, the use of alternative, low-cost materials could address the limitations of sand, particularly for the removal of emerging contaminants, and address European legislation which fosters the development of a circular economy, in which materials are used effectively. This review assesses the suitability of potential media by quantifying their adsorption potential across a variety of common drinking water contaminants. The media investigated were fly ash, Bayer residue, ground granular blast furnace slag, coconut shell, tea/coffee waste, rice husk, crushed concrete, masonry waste, and wood waste. There is a potential for the use of these media in the water treatment sector, although certain precautions must be taken to ensure any concerns are mitigated, such as release of metals into water. Recommendations, following this review, include testing the media in large-scale applications, and also constructing filters so as potential media are placed in layers to harness their contrasting adsorptive potentials.Environmental Protection Agency (EPA) (​Grant no: 2012-W-PhD-5)2018-07-2