Potential Alternative Reuse Pathways for Water Treatment Residuals: Remaining Barriers and Questions—a Review

Abstract

Water treatment residuals (WTRs) are byproducts of the coagulation and flocculation phase of the drinking water treatment process that is employed in the vast majority of water treatment plants globally. Production of WTRs are liable to increase as clean drinking water becomes a standard resource. One of the largest disposal routes of these WTRs was via landfill, and the related disposal costs are a key driver behind the operational cost of the water treatment process. WTRs have many physical and chemical properties that lend them to potential positive reuse routes. Therefore, a large quantity of literature has been published on alternative reuse strategies. Existing or suggested alternative disposal routes for WTRs can be considered to fall within several categories: use as a pollutant and excess nutrient absorbent in soils and waters, bulk land application to agricultural soils, use in construction materials, and reuse through elemental recovery or as a wastewater coagulant. The main concerns and limitations restricting current and future beneficial uses of WTRs are discussed within. This includes those limitations linked to issues that have received much research attention such as perceived risks of undesirable phosphorous immobilisation and aluminium toxicity in soils, as well as areas that have received little coverage such as implications for terrestrial ecosystems following land application of WTRs.

Trialling Water‐Treatment Residuals in the Remediation of Former Mine Site Soils: Investigating Improvements Achieved for Plants, Earthworms, and Soil Solution

“…The small but significant decreases in Pb assimilation by plants observed for WTR treatments in almost all cases, in contrast with the no effect and even increases observed in some lime treatments, confirm the Pb sorbing capacity of WTRs and the associated potential environmental benefits from their field applications that have been discussed in the literature (Turner et al 2019). In both trials, the treatments decreased As assimilation relative to control in seep 3, in agreement with a previously published study (Sarkar et al 2007) that showed the effectiveness of WTRs at immobilizing As in As‐contaminated soils.…”

Laboratory evaluation of alum, ferric and ferrous-water treatment residuals for removing phosphorous from surface water

“…Fe2-WTR had the largest particle sizes with 69.35% gravel, 27.35% sand and 1.45% silt/clay. As particle size WTRs with a smaller mean particle size can absorb greater amounts of PO 4 ( Turner et al., 2019 ), this may impact the extent of adsorption during isotherm experiments. The Fe2-WTR depicted a greater fluctuation in Fe content for the five replicates.…”

“…During coagulation treatment, the dominant reactions with alum, ferric chloride and ferrous chloride follow those shown in Eqs. (1) , (2) , (3) , and (4) ( Reynolds and Richards, 1996 ; Ebeling et al., 2003 ; Turner et al., 2019 ). …”

Application of waste treatment sludge from water treatment in brick production

“…Alum sludge is a by-product of the treatment plants that use aluminium salt as coagulant. The treatment uses coagulants, such as aluminium sulphate or also known as alum, iron-based salts ferric chloride, and ferric sulphate, which are the resultants of chemical reaction of Al and Fe salts in alkaline conditions to form hydroxide precipitates that remove impurities via coprecipitation, sorption, flocculation, and settling (Dassanayake et al, 2015;Turner et al, 2019).…”