Re-utilization of drinking water treatment residuals (DWTR): a review focused on the adsorption of inorganic and organic contaminants in wastewater and soil

Abstract

Drinking water treatment residuals (DWTR) are produced in very large quantities worldwide and many applications are investigated to reuse this type of material for combined economic and environmental incentives. This review focuses on the versatile properties of DWTR as a low-cost and low-toxicity adsorbent for wastewater treatments for a variety of contaminants such as trace metals and metalloids, nutrients, dyes, gases, and pesticides. Most studies report the best laboratory conditions of adsorption in consideration of the main controlling factors of solution pH, dosages of adsorbent, concentrations of adsorbates, and contact times with solutions of well-controlled chemical composition. Kinetic studies and common adsorption models are also generally reported. The adsorptive properties of DWTRs are also utilized for soil remediation and amendment to control the levels of essential nutrients such as phosphorus and nitrogen. Abundant literature exists to propose the inclusion of DWTR in various construction materials such as cement, bricks, geopolymers, and agricultural applications. It is somehow puzzling to realize that real-world applications are so limited in comparison to the large number of studies and publications on the subject of using DWTR. It also appears that adsorption results are mostly obtained using well-controlled conditions with synthetic solutions of selected contaminants and rarely with real wastewater samples. The transfer of laboratory results to real systems for industrial and commercial applications has been so far very limited, possibly due to limited legislation and to some reluctance from those organizations to use DWTR as a potential substitute in their respective process.