Improvement of chlorine stability by natural organic matter removal using a combination of biologically activated carbon with coagulation in drinking water treatment

Abstract

This study focuses on the feasibility of biologically activated carbon (BAC) to enhance natural organic matter (NOM) removal by subsequent coagulation. This will reduce chlorine demand and it is expected that the removal would also reduce disinfection by-products (DBP). The NOM is a heterogeneous mixture of complex organic materials abundantly occurs in all natural water sources. These organic matters are the potential precursors for the formation of carcinogenic DBP and cause several other water quality problems. Aimed mainly at removing particles in the water, the coagulation process, the major conventional water treatment method, removes only a small amount of higher molecular weight (MW) fractions of NOM. To remove a higher amount of organic matter, larger doses of coagulant, such as ferric or aluminium salts, need to be added. In a normal water treatment plant, coagulation tank is followed by flocculation tank and sedimentation basin to remove the flocs formed. With the requirement to process water quickly, especially in the treatment of low turbidity water the sedimentation tank is avoided and only smaller doses of coagulant are applied and subjected to direct filtration, such as in treatment plants of Sydney Water. Hence, the challenge is to remove more NOM effectively and increase the chlorine stability without increasing the coagulant dose. The BAC process is a cost-effective and environmentally friendly water treatment method for removing biodegradable organic matters (BOM). It is used as a polishing step followed by coagulation or ozonation. It is well known that BAC removes NOM of hydrophilic nature and smaller MW which is less amenable to removal by the coagulation and many toxic and endocrine compounds which are not otherwise removed. In addition, it is known the biological activities increase soluble microbial products (SMP) which in turn helped in aiding the NOM removal by subsequent coagulation in recycled wastewater. The study, for the first time, explores the feasibility of using BAC as a pre-treatment of surface water to traditional coagulation process, equipped with direct filtration.

Date of Award	2018
Original language	English