Occurrence and Human-Health Risk of Disinfection Byproducts in Recycled Water in Abu Dhabi

Abstract

Globally, freshwater resources are increasingly depleted and water reuse is emerging as a sustainable alternative. During water treatment, disinfection is practiced to inactivate pathogenic microorganisms. A setback of disinfection is the production of disinfection byproducts (DBPs) by the reaction between disinfectants and residual organic matter. Over the years, carcinogenic risk has been linked to exposure to DBPs. This study evaluated human health risk from exposure to a category of DBPs called trihalomethanes (THMs) in recycled water in Abu Dhabi. Samples were collected and analyzed between January and December 2011, from the Mafraq wastewater treatment plant (MWWTP) and Masdar membrane bioreactor (MBR) plant. MWWTP uses activated sludge treatment while Masdar uses membrane bioreactor technology. Sample analysis was divided into pre and post-disinfection measurements. Pre-disinfection measurements included pH, total organic carbon (TOC), bromide and chloride. Post-disinfection measurements included total THM (TTHM), residual chlorine and total THM formation potential (THMFP). Highest TTHM was observed in samples during summer months. During this time, highest TTHM in samples from MWWTP was 70.05±0.77μg/L while highest TTHM of 42.15±0.59μg/L was recorded in samples from Masdar. Mean THMFP in sample from MWWTP was 96.08±0.16μg/L and 68.24±0.31μg/L in sample from Masdar. Also, bromide concentration, pH and TOC concentration were higher in samples from MWWTP. These, in combination with other parameters like temperature promoted a THM speciation in samples from MWWTP in the direction of brominated THMs. However, THM speciation in samples from Masdar was in the direction of chlorinated THMs. Human exposure assessment was conducted using the outdoor box exposure model. Dermal absorption and vapor inhalation are the exposure routes considered in this study. Receptors included a residential adult and child and a site worker. Risk calculation showed that vapor inhalation had the highest risk estimate. Inhalation exposure of residential adult and child to chloroform only for THMFP concentration in Masdar effluent exceeded the acceptable risk level of 10-6 defined by the USEPA. No significant health risk was posed to the site worker at any level of exposure to THM.

Date of Award	Dec 2012
Original language	American English
Supervisor	Farrukh Ahmad (Supervisor)