Carbonaceous and nitrogenous DBPs are a significant current regulatory concern for water utilities and pose future challenges. My research group is working on understanding the occurrence and structure of DBP precursors, how to remove the precursors and factors that influence DBP formation. Several projects are currently underway as of 2014:
- Water Research Foundation #4370 – Controlling the Formation of Nitrosamines During Water Treatment (Krasner, Mitch, Westerhoff, Chen, Skadsen). The objective of this project is to develop improved strategies for minimizing nitrosamine formation during drinking water treatment and to develop treatment guidance for utilities. Here are two example papers: Formation Precursors Control & Occurrence of Nitrosamines in Drinking Water_A review_Water Resarch 2013 and 2013_Adsorption of NDMA Precursors by PAC and GAC
- Water Research Foundation #4499 – Relative Importance and Contribution of Anthropogenic and Natural Sources of Nitrosamine Precursors (Westerhoff, Herckes, Andrews, Thurman, Ferrer, Bukhari). The goal of this project is to develop approaches to characterize relative sources of NA precursors (natural versus wastewater origins) and to understand how these sources influence treatability of the precursors to minimize NA formation. The benefit of this research is that identifying and understanding the sources of NA precursors will allow for better mitigation strategies (e.g., at wastewater treatment plants, in watersheds, in drinking water treatment plants) and potentially may help identify appropriate surrogates.
- Several related projects are underway with private funding to investigate in-situ regeneration of granular activated carbon (GAC) as a means of control DBP precursors or trace organic pollutants.
Summaries of past projects (under-development)
USEPA Grant # R 826831-01-0 Final Report June 2002 – Click Here to download PDF file of Final Report Investigators Paul Westerhoff, David Reckhow, Gary Amy, Zaid Chowdhury Executive Summary The water industry faces new challenges in understanding and controlling disinfection by-product (DBP) formation as health concerns demonstrate a need for more stringent regulatory DBP requirements. Mechanistic tools for understanding and predicting the rate and extent of DBP formation are required in order to facilitate the evaluation of DBP control alternatives. The goal of this project was to develop and calibrate an accurate kinetic-based model for several chlorinated DBPs of interest. The model predicts DBPs (e.g., four THM species (THM4) and nine HAA species (HAA9)) as a function of DOC, disinfectant level (type and dosage), reaction time, temperature, pH, and bromide concentrations. The project had the following specific objectives:
- Compile existing databases on DBP formation experiments into a single Unified Database. Some data from the compiled database were used to develop and/or verify mechanistic DBP prediction equations. Data deficiencies were identified.
- Develop and calibrate numerical models for predicting the behavior of disinfectants (free-chlorine) and the formation of DBPs (THMs and HAAs) and improve DBP prediction accuracy over existing empirical DBP models through consideration of formation mechanisms and DBP stability. Controlled experiments were performed to assess inorganic reactions, disinfectant decay, DBP formation, and DBP stability. Additional laboratory experiments were performed to augment the Unified Database, and overcome data deficiencies.
- Develop an easy-to-use computer model capable of predicting DBP formation, through a combination of mechanistic subroutines, as a function of disinfectant decay and water quality conditions.
Existing databases were found to have several deficiencies limiting their usefulness for calibrating mechanistic models. These include lack of short-term kinetic chlorine consumption and/or THM plus HAA species formation. Bench-scale experiments were therefore conducted to fill the datagaps. The purpose of the bench-scale experiments was to obtain a wide range of NOM material from natural waters that simulated a range of treatment (NOM removal processes: coagulation, softening, ozonation, activated carbon sorption, and ultrafiltration) and disinfection (chlorine dose) conditions representative of full-scale water treatment facilities. Based on the literature reports of mechanisms involved in chlorination process and in light of previous observations during chlorination of natural waters, a comprehensive mechanistic model was developed. The mechanistic model simulates DBP formation as a set of reactions between chlorine, bromine, and natural organic matter (NOM) as represented by three classes of reactive-sites: instantaneous, fast, and slow reacting NOM sites. Mechanistic models were parameterized for kinetic constants, and NOM reactive site concentrations optimized to fit observed data. It was concluded that chlorine decay and DBP formation were correlated, and less than 5% of the DOC concentration was present as chlorine reactive and DBP precursor material. The mechanistic models were coded into the existing USEPA Water Treatment Plant Simulation model (Version 2.1).
USEPA Grant # R 826835-01-0
Paul Westerhoff, Ph.D., PE
Department of Civil and Environmental Engineering
Arizona State University
Tempe, AZ 85287