Ultraviolet absorbance monitoring for removal of DBP-precursor in waters with variable quality: Enhanced coagulation revisited.

Enhanced coagulation can be an effective way to reduce disinfection by-product (DBP) precursor concentrations. Where turbidity is not extremely high, the natural organic matter concentration evaluated by total or dissolved organic carbon concentration or UV absorbance is known to be the most important factor for determining the adequate coagulant dose. Yet, treatment plant operators are often faced with difficult decisions when it comes to coagulant dosages: Should coagulation efforts and coagulant doses be consistent year-round when water quality changes seasonally? Should the coagulant dose be increased when DBP standards are not met, or has the maximum removal of DBP precursors been reached? The objective and novelty of this study is to revisit the concept of enhanced coagulation and to determine optimal coagulation guidelines based not just on the removal of common indicators such as DOC but on the removal of actual DBP precursors.

Multi-wavelength models expand the validity of DBP-differential absorbance relationships in drinking water.

Differential UV absorbance (ΔA) is an important indicator that could allow operators and utility managers to routinely monitor disinfection by-product (DBP) concentrations, even in real-time applications, without the limitations of regulatory sampling and analyses. While determination coefficients between differential UV absorbance at a single wavelength (often 272 nm) and chlorination DBP concentrations are usually very high (R > 0,90), the fitting parameters of these relationships vary from one water source to another, or vary within the same water source depending on the time of year. The objectives of this study are to apply multiple regression models to a rich database of ΔA and DBPs (trihalomethanes (THMs) and haloacetic acids (HAAs)) that was generated from lab experiments using multiple waters with low bromide concentrations, in order to identify wavelengths that improve the applicability of DBP-ΔA relationships, as well as develop a widely applicable multi-wavelength DBP-ΔA relationship.

Relationships between DBP concentrations and differential UV absorbance in full-scale conditions.

Differential UV spectroscopy, defined as the difference in UV absorbance spectra before and after chlorination, has shown great potential to predict disinfection by-product (DBP) concentrations at laboratory scale. However, so far, no results have been reported on the full scale application of differential UV spectroscopy in drinking water treatment facilities. The objectives of this study are to determine if relationships can be developed between differential UV absorbance and DBP concentrations, for both regulated and unregulated DBPs, in a full-scale facility and to determine if these relationships vary throughout the year with variations in raw water quality and treatment conditions.