Mohamed S. Siddiqui

Ozone enhanced removal of natural organic matter from drinking water sources

Abstract The use of ozone as a pre-oxidant or intermediate oxidant in drinking-water treatment is becoming increasingly common. The ozonation of natural source waters containing natural organic matter produces biodegradable by-products such as organic acids, aldehydes, and ketoacids. These organic by-products serve as carbon source for bacteria, potentially causing regrowth problems in distribution systems. The measurement of biodegradable dissolved organic carbon (BDOC) provides quantitative insight into the amount of BDOC that is present. In drinking-water treatment, removal of BDOC can also reduce the formation potential of chlorination disinfection by-products such as trihalomethanes and haloacetic acids. Removal of BDOC was optimal at an applied ozone:DOC ratio of 2:1 (mg/mg) for source waters containing DOC levels ranging from 3 to 6 mg/liter. The use of biotreatment resulted in a 40–50% decrease in DOC, a 90–100% reduction in aldehydes, and a 40–60% reduction in trihalomethane formation potential. No removal of bromate ion and dibromoacetic acid was observed. A positive correlation was obtained between BDOC and assimilable organic carbon; both parameters indicate a tendency to plateau at an applied ozone/DOC weight ratio of 2:1.

Membranes for the control of natural organic matter from surface waters

A range of nanofiltration (NF) modules was evaluated to determine rejection of disinfection by-product (DBP) precursors from low turbidity surface waters. Dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP), and chloral hydrate formation potential (CHFP) rejections averaged 90, 97, 94, and 86%, respectively. Rejections of bromide ion, an inorganic precursor, ranged from 40-80%. Pretreatment using microfiltration (MF) alone before NF provided some removal of turbidity but not enough to maintain the initial flux and recovery of the NF unit. NF runs were sustained over 30 days; however, some adverse changes in operational conditions were observed, and significant pressure increases were necessary to maintain flux. Precursor rejections by NF following MF varied little over time frames of up to 30 days. MF was only moderately eAective in particle removals, with virtually no DBP precursor removal provided by MF. Ultrafiltration (UF) alone did not exhibit significant changes in operational conditions over a 30-day time frame; however, only modest precursor (<30% DOC) removal was observed. 7 2000 Elsevier Science Ltd. All rights reserved

Bromate Destruction by UV Irradiation and Electric Arc Discharge

Abstract Bromate ion destruction by UV irradiation using either a low pressure mercury lamp or a medium pressure mercury lamp has been evaluated. A low pressure lamp which emits radiation predominantly at < 200 nm was more effective than the UV lamp which emits radiation at 254 nm, since bromate ion has a peak absorbance of about 195 nm. Bromate ion was shown to be reduced to bromide ion with bromine as an intermediate. Bromate ion destruction using a low pressure mercury lamp (< 200 nm) ranged from 3 to 38% for doses ranging from 23 to 228 mW-s/cm2; 7-46% destruction was achieved using a medium pressure lamp with initial bromate ion concentrations of 11-38 μg/L and doses ranging from 60 to 550 mW-s/cm2. A new innovative electric arc discharge method also has been evaluated and compared with UV irradiation. The electric arc discharge method destroyed 12-45% bromate ion for doses ranging from 130 to 1300 mW-s/cm2.

Empirically and Theoretically–Based Models for Predicting Brominated Ozonated By–Products

Abstract During water treatment, ozonation of waters containing bromide ion producesboth organic and inorganic disinfection byproducts. Bromide ion concentrations in U.S. waters range from 0.01 to 2 mg/L (Krasner, 1989). Bromoformand dibromoacetic acid (DBAA) are the major organic byproducts and bromateion is the major inorganic byproduct derived from ozonation. Bromoform is a known carcinogen and the existence of bromate ion in water supplies also is of public health concern (Lykins, 1986). Bromate ion causes renal failure and hearing loss in laboratory animals and in human beings (Kruithof, 1992). The provisional guideline for bromate ion as proposed by the World Health Organization is 25 pg/L and may be exceeded in water treatment processesusing ozone. Also draft drinking water regulations in the U.S. will specify a maximum contaminant level (MCL) of 10 µg/L for bromate ion and a bestavailable treatment (BAT) of pH adjustment.

MODELING DISSOLVED OZONE AND BROMATE ION FORMATION IN OZONE CONTACTORS

Many drinking water utilities that use source waters with significant bromide ion levels are currently seeking disinfection regimes that will minimize the formation of brominated disinfection byproducts while providing adequate disinfection. While ozonation appears to be a promising option for achieving these goals, the uncertainty of future drinking water regulations has developed a need for predicting actual disinfection byproduct formation prior to the costly investment for upgrading existing treatment facilities. The models developed in this paper provide comparisons of ozonation application methods, providing a basis for minimizing bromate and aiding in future design considerations. Theoretical and empirical models for the determination of ozone transferred, dissolved ozone concentrations, and bromate formation have been derived and compared with pilot-scale and full-scale data; a good agreement has been observed between the actual data and the predicted data, showing the validity of these models. True-batch bromate formation more closely simulated pilot-scale and full-scale data. Bromate formation in one stage vs two stage ozone contactors and different reactor configurations have been compared. Ozone gas phase concentration appears to have an effect on bromate formation as well.

Modelling effects of bromide ion concentration on the formation of brominated trihalomethanes

A series of statistically‐based models have been developed for predicting the formation of individual trihalomethane (THM) species, ranging from chloroform to bromoform, as a function of various reaction conditions. These equations allow a quantitative assessment of bromide effects on overall THM formation as well as THM speciation.