Gary L. Amy

Disinfection by-product formation during seawater desalination: A review.

Due to increased freshwater demand across the globe, seawater desalination has become the technology of choice in augmenting water supplies in many parts of the world. The use of chemical disinfection is necessary in desalination plants for pre-treatment to control both biofouling as well as the post-disinfection of desalinated water. Although chlorine is the most commonly used disinfectant in desalination plants, its reaction with organic matter produces various disinfection by-products (DBPs) (e.g., trihalomethanes [THMs], haloacetic acids [HAAs], and haloacetonitriles [HANs]), and some DBPs are regulated in many countries due to their potential risks to public health. To reduce the formation of chlorinated DBPs, alternative oxidants (disinfectants) such as chloramines, chlorine dioxide, and ozone can be considered, but they also produce other types of DBPs. In addition, due to high levels of bromide and iodide concentrations in seawater, highly cytotoxic and genotoxic DBP species (i.e., brominated and iodinated DBPs) may form in distribution systems, especially when desalinated water is blended with other source waters having higher levels of organic matter. This article reviews the knowledge accumulated in the last few decades on DBP formation during seawater desalination, and summarizes in detail, the occurrence of DBPs in various thermal and membrane plants involving different desalination processes. The review also identifies the current challenges and future research needs for controlling DBP formation in seawater desalination plants and to reduce the potential toxicity of desalinated water.

Ozonation of aquatic organic matter and humic substances: An analysis of surrogate parameters for predicting effects on trihalomethane formation potential

Abstract Ozone represents a potential oxidant for controlling trihalomethanes (THMs) during water treatment. The results presented herein indicate that partial oxidation of THM precursors by ozone produces by‐products which are lesa reactive in forming THMs upon chlorination. It is demonstrated that surrogate parameters such as nonvolatile total organic carbon, UV absorbance, and fluorescence are capable of monitoring the performance of the ozonation process in reducing the THM formation potential of waters containing THM precursors.

Organic micropollutants in aerobic and anaerobic membrane bioreactors: Changes in microbial communities and gene expression

Organic micro-pollutants (OMPs) are contaminants of emerging concern in wastewater treatment due to the risk of their proliferation into the environment, but their impact on the biological treatment process is not well understood. The purpose of this study is to examine the effects of the presence of OMPs on the core microbial populations of wastewater treatment. Two nanofiltration-coupled membrane bioreactors (aerobic and anaerobic) were subjected to the same operating conditions while treating synthetic municipal wastewater spiked with OMPs. Microbial community dynamics, gene expression levels, and antibiotic resistance genes were analyzed using molecular-based approaches. Results showed that presence of OMPs in the wastewater feed had a clear effect on keystone bacterial populations in both the aerobic and anaerobic sludge while also significantly impacting biodegradation-associated gene expression levels. Finally, multiple antibiotic-type OMPs were found to have higher removal rates in the anaerobic MBR, while associated antibiotic resistance genes were lower.

Coagulation and adsorption of humic substances: An analysis of surrogate parameters for predicting effects on trihalomethane formation potential

Abstract Alum coagulation and activated carbon adsorption are effective water treatment processes for removing trihalomethane precursors. Nonpurgeable organic carbon (NPOC), UV absorbance, and fluorescence can serve as surrogate parameters for predicting the trihalomethane formation potential (THMFP) of a water source from its untreated state through various degrees of treataent by these processes. Multiplicative parameters such as the product of UV absorbance and NPOC can also function as effective surrogates.

Effect of pH and Calcium on the Adsorptive Removal of Cadmium and Copper by Iron Oxide–Coated Sand and Granular Ferric Hydroxide

AbstractIron oxide–coated sand (IOCS) and granular ferric hydroxide (GFH) were used to study the effect of Ca2+ and pH on the adsorptive removal of Cu2+ and Cd2+ from groundwater using batch adsorption experiments and kinetic modeling. It was observed that Cu2+ and Cd2+ were not stable in synthetic waters. The extent of precipitation increased with increasing pH. Removal of Cu2+ and Cd2+ was achieved through both precipitation and adsorption, with IOCS showing higher adsorption efficiency. Increase of pH (from 6 to 8) resulted in a higher overall removal efficiency of both Cu2+ and Cd2+, with precipitation as predominant removal mechanisms at higher pH values, especially for Cu2+. An increase in Ca2+ concentration increased the precipitation of Cu2+ [as Cu2(OH)2CO3 and Cu3(OH)2(CO3)2] and Cd2+ [as Cd(OH)2 and CdCO3]. In addition, Ca2+ competes with Cu2+ and Cd2+ for surface adsorption sites on IOCS and GFH, and reduces their adsorption capacity. The kinetic modeling revealed that the adsorption of Cd2+ on...

Case study approach to modeling historical disinfection by-product exposure in Iowa drinking waters

In the 1980s, a case-control epidemiologic study was conducted in Iowa (USA) to analyze the association between exposure to disinfection by-products (DBPs) and bladder cancer risk. Trihalomethanes (THMs), the most commonly measured and dominant class of DBPs in drinking water, served as a primary metric and surrogate for the full DBP mixture. Average THM exposure was calculated, based on rough estimates of past levels in Iowa. To reduce misclassification, a follow-up study was undertaken to improve estimates of past THM levels and to re-evaluate their association with cancer risk. In addition, the risk associated with haloacetic acids, another class of DBPs, was examined. In the original analysis, surface water treatment plants were assigned one of two possible THM levels depending on the point of chlorination. The re-assessment considered each utility treating surface or groundwater on a case-by-case basis. Multiple treatment/disinfection scenarios and water quality parameters were considered with actual DBP measurements to develop estimates of past levels. The highest annual average THM level in the re-analysis was 156μg/L compared to 74μg/L for the original analysis. This allowed the analysis of subjects exposed at higher levels (>96μg/L). The re-analysis established a new approach, based on case studies and an understanding of the water quality and operational parameters that impact DBP formation, for determining historical exposure.

MEASUREMENT OF MOLECULAR WEIGHT DISTRIBUTIONS OF ORGANIC HALIDE IN KRAFT MILL WASTE STREAMS, WASTE SOLIDS AND PULP

Abstract Analytical procedures were developed for determining the apparent molecular weight (AMW) distribution of organic halide in both liquid and solid pulp and paper process components. The techniques included molecular weight separations using ultrafiltration (UF) and determinations using adsorption‐pyrolysis‐microcoulometry (AC/MC). Correction coefficients for rejection properties of UF membranes were determined using a diafiltration technique.

The interplay between natural organic matter and bromide on bromine substitution

This study examined the interplay between bromide and DOM characteristics, described with SUVA254, in terms of formation and speciation of selected DBPs [trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs)] during chlorination under various water treatment conditions. Cytotoxicity evaluations were also conducted based on the types and amounts of DBPs formed and their corresponding cytotoxicity index values. The results showed that the formation of THMs and HAAs increased as the specific UV absorbance at 254 nm (SUVA254) of the waters increased; however, there was no clear trend for HANs. THM and HAN formation increased with increasing bromide levels, while there was no bromide effect on the HAA formation. Lower HAA5 (monochloroaceticacid, monobromoaceticacid, dichloroaceticacid, trichloroaceticacid, dibromoaceticacid) to HAA9 (monochloroaceticacid, monobromoaceticacid, dichloroaceticacid, trichloroaceticacid, dibromoaceticacid, bromochloroaceticacid, bromodichloroaceticacid, dibromochloroaceticacid, tribromoaceticacid) ratios, independent of SUVA254, were observed with increasing bromide levels. Bromine substitution factor (BSF) values were in the order of BSFDHAN > BSFTHAA > BSFTHM ≈ BSFDHAA. BSF values for all class of DBPs decreased with increasing SUVA254. TOX formation increased with increasing SUVA254 without an impact of bromide concentration. UTOX/TOX ratios were higher in treated low SUVA254 waters than raw waters having higher SUVA254 values, and they decreased with increasing initial bromide concentration in all sources. Increasing bromide concentration from 0.5 μM to 10 μM elevated the calculated cytotoxicity index values of waters. Despite their much lower (approximately ~10 times) formation as compared to THMs and HAAs, HANs controlled the calculated cytotoxicity of studied waters.

Formation of regulated and unregulated disinfection byproducts during chlorination of algal organic matter extracted from freshwater and marine algae

Seasonal algal blooms in freshwater and marine water can increase the input of algal organic matter (AOM) to the pool of dissolved organic matter. The impact of bromide (Br-) and iodide (I-) on the formation of regulated and unregulated disinfection byproducts (DBPs) was studied from chlorination of AOM solutions extracted from three species of cultured isolates of freshwater and marine algae (Microcystis aeruginosa (MA), Synechococcus (SYN), and Alexandrium tamarense (AT)). Comparable concentrations of DBPs were formed from three types of AOM. In the absence of Br-, trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetaldehydes (HALs) were the main groups of DBP formed, and haloacetonitriles (HANs) were formed at lower concentrations. In contrast, the formation of iodinated THMs was <8 nM (1.7 μg/L) since most of initial I- was oxidized to iodate. Increasing initial Br- concentrations increased the formation of THMs and HANs, while concentrations of total organic halogen and HAA remained stable. On the contrary, total HAL concentrations decreased due to the instability of bromated HALs. Decreasing the specific UV absorbance (SUVA) value of AOM favours bromine substitution since bromine more preferentially reacts with low reactivity organic matter than chlorine. Increasing the pH enhanced the formation of THMs but decreased the formation of HANs. Concentrations of HANs and HALs decreased at high pH (e.g., 9.0), high initial chlorine concentration and long reaction time due to the decomposition. Based on the cytotoxicity calculations, unregulated HANs and HALs were the main contributors for the total toxicity of DBPs measured, even though based on the weight regulated THMs and HAAs predominated.

Direct and Indirect Seawater Desalination by Forward Osmosis

Abstract Forward osmosis (FO) is an emerging membrane technology with a range of possible water treatment applications including desalination. The FO process itself can directly desalt seawater as a feed solution by employing a draw solution with higher osmotic pressure than seawater. However, the energetics of product water recovery and draw solution reuse is not favorable. Alternatively, the FO process using seawater as a natural draw solution and quality-impaired water as the feed can potentially couple with low-pressure reverse osmosis as a hybrid to be a lower-energy desalination process, in which indirect desalination is achieved. Most organic fouling in FO desalination process is reversible. However, the mechanism of scaling formation in FO desalination is more complicated than the conventional RO process. Both feed and draw solution can influence the scaling formation and its reversibility. The economic feasibility of FO desalination process depends on the operational mode (direct and indirect) as well as the plant scale and level of commercialization. Although there are still some choke points in the current deployment of FO desalination, the future development of efficient draw solution and novel FO membrane will significantly promote FO desalination technology.