Organic matter biofiltration performance modeling: Influence of influent water quality, operating conditions, and biomass.

The impact of source water dissolved organic matter (DOM) origin, empty bed contact time (EBCT), temperature, and pretreatment methods on biofiltration performance was evaluated and predictive models based on experimental data were developed. Three DOM source water types, terrestrial, microbial, and treated wastewater (WW) effluent, were utilized. A model was developed to predict biofilter performance for dissolved organic carbon (DOC) removal based on the influent biodegradable DOC (BDOC) fraction, a single active biomass measurement from the top of the filter and the filter EBCT. A biomass distribution model was developed to predict total active biomass throughout the filter based on a single biomass measurement from the top of the filter. The measured BDOC fractions were 21 % for the nonWW impacted source waters, 36 % for the WW effluents and 62 % for the ozonated WW effluents. At an EBCT of 15 min, biofilters removed between 7 and 21 % of the DOC (19 to 50 % for BDOC) depending on the DOM type and use of ozonation. When the EBCT decreased to 5 min DOC removal decreased by 40 % and when increased to 30 min removal increased by 42 %. When the temperature decreased from 22 °C to 6 °C DOC removal was 33 % lower and when increased to 28 °C removal was 42 % higher. ATP values were found to be a function of temperature and DOM origin, as the average ATP values from the WW effluent biofilters were almost double that of the non-WW impacted sources and pre-ozonation of the WW effluent yielded values three times higher. The model was applied to the results of 27 different biofilter runs at three EBCTs yielding one distinct rate constant for the non-WW impacted source waters and one rate constant for the WW effluents. The model was successfully applied to the results of 19 filter runs from the literature and to those from a pilot plant over 6 months of operation.

Control of Pre-formed Halogenated Disinfection Byproducts with Reuse Biofiltration.

Disinfection byproduct (DBP) pre-formation is a major issue when prechlorination is used before or during advanced treatment of impacted drinking water sources. Control strategies for pre-formed DBPs before final disinfection, especially for currently nonregulated although highly toxic DBP species, are not yet established. This study evaluated the biodegradation potential of pre-formed DBPs, including haloacetonitriles (HANs), haloacetamides (HAMs), and haloacetaldehydes (HALs), during biofiltration with sand, anthracite, and biological activated carbon of three wastewater effluents under potable reuse conditions. Up to 90%+ removal of di- and trihalogenated HANs, HAMs, and HALs was observed, and removal was associated with active heterotrophic biomass and removal of biodegradable organic carbon. Unlike the microbial dehalogenation pathway of haloacetic acids (HAAs), removal of HANs and HAMs appeared to result from a biologically mediated hydrolysis pathway (i.e., HANs to HAMs and HAAs) that may be prone to inhibition. After prechlorination, biofiltration effectively controlled pre-formed DBP concentrations (e.g., from 271 µg/L to as low as 22 µg/L in total) and DBP-associated calculated toxicity (e.g., 96%+ reduction). Abiotic residual adsorption capacity in biological activated carbon media was important for controlling trihalomethanes. Overall, the toxicity-driving DBP species exhibited high biodegradation potential and biofiltration showed significant promise as a pre-formed DBP control technology.

Impacts of carbon-based advanced treatment processes on disinfection byproduct formation and speciation for potable reuse.

For the potable reuse of municipal wastewater effluent, carbon based advanced treatment (CBAT) using coagulation, ozonation, biofiltration and/or granular activated carbon (GAC) adsorption is a promising approach for controlling disinfection byproduct (DBP) formation. However, CBAT can also favor a shift in DBP formation to more toxic brominated DBP species. To protect public health, treatment-specific DBP formation and speciation trends need to be identified and understood. First, this study systematically evaluated the treatment of six wastewater effluents with four CBAT process trains (experimental n was 55) and measured DBP formation and speciation trends. Overall, CBAT decreased DBP formation by >90% and GAC preferentially removed highly-reactive effluent organic matter as indicated by lower yields of both highly-forming and highly-toxic classes of carbonaceous and nitrogenous DBPs. Since GAC treatment also induced systematic speciation changes by increasing the ratio of bromide to dissolved organic matter, the second part of this study focused on understanding the health impacts of DBP speciation changes on calculated additive toxicity (CAT). Based on the evaluation of 20 DBPs, measured using established methods, the CAT values from cyto- and genotoxicity metrics decreased by as much as 85% due to high levels of precursor removal by GAC. Expanding the evaluation to include 52 DBPs, measured using more extensive analytical methods, resulted in the same conclusions. This study also developed a "speciation potency" metric, that re-scales class-by-class speciation trends using toxic potency factors (e.g., cytotoxicity [LC50]). The observed shifts in DBP speciation after treatment increased the class-level toxic potency factors by up to a factor of 4; a greater amount of precursor removal is required for treatment to reduce toxicity, which was achieved with CBAT trains. This proposed approach of combining speciation potency with DBP yields enables evaluation of DBP-associated risk with easily measured surrogates (i.e., bromide and dissolved organic carbon [DOC]). By identifying and quantitatively comparing DBP formation and speciation trends over multiple wastewater effluents and treatment trains, this study demonstrates that CBAT can be a robust approach to DBP precursor removal for potable reuse.

Pre-pyrolysis metal and base addition catalyzes pore development and improves organic micropollutant adsorption to pine biochar.

Biochars were produced from pine feedstock pretreated with aqueous base, NaOH, at pH 9 and 11, and alkali and alkaline earth metals (AAEMs) Na, K, Ca, and Mg at 10-3 and 1 M. The effects of base and AAEM feedstock pretreatment on biochar surface area, pore size distribution, and adsorption capacity of two organic micropollutants (OMPs), 2,4-dichlorophenoxyacetic acid and sulfamethoxazole, from surface water with background dissolved organic matter (DOM) were evaluated. Base pretreatment significantly increased surface area within micropores (<2 nm diameter). AAEM pretreatment caused pore widening, increasing surface area within pores >2 nm in diameter. The catalytic activity of AAEMs, assessed by generation of non-micropore surface area, decreased in the following order: Ca > K > Na > Mg. All pretreated biochars outperformed untreated biochar for OMP adsorption. Biochar pretreated by aqueous base at pH 11 showed over an order of magnitude increase in OMP adsorption, nearly matching the performance of commercial activated carbon. OMP adsorption from surface water was positively correlated with biochar micropore surface area and negatively correlated with non-micropore surface area, which was linked to higher levels of DOM competition. Base and AAEM pretreatment of biochar feedstocks can increase OMP adsorption for water treatment applications by tuning pore structure and surface area.

Removal of effluent organic matter with biofiltration for potable reuse: A review and meta-analysis.

Biofiltration, historically used for biodegradable organic matter (BOM) removal in drinking water treatment, is being increasingly applied for potable reuse which requires unique characterization. This review and meta-analysis evaluates BOM occurrence as part of bulk wastewater effluent organic matter (EfOM), quantifies the roles of operational parameters to achieve EfOM removal in biofilters, and identifies research gaps which may be fruitful for understanding reuse biofilter performance. Literature data (n = 76) indicates EfOM has a high biodegradable fraction (median 26%), which after typical ozone doses is higher (57%). A biofiltration performance dataset (n = 160 across 42 WWTP effluents) shows that EfOM removal of 35-40% can be expected when design parameters are optimized. Specifically, higher EfOM removal is achieved by adding pre-ozonation and use of biological activated carbon (BAC) media, with comparatively smaller impacts of increasing ozone dose or increasing empty bed contact time under typical scenarios. Combined, these factors strongly correlate with observed EfOM removal (r2 = 0.64) after accounting for confounding by adsorptive removal in BAC media with fewer than 20,000 bed volumes treated. Future research that quantifies the occurrence of BOM, biomass activity on filter media, steady-state removal by BAC, and impacts of longer empty bed contact times in potable reuse scenarios could impact optimization strategies to meet or exceed biofilter performance observed to date.

Controlling disinfection byproducts from treated wastewater using adsorption with granular activated carbon: Impact of pre-ozonation and pre-chlorination.

This study measured chlorine- and chloramine-reactive precursors using formation potential (FP) tests of nine U.S. Environmental Protection Agency (EPA) regulated and 57 unregulated disinfection byproducts (DBPs) in tertiary-filtered wastewater before and after pilot-scale granular activated carbon (GAC) adsorption. Using breakthrough of precursor concentration and of concentration associated calculated cytotoxicity and genotoxicity (by correlating known lethal concentrations reported elsewhere), the performance of three parallel GAC treatment trains were compared against tertiary-filtered wastewater: ozone/GAC, chlorine/GAC, and GAC alone. Results show GAC alone was the primary process, versus ozone or chlorine alone, to remove the largest fraction of total chlorine- and chloramine-reactive DBP precursors and calculated cytotoxicity and genotoxicity potencies. GAC with pre-ozonation removed the most chlorine- and chloramine-reactive DBP precursors followed by GAC with pre-chlorination and lastly GAC without pre-treatment. GAC with pre-ozonation produced an effluent with cytotoxicity and genotoxicity of DBPs from FP that generally matched that of GAC without pre-oxidation; meanwhile removal of toxicity was greater by GAC with pre-chlorination. The cytotoxicity and genotoxicity of DBPs from FP tests did not scale with DBP concentration; for example, more than 90% of the calculated cytotoxicity resulted from 20% of the DBPs, principally from haloacetaldehydes, haloacetamides, and haloacetonitriles. The calculated cytotoxicity and genotoxicity from DBPs associated with FP-chloramination were at times higher than with FP-chlorination though the concentration of DBPs was five times higher with FP-chlorination. The removal of DBP precursors using GAC based treatment was at least as effective as removal of DOC (except for halonitromethanes for GAC without pre-oxidation and with pre-chlorination), indicating DOC can be used as an indicator for DBP precursor adsorption efficacy. However, the DOC was not a good surrogate for total cytotoxicity and genotoxicity breakthrough behavior, therefore, unregulated DBPs could have negative health implications that are disconnected from general water quality parameters, such as DOC, and regulated classes of DBPs. Instead, cytotoxicity and genotoxicity correlate with the concentration of specific classes of unregulated DBPs.

Sorption, coagulation, and biodegradation for graywater treatment.

Population growth and climate change are exacerbating water scarcity. Graywater recycling could reduce water demand but it is not commonly practiced because of high treatment costs. Biochar, an emerging low-cost alternative sorbent with potential environmental benefits for graywater treatment, was compared to activated carbon (AC) for removing dissolved organic carbon (DOC) from graywater. The impact of pretreatments (coagulation, biodegradation) were also evaluated. Among five biochars tested, a wood-based biochar was the most effective for graywater treatment, but AC removed more DOC. Sorption resulted in a greater percent removal of ultraviolet (UV) absorbance than DOC or free chlorine demand. Graywater regulations could not be met by sorption alone but could be met with pretreatment before sorption. After biodegradation, irrigation and toilet flushing treatment targets could be achieved with AC doses less than 0.7 g/L, while a biochar dose of about 1 g/L was needed to achieve the irrigation treatment targets. For DOC removal, alum coagulation at a dose of 30 mg/L was a less effective pretreatment than biodegradation. Pretreatment and sorption to decrease turbidity and increase UV transmittance could be effective for the potential use of UV disinfection, thus creating an effective graywater non-potable reuse approach.

Granular Activated Carbon Adsorption of Carcinogenic Volatile Organic Compounds at Low Influent Concentrations.

The effectiveness of granular activated carbon (GAC) for carcinogenic volatile organic compounds (cVOCs) has not been evaluated in the low- to sub- microgram per liter range. Rapid small scale column tests (RSSCTs) were employed to determine the GAC performance at empty bed contact times (EBCTs) of 7.5 and 15 minutes for 13 cVOCs at a target influent concentration of 5 µg/L in a typical groundwater matrix. Breakthrough was assessed for vinyl chloride, dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropropane, carbon tetrachloride, 1,3-butadiene, 1,1,1,2-tetrachloroethane, 1,2,3-trichloropropane, trichloroethylene and tetrachloroethylene. The throughput to breakthrough was found to be linearly correlated to capacities calculated with single-solute equilibrium isotherm parameters. Modest decreases, 9 to 13% on average, in throughput to 50% and 75% breakthrough were found when the EBCT was increased from 7.5 to 15 minutes. The carbon use rate (CUR), when scaled to simulate full-scale adsorption, indicated that GAC would be a viable technology for seven of the VOCs evaluated, with a CUR threshold less than 0.2 lbs/1000 gal. It may be possible to use 1,1 DCA and 1,2 DCA as surrogates for assessing chemicals near the feasibility limit.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Does Granular Activated Carbon with Chlorination Produce Safer Drinking Water? From Disinfection Byproducts and Total Organic Halogen to Calculated Toxicity.

Granular activated carbon (GAC) adsorption is well-established for controlling regulated disinfection byproducts (DBPs), but its effectiveness for unregulated DBPs and DBP-associated toxicity is unclear. In this study, GAC treatment was evaluated at three full-scale chlorination drinking water treatment plants over different GAC service lives for controlling 61 unregulated DBPs, 9 regulated DBPs, and speciated total organic halogen (total organic chlorine, bromine, and iodine). The plants represented a range of impacts, including algal, agricultural, and industrial wastewater. This study represents the most extensive full-scale study of its kind and seeks to address the question of whether GAC can make drinking water safer from a DBP perspective. Overall, GAC was effective for removing DBP precursors and reducing DBP formation and total organic halogen, even after >22 000 bed volumes of treated water. GAC also effectively removed preformed DBPs at plants using prechlorination, including highly toxic iodoacetic acids and haloacetonitriles. However, 7 DBPs (mostly brominated and nitrogenous) increased in formation after GAC treatment. In one plant, an increase in tribromonitromethane had significant impacts on calculated cytotoxicity, which only had 7-17% reduction following GAC. While these DBPs are highly toxic, the total calculated cytotoxicity and genotoxicity for the GAC treated waters for the other two plants was reduced 32-83% (across young-middle-old GAC). Overall, calculated toxicity was reduced post-GAC, with preoxidation allowing further reductions.

Biodegradable organic matter and rapid-rate biofilter performance: A review.

Biodegradable organic matter (BOM), found in all surface waters, is a challenge for drinking water utilities because it can lead to distribution system bio-regrowth, react to form disinfection by-products, or be a specific compound of concern. A critical review of BOM (occurrence and oxidant effects) and rapid-rate biofiltration performance (preozonation, backwashing with an oxidant, empty bed contact time (EBCT) and temperature) was carried out. An extensive literature data analysis (n = 100) found total organic carbon (TOC) in nonozonated water is comprised of 20% (median) biodegradable organic carbon (BDOC) and 3% (median) assimilable organic carbon (AOC). For ozonated waters (n = 103), these values increased to 30% (median) BDOC and 9% (median) AOC. For all operation conditions (n = 117), biofilters (12 min average EBCT) removed 12% (median) of the influent TOC with higher removals for ozonated waters, 15% (median), compared to nonozonated waters, 10% (median). As temperature increased from ≤10 °C to ≥20 °C, TOC removal increased from 10% to 17% (median). This review demonstrates biofiltration can be an efficient treatment technology to remove a portion of the BOM from the filter influent and should be optimized to achieve maximum removal.

Simplified Modeling of Organic Contaminant Adsorption by Activated Carbon and Biochar in the Presence of Dissolved Organic Matter and Other Competing Adsorbates.

Cyclohexanol, phenol, benzoic acid, and phenanthrene fractional removal (italicized words are defined within the main text) by pulverized granular activated carbon and biochar adsorption in deionized water and stormwater was independent of target-adsorbate initial concentrations (C0) when C0s were below concentration thresholds. This permits a simple-modeling approach. C0-independent removal in deionized water at low-target-adsorbate concentrations potentially suggests that DOM in the deionized water induce a competitive effect that causes deviations from the Freundlich model. The Ideal Adsorbed Solution Theory-Equivalent Background Compound model was used to determine the magnitude of concentration thresholds and the competitive effect of stormwater DOM and possibly deionized water DOM. These competing substances' competitive effects were influenced by target-compound adsorbability and structure. Concentration thresholds positively correlate with competing substances' competitive effect and negatively correlate with target-adsorbate-Freundlich 1/n values. In deionized water, concentration thresholds increase as target-compound adsorbability decreases. In stormwater, concentration thresholds do not correlate with adsorbability, potentially because stormwater DOM is better suited to compete for aromatic-compound-adsorption sites. The extent known-competitor adsorbates decrease target-adsorbate removal in the presence of DOM is investigated, which depends on the competing adsorbates' relative adsorbabilities and if they adsorb to a different subpopulation of adsorption sites.

Evaluating Activated Carbon Adsorption of Dissolved Organic Matter and Micropollutants Using Fluorescence Spectroscopy.

Dissolved organic matter (DOM) negatively impacts granular activated carbon (GAC) adsorption of micropollutants and is a disinfection byproduct precursor. DOM from surface waters, wastewater effluent, and 1 kDa size fractions were adsorbed by GAC and characterized using fluorescence spectroscopy, UV-absorption, and size exclusion chromatography (SEC). Fluorescing DOM was preferentially adsorbed relative to UV-absorbing DOM. Humic-like fluorescence (peaks A and C) was selectively adsorbed relative to polyphenol-like fluorescence (peaks T and B) potentially due to size exclusion effects. In the surface waters and size fractions, peak C was preferentially removed relative to peak A, whereas the reverse was found in wastewater effluent, indicating that humic-like fluorescence is associated with different compounds depending on DOM source. Based on specific UV-absorption (SUVA), aromatic DOM was preferentially adsorbed. The fluorescence index (FI), if interpreted as an indicator of aromaticity, indicated the opposite but exhibited a strong relationship with average molecular weight, suggesting that FI might be a better indicator of DOM size than aromaticity. The influence of DOM intermolecular interactions on adsorption were minimal based on SEC analysis. Fluorescence parameters captured the impact of DOM size on the fouling of 2-methylisoborneol and warfarin adsorption and correlated with direct competition and pore blockage indicators.

Drinking water treatment response following a Colorado wildfire.

Wildfires can greatly alter the vegetation, soils, and hydrologic processes of watersheds serving as drinking water supplies, which may negatively influence source water quality and treatment. To address wildfire impacts on treatment, a drinking water intake below a burned watershed and an upstream, unburned reference site were monitored following the High Park wildfire (2012) in the Cache la Poudre watershed of northern Colorado, USA. Turbidity, nutrients, dissolved organic matter (DOM) character, coagulation treatability, and disinfection byproduct formation were evaluated and compared to pre-fire data. Post-fire paired spatial differences between the treatment plant intake and reference site for turbidity, nitrogen, and phosphorus increased by an order of magnitude compared to pre-fire differences. Fluorescence index (FI) values were significantly higher at the intake compared to the reference site (Δ = 0.04), and higher than pre-fire years, suggesting the wildfire altered the DOM character of the river. Total trihalomethane (TTHM) and haloacetonitrile (HAN4) formation at the intake were 10.1 µg L-1 and 0.91 µg L-1 higher than the reference site. Post-fire water was amenable to conventional treatment at a 10 mg L-1 higher average alum dose than reference samples. The intake was also monitored following rainstorms. Post-rainstorm samples showed the maximum observed FI values (1.52), HAN4 (3.4 µg mgC-1) and chloropicrin formation yields (3.6 µg mgC-1), whereas TTHM and haloacetic acid yields were not elevated. Several post-rainstorm samples presented treatment challenges, and even at high alum doses (65 mg L-1), showed minimal dissolved organic carbon removal (<10%). The degraded water quality of the post-rainstorm samples is likely attributed to the combined effects of runoff from precipitation and greater erosion following wildfire. Wildfire impacts cannot be separated from rainfall effects due to the lack of post-rainstorm samples from the reference site. Results suggest for this study region, wildfire may have consequences for influent water quality, coagulant dosing, and DBP speciation.

Environmental Comparison of Biochar and Activated Carbon for Tertiary Wastewater Treatment.

Micropollutants in wastewater present environmental and human health challenges. Powdered activated carbon (PAC) can effectively remove organic micropollutants, but PAC production is energy intensive and expensive. Biochar adsorbents can cost less and sequester carbon; however, net benefits depend on biochar production conditions and treatment capabilities. Here, life cycle assessment was used to compare 10 environmental impacts from the production and use of wood biochar, biosolids biochar, and coal-derived PAC to remove sulfamethoxazole from wastewater. Moderate capacity wood biochar had environmental benefits in four categories (smog, global warming, respiratory effects, noncarcinogenics) linked to energy recovery and carbon sequestration, and environmental impacts worse than PAC in two categories (eutrophication, carcinogenics). Low capacity wood biochar had even larger benefits for global warming, respiratory effects, and noncarcinogenics, but exhibited worse impacts than PAC in five categories due to larger biochar dose requirements to reach the treatment objective. Biosolids biochar had the worst relative environmental performance due to energy use for biosolids drying and the need for supplemental adsorbent. Overall, moderate capacity wood biochar is an environmentally superior alternative to coal-based PAC for micropollutant removal from wastewater, and its use can offset a wastewater facility's carbon footprint.

Biochar sorbents for sulfamethoxazole removal from surface water, stormwater, and wastewater effluent.

This study examined sorption of the human and veterinary antibiotic sulfamethoxazole (SMX) at environmentally relevant concentrations from laboratory clean water, surface water, stormwater, and wastewater effluent to wood and wastewater-sludge derived biochars produced under a wide range of conditions. SMX sorption by commercial powdered activated carbon (PAC) was also quantified as a benchmark. Wood-based biochar produced around 850 °C performed similarly to PAC. Biochar sorption capacity increased with surface area up to ∼400 m(2)/g. However, a further increase in surface area did not correspond to an increase in sorption capacity. Sorbent H:C ratios correlated with SMX uptake by PAC and wood-based biochars, but not for the sludge-based biochars. This is possibly due to an indirect influence of the high ash content in sludge-based biochars, as the isolated ash fraction exhibited negligible SMX sorption capacity. The presence of dissolved organic matter (DOM) in the natural and anthropogenic waters fouled most of the sorbents (i.e., decreased SMX uptake). The sludge-based biochars experienced less DOM fouling relative to wood-based biochar, particularly in the wastewater effluent. Biochar and PAC sorption kinetics were similar when examined over a contact time of four-hours, suggesting their performance ranking would be consistent at contact times typically utilized in water treatment systems. In the presence of DOM, SMX relative removal (C/C0) was independent of SMX initial concentration when the initial concentration was below 10 µg/L, thus permitting the relative removal results to be applied for different SMX initial concentrations typical of environmental and anthropogenically impacted waters.

Modeling Source Water TOC Using Hydroclimate Variables and Local Polynomial Regression.

To control disinfection byproduct (DBP) formation in drinking water, an understanding of the source water total organic carbon (TOC) concentration variability can be critical. Previously, TOC concentrations in water treatment plant source waters have been modeled using streamflow data. However, the lack of streamflow data or unimpaired flow scenarios makes it difficult to model TOC. In addition, TOC variability under climate change further exacerbates the problem. Here we proposed a modeling approach based on local polynomial regression that uses climate, e.g. temperature, and land surface, e.g., soil moisture, variables as predictors of TOC concentration, obviating the need for streamflow. The local polynomial approach has the ability to capture non-Gaussian and nonlinear features that might be present in the relationships. The utility of the methodology is demonstrated using source water quality and climate data in three case study locations with surface source waters including river and reservoir sources. The models show good predictive skill in general at these locations, with lower skills at locations with the most anthropogenic influences in their streams. Source water TOC predictive models can provide water treatment utilities important information for making treatment decisions for DBP regulation compliance under future climate scenarios.

Effect of DOM Size on Organic Micropollutant Adsorption by GAC.

Granular activated carbon (GAC) adsorption of the micropollutants 2-methylisoborneol (MIB) and warfarin (WFN) at ng/L levels was investigated in five waters with isolated natural dissolved organic matter (DOM) held at a constant dissolved organic carbon concentration. Each water was evaluated for competitive adsorption effects based on the pretreatment of ultrafiltration, coagulation, and additional background micropollutants. Using the breakthrough with unfractionated DOM as a baseline, on average, the water with lower molecular weight (MW) DOM decreased MIB and WFN adsorption capacity by 59%, whereas the water with higher MW DOM increased MIB and WFN adsorption capacity by 64%. All waters showed similar decreasing MIB and WFN adsorption capacity with increasing empty bed contact time (EBCT), with more dramatic effects seen for the more strongly adsorbing WFN. On average, MIB and WFN adsorption kinetics were two times slower in the water with higher MW DOM compared to the water with lower MW DOM, as described by the intraparticle pore diffusion tortuosity. Increased adsorption competition from 27 micropollutants other than MIB and WFN at environmentally relevant concentrations had little to no effect on MIB and WFN breakthrough behavior. Any competitive effect from background micropollutants became indiscernible at longer EBCTs.

Full- and pilot-scale GAC adsorption of organic micropollutants.

Granular activated carbon (GAC) adsorption of 30 environmentally relevant micropollutants (MP) from four surface waters was investigated at the pilot-scale with empty bed contact times (EBCTs) of 7 and 15 min. An increase in background dissolved organic matter resulted in more and earlier MP breakthrough. Compared to an EBCT of 7 min, MP breakthrough at an EBCT of 15 min demonstrated 52% later breakthrough on average for five MPs on a throughput basis. A regression model was developed with data from three waters to predict MP throughput in bed volumes to 10% breakthrough (BV10%) based on the influent dissolved organic carbon concentration and the MP pH-dependent octanol-water partition coefficient, polarizability, and molecular volume. The regression model over predicted full-scale BV10% values when applied to a wastewater-water impacted water source and to GAC with a larger particle diameter, for which a particle size adjustment was able to account for most of the difference.

Modeling nonequilibrium adsorption of MIB and sulfamethoxazole by powdered activated carbon and the role of dissolved organic matter competition.

This study demonstrates that the ideal adsorbed solution theory-equivalent background compound (IAST-EBC) as a stand-alone model can simulate and predict the powdered activated carbon (PAC) adsorption of organic micropollutants found in drinking water sources in the presence of background dissolved organic matter (DOM) under nonequilibrium conditions. The IAST-EBC represents the DOM competitive effect as an equivalent background compound (EBC). When adsorbing 2-methylisoborneol (MIB) with PAC, the EBC initial concentration was a similar percentage, on average 0.51%, of the dissolved organic carbon in eight nonwastewater impacted surface waters. Using this average percentage in the IAST-EBC model yielded good predictions for MIB removal in two nonwastewater impacted waters. The percentage of competitive DOM was significantly greater in wastewater impacted surface waters, and varied markedly in DOM size fractions. Fluorescence parameters exhibited a strong correlation with the percentage of competitive DOM in these waters. Utilizing such correlations in the IAST-EBC successfully modeled MIB and sulfamethoxazole adsorption by three different PACs in the presence of DOM that varied in competitive effect. The influence of simultaneous coagulant addition on PAC adsorption of micropollutants was also investigated. Coagulation caused the DOM competitive effect to increase and decrease with MIB and sulfamethoxazole, respectively.