Kyle K. Shimabuku

Granular activated carbon adsorption of MIB in the presence of dissolved organic matter

Based on the results of over twenty laboratory granular activated carbon (GAC) column runs, models were developed and utilized for the prediction of 2-methylisoborneol (MIB) breakthrough behavior at parts per trillion levels and verified with pilot-scale data. The influent MIB concentration was found not to impact the concentration normalized breakthrough. Increasing influent background dissolved organic matter (DOM) concentration was found to systematically decrease the GAC adsorption capacity for MIB. A series of empirical models were developed that related the throughput in bed volumes for a range of MIB breakthrough targets to the influent DOM concentration. The proportional diffusivity (PD) designed rapid small-scale column test (RSSCT) could be directly used to scale-up MIB breakthrough performance below 15% breakthrough. The empirical model to predict the throughput to 50% breakthrough based on the influent DOM concentration served as input to the pore diffusion model (PDM) and well-predicted the MIB breakthrough performance below a 50% breakthrough. The PDM predictions of throughput to 10% breakthrough well simulated the PD-RSSCT and pilot-scale 10% MIB breakthrough.

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 facilitys carbon footprint.

Sunlight-driven photochemical halogenation of dissolved organic matter in seawater: a natural abiotic source of organobromine and organoiodine.

Reactions of dissolved organic matter (DOM) with photochemically generated reactive halogen species (RHS) may represent an important natural source of organohalogens within surface seawaters. However, investigation of such processes has been limited by difficulties in quantifying low dissolved organohalogen concentrations in the presence of background inorganic halides. In this work, sequential solid phase extraction (SPE) and silver-form cation exchange filtration were utilized to desalt and preconcentrate seawater DOM prior to nonspecific organohalogen analysis by ICP-MS. Using this approach, native organobromine and organoiodine contents were found to range from 3.2-6.4 × 10(-4) mol Br/mol C and 1.1-3.8 × 10(-4) mol I/mol C (or 19-160 nmol Br L(-1) and 6-36 nmol I L(-1)) within a wide variety of natural seawater samples, compared with 0.6-1.2 × 10(-4) mol Br/mol C and 0.6-1.1 × 10(-5) mol I/mol C in terrestrial natural organic matter (NOM) isolates. Together with a chemical probe method specific for RHS, the SPE+ICP-MS approach was also employed to demonstrate formation of nanomolar levels of organobromine and organoiodine during simulated and natural solar irradiation of DOM in artificial and natural seawaters. In a typical experiment, the organobromine content of 2.1 × 10(-4) mol C L(-1) (2.5 mg C L(-1)) of Suwannee River NOM in artificial seawater increased by 69% (from 5.9 × 10(-5) to 1.0 × 10(-4) mol Br/mol C) during exposure to 24 h of simulated sunlight. Increasing I(-) concentrations (up to 2.0 × 10(-7) mol L(-1)) promoted increases of up to 460% in organoiodine content (from 8.5 × 10(-6) to 4.8 × 10(-5) mol I/mol C) at the expense of organobromine formation under the same conditions. The results reported herein suggest that sunlight-driven reactions of RHS with DOM may play a significant role in marine bromine and iodine cycling.

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.

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.

Optimization of strong-base anion exchange O&M costs for hexavalent chromium treatment

Hexavalent chromium [Cr(VI)] in drinking water is pending regulation in California and is being considered for regulation in other locations. While strong-base anion exchange (SBA-IX) can efficiently remove Cr(VI) to low-levels that may be required to comply with future MCLs, operational and maintenance (O&M) costs can be considerable if the spent brine is disposed of as hazardous waste. Through bench- and pilot-scale experiments and full-scale demonstrations, this study examined the ability of emerging and established brine treatment and reuse techniques as well as recently developed resins to decrease O&M costs. When profiling anion elution during regeneration with nanofiltration treated and untreated spent brine, it appeared that at least 1 and 3 reuse cycles were feasible, respectively. Stannous- and ferrous-based reductants were more efficient than sulfur-based reductants when treating spent brine. Bed volumes to 8 μg/L chromium breakthrough with 7 resins varied by as much as a factor of 2 and correlated (R2 = 0.84) with resin total exchange capacities. Spent brine reuse, segmented regeneration (an optimized brine reuse method), ferrous reduction, and nanofiltration of spent brine were estimated to decrease O&M costs by 30, 70, 63, and 61%, respectively. Selection of high performing resins was the most simple way to decrease O&M costs (up to 70% savings). The sum of nitrate and sulfate raw water equivalent concentrations was found to be the principal water quality parameter that influenced the performance of 4 resins in 7 different groundwaters because nitrate and sulfate concentrations were orders of magnitude greater than chromium concentrations. Resins with higher chromium capacities eluted more co-contaminants including arsenic, selenium, uranium, and vanadium because they likely had higher co-contaminant capacities. Co-contaminant elution was found to be complex because associations can form between regenerant and co-eluting anions. Sodium chloride was the most efficient regenerant, though other regenerants provided benefits such as enhanced uranium elution most likely by complexing with uranium to inhibit its precipitation. Nitrate peaking was found to be limited even when reusing untreated and nanofiltration treated spent brine.

Influence of biochar thermal regeneration on sulfamethoxazole and dissolved organic matter adsorption

Biochar is emerging as a cost-effective, environmentally-sustainable adsorbent for removing organic contaminants (OC) from wastewater, stormwater, and drinking water, but strategies for managing exhausted biochar are needed. Here, pine biochar generated at 850 °C was exhausted by background dissolved organic matter isolated from surface water [dissolved organic carbon ∼4.2 mg L−1, UV-absorbance at 254 nm (UVA254) ∼0.10 cm−1] and sulfamethoxazole (SMX) [∼200 ng L−1], in a column. Exhausted biochar underwent a semi-oxic-thermal-regeneration step at 600 °C (i.e., heat treatment). SMX and UVA254 adsorption capacity and breakthrough were evaluated in rapid small-scale column tests (RSSCTs). Relative to fresh biochar, heat treated biochar that had been exhausted exhibited ∼3.5-fold and ∼3-fold greater SMX and UVA254 adsorption capacities, respectively, and ∼3-fold increase in adsorption efficiency (i.e., mass loss-adjusted SMX adsorption capacity). When applying the heat treatment to fresh biochar, a similar improvement in adsorption capacity was observed. Adsorption capacity and BET surface area were positively correlated and continued to increase after a second exhaustion–regeneration cycle, but the adsorption efficiency remained the same due to mass loss. SMX breakthrough correlated with that of UVA254, which provides the basis for a rapid, inexpensive method to predict OC breakthrough. Heat-treated biochars SMX adsorption capacity was ∼20% of activated carbons. Greater empty-bed-contact times increased the SMX adsorption capacity of heat-treated biochar. These results suggest that thermal regeneration could enhance the economic and environmental sustainability of biochar sorbents.