Tanju Karanfil

Probing reactivity of dissolved organic matter for disinfection by-product formation using XAD-8 resin adsorption and ultrafiltration fractionation.

The disinfection by-product (DBP) reactivity (yield and speciation upon reaction with chlorine) of dissolved organic matter (DOM) isolated from two surface waters was investigated. The source waters, each having significantly different specific ultraviolet absorbance (SUVA254), molecular weight (MW) distribution and polarity, were fractionated using XAD-8 resin adsorption and ultrafiltration (UF), with good DOM mass balance closures (based on dissolved organic carbon). It was found that such fractionation preserved both the SUVA and the reactivity of the source waters, as demonstrated by statistically similar DBP formation and speciation from chlorinated source water and source waters reconstituted from XAD-8 or UF fractions. In addition, there was no evidence of synergistic effects among DOM components when reacting with chlorine. Consistent trends between DBP yields and MW were not found. Hydrophobic fractions of DOM (isolated by XAD-8) were the most reactive DOM components; however, hydrophilic components also showed appreciable DBP yields, contributing up to 50% of total DBP formation. In contrast, strong and unique correlations were observed between the SUVA of individual fractions and their trihalomethane (THM) and haloacetic acid (HAA9) yields, confirming that the aromaticity of DOM components is more directly related to reactivity than other physicochemical properties. The finding of a single correlation independent of the fractionation process employed is notable because XAD-8 adsorption and UF fractionate DOM by significantly different mechanisms. These results confirm that SUVA is a distributed parameter that reflects DOM heterogeneity. Therefore, the SUVA distribution within natural water represents an important property that can be used as a reliable predictor of DBP formation. Finally, bromine appears to be more effectively incorporated into low UV-absorbing (i.e., low SUVA), low MW and hydrophilic DOM fractions.

Adsorption of Aromatic Compounds by Carbonaceous Adsorbents: A Comparative Study on Granular Activated Carbon, Activated Carbon Fiber, and Carbon Nanotubes

Adsorption of three aromatic organic compounds (AOCs) by four types of carbonaceous adsorbents [a granular activated carbon (HD4000), an activated carbon fiber (ACF10), two single-walled carbon nanotubes (SWNT, SWNT-HT), and a multiwalled carbon nanotube (MWNT)] with different structural characteristics but similar surface polarities was examined in aqueous solutions. Isotherm results demonstrated the importance of molecular sieving and micropore effects in the adsorption of AOCs by carbonaceous porous adsorbents. In the absence of the molecular sieving effect, a linear relationship was found between the adsorption capacities of AOCs and the surface areas of adsorbents, independent of the type of adsorbent. On the other hand, the pore volume occupancies of the adsorbents followed the order of ACF10 > HD4000 > SWNT > MWNT, indicating that the availability of adsorption site was related to the pore size distributions of the adsorbents. ACF10 and HD4000 with higher microporous volumes exhibited higher adsorption affinities to low molecular weight AOCs than SWNT and MWNT with higher mesopore and macropore volumes. Due to their larger pore sizes, SWNTs and MWNTs are expected to be more efficient in adsorption of large size molecules. Removal of surface oxygen-containing functional groups from the SWNT enhanced adsorption of AOCs.

Adsorption of synthetic organic chemicals by carbon nanotubes: Effects of background solution chemistry

With the significant increase in the production and use of carbon nanotubes (CNTs), they will be inevitably released into aquatic environments. Therefore, the fate and transport of CNTs in aqueous solutions have attracted extensive attention. In the present work, the effects of natural organic matter (NOM), solution pH and ionic strength on adsorption of three synthetic organic chemicals (SOCs) by both pristine and surface functionalized single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were investigated. The three SOCs (phenanthrene, biphenyl, and 2-phenylphenol) with different planarity, polarity, and hydrogen/electron-donor/acceptor ability, representing typical scenarios for the SOC-CNT interactions, were employed as probe molecules. Among the three background solution characteristics examined, NOM showed the most significant effect on SOC adsorption, while solution pH and ionic strength exhibited minimal or negligible impacts. The presence of NOM greatly suppressed the SOC adsorption by CNTs, and the impact on the SWNTs was higher than that on the MWNTs. The planarity and hydrophobicity of SOCs were two important factors determining the effects of NOM, solution pH and ionic strength on their adsorption by CNTs.

Adsorption of aromatic organic contaminants by graphene nanosheets: comparison with carbon nanotubes and activated carbon.

Adsorption of two synthetic organic compounds (SOCs; phenanthrene and biphenyl) by two pristine graphene nanosheets (GNS) and one graphene oxide (GO) was examined and compared with those of a coal base activated carbon (HD4000), a single-walled carbon nanotube (SWCNT), and a multi-walled carbon nanotube (MWCNT) in distilled and deionized water and in the presence of natural organic matter (NOM). Graphenes exhibited comparable or better adsorption capacities than carbon nanotubes (CNTs) and granular activated carbon (GAC) in the presence of NOM. The presence of NOM reduced the SOC uptake of all adsorbents. However, the impact of NOM on the SOC adsorption was smaller on graphenes than CNTs and activated carbons. Furthermore, the SOC with its flexible molecular structure was less impacted from NOM preloading than the SOC with planar and rigid molecular structure. The results indicated that graphenes can serve as alternative adsorbents for removing SOCs from water. However, they will also, if released to environment, adsorb organic contaminants influencing their fate and impact in the environment.

Performance of a hybrid reverse osmosis-constructed wetland treatment system for brackish oil field produced water

Using constructed wetlands, produced waters from oil fields (i.e., waters that have been in contact with oil in situ) can be treated to enhance water quality for irrigation purposes, or subsequent discharge to receiving aquatic systems. In produced water containing elevated levels of salt (i.e., brackish-produced waters), the ability to decrease the conductivity of the produced water may influence potential reuse of the water for irrigation purposes. The objectives of this research were (1) to determine the efficacy of a pilot-scale hybrid reverse osmosis (RO)-constructed wetland system for treatment and reuse of produced waters from an oil field, and (2) to assess the quality of treated water in terms of physicochemical characteristics and toxicity influencing reuse of the water for irrigation or other designated uses. Specifically, the performance of the hybrid treatment system was examined in terms of outflow water conductivity, total dissolved solids (TDS), and toxicity using Ceriodaphnia dubia and Pimephales promelas in 7-day static/renewal exposure tests. Prior to treatment, significant mortality was observed for C. dubia and P. promelas exposed for 7 days to 6.25% untreated produced water. Following treatment through the hybrid system, no significant mortality was observed in C. dubia or P. promelas exposed to 100% treated produced water when compared to the control organisms. The pilot-scale RO-constructed wetland system effectively decreased conductivity by 95% and TDS by 94% in the brackish produced water tested in this study. Following treatment, the produced water was suitable for irrigation or discharge to surface waters. Therefore, hybrid RO-constructed wetland treatment systems present a viable alternative for treatment and reuse of produced waters from oil fields.

Halonitromethane formation potentials in drinking waters.

Halonitromethanes (HNMs) are highly cyto- and genotoxic nitrogenous disinfection by-products (DBPs) that have been detected in some water distribution systems. In this study, a systematic investigation was conducted to examine the formation potential of HNMs in drinking waters under different oxidation conditions. Formation potential tests of samples obtained from various drinking water sources showed that ozonation-chlorination produced the highest HNM yields followed by in the order of chlorination, ozonation-chloramination, and chloramination. Similar or higher HNM yields were observed in the treated waters (i.e., after conventional water treatment) than in the raw waters, indicating that hydrophilic natural organic matter (NOM) components that are not effectively removed by conventional treatment processes are likely the main precursors of HNMs. This was further confirmed by examining HNM formation potentials of NOM fractions obtained with resin fractionation. Hydrophilic NOM fractions (HPI) showed significantly higher HNM yields than hydrophobic (HPO) and transphilic (TPH) fractions. The correlation analysis of HNM formation potentials during ozonation-chlorination with various water quality parameters showed the best correlation between the HNM yields and the ratio of dissolved organic carbon to dissolved organic nitrogen concentrations in the water samples tested.

Formation of disinfection by-products in indoor swimming pool water: The contribution from filling water natural organic matter and swimmer body fluids

The contribution and role of different precursors in the formation of three class of disinfection by-products (DBPs) [trihalomethanes (THMs), haloacetic acids (HAAs), and halonitromethanes (HNMs)] in swimming pool waters were examined using filling waters obtained from five drinking water treatment plant (WTP) effluents and three body fluid analogs (BFAs). BFAs exerted higher chlorine demands as compared to natural organic matter (NOM) in filling waters. BFAs exhibited higher HAA formation potentials than THM formation potentials, while the opposite was observed for the filling water NOM. There was no appreciable difference in the HNM formation potentials of BFAs and filling water NOM. Different components in the BFAs tested exhibited different degree and type of DBP formation. Citric acid had significantly higher THM and HAA yields than other BFA components. The effect of temperature was greater on THM formation, whereas the effect of contact time had more impact on HAA formation. Experiments with filling waters collected from WTP effluents at three different times showed more variability in HAA than THM formation at the WTPs studied.

The effects of dissolved natural organic matter on the adsorption of synthetic organic chemicals by activated carbons and carbon nanotubes.

Understanding the influence of natural organic matter (NOM) on synthetic organic contaminant (SOC) adsorption by carbon nanotubes (CNTs) is important for assessing the environmental implications of accidental CNT release and spill to natural waters, and their potential use as adsorbents in engineered systems. In this study, adsorption of two SOCs by three single-walled carbon nanotubes (SWNTs), one multi-walled carbon nanotube (MWNT), a microporous activated carbon fiber (ACF) [i.e., ACF10] and a bimodal porous granular activated carbon (GAC) [i.e., HD4000] was compared in the presence and absence of NOM. The NOM effect was found to depend strongly on the pore size distribution of carbons. Minimal NOM effect occurred on the macroporous MWNT, whereas severe NOM effects were observed on the microporous HD4000 and ACF10. Although the single-solute adsorption capacities of the SWNTs were much lower than those of HD4000, in the presence of NOM the SWNTs exhibited adsorption capacities similar to those of HD4000. Therefore, if released into natural waters, SWNTs can behave like an activated carbon, and will be able to adsorb, carry, and transfer SOCs to other systems. However, from an engineering application perspective, CNTs did not exhibit a major advantage, in terms of adsorption capacities, over the GAC and ACF. The NOM effect was also found to depend on molecular properties of SOCs. NOM competition was more severe on the adsorption of 2-phenylphenol, a nonplanar and hydrophilic SOC, than phenanthrene, a planar and hydrophobic SOC, tested in this study. In terms of surface chemistry, both adsorption affinity to SOCs and NOM effect on SOC adsorption were enhanced with increasing hydrophobicity of the SWNTs.

Comparative analysis of halonitromethane and trihalomethane formation and speciation in drinking water: the effects of disinfectants, pH, bromide, and nitrite.

A bench-scale study was performed to investigate formation and speciation of halonitromethanes (HNMs) in raw and treated waters obtained from a drinking water treatment plant. HNM species were measured after chlorination, ozonation-chlorination, chloramination, and ozonation-chloramination, and compared with trihalomethanes (THMs). Pre-ozonation before chlorination resulted in enhanced HNM formation, producing trihalogenated HNMs as major species. Formation of THMs showed very a different formation pattern from HNM formation such that it was much higher in the raw than the treated water, and decreased after pre-ozonation. These findings indicated that precursors and formation pathways for HNMs and THMs are not the same. Increases in pH and bromide concentrations increased HNM and THM formation during ozonation-chlorination and THM formation during chlorination. The bromide effect shifted the formation of HNMs and THMs toward brominated species, with its impact being greater in the treated than raw water. On the other hand, there was no pH or bromide effect on HNM formation during chlorination. The presence of nitrite increased HNM formation under both chlorination and ozonation-chlorination conditions, but it had no influence on THM formation. HNM formation during ozonation-chloramination remained about 1 microg/L level even at the highest bromide and nitrite concentrations. Monochloramination alone did not form any measurable HNMs. The results indicated that the use of chloramine can be an effective way to minimize HNM formation at typical drinking water treatment conditions.

The roles of tertiary amine structure, background organic matter and chloramine species on NDMA formation.

N-nitrosodimethylamine (NDMA), a probable human carcinogen, is a disinfection by-product that has been detected in chloraminated and chlorinated drinking waters and wastewaters. Formation mechanisms and precursors of NDMA are still not well understood. The main objectives of this study were to systematically investigate (i) the effect of tertiary amine structure, (ii) the effect of background natural organic matter (NOM), and (iii) the roles of mono vs. dichloramine species on the NDMA formation. Dimethylamine (DMA) and 20 different tertiary aliphatic and aromatic amines were carefully examined based on their functional groups attached to the basic DMA structure. The wide range (0.02-83.9%) of observed NDMA yields indicated the importance of the structure of tertiary amines, and both stability and electron distribution of the leaving group of tertiary amines on NDMA formation. DMA associated with branched alkyl groups or benzyl like structures having only one carbon between the ring and DMA structure consistently gave higher NDMA yields. Compounds with electron withdrawing groups (EWG) reacted preferentially with monochloramine, whereas compounds with electron donating group (EDG) showed tendency to react with dichloramine to form NDMA. When the selected amines were present in NOM solutions, NDMA formation increased for compounds with EWG while decreased for compounds with EDG. This impact was attributed to the competitions between NOM and amines for chloramine species. The results provided additional information to the commonly accepted mechanism for NDMA formation including chloramine species reacting with tertiary amines and the role of the leaving group on overall NDMA conversion.