High Concentrations Of Natural Organic Matter Research Articles

Effect and mechanisms of pollutant removal in tetrachloroethylene contaminated water by persulfate-dithionite remediation system

Tetrachloroethylene (PCE) is a common organic pollutant in industrial process, and the scope and extent of PCE pollution to groundwater are increasing in recent years. In this study, an emerging and effective method was used to purify PCE contaminated water by activating persulfate (PS) with dithionite (DTN). The addition ratio of PS and DTN were optimized in the removal of PCE by PS-DTN system and the optimal molar ratio of PS to DTN was 1 to 1 at the maximum PCE removal rate, and it was applicable in the pH range of 3–12. In PCE simulated wastewater, PCE removal rate in PS-DTN system exceeded 90% within 48 h, which was 66% higher than that in PS-NaOH system, and the degradation process followed pseudo-first-order kinetics with the reaction rate constant being 0.068 h−1. The dominant active species in PS-DTN system was proved to be sulfate radical on PCE degradation based on the radical quenching experiments and ESR analysis. HCO3− and low concentration of natural organic matter (NOM) could promote the removal of PCE, while Cl− and high NOM concentration had no adverse effect on PCE degradation. Few chlorinated intermediates (<2.77%) were produced and the dechlorination rate of PCE reached 95%, indicating a low secondary pollution risk. In simulated groundwater containing aquifer media, PS-DTN system could still degrade PCE to a certain extent, but the non-target reaction triggered by iron minerals on the medium mainly inhibited PCE degradation. The study showed that PS-DTN system was promising in degrading organic pollutants in groundwater.

Enhanced virus inactivation by copper and silver ions in the presence of natural organic matter in water

Natural organic matter (NOM) is present in water matrix that serves as a drinking water source. This study examined the effect of low and high NOM concentrations on inactivation kinetics of a model RNA virus (MS2) and a model DNA virus (PhiX 174) by copper (Cu2+) and/or silver (Ag+) ions. Cu and Ag are increasingly applied in household water treatment (HHWT) systems. However, the impact of NOM on their inactivation kinetics remains elusive despite its importance for their application. The presence of NOM in water led to faster virus inactivation by Cu2+ but slower by Ag+. The fastest inactivation kinetics of MS2 (Kobs = 4.8 h−1) were observed by Cu in water containing high NOM (20 mg C/L). Meanwhile, for PhiX 174, the fastest inactivation kinetics (av. Kobs = 3.5 h−1) were observed by Cu and Ag synergism in water containing high NOM. Altogether, it can be concluded that the combination of Cu and Ag is promising as a virus disinfectant in treatment options allowing for multiple hours of residence time such as safe water storage tanks.

Adsorption-desorption of organic micropollutants by powdered activated carbon and coagulant in drinking water treatment

The addition of powdered activated carbon (PAC) and a coagulant during the coagulation-flocculation process is an easy and common option for tackling pollution peaks from organic micropollutants (OMPs) in the production of drinking water. However, the adsorption-desorption mechanisms during this process have not been thoroughly explored. Thus, this research aims to study the mechanisms involved and the impact of the operating conditions when PAC and coagulant are simultaneous used. A commercial PAC with a BET-specific surface area of 961 m2/g, and ferric chloride (FeCl3) were added simultaneously to three different waters spiked with 15 OMPs (pesticides and pharmaceuticals). Different parameters such as PAC and coagulant dosage, pH, contact time and the nature/content of the natural organic matter (NOM) were examined. Results showed that using coagulant + PAC reduced OMP adsorption efficiency, whereas increasing PAC dosage and extending contact time enhanced OMP removal efficiency. Furthermore, a high concentration of NOM affected micropollutant adsorption by competing for adsorption sites. This study highlights for the first time an unexpected phenomenon that significantly affects overall efficiency: i.e. OMPs adsorbed during the slow mixing step that desorbed during the sedimentation step. Desorption sometimes reduced by >30 % the overall efficiency of OMP removal. The parameters that affected efficiency loss were pH, contact time, NOM concentration, and PAC and FeCl3 dosage. Some operational adaptations could be considered regarding these parameters to avoid or reduce desorption, making the process more cost-effective.

Organic matter removal and antifouling performance of sulfonated polyaniline nanofiltration (S-PANI NF) membranes

Natural organic matter (NOM) removal from water prior to other treatment processes can improve treatment efficiency and final water quality. Here, NOM removal across five size fractions by newly developed sulfonated polyaniline nanofiltration (S-PANI NF) membranes was compared with a commercial membrane and conventional adsorption-coagulation-flocculation, optimized for NOM removal. Artificially prepared surface water and seawater containing 10 – 100 mg C L−1 NOM extract and a stabilized landfill leachate served as test solutions. S-PANI NF membranes showed best NOM separation performance for both surface and seawater followed by the commercial membrane and conventional treatment. For landfill leachate conventional treatment had the best performance followed by S-PANI NF membranes. S-PANI performed slightly better in removal of chemical oxygen demand (COD) (74%) compared to the commercial membrane (70%) and conventional treatment (70%). Both membranes performed consistent with increasing salinity and NOM concentration, while experiencing a modest carryover at higher salinity. During long-term fouling S-PANI exhibited slower growth in transmembrane pressure (TMP), less affinity towards organic matter and higher flux recovery compared to the commercial membrane, particularly at high NOM concentration. This is the first study to investigate S-PANI membranes for water treatment applications and under high-fouling conditions. Results indicate S-PANI NF membranes are promising for such applications. In addition, this study also provides an inter-process comparison for NOM removal over an extreme range of water matrix conditions.

Photocatalytic degradation of a typical macrolide antibiotic roxithromycin using polypropylene fibre sheet supported N–TiO2/graphene oxide composite materials

ABSTRACT The post-treatment of recycling the fine photocatalyst nanoparticles restricts their application. In this study, a new photocatalytic material was synthesized by immobilizing the N-doped TiO2 and graphene oxide (GO) composite on polypropylene (PP) (N–TiO2/GO/PP) fibre sheet, and characterized based on X-ray diffraction spectroscopy (XRD), Raman spectroscopy and Scanning Electron Microscope (SEM). The photocatalytic activity was evaluated using roxithromycin (ROX) as a typical antibiotic pollutant. XRD, Raman spectra and SEM images proved that N–TiO2/GO/PP fibre sheet was successfully synthesized. The photocatalytic degradation of 10 mg L−1 ROX can reach up to 90% and the degradation rate constant was 0.2299 h−1 in surface water with the application amount of TiO2/GO/PP fibre sheet of 24.6 cm × 2.7 cm and reaction time of 9 h under the irradiation of simulated sunlight. The application amount of TiO2/GO/PP fibre sheet, initial concentration of ROX and water matrix significantly affect the degradation of ROX. A low concentration of natural organic matter (NOM) slightly promoted the degradation of ROX, while a high concentration of NOM significantly inhibited the degradation of ROX. Alkaline condition (pH 8–9) is favourable for the photocatalytic degradation of ROX by TiO2/GO/PP fibre sheet. The photocatalytic reactivity of the TiO2/GO/PP fibre sheet showed no significant decrease after three runs. Two primary degradation products of ROX were identified and they showed lower ecotoxicity than ROX. The results demonstrate that the new synthesized TiO2/GO/PP fibre sheet shows promising application prospects in the treatment of antibiotics in wastewater and surface waters.

The degradation of chloramphenicol by O3/PMS and the impact of O3-based AOPs pre-oxidation on dichloroacetamide generation in post-chlorination

The frequent detection of chloramphenicol (CAP) in wastewater and surface water gives rise to concerns on its fatal myelosuppression and aplastic anemia. Recently, the combination of ozone and peroxymonosulfate (O3/PMS) has received wide attention in removing pollutants due to the multiple oxidants (i.e., O3, hydroxyl radicals (OH) and sulfate radicals (SO4−)) existed therein. This study showed that O3/PMS could effectively degrade CAP under various conditions. The second-order rate constant of CAP with O3, OH and SO4− was 0.291±0.005, 2.27(±0.03)×109 and 1.02±0.02×108M-1s-1, respectively. The degradation efficiency of CAP was significantly enhanced as PMS concentration or pH increased. Bicarbonate (HCO3−) at concentration of 5 mM slightly inhibited CAP degradation at pH 7. Chloride (Cl−) at concentration of 0.5 mM enhanced CAP removal at pH 7, while this enhancement gradually weakened as Cl− concentration further increased. The degradation efficiency of CAP first increased with increasing natural organic matter (NOM) concentrations (0.1–0.3 mg/L), while it was completely suppressed at higher NOM concentrations (0.5 mg/L). Four degradation products in total of CAP were identified in O3-based processes (i.e., O3, O3/TBA, O3/H2O2, O3/PMS and O3/PMS/tert-butyl alcohol (TBA) systems. Besides, these transformation products by OH, SO4− and/or O3 were also distinguished. Finally, the impact of O3/PMS pre-oxidation on the formation of dichloroacetamide (DCAcAm) from CAP during post-chlorination process was investigated. Compared with the traditional O3 and O3/H2O2 processes, O3/PMS pre-oxidation generally led to the least generation of DCAcAm under similar conditions, where SO4− rather than OH was conducive to relieve the formation of DCAcAm. Moreover, the presence of NOM obviously alleviated the formation of DCAcAm by O3/PMS pre-oxidation.

Insights into heterogeneous Fenton-like systems catalyzed by novel magnetic yolk-shell structures for the removal of acetaminophen from aquatic environments

In this study, novel magnetic yolk-shell structures (Fe3O4@SiO2 and Fe3O4@SiO2@Cu) were used as heterogeneous Fenton-like catalysts for the degradation of acetaminophen (ACTM) under different experimental conditions. Important factors that affected their catalytic performance were investigated, including catalysts dosage, oxidant concentrations, pH, ionic strength (IS), and natural organic matter (NOM). In addition, the NOM was isolated into different molecular size fractions, and their characterization and influence on ACTM degradation were examined to provide insight into NOM behavior in the system. The results showed that the degradation of ACTM was promoted with increases of the investigated Fe3O4 dosages. The degradation efficiencies were also enhanced as the H2O2 concentration increased from 5.0 to 15.0 mM, but they were decreased at a higher dosage of H2O2 (25 mM). The degradation was inhibited as the pH increased, but it was an insignificant difference when the pH increased from 5.0 to 7.0 in the case of Fe3O4@SiO2@Cu as the catalyst. Electrochemical analysis indicated that NOM at a certain concentration could enhance the electron transfer reactions. However, NOM was observed to have different effects on the two catalysts. Fe3O4@SiO¬2@Cu catalytic activity was accelerated when the NOM concentration was below 30.0 mg/L, and it was retarded at higher NOM concentrations, while the catalytic activity of Fe3O4@SiO2 was inhibited at all ranges of the investigated NOM concentrations. The presence of different NOM size fractions in the systems resulted in various behaviors of the catalysts in the degradation of ACTM.

Impact of background water quality on disinfection performance and silver release of immobilized silver nanoparticles: Modeling disinfection kinetics, bactericidal mechanism and aggregation behavior

An aminosilane-based surface functionalization strategy was adopted to immobilize silver nanoparticles (AgNPs) on to silica materials to minimize leaching of silver into the aqueous environment. The disinfection potential and silver release of immobilized-AgNPs and chloridized silver surfaces were investigated for simulated lake water under varying water chemistry conditions. While the presence of both hardness and natural organic matter (NOM) adversely affected the disinfection kinetics and silver release from immobilized-AgNPs, alkalinity had only minor impact on disinfection performance over the concentration range 30–600 mg L−1. The higher disinfection efficacy of immobilized-AgNPs was ascribed to their contact-killing mechanism of action. In contrast, chloridized Ag that caused disinfection through the release of silver ions showed lower disinfection efficacy. Divalent cations and NOM greatly influenced the surface characteristics and morphology of the immobilized-AgNPs. However, immobilized AgNPs were more shielded than colloidal AgNPs when exposed to similar harsh conditions characterized by high hardness and NOM concentration. Under all the tested conditions, where 100% disinfection was achieved, the amount of silver release from immobilized AgNPs was less than 22 µg L−1, which is well below the USEPA permissible limit. The disinfection kinetics of immobilized-AgNPs was best fitted by the Hom model (R2 = 0.974), where its lumped parameters kh and m were found to vary with variation in background water quality. Sensitivity analyses indicated that for ‘m’ value higher than 1.9, complete disinfection could not be achieved regardless of many fold increase in ‘kh’ value.

Degradation behavior of triclosan by co-exposure to chlorine dioxide and UV irradiation: influencing factors and toxicity changes.

This study investigated the transformation of triclosan (TCS) following co-exposure to UV irradiation and ClO2. Special attention was given to understand the influencing of water quality parameters and toxicity changes during the co-exposure process. The results show that the co-exposure process prompted TCS elimination quickly and effectively, with more than 99% of TCS degraded under the experimental conditions. The molar yield ratios of 2,4-dichlorophenol/TCS (2,4-DCP/TCS) were calculated to be 35.81-74.49%; however, the by-product of 2,8-dichlorodibenzop-dioxin (2,8-Cl2DD) was not detected. The TCS degradation was sensitive to ClO2 dosage, pH, H2O2, and natural organic matter (NOM), but not to the carbonate (CO32-) concentration. Neutral and slightly alkaline condition were favorable to TCS elimination. The TCS removal rate increased from 85.33 to 99.75% when the ClO2 concentration increased from 0.25 to 1.5mgL-1. TCS degradation can be promoted at low NOM level (1, 3, and 5mgL-1), whereas was inhibited at high NOM concentrations of 7 and 9mgL-1. While adding H2O2, the degradation rate of TCS increased with increasing H2O2 concentration from 1 to 3mgL-1; however, too low or overdosed H2O2 (0.5 and 5mgL-1) hindered TCS degradation. Based on the results of a microtox bioassay, the toxicity did not change following the co-exposure process.

Transformation of 17α-ethinylestradiol by simultaneous photo-enzymatic process in Humic water

The fate of estrogens in surface water is mainly dependent on two processes, i.e. photodegradation and biotransformation. Each of the separate process is invariably of interest, but research on the combination of the two processes has rarely been explored. In the present work, the transformation of 17α-ethinylestradiol (EE2) by simultaneous photochemical and enzymatic process in water was systematically investigated. The combined transformation rate of EE2 (0.057 h−1) in the presence of natural organic matter (NOM) and horseradish peroxidase (HRP) under simulated sunlight irradiation was markedly faster than that in the presence of NOM only (0.032 h−1). Similar pattern was also observed in real water matrix sampled from Taihu Lake. Further study revealed that the photodegradation and enzymatic transformation of EE2 were dramatically affected by NOM concentrations ranging from 0 to 20 mgC L−1. NOM was found to invariably accelerate the photodegradation of EE2 with increasing concentration. On the contrary, the transformation rate of EE2 mediated by HRP was decreased along with the increase of NOM concentration. The reason may be that HRP was prone to be inactivated in solution with high NOM concentration. The transformation experiment of EE2 at ambient level under sunlight confirmed the significant contribution of HRP to the degradation of EE2 in the presence of NOM. The results indicated that oxidation mediated by HRP was an essential fate of EE2 and other congener contaminants in aquatic environment.

Raw Water Quality and Pretreatment in Managed Aquifer Recharge for Drinking Water Production in Finland

The main objective of managed aquifer recharge (MAR) in Finland is the removal of natural organic matter (NOM) from surface waters. A typical MAR procedure consists of the infiltration of surface water into a Quaternary glaciofluvial esker with subsequent withdrawal of the MAR treated water from wells a few hundred meters downstream. The infiltrated water should have a residence time of at least approximately one month before withdrawal to provide sufficient time for the subsurface processes needed to break down or remove humic substances. Most of the Finnish MAR plants do not have pretreatment and raw water is infiltrated directly into the soil. The objectives of this paper are to present MAR experiences and to discuss the need for and choice of pretreatment. Data from basin, sprinkling, and well infiltration processes are presented. Total organic carbon (TOC) concentrations of the raw waters presented here varied from 6.5 to 11 mg/L and after MAR the TOC concentrations of the abstracted waters were approximately 2 mg/L. The overall reduction of organic matter in the treatment (with or without pretreatment) was 70%-85%. Mechanical pretreatment can be used for clogging prevention. Turbidity of the Finnish lakes used as raw water does not necessitate pretreatment in basin and sprinkling infiltration, however, pretreatment in well infiltration needs to be judged separately. River waters may have high turbidity requiring pretreatment. Biodegradation of NOM in the saturated groundwater zone consumes dissolved oxygen. Thus, a high NOM concentration may create conditions for dissolution of iron and manganese from the soil. These conditions may be avoided by the addition of chemical pretreatment. Raw waters with TOC content up to at least approximately 8 mg/L were infiltrated without any considerations of chemical pretreatment, which should be evaluated based on local conditions.

Natural organic matter resistant powder activated charcoal supported titanate nanotubes for adsorption of Pb(II)

Titanate nanotubes (TNTs) have been shown effective for adsorption of heavy metals due to large specific surface area and outstanding ion-exchange property. However, the adsorption capacity is severely suppressed in the presence of natural organic matter (NOM) due to TNTs’ poor interactions with NOM. In this study, powder activated charcoal supported TNTs (TNTs@PAC) were synthesized through a one-step hydrothermal method, and tested for adsorption of Pb(II) in the presence of high concentrations of NOM. TNTs@PAC showed both rapid adsorption kinetics, and high capacity for Pb(II), as well as strong resistance to NOM. Most adsorption occurred in the first 60min, and the maximum Langmuir capacity of Pb(II) was determined to be 318.5mg/g. Notably, a model humic acid (HA) showed negligible effect on Pb(II) adsorption. The primary adsorption mechanism was demonstrated to be ion exchange between Pb(II) and interlayered Na+ in TNTs, and, in the presence of humic acid, interactions between PAC and the NOM-Pb complexes. The spent material can be easily regenerated and reused for multiple Pb(II) adsorption cycles. The excellent adsorption performance combined with high NOM-resistance make TNTs a promising nanomaterial for remediation of heavy-metals contaminated waters.

Critical role of natural organic matter in photodegradation of methylmercury in water: Molecular weight and interactive effects with other environmental factors

Photodegradation is the main depletion pathway of methylmercury (MeHg) in surface water. However, the underlying mechanism of MeHg photodegradation is still not well understood. In this study, the critical role of natural organic matter (NOM) from Suwannee River natural organic matter of the International Humic Substance Society, especially its molecular weight, and the impacts of other related environmental factors in MeHg photodegradation were investigated. We observed that MeHg cannot photo-degrade in de-ionized water, excluding the direct photodegradation of MeHg. While either NOM or Fe3+ alone induced MeHg photodegradation, co-existing NOM significantly inhibited the Fe3+-induced degradation, highlighting the critical and complex role of NOM in MeHg photodegradation. Additionally, MeHg exhibited different photodegradation rates in the presence of molecular weight fractionated natural organic matter (Mf-NOM). More importantly, high concentration of NOM caused light attenuation significantly inhibited the photodegradation of MeHg, which was more significant for high molecular weight Mf-NOM. In the presence of Mf-NOM, MeHg photodegradation was also affected by light quality, pH and co-existing Cl− and NO3−. The study is helpful for a better understanding of the critical role of NOM and other environmental factors on MeHg photodegradation in surface water.

Sunlight inactivation of somatic coliphage in the presence of natural organic matter

Long wavelengths of sunlight spectrum (UVA and visible light), as well as natural organic matter (NOM) are important environmental factors affecting survival of viruses in aquatic environment through direct and indirect inactivation. In order to understand the virus inactivation kinetics under such conditions, this study investigated the effects of Suwannee River natural organic matter (NOM) on the inactivation of a somatic coliphage, phiX174, by UVA and visible light. Experiments were carried out to examine the virucidal effects of UVA/visible light, assess the influence of SRNOM at different concentrations, and identify the effective ROS in virus inactivation. The results from this study showed that the presence of NOM could either enhance virus inactivation or reduce virus inactivation depending on the concentration, where the inactivation rate followed a parabolic relationship against NOM concentration. The results indicated that moderate levels of NOM (11ppm) had the strongest antiviral activity, while very low or very high NOM concentrations prolonged virus survival. The results also showed that OH▪ was the primary ROS in causing phiX174 (ssDNA virus) inactivation, unlike previous findings where 1O2 was the primary ROS causing MS2 (ssRNA virus) inactivation. The phiX174 inactivation by OH∙ could be described as k=3.7✕1013[OH∙]+1.404 (R2=0.8527).

Comparison of different combined treatment processes to address the source water with high concentration of natural organic matter during snowmelt period

The source water in one forest region of the Northeast China had very high natural organic matter (NOM) concentration and heavy color during snowmelt period. The efficiency of five combined treatment processes was compared to address the high concentration of NOM and the mechanisms were also analyzed. Conventional treatment can hardly remove dissolved organic carbon (DOC) in the source water. KMnO4 pre-oxidization could improve the DOC removal to 22.0%. Post activated carbon adsorption improved the DOC removal of conventional treatment to 28.8%. The non-sufficient NOM removal could be attributed to the dominance of large molecular weight organic matters in raw water, which cannot be adsorbed by the micropore upon activated carbon. O3+activated carbon treatment are another available technology for eliminating the color and UV254 in water. However, its performance of DOC removal was only 36.4%, which could not satisfy the requirement for organic matter. The limited ozone dosage is not sufficient to mineralize the high concentration of NOM. Magnetic ion-exchange resin combined with conventional treatment could remove 96.2% of color, 96.0% of UV254 and 87.1% of DOC, enabling effluents to meet the drinking water quality standard. The high removal efficiency could be explained by the negative charge on the surface of NOM which benefits the static adsorption of NOM on the anion exchange resin. The results indicated that magnetic ion-exchange resin combined with conventional treatment is the best available technology to remove high concentration of NOM.

Bioaccumulation of waterborne Ni in Dreissena polymorpha: A stable isotope experiment to assess the effect of zinc, calcium, and dissolved organic matter

The effect of Ca, Zn, and dissolved natural organic matter (NOM) on waterborne Ni accumulation was investigated in a freshwater mussel. An enriched stable metal isotope tracer was required to measure the Ni uptake rate accurately. Zebra mussels were exposed to environmentally relevant concentrations of (62) Ni (from 0.5 to 8 µg/L) for 48 h in media spiked with Ca, Zn, or dissolved NOM. The (62)Ni uptake was inhibited by Ca (from 0.138 ± 0.021 to 0.061 ± 0.010 L/g/d for Ca concentrations ranging from 43 to 133 mg/L) and enhanced by Zn (from 0.051 ± 0.006 to 0.109 ± 0.007 L/g/d for Zn concentrations ranging from 6.6 to 38.3 µg/L). The mechanisms behind the synergistic effect of Zn remain unclear, yet it can be hypothesized that Ni uptake is facilitated by Zn-dependent transport sites. To formalize the effects of Ca and Zn, a model was proposed to express the Ni uptake rate as a function of the mussels' filtration rate and of Ca and Zn concentrations. The (62)Ni uptake increased at low NOM concentrations and decreased at higher concentrations. This could be explained by the influence of NOM on both the speciation of Ni and the filtration activity of mussels. At high NOM concentrations, a modification of the membrane's permeability might also have favored Ni uptake, although this was not clearly established in this study. Therefore, the effect of water composition on Ni bioavailability to zebra mussels cannot be predicted by competition and complexation models alone, because it also influences the animal's physiology.

Simultaneous Removal of Nitrate and Natural Organic Matter from Drinking Water Using a Hybrid Heterotrophic/Autotrophic/Biological Activated Carbon Bioreactor.

Simultaneous removal of nitrate ([Formula: see text]) and natural organic matter (NOM) from drinking water using a hybrid heterotrophic/autotrophic/BAC bioreactor (HHABB) was studied in continuous mode. The HHABB consisted of three compartments: ethanol heterotrophic part, sulfur autotrophic part, and biological activated carbon (BAC)-part (including anoxic and aerobic sections). Experiments were performed with [Formula: see text] concentration 30 mg N/L, [Formula: see text] loading rate 0.72 kg N/m(3)/d, C : N ratio 0.53, and three concentrations of NOM (0.6, 2.6, and 5.7 mg C/L). Overall denitrification rate and efficiency of the HHABB were not affected by NOM concentration and were in the suitable ranges of 0.69-0.70 kg N/m(3)/d and 96.0%-97.7%, respectively. NOM removal at concentration 0.6 mg C/L was not efficient because of organic carbon replacement as soluble microbial products. At higher NOM concentrations, total NOM removal efficiencies were 55%-65%, 55%-70%, and 55%-65% for dissolved organic carbon, trihalomethane formation potential, and UV absorbance at 254 nm (UV(254)), respectively. The more efficient compartments of the HHABB for the removal of NOM were the ethanol heterotrophic phase and aerobic BAC-phase. The efficiency of the HHABB in the removal of NOM was considerable, and the effluent dissolved organic carbon and trihalomethane formation potential concentrations were relatively low. This study indicated that the HHABB without the anoxic BAC-phase could be a feasible alternative for simultaneous removal of [Formula: see text] and NOM from drinking water at full scale.

Biofilm control in water by advanced oxidation process (AOP) pre-treatment: effect of natural organic matter (NOM)

The main goal of this study was to examine the influence of natural organic matter (NOM) on the efficiency of H₂O₂/UV advanced oxidation process (AOP) as a preventive treatment for biofilm control. Pseudomonas aeruginosa PAO1 biofilm-forming bacteria were suspended in water and exposed to various AOP conditions with different NOM concentrations, and compared to natural waters. H₂O₂/UV prevented biofilm formation: (a) up to 24 h post treatment - when residual H₂O₂ was neutralized; (b) completely (days) - when residual H₂O₂ was maintained. At high NOM concentrations (i.e. 25 mg/L NOM or 12.5 mg/L DOC) an additive biofilm control effect was observed for the combined H₂O₂/UV system compared to UV irradiation alone, after short biofilm incubation times (<24 h). This effect was H₂O₂ concentration dependent and can be explained by the high organic content of these water samples, whereby an increase in NOM could enhance (•)OH production and promote the formation of additional reactive oxygen species. In addition, maintaining an appropriate ratio of bacterial surviving conc.: residual H₂O₂ conc. post-treatment could prevent bacterial regrowth and biofilm formation.

Ballasted Flotation with Glass Microspheres for Removal of Natural Organic Matter

Low density microspheres were used to float flocs formed from the coagulation of natural organic matter (NOM) using ferric sulphate coagulant. Microspheres were visually observed to be incorporated into the floc structure during the coagulation phase. In comparison with conventional flotation with air bubbles, the residual turbidity after flotation using the microspheres was very favorable and did not impact on overall NOM removal. Spheres of the lowest density and largest particle size gave the most rapid floc clearance, but the residual turbidity after 10 minutes flotation was similar for all of the spheres investigated. The results of this work have shown that floating microspheres offer an effective, energy efficient alternative to conventional dissolved air flotation for the removal of flocs containing high concentrations of NOM.

Abiotic properties of landfill leachate controlling arsenic release from drinking water adsorbents

In this study, As leaching from five arsenic bearing solid residuals (ABSRs) comprised of the iron hydroxide adsorbent Bayoxide E33 used in long-term operations was evaluated in leaching trials using California Waste Extraction Test (CalWET) and Toxicity Characteristic Leaching Protocol (TCLP) leachate solutions, a landfill leachate (LL), and synthetic leachate (SL). The initial As loading of the media, which reflects the influence of source water chemistry and varying treatment conditions at the point of removal, strongly influenced the magnitude of As release. The chemical composition of the leachate also influenced As release and demonstrated the relative importance of different release mechanisms, namely media dissolution, pH-dependent sorption/desorption, and ion exchange. The CalWET solution, which partially dissolved the iron-based media, resulted in 100 times more As release than did the TCLP solution, which did not dissolve the media. The LL had a higher pH than the TCLP solution, and even though its organic carbon content was lower it tended to release more As. Tests with the SL were conducted to determine the influence of variations in leachate pH, phosphate, bicarbonate, sulfate, silicate, and natural organic matter (NOM). Release increased at high pH, in the presence of high concentrations of phosphate and bicarbonate, and in the presence of high NOM concentrations. For pH, this reflects the pH-dependence of sorption reactions, whereas for the anions and NOM, direct competition appeared important. Similar to the CalWET solution, excess NOM dissolved portions of the media thereby facilitating As release. In general, our results suggest that estimating As release into landfills will remain a challenge as it depends upon As loading, which reflects site-specific properties, and the composition of the leachate, which varies from landfill to landfill.