Effect of functional groups of humic substances on uf performance

Two-phase system model to predict hydrophobic organic compound partition to heterogeneous soil dissolved organic matter across China

Soil dissolved organic matter (SDOM) is an important part of the DOM pool in terrestrial systems, influencing the transport and fate of many pollutants. In this study, SDOMs from different regions across China were compared by a series of spectroscopic methods, including UV‒vis spectroscopy, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, and the hydrophobicity was quantified by partition coefficients of SDOM in the aqueous two-phase system (KATPS). The molecular weight, aromaticity, and hydrophobicity of SDOM from different regions exhibited strong heterogeneity, KATPS combined with UV‒vis and fluorescence indices can be readily used for differentiating heterogeneous SDOM, and SDOMs were compositionally and structurally different from DOMs in aquatic systems based on spectral characterization. Importantly, the two-phase system (TPS) model has only been validated by DOMs in freshwater systems, and good organic carbon‒water partition coefficient (KOC) predictive power (RMSE = 0.11) could be provided by the TPS model when applied to heterogeneous SDOM without calibration, showing its broad applicability. Our results demonstrate the applicability of the TPS model for predicting the sorption behavior of terrestrial DOM, broadening the application scope of the TPS model and indicating its potential as a routine model for the risk assessment of hydrophobic organic compounds (HOCs) in organic contaminated sites.

Spectroscopic studies of the role of dissolved organic matter in acenaphthene photodegradation in liquid water and ice

The effect of concentration and origin of dissolved organic matter (DOM) on acenaphthene (Ace) photodegradation in liquid water and ice was investigated, and the components in DOM which were involved in Ace photodegradation were identified. The DOM samples included Suwannee River fulvic acid (SRFA), Elliott soil humic acid (ESHA), and an effluent organic matter (EfOM) sample. Due to the production of hydroxyl radical (•OH) and triplet excited-state DOM (3DOM*) which react with Ace, DOM had promotion effects on Ace photodegradation. However, the promotion effects of DOM were prevailed over by their suppressing effect of DOM including screening light effect, intermediates reducing effect and RS quenching effect, and thus, the photodegradation rates of Ace decreased in the presence of the three DOM with concentrations of 0.5-7.5 mg C/L in liquid water and ice. ESHA had higher light absorption and thus had higher screening light effect on Ace photodegradation in liquid water than SRFA and EfOM. At each DOM concentration, ESHA exhibited higher promotion effect on Ace photodegradation than SRFA and EfOM, in liquid water and ice. The binding of Ace with DOM was indicated by decreases in fluorescence intensity of Ace when coexisted with DOM. However, the binding of Ace to DOM played an unimportant role in suppressing Ace photodegradation. The photodegradation behavior of fluorophores in Ace with DOM present in ice was not similar to that in liquid water. C-O, C═O, carboxyl groups O-H and aliphatic C-H functional groups in DOM were involved in the interaction of DOM with Ace. The presence of Ace seemed to have no influence on the photodegradation behavior of functional groups in DOM.

Further treatment of coking wastewater treated in A2O-MBR by the nanofiltration-powder activated carbon hybrid system

In this study, further treatment of coking wastewater treated in anoxic-oxic-membrane bioreactor (A2O-MBR) was investigated to meet the standards of the ministry by means of nanofiltration (NF) (with two different membranes and different pressures), microfiltration -powder activated carbon (MF-PAC) hybrid system and NF-PAC (with two different membranes and five different PAC concentrations) hybrid system. In addition to the parameters determined by the ministry, other parameters such as ammonium, thiocyanate (SCN-), hydrogen cyanide (HCN), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), color were also examined to evaluate the flux performance and treatment efficiency of the hybrid processes. According to the results, chemical oxygen demand (COD) in the NF process, COD and total cyanide (T-CN) in the MF-PAC process could not meet the discharge standards. As for the NF-PAC hybrid system, XN45 membrane met the discharge standards in all parameters (COD = 96±1.88 mg/L, T-CN =<0,02 mg/L, phenol =<0.05 mg/L), with a recovery rate of 78% at 0.5 g/L PAC concentration.

Study on Treatment of Tiny Pollution Water with PAC-HUM System in Kuitun River

Kuitun city, Xinjiang is dry and short of water, so it is urgent to treat and utilize all kinds of unconventional water. In view of this problem, we conducted a study on the treatment of tiny pollution water in Kuitun River. We investigated the effect of dosage of powder activated carbon (PAC) on hollow-fiber ultrafiltration membrane (HUM) performance. The results show that the stable operation time of hollow fiber ultrafiltration membranes lengthened and the rate of reduction of the flux was reduced when the PAC dosage was increased. The addition of PAC had no obvious effect on the resistance of membrane filtration. We conducted experiments to evaluate the effect of ultrafiltration of tiny pollution water in combination with PAC. When the parameters of operation and PAC dosage were appropriately regulated, the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH₃-N) and ferric ions (Fe) reached 62%, 32% and 90%, respectively. When the PAC dosage was 200 mg/L, 100 mg/L and 150 mg/L, the highest removal rates were achieved under normal temperature and pressure. The effluent COD was less than 5.0 mg/L, NH₃-N was less than 1.5 mg/L and Fe was less than 0.5 mg/L, achieving better results than the quality standard of surface water (GB3838-2002). The treated water can be discharged into the river or recirculated to utilities. The fouled membrane was cleaned by water rinsing, water/acid rinsing and water/alkali rinsing, with recovery ratios of 44%, 81% and 88%, respectively. The results of this study can serve as a foundation for the efficient utilization of water resources and the development of new water treatment technologies in Xinjiang.

Self-aggregation of soil humic acids with respect to their structural characteristics

The main goal of this work was to estimate the influence of carboxyl and phenolic groups, as well as aromatic, aliphatic and polysaccharide components, on the soil humic acids (HA) self-aggregation process. Soil HAs (Leptosol and Regosol) were separated using base resin getting fractions with different functional group contents. Blocking of carboxyl groups was performed using the esterification procedure to estimate the participation of each functional group in the HA aggregation. The presence of HA structural components was evaluated by potentiometric titration and ATR-FTIR. The aggregation was monitored at pH 3 using Dynamic Light Scattering. Results indicated that the higher group content, the HA aggregation is less pronounced. A significant positive correlation of aliphatic C and aggregate size revealed their dominant influence in the HA self-aggregation. A lower abundance of aliphatic C in HA fractions could be considered as not sufficient to start the process. An increase of aromatic C in esters likely pointed out to its participation in hydrophobic bonding and, consequently, more pronounced aggregation. The relation of HA self-aggregate size with carboxyl and phenolic group, as well as aliphatic C, at low pH, could be considered universal regardless of the structural characteristics of the original or modified HA forms.

Influences of humic-rich natural materials on efficiencies of UASB reactor: A comparative study

Two humic-rich natural materials namely peat soil and lignite were supplemented in up-flow anaerobic sludge blanket (UASB) bioreactors for the treatment of phenolic wastewater. Peat soil improved phenol degradation and resistance to shock load; ultimately, contributing to higher COD removal efficiency (83.3%), methane production (4532 mL d^-1), and better reactor's stability. Accordingly, the amount of extracellular polymeric substances (EPS) and coenzyme F₄₂₀ in sludge were increased to 1.3-fold and 2.5-fold, respectively, as compared to the control treatment. The addition of lignite however displayed poor phenol degradation and no effects on the secretion of EPS and F₄₂₀. The peat soil significantly influenced the microbial community structures, whereas the effect of lignite was inconspicuous. In the presence of peat soil, the abundance of syntrophic fermentation bacteria and methanogens was significantly increased. This study illustrates the potential use of peat soil in UASB for the treatment of phenolic wastewaters.

Feasibility of H2O2 cleaning for forward osmosis membrane treating landfill leachate

This study reports landfill leachate treatment by the forward osmosis (FO) process using hydrogen peroxide (H₂O₂) for membrane cleaning. Although chemical cleaning is an effective method for fouling control, it could compromise membrane integrity. Thus, understanding the impact of chemical cleaning on the forward osmosis membrane is essential to improving the membrane performance and lifespan. Preliminary results revealed a flux recovery of 98% in the AL-FS mode (active layer facing feed solution) and 90% in the AL-DS (draw solution faces active layer) using 30% H₂O₂ solution diluted to 3% by pure water. The experimental work investigated the effects of chemical cleaning on the polyamide active and polysulfone support layers since the FO membrane could operate in both orientations. Results revealed that polysulfone support layer was more sensitive to H₂O₂ damage than the polyamide active at a neutral pH. The extended exposure of thin-film composite (TFC) FO membrane to H₂O₂ was investigated, and the active layer tolerated H₂O₂ for 72 h, and the support layer for only 40 h. Extended operation of the TFC FO membrane in the AL-FS based on a combination of physical (hydraulic flushing with DI water) and H₂O₂ was reported, and chemical cleaning with H₂O₂ could still recover 92% of the flux.

Precoating membranes with submicron super-fine powdered activated carbon after coagulation prevents transmembrane pressure rise: Straining and high adsorption capacity effects

Commercially available powdered activated carbon (PAC) with a median diameter of 12-42 μm was ground into 1 μm sized superfine PAC (SPAC) and 200 nm sized submicron SPAC (SSPAC) and investigated as a pretreatment material for the prevention of hydraulically irreversible membrane fouling during a submerged microfiltration (MF) process. Compared with PAC and SPAC, SSPAC has a high capacity for selective biopolymer adsorption, which is a characteristic found in natural organic matter and is commonly considered to be a major contributor to membrane fouling. Precoating the membrane surface with SSPAC during batch filtration further removes the biopolymers by straining them out. In lab-scale membrane filtration experiments, an increase in the transmembrane pressure (TMP) was almost completely prevented through a precoating with SSPAC based on its pulse dose after coagulation pretreatment. The precoated SSPAC formed a dense layer on the membrane preventing biopolymers from attaching to the membrane. Coagulation pretreatment enabled the precoated activated carbon to be rinsed off during hydraulic backwashing. The functionality of the membrane was thereby retained for a long-term operation. Precoating the membranes with SSPAC after coagulation is a promising way to control membrane fouling, and efficiently prevents an increase in the TMP because of the straining effect of the SSPAC and the high capacity of the SSPAC to adsorb any existing biopolymers.

Molecular traits of phenolic moieties in dissolved organic matter: Linkages with membrane fouling development

Phenolic moieties are important constituents in dissolved organic matter (DOM) in natural and engineered systems. However, their roles in membrane fouling mechanism during drinking water treatment by ultrafiltration (UF) have remained elusive. Herein, by using water insoluble polyvinylpolypyrrolidone (PVPP) resins, we sequestered the phenolic moieties from a model DOM (Suwannee River DOM, SRDOM) and characterized their molecular profiles using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Subsequently, their roles in UF membrane fouling propensity were investigated using reconstituted DOM solutions with various concentrations of phenolic moieties. The results showed that the phenolic moieties were of higher molecular weight and rich in unsaturation cyclic structures and oxygen-rich groups. Van Krevelen diagrams revealed that the sequestered sample was rich in aromatics structures and tannins-like compounds while contained less alicyclic organic acids in comparison with the original SRDOM, which was consistent with the aromaticity index (AI) analysis. UF experiments showed that the more phenolic moieties in DOM solution, the severer decline of flux was observed. The phenolic moieties played a significant role in membrane irremovable fouling due to the hydrophobic interactions and their higher molecular weight as evidenced by membrane cleaning tests. By surface characterization, the SRDOM fouled membrane was identified to have a higher water contact angle value and abundant C-O groups, likely due to the adsorption of more hydrophobic phenolic moieties. Overall, these findings highlighted links between phenolic moieties and membrane fouling development, and implied that membrane performance could be improved by pre-removal of phenolic moieties in DOM.

Analysis of organic foulants in the coagulation-microfiltration process for the treatment of Taihu Lake

This paper analysed organic foulants in the coagulation-microfiltration process for Taihu Lake treatment. High-performance size-exclusion chromatography (HPSEC) and fluorescence excitation-emission matrices (EEM) were applied to elucidate the influence of characteristics of organics on microfiltration (MF) membrane fouling. Results showed that coagulation pretreatment could extend the operation duration of MF based on the fact that pretreatment could effectively remove macromolecular substances as well as a portion of small molecular weight (MW) organics. The analysis of foulants indicated that organics of strong hydrophobic acids (SHA) and neutral hydrophilic (Neut) fractions (based on hydrophobicity) and medium and small MW components (based on MW distribution) contributed greatly to irreversible fouling. EEM fluorescence analysis of chemical solutions exhibited that aromatic proteins and soluble microbial products were mainly a response to irreversible fouling.

Effect of Functional Chemistry on the Rejection of Low-Molecular Weight Neutral Organics through Reverse Osmosis Membranes for Potable Reuse

Potable reuse facilities must be designed and operated to minimize the presence of contaminants of emerging concern (CECs) and other trace organics in the product water. Reverse osmosis (RO) is incorporated into the process train of many potable reuse facilities and has been demonstrated to achieve excellent removal of many, but not all, organic compounds. Organics that may be poorly removed by RO include low-molecular weight (MW) neutral compounds. This laboratory study examined the rejection of 73 low-MW neutral organics through a commercial RO membrane that is commonly used in potable reuse applications. The organics were selected using a reductionist approach so that the effect of individual functional groups on rejection could be ascertained. The research demonstrated that halogens, carbonyl functional groups, C═C double bonds, and aromaticity decrease rejection, that methyl and hydroxyl functional groups increase rejection, and that the position of functional groups in structural isomers has a significant effect on rejection. The results help explain the discrepancies and inconsistencies in RO rejection of neutral organics that are observed when considered from the conventional perspective of molecular size and hydrophobicity.

Ozonation reactivity characteristics of dissolved organic matter in secondary petrochemical wastewater by single ozone, ozone/H2O2, and ozone/catalyst

Advanced oxidation methods (e.g., ozonation systems) are used for control of recalcitrant pollutants in secondary petrochemical wastewater. For the selection of the optimal wastewater treatment method, we compared the reactivity characteristics of dissolved organic matter (DOM) in three common ozone treatment processes: single ozone, ozone/H₂O₂, and ozone/catalyst. The raw and ozonated DOM were fractionated into six fractions using ion exchange resins. Fluorescence spectroscopy and size exclusion chromatography were employed to characterize the fractions. The results showed that the single ozone system transformed hydrophobic components into hydrophilic components, but exhibited low mineralization ability. By contrast, the increase in hydrophilic acid fractions transformed from other fractions in the ozonation process were further mineralized in the ozone/H₂O₂ and ozone/catalyst systems. Ozone/H₂O₂ preferentially reduced hydrophobic bases, whereas ozone/catalyst preferentially reduced hydrophilic neutral components. However, ozone/H₂O₂ exhibited low selectivity in degrading organic compounds of different molecular weights. The highest total organic carbon (TOC) removal efficiency was achieved in the ozone/catalyst system, which promoted the transformation from fulvic acid- and humic acid-like substances into aromatic proteins and soluble microbial by-product-like substances. The single ozone system transformed high-molecular-weight compounds into low-molecular-weight compounds, resulting in an unsatisfactory TOC removal efficiency. By contrast, the ozone/catalyst system selectively removed the residual low-molecular-weight compounds in the reaction with ozone. This might have contributed to the high TOC removal efficiency of the ozone/catalyst treatment. These results can be used by other researchers and engineers to inform the selection of optimal ozone treatment based on wastewater characteristics.

Removal of precursors and disinfection by-products (DBPs) by membrane filtration from water; a review

Disinfection by-products (DBPs) have heterogeneous structures which are suspected carcinogens as a result of reactions between NOMs (Natural Organic Matter) and oxidants/disinfectants such as chlorine. Because of variability in DBPs characteristics, eliminate completely from drinking water by single technique is impossible. The current article reviews removal of the precursors and DBPs by different membrane filtration methods such as Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) techniques. Also, we provide an overview of existing and potentially Membrane filtration techniques, highlight their strengths and drawbacks. MF membranes are a suitable alternative to remove suspended solids and colloidal materials. However, NOMs fractions are effectively removed by negatively charged UF membrane. RO can remove both organic and inorganic DBPs and precursors simultaneously. NF can be used to remove compounds from macromolecular size to multivalent ions.

Effect of SiO2 nanoparticles on the removal of natural organic matter (NOM) by coagulation

In order to evaluate effect of engineered nanoparticles on the removal of natural organic matter (NOM), ENPs water sample (WATERNP), and common water sample (WATERCOMMON) were prepared by mixing the SiO2 nanoparticles (SiO2 NPs, 50 nm) and common SiO2 particles (2 μm) with water from Xiaoqing River. The removal variation, NOM fractionation, flocs properties, and IR spectra were investigated after polyaluminum chloride (PAC) coagulation. The results revealed that although the removal efficiencies of turbidity and NOM from WATERNP were moderately lower than those from WATERCOMMON, the fluorescence intensities of soluble microbial byproduct-like, humic acid-like, and aromatic protein II in coagulated WATERNP were lower than that in coagulated raw water and WATERCOMMON. What's more, flocs of WATERNP showed the smallest size and highest fractal dimension as compared with other water samples, except for those obtained at B = 2.0.

Comparison of UV/hydrogen peroxide and UV/peroxydisulfate processes for the degradation of humic acid in the presence of halide ions

This study compared the behaviors of two classic advanced oxidation processes (AOPs), hydroxyl radical-based AOPs ((•)OH-based AOPs) and sulfate radical-based AOPs (SO4 (•-)-based AOPs), represented by UV/ hydrogen peroxide (H2O2) and UV/peroxydisulfate (PDS) systems, respectively, to degrade humic acid (HA) in the presence of halide ions (Cl(-) and Br(-)). The effects of different operational parameters, such as oxidant dosages, halide ions concentration, and pH on HA degradation were investigated in UV/H2O2/Cl(-), UV/PDS/Cl(-), UV/H2O2/Br(-), and UV/PDS/Br(-) processes. It was found that the oxidation capacity of H2O2 and PDS to HA degradation in the presence of halides was nearly in the same order. High dosage of peroxides would lead to an increase in HA removal while excess dosage would slightly inhibit the efficiency. Both Cl(-) and Br(-) would have depressing impact on the two AOPs, but the inhibiting effect of Br(-) was more obvious than that of Cl(-), even the concentration of Cl(-) was far above that of Br(-). The increasing pH would have an adverse effect on HA decomposition in UV/H2O2 system, whereas there was no significant impact of pH in UV/PDS process. Furthermore, infrared spectrometer was used to provide the information of degraded HA in UV/H2O2/Cl(-), UV/PDS/Cl(-), UV/H2O2/Br(-), and UV/PDS/Br(-) processes, and halogenated byproducts were identified in using GC-MS analysis in the four processes. The present research might have significant technical implications on water treatment using advanced oxidation technologies.

Microfiltration process for surface water treatment: irreversible fouling identification and chemical cleaning

Irreversible fouling before (left) and after (right) chemical cleaning.

Effects of chlorination operating conditions on trihalomethane formation potential in polyaluminum chloride-polymer coagulated effluent

In this study, coagulation performance of polyaluminum chloride (PAC) and PAC-lignin acrylamide (PAC+LAM) in reservoir water treatment was contrastively analyzed. Effects of operating conditions including chlorine dose, contact time and pH on the formation potential of trihalomethanes (THMs) during chlorination in coagulated effluent were also investigated. Comparing with PAC, PAC+LAM achieved higher efficiency in the removal of THMs precursors. TTHM yield in unfiltered water samples (UW) was greater than that of filtered water (FW) due to the residual dissolved organic matter (DOM) in the suspended particles or micro flocs. Meanwhile, operating conditions during chlorination had a significant influence on THMs formation potential. With chlorine dose rising, mass ratio of CHCl3 to TTHM increased, whereas that of CHBr2Cl decreased due to higher Cl2/Br(-) molar ratio. TTHM and CHCl3 levels rose with the increase of pH. Under a given chlorination condition, there was a minor effect of contact time on THM speciation.

Pretreatment and membrane hydrophilic modification to reduce membrane fouling

The application of low pressure membranes (microfiltration/ultrafiltration) has undergone accelerated development for drinking water production. However, the major obstacle encountered in its popularization is membrane fouling caused by natural organic matter (NOM). This paper firstly summarizes the two factors causing the organic membrane fouling, including molecular weight (MW) and hydrophilicity/hydrophobicity of NOM, and then presents a brief introduction of the methods which can prevent membrane fouling such as pretreatment of the feed water (e.g., coagulation, adsorption, and pre-oxidation) and membrane hydrophilic modification (e.g., plasma modification, irradiation grafting modification, surface coating modification, blend modification, etc.). Perspectives of further research are also discussed.

Removal of Synthetic Organic Foulants by Granular Activated Carbon Filters and Ultrafiltration Membrane

In this study granular activated carbon (GAC) was used as pretreatment for foul control in ultrafiltration (UF) membrane process. First the adsorptive parameters for phenol, chlorophenol, nitrophenol and hydroquinone on GAC were determined. The equilibrium data fits well to Langmuir adsorption isotherm rather than Freundlich model. Breakthrough curves were obtained from fixed bed experiments and column parameter were calculated from it. GAC filters were then used in combination with UF membrane system. The percent retentions of the four organic substances under study were determined and the declines in flux were observed. The problems associated with powdered activated carbon like cake formation over membrane surface, long back wash time and blackening of pipes were not observed for GAC.

Effect of membrane properties on the performance of a hybrid GAC and ultrafiltration process for water treatment

The performance of a hybrid granular activated carbon (GAC) and ultrafiltration (UF) process for water treatment was investigated using five types of UF membranes. The removal percentages for chemical oxygen demand (COD(Mn)), particles (> or = 2 microm) and total bacteria by the hybrid process were 30-40%, 98-99% and 76-92%, respectively. No invertebrates were detected in the hybrid process effluent. Transmembrane pressure and specific permeate flux (SPF) of the five types of membranes varied. With decreasing membrane pore sizes, removal of COD(Mn) and particles increased, whereas SPF firstly decreased and then increased. Hydrophilic membranes had a relatively high COD(Mn) removal potential, but did not obviously affect particle removal or SPF.

Comparison of dissolved organic matter fractions in a secondary effluent and a natural water

This research compared the structural and chemical characteristics among dissolved organic matter (DOM) fractions within the same source and among different origins. Samples taken from the Taiping Wastewater Treatment Plant (TWTP) (Harbin, China) and from the Songhuajing River (SR), Heilongjiang Province, China were chosen to represent waters containing DOM of wastewater origin and of natural-water origin, respectively. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The SR fractions were more UV-sensitive and more reactive with chlorine in formation of trihalomethanes (THMs) than the TWTP secondary effluent (TSE) fractions. The aromatic character peaks in the Fourier-transform infrared (FT-IR) spectra of SR fractions were clearer than those of TSE fractions. On the other hand, the peaks of carbohydrates in TSE fractions were more prominent in comparison with SR fractions. In addition, the amide-2 peak was present in the spectra of all the five TSE fractions but not visible in the spectra of SR fractions. The fluorescence results showed that SR DOM fractions contained more fulvic acid-like fluorescent compounds while TSE DOM fractions had higher amounts of protein-like fluorescent components.

A coagulation-powdered activated carbon-ultrafiltration--multiple barrier approach for removing toxins from two Australian cyanobacterial blooms

Cyanobacteria are a major problem for the world wide water industry as they can produce metabolites toxic to humans in addition to taste and odour compounds that make drinking water aesthetically displeasing. Removal of cyanobacterial toxins from drinking water is important to avoid serious illness in consumers. This objective can be confidently achieved through the application of the multiple barrier approach to drinking water quality and safety. In this study the use of a multiple barrier approach incorporating coagulation, powdered activated carbon (PAC) and ultrafiltration (UF) was investigated for the removal of intracellular and extracellular cyanobacterial toxins from two naturally occurring blooms in South Australia. Also investigated was the impact of these treatments on the UF flux. In this multibarrier approach, coagulation was used to remove the cells and thus the intracellular toxin while PAC was used for extracellular toxin adsorption and finally the UF was used for floc, PAC and cell removal. Cyanobacterial cells were completely removed using the UF membrane alone and when used in conjunction with coagulation. Extracellular toxins were removed to varying degrees by PAC addition. UF flux deteriorated dramatically during a trial with a very high cell concentration; however, the flux was improved by coagulation and PAC addition.

Isolation and screening of natural organic matter-degrading fungi

Drinking water quality and its treatment are negatively impacted by the presence of coloured natural organic matter (NOM) derived from the breakdown of animal and plant materials. Ligninolytic fungi (i.e., white rot fungi - WRF) secrete non-specific oxidative enzymes that can oxidise a wide range of recalcitrant organic compounds. The potential for these organisms to decolourise concentrated aquatic NOM was investigated. Twenty-one isolates from diverse fungal genera were screened using NOM plate assays. Four WRF strains: Trametes sp., Polyporus sp., Trametes versicolor ATCC 7731 and Bjerkandera adusta, which displayed good NOM decolourisation on solid medium were further investigated in shake-flask culture using concentrated NOM as the only source of nutrients. Of these, B. adusta demonstrated the greatest decolourisation (65% for 100 mg C L(-1) NOM). NOM decolourisation coincided with ligninolytic enzyme activity and decrease in average molecular weight of NOM. The expression of the oxidative enzymes (manganese peroxidase (MnP), lignin peroxidase and laccase (Lac)) varied with fungal strain. The enzyme activities of Polyporus sp. and the two Trametes strains were significantly greater than those of B. adusta, although their decolourisation was less. For the Trametes and Polyporus sp., Lac activity was greatest, whereas for B. adusta MnP activity was greatest, suggesting its predominant role in the decolourisation process. This research demonstrates the significant potential for WRF in NOM removal so long as the enzyme activity can be controlled.

Behavior and characteristics of dissolved organic matter during column studies of soil aquifer treatment

Soil column experiments were performed to investigate the behavior and characteristics of dissolved organic matter (DOM) during soil aquifer treatment (SAT), and to differentiate among the mechanisms responsible for the changes in the structural and functional properties of DOM during SAT. To determine the biological transformation of DOM, biodegradability tests using a biodegradation-column system were conducted. DOM was fractionated using XAD resins into 5 fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Dissolved organic carbon (DOC) was removed by 70% during SAT, and the sorption and anaerobic biodegradation in SAT led to a DOC reduction of 27.4%. The significant changes in fluorescence properties of DOM were observed during SAT. However, the sorption and anaerobic biodegradation in SAT seemed to have no significant effect on the chemical structure of fluorescing constituents in DOM. The DOM fractions exhibited different changes in Fourier-transform infrared (FT-IR) spectra characteristics during SAT. Biodegradation resulted in the enrichment of aromatic structures and the decreased content of the oxygen-containing functional groups, such as CO and C-O, in DOM. On the other hand, the production of C-O and amide-2 functional groups occurred as a result of the sorption combined with anaerobic biodegradation in SAT.

Effect of bromide ion on isolated fractions of dissolved organic matter in secondary effluent during chlorination

The role of bromide ion in the trihalomethane (THM) formation and structure of dissolved organic matter (DOM) during chlorination of the secondary effluent taken from the Wenchang Wastewater Treatment Plant (Harbin, China) was investigated. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The patterns of individual THM species with increased bromide concentrations were similar for all DOM fractions. The THM speciation as well as halogen fraction for these five fractions followed similar trends with the Br(-)/Cl(2) ratio. Chlorination resulted in decreased ultraviolet (UV) absorbance across wavelengths from 250 to 280 nm for DOM fractions whether bromide ions existed or not, and bromide addition led to lower differential UV absorbance values. Fourier-transform infrared (FT-IR) results indicated that chlorination, whether bromide ions existed or not, resulted in the near elimination of aromatic CH and amide peaks, increased CO absorption intensity and occurrence of CO and CCl peaks for HPO-A, HPO-N, TPI-A and TPI-N. Furthermore, bromide addition in chlorination led to the occurrence of CBr peak for all four fractions.

Effect of membrane character and solution chemistry on microfiltration performance

To help understand and predict the role of natural organic matter (NOM) in the fouling of low-pressure membranes, experiments were carried out with an apparatus that incorporates automatic backwashing and long filtration runs. Three hollow fibre membranes of varying character were included in the study, and the filtration of two different surface waters was compared. The hydrophilic membrane had greater flux recovery after backwashing than the hydrophobic membranes, but the efficiency of backwashing decreased at extended filtration times. NOM concentration of these waters (7.9 and 9.1mg/L) had little effect on the flux of the membranes at extended filtration times, as backwashing of the membrane restored the flux to similar values regardless of the NOM concentration. The solution pH also had little effect at extended filtration times. The backwashing efficiency of the hydrophilic membrane was dramatically different for the two waters, and the presence of colloid NOM alone could not explain these differences. It is proposed that colloidal NOM forms a filter cake on the surface of the membranes and that small molecular weight organics that have an adsorption peak at 220nm but not 254nm were responsible for "gluing" the colloids to the membrane surface. Alum coagulation improved membrane performance in all instances, and this was suggested to be because coagulation reduced the concentration of "glue" that holds the organic colloids to the membrane surface.

Trihalomethane formation potential of organic fractions in secondary effluent

Organic matter is known to be the precursor of numerous chlorination by-products. Organic matter in the secondary effluent from the Wenchang Wastewater Treatment Plant (Harbin, China) was physically separated into the following fractions: particulate organic carbon (1.2-0.45 microm), colloidal organic carbon (0.45-0.1 microm), fine colloidal organic carbon (0.1-0.025 microm), and dissolved organic carbon (DOC) (< 0.025 microm). Moreover, < 0.45 microm fraction was chemically separated into hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). The chlorine reactivity of these organic fractions obtained from both size and XAD fractionations were evaluated. The structural and chemical compositions of the HPO-A, HPO-N, TPI-A, and TPI-N isolates were characterized using elemental analysis (C, H, O, and N), Fourier transform infrared spectroscopy (FT-IR), and proton nuclear magnetic resonance spectroscopy (1H-NMR). Results showed that DOC was dominant in terms of total concentration and trihalomethane formation potential (THMFP), and there was no statistical difference in both specific THMFP (STHMFP) and specific ultraviolet light absorbance among the 0.45, 0.1, and 0.025 microm filtrates. HPO-A had the highest STHMFP compared to other chemical fractions. HPO-A, HPO-N, TPI-A, and TPI-N contained 3.02%-3.52% of nitrogen. The molar ratio of H/C increased in the order of HPO-A < HPO-N < TPI-A < TPI-N. The O/C ratio was relatively high for TPI-N as compared to those for the other fractions. 1H-NMR analysis of the four fractions indicated that the relative content of aromatic protons in HPO-A was significantly higher than those in the others. The ratio of aliphatic to aromatic protons increased in the order of HPO-A < HPO-N < TPI-A < TPI-N. FT-IR analysis of the four fractions showed that HPO-A had greater aromatic C[double bond]C content whereas HPO-N, TPI-A, and TPI-N had greater aliphatic C--H content. TPI-N contained more oxygen-containing functional groups than the other fractions.

Characterization of aquatic humic substances to DBPs formation in advanced treatment processes for conventionally treated water

An advanced water treatment demonstration plant consisted of ozone/granular activated carbon processes was operated to study feasibility of the processes. Natural organic matter (NOM) from raw and process waters at the demonstration plant was isolated into humic and non-humic fractions by physicochemical fractionation method to investigate characteristics of humic fraction (i.e., humic substances, HS) as a predominant haloform reactant. Ozone did not significantly oxidize the carboxylic fraction (from 39.1 to 35.9%), while GAC removed some of the carboxylic fraction (from 35.9 to 29.1%). Formation potential of trihalomethanes (THMs) as compared to haloacetic acids formation potential (HAAFP) was highly influenced by HS. Higher yields of THMs resulted from chlorination of HS with a higher phenolic content and phenolic fraction in the HS gradually decreased from 60.5% to 15.8% through the water treatment. The structural and functional changes of HS were identified by elemental, Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance ((1)H NMR) analyses, and these results were mutually consistent. The functional distribution data obtained by using A-21 resin could be used to support the interpretation of data obtained from the spectroscopic analyses. Decreases in ratio of UV absorbance at 253 nm and 203 nm (A(253)/A(203)) and DBPFPs/DOC showed consistent trends, therefore, A(253)/A(203) ratio may be a good indicator for the disinfection by-product formation potentials (DBPFPs).

Transformations of particles, metal elements and natural organic matter in different water treatment processes

Characterizing natural organic matter (NOM), particles and elements in different water treatment processes can give a useful information to optimize water treatment operations. In this article, transformations of particles, metal elements and NOM in a pilot-scale water treatment plant were investigated by laser light granularity system, particle counter, glass-fiber membrane filtration, inductively coupled plasma-optical emission spectroscopy, ultra filtration and resin absorbents fractionation. The results showed that particles, NOM and trihalomethane formation precursors were removed synergistically by sequential treatment of different processes. Pre-ozonation markedly changed the polarity and molecular weight of NOM, and it could be conducive to the following coagulation process through destabilizing particles and colloids; mid-ozonation enhanced the subsequent granular activated carbon (GAC) filtration process by decreasing molecular weight of organic matters. Coagulation-flotation and GAC were more efficient in removing fixed suspended solids and larger particles; while sand-filtration was more efficient in removing volatile suspended solids and smaller particles. Flotation performed better than sedimentation in terms of particle and NOM removal. The type of coagulant could greatly affect the performance of coagulation-flotation. Pre-hydrolyzed composite coagulant (HPAC) was superior to FeCl3 concerning the removals of hydrophobic dissolved organic carbon and volatile suspended solids. The leakages of flocs from sand-filtration and microorganisms from GAC should be mitigated to ensure the reliability of the whole treatment system.

Enhanced coagulation in a typical North-China water treatment plant

The characteristics of typical source waters in northern China and their enhanced coagulation features were studied in this paper. Through bench scale tests, a composite coagulant (HPAC) was selected for this kind of high alkalinity and pH water. It can be 30% more efficient in organic matter (OM) removal than the traditional coagulants (AlCl(3), FeCl(3)), and polyaluminum chloride (PACl), especially more efficient in removing high SUVA, hydrophobic and high molecular weight dissolved organic matter (DOM). It is found that some DOM with low SUVA has precedence over that with high SUVA to be removed at conventional dosages in some seasons, and that the priority of DOM removal is in the same sequence for all the coagulants. DOM with high SUVA is not always more easily removed. When applying HPAC as coagulant, flotation process can remove hydrophobic OM more efficiently than sedimentation process in pilot scale tests.

Ultrafiltration with in-line coagulation for the removal of natural humic acid and membrane fouling mechanism

Experimental and theoretical analysis were made on the natural humic acid removal and the membrane fouling of ultrafiltration (UF) with in-line coagulation. The results showed dissolved organic carbon (DOC) and UV254 removals by the UF with in-line coagulation at pH 7 were increased from 28% to 53% and 40% to 78% in comparison with direct UF treatment respectively. At the same time, the analysis of high performance liquid chromatography showed that UF with coagulation had significant improvement of removal of humic acid with molecular weights less than 6000 Da in particular. Compared to direct UF, the in-line coagulation UF also kept more constant permeate flux and very slight increase of transmembrane pressure during a filtration circle. Two typical membrane fouling models were used by inducing two coefficients Kc and Kp corresponding to cake filtration model and pore narrowing model respectively. It was found that membrane fouling by pore-narrowing effect was effectively alleviated and that by cake-filtration was much decreased by in-line coagulation. Under the condition of coagulation prior to ultrafiltration at pH 7, the cake layer formed on the membrane surface became thicker, but the membrane filtration resistance was lower than that at pH 5 with the extension of operation time.

Effect of chlorine on adsorption/ultrafiltration treatment for removing natural organic matter in drinking water

In drinking water treatment, prechlorination is often applied in order to control microorganisms and taste-and-odor-causing materials, which may influence organics removal by adsorption and membrane filtration. Thus, the addition of chlorine into an advanced water treatment process using a hybrid of adsorption and ultrafiltration (UF) was investigated in terms of natural organic matter (NOM) removal and membrane permeability. A comparison between two adsorbents, iron oxide particles (IOP) and powdered activated carbon (PAC), was made to understand the sorption behavior for NOM with and without chlorination. Chlorine modified the properties of dissolved and colloidal NOM in raw water, which brought about lower TOC removal, during IOP/UF. The location of IOPs, whether they were in suspension or in a cake layer, affected NOM removal, depending on the presence of colloidal particles in feedwater. Chlorine also played a role in reducing the size of particulate matter in raw water, which could be in close association with a decline in permeate flux after chlorination.

Studies on the effect of humic acids and phenol on adsorption-ultrafiltration process performance

Application of pressure-driven membrane processes, such as ultrafiltration (UF) and microfiltration (MF) for surface water treatment have become very popular during last decades. Membrane fouling by humic substances (HS) is one of the major limiting factors in these processes. In order to alleviate the unfavorable effects of the presence of HS in the feed on the process performance UF and MF are often combined with adsorption on powdered activated carbon (PAC). The main goal of the present study was to evaluate the effect of humic acid (HA) on membrane fouling during UF. Moreover, the effect of PAC addition to the feed on UF process, especially on flux decline was determined. The applicability of the adsorption-ultrafiltration (PAC/UF) system to purification of water containing low (phenol) and high molecular (HA) was also investigated. Three different polymer UF membranes, prepared from polysulfone (PSF), cellulose acetate (CA) or polyacrylonitrile (PAN) were applied. It was found that the membranes prepared from PSF and CA are very susceptible to fouling caused by HA. The permeate flux decreased for ca. 50% during UF of HA solution through the PSF membrane and for ca. 45%-through the CA membrane. In the case of the PAN membrane, a negligible effect of HA on the flux was observed. On the basis of the FTIR spectra it was found that the drop in the permeate flux through these membranes may result from interactions between the negatively charged functional groups present on the membrane surface, such as carboxyl groups (CA) and sulfone groups (PSF) with HA, which results in coating of the membrane surface with HA. When PAC was added to the feed containing HA, the permeate flux through the CA and PAN membranes was maintained on a practically unchanged level. However, in case of the PSF membrane, a 50% drop in the permeate flux in comparison with the flux value, when process was conducted without PAC addition was observed. That was supposed to be due to attractive forces among hydrophobic PAC particles, HA molecules and PSF membrane surface. The performed studies showed that the application of PAC/UF system was very effective in the removal of organic substances having both, low and high molecular weights. The role of PAC suspended in a feed in the PAC/UF system is the adsorption of low molecular organic compounds, which cannot be removed by UF alone.