Natural organic matter removal by coagulation during drinking water treatment: a review

Modelling the regional variability of the probability of high trihalomethane occurrence in municipal drinking water

The regional variability of the probability of occurrence of high total trihalomethane (TTHM) levels was assessed using multilevel logistic regression models that incorporate environmental and infrastructure characteristics. The models were structured in a three-level hierarchical configuration: samples (first level), drinking water utilities (DWUs, second level) and natural regions, an ecological hierarchical division from the Quebec ecological framework of reference (third level). They considered six independent variables: precipitation, temperature, source type, seasons, treatment type and pH. The average probability of TTHM concentrations exceeding the targeted threshold was 18.1%. The probability was influenced by seasons, treatment type, precipitations and temperature. The variance at all levels was significant, showing that the probability of TTHM concentrations exceeding the threshold is most likely to be similar if located within the same DWU and within the same natural region. However, most of the variance initially attributed to natural regions was explained by treatment types and clarified by spatial aggregation on treatment types. Nevertheless, even after controlling for treatment type, there was still significant regional variability of the probability of TTHM concentrations exceeding the threshold. Regional variability was particularly important for DWUs using chlorination alone since they lack the appropriate treatment required to reduce the amount of natural organic matter (NOM) in source water prior to disinfection. Results presented herein could be of interest to authorities in identifying regions with specific needs regarding drinking water quality and for epidemiological studies identifying geographical variations in population exposure to disinfection by-products (DBPs).

Removing of Disinfection By-Product Precursors from Surface Water by Using Magnetic Graphene Oxide

The magnetic graphene oxide (MGO) was successfully synthesised by the in situ chemical co-precipitation method with Fe3+, Fe2+ and graphene oxide (GO) in laboratory and, was used as an adsorbent for disinfection by-product (DBP) precursors removing from four natural surface water samples. The results indicate that various DBPs formation significantly decreased by 7-19% to 78-98% for the four samples after MGO treatment and, the treatment process was rapidly reached equilibrium within 20 minutes. The DBP precursors removal efficiency decreased with the increasing pH value from 4 to 10. Hydrophobic compounds (humic acid and fulvic acid) are more sensitive to MGO, whereas hydrophilic and nitrogenous compounds (aromatic proteins) are more insensitive. MGO could be regenerated by using 20% (v/v) ethanol and, the DBP precursors removal efficiency can stay stable after five cycles. These results indicate that MGO can be utilized as a promising adsorbent for the removal of DBP precursors from natural surface water.

Algal control and enhanced removal in drinking waters in Cairo, Egypt

Algal blooms at the major water treatment plants in Egypt have been reported since 2006. While previous studies focused on algal types and their correlation with disinfection by-products, correlation between raw water quality and algal blooms were not explored. Therefore, a survey of Nile water quality parameters at a major water intake in the Greater Cairo Urban Region was conducted from December 2011 to November 2012. Bench-scale experiments were conducted to evaluate the effectiveness of the conventional chloride/alum treatment compared with combined Cl/permanganate pre-oxidation with Al and Fe coagulants during the outbreak period. Addition of permanganate (0.5 mg/L) significantly reduced the chlorine demand from 5.5 to 2.7 mg/L. The applied alum coagulant dose was slightly reduced while residual Al was reduced by 27% and the algal count by 50% in the final treated waters. Applying ferric chloride and ferric sulfate as coagulants to waters treated with the combined pre-oxidation procedure effectively reduced algal count by 60% and better the total organic carbon reduction and residual aluminum in the treated water. Multivariate statistical analysis was used to identify the relationship between water quality parameters and occurrence of algae and to explain the impact of coagulants on the final water quality.

Tracking changes in the optical properties and molecular composition of dissolved organic matter during drinking water production

Absorbance, 3D fluorescence and ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) were used to explain patterns in the removal of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) at the molecular level during drinking water production at four large drinking water treatment plants in Sweden. When dissolved organic carbon (DOC) removal was low, shifts in the dissolved organic matter (DOM) composition could not be detected with commonly used DOC-normalized parameters (e.g. specific UV254 absorbance - SUVA), but was clearly observed by using differential absorbance and fluorescence or ESI-FT-ICR-MS. In addition, we took a novel approach by identifying how optical parameters were correlated to the elemental composition of DOM by using rank correlation to connect optical properties to chemical formulas assigned to mass peaks from FT-ICR-MS analyses. Coagulation treatment selectively removed FDOM at longer emission wavelengths (450-600 nm), which significantly correlated with chemical formulas containing oxidized carbon (average carbon oxidation state ≥ 0), low hydrogen to carbon ratios (H/C: average ± SD = 0.83 ± 0.13), and abundant oxygen-containing functional groups (O/C = 0.62 ± 0.10). Slow sand filtration was less efficient in removing DOM, yet selectively targeted FDOM at shorter emission wavelengths (between 300 and 450 nm), which commonly represents algal rather than terrestrial sources. This shorter wavelength FDOM correlated with chemical formulas containing reduced carbon (average carbon oxidation state ≤ 0), with relatively few carbon-carbon double bonds (H/C = 1.32 ± 0.16) and less oxygen per carbon (O/C = 0.43 ± 0.10) than those removed during coagulation. By coupling optical approaches with FT-ICR-MS to characterize DOM, we were for the first time able to confirm the molecular composition of absorbing and fluorescing DOM selectively targeted during drinking water treatment.

Surface-Mediated Extraction and Photoresponse Modulation of Bisphenol A Derivatives: A Computational Study

2,2'-bis(4-hydroxyphenyl) propane (BPA) and its metabolites 4-methyl-2,4-bis(p-hydroxyphenyl)pent-2-ene (M-1) and 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (M-2) are common in drinking water and hard plastics and thus pose serious health hazards. These are also known as endocrine disrupting chemicals (EDCs). In this paper, we discuss the surface-mediated adsorption mechanism and subsequent changes in the electronic structure of EDCs. This is in view of their separation from environment and possible photodecomposition. Computational investigation based on density functional theory and ab initio molecular dynamics was performed on bisphenol compounds (BPA, M-1, and M-2) as guest and affinity-based separation media as substrate. Static properties (at 0 K) and conformational dynamics upon physisorption (at T = 300 K) depict the potential of 2H-MoS2 surface for reversible adsorption/desorption and selective isolation of these EDCs. In contrast, layered graphene supports very strong surface adsorption and assures complete removal of EDCs. In particular, optical response of the EDCs gets tuned upon surface adsorption. Hence, understanding the surface adsorption and modulation of the electronic structure would reveal possible means for extraction and photodegradation of a major class of environmental pollutants by specific choice of surface.

The impact of interactions between algal organic matter and humic substances on coagulation

This study focuses on the effects of molecular interactions between two natural organic matter (NOM) fractions, peptides/proteins derived from cyanobacterium Microcystis aeruginosa (MA proteins) and peat humic substances (HS), on their removal by coagulation. Coagulation behaviour was studied by the jar tests with MA protein/HS mixtures and with single compounds (MA proteins or HS). Aluminium sulphate was used as a coagulant. Besides MA proteins, bovine serum albumin (BSA) was used as a model protein. For the MA protein/HS mixture, the removal rates were higher (80% versus 65%) and the dose of coagulant substantially lower (2.8 versus 5.5 mg L(-1) Al) than for coagulation of single HS, indicating the positive effect of protein-HS interactions on the coagulation process. The optimum coagulation pH was 5.2-6.7 for MA proteins and 5.5-6 for HS by alum. The optimum pH for the removal of MA protein/HS mixture ranged between pH 5.5-6.2, where the charge neutralization of negatively charged acidic functional groups of organic molecules by positively charged coagulant hydroxopolymers lead to coagulation. MA proteins interacted with HS, probably through hydrophobic, dipole-dipole and electrostatic interactions, even in the absence the coagulant. These interactions are likely to occur within a wide pH range, but they result in coagulation only at low pH values (pH < 4). At this pH, the negative charge of both MA proteins and HS was suppressed due to the protonation of acidic functional groups and thus the molecules could approach and combine forming aggregates. Virtually the same trends were observed in the experiments with HS and BSA, indicating that BSA is a suitable model for MA proteins under experimental conditions used in this study. The study showed that increases in organic content in source water due to the release of algae products may not necessarily entail deterioration of the coagulation process and a rise in coagulant demand.

The effect of vegetation and soil texture on the nature of organics in runoff from a catchment supplying water for domestic consumption

The influence of vegetation and soil texture on the concentration and character of dissolved organic matter (DOM) present in runoff from the surface and sub-surface of zero order catchments of the Myponga Reservoir-catchment (South Australia) was investigated to determine the impacts of catchment characteristics and land management practices on the quality of waters used for domestic supply. Catchments selected have distinct vegetative cover (grass, native vegetation or pine) and contrasting texture of the surface soil horizon (sand or clay loam/clay). Water samples were collected from three slope positions (upper, middle, and lower) at soil depths of ~30 cm and ~60 cm in addition to overland flows. Filtered (0.45 μm) water samples were analyzed for dissolved organic carbon (DOC) and UV-visible absorbance and by F-EEM and HPSEC with UV and fluorescence detection to characterize the DOM. Surface and sub-surface runoff from catchments with clay soils and native vegetation or grass had lower DOC concentrations and lower relative abundances of aromatic, humic-like and high molecular weight organics than runoff from sandy soils with these vegetative types. Sub-surface flows from two catchments with Pinus radiata had similar DOC concentrations and DOM character, regardless of marked variation in surface soil texture. Runoff from catchments under native vegetation and grass on clay soils resulted in lower DOC concentrations and hence would be expected to have lower coagulant demand in conventional treatment for potable water supply than runoff from corresponding sandy soil catchments. However, organics in runoff from clay catchments would be more difficult to remove by coagulation. Surface waters from the native vegetation and grass catchments were generally found to have higher relative abundance of organic compounds amenable to removal by coagulation compared with sub-surface waters. Biophysical and land management practices combine to have a marked influence on the quality of source water used for domestic supply.

Combination of powdered activated carbon and powdered zeolite for enhancing ammonium removal in micro-polluted raw water

Even zeolite is promising in ammonia pollution disposing, its removal efficiency is frequently interfered by organics. As activated carbon has good removal efficiency on organic contaminants, combination of two adsorbents may allow their respective adsorption characteristics into full play. This paper provides a performance assessment of the combination for enhancing ammonium removal in micro-polluted raw water. Gel-filtration chromatography (GFC) was carried out to quantify the molecular weight (MW) range of organic contaminants that powdered activated carbon (PAC) and powdered zeolite (PZ) can remove. The polydispersity difference which also calculated from GFC may indicate the wider organic contaminants removal range of PAC and the relatively centralized removal range of PZ. The jar tests of combination dosing confirm a synergistic effect which promotes ammonium removing. Nevertheless, it also shows an antagonism hindering the due removal performance of the two adsorbents on CODMn, while it is not much evident on UV254. Furthermore, a comparison study with simulated coagulation-sedimentation process was conducted to evaluate the optimum dosing points (spatial and temporal) of PAC and PZ among follows: suction well, pipeline mixer, early and middle phase of flocculation. We suggest to dose both two adsorbents into the early phase of flocculation to maximize the versatile removal efficiency on turbidity, ammonium and organic contaminants.

Integrated in-line coagulation-aerated ultrafiltration for drinking-water production: A case study from laboratory to pilot plant

A pilot-scale study was made for drinking-water production from low-quality influents with in-line coagulation as pre-treatment of aerated ultrafiltration. Optimum flocculation parameters were previously determined in the laboratory, searching for large and strong flocs that could resist aeration without increasing the membrane fouling. Nevertheless, the comparison of the jar tests and the pilot-scale results showed that the former could help pre-dimensioning the flocculation facilities but could not precisely reproduce the behavior of the flocs in the membrane tank. The optimum coagulant dosage enabled the highest dissolved organic carbon (DOC) removal without affecting membrane fouling. Additionally, as opposed to the jar-test results, long retention times led to the lowest fouling rates while the velocity gradient affected neither the effluent quality nor the membrane fouling. These findings suggested that the influence of the flocculation parameters was masked by aeration inside the membrane tank but, even so, 43% and 82% DOC and UVA254 removals, respectively, were reached. Furthermore, the growth of the total membrane resistance with time was logarithmic instead of linear, confirming the suitability of the pre-treatment for low-quality influents.

Heavy Rainfall Impacts on Trihalomethane Formation in Contrasting Northwestern European Potable Waters

There is emerging concern over the impact of extreme events such as heavy rainfall on the quality of water entering the drinking water supply from aboveground sources, as such events are expected to increase in magnitude and frequency in response to climate change. We compared the impact of rainfall events on streamwater quality in four contrasting upland (peatland and mineral soil) and lowland agricultural catchments used to supply drinking water in France (Brittany) and the United Kingdom (North Wales) by analyzing water samples collected before, during, and after specific events. At all four streams, heavy rainfall led to a considerable rise in organic matter concentration ranging from 48 to 158%. Dissolved organic carbon (DOC) quality, as determined using specific ultraviolet absorbance, changed consistently at all sites during rainfall events, with a greater proportion of aromatic and higher molecular weight compounds following the onset of rainfall. However, the change in DOC quality and quantity did not significantly alter the trihalomethane formation potential. We observed small increases in trihalomethane (THM) generation only at the Welsh peatland and agricultural sites and a small decrease at the Brittany agricultural site. The proportion of brominated THMs in chlorinated waters was positively correlated with bromide/DOC ratio in raw waters for all sites and hydrological conditions. These results provide a first indication of the potential implications for surface-based drinking water resources resulting from expected future increases in rainfall event intensity and extension of dry periods with climate changes.

Dissolved effluent organic matter: Characteristics and potential implications in wastewater treatment and reuse applications

Wastewater reuse is currently considered globally as the most critical element of sustainable water management. The dissolved effluent organic matter (dEfOM) present in biologically treated urban wastewater, consists of a heterogeneous mixture of refractory organic compounds with diverse structures and varying origin, including dissolved natural organic matter, soluble microbial products, endocrine disrupting compounds, pharmaceuticals and personal care products residues, disinfection by-products, metabolites/transformation products and others, which can reach the aquatic environment through discharge and reuse applications. dEfOM constitutes the major fraction of the effluent organic matter (EfOM) and due to its chemical complexity, it is necessary to utilize a battery of complementary techniques to adequately describe its structural and functional character. dEfOM has been shown to exhibit contrasting effects towards various aquatic organisms. It decreases metal uptake, thus potentially reducing their bioavailability to exposed organisms. On the other hand, dEfOM can be adsorbed on cell membranes inducing toxic effects. This review paper evaluates the performance of various advanced treatment processes (i.e., membrane filtration and separation processes, activated carbon adsorption, ion-exchange resin process, and advanced chemical oxidation processes) in removing dEfOM from wastewater effluents. In general, the literature findings reveal that dEfOM removal by advanced treatment processes depends on the type and the amount of organic compounds present in the aqueous matrix, as well as the operational parameters and the removal mechanisms taking place during the application of each treatment technology.

Ultrafiltration of natural organic matter from water by vertically aligned carbon nanotube membrane

In this study vertically aligned carbon nanotubes (VA-CNT) was grown on anodized aluminum oxide (AAO) substrate. The synthesized AAO-CNT membrane was characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM), contact angle and BET. The pure water flux, humic acid (HA) (as representative of natural organic matters) rejection and fouling mechanism were also evaluated. The fabricated membrane has pore density of 1.3 × 10(10) pores per cm(2), average pore size of 20 ± 3 nm and contact angle of 85 ± 8(o). A significant pure water flux of 3600 ± 100 L/m(2).h was obtained at 1 bar of pressure by this membrane due to the frictionless structure of CNTs. High contact angle exhibited the hydrophobic property of the membrane. It was revealed that HA is primarily rejected by adsorption in the membrane pores due to hydrophobic interactions with HA. Flux decline occurred rapidly through both cross flow and dead end filtration of the HA. Based on the blocking laws, internal pore constriction is dominant fouling mechanism in which HA adsorbs in membrane pores results in pores blockage and flux decline.

Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring

Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A.D. 1450-1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.

Refractory organic pollutants and toxicity in pulp and paper mill wastewaters

This review describes medium and high molecular weight organic material found in wastewaters from pulp and paper industry. The aim is to review the versatile pollutants and the analysis methods for their determination. Among other pollutants, biocides, extractives, and lignin-derived compounds are major contributors to harmful effects, such as toxicity, of industrial wastewaters. Toxicity of wastewaters from pulp and paper mills is briefly evaluated including the methods for toxicity analyses. Traditionally, wastewater purification includes mechanical treatment followed by chemical and/or biological treatment processes. A variety of methods are available for the purification of industrial wastewaters, including aerobic and anaerobic processes. However, some fractions of organic material, such as lignin and its derivatives, are difficult to degrade. Therefore, novel chemical methods, including electrochemical and oxidation processes, have been developed for separate use or in combination with biological treatment processes.

Reducing the chlorine dioxide demand in final disinfection of drinking water treatment plants using activated carbon

Chlorine dioxide is one of the most widely employed chemicals in the disinfection process of a drinking water treatment plant (DWTP). The aim of this work was to evaluate the influence of the adsorption process with granular activated carbon (GAC) on the chlorine dioxide consumption in final oxidation/disinfection. A first series of tests was performed at the laboratory scale employing water samples collected at the outlet of the DWTP sand filter of Cremona (Italy). The adsorption process in batch conditions with seven different types of GAC was studied. A second series of tests was performed on water samples collected at the outlet of four GAC columns installed at the outlet of the DWTP sand filter. The results showed that the best chlorine dioxide demand (ClO2-D) reduction yields are equal to 60-80% and are achieved in the first 30 min after ClO2 addition, during the first 16 days of the column operation using a mineral, coal-based, mesoporous GAC. Therefore, this carbon removes organic compounds that are more rapidly reactive with ClO2. Moreover, a good correlation was found between the ClO2-D and UV absorbance at wavelength 254 nm using mineral carbons; therefore, the use of a mineral mesoporous GAC is an effective solution to control the high ClO2-D in the disinfection stage of a DWTP.

Occurrence and behaviors of fluorescence EEM-PARAFAC components in drinking water and wastewater treatment systems and their applications: a review

Fluorescence excitation emission matrices-parallel factor analysis (EEM-PARAFAC) is a powerful tool for characterizing dissolved organic matter (DOM), and it is applied in a rapidly growing number of studies on drinking water and wastewater treatments. This paper presents an overview of recent findings about the occurrence and behavior of PARAFAC components in drinking water and wastewater treatments, as well as their feasibility for assessing the treatment performance and water quality including disinfection by-product formation potentials (DBPs FPs). A variety of humic-like, protein-like, and unique (e.g., pyrene-like) fluorescent components have been identified, providing valuable insights into the chemical composition of DOM and the effects of various treatment processes in engineered systems. Coagulation/flocculation-clarification preferentially removes humic-like components, and additional treatments such as biological activated carbon filtration, anion exchange, and UV irradiation can further remove DOM from drinking water. In contrast, biological treatments are more effective for protein-like components in wastewater treatments. PARAFAC components have been proven to be valuable as surrogates for conventional water quality parameter, to track the changes of organic matter quantity and quality in drinking water and wastewater treatments. They are also feasible for assessing formations of trihalomethanes and other DBPs and evaluating treatment system performance. Further studies of EEM-PARAFAC for assessing the effects of the raw water quality and variable treatment conditions on the removal of DOM, and the formation potentials of various emerging DBPs, are essential for optimizing the treatment processes to ensure treated water quality.

Resolving the multifaceted mechanisms of the ferric chloride thrombosis model using an interdisciplinary microfluidic approach

The mechanism of action of the widely used in vivo ferric chloride (FeCl3) thrombosis model remains poorly understood; although endothelial cell denudation is historically cited, a recent study refutes this and implicates a role for erythrocytes. Given the complexity of the in vivo environment, an in vitro reductionist approach is required to systematically isolate and analyze the biochemical, mass transfer, and biological phenomena that govern the system. To this end, we designed an "endothelial-ized" microfluidic device to introduce controlled FeCl3 concentrations to the molecular and cellular components of blood and vasculature. FeCl3 induces aggregation of all plasma proteins and blood cells, independent of endothelial cells, by colloidal chemistry principles: initial aggregation is due to binding of negatively charged blood components to positively charged iron, independent of biological receptor/ligand interactions. Full occlusion of the microchannel proceeds by conventional pathways, and can be attenuated by antithrombotic agents and loss-of-function proteins (as in IL4-R/Iba mice). As elevated FeCl3 concentrations overcome protective effects, the overlap between charge-based aggregation and clotting is a function of mass transfer. Our physiologically relevant in vitro system allows us to discern the multifaceted mechanism of FeCl3-induced thrombosis, thereby reconciling literature findings and cautioning researchers in using the FeCl3 model.

Coagulation behavior and floc properties of compound bioflocculant-polyaluminum chloride dual-coagulants and polymeric aluminum in low temperature surface water treatment

This study was intended to compare coagulation behavior and floc properties of two dual-coagulants polyaluminum chloride-compound bioflocculant (PAC-CBF) (PAC dose first) and compound bioflocculant-polyaluminum chloride (CBF-PAC) (CBF dose first) with those of PAC alone in low temperature drinking water treatment. Results showed that dual-coagulants could improve DOC removal efficiency from 30% up to 34%. Moreover, CBF contributed to the increase of floc size and growth rate, especially those of PAC-CBF were almost twice bigger than those of PAC. However, dual-coagulants formed looser and weaker flocs with lower breakage factors in which fractal dimension of PAC-CBF flocs was low which indicates a looser floc structure. The floc recovery ability was in the following order: PAC-CBF>PAC alone>CBF-PAC. The flocculation mechanism of PAC was charge neutralization and enmeshment, meanwhile the negatively charged CBF added absorption and bridging effect.

An evaluation on different origins of natural organic matters using various anodes by electrocoagulation

In this investigation, natural organic matters (NOM) of different origins (commercial, terrestrial and natural water) were treated by electrocoagulation (EC) process using aluminum, iron and hybrid electrodes. Electrode type effect on removal efficiency was observed for each NOM (commercial, terrestrial, and natural). The results were presented as dissolved organic carbon (DOC) (mg L(-1)) and UV/VIS absorbance (cm(-1)). The specific UV absorbance (SUVA) was determined before and after treatment of water. The lowest effluent concentration was obtained as 5.05 mg L(-1) with hybrid electrode for natural NOM source at its original pH 7.3. In addition, among the metal types, the best UV-abs-254 removal efficiency was obtained as 92.4% with 0.0312 cm(-1) by hybrid electrode at the end of the process. The color removal efficiency of water occurred successfully by Al and hybrid electrodes. Aquatic NOM source was the most resistant to EC treatment with DOC reduction of 71.1%, 59.8%, and 68.6% for Al, Fe and hybrid electrodes, respectively. Zeta potential and floc size of colloids were observed during the process for the determination of destabilization level of natural organic matters in EC process. Fast coagulation or flocculation and incipient instability were formed during electrolysis time for Al and Fe electrode, respectively. SUVA value was reduced to below 2 for three NOM sources studied. The EC process was shown to be a viable for different NOM sources with various metals.

Mitigation of Humic Acid Inhibition in Anaerobic Digestion of Cellulose by Addition of Various Salts

Humic compounds are inhibitory to the anaerobic hydrolysis of cellulosic biomass. In this study, the impact of salt addition to mitigate the inhibitory effects of humic compounds was investigated. The experiment was conducted using batch tests to monitor the anaerobic hydrolysis of cellulose in the presence of humic acid. Sodium, potassium, calcium, magnesium and iron salts were tested separately for their efficiency to mitigate humic acid inhibition. All experiments were done under mesophilic conditions (30 °C) and at pH 7. Methane production was monitored online, using the Automatic Methane Potential Test System. Methane production, soluble chemical oxygen demand and volatile fatty acid content of the samples were measured to calculate the hydrolysis efficiencies. Addition of magnesium, calcium and iron salts clearly mitigated the inhibitory effects of humic acid and hydrolysis efficiencies reached up to 75%, 65% and 72%, respectively, which were similar to control experiments. Conversely, potassium and sodium salts addition did not mitigate the inhibition and hydrolysis efficiencies were found to be less than 40%. Mitigation of humic acid inhibition via salt addition was also validated by inductively coupled plasma atomic emission spectroscopy analyses, which showed the binding capacity of different cations to humic acid.

Feasibility of sulfide control in sewers by reuse of iron rich drinking water treatment sludge

Dosage of iron salt is the most commonly used method for sulfide control in sewer networks but incurs high chemical costs. In this study, we experimentally investigate the feasibility of using iron rich drinking water treatment sludge for sulfide control in sewers. A lab-scale rising main sewer biofilm reactor was used. The sulfide concentration in the effluent decreased from 15.5 to 19.8 mgS/L (without dosing) to below 0.7-2.3 mgS/L at a sludge dosing rate achieving an iron to total dissolved inorganic sulfur molar ratio (Fe:S) of 1:1, with further removal of sulfide possible by prolonging the reaction time. In fact, batch tests revealed an Fe consumption to sulfide removal ratio of 0.5 ± 0.02 (mole:mole), suggesting the possible occurrence of other reactions involving the removal of sulfide. Modelling revealed that the reaction between iron in sludge and sulfide has reaction orders of 0.65 ± 0.01 and 0.77 ± 0.02 with respect to the Fe and sulfide concentrations, respectively. The addition of sludge slightly increased the total chemical oxidation demand (tCOD) concentration (by approximately 12%) as expected, but decreased the soluble chemical oxidation demand (sCOD) concentration and methane formation by 7% and 20%, respectively. Some phosphate removal (13%) was also observed at the sludge dosing rate of 1:1 (Fe:S), which is beneficial to nutrient removal from the wastewater. Overall, this study suggests that dosing iron-rich drinking water sludge to sewers could be an effective strategy for sulfide removal in sewer systems, which would also reduce the sludge disposal costs for drinking water treatment works. However, its potential side-effects on sewer sedimentation and on the wastewater treatment plant effluent remain to be investigated.

Chemical treatment response to variations in non-point pollution water quality: results of a factorial design experiment

Chemical treatment of non-point derived pollution often suffers from undesirable oscillations in purification efficiency due to variations in runoff water quality. This study examined the response of the chemical purification process to variations in water quality using a 2(k) factorial design for runoff water rich in humic substances. The four k factors evaluated and the levels applied were: organic matter as dissolved organic carbon (DOC) (20-70 mg/L), suspended solids (SS) (10-60 mg/L), initial water pH (4.5-7), and applied coagulant dosage (ferric sulphate) (35-100 mg/L). Indicators of purification efficiency were residual concentration of DOC, SS and total phosphorus (tot-P). Analysis of variance and factor effect calculations showed that the initial DOC concentration in raw water samples and its interactions with the coagulant dosage applied exerted the most significant influence on the chemical purification process, substantially affecting the residual concentration of DOC, SS and tot-P. The variations applied to the factors SS and pH only slightly affected purification efficiency. The results can be used in the design of purification systems with high organic matter load variation, e.g. peat extraction runoff.

Effects of coagulation on the removal of natural organic matter, genotoxicity, and precursors to halogenated furanones

Natural organic matter (NOM) in drinking water can react with disinfectants to form disinfection by-products (DBPs). Halogenated furanones are a group of emerging DBPs that can account for 20-60% of the total mutagenicity observed in drinking water. This study examined the impacts of bench-scale coagulation and subsequent chlorination on DBP formation as well as genotoxicity using three source waters located in Ontario, Canada. Two halogenated furanones 3-chloro-4-(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA) were analyzed; along with trihalomethanes (THMs), haloacetic acids (HAAs), and absorbable organic halides (AOX). NOM was quantified using liquid chromatography-organic carbon detection (LC-OCD). Measured MX and MCA formation was 6.9-15.3 ng/L and 43.2-315 ng/L following optimized coagulation and subsequent chlorination of the three waters tested. DBP formation and speciation were evaluated as a function of the specific NOM fractions present in the source waters. Humics, building blocks, and biopolymers were highly correlated with DBP formation. Correlations between DBPs were also investigated and a potential relationship between MCA and/or MX vs. HAAs was observed. MX was the only measured DBP that contributed to genotoxicity, representing less than 0.001% of AOX by mass but responsible for 40-67% of the genotoxic response in chlorinated Ottawa River water samples. Genotoxic potential decreased with alum dosages, signifying that coagulation was effective at removing genotoxic DBP precursors.

Removal of soluble microbial products as the precursors of disinfection by-products in drinking water supplies

Water pollution worsens the problem of disinfection by-products (DBPs) in drinking water supply. Biodegradation of wastewater organics produces soluble microbial products (SMPs), which can be important DBP precursors. In this laboratory study, a number of enhanced water treatment methods for DBP control, including enhanced coagulation, ozonation, and activated carbon adsorption, were evaluated for their effectiveness in treating SMP-containing water for the DBP reduction purpose. The results show that enhanced coagulation with alum could remove SMPs only marginally and decrease the DBP formation potential (DBPFP) of the water by less than 20%. Although ozone could cause destruction of SMPs in water, the overall DBPFP of the water did not decrease but increased after ozonation. In contrast, adsorption by granular activated carbon could remove the SMP organics from water by more than 60% and reduce the DBPFP by more than 70%. It is apparent that enhanced coagulation and ozonation are not suitable for the removal of SMPs as DBP precursors from polluted water, although enhanced coagulation has been commonly used to reduce the DBP formation caused by natural organic matter. In comparison, activated carbon adsorption is shown as a more effective means to remove the SMP content from water and hence to control the wastewater-derived DBP problem in water supply.

Transformation of sulfonylurea herbicides in simulated drinking water treatment processes

Sulfonylurea herbicides (SUs) were detected in natural waters and could be potentially exposed to human beings via portable use. Thus, the removal of five representative SUs in simulated water treatment processes including coagulation, activated carbon adsorption, and chlorination disinfection was systematically investigated. Results showed that coagulation had little effect on the removal of the herbicides with the average removal less than 10 %. Powder-activated carbon adsorption was apparently more effective with removal rates of 50 ~ 70 %. SUs were also partially removed in chlorination process. A complete removal was achieved when the three treatments were performed in series. However, it was found that parts of the SUs were transformed into certain stable products with triazine/pyrimidine structures which might be of potential health risks in chlorination process. Thus, current drinking water treatment processes are not likely to provide sufficient protection for human population from exposure to SUs.

The fate of Microcystis aeruginosa cells during the ferric chloride coagulation and flocs storage processes

Microcystis blooms could cause severe problems for drinking water supplies with their associated microcystins (MCs). As the majority of MCs are retained inside the cells, the effective removal of the intact Microcystis cells to avoid the release of additional MCs plays an important role in drinking water treatment. This study evaluated the effect of ferric chloride (FeCl3) coagulation and the flocs storage process on the integrity of Microcystis aeruginosa cells and the intracellular MCs release (and possible degradation) in both processes. Multiple analysis techniques including scanning electron microscopy and chlorophyll fluorescence were used to assess the integrity of M. aeruginosa. In the coagulation process, the coagulant dosage and mechanical actions caused no cell damage, and all the cells remained intact. Furthermore, 100 mg/L FeCl3 was effective in removing the extracellular MCs. In the flocs storage process, a number of intracellular MCs were released into the supernatant, but the cells remained viable up to 10 d.

Assessing trihalomethanes (THMs) and N-nitrosodimethylamine (NDMA) formation potentials in drinking water treatment plants using fluorescence spectroscopy and parallel factor analysis

The formation of disinfection byproducts (DBPs) is a major challenge in drinking water treatments. This study explored the applicability of fluorescence excitation-emission matrices and parallel factor analysis (EEM-PARAFAC) for assessing the formation potentials (FPs) of trihalomethanes (THMs) and N-nitrosodimethylamine (NDMA), and the treatability of THM and NDMA precursors in nine drinking water treatment plants. Two humic-like and one tryptophan-like components were identified for the samples using PARAFAC. The total THM FP (TTHM FP) correlated strongly with humic-like component C2 (r=0.874), while NDMA FP showed a moderate and significant correlation with the tryptophan-like component C3 (r=0.628). The reduction by conventional treatment was more effective for C2 than C3, and for TTHM FP than NDMA FP. The treatability of DOM and TTHM FP correlated negatively with the absorption spectral slope (S275-295) and biological index (BIX) of the raw water, but it correlated positively with humification index (HIX). Our results demonstrated that PARAFAC components were valuable for assessing DBPs FP in drinking water treatments, and also that the raw water quality could affect the treatment efficiency.

Engineered nanoparticles and organic matter: a review of the state-of-the-art

Growth in the development and production of engineered nanoparticles (ENPs) in recent years has increased the potential for interactions of these nanomaterials with aquatic and terrestrial environments. Carefully designed studies are therefore required in order to understand the fate, transport, stability, and toxicity of nanoparticles. Natural organic matter (NOM), such as the humic substances found in water, sediment, and soil, is one of the substances capable of interacting with ENPs. This review presents the findings of studies of the interaction of ENPs and NOM, and the possible effects on nanoparticle stability and the toxicity of these materials in the environment. In addition, ENPs and NOM are utilized for many different purposes, including the removal of metals and organic compounds from effluents, and the development of new electronic sensors and other devices for the detection of active substances. Discussion is therefore provided of some of the ways in which NOM can be used in the production of nanoparticles. Although there has been an increase in the number of studies in this area, further progress is needed to improve understanding of the dynamic interactions between ENPs and NOM.

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.

Removal of organic matter from surface water during coagulation with sludge flotation and rapid filtration - a full-scale technological investigation

Coagulation with sludge flotation and rapid filtration was selected as a surface water treatment technology to be optimised with a full-scale investigation, which was carried out in Poland between August and October 2013. The river water treated was characterized by low alkalinity, high-temperature variability and a high organic matter content. In the course of technological studies, the processes of coagulation with sludge flotation and rapid filtration were analysed. The studies were performed in the most adverse conditions for the applied technology i.e. during the period of algal bloom and subsequent decomposition of dead plankton. Throughout the study, the river water contained mainly dissolved organic matter, with occasional increases in the concentration of the undissolved fraction during algal bloom. The undissolved total organic carbon (TOC) fraction was effectively removed through coagulation while small doses of ClO₂added prior to coagulation enhanced the process. The process of coagulation using high-coagulant doses at pH = 6.5 did not provide a reduction in the TOC value below the level of 4 mg C/L required for treated water. The effect was achieved by adding powdered activated carbon (PAC) before the filters. The coagulation products were characterised by low-hydraulic resistance which should be taken into account at the stage of water delivery to the filters, after flotation.

Absorption and fluorescence properties of chromophoric dissolved organic matter: implications for the monitoring of water quality in a large subtropical reservoir

The development of techniques for real-time monitoring of water quality is of great importance for effectively managing inland water resources. In this study, we first analyzed the absorption and fluorescence properties in a large subtropical reservoir and then used a chromophoric dissolved organic matter (CDOM) fluorescence monitoring sensor to predict several water quality parameters including the total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), dissolved organic carbon (DOC), and CDOM fluorescence parallel factor analysis (PARAFAC) components in the reservoir. The CDOM absorption coefficient at 254 nm (a(254)), the humic-like component (C1), and the tryptophan-like component (C3) decreased significantly along a gradient from the northwest to the lake center, northeast, southwest, and southeast region in the reservoir. However, no significant spatial difference was found for the tyrosine-like component (C2), which contributed only four marked peaks. A highly significant linear correlation was found between the a(254) and CDOM concentration measured using the CDOM fluorescence sensor (r(2) = 0.865, n = 76, p < 0.001), indicating that CDOM concentrations could act as a proxy for the CDOM absorption coefficient measured in the laboratory. Significant correlations were also found between the CDOM concentration and TN, TP, COD, DOC, and the maximum fluorescence intensity of C1, suggesting that the real-time monitoring of CDOM concentrations could be used to predict these water quality parameters and trace the humic-like fluorescence substance in clear aquatic ecosystems with DOC <2 mg/L and total suspended matter (TSM) concentrations <15 mg/L. These results demonstrate that the CDOM fluorescence sensor is a useful tool for on-line water quality monitoring if the empirical relationship between the CDOM concentration measured using the CDOM fluorescence sensor and the water quality parameters is calibrated and validated.

Effect of water treatment additives on lime softening residual trace chemical composition--implications for disposal and reuse

Drinking water treatment residues (WTR) offer potential benefits when recycled through land application. The current guidance in Florida, US allows for unrestricted land application of lime softening WTR; alum and ferric WTR require additional evaluation of total and leachable concentrations of select trace metals prior to land application. In some cases a mixed WTR is produced when lime softening is accompanied by the addition of a coagulant or other treatment chemical; applicability of the current guidance is unclear. The objective of this research was to characterize the total and leachable chemical content of WTR from Florida facilities that utilize multiple treatment chemicals. Lime and mixed lime WTR samples were collected from 18 water treatment facilities in Florida. Total and leachable concentrations of the WTR were measured. To assess the potential for disposal of mixed WTR as clean fill below the water table, leaching tests were conducted at multiple liquid to solid ratios and under reducing conditions. The results were compared to risk-based soil and groundwater contamination thresholds. Total metal concentrations of WTR were found to be below Florida soil contaminant thresholds with Fe found in the highest abundance at a concentration of 3600 mg/kg-dry. Aluminum was the only element that exceeded the Florida groundwater contaminant thresholds using SPLP (95% UCL = 0.23 mg/L; risk threshold = 0.2 mg/L). Tests under reducing conditions showed elevated concentrations of Fe and Mn, ranging from 1 to 3 orders of magnitude higher than SPLP leachates. Mixed lime WTR concentrations (total and leachable) were lower than the ferric and alum WTR concentrations, supporting that mixed WTR are appropriately represented as lime WTR. Testing of WTR under reducing conditions demonstrated the potential for release of certain trace metals (Fe, Al, Mn) above applicable regulatory thresholds; additional evaluation is needed to assess management options where reducing conditions may develop.

Synthesis and application of a quaternary phosphonium polymer coagulant to avoid N-nitrosamine formation

Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) are widely used for coagulating and removing negatively charged particles and dissolved organic matter (DOM) from drinking water. Their use, however, has been linked to the formation of carcinogenic N-nitrosamines as byproducts during chloramine-based drinking water disinfection. In this study, a novel quaternary phosphonium cationic polymer, poly(diallyldiethylphosphonium chloride) (polyDADEPC), was synthesized such that the quaternary nitrogen atom of polyDADMAC was substituted with a phosphorus atom. Formation potential tests revealed that even under strong nitrosation conditions, polyDADEPC and related lower-order P-based compounds formed oxygenated and not nitrosated products. Bench-scale jar tests using three different source waters further demonstrated that polyDADEPC achieved coagulation performance comparable to commercial polyDADMACs for particle and DOM removals within the typical dose range used for drinking water treatment. This work highlights the potential use of a phosphonium coagulant polymer, polyDADEPC, as a viable alternative to polyDADMAC to avoid nitrosated byproduct formation during chloramination.

The fate and importance of organics in drinking water treatment: a review

In the pioneer days, the main driving forces for research of organics in drinking water treatment (DWT) were human health risks and optimisation of technology. The focus was on natural organic matter (NOM) structure, disinfection by-products (DBPs) formation, NOM removal by means of coagulation, adsorption, and oxidation, and development of the most efficient water treatment trains. Surprisingly, after decades of research, rapid development of analytical techniques and progress in risk assessment, the same driving forces are still in the limelight - although the topics have changed slightly. The attention switched from trihalomethanes to a new generation of DBPs. The definition of hydrophilic/hydrophobic NOM depends on the technique used for characterisation. It has become evident that numerous organic compounds can threaten water supply sources. Some of them had been ignored or overlooked in the past, but have recently been detected by advanced analytical tools even in drinking water. Prioritisation becomes priority per se. As far as processes are concerned, mainstream research has been following three lines: fouling mechanisms, application of hybrid processes and interactions between synthetic organic chemicals, other water constituents and materials used in DWT. Significant development has been made in membrane technology. This paper presents a broad overview of the recent organics research. Although the state-of-the-art technologies seem to have an answer to each and every question raised, it is still necessary to deal with specific problems on a case-by-case basis mainly due to the unique nature of NOM and different xenobiotics that may appear in various types of waters. In the end, human health risk, which derives from the presence/absence of organics, is only the tip of the iceberg - underneath lies a whole new universe - the socio-economic aspect of water treatment and quality that deserves much more attention.

Changes in the quality of river water before, during and after a major flood event associated with a La Niña cycle and treatment for drinking purposes

The treatment of organics present in the lower reaches of a major river system (the Murray-Darling Basin, Australia) before (March-July 2010), during (December 2010-May 2011) and after (April-December 2012) a major flood period was investigated. The flood period (over 6months) occurred during an intense La Niña cycle, leading to rapid and high increases in river flows and organic loads in the river water. Dissolved organic carbon (DOC) increased (2-3 times) to high concentrations (up to 16mg/L) and was found to correlate with river flow rates. The treatability of organics was studied using conventional jar tests with alum and an enhanced coagulation model (mEnCo©). Predicted mean alum dose rates (per mg DOC) were higher before (9.1mg alum/mg DOC) and after (8.5mg alum/mg DOC) than during the flood event (8.0mg alum/mg DOC), indicating differences in the character of the organics in raw waters. To assess the character of natural organic matter present in raw and treated waters, high performance size exclusion chromatography with UV and fluorescence detectors were used. During the flood period, high molecular weight UV absorbing compounds (>2kDa) were mostly detected in waters collected, but were not evident in waters collected before and afterwards. The relative abundances of humic-like and protein-like compounds during and following the flood period were also investigated and found to be of a higher molecular weight during the flood period. The treatability of the organics was found to vary over the three climate conditions investigated.

Water engineering. Reducing sewer corrosion through integrated urban water management

Sewer systems are among the most critical infrastructure assets for modern urban societies and provide essential human health protection. Sulfide-induced concrete sewer corrosion costs billions of dollars annually and has been identified as a main cause of global sewer deterioration. We performed a 2-year sampling campaign in South East Queensland (Australia), an extensive industry survey across Australia, and a comprehensive model-based scenario analysis of the various sources of sulfide. Aluminum sulfate addition during drinking water production contributes substantially to the sulfate load in sewage and indirectly serves as the primary source of sulfide. This unintended consequence of urban water management structures could be avoided by switching to sulfate-free coagulants, with no or only marginal additional expenses compared with the large potential savings in sewer corrosion costs.

Aluminum-humic colloid formation during pre-coagulation for membrane water treatment: mechanisms and impacts

Precoagulation has been widely used by low pressure membrane filtration (LPMF) plants to reduce membrane fouling and increase natural organic matter (NOM) removal. Formation of aluminum and aluminum-NOM moieties plays a fundamental role in this important water treatment process. This study comprehensively investigated the mechanisms of aluminum-NOM species formation during precoagulation and their impacts on LPMF performance. The results show that, at low alum doses, e.g. 0.5 mg and 1.0 mg Al L(-1), humic substances (HS) and Al species (amorphous Al(OH)3, or Al(OH)3(am)) reacted to form small Al(OH)3(am)-HS colloids. Increases in alum dose resulted in sequential transitions of the Al-HS moieties to larger particles and, eventually, precipitates. Compared to waters containing only naturally occurring organic colloids (OC) or HS, the coexistence of OC and HS facilitated the formation of Al-HS precipitates, thereby increasing the removal of HS by 7-15%, but the removal of OC was decreased by 3-20%. Interestingly, these transitions in Al-HS moieties did not affect membrane fouling. Both short-term and long-term filtration results demonstrate that OC, rather than the Al(OH)3(am)-HS colloids, primarily caused membrane fouling. These findings highlight the dynamics of particulate Al-NOM formation during precoagulation and its relationship with membrane fouling, which can be utilized to optimize the operation of integrated precoagulation-LPMF systems on full-scale installations.

Occurrence and fate of ozonation by-products at a full-scale drinking water treatment plant

The occurrence and fate of carbonyl compounds as ozonation by-products at a full scale drinking water treatment plant (DWTP) were studied for one year. Raw water and samples after the main treatment processes (pre-ozonation, coagulation/flocculation, sand filtration, main ozonation, filtration through granular activated carbon and chlorination) were collected on a monthly basis. Pre-ozonation led to the formation of carbonyl compounds at concentrations of 67.3 ± 43.3 μg/l as sum of 14 carbonyl compounds whereas lower concentrations were determined after the main ozonation process, 32.8 ± 22.3 μg/l. The dominant compounds were formaldehyde, acetaldehyde, glyoxal and methyl glyoxal contributing to 65% of total carbonyl content. The DOC reactivity in formation of carbonyl compounds varied through the year exhibiting the higher values in spring. Coagulation/flocculation and sand filtration significantly removed (64-80%) the carbonyl compounds formed at the pre-ozonation step. The removal efficiency of filtration through granular activated carbon showed great variation ranging from 15 to 62%. Finally, the concentrations of carbonyl compounds in finished water were low, close to detection limits, revealing the efficiency of DWTP in the removal of this class of ozonation by-products.

Influence of drinking water treatments on chlorine dioxide consumption and chlorite/chlorate formation

Disinfection is the last treatment stage of a Drinking Water Treatment Plant (DWTP) and is carried out to maintain a residual concentration of disinfectant in the water distribution system. Chlorine dioxide (ClO2) is a widely used chemical employed for this purpose. The aim of this work was to evaluate the influence of several treatments on chlorine dioxide consumption and on chlorite and chlorate formation in the final oxidation/disinfection stage. A number of tests was performed at laboratory scale employing water samples collected from the DWTP of Cremona (Italy). The following processes were studied: oxidation with potassium permanganate, chlorine dioxide and sodium hypochlorite, coagulation/flocculation with ferric chloride and aluminum sulfate, filtration and adsorption onto activated carbon. The results showed that the chlorine dioxide demand is high if sodium hypochlorite or potassium permanganate are employed in pre-oxidation. On the other hand, chlorine dioxide leads to the highest production of chlorite and chlorate. The coagulation/flocculation process after pre-oxidation shows that chlorine dioxide demand decreases if potassium permanganate is employed as an oxidant, both with ferric chloride and aluminum sulfate. Therefore, the combination of these processes leads to a lower production of chlorite and chlorate. Aluminum sulfate is preferable in terms of the chlorine dioxide demand reduction and minimization of the chlorite and chlorate formation. Activated carbon is the most effective solution as it reduced the chlorine dioxide consumption by about 50% and the DBP formation by about 20-40%.