naturalorganicmatter from aqueous solutions by electrocoagulation . J Adv Environ Health Res 2014;
In recent decades, due to the sever pollution of water resources such as rivers, seas, and reservoirs by wastewater from domestic, industrial, and agricultural sources, the concentration of water contaminants has increased dramatically. Among water pollutants, organic pollutants are important due to their high quantities and ranges in water resources, an elevated concentration, specific properties, and
CONCLUSION AND OUTLOOK
Although occurring in varying proportions, naturalorganicmatter is ubiquitous in source waters. The environmental and
health risks associated with NOM include DBP formation, reducing WTP efficiency, facilitating bacterial re-growth in the water distribution system, and objectionable organoleptic properties. Owing to the expensive equipment used in NOM characterisation, it is not possible to routinely monitor the levels and character of NOM in source waters. This applies as much to South Africa as to the rest of the world. In light of this, central analytical facilities accessible to a number of WTPs can be established for NOM control. Alternatively, surrogate parameters such as DOC and TOC can be monitored instead. The six water quality regions of South Africa imply different strategies for NOM abatement. Water utility companies are only just beginning to appreciate the need to monitor NOM.
shallow well aquifers. These substances plus tannic acid are the major fraction of Dissolved OrganicMatter (DOM) in water. These substances are oxidized very slowly and their solubility in water may vary with pH. The dissolved fraction of NOM may not be fully removed using conventional water treatment practices and have been shown to produce by- products such as trihalomethane during disinfection. The organic compounds in surface waters and ground waters arise from natural and athropogenic sources. Naturalorganicmatter (NOM) is either formed in place or is formed outside of the water body and then transported into the water body (Wershaw, 2005).
Because of compositional differences between organicmatter from the treated wastewater and river water, 31-35 effluent organicmatter inputs may alter the photochemical characteristics of waters downstream from WWTPs, compared to upstream river waters. Although the structural composition of organicmatter in treated municipal effluent has not been characterized as extensively as riverine DOM, effluent organicmatter does contain a large contribution of protein- and carbohydrate-rich components originating from microbial metabolism 36,37 that can account for up to 80% of the effluent total organic carbon 38 Greater yields of 3 OM*, 1 O2 and OH• have been reported for effluent organicmatter than for reference humic substances and naturalorganicmatter samples. 26-30 However, our previous work simulating effluent discharge mixing scenarios showed that the 3 OM* photoreactivity and, to a lesser extent, the 1 O2 photoreactivity of effluent organicmatter was not additive and even inhibited upon mixing with river water DOM. 27 This implies that the potential for effluent organicmatter-produced reactive species to react with micropollutants released from WWTPs will be lower than expected under given discharge scenarios. Although faster indirect photodegradation rates of pharmaceutical compounds have been reported for treated effluent samples than for natural waters, 8,39 comparisons have not been made under more typical environmental conditions in which effluent organicmatter is mixed with naturalorganicmatter in aquatic systems.
Methylation of tracer and ambient mercury ( 200 Hg and 202 Hg, respectively) equilibrated with four different naturalorganicmatter (NOM) isolates was investigated in vivo using the Hg-methylating sulfate-reducing bacterium Desulfobulbus propionicus 1pr3. Desulfobulbus cultures grown fermentatively with environmentally representative concentrations of dissolved NOM isolates, Hg[II], and HS − were assayed for absolute methylmercury (MeHg) concentration and conversion of Hg(II) to MeHg relative to total unfiltered Hg(II). Results showed the 200 Hg tracer was methylated more efficiently in the presence of hydrophobic NOM isolates than in the presence of transphilic NOM, or in the absence of NOM. Different NOM isolates were associated with variable methylation efficiencies for either the 202 Hg tracer or ambient 200 Hg. One hydrophobic NOM, F1 HpoA derived from dissolved organicmatter from the Florida Everglades, was equilibrated for different times with Hg tracer, which resulted in different methylation rates.
These previous model-testing studies have involved proton and metal binding at the 25
most abundant, lowest affinity, binding sites of naturalorganicmatter. Potentially toxic metals such as Ni, Cu, Zn, Cd and Pb will generally be present at relatively low concentrations, even in polluted waters, and so less abundant, higher affinity, sites will be important. The existence and influence of the high affinity sites in humic substances have come to prominence in the research agenda, following the experimental and modelling work 30
3.3. Analytical Measurements
To address the aim of monitoring the amount of naturalorganicmatter in Toowoomba water sources and to determine the characteristics of the water, tests are to be carried out to measure NOM-related parameters of each of the water sources. Some of these water quality parameters are those that are also important for compliance with the US EPA’s treatment technique requirement of the DBPR. This will be completed for a ten week period on a weekly basis when the water samples are collected. To obtain consistent and accurate results, the methods described by Standard Methods For The Examination Of Water & Wastewater 2005) will be followed, which is the recommendation made by the publication ‘Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual’ (Agency 1999). Each of the tests which are to be completed is explained in detail in the following sections.
c Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai Johor, Malaysia Received 13 July 2005; accepted 13 October 2005
Membrane application in surface water treatment provides many advantages over conventional treatment. However, this effort is hampered by the fouling issue, which restricts its widespread application due to increases in hydraulic resistances, operational and maintenance costs, deterioration of productivity and frequency of membrane regeneration problems. This paper discusses naturalorganicmatter (NOM) and its components as the major membrane foulants that occur during the water filtration process, possible fouling mechanisms relating to reversible and irreversible of NOM fouling, current techniques used to characterize fouling mechanisms and methods to control fouling. Feed properties, membrane characteristics, operational conditions and solution chemistry were also found to strongly influence the nature and extent of NOM fouling. Findings of such studies are highlighted. The understanding of the combined roles of controlling factors and the methods used is very important in order to choose and optimize the best technique and conditions during surface water treatment. The future potential of membrane application for NOM removal is also discussed.
Abstract. This paper defines landscape-scale patterns in the character of naturalorganicmatter (NOM) and tests for rela- tionships to catchment soil, vegetation and topography. The drainage network of a boreal catchment, subcatchment size 0.12–78 km 2 , in Northern Sweden was sampled in August 2002 during a period of stable low water flow. The NOM was characterized with UV/Vis spectroscopy, fluorescence, XAD-8 fractionation (%humic substances), gel permeation chromatography (apparent molecular weight), and elemental composition (C:N). The largest spatial variation was found for C:N, absorbance ratio, and specific visible absorptivity. The lowest variation was in fluorescence index, %humic sub- stances and molecular retention time. The variation in to- tal organic carbon (TOC), iron and aluminium concentration was more than twice that of C:N. Between headwater and downstream sites no significant changes were distinguished in the NOM character. At stream reaches, junctions and lakes little change (<10%) in NOM character was observed. Com- mon factor analysis and partial least squares regression (PLS) revealed that the spatial variation in surface coverage of lakes and mires could explain some of the variation of TOC and NOM character. Our suggestion is that the mosaic of land- scape elements (different amounts of water from lakes, for- est soil and mires) delivers NOM with varying characteristics to a channel network that mixes conservatively downstream, with possible small changes at some stream reaches, junc- tions and lakes.
The THM forming potential is the most reliable indicator in evaluation of organicmatter removal during drinking water treatment processes. The results have shown that the reaction producing THMs follows sec- ond order kinetics. The second order rate constant ranged from 0.024 M -1 s -1 to 0.065 M -1 s -1 at 22 °C and pH
= 8.2 for 96 hours. The removal of 78.4% of naturalorganicmatter, by adsorption on anionic exchange res- ins, resulted in the THM forming potential reduction by 63.1%. Various fractions of naturalorganicmatter differ in their reactivity with chlorine, which is important when it comes to selection of the adsorption me- dium in the drinking water treatment processes.
The performance of a conventional sequence (pre-ozonation, coagulation/flocculation/sedimentation, filtration, disinfection) and two advance sequences (pre-ozonation, nanofiltration; pre-ozonation, coagulation/flocculation/sedimentation, nanofiltration) on the removal of naturalorganicmatter (NOM) and disinfection by-products (DBPs) formation potential was evaluated. Raw and treated waters were characterized in terms of molecular weight, which includes the amount of NOM removed and the qualitative changes in the NOM characteristics (molecular weight and hydrophobicity) since they could be directly related with the DBPs formation. The results demonstrate that, for the type of raw water analysed (hydrophilic with low dissolved organic carbon content), both treatment sequences remove larger molecular weight compounds. However, the sequences with nanofiltration have a higher percentage of low molecular weight compounds removed, when compared with conventional sequence, thus the water from nanofiltration sequences will have lower DBPs formation potential.
This study is the first attempt to investigate the effect of total hardness and ionic strength on coagulation performance and the floc characteristics of titanium tetrachloride (TiCl 4 ). Membrane fouling under different total hardness and ionic strength conditions was also evaluated during a coagulation-ultrafiltration (C-UF) hybrid process. Coagulation experiments were performed with two simulated waters, using humic acid (HA, high molecular weight) and fulvic acid (FA, relatively low molecular weight), respectively, as model naturalorganicmatter (NOM). Results show that both particle and organicmatter removal can be enhanced by increasing total hardness and ionic strength. Floc characteristics were significantly influenced by total hardness and ionic strength and were improved in terms of floc size, growth rate, strength, recoverability and compactness. The results of the UF tests show that the pre-coagulation with TiCl 4 significantly improves the membrane permeate fluxes.
and the nature o f minerals) is as indispensable as the identification o f the pollutants.
Arsenic chemistry in soils has been well studied with numerous publications in the literature concerning the high sorptive capacity o f soils for As. Arsenic has been known to have a high affinity for oxide surfaces, which is affected by several biogeochemical factors such as soil texture, organicmatter, nature and constituents o f minerals, pH, redox potential and competing ions (Adriano, 1986; McArthur et al., 2004). Adsorption reactions at the solid-water interface is the predominate mechanism controlling transport o f As in many soil and groundwater systems (Stollenwerk, 2003). Soil properties will have a major effect on metal mobility, hydrous oxides o f Fe, Al, and Mn, and clay minerals are commonly associated with aquifer solids and have been shown to be significant adsorbents o f As (Inskeep et al., 2002). The extent o f As adsorption is also influenced by the chemistry o f the aqueous phase including pH, As speciation, and the presence and concentration o f naturalorganicmatter (NOM) and competing ions. Arsenic adsorption onto metal oxide surfaces is dominated by electrostatic attraction initially. The surface o f a metal oxide consists o f metal atoms surrounded by oxygen atoms. Hydrogen atoms from surrounding water will attach themselves to the outlying oxygen atoms. The surface oxygen atoms, hydroxyl groups, and water molecules act as exchangeable ligands.
Acknowledgements. This study was part of a project about naturalorganicmatter (NOM) in drinking water distribution networks. Subsidy for the NOM project was provided by Senter Novem. The project is a joint research project of KWR watercycle research institute, UNESCO-IHE, Delft University of Technology, the water supply Companies Vitens and Waternet, water cycle company for Amsterdam and surrounding areas. The MIEX ® pilot plant was provided by Orica Watercare, the authors would like to acknowledge the dedicated support from Orica Watercare personnel.
time if conditions, such as physical disconnection between organicmatter and microbial communities and energy or nutrient limitation, prevail (Schmidt et al., 2012). At least one study has investigated microbial communities in the Pleistocene sediments. Lawati et al. (2012) demonstrated that the Pleistocene sediments contain a very low abundance of microbial population, which they concluded could be responsible for lower As concentrations in the groundwater. This microbial limitation may explain why the organicmatter in the groundwater seems, from our absorbance and fluorescence analyses, to be relatively fresh and unprocessed by microorganisms. However, the high FI values and low terr:microb ratios we measured in groundwater of the Pleistocene aquifer suggest that microbial constituents should be elevated rather than lacking in this setting. To gain more clarity on the presence and role of microbes in DOM processing and to better understand why the cascade of reductive dissolution is not underway in the Pleistocene aquifer, the composition of the microbial consortia and other factors that influence Fe reductive dissolution must be further explored.
Membranes are considered an alternative filtration process and consist of polymeric layers with very small pores that physically strain particles, pathogens, and so on from the influent water. Membranes are classified according to both the pore size and the amount of pressure required to force the water through the membranes. Low-pressure membranes (microfiltration and ultrafiltration) have larger pore sizes and are used for filtration, while high-pressure membranes (nanofiltration and reverse osmosis) have much smaller pore sizes and are used to modify the chemical characteristics of water being treated. Because low-pressure membranes rely on a physical removal process, i.e., straining, the size of the pores determines what contaminants can be removed from the process. Ultrafiltration membranes can remove a portion of the smaller par- ticles that could pass microfiltration membranes. These membranes can be used as a replacement for coagulation, flocculation, sedimentation, and filtration, or can be used as a polishing step behind any combination of these processes. Because microfiltration and ultrafiltration membranes do not remove dissolved constituents such as arsenic or iron in groundwater or NOM in the form of dissolved organic carbon, some form of pretreatment such as coagulation, and perhaps clarification, may be needed prior to microfiltration or ultrafiltration if removal of dissolved substances is necessary. In this situation, information contained in this manual can be helpful for optimizing the pretreatment processes.
Detailed studies on five forested headwater catchments revealed that stream discharge and soil temperature were the main drivers of NOM variability. In addition, a small headwater catchment at the Swedish West Coast was substantially influenced by sea-salt deposition, which suppressed NOM mobilization. A modified version of RIM with discharge and soil temperature as variables could successfully simulate NOM dynamics in all five catchments. Riparian soil organicmatter content and distribution was hypothesized to be the underlying control on NOM response to discharge and soil temperature. Catchments where NOM was sensitive to discharge displayed stronger gradients in soil NOM concentrations than did catchments with weak discharge sensitivity.