Reduction Of Natural Organic Matter Research Articles

Redox controls on anaerobic ammonium oxidation coupled to reduction of natural organic matter in paddy ecosystems

Redox controls on anaerobic ammonium oxidation coupled to reduction of natural organic matter in paddy ecosystems

Role of visible light photocatalysis in alleviation and mechanism transformation of ultrafiltration membrane fouling caused by natural organic matter

In this study, a novel composite based on bismuth oxide, reduced graphene oxide and titanium dioxide (labeled as BRGT) was utilized for visible light photocatalysis to mitigate ultrafiltration membrane fouling caused by natural organic matter (NOM). The results show that the coexistence of NOM and the BRGT composite (without photocatalysis) did not aggravate membrane fouling, and the membrane preferentially retained a high molecular weight, hydrophobic component of NOM that formed a dense cake layer with BRGT composite. As the photocatalysis time increased, the extent of membrane fouling was alleviated. The maximum specific flux recovered from 0.21 to 0.73 at 60 min, and the hydraulic reversible and irreversible resistances ere 1.15 × 1010 and 4.23 × 1010 m−1, respectively. The reduction of NOM in the feed water, especially the removal of UV254, played a significant role in the alleviation of membrane fouling. Additionally, the changes in the properties of NOM, including the reduction of fluorescent humic and protein/polyphenol components corresponding to reversible and irreversible fouling, respectively, the photo-degradation of high molecular weight NOM into low molecular weight NOM (such as low molecular weight-acids), and the conversion of hydrophobic fractions into hydrophilic fractions, contributed to the mitigation of membrane fouling. We also found a strong negative correlation between the roughness of the cake layer and irreversible fouling. Overall, the changes in the properties of NOM in feed water can hinder or even inhibit the formation of the cake layer, and the use of visible light photocatalysis of the BRGT composite has great potential to alleviate ultrafiltration membrane fouling caused by natural organic matter.

Impact of extended versus typical rapid mixing HRTs on continuous-flow coagulation-ultrafiltration

Although bench-scale coagulation-ultrafiltration (UF) studies are typically conducted using batch systems, continuous-flow systems allow operational parameters to be more readily evaluated and optimized over consecutive permeation cycles. When simulating coagulation-UF at bench-scale using continuous-flow systems, relevant reactor volumes require flowrates ≥1 L/min in order to achieve hydraulic retention times (HRTs) typical of full-scale rapid mixing (30 s to several minutes). In the present study, HRTs of 2 and 20 min were evaluated to determine their impact on particle properties (size, structure, and concentration) as well as UF performance (fouling resistance, reduction of natural organic matter) over a range of alum dosages. While not practical at full-scale, a 20 min HRT has been previously applied at bench-scale to reduce the overall volume of water required to conduct continuous-flow coagulation-UF studies. However, potential impacts on steady-state particle properties and subsequent UF performance not been clearly elucidated. Results from this study suggest that increasing HRT significantly increases steady-state particle size and concentration, as well as reduces total/hydraulically irreversible UF fouling resistance and improves hydraulic cleaning efficiency. Despite reduced fouling when considering a longer HRT, significant differences in particle properties and UF performance suggest that HRT values equivalent to those typically applied during full-scale rapid mixing (30 s to several minutes) must be considered in order to produce results relevant to full-scale.

Comparative study on polychlorinated biphenyl sorption to activated carbon and biochar and the influence of natural organic matter

The sorption isotherms of polychlorinated biphenyls (PCBs) on carbons (coal based activated carbon named AC and hardwood derived biochar named BC) and natural organic matter (NOM) loaded carbons were examined and carbon-water partition coefficients (KC-W-PCB) were calculated. The purpose was to accurately predict the effectiveness of in-situ carbon treatments on the sediment impacted with hydrophobic organic chemicals (HOCs). For 1 month sorption, AC KC-W-PCB values were significantly higher than BC, corresponding to the much larger surface area (particularly in mesopores) for AC. BC KC-W-PCB values were correlated with PCB total surface area (TSA) and octanol-water partition coefficient (logKow). After loading with NOM, AC adsorption to PCBs strongly reduced and the fitted Freundlich exponents (n) decreased with increasing NOM level. However, NOM loading slightly impacted BC sorption and exhibited an opposite effect on BC n values. It is illustrated that the sorption mechanisms are different between AC and BC thereby the influences of NOM on sorption characteristics differ vastly. As the sorption time increased from 1 month to 6 months, an increase is observed in BC sorption extent but simultaneously NOM reduction effect on BC sorption increases, implying that more accurately evaluating BC application as an in-situ sorbent amendment for HOC impacted sediment need further investigation. On the contrary, AC adsorption attenuation caused by NOM coating greatly decreases over time, encouraging AC application as a sediment amendment.

Effect of peroxymonosulfate oxidation activated by powdered activated carbon for mitigating ultrafiltration membrane fouling caused by different natural organic matter fractions

Powdered activated carbon (PAC) adsorption has been widely applied prior to ultrafiltration membrane for potable water production. However, the impact of PAC adsorption on membrane fouling was still controversial. To solve this problem, combined PAC and peroxymonosulfate (PMS) pretreatment was proposed in this study. The application of PAC/PMS for mitigating membrane fouling by natural organic matter (NOM) has been evaluated, and compared with PMS oxidation or PAC adsorption alone. The influence of NOM fractions on the control efficiency was also investigated using humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA), and their mixture (HA-BSA-SA). The performance was examined through normalized flux decline, fouling resistances analysis, scanning electron microscopy, and model fits. The results indicated that PAC and PMS exhibited a remarkable synergistic effect in the reduction of NOM, with the DOC reduction rates of 53.6%, 24.3%, 27.1% and 31.4% for HA, BSA, SA and HA-BSA-SA, respectively. PAC adsorption exhibited limited influence on mitigating membrane fouling, and the co-existence of PAC and HA even exacerbated fouling due to the synergistic fouling effect between them. By contrast, PAC/PMS pretreatment efficiently reduced both reversible and irreversible fouling resistances. The control efficiency was closely associated with the NOM fractions in the feed water, and followed the order of SA > HA-BSA-SA > BSA > HA. The fouling mitigation by PAC/PMS was attributed to both PAC adsorption and oxidation with SO4− and OH. The experimental results are expected to provide a feasible strategy of PAC/PMS for fouling mitigation, and simultaneously solve the problem faced by PAC adsorption.

Pilot-scale iron electrocoagulation treatment for natural organic matter removal

ABSTRACTThe efficacy of electrocoagulation at a pilot-scale as an alternative drinking water treatment technology to conventional coagulation is explored. A novel reactor was integrated into a pilot plant at the surface water supply of a small, remote community. Using iron anodes, the effect of metal loading (ML), current density and inter-electrode gap on the reduction of natural organic matter (NOM) was studied. Dissolved organics were characterized by large fractions of low molecular weight (<750 Da) hydrophilic carbon structures with lower charge density. A greater reduction in UV254 was yielded compared to dissolved organic carbon, indicating better removal of larger molecular weight fractions of NOM. As ML dosages increased from 27.8 to 60.8 mg/L, specific ultraviolet absorbance decreased from 1.92 ± 0.14 to 1.60 ± 0.10 L/m•mg respectively, from an initial raw water value of 2.21 L/m•mg. No clear trend was observed for the effect of current density and inter-electrode gap for NOM, however ML was the primary variable dictating the process’ effectiveness. Energy requirements were observed to vary greatly and were highly dependent on ML, current density and inter-electrode gap; variables that all effect the operating potential and resistance. In general, conditions that yielded the greatest reduction of NOM, a 1 mm gap and 4-cell configuration, had energy requirements between 0.480 and 0.602 kWh/m3 of water treated.

Anaerobic Ammonium Oxidation Linked to Microbial Reduction of Natural Organic Matter in Marine Sediments

Identification of microbial processes driving the loss of nitrogen from the oceans is of paramount relevance as these processes affect primary productivity in these ecosystems, which ultimately affects global biogeochemical cycles. Denitrification and anammox (anaerobic ammonium oxidation coupled to nitrite reduction) are the only identified processes so far that lead to nitrogen loss in marine environments. Here we provide stoichiometric and spectroscopic evidence, as well as tracer analysis with [15N]ammonium, revealing that anaerobic ammonium oxidation linked to the microbial reduction of natural organic matter (NOM) fuels nitrogen loss in marine sediments from the eastern tropical North Pacific coast. Tracer analysis revealed that the NOM-dependent anammox process was responsible for producing ∼1.5 μg of 15N2 (g of sediment)−1 day–1 after incubation for 27 days in sediment incubations amended with Pahokee peat, while intrinsic NOM present in the sediment promoted the production of ∼0.4 μg of 15N2 (g o...

Sustainable drinking water quality improvement by managed aquifer recharge in Tuusula region, Finland

Managed aquifer recharge (MAR) is used for drinking water quality improvement in Finland. Finnish lakes are typically humic-containing natural organic matter (NOM). A typical MAR plant includes infiltration of lake or river water into an unconfined esker aquifer and withdrawal of water from wells, a few hundred meters downstream. The infiltrated water should have a residence time of at least around 1 month before withdrawal to provide time for processes needed to break down or remove NOM. Since 1979, Tuusula Region Water Utility (TRWU) has produced drinking water from lake water using managed aquifer recharge. TRWU operates two MAR plants which do not use precipitation and disinfection chemicals. Raw water is infiltrated without any pretreatment. TRWU has experience from basin, sprinkling, and well infiltration. NOM is reduced from 7.7 to 2.1–2.6 mgTOC/l before abstraction of the water from wells. Abstracted water is post-treated by limestone filtration and disinfected by ultra-violet radiation before pumping for distribution. A specific feature of the MAR process is the delayed influence of the raw water temperature on the abstracted water temperature. Design and operational experiences of the MAR plants are presented and discussed. Special emphasis is given for NOM reduction, temperature effects, comparison of infiltration techniques, and costs.

Anaerobic Methane Oxidation Driven by Microbial Reduction of Natural Organic Matter in a Tropical Wetland.

Wetlands constitute the main natural source of methane on Earth due to their high content of natural organic matter (NOM), but key drivers, such as electron acceptors, supporting methanotrophic activities in these habitats are poorly understood. We performed anoxic incubations using freshly collected sediment, along with water samples harvested from a tropical wetland, amended with 13C-methane (0.67 atm) to test the capacity of its microbial community to perform anaerobic oxidation of methane (AOM) linked to the reduction of the humic fraction of its NOM. Collected evidence demonstrates that electron-accepting functional groups (e.g., quinones) present in NOM fueled AOM by serving as a terminal electron acceptor. Indeed, while sulfate reduction was the predominant process, accounting for up to 42.5% of the AOM activities, the microbial reduction of NOM concomitantly occurred. Furthermore, enrichment of wetland sediment with external NOM provided a complementary electron-accepting capacity, of which reduction accounted for ∼100 nmol 13CH4 oxidized · cm-3 · day-1 Spectroscopic evidence showed that quinone moieties were heterogeneously distributed in the wetland sediment, and their reduction occurred during the course of AOM. Moreover, an enrichment derived from wetland sediments performing AOM linked to NOM reduction stoichiometrically oxidized methane coupled to the reduction of the humic analogue anthraquinone-2,6-disulfonate. Microbial populations potentially involved in AOM coupled to microbial reduction of NOM were dominated by divergent biota from putative AOM-associated archaea. We estimate that this microbial process potentially contributes to the suppression of up to 114 teragrams (Tg) of CH4 · year-1 in coastal wetlands and more than 1,300 Tg · year-1, considering the global wetland area.IMPORTANCE The identification of key processes governing methane emissions from natural systems is of major importance considering the global warming effects triggered by this greenhouse gas. Anaerobic oxidation of methane (AOM) coupled to the microbial reduction of distinct electron acceptors plays a pivotal role in mitigating methane emissions from ecosystems. Given their high organic content, wetlands constitute the largest natural source of atmospheric methane. Nevertheless, processes controlling methane emissions in these environments are poorly understood. Here, we provide tracer analysis with 13CH4 and spectroscopic evidence revealing that AOM linked to the microbial reduction of redox functional groups in natural organic matter (NOM) prevails in a tropical wetland. We suggest that microbial reduction of NOM may largely contribute to the suppression of methane emissions from tropical wetlands. This is a novel avenue within the carbon cycle in which slowly decaying NOM (e.g., humic fraction) in organotrophic environments fuels AOM by serving as a terminal electron acceptor.

Integrity breaches in a hollow fiber nanofilter – Effects on natural organic matter and virus-like particle removal

Ultrafiltration and nanofiltration have become common methods to treat surface water for drinking water purposes. Common aims of a membrane step are removal of natural organic matter (NOM), softening or adding an extra microbiological or chemical barrier. In most cases, the membrane is considered a good disinfection step; commonly the viral removal is at least 4–log. To ensure a working disinfection, reliable integrity tests are required. In the present pilot study with a hollow fiber nanofilter, the membrane achieved a high NOM reduction, and the difference in parameters related to NOM quality before and after treatment proved to be useful indicators of integrity breaches. Changes in total organic carbon (TOC) concentration, UV-absorbance at 254 nm (UVA254) and fluorescence derived parameters in the permeate flow were related to leaking fibers. On average, UVA254 in the permeate was 3 times higher for a membrane with compromised fibers (0.041 cm−1) compared to an intact membrane (0.013 cm−1), while TOC was less than 2 times as high on average. Thus, this membrane had a higher reduction of UVA254 than TOC and the sensitivity for changes from leakage was higher. Therefore, it is suggested that UVA254 could be used as an indicator for membrane integrity. Additionally, there is a significant (P < 0.01) difference in fluorescence derived parameters between a leaking and an intact fiber, showing that fluorescence also has potential to be applied for online monitoring of membrane processes. During fiber failure, around 2% of the permeate flow passes through one single leaking fiber. The transport depends on the distance between the inflow and the leak, which in most cases are similar and most likely close to the middle of the fiber.

Fluorescence spectroscopy for monitoring reduction of natural organic matter and halogenated furanone precursors by biofiltration

The application of fluorescence spectroscopy to monitor natural organic matter (NOM) reduction as a function of biofiltration performance was investigated. This study was conducted at pilot-scale where a conventional media filter was compared to six biofilters employing varying enhancement strategies. Overall reductions of NOM were identified by measuring dissolved organic carbon (DOC), and UV absorbance at 254 nm, as well as characterization of organic sub-fractions by liquid chromatography–organic carbon detection (LC-OCD) and parallel factors analysis (PARAFAC) of fluorescence excitation-emission matrices (FEEM). The biofilter using granular activated carbon media, with exhausted absorptive capacity, was found to provide the highest removal of all identified PARAFAC components. A microbial or processed humic-like component was found to be most amenable to biodegradation by biofilters and removal by conventional treatment. One refractory humic-like component, detectable only by FEEM-PARAFAC, was not well removed by biofiltration or conventional treatment. All biofilters removed protein-like material to a high degree relative to conventional treatment. The formation potential of two halogenated furanones, 3-chloro-4(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA), as well as overall treated water genotoxicity are also reported. Using the organic characterization results possible halogenated furanone and genotoxicity precursors are identified. Comparison of FEEM-PARAFAC and LC-OCD results revealed polysaccharides as potential MX/MCA precursors.

Reduction of natural organic matter by an electrolytic process, conventional coagulation and direct descending filtration in a pilot-scale water treatment system

Research Article| September 24 2014 Reduction of natural organic matter by an electrolytic process, conventional coagulation and direct descending filtration in a pilot-scale water treatment system Victor Cochrane Santiago Sampaio; Victor Cochrane Santiago Sampaio 1Departamento de Engenharia Hidráulica e Ambiental, Universidade Federal do Ceará, Bloco 713, Avenida Humberto Monte S/N, Campus do Pici, Fortaleza-CE, CEP 60451-970, Brasil E-mail: cochrane@ibest.com.br Search for other works by this author on: This Site PubMed Google Scholar Eliezer Fares Abdala Neto; Eliezer Fares Abdala Neto 1Departamento de Engenharia Hidráulica e Ambiental, Universidade Federal do Ceará, Bloco 713, Avenida Humberto Monte S/N, Campus do Pici, Fortaleza-CE, CEP 60451-970, Brasil Search for other works by this author on: This Site PubMed Google Scholar Ari Clecius Alves de Lima; Ari Clecius Alves de Lima 1Departamento de Engenharia Hidráulica e Ambiental, Universidade Federal do Ceará, Bloco 713, Avenida Humberto Monte S/N, Campus do Pici, Fortaleza-CE, CEP 60451-970, Brasil Search for other works by this author on: This Site PubMed Google Scholar Isabel Cristina Lima Freitas; Isabel Cristina Lima Freitas 2Gerência de Desenvolvimento Operacional, Pesquisa e Inovação, Estação de Tratamento de Água – Gavião, Companhia de Água e Esgoto do Ceará, Fortaleza-CE, Brasil Search for other works by this author on: This Site PubMed Google Scholar Marisete Dantas de Aquino Marisete Dantas de Aquino 2Gerência de Desenvolvimento Operacional, Pesquisa e Inovação, Estação de Tratamento de Água – Gavião, Companhia de Água e Esgoto do Ceará, Fortaleza-CE, Brasil Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2015) 64 (2): 168–175. https://doi.org/10.2166/aqua.2014.049 Article history Received: April 09 2014 Accepted: August 16 2014 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Victor Cochrane Santiago Sampaio, Eliezer Fares Abdala Neto, Ari Clecius Alves de Lima, Isabel Cristina Lima Freitas, Marisete Dantas de Aquino; Reduction of natural organic matter by an electrolytic process, conventional coagulation and direct descending filtration in a pilot-scale water treatment system. Journal of Water Supply: Research and Technology-Aqua 1 March 2015; 64 (2): 168–175. doi: https://doi.org/10.2166/aqua.2014.049 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Recently, alternative water treatment systems have been implemented due to the eutrophication of reservoirs, in which high concentrations of organic matter prevent the use of conventional water treatment methods. This paper presents a study on the electrolytic process for water treatment using an alternating current. A reactor with iron and stainless steel electrodes was built and introduced into a water treatment system equipped with conventional coagulation with alum and direct descending filtration. Factors such as pH levels, turbidity, colour, and reductions in the specific UV absorbance were evaluated. The results showed a significant reduction in the specific UV absorbance between raw water and treated water (19.51–26.45%). Furthermore, the reactor did not significantly change the pH of the water. The average turbidity of the treated water was less than or equal to 0.5 NTU, and the average colour reached 2 HU, classifying the treated water as drinking water according to the current ordinance in Brazil. The cost of the electricity used by the reactor was $0.10 per cubic metre of water produced. electrolytic process, natural organic matter, water treatment © IWA Publishing 2015 You do not currently have access to this content.

In-line coagulation to reduce high-pressure membrane fouling in an integrated membrane system: a case study

Membrane fouling is a critical problem for many nanofiltration (NF) membrane plants. This study demonstrated that the poor spaces of the NF membrane were decreased for the deposition of natural organic matter (NOM) on the membrane surface. In-line coagulation was added prior to the low-pressure filtration step to remove more organic material by microfiltration (MF), thereby improving the quality of the feed-water entering the NF membranes. Three different types of coagulants, i.e. aluminum sulfate, ferric chloride, and polyaluminum chloride, with their different levels at different pH values were used for this study. The optimal dose of each coagulant was determined, and the impact on the NF membrane was assessed by batching and running 20 L of post-coagulation MF permeate through a bench-scale NF membrane for 200 h. Ferric chloride was found to perform the best of these three tested coagulants to reduce NF pressure fouling by reduction of NOM in the NF feed-water. High performance size exclusion chromatography study revealed that higher molecular weight fractions of NOM removed preferentially due to in-line coagulation processes. The scanning electron microscopy analysis of the fouled NF membrane trial revealed that the foulant layer consisted of a very large quantity of inorganic and organic matter, bacteria, which resulted in a very rough surface topography.

Evaluating UV/H2O2, UV/percarbonate, and UV/perborate for natural organic matter reduction from alternative water sources

Natural organic matter (NOM) continues to increase in drinking water sources due to many factors, including changes in land use and global climate. Water treatment facilities will need to evaluate the best treatment options to account for these higher NOM levels. The UV/H2O2 advanced oxidation process (AOP) is one treatment option that has shown success at reducing high levels of NOM. As a result, this study evaluated the UV/H2O2 for the reduction of NOM in a high NOM water matrix, the Florida Everglades. In addition to liquid H2O2, sodium percarbonate and sodium perborate were used as oxidants to evaluate their performance as alternatives to liquid H2O2. Results showed that all three oxidants were able to reduce aromatic carbon (UV254) by 46–66% and dissolved organic carbon (DOC) by 11–19% at UV fluences of 2.6–2.7Jcm−2 and an H2O2 dose of 100mgL−1. When the UV fluences were increased to 21.8–26.1Jcm−2 at an H2O2 dose of 100mgL−1, UV254 reduction increased to 79–97% and DOC to 42–82% for all three oxidants. All three oxidants performed statistically similar for UV254 reduction. However, for DOC reduction, H2O2 performed statically better than both percarbonate and perborate, and perborate performed statistically better than percarbonate. While the UV/H2O2 AOP is effective for NOM reduction in high NOM waters, advances in electrical efficiency are needed to make it economically feasible.

Effects of ozonation and temperature on the biodegradation of natural organic matter in biological granular activated carbon filters

Abstract. Four pilot (biological) granular activated carbon ((B)GAC) filters were operated to quantify the effects of ozonation and water temperature on the biodegradation of natural organic matter (NOM) in (B)GAC filters. The removal of dissolved organic carbon (DOC), assimilable organic carbon (AOC) and oxygen and the production of carbon dioxide were taken as indicators for NOM biodegradation. Ozonation stimulated DOC and AOC removal in the BGAC filters, but had no significant effect on oxygen consumption or carbon dioxide production. The temperature had no significant effect on DOC and AOC removal, while it had a positive effect on oxygen consumption and carbon dioxide production. Multivariate linear regression was used to quantify these relationships. In summer, the ratio between oxygen consumption and DOC removal was approximately 2 times the theoretical maximum of 2.6 g O2 g C−1 and the ratio between carbon dioxide production and DOC removal was approximately 1.5 times the theoretical maximum of 3.7 g CO2 g C−1. The production and loss of biomass, the degassing of (B)GAC filters, the decrease in the NOM reduction degree and the temperature effects on NOM adsorption could only partly explain these excesses and the non-correlation between DOC and AOC removal and oxygen consumption and carbon dioxide production. It was demonstrated that bioregeneration of NOM could explain the excesses and the non-correlation. Therefore, it was likely that bioregeneration of NOM did occur in the (B)GAC pilot filters.

Reduction of natural organic matter by nanofiltration process

The objectives of this investigation were to characterize natural organic matter (NOM) in Kin-men raw water, to evaluate the performance of the nanofiltration (NF) membrane process for NOM removal, and to determine the good engineering practice (GEP) of the NF 270 membrane filtration performance. Three different samples: (1) raw water collected from the Tai Lake in Kin-men, Taiwan; (2) ultrafiltration (UF) pre-treated water; and (3) sand filtration (SF) treated water after the coagulation and sedimentation processes were employed in this study. The hydrophobic component (58%) was the predominant NOM fraction, and the NOM molecular weight was distributed broadly, i.e., lower than 1 kDa (30%), 1–5 kDa (32%) and larger than 5 kDa (38%). Hydrophobic NOM easily accumulated on the NF membrane surface and resulted in flux decline. The SF–NF was the proposed treatment process because it can reduce the NOMs effectively with lower energy consumption than UF–NF. It was noted that the dissolved organic carbon (DOC) rejection ratio was not affected by changing cross-flow velocity. However, at lower cross-flow velocity (0.15 m s −1), the reduction of organic matter in water sample was higher than that at higher cross-flow velocity (0.30 m s −1). By integrating the experimental results, it was concluded that a transmembrane pressure of 690 kPa and a cross-flow velocity of 0.30 m s −1 exhibited the GEP, yielding about 94% of both DOC and UV 254 reduction.

Use of GAC after enhanced coagulation for the removal of natural organic matter from water for purification

Filtration with granular activated carbon (GAC) after an enhanced coagulation (EC) process was evaluated in order to determine the effectiveness of GAC in the reduction of natural organic matter (NOM), which should result in much lower formation of trihalomethane in the disinfection step. The results show that a combination of EC and GAC considerably reduces the organic matter content, which is mainly fulvic acid. This type of organic matter is removed with high coagulant dosages which neutralize their high anionic charge. A further reduction of NOM is achieved due the adsorption of NOM by GAC. As a result, the average trihalomethane (THM) concentration was only 14.5±5 μg L−1. Enhanced coagulation alone decreased the NOM concentration by 50%, but the remaining NOM reacted in the chlorination step and a higher average THM concentration was found (38±23 μg L−1). An average THM concentration of 73.8±41.2 μg L−1 was found at the drinking water plant of Boaco when conventional treatment was used. This THM concentration sometimes exceeds the maximum contaminant level of 80 μg L−1 established by the United States Environmental Protection Agency (USEPA), but not the Nicaraguan threshold of 460 μg L−1.

Optimizing treatment for reduction of disinfection by-product (DBP) formation

Recent studies in communities in greater Cairo, Egypt have identified trihalomethanes (THMs) and haloacetic acids (HAAs) at levels that exceed regulatory limits depending upon the season. The objective of this study was to better understand the formation of DBPs in Nile River source water with a view toward optimizing conventional treatment, focusing on enhanced coagulation, to achieve reduction in DBP formation potential (FP) in a cost-effective scheme. To this end, characterisation of natural organic matter (NOM) in Nile raw water and after treatment by fractionating according to hydrophobic-hydrophilic properties was included in the analysis. Seasonal variations in raw water quality were found to be important for achieving optimum reduction of turbidity and DBP formation. In summer, alkalinity is lower; therefore, enhanced coagulation with 30 mg/L alum can be done at pH 6 without excessive additions of acid, and satisfactory reductions in turbidity and DBPs attained. During the remainder of the year, high alkalinity results in enhanced coagulation at about pH 6.5 and notably lower reduction of NOM, THMFP, and HAAs versus summer conditions. Supplementing enhanced coagulation with 10 mg/L PAC is highly recommended for these conditions as it improves removal of all DBP indicators. The transphilic fraction was the main contributor to DBP formation and the primary fraction removed by enhanced coagulation for achieving gains in THMFP reduction.

Optimizing alum coagulation for turbidity, organics, and residual Al reductions

Increases in residual dissolved Al from alum coagulation associated with low water temperatures should be minimised to avoid problems in the distribution mains and as a precautionary approach to possible health effects of Al. Temperature-controlled jar-tests (0.1 to 17.0°C) were used to evaluate optimisation of a plant using alum coagulation at pH 6.0 followed by activated silicate addition. pH adjustment was assessed during coagulation and flocculation (i.e. before and after activated silicate) in order to control residual Al by precipitation without affecting turbidity and natural organic matter (NOM) reductions. The effects on NOM reduction were marginal until pH 6.4 in all conditions tested. Turbidity reductions by sedimentation considerably worsened when increasing pH, especially at the lowest temperature. Experimental conditions to eliminate this negative effect were found to be by increasing the pH after silicate addition (from the coagulation pH of 6.0 to between 6.1 and 6.3). By pH adjustments after silicate addition, up to 90% decrease in dissolved Al could be obtained at pH ∼6.8 (from 180 to ∼20 μg/L) at low temperatures. At this pH level, however, turbidity reduction reached minimal values (10–20%) while NOM reduction was clearly affected, indicating partial NOM re-dissolution. Slight pH adjustments of coagulation pH (up to 6.1) or flocculation pH (up to 6.3—after silicate addition) promised significant dissolved Al minimization (down to ∼50 μg/L) without compromising turbidity or NOM reductions.

GPE 2007 - Utilization of the Coagulation Diagram in the Evaluation of the Natural Organic Matter (NOM) Removal for Obtaining Potable Water

The natural organic matter (NOM) is a mixture of many organic compounds that can be dispersed in superficial water. The NOM is due to the compounds formed in the biologic degradation process of the vegetable organic matter and its interaction with the clay and the other hydrographic basin soil constituents, besides algae and other microorganism activity. Many researchers have obtained results that indicate that the coagulation/flocculation process is an effective process in the NOM reduction without committing the non-stabilization colloidal particles. So, with the intuit to guarantee a better final water quality in the water treatment plants, different studies were evaluated based on the coagulation diagram for obtaining the best concentration of the chitosan coagulant as function of the pH for the NOM removal for obtaining potable water. The data for the coagulation diagram construction will be obtained by a series of tests in a jar-test apparatus. Different concentrations of the coagulant solution (0.1% w/v of chitosan) will be studied. The pH will be varied (4.0 – 8.5) with sodium hydroxide solution (NaOH) and hydrochloric acid (HCl) 25 and 50%. The rapid mixture gradient, the coagulation time, the slow mixture gradient and the flocculation time will be maintained constant during this experiment. The process efficiency will be evaluated by the color, turbidity and compounds with absorption in UV-254nm removal. The best results of removal were found for the chitosan in the concentration of 1.0mg/L and pH between 4.0-5.0, approximately.