Dissolved Organic Carbon Removal Rates Research Articles

Intensive coagulation of secondary effluent to mitigate reverse osmosis membrane fouling at low temperatures: Strategies of pre-oxidation and coagulant aids addition

Conventional coagulation-sedimentation, typically used as a pretreatment for ultrafiltration-reverse osmosis, is ineffective in solving the problem of reverse osmosis membrane fouling at low temperatures. In this study, the coagulation enhancement effect of pre-oxidation and the addition of coagulant aids on conventional coagulation with polyaluminum chloride as a coagulant was investigated. The results showed that the addition of fly ash, powdered activated carbon, or diatomite as coagulant aids improved the reduction of turbidity, dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254), and also reduced the residual content of dissolved aluminum ions. Among them, diatomite was superior. Pre-oxidation before conventional coagulation increased the reduction of turbidity and UV254 by about 50 % and doubled the removal of proteins, polysaccharides, and DOC compared to conventional coagulation. Ozone was superior to sodium hypochlorite. The combination of ozone pre-oxidation and diatomite addition with conventional coagulation further increased the pollutant removal rate, with the removal rates of turbidity, UV254, polysaccharides, proteins, and DOC reaching 82.20 %, 52.35 %, 26.34 %, 24.89 %, and 26.38 %, respectively. In addition, the residual content of dissolved aluminum ions decreased to 0.84 mg/L. The reverse osmosis filtration simulation test showed that pretreating the feed water with the enhanced coagulation by the combination of ozone pre-oxidation and diatomite addition resulted in a slower decrease in membrane flux, reduced foulant content on the membrane surface, and the smallest increase in contact angle. The results of this research may offer a viable pretreatment method to reduce fouling in reverse osmosis membranes operating at low temperatures.

Au-TiO2 nanoparticles enabled catalytic treatment of oil and gas produced water in slurry and vacuum membrane distillation systems

Produced water (PW) treatment and reuse provide a promising alternative to address freshwater scarcity and reduce the environmental impacts associated with PW disposal. Efficient treatment of PW is challenging due to its complex matrix and hypersalinity. This study developed innovative gold-doped titania (Au-TiO2) nanoparticles to enable effective treatment of PW collected from the Permian Basin with salinity of ∼118 g/L. The mechanisms of removing organics and ammonia in PW in slurry and vacuum membrane distillation (VMD) systems were investigated via thermocatalysis, photocatalysis, and photo-thermocatalysis. Photocatalysis and photo-thermocatalysis were found more effective for organic removal than thermocatalysis. A baseline study using glucose as a representative of easily degradable organic carbon showed that thermocatalysis and photocatalysis mineralized 23.2 % and 93.1 % glucose, respectively. However, photo-thermocatalysis and thermocatalysis degraded only 17.4 % and 7.5 % dissolved organic carbon (DOC), and 56.2 % and 49.2 % NH3-N in PW, respectively. Au-TiO2 coating on ceramic membranes improved the distillate flux of photo-thermocatalytic membrane distillation (PMD) compared to no catalysts coating in VMD (7.14 versus 6.75 kg per hour per m2). Both PMD and VMD rejected >99.9 % of salts and >96 % DOC, and PMD had slightly higher DOC and salt removal rates. In contrast, normalized permeate flux using pristine membranes (hydrophobically modified without catalysts coating) decreased to zero after 29 h of operation while normalized flux with TiO2-coated membranes under UV on and UV off were 57.5 % and 53.7 % on average, which is much lower than that with Au-TiO2 coated membranes in both UV on (91.3 %) and UV off (88.1 %) cases, indicating Au-TiO2 coating significantly improved membrane anti-fouling propensity and durability during treatment of complex PW. Targeted analysis of three groups of petroleum hydrocarbons and 70 volatile organic compounds showed that only 2-butanone and acetone were detected in the distillates with removal efficiencies of 80 % for 2-butanone in both PMD and VMD, and acetone was removed by 75.4 % in PMD and 69.2 % in VMD. Au-TiO2 nanoparticles demonstrated excellent catalytic performance for PW treatment in slurry and immobilized PMD systems.

Mechanisms Underpinning the Net Removal Rates of Dissolved Organic Carbon in the Global Ocean

AbstractWith almost 700 Pg of carbon, marine dissolved organic carbon (DOC) stores more carbon than all living biomass on Earth combined. However, the controls behind the persistence and the spatial patterns of DOC concentrations on the basin scale remain largely unknown, precluding quantitative assessments of the fate of this large carbon pool in a changing climate. Net removal rates of DOC along the overturning circulation suggest lifetimes of millennia. These net removal rates are in stark contrast to the turnover times of days to weeks of heterotrophic microorganisms, which are the main consumers of organic carbon in the ocean. Here, we present a dynamic “MICrobial DOC” model (MICDOC) with an explicit representation of picoheterotrophs to test whether ecological mechanisms may lead to observed decadal to millennial net removal rates. MICDOC is in line with >40,000 DOC observations. Contrary to other global models, the reactivity of DOC fractions is not prescribed, but emerges from a dynamic feedback between microbes and DOC governed by carbon and macronutrient availability. A colimitation of macronutrients and organic carbon on microbial DOC uptake explains >70% of the global variation of DOC concentrations, and governs characteristic features of its distribution. Here, decadal to millennial net removal rates emerge from microbial processes acting on time scales of days to weeks, suggesting that the temporal variability of the marine DOC inventory may be larger than previously thought. With MICDOC, we provide a foundation for assessing global effects on DOC related to changes in heterotrophic microbial communities in a future ocean.

Efficient electrochemical oxidation of refractory organics in actual petrochemical reverse osmosis concentrates by Ti/SnO2-Sb mesh anode

The efficient treatment of refractory organics in reverse osmosis concentrate (ROC) is a critical issue for achieving emission reduction or even zero emission in the petrochemical industry. A simple and efficient electrocatalytic process was proposed for treating actual petrochemical ROC using a highly active self-assembling Ti/SnO2-Sb anode. The Ti/SnO2-Sb anode was prepared by using citric acid (CA) and ethylene glycol (EG) as precursors, with a mole ratio of Sn:Sb of 5:1 and a metal salts to CA to EG mole ratio of 1:3:16. The resulting electrode surface had a complete mesh pit structure after calcination at 550 ºC. Several key factors were found to affect the degradation of dissolved organic carbon (DOC), including current density, chloride ion concentration, Fe (II) concentration, and acidity. The presence of chloride ions on the anode surface significantly improved the conversion efficiency of hydroxyl radicals, which played a crucial role in the oxidation of the organics. Additionally, near the cathode, oxidative radicals such as H2O2 and O2-∙ were generated, while hydroxyl radicals were produced with the addition of Fe (II) and H+. Under a current density of 20 mA·cm−2, the Ti/SnO2-Sb anode achieved a COD removal rate of 94.5% and a DOC removal rate of 43.4%.

The removal of dissolved organic matter by marine sponges is a function of its composition and concentration: An in situ seasonal study of four Mediterranean species

Sponges are unique among metazoans in their ability to use dissolved organic matter (DOM), the largest pool of organic matter in the ocean, as a major food source. The effect of variations in DOM abundance and composition on its uptake by sponges has rarely been studied. We examined, in situ, the seasonal uptake of DOM by four sponges [2 species with high microbial abundance (HMA) and 2 with low microbial abundance (LMA)] in the northwestern Mediterranean. Dissolved organic carbon (DOC) showed a strong seasonality with 3-fold higher concentrations in fall-winter (256 ± 16 μmol L−1, mean ± SE) than in spring-summer (88 ± 3 μmol L−1). Dissolved organic nitrogen (DON) showed the opposite trend, with higher summer concentrations (8.9 ± 0.4 μmol L−1) and mean concentrations of 2.5–3.4 μmol L−1 in the other seasons. DOC removal by all sponge species increased linearly with its ambient concentration, but only above a DOC removal threshold that was threefold higher in fall-winter (198 μmol L−1) than in spring-summer (74 μmol L−1). All species showed a concentration-dependent DON removal, but LMA sponges removed more DON than HMA sponges. The DOC removal rate (normalized to sponge volume) was 2–3 times higher in fall-winter, when ambient DOC levels were high, than in spring-summer. Sponges efficiently removed clusters of the fluorescent DOM (FDOM) associated with protein-rich DOM, but not those associated with humic material. The clear threshold for DOC removal and the protein-like FDOM uptake pattern suggest that the quality and quantity of DOM control its removal and transformation by marine sponges. Our results indicate that marine sponges transform the composition of the coastal DOM pool, thereby affecting its fate. It is postulated that the DOM excreted by the sponges is more recalcitrant; consequently, sponge activity enhances carbon sequestration in benthic habitats in a similar fashion to that of the oceanic ‘microbial pump’.

Degradation of Agro-Industrial Wastewater Model Compound by UV-A-Fenton Process: Batch vs. Continuous Mode.

The degradation of a model agro-industrial wastewater phenolic compound (caffeic acid, CA) by a UV-A-Fenton system was investigated in this work. Experiments were carried out in order to compare batch and continuous mode. Initially, batch experiments showed that UV-A-Fenton at pH 3.0 (pH of CA solution) achieved a higher generation of HO•, leading to high CA degradation (>99.5%). The influence of different operational conditions, such as H2O2 and Fe2+ concentrations, were evaluated. The results fit a pseudo first-order (PFO) kinetic model, and a high kinetic rate of CA removal was observed, with a [CA] = 5.5 × 10-4 mol/L, [H2O2] = 2.2 × 10-3 mol/L and [Fe2+] = 1.1 × 10-4 mol/L (kCA = 0.694 min-1), with an electric energy per order (EEO) of 7.23 kWh m-3 order-1. Under the same operational conditions, experiments in continuous mode were performed under different flow rates. The results showed that CA achieved a steady state with higher space-times (θ = 0.04) in comparison to dissolved organic carbon (DOC) removal (θ = 0-0.020). The results showed that by increasing the flow rate (F) from 1 to 4 mL min-1, the CA and DOC removal rate increased significantly (kCA = 0.468 min-1; kDOC = 0.00896 min-1). It is concluded that continuous modes are advantageous systems that can be adapted to wastewater treatment plants for the treatment of real agro-industrial wastewaters.

Potassium ferrate enhances ozone treatment of pharmaceutical wastewaters: Oxidation and catalysis

This work verified the ability of potassium ferrate to catalyse ozone-driven oxidation of refractory organic matter in a secondary effluent of a wastewater treatment plant at a local pharmaceutical factory. The effect of potassium ferrate reduction products on ozone decomposition was investigated by evaluating the variation in ozone concentration in water. The mechanisms were revealed by separating residual potassium ferrate reduction products from solutions and analysing the dissolved organic carbon (DOC), ultraviolet absorption (UV254), and fluorescent organics. The results showed that (1) the decomposition rate of aqueous ozone was higher with the potassium ferrate reduction products than without them, implying the catalytic ability on ozone decomposition. (2) The reduction products of potassium ferrate during ozone treatment resulted in an increase of 14.9 % in the DOC removal rate and 29.03 % in the UV254 removal rate compared with the results of treatment with potassium ferrate alone. These results show that the reduction products of potassium ferrate can promote ozone oxidation of refractory organic compounds in secondary effluents, and a multistage oxidation system in which potassium ferrate combined with ozone is technically feasible. To the best of our knowledge, this is the first study to verify that the synergistic effect of ferrate (VI)–ozone is due to the catalytic effect of reduction products on ozone oxidation.

Leachate degradation using solar photo-fenton like process: Influence of coagulation-flocculation as a pre-treatment step

The effectiveness of using solar photo-Fenton-like processes to degrade sanitary landfill leachates was investigated. Leachate samples exhibited varying composition, owing to a mixture of older and younger effluents from a former dump site subsequently converted into a sanitary landfill. Coagulation assays (jar test) using Al3+, Fe2+, and Fe3+ in the 240–800 mg L–1 range were performed to evaluate optimal coagulant concentration for abatement of chemical oxygen demand (COD) and dissolved organic carbon (DOC). A high COD (53%) and DOC (72%) removal rates were obtained for Al3+ but there was a very substantial increase in the turbidity. Optimal coagulant concentration was then adopted, and the effluents were subjected to photo-Fenton processes at laboratory scale. At this scale, coagulation by Fe3+ at 240 mg L–1 combined with a photo-Fenton-like method exhibited superior performance, with 66% DOC removal by coagulation and over 70% DOC removal using the photo-Fenton-like process. Solar photodegradation was conducted for 180 min at [Fe3+] ≈ 100 mg L–1, pH = 3.0 ± 0.3, and [H2O2] = 50–250 mg L–1 at a solar pilot plant. Use of solar photo-Fenton-like processes improved effluent biodegradability, irrespective of coagulation pretreatment, and also reduced leachate toxicity, as shown by acute ecotoxicity tests using Lactuca sativa seeds, Allium cepa bulbs, and Artemia salina, proving to be a promising treatment method in line with the National Solid Waste Policy, which promotes and encourages non-generation, reduction, reuse, recycling, the treatment of solid waste, and the environmentally appropriate final disposal of tailings.

Purification of hydrazine hydrate waste salt using a water washing based integrated process for the production of sodium hydrate via ion-exchange membrane electrolysis

One of the effective reuse application for waste salt, sodium chloride (NaCl), from a near-zero discharge process is the production of sodium hydrate (NaOH) by ion-exchange membrane electrolysis. However, the organic contaminants must be effectively removed from the waste salt before reuse to prevent the rise of cell voltage. In this study, a low-cost near-zero discharge integrated process was proposed for purifying and reusing waste NaCl from the hydrazine hydrate (N2H4) manufacturing process. In the integrated process, water washing followed by activated carbon adsorption was applied to purify the waste salt to meet the requirements for NaOH production using ion-exchange membrane electrolysis. Washing the salt at a water/salt ratio of 5:8, 88.5% of dissolved organic carbon (DOC) was removed, with 25% loss of salt in water washing. Saturated salt solution prepared from the salt after water washing was treated with activated carbon at a dose of 500 mg/L to further remove 10% DOC. Then the salt in the washing wastewater was obtained through evaporation and crystallization and further purified using pyrolysis, with a DOC removal over 99.17% at a temperature >500 °C. Evaluation using an ion-exchange membrane electrolysis system running for 42 h showed, that the voltage in treating purified salt by water washing and activated carbon adsorption was almost the same as that for pure salt, suggesting that the substances causing the rise of cell voltage were mostly removed. Meanwhile, though direct pyrolysis exhibited a DOC removal rate as high as 99.29% at a temperature >500 °C, the treatment cost is estimated to be 500 RMB/t, while the integrated process treatment cost is estimated to be 224.38 RMB/t. This study proposes a feasible way to reuse the waste salt from N2H4 manufacturing process.

DOM Biological Lability in an Estuarine System in Two Contrasting Periods

Estuarine processes play a key role in determining the amount and quality of land-derived dissolved organic matter (DOM) reaching the oceans. Microbial-mediated reactions can affect the concentration, quality, and bioavailability of DOM within an estuary. In this study, we investigated biological DOM removal in a small estuary and its variability in two contrasting seasons (spring and autumn) characterized by natural differences in the concentration and quality of the riverine DOM. Two incubation experiments were carried out using natural DOM and heterotrophic prokaryotes community collected at the estuary in March and September. Dissolved organic carbon (DOC) concentration, DOM fluorescence, and the heterotrophic prokaryotes abundance (HPA) showed marked differences between the two seasons. These parameters were followed through time for up to two months. Despite the marked differences in the initial conditions, the DOC removal rates were surprisingly similar in the two periods (16 µM DOC month−1 in March and 18 µM DOC month−1 in September), with the biggest removal in the first 48 h. The trend of fluorescent DOM (FDOM) during the incubation showed marked differences between the two periods. In March, the net removal of all the FDOM components was observed consistently with the decrease in DOC; whereas, in September, the net production of humic-like substances was observed.

UV-C-activated persulfate oxidation of a commercially important fungicide: case study with iprodione in pure water and simulated tertiary treated urban wastewater.

Recently, the European Food Safety Authority (EFSA) has banned the use of iprodione (IPR), a common hydantoin fungicide and nematicide that was frequently used for the protective treatment of crops and vegetables. In the present study, the treatment of 2mg/L (6.06μM) aqueous IPR solution through ultraviolet-C (UV-C)-activated persulfate (PS) advanced oxidation process (UV-C/PS) was investigated. Baseline experiments conducted in distilled water (DW) indicated that complete IPR removal was achieved in 20min with UV-C/PS treatment at an initial PS concentration of 0.03mM at pH = 6.2. IPR degradation was accompanied with rapid dechlorination (followed as Cl- release) and PS consumption. UV-C/PS treatment was also effective in IPR mineralization; 78% dissolved organic carbon (DOC) was removed after 120-min UV-C/PS treatment (PS = 0.30mM) compared with UV-C at 0.5W/L photolysis where no DOC removal occurred. LC analysis confirmed the formation of dichloroaniline, hydroquinone, and acetic and formic acids as the major aromatic and aliphatic degradation products of IPR during UV-C/PS treatment whereas only dichloroaniline was observed for UV-C photolysis under the same reaction conditions. IPR was also subjected to UV-C/PS treatment in simulated tertiary treated urban wastewater (SWW) to examine its oxidation performance and ecotoxicological behavior in a more complex aquatic environment. In SWW, IPR and DOC removal rates were inhibited and PS consumption rates decreased. The originally low acute toxicity (9% relative inhibition towards the photobacterium Vibrio fischeri) decreased to practically non-detectable levels (4%) during UV-C/PS treatment of IPR in SWW.

Antibiotic resistance genes removal and membrane fouling in secondary effluents by combined processes of PAC/BPAC-UF.

Antibiotic resistance genes (ARGs), as emerging environmental contaminants, are becoming a threat to human health. In this study, the combined processes of powdered activated carbon (PAC)/biological PAC (BPAC)-ultrafiltration (UF) were adopted to reduce the levels of ARGs in secondary effluents from a wastewater treatment plant. The removal of dissolved organic carbon (DOC) and the change of normalized flux in the UF process were investigated. In addition, the structural characteristics of the microorganisms of the BPAC were analyzed. The results showed that the appropriate dosage of PAC and BPAC was 40 mg/L. At this dosage, PAC/BPAC-UF combined processes could effectively remove the ARGs in secondary effluents by 1.26-2.69-log and 1.55-2.97-log, respectively; and the removal rates of DOC would be 60.7% and 54.1%, respectively. Relative to the direct UF, the membrane fluxes of the two combined processes were increased by 15.6% and 25.1%, respectively. Significant removal correlations were found between ARGs, intI1, DOC and 16SrDNA. These results revealed that the PAC/BPAC-UF combined process might play a promising role in ARG reduction in secondary effluents from wastewater treatment plants.

Assessing the Self-Purification Capacity of Surface Waters in Lake Baikal Watershed

The removal of trace metals (TM), dissolved organic carbon (DOC), mineral nitrogen (Nmin.), and polycyclic aromatic hydrocarbons (PAHs) from the water of Lake Baikal and its tributaries was evaluated. The contaminant removal rate (CRR) and the contaminant removal capacity (CRC) were used as water self-purification parameters. The CRR was calculated as the difference between contaminant mass flow rates at downstream and upstream gauging stations. The CRC was calculated as the quotient of the CRR and the change in water discharge between downstream and upstream gauging stations. Whether the CRR and CRC have positive or negative values depends on whether contaminant release or removal occurs in the water body. The CRR depends on the size of the water body. The lowest and the highest CRRs observed for Baikal were equal to −15 mg/s (PAHs) to −7327 g/s (DOC), whereas the highest PAH and DOC removal rates observed for Selenga River (the major Baikal tributary) in summer were equal to −9 mg/s and −3190 g/s correspondingly. The highest PAH and DOC removal rates observed for small tributaries were equal to 0.0004 mg/s and −0.7 g/s respectively. The amplitude of annual CRR oscillations depends on contaminant abundance. The highest amplitude was typical for most abundant contaminants such as Nmin. and DOC. In unpolluted sections of the Selenga River the highest rates of N and C removal (−85 g/s and −3190 g/s, respectively) were observed in summer and the lowest rates (4 g/s and 3869 g/s, respectively) were observed in the spring. The lowest amplitude was typical for PAHs and some low-abundance TM such as V and Ni. The highest summer rates of V and Ni removal were equal to −378 mg/s and −155 mg/s respectively, whereas lowest spring rates are equal to 296 mg/s and 220 mg/s. The intermediate CRR amplitudes were typical for most abundant TM such as Sr, Al, and Fe. The spatial CRR variability depends on water chemistry and the presence of pollution sources. The lowest (up to 38 g/s) rates of Nmin. removal was observed for polluted lower Selenga sections characterized by low water mineralization and high DOC concentrations. The highest rates (−85 g/s) were observed for unpolluted upper sections. Seepage loss from the river to groundwater was also recognized as an important means of contaminant removal. The CRC values depend mostly on water residence time. The DOC removing capacity value of Baikal (−26 g/m3) were lower than those of Selenga in summer (−35 g/m3) but higher than the CRCs of all tributaries during the other seasons (from 30 mg/m3 to −10 g/m3).

Tungsten Trioxide (WO3)-assisted Photocatalytic Degradation of Amoxicillin by Simulated Solar Irradiation

This study investigates the photocatalytic degradation of amoxicillin (AMO) by simulated solar irradiation using WO3 as a catalyst. A three-factor-three-level Box-Behnken design (BBD) consisting of 30 experimental runs is employed with three independent variables: initial AMO concentration, catalyst dosage, and pH. The experimental results are analyzed in terms of AMO degradation and mineralization, the latter of which is measured using dissolved organic carbon (DOC). The results show that the photocatalytic degradation of AMO follows pseudo-first-order kinetics. AMO degradation efficiency and the pseudo-first-order rate constants decrease with increasing initial AMO concentration and pH and increase with increasing catalyst dosage. Though AMO degradation is almost fully complete under the experimental conditions, DOC removal is much lower; the highest DOC removal rate is 35.82% after 180 min. Using these experimental results, second-order polynomial response surface models for AMO and DOC removal are constructed. In the AMO removal model, the first-order terms are the most significant contributors to the prediction, followed by the quadratic and interaction terms. Initial AMO concentration and pH have a significant negative impact on the photocatalytic degradation of AMO, while catalyst dosage has a significant positive impact. In contrast, in the DOC removal model, the quadratic terms make the most significant contribution to the prediction and the first-order terms the least. The optimal conditions for the photocatalytic degradation of AMO are found to be an initial AMO concentration of 1.0 μM, a catalyst dosage of 0.104 g/L, and a pH of 4, under which almost complete removal of AMO is achieved (99.99%).

Interdependence between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge in semi-continuous reactors.

The objective of the present work was to analyze the interrelationship between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge (AS) in semi-continuous reactors (SCRs). AS were obtained from three SCRs fed with glucose, acetate or peptone. AS from these reactors were used as inocula for three SCRs that were fed with each biogenic substrate, and for three SCRs that were fed with the biogenic substrate and BPA. In all cases, dissolved organic carbon (DOC), BPA, total suspended solids (TSS) and respirometric measurements were performed. Although BPA could be removed in the presence of all the tested substrates, AS grown on acetate exhibited the longest acclimation to BPA. Reactors fed with peptone attained the lowest TSS concentration; however, these AS had the highest specific BPA degradation rate. Specific DOC removal rates and respirometric measurements demonstrated that the presence of BPA had a negligible effect on the removal of the tested substrates. A mathematical model was developed to represent the evolution of TSS and DOC in the SCRs as a function of the operation cycle. Results suggest that the main effect of BPA on AS was to increase the generation of microbial soluble products. This work helps to understand the relationship between the biodegradation of BPA and readily biodegradable substrates.

Optimized removal of natural organic matter by ultrasound-assisted coagulation of recycling drinking water treatment sludge

In previous work we have shown that recycling pre-sonicated drinking water treatment sludge (DWTS) could improve coagulated water quality. Here, the removal of naturally occurring organic matter of source water was further optimized using response surface methodology (RSM) with Box-Behnken Design (BBD). The four variables, i.e., volumetric recycling ratio of DWTS, energy density, ultra-sonication time and duty cycle in an experimental jar test of ultrasound assisted flocculation-coagulation were optimized. All the variables showed a significant effect on dissolved organic carbon (DOC) removal of source water (p < .05), of which the duty cycle had a stronger effect on the removal performance compared to the other independent variables. The predicted optimal DOC removal rate was 36.94%, and this matched well the observed performance of 36.54 ± 0.56%, obtained by ultra-sonicating the sludge prior to recycling using a power input of 1.015 W/mL, an ultra-sonication time of 9 min 50 s, and a duty cycle of 80%, while the volumetric recycling ratio of DWTS was 5.8%. The natural organic matter fractions in the coagulated water samples indicated that recycling sonicated DWTS that had been washed prior to recycling in order to remove solubilized extracellular polymers could enhance removal of hydrophobic acids and 3–30 kDa fractions, but this treatment increased the presence of substances with molecular weight <3 kDa. Humic-like substances were effectively removed while tyrosine-like substances could be enriched. Sludge samples (raw DWTS, sonicated DWTS, sludge formed by recycling raw DWTS, and sludge formed by recycling sonicated DWTS without solubilized extracellular organics) were characterized by XRF, X-ray diffraction patterns and FE-SEM-EDS to reveal possible physical characteristics that could be related to the DOC removal performance.

Modeling rates of DOC degradation using DOM composition and hydroclimatic variables

AbstractThe fluvial fluxes of dissolved organic carbon (DOC) from peatlands form an important part of that ecosystem's carbon cycle, contributing approximately 35% of the overall peatland carbon budget. The in‐stream processes acting on the DOC, such as photodegradation and biodegradation, can lead to DOC loss and thus contribute CO2 to the atmosphere. The aim of this study was to understand what controls the rates of DOC degradation. Water samples from a headwater, peat‐covered catchment, were collected over a 23 month period and analyzed for the DOC degradation rate and dissolved organic matter (DOM) composition in the context of hydroclimatic monitoring. Measures of DOM composition included 13C solid‐state nuclear magnetic resonance spectroscopy, bomb calorimetry, and elemental analysis. Regression analysis showed that there was a significant role for the composition of the DOM in controlling degradation with degradation rates significantly increasing with the proportion of aldehyde and carboxylic acid functional groups but decreasing with the proportion of N‐alkyl functional groups. The highest rates of DOC degradation occurred when aldehyde functionality was at its greatest and this occurred on the recession limb of storm hydrographs. Including this knowledge into models of fluvial carbon fate for an 818 km2 catchment gave an annual average DOC removal rate of 67% and 50% for total organic carbon, slightly lower than previously predicted. The compositional controls suggest that DOM is primarily being used as a ready energy source to the aquatic ecosystem rather than as a nutrient source.

Application of Fe-doped TiO2 specimens for the solar photocatalytic degradation of humic acid

This study aimed to assess solar photocatalytic activity of Fe-doped TiO2 specimens for the degradation of natural organic matter (NOM) represented by a model humic acid (HA). Fe-doped TiO2 specimens (P-25 and UV-100) were prepared by a wet impregnation method. Humic acid (molecular size<100kDa) was characterized by UV–vis and fluorescence spectroscopic parameters and dissolved organic carbon (DOC) content both prior to and following solar photocatalysis. Molecular size fractionation data revealed a shift to lower molecular size fractions i.e.: 30kDa, 10kDa and 3kDa being more pronounced in case of Fe-doped UV-100 in comparison to Fe-doped P-25. Excitation-emission matrix (EEM) fluorescence features of indicated humic molecular size fractions did not illustrate any significant difference related to the formation of new fluorophoric regions but displayed the shift from humic-like fluorophores to fulvic-like fluorophores even in 3kDa fraction indicating that humic acid followed a photocatalyst type independent pathway via solar photocatalysis. Slower DOC removal rates were attained for Fe-doped TiO2 specimens with respect to bare specimens indicating the importance of substrate properties rather than the inefficiency of visible light activation by metal doping of photocatalyst.

Photocatalytic Removal of Microbiological Consortium and Organic Matter in Greywater

This study aimed to investigate TiO2 photocatalytic degradation of synthetically-prepared greywater samples with differing compositional contents of organic matter (OM), anion concentration, and microbiological consortium. Treatment efficiency was followed through removal of organic matter content in terms of dissolved organic carbon (DOC), specific spectroscopic parameters, and bacterial inactivation. Photocatalytic degradation kinetics were expressed by pseudo first-order kinetic modeling. The best DOC removal rates were attained for greywater samples containing OM with lower molecular size fractions. In addition, either enhancing or reducing the effect of common anions as radical scavengers were observed depending on the composition and concentration of variables in the greywater matrix. Moreover, possibility of a photocatalytic disinfection process was found to be of a bacteria type specific in OM-loaded synthetic greywater samples. Photocatalytic destruction of fecal streptococci required longer irradiation periods under all conditions. Bacterial removal rates were found to be in the order of total coliform &gt; fecal coliform &gt; fecal streptococci, for low organic load greywater, and fecal coliform &gt; total coliform &gt; fecal streptococci, for high organic load greywater.

Tracing dissolved organic carbon and trihalomethane formation potential between source water and finished drinking water at a lowland and an upland UK catchment

Rising dissolved organic carbon (DOC) concentrations in many upland UK catchments represents a challenge for drinking water companies, in particular due to the role of DOC as a precursor in the formation of trihalomethanes (THMs). Whereas traditionally, the response of drinking water companies has been focussed on treatment processes, increasingly, efforts have been made to better understanding the role of land use and catchment processes in affecting drinking water quality. In this study, water quality, including DOC and THM formation potential (THMFP) was assessed between the water source and finished drinking water at an upland and a lowland catchment. Surprisingly, the lowland catchment showed much higher reservoir DOC concentrations apparently due to the influence of a fen within the catchment from where a major reservoir inflow stream originated. Seasonal variations in water quality were observed, driving changes in THMFP. However, the reservoirs in both catchments appeared to dampen these temporal fluctuations. Treatment process applied in the 2 catchments were adapted to reservoir water quality with much higher DOC and THMFP removal rates observed at the lowland water treatment works where coagulation–flocculation was applied. However, selectivity during this DOC removal stage also appeared to increase the proportion of brominated THMs produced.