Dissolved Organic Carbon Removal Efficiency Research Articles

Performance of BAC for DBPs precursors’ removal for one year with micro-polluted lake water in East-China

ABSTRACT Effectiveness of biological activated carbon (BAC) filter in removing disinfection byproducts (DBPs) precursors of micro-polluted lake water for one year was conducted. The formation potential (FP) of DBPs (trihalomethanes (THMs), haloacetic acids (HAAs) and Nitrosamines (NAs)), dissolved organic carbon (DOC), molecular weight (MW) distribution and excitation emission matrix fluorescence (EEM) of dissolved organic material (DOM) in the influent and effluent of BAC were determined. The results indicated that the removal efficiency (RE) of DOC ranged from 42.9–28.3%. Neither virgin GAC nor long-term operated BAC could efficiently dispose of THMs and HAAs precursors (RE from 35.2–18.8%, from 42 to 8.4%, respectively), however, BAC still showed good ability in removal of NAs precursors after a year operation, of which RE just dropped from 81.7–69.6%. There was strong correlation between RE of NAs precursors and DOC with small MW (<0.5 kDa). The removal of HAAs precursors showed relatively close relation to aromatic protein-like components and soluble microbial pollutants (SMPs). Weak direct relationship was found between the water quality parameters and THMs precursors.

Control of Coagulant Dosing for Humic Substances Based on Ultraviolet Spectrum Analysis

Humic substance (HS) is a main component of dissolved organic matter in the aquatic environment and significantly affects water treatment processes. To investigate the applicability and principle of UV spectrum analysis for coagulation control, laboratory jar tests were conducted with synthetic waters that had varying concentrations of HS and kaolinite. Thus, the influence of water quality conditions on the optimal coagulant dose (OCD) was determined and further correlated to Specific Ultraviolet Absorbance (SUVA254) and the ultraviolet spectral slopes of the coagulated water. Subsequently, the relationship between the UV spectral slopes and organic fractionation was further identified by using size exclusion chromatography (SEC). The results showed that the coagulant demands of the synthetic waters were positively related to dissolved organic carbon (DOC). Consequently, a stoichiometric relationship (0.61 mg·mg-1 calculated as Al/DOC) was found between the coagulant demand and initial DOC of the synthetic water. As the coagulant dose increased, SUVA254 decreased from 8.9 L·(mg·m)-1 to a steady level of 2.0 L·(mg·m)-1 and the removal efficiency of DOC was positively correlated with SUVA254. Spectral slopes in different wavelength ranges had showed similar tendencies, with S275-295 having the best correlation with SUVA254 (R2=0.81). Furthermore, SEC results demonstrated that coagulation preferentially removed humic substances, leading to reduced humification. As a result, S275-295 had the highest correlation with the portion of UVA254 contributed by humic substances in water. Therefore, online measurement of ultraviolet spectral slopes was an important aspect in the control of coagulant dosing.

Fenton oxidation of municipal secondary effluent: comparison of Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts

The advanced treatment of municipal secondary effluent by heterogeneous and homogeneous Fenton processes using Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts was studied and compared. Sulfamethazine (SMT) was spiked in the effluent to examine the effectiveness of the emerging contaminant removal. The Fe/Ce-RGO catalyst was characterized using a scanning electron microscope (SEM) and cycle voltammetry curves. The removal of dissolved organic carbon (DOC), soluble chemical oxygen demand (SCOD), SMT, and ultraviolet-visible spectroscopy in 254nm (UV254) of municipal secondary effluents was examined. The DOC removal efficiency of secondary effluent (without addition of SMT) was 36.30% and 11.74% using Fe/Ce-RGO and Fe2+ as catalysts, respectively. The removal efficiency of DOC, SCOD, and SMT in heterogeneous Fenton process was higher than that in homogeneous Fenton process. The changes of three-dimensional excitation-emission matrix (3DEEM) fluorescence, soluble microbial products (SMPs), humic acids, and UV254 were determined, and the results indicated that UV254, aromatic proteins, and humic acids decreased rapidly in both processes; however, polysaccharides and protein-like substances were difficult to degrade. Although some toxic substances produced after Fenton-like treatment, the biodegradability of the treated effluent was enhanced.

Removal of dissolved organic matter from raw water using zero valent iron -carbonaceous conjugated microporous polymer nanocomposites

There are a limited number of potentially scalable low-cost treatment methods for removing organic pollutants in water. In this study, a magnetic zero valent iron-carbonaceous conjugated microporous polymer nanocomposite (ZVI-CCMP) was synthesized from ZVI and waste polystyrene via the liquid phase reduction method, and used in a batch system for the removal of dissolved organic carbon (DOC) in water from a water treatment plant (WTP) in Pretoria, South Africa. The results were compared to the DOC removal efficiency of the WTP. The surface morphology of the nanocomposites as characterized using scanning electron microscopy showed heterogeneous ZVI nanastructures dispersed on the CCMP surface. Fourier transform infrared spectroscopy showed that the functional groups on the ZVI-CCMP surface were predominantly CC and C-C from quinonoid motifs, aliphatic chain conjugation, and C-S groups originating from the introduced sulphonic moieties. Batch experiment data indicated that ZVI-CCMP adsorbed significantly (p = 0.01) more DOC than ZVI, demonstrating the synergistic effect of ZVI activation. Whereas the WTP removed up to 24.3% DOC, ZVI and ZVI-CCMP removed 64 and 75%, respectively after a contact time of 30 min. Thus, compared to the processes used by the WTP, batch experiments using ZVI and ZVI-CCMP were 41 (p = 0.00) and 52% (p = 0.01) superior, respectively, demonstrating the potential of these materials to be upscaled for pilot and real life applications. While polystyrene has been used in the ZVI composites and the synthesis and evaluation of ZVI decorated carbon based materials has been widely studied, ZVI-CCMP based materials have not been reported. The objectives were: (1) to synthesise and characterise ZVI-CCMP nanocomposites; (2) to evaluate the removal of DOC in real water samples by ZVI and ZVI-CCMP; and (3) to compare the relative efficiency of ZVI-CCMP to that of the water treatment process through the measurement of DOC. Using CCMP nanocomposites to treat water is potentially a low-cost and environmentally friendly alternative for reducing the adverse public health and environmental risks associated with waste polystyrene.

Electricity generation potential of poultry droppings wastewater in microbial fuel cell using rice husk charcoal electrodes

BackgroundPoultry droppings from poultry farms and rice husks obtained from rice milling process are generally considered as wastes and discarded in Nigeria. Although many studies have shown that microbial fuel cells (MFCs) can generate electricity from organic wastes, little or no study have examined MFCs for generating electricity from poultry droppings and rice husk as electrode material.FindingsLaboratory-scale double-chamber MFCs were inoculated with concentrations of poultry droppings wastewater and supplied with rice husk charcoal as anode and cathode electrodes for electricity generation. Power outputs and dissolved organic carbon (DOC) removal efficiencies were compared between MFCs using rice husk charcoal (RHCE) as electrode and those using carbon cloth (CCE) as electrodes. The RHCE-MFC 2 containing 477 mg L−1 dissolved organic carbon produced a volumetric power density of 6.9 ± 3.1 W m−3 which was higher than the control and the CCE-MFCs by a factor of 2 and achieved at DOC removal efficiencies of 40 ± 1.2%.ConclusionsThe results suggest that poultry droppings wastewater is a feasible feedstock for generating electricity in MFCs. The findings also suggest that rice husk charcoal is a potentially useful electrode material in MFCs.

Evaluation of cationic polyacrylamide-based hybrid coagulation for the removal of dissolved organic nitrogen.

Dissolved organic nitrogen (DON) is an important component of aquatic environment of which amount impacts water quality. Thus, removal of DON has attracted wide attention. At present, it is difficult for common coagulation to remove DON from the aquatic environment. The cationic polymers can help to improve the removal efficiency of DON to some extent, but the underlying mechanism of the ascension is not clear. In order to grasp its removal behavior and further improve the removal efficiency of DON in the future, we evaluated the effect of a hybridized coagulant of polyacrylamide with iron-based coagulant on removal of aquatic DON. A higher floc growth rate (119.82μm/min) and recovery factors (26.96) were found in the hybrid coagulation. The parameters affecting the DON and the dissolved organic carbon (DOC) included the molar ratio of Zn to Fe (nZn/nFe), CPAM content, and molar ratio of OH to Fe (nOH/nFe): nZn/nFe had a larger influence in DON removal than CPAM content; CPAM had a larger influence in the DOC removal; nOH/nFe played a moderate effect between CPAM and nZn/nFe. Mutual effect of hybrid coagulants indicated the colloidal species to be helpful in enhancing DOC and DON removal. Other parameters affecting coagulation performance included the pH: the estimated maximum DON removal efficiency occurred at pH 6, DOC removal efficiency at pH 8. The above results found in this study showed that DON removal was affected by the ingredient and the species composition of the hybrid coagulant, and the water environmental parameter. The enhanced efficiency of DON removal in the presence of CPAM was mainly attributed to the increased adsorption-bridging and sweep-floc.

Removal of micropollutants from Sakarya River water by ozone and membrane processes.

The removal of some pollutants in the Sakarya River was investigated in this study. Sakarya River located in Turkey flows from the northeast of Afyonkarahisar City to the Black Sea. Nineteen different micropollutants including trihalomethanes (THMs), haloacetic acids (HAAs), endocrine disrupting compound (EDC) and pharmaceuticals personal care product (PPCP) groups, and water quality parameters such as dissolved organic carbon (DOC), ultraviolet absorbance at 254nm wavelength (UV254), hardness, and conductivity values were examined. To remove the micropollutants and improve the water quality, the treatment was performed with ozone, microfiltration (MF), and ultra-filtration (UF) membranes. The highest treatment efficiency was obtained with 1mg/L ozone dosage and UP005 UF membrane. The trihalomethan formation potential (THMFP) and haloacetic acid formation potential (HAAFP) decreased with ozone + membrane at a concentration of 79 and 75%, respectively. After the treatment with ozone + membrane, the concentration of the micropollutants in the EDC and PPCP group remained below the detection limit. It was found that by using only membrane and only ozone, the maximum DOC removal efficiency achieved was 46 and 18%, respectively; and with ozone + membrane, this efficiency increased up to 82%. The results from the High-Pressure Size Exclusion Chromatography (HPSEC) analyses pointed that the substances with high molecular weight were converted into substances with low molecular weight after the treatment. The Fourier Transform Infrared (FTIR) analysis results showed that the aromatic and aliphatic functional groups in water changed after the treatment with ozone and that the peak values decreased more after the ozone + membrane treatment.

Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests

Poly- and perfluoroalkyl substances (PFASs) have been detected in drinking water at relatively high concentrations throughout the world which has led to implementation of regulatory guidelines for specific PFASs in drinking water in several European countries and in the U.S. The Swedish National Food Agency has determined that the drinking water of over one third of the country's municipal consumers is at risk or already affected by PFAS contamination. The present study investigated the effects of perfluorocarbon chain length, functional group and isomer structure (branched or linear) on removal of multiple PFASs using granular activated carbon (GAC, Filtrasorb® 400) and anion exchange (AE, Purolite® A600) column experiments. The removal of 14 different PFASs, i.e. the C3C11, C14 perfluoroalkyl carboxylic acids (PFCAs) (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, PFTeDA), perfluorooctane sulfonamide (FOSA), and the C4, C6, C8 perfluoroalkyl sulfonic acids (PFSAs) (PFBS, PFHxS, PFOS), was monitored for a 217 day period. The results indicate the selective nature of PFAS removal as the absorbents are loaded with PFASs and dissolved organic carbon (DOC). A clear relationship between perfluorocarbon chain length and removal efficiency of PFASs using GAC and AE was found while PFASs with sulfonate functional groups displayed greater removal efficiency than those with carboxylate groups. Similarly, time to column breakthrough increased with increasing perfluorocarbon chain length and was greater for the PFSAs than the PFCAs for both GAC and AE. Shorter carbon chained PFASs such as PFBA, PFPeA, PFHxA showed desorption behavior and long-chained PFASs showed increased removal towards the end of the experiment indicating agglomeration or micelle development. Linear isomers of PFOS, PFHxS, and perfluorooctane sulfonamide (FOSA) had greater column removal efficiencies using GAC (and also for AE at greater bed volume throughput) than the branched and this difference increased at greater bed volume throughputs. The GAC and AE columns showed a poor correlation between DOC and PFAS removal efficiency. The results indicate that designers and operators of AE and GAC treatment processes must take into consideration the selective nature of PFAS removal and associated desorption of short-chain PFCAs during co-removal of multiple PFASs.

Hybrid electrocoagulation/electroflotation/electrodisinfection process as a pretreatment for seawater desalination

The main objective of this study was to examine the feasibility of a hybrid electrocoagulation/electroflotation/electrodisinfection (EC/EF/ED) process in treating seawater prior to desalination treatment using reverse osmosis process. Residual dissolved organic carbon (DOC) and heterotrophic bacteria concentrations were measured. A continuous treatment using aluminium electrodes was investigated, which lead to a complex gas-liquid-solid mixture in which aluminium flocs and hydrogen gas bubbles enhanced pollution removal. Experimental results showed that DOC removal efficiency increased when the current density increased and when the inlet flow rate decreased. The best performance of DOC removal (69.0%) was recorded while imposing 20mA/cm2 and 320s residence time when inflow pH was 4. Heterotrophic bacteria were completely removed for the highest current densities (20mA/cm2). In the EC process, a low concentration of total chlorine species (up to 0.45mg/L) resulting from the oxidation of chloride anions was formed, which promoted the removal of microorganisms, even though these were mainly removed by the coupled effects of the electric field and the bacteria entrapment in hydroxide flocs. Finally, EC/EF/ED as a one-step pretreatment method was shown to be efficient to replace the conventional methods prior to desalination by reverse osmosis as it was proved to remove efficiently organic matter and microorganisms from seawater: with 0.8L/h and 14mA/cm2, 50% of DOC and nearly all the microorganisms could be removed at less than 0.5kWh/m3.

Linking the mobilization of dissolved organic matter in catchments and its removal in drinking water treatment to its molecular characteristics

Drinking water reservoirs in the Northern Hemisphere are largely affected by the decadal-long increase in riverine dissolved organic carbon (DOC) concentrations. The removal of DOC in drinking water treatment is costly and predictions are needed to link DOC removal efficiency to its mobilization in catchments, both of which are determined by the molecular composition. To study the effect of hydrological events and land use on the molecular characteristics of dissolved organic matter (DOM), 36 samples from three different catchment areas in the German low mountain ranges, with DOC concentrations ranging from 3 to 32 mg L−1, were examined. Additionally, nine pairs of samples from downstream drinking water reservoirs were analyzed before and after flocculation. The molecular composition and the age of DOM were analyzed using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and radiocarbon (14C) analysis. At elevated discharge in a forested catchment comparatively younger, more oxygenated and unsaturated molecules of higher molecular weight were preferentially mobilized, likely linked to the reductive mobilization of iron. DOM with highly similar molecular characteristics (O/C ratio > 0.5, m/z > 500) could also be efficiently removed through flocculation in drinking water treatment. The proportion of DOM removed through flocculation ranged between 43% and 73% of DOC and was highest at elevated discharge. In catchment areas with a higher percentage of grassland and agriculture a higher proportion of DOM molecules containing sulfur and nitrogen was detected, which in turn could be less efficiently flocculated. Altogether, it was shown that DOM that is released during large hydrological events can be efficiently flocculated again, suggesting a reversal of similar chemical mechanisms in both processes. Since the occurrence of heavy rainfall events is predicted to increase in the future, event-driven mobilization of DOC may continue to challenge drinking water production.

Hydrodynamic cavitation in combination with the ozone, hydrogen peroxide and the UV-based advanced oxidation processes for the removal of natural organic matter from drinking water

Natural organic matter in drinking water is causing concern especially due to the formation of disinfection by-products (DBPs) by chlorine, as these are proven to have adverse health effects on consumers. In this research, humic acid was used as a source of dissolved organic carbon (DOC) in drinking water (up to 3mgL−1). The efficiency of DOC removal was studied by applying O3, H2O2/O3, H2O2/UV and O3/UV advanced oxidation processes (AOPs) alone and combined with hybrid hydrodynamic cavitation (HC), generated by an orifice plate, as this technology recently shows promising potential for the treatment of water, containing recalcitrant organic substances. It was observed that the combined treatment by HC could significantly affect the performance of the applied AOPs, with as little as 3–9 passes through the cavitation generators. For O3 and H2O2 dosages up to 2 and 4mgL−1, respectively, and UV dosage up to 300mJcm−2, HC enhanced DOC removal by 5–15% in all combinations, except for O3/UV AOPs. Overall, the potential benefits of HC for DOC removal were emphasized for low ratio between applied oxidants to DOC and high UV absorbance of the sample. Investigated DBPs formation potentials require special attention for H2O2/UV AOPs and combinations with HC.

Does the combination of biochar and clinoptilolite enhance nutrient recovery from the liquid fraction of biogas digestate?

ABSTRACTConcentrating nutrients on biochar and clinoptilolite and subsequently using the nutrient-enriched sorbents as a fertiliser could be an alternative way to manage nutrients in digestate. In this study, we investigated the use of biochar and clinoptilolite columns in removing ammonium, potassium, orthophosphate and dissolved organic carbon (DOC) from the liquid fraction of digestate. Our objectives were to investigate the effect of the initial loading ratio between liquid and biochar on nutrient removal, and to investigate the effect of combining biochar with clinoptilolite on nutrient and DOC removal efficiency. Increasing the initial loading ratios increased nutrient concentrations on biochar to 8.61 mg NH4-N g−1, 1.95 mg PO4-P g−1 and 13.01 mg DOC g−1, but resulted in decreasing removal efficiencies. The combination of biochar and clinoptilolite resulted in improved ammonium, potassium and DOC removal efficiencies compared to biochar alone, but did not significantly change PO4-P removal efficiencies. Removal efficiencies with combined sorbents were up to 67% for ammonium, 58% for DOC and 58% for potassium. Clinoptilolite showed higher removal efficiencies compared to biochar alone, and combining clinoptilolite with biochar improved only total P removal efficiency. Concentrating nutrients with clinoptilolite and biochar may be an option when both sorbents are available at low cost.

The effect of Iron Ion on Removal Efficiency of Dissolved Organic Carbon (DOC) Using UV/TiO2

&lt;div&gt; &lt;p&gt;Most of water sources throughout the world contain natural organic matter (NOM), which is the best description as a complex mixture of organic compounds. The effect of iron ion on removal efficiency of dissolved organic carbon (DOC) using UV/TiO&lt;sub&gt;2&lt;/sub&gt; photo catalytic oxidation (TiO&lt;sub&gt;2&lt;/sub&gt;) was examined. In this quasi-experimental study, the different variables such as pH value, contact time, various concentrations of TiO&lt;sub&gt;2&lt;/sub&gt;, FeCl&lt;sub&gt;2&lt;/sub&gt; on the removal efficiency of DOC by the UV/TiO&lt;sub&gt;2&lt;/sub&gt; on raw water of Zayandehroud in Isfahan were studied. The results were analyzed by using Pearson correlation coefficient test and SPSS software. Removal efficiency DOC improved as the amount of catalyst was increased. Maximum removal efficiency was achieved during acidic conditions (pH=3) within 60 minutes of contact time. The removal efficiency of DOC by the UV/TiO&lt;sub&gt;2&lt;/sub&gt; decreased with increase of contact time. The presence of iron ions increased the rate of DOC removal by the UV/TiO&lt;sub&gt;2&lt;/sub&gt;. Removal efficiency of dissolved organic carbon increased when ionic strength and initial concentration of Ferric Chloride was increased. Also, by adding particles of Ferric Chloride, Removal of dissolved organic carbon increased to 98% in comparison with absence of iron ion (78%).&lt;/p&gt; &lt;/div&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Treatment of Sanitary Landfill Leachate by Photo-Fenton Process: Effect of the Matrix Composition

In this study it was evaluated the role of the composition of sanitary landfill leachate on the removal of dissolved organic carbon (DOC) by photo-Fenton process. The composition of the matrix (high turbidity and color, as well as presence of inorganic ions sulfate and chloride) does not reduce the efficiency of DOC removal by photo-Fenton reactions, but influences significantly the reaction time and consumption of H2O2. An expressive increase in the efficiency of DOC removal occurred for concentrations of Fe2+ between 50 and 100 mg L-1, remaining constant in the range between 100 and 200 mg L-1. On the other hand, the pre-treatment of this effluent by coagulation-flocculation before the photo-Fenton process is recommended, since a similar efficiency of DOC removal, between 70 and 77%, was achieved using only 17% of the time and 7% of H2O2 necessary for the treatment of raw leachate treatment.

Role of self-assembly coated Er3+: YAlO3/TiO2 in intimate coupling of visible-light-responsive photocatalysis and biodegradation reactions

Conventionally used ultraviolet light can result in dissolved organic carbon (DOC) increasing and biofilm damage in intimate coupling of photocatalysis and biodegradation (ICPB). Visible-light-responsive photocatalysis offers an alternative for achieving ICPB. In this study, composite-cubes were developed using self-assembly to coat a thin and even layer of visible-light-responsive photocatalyst (Er3+: YAlO3/TiO2) on sponge-type carriers, followed by biofilm cultivation. The degradations of phenol (50mgL−1) were compared for four protocols in circulating beds: adsorption (AD), visible-light-responsive photocatalysis (VPC), biodegradation (B), and intimately coupled visible-light-responsive photocatalysis and biodegradation (VPCB). The phenol and DOC removal efficiencies using VPCB in 16h were 99.8% and 65.2%, respectively, i.e., higher than those achieved using VPC (71.6% and 50.0%) or B (99.4% and 58.2%). The phenol removal of 96.3% could be obtained even after 3 additional cycles. The 6.17-min intermediate detected by HPLC, continuously accumulated for VPC, appeared at 1–6h and then was completely removed for VPCB in 10h. ICPB was further illustrated in that most of the biofilm was protected in the carrier interiors, with less protection on the carrier exterior in VPCB. A self-regulation mechanism that helped photocatalyst exposure to visible-light irradiation was identified, promoting the combined photocatalysis and biodegradation.

Inline coagulation–ultrafiltration as the pretreatment for reverse osmosis brine treatment and recovery

To help resolve issues associated with reverse osmosis (RO) brine handling for inland water reuse plants, RO brine treatment and recovery from NEWater factory was demonstrated in a laboratory using a low cost, less footprint and low energy consumption pretreatment method of inline coagulation–ultrafiltration (UF). Polyaluminum chloride (PACl), aluminum chlorohydrate (ACH) and ferric chloride (FeCl3) were chosen as the coagulants. PACl and ACH attained dissolved organic carbon (DOC) removal of 31% and 27% respectively at the optimal dosage (0.556mM as Al), while FeCl3 outperformed PACl and ACH at this molar dosage, reaching up to 60% of DOC removal. At the optimal pH (pH7), FeCl3 was again more superior with the highest DOC removal efficiency of 55%. FeCl3 also presented the highest phosphate (>99%) and silica removals (14%) at its optimum dosage and pH. Liquid chromatography-organic carbon detector (LC-OCD) and fluorescence excitation–emission matrix (EEM) were used to characterize the DOC fractions removed by inline coagulation-UF. For LC-OCD, FeCl3 revealed higher removal efficiency for almost all the DOC fractions ranging from low to high molecular weight. These results suggest that the inline-coagulation (FeCl3)-UF pretreatment is potential in reducing the fouling tendency of downstream RO because of its high DOC and phosphate removal efficiency.

Coagulation performance and membrane fouling of polyferric chloride/epichlorohydrin–dimethylamine in coagulation/ultrafiltration combined process

Polyferric chloride (PFC) and epichlorohydrin–dimethylamine (DAM–ECH) with different PFC (as Fe3+)/DAM–ECH mass ratios (MR) and dose methods were used in the treatment of humic acid–kaolin (HA–kaolin) simulated water under different pH conditions. Coagulation performance, floc characteristics and membrane fouling of PFC/DAM–ECH in coagulation–ultrafiltration (C–UF) process were investigated in this study. Results showed that the optimum coagulation performance was achieved when PFC dose was 15mg/L with PFC/DAM–ECH MR of 2:1 under pH6.0. Opposite adding sequence (DAM–ECH/PFC) would reduce UV254 (ultraviolet adsorption at 254nm) and DOC (dissolved organic carbon) removal efficiency. Addition of DAM–ECH on the basis of PFC produced larger and stronger flocs with better regrowth ability. Proper dosage of DAM–ECH under certain coagulation condition could achieve the best coagulation performance and keep the UF membrane operating under a preferable status. Results of this study would be beneficial for application of composite coagulant PFC–DAM–ECH and DAM–ECH as coagulant aid in water treatment processes.

Reverse osmosis concentrate treatment by a PAC countercurrent four-stage adsorption/MF hybrid process

In this study, in order to reduce the impact of reverse osmosis concentrate (ROC) on the receiving body of water and/or improve the recovery rate of reverse osmosis (RO) system by reusing the treated ROC as a feeding, a powdered activated carbon (PAC) countercurrent four-stage adsorption/MF hybrid process was developed for organic removal from ROC. The process could achieve good organic removal at lower PAC consumption. For dissolved organic carbon (DOC) removal efficiency of 70.0%, the PAC dose was 21.6% less than that in countercurrent two-stage adsorption and 50.9% less than that in single-stage adsorption. The calculation method for correlating removal efficiency and PAC dose was deduced and validated. The validation result showed that the relative error between the average experimental DOC removal efficiency and the calculated one was less than 5% throughout the experiment, exhibiting good accuracy for the calculation method. Compared with countercurrent two-stage adsorption, the membrane fouling in the new process could be mitigated to a certain extent. The total number of sub-cycles in a cycle (n) influenced the hydraulic retention time (HRT) and the total volume of the reactors. Results showed that the HRT increased as n increased.

Effects of Al species on coagulation efficiency, residual Al and floc properties in surface water treatment

Effects of coagulant dosage and solution pH on the coagulation behaviors using three different Al-based coagulants were studied in terms of dissolved organic carbon (DOC) removal efficiency and residual Al. The coagulants used in this study were aluminum chloride (AlCl3), Al13O4(OH)247+ polymer (Al13) and (AlO4)2Al28(OH)5618+ polymer (Al30). Surface water from a typical water treatment plant in the north China was used to conduct the experiments. The results showed that DOC removal efficiency correlated well to the content of medium polymerized species (Alb), while the flocs formed by Alb were not as large as those formed by colloidal or gel species (Alc). Monomeric species (Ala) showed a high ability to react with some unsatisfied coordinate bonds of organic matter to facilitate DOC removal, and it was the most unstable species, which could be easily transformed into in-situ Alb species. Compared to preformed Alb, in-situ Alb could remove DOC more efficiently and the flocs were much larger via the mechanism of further hydrolysis and transfer into Alc during coagulation. Results showed that pH had significant effects on residual Al, the total residual dissolved Al achieved the minimal concentrations in the neutral pH region. The results of molecular weight (MW) distribution of residual Al showed large differences at the given coagulation pH, and monomeric species were the predominant Al species at pH 6.0 and pH 8.0 for all coagulants.

The effects of Fe–Mn oxide and TiO2/α-Al2O3 on the formation of disinfection by-products in catalytic ozonation

The catalytic activity of Fe–Mn oxide and TiO2/α-Al2O3 catalysts toward the ozonation of natural organic matter (NOM) and a model compound (p-chlorobenzoic acid, pCBA) was investigated in a heterogeneous catalytic ozonation process (HCOP). The monitored parameters in this study included pCBA, dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254), trihalomethanes (THMs), and nine haloacetic acids (HAA9). The Fe–Mn oxide catalyst significantly enhanced the decomposition (kd) of dissolved ozone (O3) and promoted the formation of hydroxyl radicals in the HCOP to a greater extent than did the TiO2/α-Al2O3 catalyst. Both catalysts (Fe–Mn oxide and TiO2/α-Al2O3) used in the HCOP showed better performance with regard to removal efficiency of DOC and UV254 than adsorption and ozonation. Moreover, the Fe–Mn oxide catalyst had higher removal efficiencies for DOC and UV254 in both the HCOP and adsorption than those of the TiO2/α-Al2O3 catalyst. The removal efficiency associated with UV254 was significantly higher than that associated with DOC. The results show that the use of Fe–Mn oxide and TiO2/α-Al2O3 in catalytic ozonation could effectively remove the precursors of disinfection by-products (DBPs), resulting in the formation of fewer THMs and HAA9. In addition, biofiltration of the HCOP treated water can further increase the removal efficiency of DPB precursors, with the type of catalyst used being less important.