Micro-polluted Surface Water Treatment Research Articles

Salt tide affecting algae-laden micropolluted surface water treatment and membrane performance based on BDD electro-oxidation coupled with ceramic membrane process

Harmful algal blooms pose an emerging threat to freshwater ecological security and human health, necessitating further study in offshore areas. In this work, boron-doped diamond electro-oxidation (BDD/EO) coupled with a ceramic membrane filtration was employed aiming to assess the salt tide affecting algae-laden water treatment involving with various natural organic matters (e.g., HA, SA, and BSA). The results have demonstrated that BDD/EO remove chlorophyll from the algae-laden water effectively due to the inactivation of algal cells. Moreover, considering the influence of salt tide, NH3–N would be mainly oxidized through the in-situ generated active chlorine at the electrode-liquid interface. In addition, in three kinds of salt tide affecting algae-laden water, TOC content in BSA group was decreasing remarkably after BDD/EO with TOC removal efficiency above 80%; while those in HA and SA groups had no obvious reducing due to the more algae cells breakage synchronous with HA and SA removal. Based on the fluorescent characteristics and particle size distribution, the generated small molecular organics after electro-oxidation might raise the pore blockage probability and the hydrophobic organic and fluorescent substances were preferentially oxidized in BDD/EO process being beneficial to reducing membrane fouling. Besides, the membrane special flux in three groups were decreasing significantly and the irreversible fouling resistance in SA group accounted for a larger proportion of the total resistance than those of HA and BSA. At last, in BDD/EO-CM process, macromolecular substances degradation rate was greater than that of small molecules based on the molecular weight distribution in three groups of salt tide affected algae-laden water treatment. In a word, this work provides effective and innovative strategies for the harmful algal bloom control and contributes interesting insights of membrane fouling performance of electrochemical coupled ultrafiltration membrane process.

Performance improvement and mechanism of composite PAC/PDMDAAC coagulant via enhanced coagulation coupled with rapid sand filtration in the treatment of micro-polluted surface water

The coagulation and filtration are widely used for surface water due to cost effectiveness therefore the need to study its’ improvements for safe drinking water that meet national standards. The performance of enhanced coagulation of composite coagulants (ECC) using poly aluminium chloride/poly di-methyl di-allyl ammonium chloride (PAC/PDMDAAC) coupled with rapid sand filtration (RSF) was studied. This was performed using jar testing, optimized, and operated at same dosage and supernatant turbidity (SDST) mode; also, the interception points for PAC and composites at baseline turbidity between 1.0 and 1.50 NTU with fixed RSF operating conditions while water parameters like turbidity, CODMn, NH3N, and zeta potentials were used as indicators for improved removal rates. Furthermore, the floc size and morphology analysis at optimum dosage combined with zeta potentials were used to explained the mechanism of ECC-RSF. The results showed that most composites out-performed PAC only, before and at the interception points; however, beyond this point, the superior performance disappears with the increasing PAC dosage above 3.0 mg/L. At the optimum dosage, composite PAC/PDMDAAC at 1.60 dL/g, 10:1 showed the best overall removal rate at SDST mode of 99.36%, 64.50%, and 66.18%, respectively for turbidity, NH3N, and CODMn. The dominant mechanism of composite coagulation is charge neutralization within the dosage range used and strengthened by adsorption-bridging due to the presence of PDMDAAC while the major mechanism during filtration is adsorption. It was concluded that depending on the raw water quality, the coagulation mode of SDST at baseline turbidity near 1.0 NTU can maximized the water quality removal for composite PAC/PDMDAAC. New operational insights about maximizing the performance of composite PAC/PDMDAAC coagulants have been put forward.

Preparation of polyvinylidene fluoride composite ultrafiltration membrane for micro-polluted surface water treatment

Blending modification of graphene oxide (GO) and deposition of silver carbonate (Ag2CO3) on the membrane surface by suction filtration was used to prepare polyvinylidene fluoride (PVDF) composite ultrafiltration (UF) membranes (denoted as PGA membranes). The effect of this strategy on the morphology and performance of the pure PVDF membrane was investigated. Owing to an increased hydrophilicity and the formation of a more open pore, the pollution resistance and permeability of the PGA membrane were improved. The pure water flux of the PGA-3 membrane (254 LMH) was increased to more than 2-fold compared to that of the neat PVDF membrane (126 LMH). In addition, the results of antifouling experiments showed that the flux recovery rate, flux decay rate, and antibacterial performance of the PGA-3 membrane was superior to those of the other membranes synthesized in this study. Finally, after conducting multi-cycle filtration experiments with lake water, the flux and recovery rate of the PGA-3 membrane was observed to be the highest, and the water quality of the lake water filtered by the PGA-3 membrane was the best. Thus, the above results indicate that this membrane modification strategy is extraordinarily effective in improving the antifouling properties and permeability of the PVDF UF membranes in practical applications.

Research on the current situation of ultrafiltration combined process in treatment of micro-polluted surface water

At present, most of the source water of domestic urban water supply treatment plants is taken from micro-polluted surface water. With the further improvement of drinking water sanitation standards, the traditional “coagulation-sedimentation-filtration-disinfection” process cannot meet the requirements of the new standards. Ultrafiltration, as the core technology in the field of water treatment in the 21st century, is increasingly applied to water treatment due to its advantages of green efficiency, simple operation, small footprint, and high degree of automation. However, the use of ultrafiltration membrane alone has some problems such as substandard water quality and serious membrane pollution. Therefore, the combination of ultrafiltration and traditional water treatment technology to treat micro-polluted surface water has become the mainstream choice for treatment plants. This article mainly introduces the current research status of domestic ultrafiltration combined technology, trying to explore more reasonable and effective ways to apply ultrafiltration membranes in actual projects.

Characterization of dissolved organic matter and membrane fouling in coagulation-ultrafiltration process treating micro-polluted surface water

Coagulation–ultrafiltration (C–UF) is widely used for surface water treatment. With the removal of pollutants, the characteristics of organic matter change and affect the final treatment efficiency and the development of membrane fouling. In this study, we built a dynamic C–UF set-up to carry out the treatment of micro-polluted surface water, to investigate the characteristics of dissolved organic matter from different units. The influences of poly aluminum chloride and poly dimethyldiallylammonium chloride (PDMDAAC) on removal efficiency and membrane fouling were also investigated. Results showed that the dosage of PDMDAAC evidently increased the UV254 and dissolved organic carbon removal efficiencies, and thereby alleviated membrane fouling in the C–UF process. Most hydrophobic bases (HoB) and hydrophobic neutral fractions could be removed by coagulation. Similarly, UF was good at removing HoB compared to hydrophilic substances (HiS) and hydrophobic acid (HoA) fractions. HiS and HoA fractions with low molecule weight accumulated on the surface of the membrane, causing the increase of transmembrane pressure (TMP). Membrane fouling was mainly caused by a removable cake layer, and mechanical cleaning was an efficient way to decrease the TMP.

Application of pulsed UV-irradiation and pre-coagulation to control ultrafiltration membrane fouling in the treatment of micro-polluted surface water

A major cause of ultrafiltration (UF) membrane fouling is the accumulation of microorganisms and their associated soluble products. To mitigate fouling the application of pulsed short-wavelength ultraviolet (UVC) light (around 254 nm) within the membrane tank together with pre-coagulation was investigated. In mini-pilot-scale tests carried out in parallel with conventional pre-treatment (CUF), the impact of pulsed UV (CUF-UV) at different UV irradiances and fluxes on the increase of trans-membrane pressure (TMP) was evaluated and explained in terms of the quantity and nature of membrane deposits in the membrane cake layer and pores.The results indicated that at a flux of 20 L m−2 h−1, the pulsed UV (1 min within 31 min cycle) at 3.17 × 10−2 W/cm2 prevented any measureable increase in TMP over a period of 32 days, while there was a fourfold increase in TMP for the conventional pre-treatment. For the CUF-UV system the concentration of bacteria and soluble microbial products was much less than the conventional CUF system, and the cake layer was thinner and contained less biopolymers (proteins and polysaccharides). In addition, the pores of the CUF-UV membrane appeared to have less organic deposits, and particularly fractions with a high molecular weight (>10 kDa).At a lower UV irradiance (1.08 × 10−2 W/cm2), or higher flux (40 L m−2 h−1) with the same UV irradiance, there was a measurable increase in TMP, indicating some fouling of the CUF-UV membrane, but the rate of TMP development was significantly lower (∼50%) than the conventional CUF membrane system. Overall, the results show the potential advantages of applying intermittent (pulsed) UVC irradiation with coagulation to control UF membrane fouling.

Influence of filtration velocity on DON variation in BAF for micropolluted surface water treatment.

Biological aerated filters (BAFs) are widely used for the treatment of micropolluted surface water. However, the biological process produces dissolved organic nitrogen (DON), which, as precursors of nitrogenous disinfection by-products, pose potential threats to drinking water safety. Therefore, to control DON in BAF effluent, it is necessary to study the influence of BAF operation parameters on DON production. In this study, the influence of filtration velocity in a BAF on DON production was investigated. Under different filtration velocity (0.5, 2, and 4m/h) conditions, profiles of DON concentrations along the media layer were measured. The profile at a filtration velocity of 0.5m/h showed a decreasing trend, and the ones under filtration velocities of 2 and 4m/h fluctuated in a small range (from 0.1 to 0.4mg/L). Moreover, the relatively high filtration velocities of 2 and 4m/h resulted in a lower level of DON concentration. Additionally, 3D excitation-emission matrix fluorescence spectroscopy was used to characterize DON. It is found that the patterns of DON at a relatively high filtration velocity condition (4m/h) were obviously different from the ones under low filtration velocity conditions (0.5 and 2m/h).

Using magnetic powder to enhance coagulation membrane filtration for treating micro-polluted surface water

The magnetic enhanced coagulation membrane filtration (MECMF) process was introduced into micro-polluted surface water treatment. The process was conducted by adding magnetic powder (MP) for enhancing coagulation. By contrasting the water quality parameters including dissolved organic carbon (DOC), UV254 and turbidity of permeates of MECMF and coagulation/flocculation membrane filtration (CFMF), results showed that the removal efficiency in the MECMF process was higher than those in the CFMF process. According to normalized flux and resistance analysis, membrane flux declined relatively slow and irreversible fouling resistance was lesser in the MECMF process. By analyzing the three-dimensional fluorescence of permeates and raw water, it was clearly shown that the permeate quality of the MECMF process was superior to that of the CFMF process apparently, which highlighted the removal of protein-like substances was more effectively in MECMF. Furthermore, the addition of MP could provide Lorentz and magnetic dipole forces between colloidal matters during coagulation, leading to the increase of collision frequency and efficiency and the formation of large size flocs with high fractal dimension. Large and high fractal dimension flocs could form a porous cake layer, which could increase water permeability. On the basic of the above findings, it was suggested that magnetic-enhanced coagulation that promoted flocs to develop could regulate cake layer structure and mitigate membrane fouling to some extent.

Micro-polluted surface water treatment and trace-organics removal pathway in a PAC-MBR system

Trace-organic contaminants elimination effectiveness and their removal pathways in a powder-activated carbon-membrane bioreactor (PAC-MBR) used for micro-polluted surface water treatment were investigated in this study. The results showed that PAC-MBR was capable of consolidating DOM elimination, enhancing trace-organic contaminants (2,4,6-trichlorophenol, nitrobenzene and trichloroethylene) removal efficiency, improving permeate biostability, and decreasing bulk organic content and specific fractional components, which was beneficial for membrane fouling mitigation. By series of well-designed batch-tests and estimation, trace-organics removal pathways were analyzed. The primary way of TCE removal was aeration volatilization, while that of NB and 2,4,6-TCP elimination was biodegradation which was greatly affected by biomass content within bulk. PAC addition was a positive way for effective trace-organics removal by increasing mixed solid adsorption capability, especially in start-up phase, and offering beneficial circumstances for biomass enrichment and functional bacteria accumulation. Thus, PAC addition into MBR is a simple and effective strategy to treat micro-polluted water resources.

Powdered activated carbon – membrane bioreactor operated under intermittent aeration and short sludge retention times for micro-polluted surface water treatment

Long sludge retention time (SRT) and continuous aeration are generally adopted in powdered activated carbon – membrane bioreactor (PAC-MBR) process for micro-polluted surface water treatment. However, in this study, the performance of a pilot-scale PAC-MBR under intermittent aeration and short SRTs (2, 4, 6, and 8 d) was investigated. The settling characteristics of sludge and the decay of dissolved oxygen (DO) concentration in the mixed liquor were examined. The results showed that intermittent aeration with proper aeration intervals barely reduced the removal efficiency of pollutants, due to the low DO consumption in the bioreactor and the low settling velocity of the sludge (mostly at the range of 0.04–0.08 m min−1). High concentration ammonia (∼3 mg L−1) could be effectively removed even at a fairly short SRT (6 d). As the SRT increased, the removal efficiencies of organic matter and ammonia increased, but the membrane fouling aggravated correspondingly. The successful adoption of intermittent aeration and short SRTs in the pilot-scale PAC-MBR implied that the results could be extrapolated to full-scale applications to reduce operating costs and alleviate membrane fouling.

Effect of PAC dosage in a pilot-scale PAC–MBR treating micro-polluted surface water

To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2g/L performed the best among 0, 1, 2 and 3g/L PAC-MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1g/L PAC-MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC system. The accumulation of organic matter in the bulk mixture of 3g/L PAC-MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2g/L PAC-MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21 days operation.

Treatment of Micro-Polluted Surface Water by Ballasted Flocculation and its Floc Structural Characteristics

In current paper, compared to the conventional coagulation, micro-sand (MS) and magnetic powder (MP) ballasted flocculation were investigated during the treatment of micro-polluted surface water by simulating ActifloTM and SiroflocTM process. Under an optimized operation condition, the optimal turbidity, CODMnand TP removal, 94.5%, 75.1% and 93.0%, respectively could be achieved by the MP process. In further research, pollutants removal efficiency at various settling time (5, 10, 15, 20 min), flocs two-dimensional fractal dimension and average size were simultaneously studied and the relationship among them was also discussed.

Pollutant removal mechanisms in a bio-diatomite dynamic membrane reactor for micro-polluted surface water purification

The bio-diatomite dynamic membrane (BDDM) reactor is an emerging micro-polluted surface water treatment technology that combines diatomite (the microorganism carrier) and a stainless steel mesh (the dynamic membrane support module). A constant water head of 20cm was designed to drive the BDDM filtration. The BDDM with sintered diatomite had good water penetration capacity, a filtration flux as high as 92L/m2h after a filtration time of 15,780min, and an effluent turbidity in the range of 0.15 NTU–0.20 NTU. The BDDM reactor effectively removed organic matter and ammonium nitrogen. The diatomite adsorption and the BDDM interception did not have high pollutant removal efficiencies. The dehydrogenase activity (DHA) of the bio-diatomite was in the range of 2.27–3.20(mg TF)/(gVSS)h, indicating good microorganism activity for organic matter removal. The PCR-DGGE analysis showed that the microbial community was very abundant. Bacteroidetes, Firmicutes, Proteobacteria (e.g. α-, β-, γ-proteobacteria), Verrucomicrobia, and Nitrospirae were dominant in the bio-diatomite mixed liquor and removed organic matter and ammonium nitrogen. The microbial degradation of pollutants by the bio-diatomite mixed liquor was primarily responsible for the pollutant removal in the BDDM reactor.

Treatment of Micro-Polluted Surface Water by the Nanomaterials Modified PVDF Ultrafiltration Membrane

The PVDF ultrafiltration membrane was modified by step in situ polymerization coupled with TiO2-PANI membrane surface modifying. It has been prepared by different oxidants, such as ammonium persulfate (APS) and ferric chloride (FeCl3). Meanwhile, application of the modified PVDF ultrafiltration membrane on treating micro-polluted surface water was studied. Turbidity removal efficiency, organic compounds and ammonia nitrogen (NH3-N) were mainly concerned. The results show that the modified PVDF UF membranes can remove 95% turbidity, UV254higher than 50% which was increased greater than the original film. When FeCl3was taken as oxidant with 0.03mol/L, less by-product, NH4+, was generated than APS. Thus, the ammonia nitrogen removal rate is as high as 85.2% and is 20% more than the original film.

Bio-diatomite dynamic membrane reactor for micro-polluted surface water treatment

This work investigated the feasibility of treating micro-polluted surface water for drinking water production with a bio-diatomite dynamic membrane reactor (BDDMR) at lab-scale in continuous-flow mode. Results indicate that the BDDMR was effective in removing COD Mn, DOC, UV 254, NH 3-N and trihalomethanes' formation potential (THMFP) at a hydraulic retention time (HRT) of 3.5 h due to its high concentrations of mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS). The removal of pollutants was mainly ascribed to microbial degradation in BDDMR because the dynamic membrane alone was much less effective in pollutant removal. Though the diatomite particles (5–20 μm) were much smaller in size than the aperture of the stainless steel support mesh (74 μm), microorganisms and their extracellular polymer substances could bind these particles tightly to form bio-diatomite particles which were completely retained by the support mesh. The analysis of molecular weight (MW) distribution by gel permeation chromatography (GPC) shows that the BDDMR could effectively remove the hydrophilic fraction of dissolved organic materials present in the raw water.