In‐line Flocculation‐Submersed MF/UF Membrane Hybrid System in Tertiary Wastewater Treatment

Abstract

Coagulation/flocculation pre‐treatment of feeds can successfully mitigate the drawbacks of membrane micro‐ and ultra filtration processes: fouling and limited ability to remove organic pollutants. Laboratory experiments conducted with a synthetic wastewater (representing biologically treated secondary effluent) using 0.1 µm pore size hollow fiber membrane showed that simple in‐line flocculation pre‐treatment with inorganic coagulants dramatically reduced membrane fouling rates. The hybrid system also ensured over 70% organic matter removal in terms of dissolved organic carbon (DOC). In the experiments in in‐line flocculation outperformed clarification pre‐treatment at optimum coagulant dosages. Differences in floc characteristics and elevated suspended solids concentrations in the membrane tank may explain this finding, but the exact causes were not investigated in this study. The beneficial effects of in‐line flocculation pre‐treatment to MF/UF separation were also confirmed in the treatment of septic tank effluent in a membrane bioreactor (MBR). The fouling rate of the 0.4 µm pore size (flat‐sheet) membrane was substantially reduced with 10–100 mg L^?1 ferric chloride coagulant doses, and total dissolved chemical oxygen demand (DCOD) removal also increased from 66% up to 93%. These findings are consistent with the results of other experimental studies and show that pre‐treatment controls submersed MF/UF filtration performance.     

Integration of immersed membrane ultrafiltration with the reuse of PAC and alum sludge (RPAS) process for drinking water treatment

Effects of PAC and alum sludge generated from water treatment process on the effluent quality and fouling of immersed UF membrane were systematically investigated with representative source of natural water and the efficiency of coagulation, PAC adsorption and RPAS to treat natural surface water prior to UF were compared. It was found that the average turbidity removal by RPAS could reach up to 80.2%, and the turbidity removal of immersed membrane UF was independent of the influent, which could be kept at 99%. Particulates were reduced after being pre-treated by different processes, and particles with sizes ranging from 0.5 to 3.5 μm and larger than 13.5 μm were effectively removed by RPAS. UF coupled with RPAS pre-treatment got the best removal for DOM compared to other processes with average DOC and UV₂₅₄ removal 54.1% and 47.2% due to the high removal in the influent of UF. The residual alum content in the effluent of RPAS with UF was less than coagulation and bacteria were almost all removed by membrane. The membrane-fouling was mitigated by pre-treatment processes at different degrees, TMP of UF coupled with RPAS process was relatively stable in 15 d of run, the adsorption of PAC and large number of Al(OH)₃ complexes and precipitates for the foulant molecules might be an important mechanism.     

Integration of immersed membrane ultrafiltration with coagulation and activated carbon adsorption for advanced treatment of municipal wastewater

A pilot-scale hollow-fiber ultrafiltration unit was installed in the wastewater treatment plant of Rethymno, Crete, Greece. The system was fed with treated unchlorinated effluent. Three sets of experiments were conducted. At first, the UF pilot unit was operated as a direct filtration unit. During the second phase, ultrafiltration was combined with the addition of a coagulant (alum). The last phase of the experiments involved the addition of activated carbon (either powdered or granular) into the system. During direct filtration, the average COD removal was 19%, while the average DOC was removed to a similar extent (25%). Effluent turbidity was practically independent of the influent turbidity with an overall average removal of 90%. Faecal and total coliform were also removed efficiently reaching average removals of 99.94% and 99.96%, respectively. Removal of heavy metals in particulate form also took place. When ultrafiltration was combined with in-line coagulation, the results were similar to those exhibited without coagulation. Combining ultrafiltration with powdered activated carbon resulted in DOC removal as high as 60%. However, after the addition of the PAC, the transmembrane pressure increased rapidly due to the formation of PAC cake on the membrane surface. Application of granular activated carbon resulted in 36% reduction of DOC without causing an increase to the trans-membrane pressure. Heavy metals present in the secondary effluent were also removed very efficiently by the GAC in the UF tank.     

Optimizing the coagulant dose to control membrane fouling in combined coagulation/ultrafiltration systems for textile wastewater reclamation

Optimal coagulation conditions need to be re-examined when coagulation is coupled to membrane filtration for wastewater treatment. This work focused on the optimization of coagulant dosing in order to control membrane fouling in ultrafiltration (UF), following coagulation for the reclamation of textile wastewater. The effects of pore size and coagulant types and dosages on flux decline were investigated using a stirred-cell UF unit. The flux was greatly enhanced for the UF membrane when a coagulant was added, whereas for the microfiltration (MF) membrane the flux decreased. This could be attributed to changes in the size of coagulated particles and their interaction with membrane pores. At a low dosage (e.g., 0.0371 mM as Al), the polyaluminum chloride (PACl) coagulant was found to control the flux decline most effectively for low ionic-strength wastewater. The optimal dose minimized the fouling and cake layer resistances, although it was sharp and dependent on influent composition. The cake layer protected the membrane from fouling, but it provided additional resistance to permeation. Analyses of turbidity, particle size, and membrane surface exhibited the characteristics of coagulated particles and their cake structures that are closely associated with flux behavior.     

MBR module design and operation

Membrane Bioreactor (MBR) technology is widely accepted today for wastewater treatment providing superior effluent quality, opportunities for water reuse, smaller footprint, and better process control. In the following paper, the development and application of hollow fibre submerged membrane modules in Membrane Bioreactors will be discussed. Early MBR systems used tubular cross flow micro-filtration (MF) or ultra-filtration (UF) membrane modules but the huge energy demand for cross flow technology limited it to heavily polluted niche applications. In the late 80’s the development of submerged membrane technology reduced the energy consumption by using aeration to induce a cross flow and withdrawing purified water by slight vacuum allowing the adoption of MBR technology to more conventional applications. Based upon the m² of membrane area sold/used worldwide, hollow fibre membrane technology is today the most successful submerged MBR technology.     

Optimization of PACl dose to reduce RO cleaning in an IMS

In order to ensure stable treated water quality and to reduce chemical costs in any treatment plant it is necessary to study and optimize the coagulant dosing control (CDC). This research focused on the affects of coagulant in the integrated membrane (UF & RO) system employed for industrial water production. The dose of coagulant (PACl) might be associated (partly) with the frequency of cleaning in the RO units, and a value of 20 abs/m in the UF permeate is the control of the dosage process. This could suggest that organic fouling is directly and indirectly (inducing biofouling as well) the cause of fouling of the RO membranes. Nevertheless, high doses of PACl could produce scaling of aluminium and, in this work minimizing PACl to prevent operational problems in RO membranes was focused.

The approach involved the study of the treatment processes, determination of the optimum dose of coagulant, evaluation of the removal efficiency of UV and DOC by coagulation. The available data, which comprised monthly/weekly measurements for a period of six years of operation, was studied and analyzed and an attempt was made to draw some conclusions for the plant regarding the coagulant dosage and the link with UV absorbance as control.

The study of the coagulant dosing control revealed that the use of simple and robust online sensors like UV measurement allows an automatic dosing control although this parameter is not found to be sufficient to fully characterize nor predict fouling during membrane operation and there is no link between UV after the UF and the cleaning frequency of the RO. Parameters, as the added value allowed to verify the doses efficiencies in UV and DOC removal. Coagulant dose depends on the level of UV absorbance in the UF permeate and it should never be higher than 20 abs/m to ensure a RO cleaning frequency as long as possible. However, it was found that the target value of 20 abs/m produced substantial over dose of coagulant — 90% of the time – when UV removal is considered only. In the same way, for coagulant doses in excess of 5 mg/L, the additional removal of UV is less than 2.5% per mg coagulant/L, which suggests that the current dose is on the high side.

Furthermore, a coagulant dose in excess of 5 mg/L did not produce significant additional UV removal, and thus a reduction from 14 mg/L (2005 dose) to ca. 7 mg/L could be considered.     

Application of hybrid coagulation–microfiltration process for treatment of membrane backwash water from waterworks

A coagulation–microfiltration (MF) system was studied to treat the discharged membrane backwash water (MBW) to meet the drinking water quality requirements. The values of dissolved organic carbon (DOC) and trihalomethanes formation potential (THMFP) in MBW were higher than those in Luan River water (LRW, the raw water for a pilot-scale membrane plant, which produced MBW used in this study), and organic matter enriched in MBW distributed mainly in molecular weight (MW) > 10k Da. When 15 mg FeCl₃/L and 15 mg/L powdered activated carbon (PAC) were added into the system, the average concentration of DOC was reduced from 5.731 mg/L in MBW to 3.377 mg/L in the treated water, and the average UV₂₅₄ was reduced from 0.047 to 0.030 cm⁻¹. The removal of organic matter was main in the range of MW > 30k Da. Efficient organic removal by the hybrid coagulation–MF system resulted in significant reduction of THMFP in the treated water. Concentrations of trihalomethanes, turbidity, bacteria and coliforms in the treated water were below the limit value of the drinking water standards. The results show that the treated water from MBW is with satisfactory organic and microbiological quality.     

Spheroidization of low-cost alumina powders for the preparation of high-flux flat-sheet ceramic membranes

Two kinds of low-cost alumina powders with irregular morphology were pretreated by spheroidization and the two spherical powders were used to prepare high-flux flat-sheet support and microfiltration (MF) membrane with high separation accuracy, respectively. It was found that the spheroidization pretreatment not only unified the morphology of alumina powder particles into spherical shape, but also narrowed the particle size distribution of the powders, which both were conducive to optimizing the performance of the as-prepared ceramic membranes. After sintering at 1350 °C, the open porosity, bending strength, average pore diameter and pure water permeability of alumina flat-sheet support from spheroidized alumina coarse powder were 44.3%, 36.3 MPa, 3.3 μm and 3240 L/h m² bar, respectively. The slurry derived from spheroidized alumina fine powder was dip-coated on the flat-sheet support to prepare MF membrane. The crack-free MF membrane with a thickness of 23.5 μm had a pore diameter of 0.12 μm and pure water permeability of 850 L/h m² bar. Additionally, the elaborated MF membrane was used to clarify aqueous suspension of carbon black with the maximum rejection rate of up to 99.7%, exhibiting excellent cleaning performance at the same time by completely restore the virgin permeate flux after backwash.     

混凝+UF作为RO进水前处理的适用性研究

本文采用混凝＋UF作为RO进水的前处理,以颖河河水为原水进行了中试实验研究,考察了混凝剂投加量、曝气量、不同抽滤时间对超滤系统的影响.结果表明：混凝剂（PAC）投加量为14mg/L,曝气量为7.08L/s时,超滤对原水浊度的平均去除率为99.2%,出水SDI平均值为1.26,完全达到反渗透进水的水质要求,且水质稳定,混凝和超滤膜联用作为RO前处理是完全适用的.     

混凝_MBR工艺处理印染废水试验研究

本试验采用混凝沉淀_MBR工艺对印染废水进行处理。试验研究表明:混凝后COD的去除率达到80%以上,BOD5的去除率达到55%以上,色度的去除率达到84%以上;再经MBR处理,出水COD低于30mg/L,BOD5低于10mg/L,色度低于30度,达到了回用水的标准。     

Optimization of flocculation conditions for the separation of TiO2 particles in coagulation-photocatalysis hybrid water treatment

TiO₂ mediated photocatalysis can decompose organic micropollutants (e.g., 1,4-dioxane) in water, but the removal of used TiO₂ particles is challenging. Although retrofitting enhances the particle separation efficiency, optimizing a coagulation/flocculation process should be most suitable for existing treatment plants. Therefore, the present study investigated the separation characteristics of TiO₂ particles added to drinking water treatment processes along with a polyaluminum coagulant. TiO₂ photocatalysts were able to achieve significant degradation of 1,4-dioxane (∼100% within 50 min) as well as dissolved organic matter (∼75% within 150 min) at a TiO₂ dose of 1.0 g/L under UV irradiation. Although the TiO₂ particle separation efficiency was sensitive to G values, maximal removal occurred at a G value of <34 s⁻¹ with a coagulant concentration of >8 mg/L as Al₂O₃. Sand filters had the capability to remove residual turbid materials and thus, the turbidity of the final product water dropped to as low as 0.1 NTU when the coagulation/flocculation process was preceded. The final effluent quality was comparable to that of a 0.45-μm membrane filter. The post separation of the TiO₂ photocatalysts dispersed for emergency water treatment to degrade 1,4-dixoane was successfully achieved with an optimal coagulant dose, proper flocculation, and sand filtration.     

Embedded nanoFeCu for sewage treatment: Laboratory-scale and pilot studies

Bimetallic nanoparticles have been widely studied for wastewater treatment, but the study of nanoFeCu for sewage treatment is minimal. In the previous work, ammonia was removed by nanoFeCu via an oxidation reaction, and nitrogen gas was released. However, the performance and reusability of nanoFeCu in treating industrial wastewater have not been reported elsewhere. This study revealed the performance of nanoFeCu for sewage treatment on both laboratory-scale and pilot-scale for the first time. A varied mass of embedded nanoFeCu (eFeCu4) was exposed to sewage water, and the quality of the effluent was measured in terms of ammonia, biological oxygen demand (BOD), and chemical oxygen demand (COD) removal. Fe²⁺ and Cu²⁺ concentrations were measured to determine the stability of eFeCu4 in nine reuse cycles. Results showed that the laboratory-scale experiment removed 20%–30% ammonia from sewage. A similar removal rate was reported in all nine cycles of reuse, which confirmed the usability and reliability of eFeCu4. In the pilot-scale study, ammonia was removed from ~22.3 to ~4.8 mg/L, while BOD and COD were reduced from ~204 to ~56 mg/L and ~71 to ~39.7 mg/L, respectively. The treated effluent quality complies with the effluent discharge standard of Malaysia, and it is also comparable with the effluent quality at sewage treatment plants in Malaysia and overseas. In conclusion, nanoFeCu could be an alternative method for sewage treatment due to its stability and pollutant removal performance. A sustainability and cost-effectiveness study should be conducted to determine the feasibility of a full-scale application.     

An advanced treatment of high-strength opium alkaloid processing industry wastewaters with membrane technology: pretreatment, fouling and retention characteristics of membranes

This paper presents the results of the laboratory and pilot-scale membrane experiments of opium alkaloid processing industry effluents. Different types of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for membrane fouling, permeate flux and their suitability in separating COD, color and conductivity. Experiments demonstrated that membrane treatment is a very promising advanced treatment option for pollution control for opium alkaloid processing industry effluents. Almost complete color removal was achieved with NF and RO membranes. COD and conductivity removals were also greater than 95% and met the current local standards. Nevertheless, pretreatment was an important factor for the NF and RO membrane applications. Membrane fouling occurred with direct NF membrane applications without UF pretreatment. The total estimated cost of the UF and NF treatment system was calculated as $0.96/m³, excluding the concentrate disposal cost.     

Application of hybrid photocatalysis systems coupled with flocculation and adsorption to biologically treated sewage effluent for organic removal

The application of a photocatalysis hybrid system coupled with flocculation and adsorption in treating biologically treated sewage effluent (BTSE) was investigated. The removal of organic matter was studied in terms of dissolved organic matter (DOC), removal of hydrophobic (HP), transphilic (TP) and hydrophilic (HL) fractions, and molecular weight (MW) distribution. The photooxidation removed the majority of MW (263, 580, 865, and 43109 daltons) within the first 30 minutes of operation. The removal of MW range of organic matter of 330 daltons was low. DOC removal of HP and TP was high (80%). DOC removal from HL fraction was, however, minimum. The photocatalytic system with simultaneous PAC adsorption and FeCl₃ flocculation removed the effluent organic matter (EfOM) up to 90%. Therefore, photocatalysis with the ferric chloride (FeCl₃) flocculation and PAC adsorption hybrid system can be a possible option in the removal of DOC from BTSE for water reuse.     

Feasibility investigation of refinery wastewater treatment by combination of PACs and coagulant with ultrafiltration

This laboratory scale study investigated the effectiveness of ultrafiltration (UF) technology for treatment of refinery wastewater using powdered activated carbons (PACs) and coagulant. Flux decline, removal rates of total organic compounds (TOCs) and the possibilities of membrane cleaning during intermittent backwashing were studied. Addition of two kinds of typical PACs, PACs-1 and PACs-2, showed that the UF unit performance by adding PACs-2 was better than that of PACs-1. Suitable amounts were 20 mg.L⁻¹. When different kinds of coagulant, HYM, HY-3, HYC-601 and HCA, were added into the wastewater samples, respectively, it indicated that the HCA system was well resistant to membrane fouling. Investigation also showed that the UF unit performance could be significantly improved by simultaneously adding 15 mg.L⁻¹ of PACs-2 and 0.8 ml.L⁻¹ of HCA into the system. The removal rates of TOCs in the wastewater were over 99%.     

Treatment of textile dye effluents using coagulation–flocculation coupled with membrane processes or adsorption on powdered activated carbon

This study describes the treatment of textile wastewater by various combinations of physicochemical and membrane processes. The basic physicochemical treatment consists in coagulation/flocculation (CF) with different coagulant and flocculant concentrations. The parameters analyzed prior and after treatment are turbidity, chemical oxygen demand (COD) and absorbance (Abs). The optimal process parameters for CF are 5 for pH, 100 mg/l for coagulant (Al₂(SO₄) ₃) of 100 mg/l and 4 mg/l for flocculant. This simple treatment by CF was inefficient concerning COD reduction and dyes deterioration. It was therefore combined with microfiltration (MF) or ultrafiltration (UF) on one hand and adsorption on powdered activated carbon (PAC) on the other. The CF/MF, CF/UF and CF/PAC combinations ensure a COD removal of 37%, 42% and more than 80% respectively and a color reduction of 65%, 74% and 50% respectively.     

Removal of nitrogen from wastewater for reusing to boiler feed-water by an anaerobic/aerobic/membrane bioreactor

The innovative process anaerobic/aerobic/membrane bioreactor (A/O/MBR) was developed to enhance pre-denitrification without the energy consumption of the recirculation pump for reusing wastewater to boiler feed-water. The performance of this bioreactor was investigated. Firstly, the septic tank wastewater with low ratio of COD/TN was disposed by a dynamic membrane bioreactor (DMBR). It was found that, although the high concentration of NO₂⁻–N in the effluent implied the potential ability of DMBR to realize shortcut nitrification and denitrification, the effluent of single DMBR was difficult to reach the criteria of reusing to boiler feed-water. Then, the process A/O/DMBR in disposing the septic tank wastewater was studied. The results indicated that this process not only accomplished the removal of 91.5% COD, 90.3% NH₄⁺–N and 60.2% TN, but also successfully realized pre-denitrification without additional recirculation pump. At last, based on the A/O/DMBR, a pilot plant A/O/MBR was built to dispose the municipal raw sewage. In the stable operation period, the average removal efficiencies for COD, NH₄⁺–N, TP and turbidity reached 90%, 95%, 70% and 99%, respectively. During the tested HRT run of 9.0 h, the effluent of COD, NH₄⁺–N, TP and turbidity was about 10 mg/L, 3 mg/L, below 1 mg/L and 1.2 NTU, respectively, which reached the criteria of the boiler feed-water in China.     

A novel Ni doped BaTiO3/h-BN nanocomposite for visible light assisted enhanced photocatalytic degradation of textile effluent and phytotoxicity evaluation

The objective of this research is to synthesize novel Ni–BaTiO₃/h-BN nanocomposites. XRD, UV–Vis, PL, FT-IR, SEM, TEM, Zeta potential, XPS, BET, EIS, Mott- Schottky and LC-MS analyses were used to analyze the nanocomposite phase structure, band gap, electron-hole recombination rate, vibrational modes, morphology, elemental analysis stability, oxidation state, pore size distribution, and electron distribution. The nanocomposites have an average particle size of 32 nm, as measured using HR-TEM microscopy. The band gap of synthesized h-BN was found to be 3.82 eV, whereas the Ni–BaTiO₃/h-BN binary nanocomposite shifts it to 2.43 eV. The nanocomposite photocatalytic efficiency was used to degrade textile effluent, followed by a phytotoxicity assessment of real textile effluent. Furthermore, the photocatalytic treatment analysis revealed that the 40 mg Ni–BaTiO₃/h-BN catalyst degraded up to 81.4% and 86% against textile effluent and crystal violet (CV) dye within 120 min under visible light, respectively, and the concentrations of numerous Physico-chemical parameters of textile effluent have significantly decreased in deteriorated textile effluent. According to a pot study, the toxicity of the degraded textile effluent was reduced following photocatalytic treatment. To examine the mechanism, the photodegradation effectiveness of the catalyst was investigated utilizing various scavengers. From the scavenger study, it is found that the holes (h⁺) contribute more to the degradation process. In real textile dye wastewater, the Ni–BaTiO₃/h-BN nanocatalyst was proved to be an excellent and low-cost degrading technique.     

Alternative for the Treatment of Leachates Generated in a Landfill of Norte de Santander–Colombia,by Means of the Coupling of a Photocatalytic and Biological Aerobic Process

In the present study, the use of heterogeneous photocatalysis TiO2/UV coupled to an activated sludge reactor was evaluated as an alternative treatment for the leachate coming from a Landfill, located in Cucuta (Colombia). TiO₂ (Degussa P-25) between 100 and 600 mg.L^?1 was used as a catalyst, semi-continuous type reactors for the photocatalysis, a batch for the biological stage, UV light with accumulated energies from 20 to 60 kJ.L^?1 were also used, a constant concentration of H₂O₂ was used as an adjuvant in all tests. The research consisted of four main phases: leachate characterization, biological treatment, optimization of photocatalytic and AOP-biological coupling. For the optimization of the photocatalytic step, an experimental design was carried out through the statistical program Statgraphics Centurion XV of factorial type 3^2 (3 levels 2 variables), modeling the results by means of a response surface, the variables of the pH and the concentration of the catalyst were included, having this as input for the response of interest the percentage (%) of DOC removal. The biological process itself provided a removal of 38 and 24% for COD and DOC, respectively. The AOP-biological coupling provided a removal of 68 and 76% in terms of COD and DOC, respectively. Thus, the coupling significantly improves the overall efficiency of the process by more than 50%, which represents a promising improvement compared to the removal of organic matter for the treatment of the same type of water using only the biological process. The results show a viable alternative for the treatment of leachate because higher removal levels are achieved in residence times, which are considered shorter than the ones in conventional processes.

     

The use of RO to remove emerging micropollutants following CAS/UF or MBR treatment of municipal wastewater

The removal of various organic micropollutants (OMPs), including six antibiotics (ERY, ROX, CLA, SMX, SMZ, and TMP), three pharmaceuticals (ibuprofen, salicylic acid, and diclofenac), one industrial product (BPA), and one hormone (cholesterol), was investigated in two pilot plants treating the same raw sewage of the Tel-Aviv WWTP. The effluent production by CAS-UF was 45 m³/h while that of MBR was 40 L/h. Each system's effluent constituted the feed for its RO, which comprised three RO steps after the CAS/UF and a semi-batch RO system after the MBR. Despite significant molecular differences between the selected OMPs, high removal rates were achieved after the RO stage (> 99% for macrolides, pharmaceuticals, cholesterol, and BPA, 95% for diclofenac, and > 93% removal of sulfonamides). However, low antibiotics concentrations and 28–223 ng/L residuals of ibuprofen, diclofenac, salicylic acid, cholesterol, and BPA in the MBR/RO and CAS-UF/RO permeates showed that although RO is an efficient removal solution, it cannot serve as an absolute barrier to OMPs. Therefore, additional treatment techniques should be considered to be incorporated aside the RO to ensure complete removal of such substances.