A two stage membrane treatment of secondary effluent for unrestricted reuse and sustainable agricultural production

Field experiments are in progress for secondary wastewater upgrading for unrestricted use for irrigation and sustainable agricultural production. The integrative treatment system for the secondary effluent polishing is based on implementing in series of two main treatment stages: ultrafiltration (UF) and reverse osmosis (RO) membrane treatment. The pilot system has the capacity of around 8 m³/h. The UF effluent is used to feed the RO membrane stage. Different mixtures of UF and RO permeates are subsequently applied for drip irrigation of various agriculture crops. The field results indicate the importance of the UF component in the removal of the organic matter and the pathogens that are still contained in the secondary effluent (the secondary effluent is obtained from a waste stabilization pond treatment system). Under specific conditions, when the dissolved solids content is relatively low, the UF effluent can be applied directly for unrestricted irrigation. In the successive RO stage most nutrients are removed, allowing applying the effluent without jeopardizing the soil fertility and the aquifers. Preliminary economic assessment indicates that the extra cost for effluent polishing via the UF stage only is in the range of 8–12 US cents/m³. The extra cost for the RO stage is as well assessed at 8–12 US cents/m³. The additional treatment expenses depend to a large extent on the quality of the incoming raw secondary effluent and local requirements at the command agricultural production sites.     

A comparative study of tertiary wastewater treatment by physico-chemical-UV process and macrofiltration–ultrafiltration technologies

A comparative study was undertaken of the economic costs and quality of effluents obtained from physicochemical-UV and macrofiltration–ultrafiltration as municipal wastewater tertiary treatments. A physicochemical-UV urban wastewater treatment system was designed for the study. Pre-treatment to UV radiation disinfection consisted of coagulation with alumina (100 mg/L), sedimentation by sludge-blanket sedimentation tank (0.8 m³/m² h) and filtration by sand-pressure filter (5.0 m³/m² h). The ultrafiltration module was equipped with flat polyvinylidenefluoride membranes (0.05 μm pore size), with pre-treatment carried out by a sandpressure filter (8.0 m³/m² h). Both systems obtained effluent of excellent physico-chemical quality (91% removal of suspended solids and 99% turbidity removal) and microbiological quality (total absence of nematode eggs, coliforms, E. coli and coliphages). However, while physico-chemical quality remained constant in both systems, microbiological quality of effluent from the UV-disinfection process was shown to depend on the quality of influent, particularly with regard to transmittance. By contrast, microbiological quality remained constant in the case of membrane technology. Other control parameters such as particulate analysis confirmed the higher quality of ultrafiltration effluent in comparison with the physico-chemical-UV process. With regard to costs, both technologies present similar variable costs, while fixed costs of the membrane installation are double those of the physico-chemical-UV process, owing particularly to the high cost of the installation itself.     

Membrane application for recovery and reuse of water from treated tannery wastewater

Secondary treated tannery wastewater contains high concentrations of Total Dissolved Solids (TDS) and other residual organic impurities, which cannot be removed by conventional treatment method. A pilot plant membrane system with a designed processing capacity of 1 m³/h, comprising of nano and reverse osmosis (RO) membrane units, accompanied by several pre-treatment operations, was evaluated in order to further treat and reuse the tannery wastewater. The maximum TD S removal efficiency of the polyamide RO membrane was more than 98%. The permeate recovery of about 78% was achieved. The water recovered from the membrane system, which had very low TDS concentration, was reused for wet finishing process in the tanneries. The reject concentrate obtained from the operation was sent to solar evaporation pans. It was evident from the study that the membrane system can successfully be applied for recovery of water from secondary treated tannery effluent, provided a suitable and effective pretreatment system prior to membrane system is employed. Combining nano and RO membranes improved the life of the membranes and permeate recovery rate.     

Membrane bioreactor with nonwoven fabrics as solid–liquid separation media for wastewater treatment

A nonwoven fabric module was utilized as a solid–liquid separation medium in a membrane bioreactor (MBR) for treating wastewater. The experimental results indicated that nonwoven fabrics had lower filtration resistance than microporous membranes in MBR applications. The optimal aeration intensity was approximately 0.01m³/m² s. The effect of mixed liquor suspended solid concentration on filtration resistance was not significant at an operating flux of under 0.8m³/m² d in the study range. The performance of nonwoven fabrics in a MBR application was further demonstrated in a pilot test. Chemical oxygen demand (COD) and suspended solids (SS) in the effluent were maintained under 60 and 10 mg/L, respectively, whereas influent COD varied from 800 to 1800mg/L. The transmembrane pressure was maintained below 5 kPa at a permeation flux of 0.18m³/m² d. The experimental results demonstrated that nonwoven fabrics maintained stable operation in MBR applications under appropriate operating conditions.     

Evaluation of coagulation and PAC adsorption pretreatments on membrane filtration for a surface water in Korea: A pilot study

Application of membrane filtration has been significantly expanded throughout the world in two decades. A project was launched to facilitate the application of membrane filtration in drinking water plants in Korea in 2004. Five pilot plants each with a capacity of 500 m³/d were installed in a Gueui Drinking Water Plant. The Han River water was a main raw water source for the plants. Key parameters of the raw water were examined. The raw water characteristics are tremendously varied with seasons and rain fall, especially in terms of turbidity and algae numbers. The operation of pretreatment was of substantial importance due to the variation of the raw water. Coagulation and powdered activated carbon adsorption were performed as pretreatment options of microfiltration. The coagulant doses were optimized with increasing turbidity compared to the conventionally used operational manual. PAC adsorption was applied to overcome fouling by high algae numbers. The addition of PAC relieved the aggravation of fouling. However, the PAC addition could not stop the undergoing fouling. A set of laboratory experiments showed that the removal of floc aggregates after coagulation and PAC was critical to maintain high water flux in the membrane system.     

Performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system for the treatment of low‐concentration domestic sewage in south China

The performance of the hydrolyzation film bed and biological aerated filter (HFB–BAF) combined system in pilot scale (with a daily treatment quantity of 600–1300 m³ d^?1), operated for 234 days, for low‐strength domestic sewage was assessed using different amounts of aeration, reflux ratios and hydraulic loading rates (HLR). In steady state it was found that the average removal efficiency of chemical oxygen demand (COD) and biological oxygen demand at 5 days (BOD₅) were 82.0% and 82.2% and the average effluent concentrations were 15.8 mg L^?1 and 9.4 mg L^?1 respectively as the HFB was running at an HLR of 1.25–1.77 m³ m^?2 h^?1 and the BAF was running at an HLR of 1.56–2.21 m³ m^?2 h^?1. In general, the removal efficiency of total nitrogen (TN) fluctuated with the HLR, gas–water ratio and reflux ratio, so the ratio of gas to water should be controlled from 2:1 to 3:1 and the reflux ratio should be as high as possible. The effluent concentration of TN was 10.4 mg L^?1 and the TN removal averaged 34.3% when the gas–water ratio was greater than 3:1 and the reflux ratio was 0.5. The effluent concentration and removal efficiency of NH₄⁺‐N averaged respectively 2.3 mg L^?1 and 78.5%. The overall reduction of total phosphorus (TP) was 30% and the average effluent concentration was 0.95 mg L^?1. The removal efficiency of linear alkylbenzene sulfonates (LAS) reached 83.8% and the average effluent concentration was almost 0.9 mg L^?1. The effluent concentration and removal efficiency of polychlorinated biphenyls (PCBs) were 0.0654 µ g L^?1 and 37.05% respectively when the influent concentration was 0.1039 µ g L^?1. The excess sludge containing water (volume 15 m³) was discharged once every 3 months. The power consumption of aeration was 0.06–0.09 kWh of sewage treated. The results show that the HFB–BAF combined technology is suitable for the treatment of low‐concentration municipal sewage in south China. Copyright © 2005 Society of Chemical Industry     

Sand filtration of wastewater for tertiary treatment and water reuse

The performance of rapid sand filters was evaluated in three tertiary wastewater treatment plants in the State of Kuwait. These plants are located at Ardiya, Rikka and Jahra, and receive municipal wastewater flows of 220,000, 95,000 and 42,000 m³ d⁻¹, respectively. The Ardiya plant uses a two-stage activated sludge process for the secondary treatment of wastewater whereas both the Rikka and Jahra plants use the extended aeration process. Daily records were obtained from each plant over a period of 1 year, and the efficiency of the tertiary sand filters was determined based on reductions in SS, VSS, BOD, and COD. Analysis of these records showed that the secondary-treated effluent quality is highly variable. Seasonal variations were observed due to nitrification and denitrification that enhance the production of nitrogen gas and carry over of sludge solids in the effluent during summer, causing more frequent backwashing of the filters. The data were also statistically analyzed using the ANOVA program. The results obtained indicated significant improvements, at 95% and 99% significance levels, in solids (SS, VSS) and organics (BOD, COD) removal by sand filtration. They also showed that, in addition to improving effluent quality, the tertiary filtration played an important role in the stability of effluent quality so as to dampen variations in the quality of secondary-treated effluent. The tertiary effluent consistently satisfied the water quality requirements for irrigation.     

Possibilities for the use of membrane processes for the pre-treatment of wastewater from the production of dried potato purée

Our research focused on the membrane separation of wastewater resulting from the production of dried potato purée. Our aim was to investigate possibilities for recycling obtained retentate back to the actual production process, and, consequently, for reducing wastewater pollution. This paper describes trials of MF and RO membrane filtration of starch wastewater. The treated water contained starch, in either granulated or gelatinized form, and solids (fine pieces of potato skins). The trials were conducted in either one or two stages. We used a pilot plant equipped with a ceramic membrane with a filtration area of 0.35 m² and pore sizes of 500 and 100 nm. We also tested an organic RO membrane (7410) in the laboratory.High permeate flux above 100 l/(m² h) was measured for the 100 nm membrane, but with considerable fouling. Filtration through this membrane resulted in high COD and BOD₅ rejection (approximately 60%), an effect which was increased by the subsequent RO filtration. The content of soluble carbohydrate, 0.011% in permeate (with 0.44% dry substance), was analyzed using high-performance anion-exchange chromatography coupled with pulsed amperometric detection.     

A combined photocatalytic slurry reactor–immersed membrane module system for advanced wastewater treatment

Photocatalysis with titanium dioxide semiconductor catalyst can effectively degrade recalcitrant organic pollutants present in biologically treated sewage effluents. Focusing on process efficiency and sustainability within a broader program, this study presents results obtained with a bench-scale hybrid treatment system. The process train comprised of a slurry (suspension) type continuous photocatalytic (CP) system and an immersed hollow fibre membrane micro-ultrafilter (MF/UF) unit. The CP reactor charged with 1 g/L P-25 catalyst removed 63% dissolved organic carbon (DOC) from a synthetic wastewater (representing biologically treated sewage effluent). The addition of 0.05 g/L of powdered activated carbon (PAC) increased DOC removal up to 76%. The start-up times to achieve 60% DOC removal were 31 min and 15 min, respectively. These results show a 16 times improvement in volumetric load over a comparable batch reactor system used in previous studies by our group.Slurry type photocatalytic reactors need subsequent particle separation to retain the catalyst in the system and allow the discharge of treated effluent. The immersed membrane module accomplished this without prior slurry settling step. Membrane feed pre-treatment with pH adjustment and particle charge neutralisation with aluminium chloride coagulant led to improved critical membrane fluxes, 15.25 L/m² h and 19.05 L/m² h, respectively. In each experiment MF/UF produced near zero turbidity permeate, completely retained the photocatalyst, and flocculation also improved the efficiency of DOC removal. Membrane fouling was controlled by particle aggregation rather than feed DOC levels, but the latter had significant impact on coagulant demand. The complete treatment train achieved up to 92% DOC reduction with 12 mg/L AlCl₃ dosage using in-line coagulation conditions. The results show that in-line coagulation offers a simple yet effective means to improve the performance of slurry type photocatalytic–MF/UF hybrid systems for advanced water and wastewater treatment applications.     

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.     

市政污水厂出水回用电厂循环水系统工艺研究

采用曝气生物滤池+高效混凝沉淀组合工艺对河北邢台某污水处理厂的二级出水进行了回用中试研究.研究表明:二级出水经组合工艺处理后,CODCr的平均去除率为63.4%-69.2%,浊度的平均去除率为91.8%-95.4%,氨氮的平均去除率为90.5%-95.9%,处理出水可以满足电厂循环冷却水水质要求.     

Application of microfiltration systems coupled with powdered activated carbon to river water treatment

A bench scale submerged microfiltration system coupled with high concentration of PAC (powdered activated carbon) was applied in order to purify a river water containing secondary effluent. The system was operated with four different modes: Run-1, -2, -3 and -4. The PAC concentration was set at 0, 4 and 40 g/L with same filtration rate of 1.0 m/d (42 L/m²/h) which correspond to Run-1, -2 and -3. In Run-4, the filtration rate was set at 0.5 m/d (21 L/m²/h) with PAC concentration of 40 g/L. The effluent turbidity showed below 0.1 NTU for all runs, and the removal rates more than 90% were observed. As for TOC removal, almost no removal of TOC was observed in Run-1 while the higher removal rates were obtained with the higher dosage of powdered activated carbon. Run-3 and 4 with PAC dose of 40 g/L showed the removal of 85% regardless of the filtration rates. Removal of UV254 was similar to that of TOC: removal of 13% at Run-1 and 90% at Run-3 and -4. As for the filtration efficiency, an average filtration time for TMP to reach 60 kPa was checked for each runs. The filtration time of around 5 days was observed in Run-1 and Run-2, 2 days in Run-3 and 60 days in Run-4. According to the results, the effluent water quality got better with higher dose of PAC and the filtration efficiency was enhanced with higher dose of PAC and lower filtration time.     

Coagulation pretreatment for a large-scale ultrafiltration process treating water from the Taihu River

A large-scale ultrafiltration (UF) system integrated with coagulation was applied to produce drinking water from the highly turbid Taihu River. This UF installation could produce 10,000 m³ drinking water per day. In this study, the effect of FeCl₃ coagulant on the performance of the UF system was evaluated. Results showed that with the integration of coagulation, not only qualified drinking water was obtained from the high turbidity raw water, but also high UF specific flux was maintained, ca.190 200 L/m²·hr·bar, and the chemical cleaning period was largely prolonged. The natural organic matter removal mechanism by coagulation was also discussed.     

不同预处理方式对超滤膜深度处理印染废水效能影响的研究

以印染废水处理站的二级出水为原水,考察了不同预处理方式(砂滤、微絮凝、微絮凝直接过滤)对超滤膜性能及其去除印染废水中污染物的影响。结果表明,砂滤随着运行时间的延长造成膜的不可逆污染,微絮凝可缓解膜污染,微絮凝直接过滤对膜污染在微絮凝基础上有所改善;不同预处理方式均能保证出水浊度小于0.1NTU;微絮凝直接过滤预处理工艺对CODCr去除率接近70%,微絮凝直接过滤处理方法能有效缓解膜污染,对浊度和有机物的去除效果较好,是较有优势的预处理工艺。     

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.     

Pilot study for reclamation of secondary treated sewage effluent

A pilot study for reclamation of secondary treated sewage effluent in Singapore was conducted using a MF/RO system with the capacity of 20 m³/d. A 0.1 μm MF membrane from Asahi and RE-4040-FL RO membrane from Saehan were used in this study. The pilot plant consists of six spiral-wound RO elements. The RO train was configured in single stage. The pilot plant was designed with automatic control system and it was operated continuously (24 h) during the study. Trial runs on various flux rates of the RO membrane at different operating pressures were conducted over 3 months. The pilot results showed that the optimal operation flux rate of the RO membrane ranged from 10 to 15 gal/f²/d (GFD) for this application. The normalized flux after CIP was 97% of the initial one. At a flux rate of 10 GFD and water recovery of 50%, the average operating pressure of 57 psi was noted corresponding to a high normalized flux of 38 L m⁻² h⁻¹ MPa⁻¹ at 25°C. Rejections of the RO membrane in terms of conductivity, TOC, ammonium and nitrate were higher than 96%,97%,90% and 85%, respectively. It was concluded that the RO permeate quality in terms of conductivity, turbidity, TOC, ammonium, nitrate, hardness, total bacteria and total coliform matched the quality of high-grade water (NEWater) for use in the electronics industry.     

A study on submerged rotating MBR for wastewater treatment and membrane cleaning

A submerged rotating membrane bioreactor (SRMBR), with a rotatable, rounded, flat-sheet Poly(vinyldiene fluoride) (PVDF) membrane module fixed on hollow axes and moved by an electromotor, was used for wastewater reclamation. It was found that the effluent COD became stable and lower than 20 mg/L after one day running. The equilibrium permeate flux increased from 42.5 to 47.5 L/m²·h with the rotation speed increasing from 15 r/min to 25 r/min. Prolonging relaxation time could alleviate membrane fouling and enhance the flux. Finally, membrane cleaning was studied. The results showed that flushing the membrane surface with water, water/NaOH and water/NaOH/HCl recovered permeate flux to 48.4%, 83.5% and 90.2% of that of the initial operation, respectively.     

Studies on internal and external water treatment at a paper and cardboard factory

The treatment of effluent from a paper/board factory that produced 280 tons of cardboard and consumed 1200 m³ of water per day was carried out. Wastewater analysis showed that the mill effluent contained 3000 mg dm^?3 suspended solids, 1400 mg dm^?3 COD (chemical oxygen demand) and 500 mg dm^?3 BOD (biochemical oxygen demand). An internal treatment cycle is suggested that involves recirculation of paper‐machine wastewater (white‐water) and may be accomplished by installing a flotation saveall (fiber recovery) unit. This arrangement reduced fresh water use by about 90%, reduced fiber loss by 80–90%, and increased board production by 13%. An external treatment process for the effluent was assessed by conducting laboratory coagulation tests (alum, ferric chloride, ferrous sulfate, and polyelectrolyte) on the whole mill effluent. Oxidation of the mill effluent using calcium hypochlorite before discharging the effluent to a lagoon offers the benefits of killing the harmful bacteria and reducing the pollution load. Copyright © 2003 Society of Chemical Industry     

Effect of an electro phosphorous removal process on phosphorous removal and membrane permeability in a pilot-scale MBR

The pilot membrane bioreactor (MBR) was equipped with an electro-coagulation process for phosphorous removal (EPR process). The effect of the EPR process on nutrient removal and membrane permeability was investigated in this study.Experiments were carried out for about 5 months with the pilot MBR that treated wastewater at a capacity of 50 m³/day. And the MBR used two different materials of the plate type membrane: polyvinylidene fluoride (PVDF) and polyethersulfone (PES). Phosphorous ion released from the anaerobic settling tank was coagulated by electrochemical reaction with aluminum ion discharged from aluminum plate electrodes in the EPR tank. The phosphate (PO₄³⁻-P) removal efficiency and the total phosphorous (TP) removal efficiency by electro-coagulation were 89.2% and 79.9%, respectively. Results of particle size distribution (PSD) analysis showed that the particle sizes of flocs were mostly in the range of 50-150 μm, and the membrane resistance decreased significantly in the MBR as the EPR proceeded. Consequently, this study showed that the EPR process was useful for reducing trans-membrane pressure (TMP) and for removal of phosphorous in the MBR, which was operated in long sludge retention time (SRT) conditions.     

固定化生物活性炭纤维处理餐饮污水

采用固定化生物活性炭纤维技术处理餐饮污水,在原水COD、油的平均质量浓度分别为961、254 mg/L时,经过砂滤、曝气、生物活性炭纤维柱后,COD去除率为84%,油的去除率为91%。试验结果表明:固定化生物活性炭纤维技术对餐饮废水有较好的处理效果,出水水质稳定,可达标排放。