Performances of RO and NF processes for wastewater reuse: Tertiary treatment after a conventional activated sludge or a membrane bioreactor

Wastewater reclamation requires processes and technologies having the ability to reduce the presence of micropollutants which are not wholly treated in conventional WWTP. Due to the complexity of membrane-solute interactions and the diversity of secondary treatment effluent (STE) matrices, deeper investigations are required to identify the major foulant species and more specifically their behaviour at high concentration in real waters. This study investigates the rejection and fouling potential of nanofiltration (NF) and low-pressure reverse osmosis (RO) membranes with two STEs sampled from i) a conventional activated sludge process coupled with ultrafiltration (CAS-UF) and from ii) a membrane bioreactor MBR (AquaRM^®, SAUR (France)). Whatever the origin of the effluent, RO seems to be the best solution to prevent pollution of tertiary effluents (expected result) but also to obtain low fouling levels. The different composition and molecular weight distribution of MBR and CAS-UF effluents can explain the different fouling behaviours that were observed.     

Application of MBR for hospital wastewater treatment in China

In China, the number of hospitals has increased to 19,712 in 2008, with the production of hospital wastewater reaching 1.29 × 10⁶ m³/d. Membrane bioreactor (MBR) technology presents a more efficient system at removing pathological microorganism compared with existing wastewater treatment systems. In the past 8 yr, over 50 MBR plants have been successfully built for hospital wastewater treatments, with the capacity ranging from 20 to 2000 m³/d. MBR can effectively save disinfectant consumption (chlorine addition can decrease to 1.0 mg/L), shorten the reaction time (approximately 1.5 min, 2.5-5% of conventional wastewater treatment process), and attain a good effect of inactivation of microorganism. Higher disinfection efficacy is achieved in MBR effluents at lower dose of disinfectant with less disinfection by-products (DBPs). Moreover, when capacity of MBR plants increases from 20 to 1000 m³/d, their operating cost decreases sharply.     

A pilot study for reclamation of a combined rinse from a nickel-plating operation using a dual-membrane UF/RO process

A pilot study for reclamation of a combined rinse from a nickel-plating operation was conducted using a dual-membrane UF/RO process. The pilot plant has a product capacity of 1.5 m³/h. The OF unit, as a pre-treatment, was operated at 90% water recovery. The RO unit was operated with a 2:1 configuration in a feed-and-bleed mode with recirculation. Trial runs on various operating pressures and water recoveries were conducted and effect of feed pH on RO permeate quality was studied. Finding a critical pH value was explored to design the feed pH for RO process to treat this particular wastewater. A long-term run for the RO unit with an optimized 75% water recovery was later carried out to study the stability of the product and the fouling tendency of membranes. The cleaning-in-place methods were investigated for both OF and RO units. The pilot plant had successfully operated for 6 months at the time of reporting, consistently producing a high-quality product water (<95 μS/cm) at an overall water recovery of 67.5%. The quality of reclaimed water was better than town water used at the factory. The product water from the pilot plant was used as a substitute for town water for in-process rinsing at the factory with no detrimental effects for 3 months. The study has successfully developed a process for recycling a combined rinse water with conductivity up to 1700 μS/cm. The design data for a full-scale plant were obtained. An economic evaluation shows that a payback within 32 months is feasible at a treatment capacity of 20 m³/h.     

膜生物反应器在水处理中的应用与新发展

综合论述了膜生物反应器的分类、结构、特点，介绍了近年来各国学者应用膜生物反应器去除废水中有机物、氮、磷等污染物所取得的研究成果、面临的问题以及膜生物系统在实际废水处理中的应用。简要阐述了膜污染的成因、机理及其对策，并指出了现阶段限制膜生物技术在我国发展的原因，展望了未来膜生物技术在我国广阔的发展前景。     

水解酸化+A/O+UF+RO处理低浓度印染废水回用工程

嘉兴某印染企业采用"水解酸化+A/O+超滤+反渗透"组合工艺对1 500 m~3/d低浓度印染废水处理装置进行深度处理及回用改造。结果表明:在进水COD、色度和SS均值分别为450 mg/L、80倍和600 mg/L时,RO出水COD、色度和SS分别为15 mg/L、3倍和1 mg/L,系统COD、色度和SS去除率分别达96.7%、96.3%和99.8%。工程总投资489.78万元,运行成本3.53元/m~3。一年来系统回用率稳定在53%左右,年节约用水24万t,年减少支出150万余元。     

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.     

Customization of ZrO2 loose/tight bilayer ultrafiltration membranes by reverse micelles-mediated aqueous sol-gel process for wastewater treatment

Two types of spherical zirconyl oxalate aqueous sols were successfully customized by a reverse micelles-mediated aqueous sol-gel process, and the sols were sequentially spin-coated on porous supports to prepare ZrO₂ loose/tight bilayer ultrafiltration membranes. After three times of spin-coating process, a defect-free ZrO₂ loose ultrafiltration membrane with pure water permeability of 110.5 ± 2.25 L m^?2 h^-1 bar^-1, molecular weight cut-off (MWCO) of 16.5 kDa and excellent rejection of up to 97.5 % for bovine serum albumin was fabricated. Then, the loose ultrafiltration membrane was used as a substrate to prepare ZrO₂ tight ultrafiltration membrane. Performances of tight ultrafiltration membrane regarding to permeability, retention of polyethylene glycol and treatment of dyes wastewater were evaluated. The tight ultrafiltration membrane with a thickness of 200 nm exhibited a pure water permeability of 22.5 ± 0.3 L m^-2 h^-1 bar^-1 and MWCO of 1150 Da. Additionally, the rejections of methyl red and methyl orange by the tight ultrafiltration membrane were both <65 %, while of alizarin red, direct red, bromocresol green and methyl blue achieved maximum values of 98.5 %, 99.2 %, 99.5 % and 99.6 %, respectively. The fouled membranes could restore the virgin performance for reuse by cleaning and low-temperature calcination.     

A/O MBR系统处理印染废水的研究

设计了一套A/O MBR系统处理印染废水,通过四个阶段的连续运行,对其COD、色度、SS、浊度等指标进行监测,确定最佳运行条件为HRT9～10 h,DO2～3 mg/L,在此条件下处理后可使印染废水的COD≤100 mg/L、色度2～16倍、浊度≈0、SS≈0、pH7～8.5.结果表明A/O MBR系统费用低、效果好,其中A/O系统可提高印染废水的可生化性,利于后续MBR的处理,最终使印染废水实现达标排放.