Domestic wastewater reclamation by submerged membrane bioreactor with high concentration powdered activated carbon for stream restoration.

This study focuses on the practical application of high concentration powdered activated carbon coupled membrane bio-reactor to domestic wastewater reclamation. The study was conducted in three parts, such as analysis of secondary domestic wastewater effluent, design and operation parameter evaluation and reclaimed water quality estimation for stream restoration. The organic concentration was 25.2-80.2 mgCOD(Cr)/L for the effluent of three domestic wastewater treatment plants. Around 50-75% of the COD was low molecular substances less than 1,000 which were quite biodegradable. The sawdust PAC was estimated to be proper adsorbent for the organics in the secondary effluents. Its Freundlich constant, K value was 5.847 and 1/n, 0.36. Using a system consists of single reactor with high concentration PAC (80 g/L) and submerged hollow fiber MF membrane module with nominal pore size of 0.1 microm, design and operation parameters were obtained, such as HRT of the bioreactor (2.5 hr), PAC concentration (80 g/L), the initial flux (less than 0.5 m/day) and intermittent suction cycle (12 min. suction and 3 min. idling). Organic removal by the system was high enough to produce reclaimed water for urban stream restoration The effluent organic concentration was at the level of 2 mg/L in terms of TOC (around 5 mg/L as COD(Cr)). Substances with molecular weight cut off < 1,000 were removed mostly by adsorption and biodegradation. Those above 1,000 were rejected at PAC cake layer on the membrane and gradually degraded by microorganisms during extended contact.     

The fouling characterization and control in the high concentration PAC membrane bioreactor HCPAC-MBR.

This study focuses on the experimental investigation to identify the effect of PAC at high concentrations on the fouling of membranes. A pilot-scale experimental apparatus was installed at a water treatment plant located downstream of Nakdong river basin, Korea. Effluent of rapid sand filter was used as influent of the system, which consists of PAC bio-reactor, submerged membrane module (hollow fiber with pore size 0.1 m) and air supply facility. PAC was dosed at 40 g/L initially and it was not replaced during the operation period. Suction type filtration was carried out at intervals of 12 min. suction and 3 min. idling. At the initial flux 0.36 m/d, the system could be operated stably for around 90 days at target trans-membrane pressure (TMP) of 40 kPa. Among total resistance of membrane filtration, cake and gel layer resistance, Rc+Rg, was the dominant fraction (more than 90% of the total) to increase the filtration pressure, which means that the filtration resistance could be controlled by the PAC cake layer and then irreversible membrane fouling could be prevented. Three minutes air backwashing every 3 days could extend the operation period to 127 days. Organics were analyzed in terms of molecular weight structure. The influent of the system consists of 15.0% and 74.4% of hydrophobic and hydrophilic natural organic matter (NOM), respectively. Hydrophobic and hydrophilic (electrostatic) interaction was the main factor on fouling of the membrane in the reactor. Hydrophobic fraction decreased slightly in the effluent, which means hydrophobic NOM removal in the reactor by adsorption. Organics accumulated in the membrane were extracted for analysis after a certain period of operation. The fraction of hydrophobic and hydrophilic organics was 41.4% and 38.9%, respectively. On the basis of the experimental results, the hydrophobic organics were the major materials causing the fouling of the membrane, which should be changed to other types of material.     

The removal of residual organic matter from biologically treated swine wastewater using membrane bioreactor process with powdered activated carbon.

The objective of this study was to characterize the mechanisms of the COD removal in the membrane bioreactor (MBR) process with powdered activated carbon (PAC) addition and to determine its optimal operation, for the removal of residual organic matters (ROM) from biologically treated swine wastewater. The MBR process with PAC showed higher removal efficiency of chemical oxygen demand (COD(Mn)) than that without PAC. When the average COD(Mn) concentration of the influent was 217 mg/L, the average COD(Mn) concentration of the permeate from the MBR with PAC was about 41.5 mg/L, indicating an approximate removal efficiency of 81%. On the other hand, the average COD(Mn) concentration of the permeate from the MBR without PAC was 172 mg/L. The PAC dosage estimated to obtain the above removal efficiency was about 0.74 g per litre of influent. Among the total residual organics removed by PAC-added MBR, 46.5% was removed by PAC adsorption, 20.8% by biodegradation, 4.4% by membrane separation, and 9.3% by enhanced microorganism activity. From these results, the MBR process with PAC was considered as a very useful treatment process for the reduction of COD(Mn) in biologically treated swine wastewater.     

Application of PTFE membrane for ammonia removal in a membrane contactor

The feasibility of a membrane contactor system for ammonia removal was studied. The mass transfer coefficient was used to quantitatively compare the effect of various operation conditions on ammonia removal efficiency. Effective removal of ammonia was possible with a Polytetrafluoroethylene (PTFE) membrane contactor system at all tested conditions. Among the various operation parameters, contact time and solution pH showed significant effect on the ammonia removal mechanism. The overall ammonia removal rate was not affected by influent suspended solution concentration unlike other pressure driven membrane filtration processes. Also the osmotic distillation phenomena which deteriorate the mass transfer efficiency can be minimized by preheating of influent wastewater. A membrane contactor system can be a possible alternative to treat high strength nitrogen wastewater by optimizing operation conditions such as stripping solution flow rate, influent wastewater temperature, and influent pH.     

不同预处理方式与微滤联用处理城市污水对比实验研究

采用微滤法处理模拟二沉池出水,以期达到城市污水回用的目的.进水采用人工配水,主要考察微滤膜对模拟二沉池出水中CODMn,氨氮(NH3-N)及UV254的去除效果,以及预处理方式对微滤膜处理工艺的影响.实验主要采用了两种预处理方式,即颗粒活性炭(GAC)吸附及聚合氯化铝(PAC)混凝.实验结果表明,单独采用微滤膜效果不明显,高锰酸钾指数的去除率仅为32.5%,氨氯去除率约为5%,且膜污染严重,通量下降很快.活性炭-微滤组合工艺对污水的CODMn去除效果较好,去除率达到88%;而混凝-徽滤工艺对UV254的去除效果较好,去除率达到87%;混凝-微滤及活性炭-微滤工艺对氨氮的去除率均不高.组合工艺比起单独使用微滤膜流量下降缓慢,混凝-徽滤工艺在4.5h内,流量没有下降,污染情况明显改善.     

pH对粉末活性炭去除有机物的影响

粉末活性炭去除水中有机物的效果受水的pH影响较大。降低水的pH,可显著提高粉末活性炭去除有机物的效果。对于黄浦江水,当pH为5.5,粉末活性炭投加量为40mg/L时,DOC和UV_(254)的去除率分别达到43.8％和36.2％。     

Evaluation of a long-term operation of a submerged nanofiltration membrane bioreactor (NF MBR) for advanced wastewater treatment.

Nanofiltration (NF) is considered as one of the most promising separation technologies to obtain a very good-quality permeate in water and wastewater treatment. A submerged NF membrane bioreactor (NF MBR) using polyamide membranes was tested for a long-term operation and the performance of the NF MBR was compared with that of a microfiltration MBR (MF MBR). Total organic carbon (TOC) concentration in the permeate of the NF MBR ranged from 0.5 to 2.0 mg/L, whereas that of the MF MBR showed an average of 5 mg/L. This could be explained by the tightness of the NF membrane. Although the concentration of organic matter in the supernatant of the NF MBR was higher than that in the permeate due to high rejection by the NF membrane, the NF MBR showed excellent treatment efficiency and satisfactory operational stability for a long-term operation.     

Three stages MBR (methanogenic, aerobic biofilm and membrane filtration) for the treatment of low-strength wastewaters

The use of a new three stages MBR process with a first methanogenic UASB stage, a second stage with aerobic biofilm growing on small carrier elements maintained in suspension and third stage with membrane filtration module is presented. The objective of the first methanogenic chamber is to diminish COD of the raw wastewater, producing a biogas rich in methane, and decrease the sludge production. In the second stage, the remaining soluble biodegradable COD is oxidized by heterotrophs. In the third stage, the membrane modules could be operated at higher fluxes than those reported for AnMBR systems, and similar to those obtained in aerobic MBRs. In this sense, the concept of these three stages MBR is to join the advantages of the methanogenic and aerobic membrane bioreactor processes, by reducing energy requirements for aeration, producing biogas with high methane percentage and a permeate with very low COD content. A synthetic wastewater was fed to the three stages MBR. COD in the influent was between 200 and 1,200 mg/L, ammonium ranged from 10 to 35 mg/L and phosphorous concentration was 8 mg/L. OLR in-between 1 and 3 kg COD/(m3 d) and a HRT of 13-21 h were applied. Temperature was between 17.5 and 23.2 degrees C. During the whole operating period the COD removal efficiencies were in the range of 90 and 96% of which in between 40 and 80% was removed in the first methanogenic chamber. Biogas production with methane content between 75 and 80% was observed. With regard to membrane operation, average permeabilities around 150 L/(m2 h bar) were achieved, operating with fluxes of 11-15 L/(m2 h).     

Pulse shear stress for anaerobic membrane bioreactor fouling control

Increase of shear stress at membrane surfaces is a generally applied strategy to minimize membrane fouling. It has been reported that a two-phase flow, better known as slug flow, is an effective way to increase shear stress. Hence, slug flow was introduced into an anaerobic membrane bioreactor for membrane fouling control. Anaerobic suspended sludge was cultured in an anaerobic membrane bioreactor (AMBR) operated with a side stream inside-out tubular membrane unit applying sustainable flux flow regimes. The averaged particle diameter decreased from 20 to 5 microm during operation of the AMBR. However, the COD removal efficiency did not show any significant deterioration, whereas the specific methanogenic activity (SMA) increased from 0.16 to 0.41 gCOD/g VSS/day. Nevertheless, the imposed gas slug appeared to be insufficient for adequate fouling control, resulting in rapidly increasing trans membrane pressures (TMP) operating at a flux exceeding 16 L/m2/h. Addition of powdered activated carbon (PAC) enhanced the effect of slug flow on membrane fouling. However, the combined effect was still considered as not being significant. The tubular membrane was subsequently equipped with inert inserts for creating a locally increased shear stress for enhanced fouling control. Results show an increase in the membrane flux from 16 L/m2/h to 34 L/m2/h after the inserts were mounted in the membrane tube.     

Simultaneous nitrification and de-nitrification in MBR.

Experiments have been carried out to get an understanding of the effect of DO, C/N ratio and pH on the performance of a bench scale membrane bioreactor (MBR) in simultaneous nitrification and denitrification. It was found that under the conditions of MLSS in the range of 8000-9000 mg/L and temperature of water in the MBR of 24 degrees C, influent COD and NH3-N in the range of 523-700 mg/L and 17.24-24 mg/L respectively, the removals of COD, NH3-N and TN were 98%, 99% and 60%; 96.5%, 0,98% and 75%; 96%, 95% and 92%; 90%,70% and 60% respectively at DO of 6, 3, 1 and 0.5 mg/L. It was also found that the changes in C/N ratio and pH in a certain range have a slight effect on COD removal but have significant influence on the removal of NH3-N and TN. The results showed that only under the conditions that each ecological factor was maintained relatively steadily, simultaneous nitrification and de-nitrification proceeded smoothly. It was found that when C/N ratio was 30, the influent pH 7.2, the temperature of water in MBR 24 degrees C and DO 1 mg/L, as optimum conditions, the removals of COD, NH3-N and TN were 96%, 95% and 92% respectively. In addition, mechanism research on simultaneous nitrification and de-nitrification in MBR has been conducted as well.     

Grey water characterization and treatment for reuse in an arid environment

Grey water from a university facilities building in Cairo, Egypt was analysed for basic wastewater parameters. Mean concentrations were calculated based on grab samples over a 16-month period. Values for chemical oxygen demand (COD) and nutrients exceeded values reported in a number of other studies of grey water, while coliform counts were also high. A submerged membrane bioreactor (SMBR) system using a hollow fibre ultrafiltration membrane was used to treat the grey water with the aim of producing effluent that meets reuse guidelines for agriculture. A test run for 50 days at constant transmembrane pressure resulted in very good removal for key parameters including COD, total suspended solids (TSS), colour, turbidity, ammonia nitrogen, anionic surfactants, and coliform bacteria. High standard deviations were observed for COD and coliform concentrations for both monthly grab samples and influent values from the 50-day SMBR experiment. SMBR effluent meets international and local guidelines for at least restricted irrigation, particularly as pertains to COD, TSS, and faecal coliforms which were reduced to mean treated values of 50 mg/L, 0 mg/L (i.e., not detected), and <50 cfu/100 mL, respectively.     

Efficient taste and odour removal by water treatment plants around the Han River water supply system.

Seven major water treatment plants in Seoul Metropolitan Area, which are under Korea Water Resources Corporation (KOWACO)'s management, take water from the Paldang Reservoir in the Han River System for drinking water supply. There are taste and odour (T&O) problems in the finished water because the conventional treatment processes do not efficiently remove the T&O compounds. This study evaluated T&O removal by ozonation, granular activated carbon (GAC) treatment, powder activated carbon (PAC) and an advanced oxidation process in a pilot-scale treatment plant and bench-scale laboratory experiments. During T&O episodes, PAC alone was not adequate, but as a pretreatment together with GAC it could be a useful option. The optimal range of ozone dose was 1 to 2 mg/L at a contact time of 10 min. However, with ozone alone it was difficult to meet the T&O target of 3 TON and 15 ng/L of MIB or geosmin. The GAC adsorption capacity for DOC in the three GAC systems (F/A, GAC and O3 + GAC) at an EBCT of 14 min is mostly exhausted after 9 months. However, substantial TON removal continued for more than 2 years (>90,000 bed volumes). GAC was found to be effective for T&O control and the main removal mechanisms were adsorption capacity and biodegradation.     

Effect of hydraulic retention time and pH on oxidation of ferrous iron in simulated ferruginous acid mine drainage treatment with inoculation of iron-oxidizing bacteria

The effect of hydraulic retention time(HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage(AMD)treatment was investigated.The simulated AMD was highly acidic(pH 2.5),rich in iron(about 1700 mg/L) and copper(about 200 mg/L),and contained high concentrations of sulfate(about 4700 mg/L).The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor(PBR).The HRT was shortened stepwise from 40 h to 20 h,13 h,and 8 h under the acidic environment at a pH value of 2.2.Then,the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT.Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions.The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT,and when the HRT exceeded 13 h,ferrous iron in AMD was almost completely oxidized.In addition,the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8.Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor,and low influent pH values are suitable for the growth of Leptospirillum.     

Natural Organic Matter and Disinfection By-products Formation Potential in Water Treatment

The performance of a conventional sequence (pre-ozonation, coagulation/ flocculation/ sedimentation, filtration, disinfection) and two non-conventional sequences (pre-ozonation, nanofiltration; and pre-ozonation, coagulation/ flocculation/ sedimentation, nanofiltration) on the removal of natural organic matter (NOM) and disinfection by-products (DBPs) formation potential was evaluated. Raw and treated waters were characterized in terms of molecular weight, which includes the amount of NOM removed and the qualitative changes in the NOM characteristics (molecular weight and hydrophobicity) since they could be directly related with the DBPs formation. The results demonstrate that, for the type of raw water analysed (hydrophilic with low dissolved organic carbon content, 0.99 L/(mg.m) and 1.31 mg DOC/L), both treatment sequences remove larger molecular weight compounds (>1,900 g/mol). Treated waters have the dominant fractions in the smaller molecular size fractions (<750 g/mol). However, the sequences with nanofiltration have a higher percentage of low molecular weight compounds removed (between 430 and 250 g/mol), when compared with conventional sequence, thus the water from nanofiltration sequences will have lower DBPs formation potential. The removal of the smallest molecular size fractions can be enhanced by optimising the water treatment process and the quality of water will improve relating with DBPs formation.     

Treatment of taste and odor material by oxidation and adsorption.

Massive blooms of blue-green algae in reservoirs produce the musty-earthy taste and odor, which are caused by compounds such as 2-MIB and geosmin. 2-MIB and geosmin are rarely removed by conventional water treatment. Their presence in the drinking water, even at low levels (ng/L), can be detected and it creates consumer complaints. So those concentrations have to be controlled as low as possible in the drinking water. The removals by oxidation (O3, Cl2, ClO2) and adsorption (PAC, filter/adsorber) were studied at laboratory and pilot plant (50 m3/d) to select suitable 2-MIB and geosmin treatment processes. The following conclusions were derived from the study. Both of the threshold odor levels for 2-MIB and geosmin appeared to be 30 ng/L as a consequence of a lab test. For any given PAC dosage in a jar-test, removal efficiencies of 2-MIB and geosmin were increased in proportion to PAC dosage and were independent of their initial concentration in raw water for the tested PAC dosages. In comparison of geosmin with 2-MIB, the adsorption efficiency of geosmin by PAC was superior to that of 2-MIB. The required PAC dosages to control below the threshold odor level were 30 mg/L for geosmin and 50 mg/L for 2-MIB at 100 ng/L of initial concentration. Removal efficiencies of odor materials by Cl2, ClO2, and O3 were very weak under the limited dosage (1.5 mg/L), however increased ozone dosage (3.8 mg O3/L) showed high removal efficiency (84.8% for 2-MIB) at contact time 6.4 minutes. According to the initial concentrations of 2-MIB and geosmin, their removal efficiencies by filter/adsorber differed from 25.7% to 88.4%. For all those, however, remaining concentrations of target materials in finished waters were maintained below 30 ng/L. The longer run-time given for the filter/adsorber, the higher the effluent concentration generated. So it is necessary that the run-time of the filter/adsorber be decreased, when 2-MIB or geosmin occurs in raw water.     

Factors causing PAC cake fouling in PAC-MF (powdered activated carbon-microfiltration) water treatment systems.

Two pilot-scale powdered activated carbon-microfiltration (PAC-MF) reactors were operated using river water pretreated by a biofilter. A high permeate flux (4 m/d) was maintained in two reactors with different particle sizes of PAC. High concentration (20 g/L) in the PAC adsorption zone demonstrated 60-80% of organic removal rates. Analysis on the PAC cake fouling demonstrated that attached metal ions play more important role than organic matter attached on PAC to the increase of PAC cake resistance. Effects of factors which may cause PAC cake fouling in PAC-MF process were investigated and evaluated by batch experiments, further revealing that small particulates and metal ions in raw water impose prominent influence on the PAC cake layer formation. Fe (II) precipitates after being oxidized to Fe (III) during PAC adsorption and thus Fe(ll) colloids display more significant effect than other metal ions. At a high flux, PAC cake layer demonstrated a higher resistance with larger PAC due to association among colloids, metals and PAC particles, and easy migration of small particles in raw water into the void space in the PAC cake layer. Larger PAC possesses much more non-uniform particle size distribution and larger void space, making it easier for small colloids to migrate into the voids and for metal ions to associate with PAC particles by bridge effect, hence speeding up and intensifying the of PAC cake fouling on membrane surface.     

Function of dynamic membrane in self-forming dynamic membrane coupled bioreactor.

The Self-Forming Dynamic Membrane Coupled Bioreactor (SFDMBR), which uses coarse pore-sized material to separate solid and liquid in bioreactors, has some advantages compared with MBR using micro-/ultra-filtration membranes, for example, low module cost and high flux. The cake layer and gel layer formed on the surface and in the pores of the material during filtration played an important role, called self-forming dynamic membrane (DM), which mainly consisted of activated sludge. In this study, the function of DM in pollutant removal was investigated. It was found that DM could remove some organic matter (12.6 mg L(-1) on average) and total nitrogen (3.01 mg L(-1) on average) in the supernatant. Colloids and organic nitrogen were partly removed by DM while DOC, ammonia nitrogen and nitrate nitrogen removal by DM varied from negative to positive, which resulted from the combination of various biological activities, e.g. nitrification, biological utilization and so on. DO concentration in DM decreased with the depth and reached zero at about 1.5-2.5 mm depth. The organic degradation activity and nitrification activity of the biomass suspended in the bioreactor were higher than those of the biomass in the cake layer, which might be caused by the low DO concentration and low organic pollutant content in DM.     

Evaluation of a MF membrane system composed of pre coagulation-sedimentation and chlorination for water reuse.

In this research, we investigated the variation of transmembrane pressure and permeate water quality in pre-coagulation and sedimentation with iron based coagulant, and chlorination of feed water for PVDF (Polyvinylidene fluoride) based MF membrane filtration. NaCIO was fed to the membrane module at a dosage of 0.5 mg/L and maintained during filtration. To observe the effect of raw water, three types of raw and processed waters, including river surface water, coagulated water and coagulated-settled water, were employed. In the case of river surface water, the transmembrane pressure increased abruptly in 500 hours operation. On the contrary, no significant increase in transmembrane pressure was observed for coagulated water and coagulated-settled water for 1200 hours operation. The turbidity of permeate was lower than the detection limit for all applied waters. The removal efficiency for humic substances in coagulated water and coagulated-settled water was approximately ten times higher than that in surface river water. And, the removal efficiency for TOC and DOC was approximately two times higher than that in surface river water. From the results of the operation, it can be observed that it is possible to maintain stable operation at 0.9 m(3)/m(2)-day filtration flux through a combination of pre-coagulation and pre-chlorination. However, the water quality of permeate was the best when the pre-coagulation-sedimentation process was combined with pre-chlorination. With respect to fouling reduction and operation efficiency increase in membrane filtration, the pre-coagulation/sedimentation process is a promising alternative.     

香兰素废水处理技术研究及工艺设计

采用预处理-加压曝气生物氧化工艺处理香兰素生产废水。反应器在200 kPa压力条件下,COD容积负荷率达5.5~8.0 kg/m3.d,进水COD质量浓度为2 000~2 500 mg/L,反应时间为8~10 h时,处理后的出水COD质量浓度小于100 mg/L,达到污水综合排放一级标准。还对加压曝气生物反应器原理、工艺流程、运行参数、工艺设计等方面进行了介绍。     

不同条件对高效菌去除污水中氨氮效果影响研究

本文研究了pH值、温度、曝气时间、茵投入量（体积比）、溶解氧、水力停留时间、进水碳氮比、冲击负荷等影响因素对氨氮去除率的影响,对项目参数进行了优化。研究结果如下：在高效菌处理氨氮废水时,为了得到较好的去除效果,pH值应控制在7．0到8．O之间;温度应控制在25℃到35℃之间;曝气时间应保持在5h到6h之间;茵投入量（体积比）应保持在0．004到0．006之间;溶解氧浓度应保持在2mg／L到3mg／L之间：水力停留时间为16h．高效茵对污水中氨氮的去除效果最佳。