Design, Cost & Benefit Analysis of a Membrane Bioreactor

Membranes

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT1) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5–3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤ 2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial pr...

Processes, 2014

Membrane fouling is one of the most important considerations in the design and operation of membrane systems as it affects pretreatment needs, cleaning requirements, operating conditions, cost and performance. Given that membrane fouling represents the main limitation to membrane process operation, it is unsurprising that the majority of membrane material and process research and development conducted is dedicated to its characterization and amelioration. This work presents the fundamentals of fouling issues in membrane separations, with specific regard to membrane fouling in Membrane Bioreactors (MBRs) and the most frequently applied preventive-control strategies. Feed pretreatment, physical and chemical cleaning protocols, optimal operation of MBR process and membrane surface modification are presented and discussed in detail. Membrane fouling is the major obstacle to the widespread application of the MBR technology and, therefore, fouling preventive-control strategies is a hot issue that strongly concerns not only the scientific community, but industry as well.

2018

In this study, effect of antiscalant usage on minimizing of membrane fouling due to high water hardness during wastewater treatment tests run by a pilot-scale membrane bioreactor (MBR) system. The membranes used in these studies were Kubota flat sheet MBR membranes made from polyethylene with a pore size of 0.4 micrometer. Preliminary tests were carried out with tap water for sixty days of operation. To investigate the applicability and the effect of antiscalant usage, four experiments (two experiments with tap water and two experiments with wastewater) were carried out and each experiment lasted for 29 days. The tests were carried out in the presence and in the absence of antiscalant. Fouling on MBR membranes was investigated by monitoring flux decline versus time. In tap water tests, unstable flux was observed initially then a flux decline due inorganic scaling. On the other hand, the flux was almost constant up to end of the experiment in the presence of antiscalant. During wastewater t...

Desalination, 2008

Membrane fouling is a principal limitation of wide application of membrane bioreactors (MBR) to wastewater treatment. In this study, to control the membrane fouling the position of a membrane module in a submerged MBR was elevated from bottom to top of the reactor. This could divide the reactor into two different zones: upper and lower. Air was not supplied at the lower zone whereas aeration was given to the upper zone where the membrane filtration was carried out. Biosolids concentration was reduced in the upper zone because the mixed liquor could be settled down to the lower zone. Therefore, membrane fouling could be lessened in the upper zone due to the reduced biosolids concentration. In this study, to verify if this newly designed MBR configuration could mitigate membrane fouling, the effect of the vertical position of the membrane module in a lab-scale MBR on membrane fouling was investigated. Furthermore, a pilot plant (50 m 3 /d) of the membrane coupled biological nutrients removal (BNR) process was designed based on the above configuration and was run for 5 months. In the lab test, the higher the membrane was located in the bioreactor, the less membrane fouling was observed. With the pilot plant operation, MLSS concentration in the upper part was lessened to 16~33% than that in the lower part of the tank where air was not supplied. It indicates that two different zones were successfully formed. The interval of periodical chemical cleanings with NaOCl was extended from 2 to 4 months, indicating that the membrane fouling was mitigated. DO concentration at the upper part was 5.3 mg/L, whereas DO at the lower part was 0.4 mg/L. Therefore, this may result in better denitrrification efficiency in the anoxic tank because the recycled sludge to the anoxic tank has low DO concentration. Nitrate concentration at the lower part of the MBR was 2.8 mg/L, whereas that at the upper part

Separation and Purification Technology, 2001

Compared with conventional wastewater treatment processes, membrane bioreactors offer several advantages, e.g. high biodegradation efficiency, smaller sludge production and compactness. However, membrane fouling is the main limitation to faster development of this process. An experimental study has been performed using hollow fibers (pore size 0.1 mm) immersed in an aerated tank for treating synthetic wastewater representative of dairy effluent. For the same organic load (5.7 kg COD/m 3 per day) the COD removal efficiency, the sludge production and fouling ability were compared in three reactors operated at different sludge ages (10, 20 and 30 days). COD removal was high: 95-97.5%. The sludge production decreased from 0.31 to 0.16 kg MLSS/kg COD removed when the sludge age increased from 10 to 30 days. Concerning the fouling ability of the sludge, a specific experiment (measurement of the specific resistance and hydraulic resistance during filtration) was designed to determine the influence on membrane fouling of the three fractions of the sludge: suspended solids, colloids and solutes. All the experiments confirm the importance of the interstitial matter -colloids and solutes -in membrane fouling. Consequently, bubbling can be expected to be only partially efficient, as bubbles are efficient for limiting particle deposition and polarisation phenomena, but not for internal fouling. Increasing the air flow rate from 1.2 to 3.6 m 3 /m 2 membrane area per hour, it was possible to decrease the total resistance -thus increasing the filtrate flux -by a ratio of 3. However, for given conditions of aeration, periodic backwashing gave an additional efficiency by decreasing internal fouling. In optimal conditions of backwashing (15 s every 5 min) the resistance could be decreased by 3.5-fold.

This work is part of a research project that aims to develop an integrated methodology for membrane fouling control, using specific chemicals which will enhance the coagulation and flocculation of compounds. For this purpose, a pilot-scale plant with fully automatic operation achieved by means of programmable logic controller (PLC) has been constructed and tested. The experimental set-up consists of four units: wastewater feed unit, bioreactor, membrane filtration unit and permeate collection unit. Synthetic wastewater was fed as the substrate for the activated sludge. The dissolved oxygen (DO) concentration of the aerobic tank was maintained in the range of 2-3 mg/L by using an aerator below the membrane module. The membrane was operated at a flux of 18 LMH while one-minute backflushing steps with clean permeate were performed every 10 min. Batch experiments included the addition of commercial and composite coagulants in mixed liquor samples obtained on a daily basis. Sludge filterability and reversible fouling was assessed in terms of filterability tests according to standard TTF method, while irreversible fouling was assessed in terms of SMP removal. Continuous experiments included the inline addition of the optimum coagulants in the pilot-scale MBR and TMP monitoring as a fundamental fouling index.

Desalination and Water Treatment, 2009

Membrane fouling in a submerged membrane bioreactor treating high strength municipal wastewater Ahmed H. Birima, Thamer A. Mohammed, Megat Johari Megat Mohd Noor, Suleyman A. Muyibi, Azni Idris, H. Nagaoka, J. Ahmed & L.A. Abdul Ghani Abstract Studying the influence of the operating parameters on membrane fouling is important in fouling control. This paper presents the interaction effects of the sludge retention time (SRT), organic loading rate (OLR) and feed temperature (T f ) on membrane fouling. A submerged membrane bioreactor (SMBR) was operated under a constant flux (11.1 l/m2 h), with different SRT, T f and OLR. A synthetic wastewater representative of high strength municipal wastewater was fed to the bioreactor. Three different levels (low, medium and high) of SRT, T f and OLR were studied. These were 25, 30 and 35 days for SRT, 20, 30 and 40°C for T f and OLR of 1.73, 4.03 6.82 kg COD/m3.d. The sustainable time (tsus) was defined as the time at which the rate of suction pressure started to increase rapidly. tsus was found to increase with low SRT and high T f . A higher OLR resulted in higher mixed liquor suspended solids (MLSS), however it did not cause a faster membrane fouling. Applying higher aeration rate enabled a longer sustainable time to be obtained. Sustainable time tsus was found to be well correlated with MLVSS/MLSS with an r 2 of 0.995. The range of MLVSS/MLSS tested varied from 74.3 to 82.3% at which tsus decreased 2.9-fold (from 175 to 60.5 h).

Journal of Membrane Science, 2013

Membrane fouling represents one of the major issues for a membrane bioreactor (MBR). Membrane fouling and high aeration requirements (for inducing shear stress to limit fouling) make MBR operation economically demanding due to high energy costs. Although several studies on MBR fouling have been performed, comprehensive knowledge on how to reduce membrane fouling and consequently save energy is still lacking. An integrated mathematical model for MBR is applied to a University of Cape Town membrane bioreactor with the final aim to reduce the energy costs. In particular, the influence of the aeration intensity, the duration of filtration/backwashing cycles, and the number of membrane cleanings are investigated. Five scenarios are analyzed and compared, each implementing different operating conditions. The features of the analyzed scenarios are quantified by employing Monte Carlo simulations and performance indices partially drawn from literature. The results provide insights about the role played by the main physical/chemical/biological processes in view of a system optimization. As expected, MBR operation at low air flow rate (qa) leads to a substantial reduction of the operational costs (specifically, 20% with respect to the suggested manufacturers ones in terms of qa). Despite such a reduction of qa, a good effluent quality is also obtained as an effect of a high biological cake thickness. Results also show that the values of filtration time (Tf) higher than those suggested by manufacturers (e.g., Tf ¼ 9 min) can be used to increase effluent quality. This study demonstrates that both energy savings and effluent quality can be improved by varying the operational variables with respect to those of the suggested manufacture. One of the main insights gained from this study is that the values of the operating variables (i.e., qa, Tb and Tf) suggested by the manufactures can be changed to obtain a system that still respects high effluent quality and is characterized by lower economical cost. The proposed modeling approach can be an useful tool for the optimization of the operating conditions in order to reduce the operational costs for MBR systems.

2005

In order to optimize some operational conditions of MBR systems, a MBR pilot plant equipped with a submerged hollow fibre membrane module was employed in this study. The pilot MBR was fed with real municipal wastewater and the filtration flux, backwashing interval, aeration frequency and temperature were varied. A filtration flux below 25 l/m2h is generally recommended, at below this

Increase in the complexity of waste water generated by industries and its detrimental effect on the environment has brought about stringent water policies. The treatment of waste water by membrane bioreactor (MBR) has gained importance in the recent decade due to its ability to produce high quality water. But fouling of membranes still remains a challenge to the researchers which made the hybrid membrane bioreactors (HMBR) to evolve. This paper reviews on the membrane characteristics, its causes of fouling and its application in different waste water treatment. It also takes a glance on different hybrid systems where MBR has been incorporated with some other pre treatment technologies.