The membrane in MBR

The summary of commercial membrane that use in MBR application is summarized as follow:

Table 1: Flatsheet membrane

Table 2: Industrial HF module

The Fouling Amelioration

The General Method

Numerous method have been developed and reported in order to limit the membrane fouling. Some of the outstanding results are already patented or even applied in industrial MBR. The aproaches for fouling limitation is very broad from selecting the suitable biological parameters to applying the pulsation of electrical current to membrane surface. It is very difficult to make the general thought that may covel all approach that has been proposed and tested.

The methods for addressing the fouling in MBR is presented in Figure 1 and Table 1. Figure 1 shows the overall scheme in addresing the fouling. In this scheme all approach for fouling limitation is being tried to be covered. This scheme is developed in the basis understanding that the fouling is result of interaction between the mixed liquor and membrane to form the fouling layer. From this definition there are three different components that participated in fouling; mixed liquor, membrane and foulant layer it self. In order to limit the membrane fouling, these component mush be exploited to certain extent.

The general strategy and method of fouling limitation is identified by the approach to exploit these factors and devided in five cluster: membrane properties (1), hydrodynamic (2), mixed liquor properties (3), and the combination among them (4 and 5). The summary of the methods that has been reported is shown in Table 1. The further discussion is given in the next sub-section of each cluster.

Figure 1: The schematic diagram of fouling limitation.

Table 1: Summary of fouling limitation methods.

MBR: An Introduction

Definition

Membrane bioreactor (MBR) is the combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor, and is now widely used for municipal and industrial wastewater treatment with plant sizes up to 80,000 population equivalent (i.e. 48 MLD).

Overview

When used with domestic wastewater, MBR processes could produce effluent of high quality enough to be discharged to coastal, surface or brackish waterways or to be reclaimed for urban irrigation. Other advantages of MBRs over conventional processes include small footprint, easy retrofit and upgrade of old wastewater treatment plants. Two MBR configurations exist: internal, where the membranes are immersed in and integral to the biological reactor; and external/sidestream, where membranes are a separate unit process requiring an intermediate pumping step.

Recent technical innovation and significant membrane cost reduction have pushed MBRs to become an established process option to treat wastewaters. As a result, the MBR process has now become an attractive option for the treatment and reuse of industrial and municipal wastewaters, as evidenced by their constantly rising numbers and capacity. The current MBR market has been estimated to value around US$216 million in 2006 and to rise to US$363 million by 2010.

MBR history and basic operating parameters

The MBR process was introduced by the late 1960s, as soon as commercial scale ultrafiltration (UF) and microfiltration (MF) membranes were available. The original process was introduced by Dorr-Olivier Inc. and combined the use of an activated sludge bioreactor with a crossflow membrane filtration loop. The flat sheet membranes used in this process were polymeric and featured pore sizes ranging from 0.003 to 0.01 μm. Although the idea of replacing the settling tank of the conventional activated sludge process was attractive, it was difficult to justify the use of such a process because of the high cost of membranes, low economic value of the product (tertiary effluent) and the potential rapid loss of performance due to membrane fouling. As a result, the focus was on the attainment of high fluxes, and it was therefore necessary to pump the mixed liquor suspended solids (MLSS) at high crossflow velocity at significant energy penalty (of the order 10 kWh/m3 product) to reduce fouling. Due to the poor economics of the first generation MBRs, they only found applications in niche areas with special needs like isolated trailer parks or ski resorts for example.

The breakthrough for the MBR came in 1989 with the idea of Yamamoto and co-workers to submerge the membranes in the bioreactor. Until then, MBRs were designed with the separation device located external to the reactor (sidestream MBR) and relied on high transmembrane pressure (TMP) to maintain filtration. With the membrane directly immersed into the bioreactor, submerged MBR systems are usually preferred to sidestream configuration, especially for domestic wastewater treatment. The submerged configuration relies on coarse bubble aeration to produce mixing and limit fouling. The energy demand of the submerged system can be up to 2 orders of magnitude lower than that of the sidestream systems and submerged systems operate at a lower flux, demanding more membrane area. In submerged configurations, aeration is considered as one of the major parameter on process performances both hydraulic and biological. Aeration maintains solids in suspension, scours the membrane surface and provides oxygen to the biomass, leading to a better biodegradability and cell synthesis.

The other key steps in the recent MBR development were the acceptance of modest fluxes (25% or less of those in the first generation), and the idea to use two-phase bubbly flow to control fouling. The lower operating cost obtained with the submerged configuration along with the steady decrease in the membrane cost encouraged an exponential increase in MBR plant installations from the mid 90s. Since then, further improvements in the MBR design and operation have been introduced and incorporated into larger plants. While early MBRs were operated at solid retention times (SRT) as high as 100 days with mixed liquor suspended solids up to 30 g/L, the recent trend is to apply lower solid retention times (around 10-20 days), resulting in more manageable mixed liquor suspended solids (MLSS) levels (10-15 g/L). Thanks to these new operating conditions, the oxygen transfer and the pumping cost in the MBR have tended to decrease and overall maintenance has been simplified. There is now a range of MBR systems commercially available, most of which use submerged membranes although some external modules are available; these external systems also use two-phase flow for fouling control. Typical hydraulic retention times (HRT) range between 3 and 10 hours. In terms of membrane configurations, mainly hollow fibre and flat sheet membranes are applied for MBR applications.

The Road Map of MBR

This first post is the guideline for the reader to follow the overall content of the blog. Like in a book, this can be considered as list of content. Each of content from this road map is linked to suitable discussion in this blog.

The content of the blog can be expand depend on the need and current popular issue on the MBR. The reader can make any suggestion of the other important issues that may be important to be put to the blog. Another information regarding the MBR online is also provided in the gadget at the bottom of the webpage.

Introduction

• Definition
• Overview
• History and fundamental improvement

MBR Fundamental

Process Operation

The Membrane in MBR

• Characteristic
  
• Preparation
  
• Modification
  
• Hollow Fiber VS Flat Sheet which one is the best
  

Important Parameters in MBR

• Biological Parameters
• Membrane filtration
• Fouling

How to Design the MBR

• Labscale
• Pilot plan
• Industrial scale

Fouling in MBR: An Introduction

• Foulant
• The Method for Fouling Autopsy
• Fouling Mitigation in MBR

MBR Market and the Future Prospect

Research Group in MBR

MBR Manufacturer

The Research Project in MBR

MBR: Hot topics

Miscellaneus