Membrane Bio Reactor MBR---Operators notebook

SOURCE:http://www.wrights-trainingsite.com/WWT%20MBR.htm
Membrane Bioreactor (MBR) in Wastewater Treatment

Description of MBR technology

The Membrane Bioreactor is a simple, but very effective combination of the activated sludge treatment process and the membrane filtration process. Imagine an activated sludge aeration basin, with sets of micro- or ultra-filtration membrane filtration modules submerged in the aeration basins, and you now have MBR.

The wastewater enters the wastewater treatment facility and passes through the usual Preliminary Treatment, and Primary Treatment processes. Some facilities then place fine screens (opening are less than 2mm in diameter) prior to the MBR reactors to remove small suspended particles such as human hair. This step is designed to reduce the potential fouling of the membranes with these fine particles. The dissolved BOD (sugars, starches, carbohydrates, etc) that is in the wastewater is then consumed by the microbes in the aeration basin, and subsequently converted into additional microorganisms, or becomes attached to the biological floc. The Mixed Liquor Suspended Solids (MLSS) is usually fairly high in MBR units, around 10,000 mg/L. (I have seen installations as high as 20,000 mg/L, and). This high MLSS concentration allows for lower hydraulic retention times (HRT) which equates to smaller aeration basins. This also equates to an activated sludge that may be fully nitrifying, as the Mean Cell Residence Time (MCRT) is usually well above 10 days. (I have seen installations with MCRT's up to 45 days. Talk about "extended aeration ashing!") The microbes are larger than the very small "perforations" or "holes" in the membranes. Pumps are attached to the membrane modules, and pull a slight vacuum that pulls water from the tank through the perforations in the membranes leaving the microorganisms behind in the tank.

 

Most all of the MBR facilities utilize fine bubble aeration in the aeration tanks, except for those areas that will have the MBR modules. These membrane module areas will usually have coarse bubble diffusers installed beneath them.

 

Some facilities may use the single tank MBR process, or the double tank MBR process. In the single tank the filtration modules are placed near the opposite end from where the primary effluent enters the tank. In a double tank configuration, designers may have an aeration tank without a filtration module in it, followed by an aeration basin with the membrane filtration unit in it. The treatment process goal in both designs is to allow for suitable time for the conversion of BOD/COD into microbial cells or at least be absorbed/flocculated with the cellular masses prior to being placed near the membrane filtration units. (We obviously do not want to have dissolved organics pass through the membranes.)   

In other installations, anoxic selectors or even anaerobic selectors may be placed prior to the MBR aeration units to achieve nitrification goals, control filamentous microbes, etc. (See the Selector's, Part 1 & Part 2 in our Operator Notebook).

 

In "traditional activated sludge facilities" a secondary clarifier(s) follows the aeration basin which allows for the microbes to settle to the bottom of the tank, and a "clarified effluent" to leave the clarifier. The MBR process obviously does NOT use a secondary clarifier, as the effluent is far cleaner than that which would be produced by a secondary clarifier. In fact, the membranes produce an effluent (filtrate) that should be given "disinfection credits!" The membrane filtration process produces an effluent extremely low in suspended solids concentration and turbidity units. The quality of this water, when the process is properly operated, is amazing. Even when it is used in wastewater treatment applications, it rivals the best potable water I have seen!

 

I have personally inspected in depth one MBR facility that operates its disinfection process just because "it's there, and our discharge treatment permit requires that we do so." This facility routinely samples and tests for coliform bacteria immediately after the MBR process PRIOR to the disinfection process, and it has without fail MET the disinfection requirements PRIOR to disinfection! Of course, it also disinfects the wastewater and samples/tests after the disinfection process, and has always met their disinfection requirements there also. This is an example of how effective the membrane filtration process is!

 

It appears that the MBR process works best if it is a fully nitrifying process. As such, one of the benefits of nitrification is the lower sludge production that results from keeping the microbes under aeration for a longer period of time, which allows them to consume almost all of the BOD, convert the BOD into microbes, and have the microbes start consuming each other (endogenous respiration.)

 

The Membrane Bioreactors

In the one membrane bioreactor installation I am familiar with, thousands of long microstrands are bundled together in modules. The strands are set vertically, with the end of end single strand connected either to the top or to the bottom header. Each strand has millions of "pores" (small openings) that open into the hollow center of each strand. The nominal pore size is 0.04 µm.

The fiber diameters are: inside 0.9mm, outside 1.9mm. If you have ever seen fly fishing line, the floating type, then you will have an idea of what these fibers look like. With a nominal pore size of 0.04 µm, it is easy to see how microbes like the "Paramecium" with a size of 200 µm, and a bacterial cell whose size between 0.5 to 1.0 µm is "filtered out" by the membranes. For reference a fine human hair 30 µm. (The symbol for micron or micrometers is "µm."

The pores in the membranes are kept open by installing coarse air bubblers beneath the modules, which help scour the membranes, and by the injection of timed back-blows of air and/or treated water inside the membranes. A routine schedule of backwashing and chemical treatment (usually injection of a chlorine bleach solution) is also incorporated into the routine maintenance of the modules. This is all designed to reduce the potential fouling and plugging of the pores within the strands.

 

There are also "plates" that are being manufactured that perform in much the same manner.

 

 

Module in the tank without Mixed Liquor

In operation with Mixed Liquor

Collection header above the tank and modules

(Please click on the above thumbnails for full-sized pictures. Please use your browser's back arrow to return here.)

 

 

DESIGN NOTES: Energy cost's also need to be accurately compared between MBR and the traditional treatment process train when evaluating a particular facility. Is the operations and maintenance staff capable of operating and maintaining this more complex treatment process given the additional training and support that is required for this process? (That is a nice way of saying, is the agency or company willing to support this effort financially?) In summary, one also needs to consider more than "just the cost." What is the "value" of this cost? In other words, "What does the MBR process, in terms of consistent effluent quality, predictable outcomes, etc., that conventional treatment trains do or do not?"

 

Make sure you have a method of controlling the dissolved oxygen concentration in each cell with an automatic air balance in each aeration cell, so that electrical energy is optimized and not wasted.

 

Insure that you have a method of controlling the treatment process flow rate between banks or trains by automatically controlling weirs, valves, or gates. Often the loading rates vary among parallel treatment trains.

 

Insure that the methods of cleaning the MBR membranes to minimize chemical and biological fouling are proven technologies. (This is not the time to be a company's R&D pilot study.)

 

ADVANTAGES

1) The effluent is of very high quality, very low in BOD (less than 5 mg/l), very low in turbidity and suspended solids. The technology produces some of the most predictable water quality known. It is fairly easy to operate as long as the operation has been properly trained, pays strict attention to the proper operation, corrective maintenance, and preventative maintenance tasks.

 

2) The "simple filtering action" of the membranes creates a physical disinfection barrier, which significantly reduces the disinfection requirements. 

 

3) The capitol cost is usually less than for comparable treatment trains.

 

4) The treatment process also allows for a smaller "footprint" as there are no secondary clarifiers nor tertiary filters which would be required to achieve similar water quality results. It also eliminates the need for a tertiary backwash surge tank, a backwash water storage tank, and for the treatment of the backwash water.

 

5) Generally speaking it produces less waste activated sludge than a simple conventional system.

 

6) If re-use is a major water quality goal, the MBR process will be a major consideration. This process produces a consistent, high water quality discharge. When followed by a disinfection process, it allows for a wide range of water re-use applications including landscape irrigation, non-root edible crops, highway median strip and golf course irrigation, and cooling water re-charge. When Reverse Osmosis (RO) water quality is required, the MBR process is an excellent candidate for preparing the water for RO treatment.

 

 

DISADVANTAGES

1) The membrane modules will need to be replaced somewhere between five (5) and ten (10) years with the current technology. While the costs have decreased over the past several years, these modules can still be classified as expensive. (The membranes "dry out" due to the flexible polymers leaching out, the closing/plugging of the pores, and the membranes becoming somewhat hard or brittle.) These costs are often offset somewhat when life-cycle costs for comparable technologies are examined. If the costs for the membrane replacement task continue to decrease then over time, then this process is even more financially viable.

 

2) In most sales pitches the MBR technology is stated as an option of replacing the secondary clarifier. Usually these clarifiers are operated with a single, very low horsepower motor, usually less than 2 HP. The electrical cost for this simple motor is significantly less than the filtrate pumps, chemical feed pumps, compressors, etc., of the MBR system. While this energy cost is significantly higher, the MBR system produces a significantly higher quality effluent that most clarifiers could never achieve.

 

3) Fouling is troublesome, and its prevention is costly. Several papers and research endeavors have concluded that up to two-thirds of the chemical and energy costs in an MBR facility are directly attributable to reducing membrane fouling. While this is costly to be sure, future advances into this area will continue to reduce these costs.

 

4) There may be cleaning solutions that require special handling, treatment, and disposal activities depending on the manufacturer. These cleaning solutions may be classified as hazardous waste depending on local and state regulations.

 

REFERENCES:
Crites, R. W. and Tchobanoglous, G, (1998) "Small and Decentralized Wastewater Management Systems," McGraw-Hill Book Company, New York, NY

 

Daigger, G.T., Crawford, G., Fernandez, A., Lozier, J.C. and Fleischer, E. "WERF Project: Feasibility of Membrane Technology for Biological Wastewater Treatment B Identification of Issues and MBR Technology Assessment Tool." Water Environment Federation 74th Annual Conference & Exposition, Atlanta, GA, CD-ROM, October 13-17, 2001.

 

Johnson, W.T. "Recent Advances in Microfiltration for Drinking Water Treatment." AWWA Annual Conference, Chicago, IL. June 20-24 1999

 

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Mobile Banking State Bank Of India SBI and EKO

One of the most ambitious companies I met with during my last trip to India in November was Eko, a mobile banking company. There are a few SMS-based bank applications in India, but Eko differs because the phone isn't just another channel for the account—it is the account. You make payments and transfer money simply by dialing numbers. It's so simple, you don't even need to understand SMS to use it.

It's an ingenious offering that doesn't try to be everything to everyone. It aims squarely at the unbanked—some 60% of India's huge population. For now, Eko is focusing on the 1,000 kilometer corridor between Delhi and Bihar.

It's a textbook case of the how hard it is to build something incredibly simple within a sandbox of tight constraints—yet that simplicity is the same thing many would argue caused Twitter's 140-character missives to become so universal. There are no extra bells and whistles with Eko's service because there's no room for them, and at the end of the day, probably little need for them.

The accounts are actually held by the State Bank of India, which insures up to 100,000 rupees per account, but Eko's customers don't ever go into banks. The "tellers" are the tiny corner groceries that dot every neighborhood and street corner in India's crammed urban areas and expansive rural areas. They are the center of commerce for those living on intermittent jobs, tips and handouts. These stores sell medications by the pill, shampoo in tiny sachets, cell phone minutes by the Paisa, and frequently extend credit when needed. Eko just seeks to give this already trusted, daily-visited vendor one more thing to sell.

The interface is simple enough for anyone to use, regardless of language or literacy. Just like filling out a check requires you to enter the payee, how much you are paying and sign it and Eko transaction has the same three elements. Eko customers type the bank's short code, then an asterisk, then the mobile number of the person you are paying, then an asterisk, then the amount, then another asterisk. Then comes the signature. That's the tricky part, but also the most important, because the account is solely on phones, which can be stolen.

Eko's founder Abhishek Sinha (pictured above amid his signage) wanted to come up with a cost-affective equivalent of an RSA token, so he created a paper version of it. Account holders get little booklets with pages of 11-digit codes. Seven digits of it are random numbers, with four randomly placed black marks, where the person enters his or her PIN. So even if the booklet is stolen, no one knows the PIN number and they still can't access the account. There's a VeriSign logo on the back of each booklet. Sinha reached out to VeriSign to see if they could come up with a better solution– instead they endorsed his.

Freedom from always having to carry cash has obvious safety and empowerment implications. But this is a hard company to build out broadly in a country like India. The very strength of the model to truly reach the unbanked—turning those trusted, neighborhood grocers into tellers—inherently makes it costly and time-consuming to build because there are so many of them serving relatively small neighborhoods and villages. Eko has 30,000 account-holders right now. "I thought it'd be a million by now," Sinha says. "We've had a lot of false starts."

There's a cost-time trade off. Since the service launched in late 2007, Eko was outsourcing the management of the grocers to a third party who sells multiple things through the channel already. But evangelizing the product takes more hand-holding, so the number of accounts wasn't growing. Since November, Eko has taken over the management of these grocer accounts assigning employees to each neighborhood and investing in street promotions, blaring its Bollywood-eque jingle extolling the virtues of banking and bedecking stores with in-store signage. Now new accounts are soaring. Eko had just 6,000 accounts before the switch in strategy. It added 10,000 in January and is now adding 10,000 every 15 days.

But costs are going up too. Sinha, who made some money founding a previous company Six DEE Telecom Solutions, has self-funded the venture until now, and in Eko got a $1.78 million grant from the World Bank and The Gates Foundation. But that money will run out this year. He's working on raising a venture round now—and hoping to get a whopping $10 million. In his previous startup he says he was turned down by literally hundreds of VCs and says that this time it's going a lot better. Indeed, he jokes, it'd be hard for it to go worse. For one thing, he's learned a 60 page PowerPoint is overkill.

Like VNL, the solar-powered, mobile equipment company that was 100% bootstrapped by the founder, this is one of those companies that is tricky to build in India. There's a huge social need and business opportunity if it hits scale, but there's also a lack of capital to support deals like this. A venture firm is more comfortable in the $3 million-to-$5 million range and a private equity firm would demand a lot more maturity of the business before it would invest. Had Sinha not invested his savings in the project, it likely wouldn't have gotten this far.

I asked several times if Sinha was worried. What if he couldn't raise the money? He laughed every time I asked with a look in his eyes of "Do you know how hard it actually is to be an Indian tech entrepreneur?" He says he's been through enough to know there's always a way. (Regular readers know there's a word for that.)

Source Of Article: http://techcrunch.com/2010/03/14/eko-mobile-banking-for-india%E2%80%99s-%E2%80%9Cdial-up%E2%80%9D-internet/

Effluent Treatment Plant- Case Study Bone Rendering Plant

Dear Sayeed,

Thanx for the info. I hope you continue to send such valuable info which slips my eye

pls note following points please.

1. The process you sent is primary treatment which is to be followed by MBR or Constructed WETLAND which we have not provided anywhere yet.

In The primary Treatment,  we have not provided UASB.  And then the foaming problem is the biggest.We have not found a solution to the foaming problem yet.

in the flow chart :

2.Balance Tank :We have a balance tank and using lime there to balance pH. NaOH is already coming mixed with water, so no need to add additional NaOH

3. DAF Unit: we are already using Ferrous sulphate, sulphuric acid and PAC there (Polymer) in  DAF.  Dosing is yet to be optimised. 

4.Denitrification:It is done in UASB tank.UASB is missing in Ashrafi and is to be added.We can convert the existing collection tank after DAF into Anaerobic condition by closing the open Top..In Malhotra,we are going for UASB tanks.

5.Nitrification: It is done in the Aeration tank.We have found an anti foaming agent from Ion Exchange by the name INDOFOAM1500, let us try that.Silicone defoamer is not working.We have not found a solution to the foaming yet..We have not used phosphoric acid in the aeration tank.This is a new info.We will try concentrated phosphoric acid when we visit kanpur this time insha Allah.

6.Ultra filtration:In its place we are using Pressure Sand filter.

These primary treatment units are to be followed by a MBR unit or a  Constructed Wet lands unit .After this water can be reused.... ZERO Discharge.

Thanx again for sending such a beautiful article.

Saleem Asraf Syed Imdaadullah,
Mobile: +919899300371
ENVO PROJECTS
New Delhi, India
Web Site :
www.envoprojects.in
www.saleemindia.blogspot.com
Follow me on Twitter : www.twitter.com/saleemasraf