Obtaining a suitable membrane for MBRs
I see a few options here:
I was not able to find any way to buy a suitable membrane module as is directly over the web (who says the internet has everything?)
The problem is that membrane bioreactors seem to be used almost exclusively for municipal wastewater treatment, so the membrane modules are pretty big to achieve a relatively low cost per unit membrane area. The bioreactor concept must be used in pharmaceuticals etc. somewhere, and maybe a membrane module for use there would be easier to get and a more suitable size.
There are, however small membrane modules that I have seen referred to a number of times in papers about small MBRs, usually made by the same companies that make the big modules for wastewater treatment – only, I’m pretty sure, the problem is they are intended to be given out to wastewater treatment engineers etc. for testing purposes. Still, it might be possible to get a hold of one of these. They might not be expensive, or the companies might even send them out for free. Zenon (general electric) and kubota are two companies that have such modules.
Zenon/general electric also sell the so-called homespring water filtration system, that uses a hollow fiber filtration module, and maybe one could be obtained as a replacement part, but it is still way too big.
Another option might be to use an ultrafiltration or microfiltration water filter cartridge, which are readily available. These are usually pleated radially, though. (I.e. a flat sheet of membrane material is folded accordion-like, then one edge is connected to the opposite edge) To keep them not too badly fouled, they could be backflushed periodically, water could be directed to flow across the membrane area longitudinaly, they could be cleaned with ultrasonic cleaning, or maybe you could take some really narrow plastic tubing, poke some holes in it for air bubbles to escape from, and actually run it along the bottom of the membrane? Then it would be like a flat plate membrane, only pleated.(edit: no, I don’t think that would work very well, had a look at some pleated filters today, and the pleats are too close together.)
I did manage to find one UF hollow fiber cartridge, which might be air scourable: https://www.wattspremier.com/products.php?product=Filter%252dPure-%28UF3%29-UF-Membrane#
You could either maybe use very narrow plastic tubing with small holes in it, and run it in between the fibers, or maybe you could just get away with putting it the path of a stream of bubbles.
There are also flat plate modules apparently made for food processing applications, maybe one of those could be obtained.
Here are a few links I collected that could be leads to hollow fiber UF or MF cartridges:
says hollow fiber microfiltration http://www.sanovivstore.com/water-filter-ionizer-plus-microfiltration-ultraviolet-disinfection.html
EDIT: This is an important issue for MBRs, so I tried looking again to see if I could find a filter. The filter flow rating for clean water (which is what the filters I have seen are usually for) should, I think, be something like 25 to 10 times the desired flow the MBR must handle, but potentially as much as 60 times, I don’t know exactly, and it will vary depending the contents of the water and the type of membrane. If the flux for new membranes with clean water seems to be about 5 lpm per m2 (that might not be right), the flux for the membrane in a bioreactor seems to stabilize at about 5 to even 40 lph per m2. The amount of calcium in the water can have a big impact on UF membranes, and if the water is being recycled repeatedly, that level might be fairly low, so that would be good.
I discovered that there are some cross flow filters, either MF or UF, that are sold to fit in reverse osmosis membrane housings, and some of which are made to treat wastewater, such as http://www.jbii.com/LiquidFiltration/Osmonics2.html , and here : http://www.appliedmembranes.com/product_catalog.htm and http://www.mikunikikai.com/mb_e/mb-500_e.htm however they might be spiral wound, which is not really suitable.
Here: http://www.sterlitech.com/37654/445463/Flat-Sheet-Membranes/Ultrafiltration-UF-Membrane.html , it’s hard to tell what the size is, though. The PVDF ones would be the best, I think. It would sure suck it if was just the actual membrane material itself, it’s hard to tell.
here is another one hollow fiber http://www.universalwater.net/sterotap.htm
might be too small : http://www.basegear.com/msr-hyperflow-water-filter.html
might be a misprint , couldn’t find anything about this filter elsewhere http://www.fernsnutrition.com/alkablue_dx.html
There may be more membranes to be found there, by searching “UF cross flow membrane” or “Mf cross flow membrane” or “(UF or MF) cross flow module” “(UF or MF) flat sheet module” “(UF or MF) flat sheet membrane” “(UF or MF) hollow fiber” etc. etc. followed by ” view cart” or something, so you actually get products you can buy instead of press releases and junk.
Update: I just found out Mitsubishi makes chlorinated polyethylene flat sheet modules commercially that would be about the right size, about 0.3 square meters each, you’d need a few. Don’t know how to get ahold of any, though I have been looking around on sites like alibaba.com, sometimes they say that the minimun order quantity is 1. There are some module there intended to be used for drinking water filtering that could maybe be modified easily (they even include the aerator foot built in), but they are pretty big, the smallest one I could find was a 4 sq meter one for $150, but I think it was PES. Should have bookmarked it now.
http://cnmiec.en.alibaba.com/product/324099439-209498042/Flat_Plate_MBR_Membrane.html says they have flat plate modules of a suitable size. Minimum order quantity is 1. Checking more of these supplier marketplace things would surely turn up more like this, as those must be standard cartridge sizes. They are an awkward rectangle shape, so you would need a flat rectangular water tank to house them. Maybe just some Al sheet metal and glue it together with RTV silicone glue, with a pan under it in case of leaks.
Also, I wonder about just turning one of those hollow fiber modules mentioned above sideways. Sure, it wouldn’t be perfect, would take some extra energy because the aeration isn’t very efficient, but if it works….
Whenever there is a refractory search like this, I occasionally try to think of new and better search terms. I searched “lab module” +mbr recently and found a commercially available module that should be just right. The sterapore SUR234L. It’s polyethylene rather than PVDF, but whatever. http://www.microsofttranslator.com/bv.aspx?ref=SERP&br=ro&mkt=en-CA&dl=en&lp=JA_EN&a=http%3a%2f%2fwww.mrc.co.jp%2fsterapore%2fhaisui_01.html