2. INTRODUCTION
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Irish company OxyMem, has become the first company to commercialise a technology that is set to
revolutionise energy usage in wastewater treatment facilities around the world.
OxyMem Membrane Aerated Biofilm Reactor (MABR) is a unique ‘attached growth biofilm (fixed
film) system’ which allows for aeration from the carrier side. It exploits a gas permeable hollow fibre
membrane which allows the oxygen to travel across the non porous wall by way of diffusion. The net
result is a set of quantifiable benefits that delivers significant ongoing value to clients.
Wastewater Treatment Basics
The treatment of wastewater on a typical wastewater treatment plant usually occurs in a number of
stages.
1. Bacteria are encouraged to thrive within this secondary biological zone of the treatment plant
so they can break down pollutants and thus clean the wastewater. As with any living organism,
in order to thrive they require food, oxygen and an agreeable environment.
2. The oxygen they require is traditionally delivered in the form of atmospheric air, through
mechanical equipment, and usually against a hydrostatic pressure as these zones are often
4-6m in water depth.
3. Rotating blade mixers, jets and/or large blowers are usually needed to push air through the
deep water, to ensure all selected bacteria receive sufficient oxygen.
The majority of energy consumed in traditional activated sludge (AS) wastewater treatment plants
is thus typically in the secondary or biological stage. This far outweighs the operational costs of
pumps, mixers, chemical addition, lighting, heating and so on.
A Brief History
At least 50% of the energy in a traditional treatment plant is consumed in simply providing oxygen
and mixing the bacteria in the secondary treatment phase. And over the past 100 years, engineers
and manufacturers have strived endlessly to increase oxygen transfer efficiency as a means to
make the approach more economical.
Ceramic Diffusers
Bubbles rising through the water, from 6 meters down, create a degree of fluid movement (mixing)
and the oxygen transfers across the thin bubble wall quite effectively.
Ceramic diffusers resemble a rigid sponge, and disperse a large delivery air stream via millions of
tiny bubbles, just above the floor of the tank.
However, while this approach has been utilised for some time, there are a number of obvious
limitations. Although the mechanics work, the porous nature of the ceramic product does not
prevent backflow and so the material is prone to blocking (fouling) over time. The units can
sometimes be fired and/or acid cleaned to improve performance after a few years in service, but
this is costly.
Rubber Membrane Diffusers
After a successful run, ceramic “diffusers” (helping diffuse air into water) gave way to rubber
membrane diffusers, where a perforated rubber sheet is mounted over a rigid base (Tube or Disc).
These standard EPDM rubber diffusers provided an ideal, lower maintenance, non return function, at
an economical price advantage over ceramics. With the recent advancements in rubber technology,
some rubber products have also been customised for industrial use.
3. INTRODUCTION
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Advances in Chemistry
Recent advances in the chemical industry have had an effect on the number of EPDM rubber
membrane installations we are seeing. Polyurethanes are becoming a more popular choice as they
offer a number of advantages including:
1/ They can maintain their “as new” condition for longer periods of operation, as they may be less
susceptible to harsh chemicals in the wastewater.
2/ Polyurethanes do not have elastomers that can leach out over time, causing hardening or
stiffening of the product.
Some manufacturers are now applying special coatings to their base rubber or polyurethane
products, to enhance performance and prolong life expectancy.
Smaller Is Not Necessarily Better
Given that lots of small bubbles have a greater surface area than fewer large bubbles,
manufacturers have focused on delivering aeration products producing smaller and smaller bubbles.
The number of perforations and surface area of the diffusers is steadily increasing, and we are
seeing small traditional discs and tubes give way to large panels. These promise minute bubbles,
fantastic distribution and low energy costs.
The concept of making the smallest bubble, with an infinitely large surface area when millions
of bubbles are released, seems logical, and one would expect an extremely high oxygen transfer
rate, but other treatment plant factors must be considered. No two wastewater treatment plants
are the same; all have varying fluid consistency, chemicals and makeup and site and mechanical
characteristics differ. Most contain solids and biological matter.
The Diffuser Drawbacks
The fact that there is a hole in a material (perforation) at all invites problems, and maintenance of
these aeration solutions can prove costly over time. Fine pores can become blocked more frequently
than larger membrane perforations, and rendered inefficient after only a short time in operation.
Similarly, an uneven distribution of air can affect oxygen transfer and mixing.
Blower back pressures will most likely be higher on systems using smaller membrane perforations,
though there is every chance that less air will be required because the system has the potential to
transfer oxygen more efficiently than a larger bubble system.
The need for large blowers and increased power costs after a time in operation, needs to be factored
in by designers.
Another significant challenge that is often overlooked, is that if the system is designed to be highly
efficient and less air is required, there may be insufficient air in the biological zone to keep the food
and bacteria in suspension. An activated sludge system only works well when the bacteria are kept
in suspension and receive food and oxygen in plentiful supply. Solids settling out in a traditional
activated sludge system can have detrimental effects.
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THERE IS
ANOTHER WAY -
MABR
OxyMem have not followed other manufacturers who utilise a perforated membrane approach. Instead,
OxyMem have gone straight to the far end of the spectrum; to bubble-less aeration, where bubbles are
not used to transfer oxygen to the wastewater.
OxyMem’s Membrane Aerated Biofilm Reactor (MABR), is based on proven biofilm technology that has
been researched for almost 30 years and on a mechanism that mirrors nature at its finest. OxyMem
have used mother nature’s millions of years of evolution and basic principles in physics and chemistry
to achieve an unparalleled aeration technology, as chemicals pass across a cell wall, on demand and
dependant on a concentration gradient.
Transfer of gases and treatment within OxyMem system
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HOW IT WORKS The OxyMem MABR is made up of multiple modules, each containing 1 million - 2 million metres of thin
walled, microbore tubes that are submerged in the wastewater. These hollow tubes, (500µm outside
diameter) have no perforations. Instead, the air inlet and outlet begin and end above the water surface,
ensuring the air in the tube is not pressurised by the hydrostatic head of water, similar to a common
snorkel.
Fouling is Good
Most astonishingly, the biofilm, the matter that fouls tiny perforations on all diffusers on the market
today, ceramic or membrane, is what enables the OxyMem MABR product to work.
The biofilm grows on the outside of the membrane tubes (the wastewater side), just as biomass
grows on the liner and rocks of a pond, and this “attached growth” is what degrades the biological
pollutants in the wastewater.
As Figure 1 illustrates, the attached biofilm simply draws any oxygen it requires across the wall of
the membrane tube, which is gas permeable and without perforations. Oxygen travels from areas
of higher concentrations (inside the membrane tube) to areas of lower concentration (inside the
bacteria) and the greater the concentration gradient, the faster the flow of oxygen. The resultant
benefits are compelling.
Figure 1: OxyMem MABR
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KEY BENEFITS A. 75% Less Energy Needed
The air in the membrane tube does not need to be pressurised to 6m; as bubbles are not being
made underwater. Instead the tubes are effectively open to the atmosphere and the air is
maintained closer to 200 mbar pressure. As a result the physical blower and motor required to
provide air is significantly smaller than on any typical diffused aeration plant.
As there are no bubbles to float up and burst at the water surface (OxyMem MABR uses bubble-less
technology), oxygen in the process air delivered does not get wasted. This results in less oxygen
being sent to the system, further reducing the size and power draw of the smaller blowers. Due
to the fact that oxygen travels across the membrane tube wall, only when required by the biofilm,
oxygen can now be used economically in treatment plants.
Demonstrations have shown that up to 95% oxygen transfer efficiencies can be achieved. For the
first time, owners can have an aeration system that does not waste crucial oxygen; and naturally
less oxygen required results in significantly lower plant operation costs.
B. 50% Less Sludge Produced
The OxyMem MABR has a low sludge yield because it converts more COD to Carbon Dioxide (CO2)
0.15kg TSS/kg COD removed. OxyMem MABR can produce up to 50% less sludge than a typical
activated sludge system. This offers savings on pumps, pumping, pipelines, storage, thickening and
sludge disposal which again can be very substantial depending on location.
C. Running on Site Within Days
OxyMem’s latest technology, requires minimal footprint (up to 80% less space needed), and can be
deployed as complete, standalone package plants needing only a hard standing area on site, or as
single cages that can be dropped into existing tanks to increase the existing treatment capacity.
Whichever approach is taken, the modules will start treating water as soon as a biofilm attaches
to the MABR membranes, usually only a few days. Once operational, OxyMem’s patented biofilm
measurement and control system helps ensure the system runs at an optimum performance.
Every cage has an off-gas capability, in real time, and an owner has easy access to all data. Trends
on oxygen uptake rate, CO2 release rate, fouling rate, automatic cleaning frequency, line pressures,
alarms etc can also be viewed.
Summary
In summary, wastewater treatment has not attracted much innovation over the years, until the
emergence of OxyMem MABR. The economic benefits of adopting OxyMem MABR are compelling,
and when married to the ease with which the solution can be deployed in a whole host of different
settings, the appeal is universal.
With entry level test units available, it is now possible to demonstrate the value at minimal
investment.
We believe OxyMem’s bubble-less MABR technology is currently the world’s most advanced and
most efficient means of transferring oxygen into wastewater. It stands to change the wastewater
aeration world as we know it today. We invite you to see for yourself.
John McConomy, Commercial Director, OxyMem Ltd
7. ABOUT US
CONTACT US
OxyMem offer an innovative approach to wastewater treatment using Membrane Aerated Biofilm
Reactor (MABR) technology to drive efficiency. This award winning technology offers users a range
of significant advantages over traditional approaches, not least in terms of performance and
cost. Clients include; Severn Trent Water, Suez (AGBAR), and The DOW Chemical Company (who
subsequently became an investor).
Visit OxyMem.com to learn more about how OxyMem’s MABR solution can deliver a transformative
impact at your wastewater plant.
T: +353 906 465 727
E: sales@oxymem.com
W: www.oxymem.com
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November 2016
