Frequently Asked Questions

What type of membranes do OxyMem use? 
OxyMem manufactures its own membranes. They are made from dense PDMS (Silicone) and have no pores. The external diameter is 510µm and the internal diameter is 300µm. Oxygen transfers across the membrane wall via diffusion, dependent on a concentration gradient. Oxygen travels from inside the micro bore tubes (where oxygen concentration is greatest), across the wall and into the biofilm (low in oxygen) where is consumed.

How much membrane is needed? 
This depends on the nature of the wastewater to be treated and what quality the wastewater must be treated to. The determining quantity is the rate of treatment per m² of membrane surface area. In our Generation 4 module we deliver 2200m² of surface area. It is important to note that unlike other fixed film applications the OxyMem carrier (membrane) is delivering the oxygen which means the biofilm is 100% active and available for treatment. Another import aspect is the amount of oxygen transferred per m² of surface area, the higher this is the more treatment that can be effected.

Why are there no bubbles in the MABR aeration process? 
The MABR does not rely on bubbles to deliver oxygen. It uses hollow fibre, gas permeable membranes, to support a fixed film ecosystem for the biology which allows for direct delivery of oxygen to the micro-organisms.

Why does the MABR use less energy than bubble diffusion? 
Essentially the MABR is less wasteful than conventional aeration processes which depend heavily on the amount of surface contact between air and wastewater. In bubble aeration typically less than 30 percent of the oxygen supplied by blowers is transferred to the wastewater resulting in an enormous energy waste. This is because energy is required to compress air in order to blow it to the bottom of a deep tank and produce air bubbles. Buoyancy forces take the bubble to the surface and, along the journey, transfers some of the oxygen to the wastewater. Once at the surface the bubble escapes back into the atmosphere resulting in lost oxygen/energy. Even with the most recent developments in fine bubble aeration technologies the maximum oxygen transfer efficiency is limited to about 35%. This is because the efficiency is influenced by the size of an air bubble, depth of the tank, and by the time it takes the bubble to get from the bottom to the top of the tank. The MABR can achieve very high oxygen transfer rates (up to 95%) even at very low operating pressures (100-200mbar) because the process does not have to overcome a hydro-static head. This results in 7X energy savings over CAS and process performance of 14kgO2/ kWh.

How much Oxygen can be delivered to the wastewater? 
OxyMem Generation 4 membranes will deliver on average 12g O2 per m² of surface area when operating on air. For the first time, it now make sense to use higher oxygen concentrations because OxyMem does not waste gas. Using enriched air (>90% oxygen) the same MABR module can deliver four times the oxygen, giving you a lot more treatment capacity for a much lower capital cost.

Can the system be retrofitted into an existing plant? 
Absolutely, OxyMem solves energy intensive wastewater treatment with an innovative ‘Drop in’ or ‘IFAS style’ deployment for wastewater aeration. OxyMem MABR can compliment existing treatment systems by delivering up to 50% additional biological capacity in an existing aeration basin (without emptying the tank!). It can also be used for replacing a legacy aeration system entirely.

How can I try MABR? 
OxyMem has a complete range of solutions for you to try MABR. We have lab scale offerings, mini MABRs for field use, and large scale packaged systems for onsite demonstration. 

Click here to Trial MABR today

Which application is the MABR best suited? 
OxyMem MABR will perform well in any environment where these challenges arise:     

- Energy neutrality is a goal    
- Sludge disposal is a challenge / costly    
- Existing treatment system is overloaded    
- Nitrification is a challenge    
- Asset can no longer meet consent    
- Existing asset (tank) needs to be upgraded    
- Footprint is limited

What are the product specifications of the MABR Module? 
We are now working with our third generation system which is now delivered in the form of a stack-able modular unit with the following specification:

Material                                        Stainless Steel
Length                                            2.1 m
Width                                              1.05 m
Height                                             2.1 m
Weight (Dry)                                   950 kg
                                          4 m³
Membrane Surface Area              2200 m²
Specific Surface Area                   490 m²/m³

What is the typical sludge yield in an OxyMem MABR? 
The Sludge yield in an OxyMem system is 0.1-0.15kgTSS per kgs COD removed.

How do you perform desludging? 
Sludge is allowed to settle in the bottom of the tank and removed using a simple removal system. This sludge is very settable with a concentration of up to 10g/l. In a Retrofit installation or IFAS, the excess biofilm would form part of the MLSS and be removed (i.e. no changes are required to the sludge removal system).

Does phosphate removal occur? 
Some phosphate removal does occur, but this is only the phosphate required for the biofilm growth. What is the systems denitrification efficiency?  Currently without trying to achieve denitrification over 50% of the oxidised Ammonia(Nitrate) is removed via denitrification. By limiting oxygen delivery, up to 90% denitrification can be achieved.

How does MABR deal with Fats Oils and Greases (FOG)? 
FOG in the wastewater will attach to the outside of the biofilm where it will be broken down. This will require extra Oxygen to break down the FOG and reduce the volume of wastewater that can be treated.Therefore it is preferable to remove FOG in advance of secondary treatment if possible.

How do you control the thickness of the biofilm? 
OxyMem systems use a patented biofilm measurement technique, which determines an effective biofilm thickness on the membrane. When the control system determines that the biofilm has grown too thick for the treatment process required, the system takes steps to automatically remove the excess biofilm.  The frequency of cleaning is dependent on the growth rate of the biofilm and the nature of the treatment process, but can vary from once a day to once every two weeks. Self cleaning will typically last 1-2 mins in duration so the energy burden us negligible.

How long do the MABR membranes last? 
OxyMem will guarantee the membranes for most applications for up to 10 years. The life expectancy is about 20 years.

How can the OxyMem system operate at such low pressures? 
The membranes in the OxyMem MABR do not contain any pores and due to the structural integrity of the membranes the lumen does not experience the external hydrostatic pressure. Similar to a swimming snorkel the air in the membrane fibres does not need to overcome hydro-static head as compared to conventional aeration systems. This allows the system to operate as much lower pressures and thus provide significant energy savings.

Where are OxyMem systems currently installed? 
OxyMem currently has a broad number of installations (at varying scales) across the globe including; UK, Ireland, Canada, Sweden, Spain, Saudi Arabia, Brazil and Japan.

Please contact us today if you would like to visit a site.

What are the OxyMem cleaning and storage procedures? 
Biofilm maintenance and control are accomplished automatically by the control system.  Since the membrane is dense and has no pores, no special cleaning is required.  Membranes are not subject to drying; they can be stored indoors, in dry conditions as long as they are protected from sunlight and physical damage.

In BNR systems the functional groups of nitrifiers and heterotrophs co-exist in the system. In high organic carbon environments can heterotrophs out-compete nitrifiers in biofilm? 
No the the Membrane Aerated Biofilm Reactor is a more balanced ecosystem. The nitrifiers are located at the base of the biofilm attached to the membrane surface, not at the surface as in other biofilm system, this means that they are protected from sloughing and erosion. The hetrotrophic bacteria grow in the outside layer where they have plenty of organic carbon and utilise nitriate and any excess oxygen that diffuses through the nitrifying layer.

If the aeration demand increases how will be the oxygen transfer maintained to prevent the system turning anaerobic? 
As the load increases the oxygen supplied can be increased by increasing the airflow through the membranes. This results in an increase in overall oxygen concentration within the membranes resulting in increased performance instantaneously. Alternatively in systems where there is a large variation in aeration demand, the Oxygen transfer rate can be increased by increasing the % of oxygen in the air supplied . This will result in more kg of oxygen being transferred for a given membrane surface area.