SOLVIA CryoMABR is a gas-permeable membrane carrying a pre-formed macroporous cryogel layer with immobilised microorganisms on its outer surface. Oxygen passes through the membrane wall straight into that layer, while the pollutants reach it from the water on the other side.
The membrane element supplies oxygen from within: air or oxygen sits in the inner cavity of the gas-permeable membrane and crosses its wall by molecular diffusion, forming no bubbles in the water. On the outside the membrane carries a macroporous cryogel layer with immobilised microorganisms, and the oxidation of the pollutants proceeds inside that layer rather than in a freely growing biofilm on the surface.
It is meant for MABR reactors, aeration tanks and plants for deep biological treatment, where the oxygen has to be brought to an immobilised microflora rather than dissolved in the bulk of the reactor. One element combines three duties: the supply of oxygen, the retention of an active microflora and the biocatalytic oxidation of the pollutants; several elements are assembled into cassette modules with gas inlet and outlet headers, including where the reactor volume is limited.
In the classical scheme air is delivered through porous diffusers or perforated pipes, the bubbles rise through the depth of the water, and only part of the oxygen has time to dissolve, the rest leaving into the atmosphere. The patent materials put the oxygen utilisation of such a supply at 5–25 %, which accounts for the share of aeration in the operating costs of treatment works.
Bubbling has a second side to it: strong mixing. For some processes it is useful, but for biofilm and immobilised systems it can be a problem: the biomass may be washed out, damaged or work unsteadily. A supply through a gas-permeable membrane is arranged differently. The oxygen does not enter the water as a bubble but crosses the wall by molecular diffusion and arrives straight at the microorganisms, so the losses with the escaping air are reduced and there is no bubble mixing in the reaction zone.
In the known MABR solutions the biofilm grows on the membrane by itself, out of the microorganisms of the wastewater, so its composition, thickness and structure are not set at the start, and the working layer depends on whichever microflora arrived with the effluent. Such a film overgrows, forms unwanted zones and detaches, and recovery after detachment takes, according to the development materials, 3–6 weeks.
The cryogel coating of SOLVIA CryoMABR is formed in advance and bound to the outer surface of the membrane as an engineered material: a macroporous structure 1–5 mm thick with microorganisms immobilised within its volume. The thickness and the properties of the layer are set at the manufacturing stage instead of adding up from whatever the wastewater brought in, and the working layer does not have to be grown on site.
Oxygen enters the cryogel from the membrane side, the organic pollutants and the nitrogen-bearing compounds from the wastewater side, and the microorganisms sit between the two opposing streams, inside the porous matrix. This is where the transfer differs from an ordinary biofilm carrier, on which the organism takes both the oxygen and the substrate from one and the same liquid.
A functional zoning may take shape within the cryogel: closer to the membrane the conditions are more aerobic, closer to the outer surface less saturated with oxygen. The development materials name this as a condition for aerobic oxidation and further biological processes at once, nitrification and denitrification among them, which means that the work of the layer is set by its depth and not by the amount of retained biomass alone.
The development materials state an oxygen utilisation of up to 92 % and a reduction of the aeration energy by 5–8 times against bubble systems. Both figures belong to the supply of oxygen through the membrane straight into the biocatalytic layer, and both are declared figures of the development rather than measurements on a working site.
A coating formed in advance shortens the way to the working regime as well: the start-up time is stated as under 24 hours against 3–6 weeks for the prototype with a self-grown biofilm, and for the same reason the return to the regime after servicing is quicker. The retention of the microflora in the macroporous matrix was checked separately — in the test example no detachment of the biomass was observed over 30 days of the experiment.
SOLVIA CryoMABR is SOLVIA's own technological development in the biological treatment of wastewater and in bubbleless aeration. The solution brings together a gas-permeable membrane, a cryogel biocatalytic coating, immobilised microorganisms and a counter-diffusion oxygen supply, and is being developed as a product platform for energy-efficient bioreactors, MABR systems, the upgrading of treatment works and compact plants for deep biological treatment. The structural parameters, the manufacturing regimes, the particulars of the coating and the composition of the biocatalytic layer are the developer's know-how and are chosen for the individual task.
With a bioactive carrier the medium holds the biofilm, while the microorganisms take the oxygen from the surrounding liquid, into which separate diffusers deliver it. Here the membrane itself serves as the element that supplies the oxygen and at the same time as the base of the biocatalytic layer: the cryogel is formed not on a passive block of carrier but on an active gas-transport element. The mechanism of oxygen mass transfer is a different one, and so is the task.
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