Membrane MBR technology revolutionizes the treatment of wastewater
The use of membranes submerged for the construction of biological reactors has experienced in recent years a great step forward which has allowed to radically alter the conception that until now had traditional wastewater treatment plants. Stations sewage S.A. It presents this revolutionary technology with its line of treatment of wastewater with membrane MBR technology.
The technology of membranes for purification of wastewater is basically based on the existence of two types of submerged membranes: membrane of hollow fibre and flat membrane. The use of one or another type of membrane membrane cassette allows to obtain a high quality of the permeated. Thus, it is not necessary to install a decanter after the biological reactor, because you get a free water of solids in suspension which, in turn, can be reused directly.
The biological reactor operates at high concentrations of sludge. Its volume is 3 to 10 times smaller than the reactor that is required in a traditional plant of activated sludge, SBR, etc. As a result of the high bacterial concentration in the reactor, there is less sludge volume. Also, the separation of the hydraulic retention time and sludge retention time allow reaching high ages of sludge. The MBR process is defined by its low power consumption: only between 0.1 and 0.3 kWh per cubic meter of treated water.
Hollow fiber membrane has a screening of less than 1 mm, which is a high risk of bottleneck. Its filtration process is carried out only by means of suction and mechanical wear is defined by the high friction between fibres and a contralavado at high pressure and flow. Hollow fiber membrane fouling control is performed by aeration and needs contravados. Also cleaning should be made more frequently and, occasionally, proceed to the occasional emptying of the tank of membranes. Repair and detection of breakage of the membranes is, in this case, complex.
On the contrary, the screening of the flat membrane is higher than 3 mm. Filtering is performed by suction or gravity, so concerning the mechanical wear, the separation of plates takes place without friction and does not need to contralavado. Control of fouling can occur by aeration or intermittent suction, chemical cleaning is of low frequency and duration, and rupture of the membranes is quickly detected and its change is easily done.
The flat membrane allows the formation of the biofilm on the surface and, by controlling its growth, increased performance of the reactor is obtained. The plates are placed in a cassette, which in turn incorporates diffusers tubes of air thick bubble at the bottom. These boards allow the ascending air drag activated sludge, glide on the surface of the membrane, drag the substances that make up the biofouling. The water passes through the membrane, while the biomass remains in the reactor. The obtained water is of high quality, free of viruses, bacteria, and solids, so it can be reused, as it regulates the Royal Decree 4620/2007 of 7 December of reclaimed water.
The selection of the number of membranes and cassettes for a sewage treatment facility will depend on the type of waste water (industrial or municipal), the working temperature and the concentration of mud. Thus, industrial wastewater always require a pilot to observe the efficacy (permeation flux) that is more advisable. Furthermore, municipal wastewater, wherever their greater share of domestic origin, it cannot be based on average values of 20 to 25 litres per square metre per hour, with 50 litres per square meter and hour at maximum value. These values will determine the number of cassettes to install. The obtaining of the permeated can be reduced if, prior to the reactor, installed a tank of homogeneity enabling laminar flows tip that fall to the floor.
The operation of the flat membranes requires that the blower of aeration is under way to facilitate the cleaning of the surface of each plate. With this system, sewage stations avoids having to washed with upstream. This type of flat membranes must work at less than 0.2 bar transmembrane pressure, can so be designed the suction system by gravity using hydrostatic of 1 to 1.5 meter water column pressure of membrane modules above. When working by aspiration through a system of pumping, the PTM may not exceed 0,2 bar. If this pressure is higher, the membrane does not works correctly, which, in most cases, means that it is necessary to carry out a chemical cleaning of the membranes.
The chemical cleaning of the flat membranes must be done at least once every six months, and in waters difficult, when the transmembrane pressure exceeds the value of 0.2 bar. The cleaning process is carried out on the spot, without having to remove any element of the MBR tank. It's an operation quick and simple, if compared to other technologies. To remove organic bowel movements that focus on the micropore membrane, stations sewage treatment plants use a diluted solution of bleach (1 liter of bleach in 20 litres of clean water, of which we will use about 3 liters of dissolution) recommended by each membrane of a square meter. Calcium, iron, aluminum and other minerals present in the ichor mixture of the reactor can produce a silting of the membranes. In order to eliminate this kind of inlaid proposes a chemical cleaning with citric and oxalic acid. In difficult waters or fatty content might require the use of other cleaning products to recover the permeability of the membrane.
