Membrane technology for wastewater treatment
Description and use of membrane technology
Pre-treated water, after traditional biological treatment by activated sludge in the sublime and by blowing through the sand filter, is pumped into the space with membrane micro filtration fibres.
The used membranes represent, in practice, a bond of hollow fibres from PP with a thickness of up to 1 mm. Pre-treated water flows by over-pressure through the surface of the fibres into the hollows of the membranes from which perfectly clean, pre-filtered water flows.
It is possible to discharge the water directly into the outflow from the water treatment plant or to accumulate it for further use for example, water for watering the garden or in households for the WC.
For the use of the treated water from the wastewater in households, the automatic device for membrane filtration was developed with a built-in mini-water unit connected to the distribution of utility water.
The long term service life of membranes is ensured by connection of the sand filter and by regular automatic treatment by pressured air from the air blower of the water treatment plant. This patent-protected solution prolongs the time of chemical regeneration of the membranes for more than 12 months.
General information about membrane technology
Semi-permeable membranes are devices in which there is very intensive mechanical treatment.
On the surface of these filters there is a biological layer which in particular cases also act as a biological and chemical treatment. The main principle is mechanical treatment. The membrane filtration is divided into several categories:
|Process||Size of separated particles|
|Micro filtration||> 0.1 micro meter used for TOPAS wastewater treatment plants|
|Ultra-filtration||10 - 100 nm|
|Nano-filtration||1 - 10 nm|
|Reverse osmosis||0,1 - 1 nm|
According to the intended use of the treated wastewater then various levels of filtration are used
Micro filtration is used for common use of treated wastewater where the size of the separated particles in most cases is sufficient for separation of bacteria, in particular Coli bacteria which is contained in wastewater.
The highest level of filtration is reverse osmosis where what is similar to distilled water is produced without the presence of a soluble compound. This process is used, for example, in medicine.
Method of the use of membrane technology in TOPAS wastewater treatment plants
In practice, membranes are used for filtration of drinking water, in various industrial applications and also for filtration of wastewater either for final treatment after the biological stage or as a direct part of the biological stage. Due to complicated character of the operation, this technology is also used abroad mainly in larger types of wastewater treatment plants with computer-controlled processing.
In TOPAS wastewater treatment plants, membranes are used behind the integrated sand filter which ensures a high level of the treatment of wastewater (98%). The technical solution protects membranes against blocking by undissolved substances and the membrane service life is significantly prolonged, as well as the intervals for chemical treatment. Visually, there is no significant difference between the quality of the water behind the sand filter and behind the membranes.
The main difference is the fact that the membranes ensure a bacterially harmless character of water and guarantees in each case the required quality of water on the outflow.
By the flow of water through the membrane there is gradual blocking and a decrease in the flow rate. In no circumstances does the blocking of membranes influence the quality of filtered water, rather the opposite where the porosity of the membranes is decreased.
On the basis of the performed analyses and testing, pre-filtered water from TOPAS wastewater treatment plants was evaluated according to the parameters of drinking water, water for swimming pools, water recommended for natural swimming pools and was also compared with the usual quality of rain water. Even if the water fulfils most of these requirements, it is not possible to consider it as drinking water.
Chemical regeneration of membrane micro filtration
Membrane micro filtration
Regeneration is performed with a decrease of the flow rate of the membranes by about 50% compared with the initial status. Chemical regeneration is performed in the water treatment plant so that the tank with membranes is filled first of all by an alkaline solution and then by the dissolved acid solution.
After use are these solutions let flow back to the inflow tank of the wastewater treatment plant where is neutralization followed by treatment of the wastewater. The whole operation of chemical regeneration lasts about 30-60 minutes and it is not necessary to be performed by a service employee.