System Description MBR (Membrane Bio Reactor)
The small purification unit was developed and dimensioned with a connection value of 8 inhabitants which for German standards means 1.2m³ sewage volume per day.
It works according to the membrane activation procedure and implements the steps sludge stabilisation, nitrification and denitrification (see dimensioning, System 1). The system consists of an initial settling tank (ST), which can optionally be single- or multiple-chambered, and the subsequent membrane reactor (MR).
The tanks can be made both of plastic and of ready-made concrete parts. If the ST is already present, it can be integrated into the system concept through necessary repair measures, whereby the MR is only added on.
- Flow chart of MBR using separate membrane reactor
The waste water of the connected residential units first flows by gravity into the ST. Flowing through the chambers, sediment and floating matter are safely held back. As a result, a part of the dirt is removed from the waste water (about 15 - 30%).
A compressed air lifter brings the waste water via a connection line out of the last chambers of the ST into the MR. If due to malfunction no water is moved and the water level therefore rises until shortly before the emergency overflow is reached, the system emits an alarm. If the fill level continues to rise, the mechanically precleaned waste water flows into the discharge via the emergency overflow, which simultaneously serves as a drain.
During operation, the compressed air lifter actively moves the waste water into the MR. As a result, fill level differences of about 30 cm can be reached in the ST; these are used as a mix and compensating volume.
The working of the membrane activation, dependent on fill level, is subdivided into the steps
? filling (and denitrification)
? standby
? filtration (and nitrification).
- Mechanical Pre treatment (Sedimentation)
- Mix and Buffer Volume (volume to be pumped to MBR reactor)
- MBR reactor no aeration (no filtration)
- MBR reactor aerated (filtration)
- Output (clean water)
1. Filling (and denitrification)
A float switch in the MR registers a lower and upper fill level. If the lower fill level (1.40 m) is reached, the denitrification sequence is activated for 30 minutes. A solenoid valve switches the air of the blower onto the compressed air lifter so the waste water is transported into the MR.
During the denitrification sequence, the MR is not ventilated. When the upper fill level (1.50 m) is reached, the solenoid valve switches back to MR ventilation. If the duration of the denitrification sequence has not been completed when the upper fill level is reached, the blower is switched off. Switchover to the filtration sequence only takes place after the time for the denitrification sequence is completed.
2. Standby operation
If the fill level in the ST has fallen so far that the upper fill level in the MR cannot be reached within the denitrification times, the system switches into standby operation. During this phase, the MR is first ventilated for 15 minutes, and then the blower is switched off for 15 minutes. After that, the system switches again to the filling operation.
These steps are repeated until the upper fill level in the MR is reached. Only then does the system switch over to filtration. This permits energy-saving operation when there is little flow to the ST.
3. Filtration (and nitrification)
The filtration and nitrification phase, which lasts 70 minutes, takes place after the filling and denitrification sequence or in standby operation. In this phase, the MR is ventilated through switching on of the blower.
The ventilation device is mounted in a ventilation box below the membrane module. It brings in the oxygen needed for biological breakdown in the form of fine bubbles and simultaneously generates an outward stream in the membrane module, which is required for cleaning the filter surfaces.
The filtrate pump suctions the filtrate out of the module with a permanently set constant volume flow of 100 l/hour. Filtrate removal is carried out in pulse/pause operation. A two minute pause, in which filtration does not take place, follows a 10-minute filtration phase.
The pause causes the membranes to relax, whereby they are intensively cleaned through the upward flow. The filtration performance is sufficiently great that the lower fill level in the MR is reached within the available 70 minutes, and the system switches over to filling again. If filtration performance drops, an alarm is triggered.
Photovoltaic powered MBR (Membrane Bio Reactor) with online monitoring
We are using the latest technology of a 3 chamber MBR (Membrane Bio Reactor) technology and adapt it for local quantity, quality and energy requirements.
- Process overview for PV MBR
A plastic tank or concrete tank can be used. All components like aeration, pumps, filters etc will be inserted within the tank. Using locally available tanks is preferred.
Installation can be indoors or outdoors.
In the last chamber of the plastic tank will be the submerged ultra filtration unit filtering out impurities down to the sizes of viruses and bacteria. No extra pressure required for the UF unit.
The water leaving this tank is well below the European bathing water guideline. In many countries it is even considered as drinking water quality.
The system is equipped with a remote monitoring using GSM modem and transmission of performance data per SMS or E-mail. Via a web interface this data can be monitored from any PC with internet connection.
- This example of a 3 chamber concrete tank with submerged ultrafiltration contains certain features: inlet, emergency overflow, air inlet, permeate outlet ultrafilter, housing, sludge pump.
