Technology description

MBR technology is part of the periodical non-stationary bio-treatment technology group. The reason to choose and to analyze the above mentioned method of treatment is simply because other physically-chemical and other subsystems of bio treatment find it hard to meet the criteria required by law.
From the mechanical point of view, and regarding the aspect of operational conditions, the use of MBR processes for the municipal wastewater treatment is very simple, and very effective. MBR process for municipal wastewater treatment requires prepared influent on the inlet in reactor, and as many reactor basins as the calculation of   process conditions requires.

Picture 1. Advantages of MBR system

There is no use for aerated sand catchers, primary or secondary sedimentary basins, or sand filtration whatsoever (picture 1).  Large scale of tolerable incoming flows in MBR system makes MBR plants very suitable for treatment of high peak loads and/or for treatment of very low incoming flows during the period of low water consumption (summer-winter). The basic advantage of using the MBR technology is that the plants are relatively small, and on the level of applied technology they have the built-in possibility for tertiary wastewater treatment, with influent low in suspended solids, KPK, BPK5, ammonia, TKN and TP (III degree of treatment). Through removal of nutrients, nutritious salts, phosphorus and nitrogen, the main reason of eutrophication is removed also.

Influent, i.e. incoming municipal wastewater in the case of MBR plant can be very loaded, i.e. much more polluted than those in classical biological systems, because of the membranes as separation units and also because of high sludge concentration (MLSS - Mixed liquor suspended solids) and low F/M (incoming load corresponded to biomass) which provides opportunity for great flexibility of biological load. Effluent quality in MBR process is much better then in any other alternative biological wastewater treatment.

Effluent in MBR Plant (picture taken on the Sv. Andrija plant)	Effluent from I degree treatment

The plants are designed for constant operation in specific conditions of hydraulic and organic load, in the way that they can operate at different daily capacities and/or summer-winter regimes.
Depending on the capacity needed, the certain bioreactors are activated. Thereby the flexibility in operation is provided, which is necessary for acceptance of eventual quick increase of incoming wastewater flow during the summer months. Also, the operator is able to simply change the cyclic sequences in order to save the operating conditions in the case of  loads lower than those projected (for example, during the start up).
The plant is designed so it can be built in several phases, since one or more reactor basins can be working, while others are not completely finished. In the same way it is possible to make all necessary repairs during the period of reduced loads.