MBBR typeactivated sludge plants

This type of plants is recommended for treating residential waste water, especially when implementing the potential of existing plants that, as often happens, have become undersized due to an increase in the number of users.

The effectiveness of such systems, based on traditional activated sludge treatment, is enhanced by fills added inside the aeration compartment. By increasing the specific surface of the tank, the fills create a much larger virtual surface for bacterial reaction. Therefore, the same type of waste water can be treated with an oxidation volume much lower than in traditional activated sludge plants.

Process description

The treatment process includes the following stages:

PRIMARY DECANTATION in an Imhoff tank, to retain floating material and any settleable solids and obtain partially clarified effluent with pollutant load cut down by approx. 30% in residential waste water, and by a variable percentage in industrial waste water according to type.

BIOLOGICAL OXIDATION as in standard activated sludge processes, sewage comes in contact with aerobic microorganisms (active sludge), which degrade organic matter. Biomass oxygenation is guaranteed by submerged aerators to keep maintenace operations to a minimum.
Bacterial biofilm, made up of aerobic and anoxic layers, forms on the surface of the fills promoting the degradation of the nourishing substances contained by incoming waste water.

FINAL DECANTATION as in standard active sludge treatment. Sludge settles on the bottom of the tanks while treated water flows off the surface along the overflow channel.

The strong points of this system lie in the lower volume of oxidation and in the fact existing plants can be enhanced by simply placing fills inside the aeration tank.

Running and maintenance

Running involves periodical checks of all associated devices (pumps, aerators or blowers, electrical panels, clocks, etc) and scheduled analysis of biomass evolution).

The quantity of microorganisms in the tank must be periodically monitored, eliminating excess bacteria if necessary. As in all biological plants, to achieve the best degree of treatment it is essential not to stress the microorganisms, hence waste water bearing chemical/physical features (pH, temperature, etc) not fully compatible to the growth and survival of the latter must be barred from the plant.

Products and technical features

Plant size varies according to specific requirements. The system is composed of precast concrete tanks, fitted with covers bearing adequately sized inspection windows for constant and effective maintenance. Airing is performed by means of high-performance submerged aerators. The overflow channel found in the secondary sedimentation tank is made of Thomson profile and fitted with a foam guard to prevent sludge from leaking into the receiving water.