Biofilter for odour removal

BFT

CATEGORY ODOUR TREATMENT
TYPOLOGY ODOUR CONTROL UNITS

WHEN TO USE IT

The biofilter for odour removal BFT type is used to control unpleasant and unhealthy odour emissions, coming from liquid and solid treatment processes of biologic origins.

HOW IT IS MADE

The biofilter for odour removal BFT type is mainly composed of: a tank containing the whole system, composed of standard panels to be assembled with bolts on site; a filter bed support system made of profiles and grating suitable to sustain the weight of the filter bed under normal operating conditions and semi-permeable containment fabric; filter bed composed of a calibrated mix of high quality wood chipps characterized by a high degree of porosity, high humidity retention and with chemical-physical features suitable for the growth and the catching on of a wide range of bacteria able to metabolize the odorous substances of natural origins or inorganic, aromatic or aliphatic synthesis; one or more centrifugal fans to suck the air to be deodorized and feed it into the biofilter; an odour pre-removal and air humidification system through a mini scrubber fed with service water and assembled directly onto the air delivery pipe to the biofilter; an automatic humidification system of the filter bed made of PVC pipings, spray nozzles and solenoid valve; a biofilter cover which allows the maintenance of the ideal conditions for the survival of the bacterial flora, avoiding the direct exposition to the sunlight which would be responsible for the uncontrolled drying of the bed; a system to control the biofilter operating parameters composed of temperature sensor and relative humidity sensor of the filter bed, directly connected to the local control panel; local electric control panel installed on board.

HOW IT WORKS

The main odorous compounds coming from water and waste treatment plants are: mainly hydrogen sulphide, mercaptans, dimethyl sulphures and ammonia. These compounds can cause breathing difficulties for the plant workers and problems to people living nearby if their concentration exceeds the human tolerability limits. The odour treatment system consists in removing or transforming the odorous compounds in order to reduce their concentration below the perception limit. This result is easily achieved by using BFT biofilters. The flow rates to be treated are about 4-6 changes per hour for areas with no presence of operators; whereas the flow rates are about 10-12 changes per hour for areas with presence of operators. The fan is conceived to suck the air to be treated and send it first to an odour pre-removal and humidification system and then from there to the biofilter. The air is fairly distributed under the bed and crosses the bed from the bottom upwards thanks to the overpressure generated by the delivery of the fan. The bacterial flora nested on the filter bed cleans the air from the odorous compounds and the purified air goes out from the top of the biofilter. The bacterial growth is automatically removed by the drainage water surplus which comes back at the inlet of the water treatment plant. The biofiltration system achieves excellent results (>99% reduction of unpleasant odours), with low operating and maintenance costs. The BFT biofilter works very well in treating hydrogen sulphide with an inlet concentration of 400 ppm maximum. The acidification tendency of the filter bed due to the air to be treated is hindered by the filter bed itself, as a consequence the pH control of the bed should only be carried out from time to time by laboratory tests or by the use of simple field instrumentation. The temperature sensor and residual humidity sensor control the correct operation of the biofilter, regulating automatically the opening time of the water solenoid valve according to the bed humidification degree.