Rotating Biological Contactor

A process cycle ideal for small-to-medium installations comprises, screening (filtergrilles), primary sedimentation with a sludge digestion chamber (Imhoff), biological wastewater treatment with RBC and secondary sludge separation via cloth filter. In compact biocombi installations offered by MITA Biorulli, biological treatment is achieved by means of a partially submerged roller-contactor upon which forms the mass of biological slime: this is created by the growth of micro-organisms which derive their nutrients from the colloids and substances dissolved in the wastewater. MITA Biorulli biocombi series installations do not need final settling tanks; their place is taken by a cloth filter, essentially comprising a horizontal drum in perforated steel sheet covered with a special filter cloth and equipped with an appropriate removal system for the separated sludge.

Maintenance is significantly reduced in comparison to traditional plant types and it can be performed by non-specialist personnel. The biological wastewater treatment phase is achieved with a biodisk, comprising parallel polypropylene disks fitted to a central shaft. The diameter varies according to the plant size, from 2,00 m to 2,40 m. The disks have 40% of their surface submerged in the water to be treated and represent an ideal support for the bacterial mass.

The cloth filter replaces the secondary settling basin; moreover it ensures a high effluent quality even when both hydraulic and/or suspended solids loadings are variable. The biologically treated water can reach the discharge only via the filter cloth. Its surface acquires a progressively increasing sludge layer which causes an increase in pressure drops. A level sensor activates a pump which, via a suction system placed in contact with the drum, draws, from inside, the water necessary to back-wash the filter cloth.

The sludge removed by the water is run back to the primary settling tank, if there is one, or elsewhere. The filter cloth is fabricated using a free-fibre “Polstoff” synthetic material, composed of innumerable overlapped small fibres which provide a very high effluent quality.

Key characteristics

• IDisks are partially submerged (40%) in the liquid to be treated.
• Deeper Tanks so lower foot print area.
• Several phases of treatment (biological treatment and sludge separation) are grouped together in a single tank.
• Process sludge removal with Mecana system cloth filter.
• Only one gearbox-motor set for movement of the biodisk and filter the filter is firmly connected to the biodisk shaft.
• Moving parts (disk and fi lter drum rotation) actioned by a motor-gearbox set with output power between 0,75 and 1,5 kW.
• Supply includes basin in treated and painted carbon-steel with easily removable modular covers in FRP and an electric control panel with IP 55 protection.
• Discharge concentrations compliant with current wastewater treatment standards.

Advantages

• Minimum energy consumption.
• Reduced maintenance.
• Easy access.
• Reduced installation space requirements (compact construction).
• Little sensitivity to sudden variations in hydraulic and/or organic loads.
• High operating safety.
• Oxygen supply without aeration or diffusion systems.
• No fl oating sludge problems.
• Low installation costs.
• Absence of odour nuisance or aerosols.
• Pre-assembled plant, ready to be put into service, complete with electric control panel fi tted on the unit which permit rapid installation and start-up.

Sectors of application

• Small communities
• Tourist complexes and camping sites
• Construction sites
• Hotels
• Schools
• Motorway service areas