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Biological Treatment Plant with Bio-discs

The functional concept on which the bio-disc treatment plant is based is essentially founded on the following principle: the biological flora, the main actor

The functional concept on which the bio-disc treatment plant is based is essentially founded on the following principle: the biological flora, the main actor in the purification process, is offered an inert support on which it can develop. The support alternately brings the flora into contact with the organic matter contained in the wastewater to be treated and with atmospheric oxygen.

The microorganisms that make up the biological flora, placed in direct contact with the two determining elements for their development and activity, directly absorb the maximum possible amount of organic matter during the immersion phase in the wastewater and the proportionally necessary oxygen during the emergence phase. Practically, this principle has been realized by constructing rollers made of polypropylene discs mounted on a slowly rotating shaft (a few revolutions per minute). The layer of bacterial flora that adheres to the discs, when it reaches a thickness of 4-5 mm, detaches in easily sedimentable flakes. The interstices between the discs never clog and allow for a continuous supply of organic matter and oxygen to the flora.

The flakes, separated from the treated water in a sedimentation tank, constitute a sludge characterized by a high content of dry substances (4%) and a high sedimentation rate.

Biological and Operational Advantages of the Plant

  • Operational Flexibility
    The biological carpet present on the discs can absorb exceptional peaks of pollutant load (even ten times the normal load) for a few hours without the quality of the effluent being affected, accelerating the growth of the flora. The same applies to peaks of hydraulic load with a large dilution of organic matter. The flora present on the discs simply reduces its activity without practically suffering lasting consequences.
  • Insensitivity to Ambient Temperature
    Given the small surface area occupied by the disc rollers, they can be protected by a cover without significant expense. Thus, the little heat provided by the wastewater and the slight exothermicity of the microorganisms' reactions maintain a temperature on the discs that allows for normal biological activity. The biorulli® system thus allows for treatment even at external temperatures of -20° C.
  • Direct Oxygen Absorption
    The flora absorbs the oxygen necessary for its life, in the exact measure, directly from the air during the emergence phase of the disc. This makes this essential phenomenon independent of the temperature, which negatively affects other types of plants where the flora absorbs oxygen previously dissolved in water. As the temperature increases, the solubility of oxygen in water decreases.
  • Operation at High Biological Loads
    The disc system can operate on wastewater with high or very high BOD5 values.
  • Insensitivity to Hydrocarbons, Mineral Oils, etc. and Their Removal
    The microorganisms present on the discs are in the ideal condition to absorb and remove fats, lubricating oils, gasoline, fuel oils, hydrocarbons, etc., as well as to develop a disaggregating action on these substances and true purification. Concentrations of 40-50 mg/l of hydrocarbons in the wastewater are easily reduced. It is therefore possible to omit a preventive de-oiling or to carry it out with very simple systems and even rough results. The hydrocarbon content in the final discharge can be reduced to 4-5 mg/l.
  • Easy Start-up and Insensitivity to Shutdowns
    The flora forms spontaneously on the discs without any need for inoculation. Formation visibly begins 7-8 days after the plant is started, and after 15-20 days, it reaches operational status. In the case of intermittent operation with shutdowns of several days, the plant returns to operational status in 2-4 days. In the case of a shutdown of about a day, the resumption of normal functionality occurs in a very short time.
  • Small Footprint
    The footprint of the system is very modest, around 0.1 m2 per inhabitant.
  • Low Energy Consumption
    The energy consumption related to the biorulli® section and clarification is about 8 kWh/year per equivalent inhabitant.
    The rollers rotate continuously even when no wastewater flows in.

Fields of Application

There are no particular limits to the use of the bio-disc treatment plant for the treatment of domestic and/or assimilated wastewater, particularly suitable for campsites and/or tourist villages with scattered cabins and accommodations. The great flexibility of the bio-disc wastewater treatment plant and its numerous installations worldwide allow us to say that it is possible to treat:

  • domestic wastewater from all types of users
  • discharges from hotels, restaurants, campsites, tourist villages, agritourisms, and other accommodation activities.
  • wastewater from fish farms and kennels
  • wastewater from agricultural companies in general and all other wastewater, including industrial.

Regulatory References

The aerobic percolator bed treatment plant is indicated as a secondary plant element by Legislative Decree 152/06 and is reported in various regional regulations, to be used together with other primary systems necessary to reduce the pollutant load of wastewater and return it to the environment as purified as possible.

IMPORTANT

The European Regulation No. 305/11 has stipulated that this type of plant must also be certified according to the CE Directive EN 12566:3 for both structural and functional parameters, the latter mandatory from July 1, 2013, through the mandatory purification performance test lasting at least 38 weeks.

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Maintenance

One of the main advantages offered by the use of the biorulli® method is the practically negligible maintenance costs due to:

  • reduced speed of the discs resulting in negligible wear of mechanical parts;
  • no control or adjustment is required for oxygen supply when loads vary. Oxygen absorption from the biological carpet is ensured even in the case of high pollutant loads since it occurs directly from the air without the mediation of water;
  • very small plants require maintenance estimated at a couple of hours weekly.
  • absence of noise and vibrations; the low speeds involved are the best guarantee of the plant's quiet operation.

Description and Operation of the Plant

  • Primary Sedimentation
    The raw discharges from the users must flow into one or more tanks (Imhoff type) that perform the following functions:

    a) physical separation of the coarser sedimentable solids
    b) digestion or stabilization of primary sludge; if such tanks exist as biological tanks (septic or not), they are used as is, with any minor modifications. Where none exist, they must be constructed according to our design. From the biological tank, the wastewater is conveyed to the biological plant by gravity, where possible, or by mechanical means.

  • Equalization and Lifting
    The function of this first phase is to balance and lift the wastewater from the arrival level to that of the subsequent flow regulator. The useful volume of this tank is calculated to manage the peaks of hydraulic load that inevitably occur throughout the day. Two submersible centrifugal pumps with open impellers are provided, suitable for lifting wastewater; one of the two serves as a backup to the other, thus ensuring greater operational safety. The pump control is activated by two float level switches with mercury bulbs: the one placed at the highest level gives consent to start, while the one at the lowest level stops the pumps.
  • Denitrification (if required)
    In this phase, the transformation of nitrate nitrogen (NO3) into nitrogen gas (N2) that is released into the atmosphere takes place. This transformation occurs through specific bacteria and in the absence of oxygen. Therefore, a tank at a constant level and properly mixed is provided, in which the waters from the biological section and part of the sedimented sludge from the final clarification tank are recycled.
  • Biological Oxidation with Bio-discs
    From the denitrification phase, the wastewater reaches the oxidation monoblock. The monoblock essentially consists of a tank containing the roller discs driven by a small gear motor. A cover made of polyester reinforced with fiberglass completes the machine and makes it suitable for outdoor operation.
    The discs are made of a polypropylene sheet with a honeycomb structure having a thickness of at least 5 mm. The process of absorption of decomposable organic substances by the formed bacterial flora occurs on them. The treated water and the fragments of bacterial flora detached from the discs are then sent to the final sedimentation tank.
  • Final Clarification
    The function of this tank is to mechanically separate the fragments of flora detached from the discs from the water coming from the biological section. These fragments constitute the so-called “supernatant sludge,” which, due to its good sedimentation properties, settles at the bottom of the tank. The sedimented sludge is then sent, via a timed pump, either to denitrification or to the Imhoff tank; if the primary tank(s) are not located near the plant, a specific local manager may be provided.