Case study / Biological biodisc purification plant

The fundamental concept of the biodisc purification plant is mainly based upon the following principle:
an inert support is offered on which the biological flora, main actor of the purification process, can develop. This support positions the flora, alternatively, in contact with the organic material in the sludge to be purified and with the atmospheric oxygen.
The biological flora microorganisms, placed in direct contact with the two decisive elements for their development and activity, directly absorb as much organic material as possible during submersion in the sludge and oxygen proportionally necessary during submersion.
Practically this principle was realized by making rollers of polypropylene discs fitted onto a low velocity rotating shaft (some rotation at 1′).
The layer of bacterial flora attached to the discs, having reached the thickness of 4-5 mm, comes away in flakes which are easily sedimentable.
The interstices between the discs never clog up thus allowing the flora of organic material and oxygen to be continuously supplied.
The flakes, separated by the purified water in a sedimentation tank, form a mud having a high content of dry substances (4%) and a very rapid sedimentation.

Biological and operative advantages of the plant:

Flexible operation
The biological carpet on the discs, in the presence of a highly polluting load (also ten times the normal load) can absorb for several hours without a reduction in quality, accelerating flora growth likewise when there are peaks in the water flow with a great reduction in the organic material load. The flora on the discs simply reduces its activity without any lasting consequences.

Environmental temperature insensitivity
As the rotor discs take up a limited amount of space, they can be protected by a cover without a great cost. Therefore the small amount of heat that the sludge emits and the slight exothermic from micro-organism reaction is enough to maintain the discs at a temperature which allows normal biological activity. Therefore the biorulli® system allows purification also when the external temperature is -20° c.

Direct oxygen absorption
The flora absorbs the oxygen it needs to thrive, in the exact measure directly from the air during the disc submersion stage. This essential phenomenon acts independently of the temperature, which reacts negatively on other types of plants where the flora absorbs oxygen previously dissolved in the water. In fact when the temperature increases the oxygen solubility in the water decreases.

Operating with high organic loads
is possible with the disc system to operate on sludge with high or very high bod5 values.

Insensitivity to hydrocarbons, mineral oils, etc. and their removal
Microorganisms present on the discs are in an ideal condition to absorb, extracting grease, lubricating oils, petrol, fuel oils, hydrocarbons, etc. as well as developing a disintegrating action on the molecules performing a true and proper purification. Levels of 40-50 mg/l of hydrocarbons in the sludge are exhausted without difficulty. Therefore it is possible to omit preventive oil removal or to conduct it with very simple systems even with approximate results. The hydrocarbon content in the final discharge can be brought back to as much as 4-5 mg/l.

Easy start-up and insensitivity to stoppages
Flora forms spontaneously on the discs without having to be grafted. The formation visibly begins 7-8 days after plant start-up and is completed after 15-20 days. In the case of intermittent operation with more days of stoppage, the plant reaches completionspontaneously in 2-4 days. If the plant only stops for about a day, it is normally operative once again in a very short time.

Small encumbrance
Plant encumbrance is very modest, about 0.1 m2 per habitant.
Low Energy consumption
Energy consumption in the biorulli® section and purification is equivalent to approx. 8 kwh/year per habitant. The rotors permanently rotate even when there is no sewage.

Fields of use
There are no specific limits to the use of the purification treatment of domestic wastewater and/or similar with the biodisc purification plant.
It is especially suitable for campsites and/or resorts where the bungalows and lodgings are spread out. Thanks to the great flexibility of the biodisc wastewater purification plant and the amount of installations all over the world, we have gained a great experience in the treatment of:
•   all types of domestic wastewater
•   discharge from hotels, restaurants, campsites, resorts, holiday farms and other type of tourist activities.
•   wastewater from fish farming and dog kennels
•   wastewater from farms
•   and all other wastewater of an industrial nature

Normative requirements
The aerobic percolator bed purifier is referred to as a secondary plant element, according to decree law 152/06 and stipulated in various regional regulations, to be used together with other primary systems, necessary to reduce the pollutant load of wastewater and to restore it to the environment as purified as possible.

IMPORTANT
European Regulation n° 305/11 also stipulates that this type of plant be certified according to the CE EN 12566:3 regulation for the structural and operational parameters, the latter being compulsory since 1 July 2013, by means of a compulsory purification performance test having a duration of at least 38 weeks.

Maintenance
One of the main advantages of this biodrum method is the very low maintenance costs thanks to:
•   reduced disc speed resulting in low mechanical parts wear;
•   no control or regulation is required for the oxygen ratio when loads vary. Oxygen absorption from the organic carpet is guaranteed also in the presence of a highly pollutant substance load as it takes place directly from the air without using water. Very small plants require two hours maintenance a week.
•   no noise or vibration
•   low speed is the best guarantee for a silent plant.
Plant description and operation

Primary sedimentation
The crude sewage from users must flow into one or more septic tanks (such as imhoff) that perform the following functions:
a) physical separation of the coarsest solid sediments
b) digestion or stabilisation of primary muds, if they exist as
cesspools (septic or non), are used as they are, with possible slight modifications, where they do not exist they must be formed according to our project.
The sludge is conveyed from the septic tank to the biological plant by difference in height, where possible, or by mechanical means.

Equalization and lifting
The function of this initial phase is that of stabilizing and conveying the sewage from the arrival point to the next flow regulator. The usable volume of this tank is calculated so as to be able to manage the water flow peaks that inevitably occur during the day. There are two submersible centrifugal electric pumps with open revolving impellers suitable for the lifting of sewage; one acts as a reserve to the other so as to have greater operating safety. The pump is controlled by two float level switches with a mercury bulb: the higher one allows ignition while the lower one stops the pumps.

Denitrification (if requested)
In this stage the nitric oxide (no3) is transformed into gaseous oxide (n2) which is released into the atmosphere. This transformation takes place by specific bacteria and without oxygen. Therefore a tank is provided at a constant and suitably mixed level in which the water coming from the biological section and part of the sedimented sludge are recycled in the final purification tank.

Biodisc organic oxidation
From the purification stage the sewage arrives at the oxidation monobloc. The monobloc is made up essentially of a tank containing the disc rotor operated by a small gear motor. A polyester cover reinforced in glass fiber completes the machine and makes it suitable for outside use. The discs are made of a polypropylene sheet with an alveolar structure having a thickness of at least 5 mm. on which the absorption process of decomposable organic structures takes place by mean of the bacterial flora which has formed. The purified water and bacterial flora fragments detached from the discs are conveyed to the final sedimentation tank.

Final purification
The function of this tank is to mechanically separate, from the water coming from the biological section, the fragments of flora that have detached themselves from the discs. These fragments make up the so-called “excess sludge” which, because of their good sedimentation properties, deposit on the bottom of the tank. The sedimented muds are sent, by means of a timed pump, either to denitrification or the imhoff cesspool; if the primary cesspools are not near the plant, a dedicated onsite manager can be involved.