AmBiocell^® Ambientalia^®, aerobic bio-cell for
stabilising the digestate.

Aerobic stabilisation of amBiocell digestate

On completion of the anaerobic digestion phase the digestate is taken from the reactor and a part of it, about 50%, will be reutilised in the mixture of the new organic matter to be treated. The remaining part is mixed with structuring ligno-cellulose material and placed in the amBiocell accelerated bioxidation cells for aerobic treatment of about 14 days.

The amBiocell reactors consist of parallelepiped modules analogous to the amBiogas ones described above and are of the following dimensions: working width max 7 metres, working length max 50 metres, height of internal bio-cell structure in reinforced concrete 5.5 metres, height at false ceiling 5.3 metres. They differ from anaerobic reactors inasmuch as there is no heating system, the structure is not airtight and there is a forced aeration system with insufflation from the flooring and suction from above.

Preparation of the mix and loading the bio-cells

The digestate and a preset percentage of structuring material are homogenised using a special mixer, fed by a mechanical shovel or polyp-grab. This phase is fundamental inasmuch as the mix must correspond to precise values with regard to the following parameters: humidity, apparent density and C:N ratio. Otherwise the evolution of the bioxidation phase will be problematical.

Before filling the bio-cell the false ceiling is fully raised so that the mechanical shovel can operate in complete safety.

The air treatment fan sucks in all vapours and foul-smelling fumes and the aspired air is conveyed to the bio-filter for purification.

On completion of filling, the false ceiling is lowered and the temperature and oxygen probes are inserted. The front hatch is closed and the controlled aerobic bioxidation process, which lasts about 14 days, is initiated by the management software.

The process is carried out with the introduction of air, regulated by ambiControl software which governs time schedules and the quantity to be delivered to the forced aeration system. Each individual bio-cell is served by a main inverter-managed fan to adjust the quantity of air necessary for the process. A part of the air (about 75 %) is re-circulated in the mass by the same fan after being partly dehumidified by a special demister.

A secondary fan sucks the remaining percentage of air from the bio-cell and conveys it to the bio-filter, while an equal percentage of outside air is introduced into the reactor.

Aeration of the biomass

The material under processing in the bio-cells requires air in order to supply oxygen to the aerobe micro-organisms responsible for bio-oxidative reactions.

The amount of oxygen needed changes with time: more at the beginning, when the fresh mix is rich in putrescible organic substances, and less at the end when the reactions have consumed much of it. This is why the fan has variable delivery governed by the inverter; on the basis of the progress of the process, evaluated by measuring the temperature of the material, the quantity of air to convey to the mass can be increased or decreased.

The process air may, depending on functional use, be distinguished as:

• “stoichiometric” air: this indicates the quantity of air strictly necessary for the carrying out of bio chemical reactions in the material, in such a way that the bioxidation reactions may take place correctly throughout the mass of material; it is a minimum quota of the total delivery.

• temperature control air: the excess air with regard to the stoichiometric quota which must be given to the material to control the development of heat and the rising of the temperature.

The ventilation plant is sized on the basis of the maximum delivery of thermometric control air.

Insufflation system with aerated flooring

The aerated flooring is created with insufflation pipes laid comb-fashion and fed by a partial recirculation fan and a demister on the air return, sized on the basis of the maximum quantity of material deposited on the flooring. The fan delivers air to a concrete conduit where the tubes are situated.

The abovementioned aerated flooring offers the following advantages:

1. Better air distribution.

2.  Low losses of capacity.

3.  The tubing is anti-blocking inasmuch as the perforations are flared and protected by a groove in the concrete which prevents compacting of materials in the hole.

4. In the case of blocking the tubing can be cleaned. In the section below the part to be insufflated, each tube is equipped with anti-blocking truncated-cone nozzles which blow air. The nozzles are protected by a gutter set in the
   surface of the flooring.

By way of the manifold collector the tubes flow into a trap for percolates which is equipped with an outer seal to prevent the leaking of air.

The pipes converge by way of the linking collector in a trap for collecting the percolates, which is equipped with a hydraulic seal to prevent air escaping from the drain.
 

Ambientalia - Anaerobic + aerobic process

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