Expansion of the Aciam composting plant: state-of-the-art technology
The project by Pal involves the expansion of the Aciam SpA plant located in Aielli (AQ) to strengthen the composting line, that moves from 25,000 t/year to 58,500 t/year, against a reduction in the capacity for the mechanical treatment of unsorted waste that moves from 58,500 t/year to 25,000 t/year, hence the overall authorization potential remains unchanged at 83,500 t/year.
PLANT INFORMATION
- Overall authorization potential: 83.500 t/y
- Organic fraction of municipal solid waste (OFMSW): 58.500 t/y
- Unsorted waste (MSW): 25.000 t/y
The project by Pal involves the expansion of the Aciam SpA plant located in Aielli (AQ) to strengthen the composting line, that moves from 25,000 t/year to 58,500 t/year, against a reduction in the capacity for the mechanical treatment of unsorted waste that moves from 58,500 t/year to 25,000 t/year, hence the overall authorization potential remains unchanged at 83,500 t/year.
Biocells
After the trituration&mixing phase, the material mixture is placed in the biocells (active phase), made in an environment characterized by dynamic confinement through aspiration of exhausted air, having at the base an aerated floor with forced ventilation which ensures the right supply of oxygen to the masses; an aerobic microbiological process is triggered inside these masses which eventually leads them to sanitation, transformation and biological stabilization. In the active phase, with biomasses that are not too wet and with adequately sized heaps, the temperature can also easily exceed 60-65°C, thus guaranteeing the conditions for the sanitisation of the treated material (at least 3 days at 55°C according to Italian legal regulations).
The insufflation of air from the floor has the following main objectives:
- supply the oxygen required by the biochemical processes of aerobic degradation of biomass;
- adjust the biomass temperature in order to optimize the process conditions;
- subtract carbon dioxide.
As a secondary effect, the air passing through the material removes water and therefore generates a drying effect.
The floor insufflation system is made of PVC pipes of 200mm diameter, moored into the casting of the floor at a constant pitch and arranged longitudinally. These pipes are fitted with conical ejection nozzles (spigots).
The oxidation phase takes place on a continuous basis (24-hour) and does not require the constant presence of operators. The process is controlled by software that monitors the biological transformation activity by checking the process parameters, paying special attention to the temperature that, being constantly monitored and recorded, must remain for at least three days over 55 °C in order to sanitise the material.
Inside the biocells the material is watered by a pipeline with leachate to increase the humidity of the mixture and also allow reuse of the leachate itself so as to limit its disposal.
The parameters of the process and of the air flow blown in the biotunnels are recorded by a special process software. The electronic operation of the process controls temperature, air flow, humidity and oxygen content.
Curing area
The system is dynamic with heaps being aerated through a forced ventilation system. The controlled aeration action at the different stages of the curing process allows to avoid anoxic phenomena, guaranteeing the oxygenation of the heaps and the removal of excess heat.
In the curing phase, humus formation processes are favoured in aerobic but not heavily oxidative conditions. In fact, in the curing stage, a lower demand for oxygen, slower biological processes and a lower temperature than that of the active phase can be observed. Each heap has its own fan for forced insufflation, air is blown under the heap through 200mm diameter PVC pipes and spigots for uniform and continuous distribution.
The temperature and humidity of each heap are monitored by software.
A feature of this composting plant is the roofing of the sheds that is flat both on the inside and on the outside of the areas. This feature has made it possible to create external air intake pipes thus allowing for easy inspection and accessibility. Moreover, better insulation was achieved thanks to the use of easy-to-install insulating panels on the roofing.
Scrubber and biofilter
The plant is fitted with a suction system that conveys the exhausted air to a special abatement plant consisting of dynamic-bed vertical washing scrubbers with a reagent dosing system and a biofilter consisting of a woody species mixture.
Refining line
The plant envisages the creation of a refining line comprising a loading hopper used to load and dose the material, a series of conveyor belts, a drum screen and a disc screen.
Compost and green area canopies made of laminated wood and corrugated roofing sheet
Two canopies were made: one for the storage of mixed composted soil conditioner and the other for the storage of lignocellulosic matrices.
Each canopy consists of a concrete screed equipped with suitable slopes to facilitate the conveyance and management of any water while the elevated structure is made of reinforced concrete cast in situ, the wooden beams are made of GL24h glulam and the roofing of green corrugated sheets.
Conclusions
The works are expected to be completed by March 2021. The construction site is an example of efficiency. In fact it has never stopped even during the Covid-19 emergency. Very stringent protocols were adopted that allowed and still allow to work safely.
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