What is ZUSOK?

What is ZUSOK? (The Solid Communal Waste Utilisation Plant)

The Solid Communal Waste Utilisation Plant in Warsaw is an exceptional venture. Although it can be associated with a combustion plant only, in reality it is a multipurpose plant, which can perform the following functions:

• sort waste and recover recyclable resources,
• thermally process waste not suitable for recycling,
• compost the organic part of the waste,
• transform the slag and ashes created during the combustion process into a granulate, harmless for the environment, which can be used as a raw material for the building industry,
• produce electric energy.

The Solid Communal Waste Utilisation Plant is located within the territory of District Targówek, ul. Gwarków 9. ZUSOK it accepts for complex utilisation 110 000 Mg of solid communal waste a year, out of that number 46 000 Mg is destined for combustion. Two identical sorting process lines have the capacity to process 416,6 tons of raw waste within two shifts. Each line has a capacity of 15 tons per hour.

Initial processing – shredding, sieving and sorting


The introductory segregation
The communal waste is delivered to the Plant by road transport. The solid waste is unloaded into yard bunkers which have a capacity of 3000m3, which is enough for 900 Mg of waste – this corresponds to 2 working days. Than the waste is transported onto two charging hoppers, which in turn power two parallel initial processing lines for the communal waste. The waste having passed through the charging hoppers find their way onto plate feeding devices, which power two hammer type mills. The mills shred the raw waste, which subsequently undergoes sorting on rotating sieves. Functioning of the mills is very important as it allows for optimal segregation of the material on rotating sieves into three groups sorted according to the size of their particles.
This allows for a maximum recovery of organic substances for composting and separating the combustible particles. The heavier and harder particles are thrown upwards from the upper cone of the mill before they find their way into the shredding zone. The particles removed by throwing are moved via an open steel channel into small containers. The shredded material is moved by chain conveyors onto the rotating sieves. Each of the rotating sieves is equipped with two sets of sieves with various hole sizes.

Three different factions can be achieved:

The rotating sieve

• Sieving (achieved by sieving through sieves with 20 mm diameter holes)
• Intermediate faction (achieved by sieving through sieves with 50 mm diameter holes, stopped at sieves with 20 mm diameter holes),
• Sifting (remaining material with particle 250/300 mm stopped at the sieve with 50-mm holes),

Sifting - material separated by the rotating sieves is delivered to a furnace container by a chain conveyor.

Sieving – directed to a gravitational separator, which aims to increase the recovery rate of the organic substances and separate out small glass particles and indifferent substances, which are taken away to a dumping place.

Intermediate organic faction from the sieves as well as the organic substances from the gravitational separator are combined and moved to a belt magnetic separator, which removes all ferrous metals. The remaining material is moved by a belt conveyor to the composting plant building.

Composting

Organic substances before composting
The composting section covers fermentation refining and treatment of the waste. The composting process is made up of the SILODA system, designed and implemented by OTVD. The system is composed of a series of concrete containers, which in the case of fermentation have a capacity sufficient for one working day and in the case of treatment their capacity is sufficient for two working days. An appropriate device for mixing the compost is patented by OTVD a paddle wheel with efficiency of 250 m3 of compost per hour.
The fermentation section can process 210 tons a day (about 15 tons per hour) of martial suitable for composting with density of 500 kg/m3 coming from the initial processing installation. This way 147 tons of raw waste per day are achieved. The difference is due to losses in the fermentation section, where the compost is kept for 12 days and nights.
During the first stage of accelerated fermentation the organic substance is submitted to intensive oxygenating via mechanical mixing of the piles with a paddle wheel and by forced ventilation with compressed air flowing through channels located in the bottom of every container. Constant aeration is ensured by operating fans.
This stage of fermentation takes place inside 12 containers lined up in two rows with 6 containers in each of them. First container in the first row is carefully filled with material submitted to composting by a swinging conveyor moving over the fields. During the process of automatic filling of the containers, the SILODA paddle wheel empties the sixth container from the second row onto a belt conveyor in order to move the compost to the refining (purifying) section. Subsequently the wheel is moved by a trolley to the fifth, fourth, third, second, and first container respectively, so that the material is moved to the neighbouring container and the first container in the second row is left empty by the end of the working day. The following day, the first container in the second row is filled by the means of the same swinging conveyor, while the SILODA paddle wheel is emptying the sixth container in the first row. The above-described process is repeated for the first row of containers.
The material remains in the fermentation section for 12 days.
Temperature inside the containers increases quickly and can reach 60-70 degrees Celsius during the first 48 hours. Oxygen necessary to avoid oxygen deficiency conditions is delivered by mixing the piles and by operating fans, which allows for optimisation of the fermentation process. The daily output from the sixth fermentation container is moved to a warehouse within the refining section.


The SILODA Wheel

Refining (purifying) of the compost

Compost from the primary fermentation is dumped onto a storage surface. A loader forms the material into piles and powers a charging buffer funnel of the refining section. The buffer funnel is equipped with a double perpetual screw, which turning inside its bottom unloads the compost onto a conveyor, which in turn powers the rotating sieve.
The sieve separates the waste into two factions:

Sieving: smaller particles from 30 mm, containing the vast majority of raw compost and some indifferent substances, which subsequently are to be sorted by gravitational separators.

Sifting: the material unsuitable for composting is moved to a container in which it will be delivered to for combustion.

The sieving fraction is submitted to processing in gravitational separators, where raw compost is divided into four factions:

1. Organic material suitable for treatment,
2. Indifferent material directed to containers, in which it will be transported to a dumping place,
3. Small particles (glass, stones etc), which are directed to the same containers as the indifferent material,
4. Light material, which is recovered in cyclone cones and directed along with the siftings from the sieves to containers in which it will be transported for combustion.

Because the processing capacity of the refining section is smaller than that of the paddle wheel, the installation is set up in such manner that the material from the sixth container is moved to a storage space nearby. The reason why compost is submitted to refining before treatment is far better efficiency of micro-organisms in a cleaner and more homogenous environment, such as refined compost. This factor leads to shortening of the reaction time and the length of the treatment stage as well as diminishing the level of requirements regarding the size of the enclosures for conducting of the treatment process.
The refining section is estimated for processing 20 tons per hour during a 7-hour working day.
The quantity of compost maturing during the treatment process amounts to 84 tons per day, while the total production of finished compost equals to 55 tons peer day. The difference is a result of losses taking place at the treatment section, where the compost is kept for 24 days. Also in this section air is delivered by fans, however the is quantity smaller than in the fermentation section.
The organic material recovered by the gravitational separators is moved by conveyors onto the compost site and formed into piles with a bulldozer. The compost is kept at the site for another two weeks, where it is left to mature.
The total time, necessary to obtain finished compost, covering initial processing fermentation, refining and treatment varies between five and six weeks. The air containing dusts is removed from the compost section building via exhaust systems of the refining sieve and the gravitational separator and delivered to the central biological filter.

The finished compost