Solid waste usually comes from communities and industrials. Solid waste comprises food scraps, paper, broken glass, scraps of wood, plastic, soil, leaves, ashes, etc. The volume of solid waste depends on sources of solid waste. The most common treatment is incineration, composting, recycling, animal feeds and sanitary landfill.
The Company’s main service is landfill because of simple process, low costs and environmental preservation. Landfill can be divided into two categories as follows:
1. Sanitary Landfill
is designed for non-hazardous waste. Sanitary Landfill has two methods, including:
Is best-suited for area with holes or low area which need to be reclaimed, such as pond, river bank or other areas which soils are digged for other usage. In this method, waste is pushed into layers, spread, compacted, covered and compacted and then filled with soil and compacted again
Is best-suited for flat land. The process begins with excavating land to construct a trench with the width of the least twice the size of equipment to be used. The depth depends on ground water level. Normally the trench has 2-3 meters in depth and slopes to one side for good drainage when it rains. The removed soil will be used as cover material. After the trench is complete, solid waste will be filed, spread and compacted in the trench.
is to cater for treated hazardous waste which passes the stabilization. This process starts with placing waste, spreading, compacting, covering (with soil) and compacting by tractor, then covering with soil and re-compacting. The area will be filled at the required level. Once the trench is filled, waste is left to decompose. During waiting for decomposing, the investigation is required and the area has to be fenced to protect any attack. During decomposing, landfill expands in volume and generating leachate (liquid from decomposition process). Leachate needs to be treated prior to discharging into water resources or can be recycled.
3. Production of Refuse Derived Fuel : RDF
Burning refuse always creates difficulties due to its uncertainty and non-homogeneousness of the refuse which varies from community and season to others. Moreover, refuse has low heating value while it has high ash volume and humidity. All these cause difficulty for combustor designer and operator and difficulty in controlling environmental impact. Processing refuse by several processes to improve its physical and chemical qualifications to transform it to ‘Refuse Derived Fuel (RDF)’ can solve the above problems and they can generate energy, too.
RDF process is to improve and transform refuse to be solid fuel having good qualifications in terms of heating value, humidity, size and density which is suitable for being fuel for boiler to generate electricity or heat. It will have constant physical and chemical compositions. General characteristics of the RDF are as follows:
- It is sanitized due to heating so it reduces risks in exposure to germs.
- It is odorless.
- The size is appropriate to feed the incinerator-boiler.
- Its density is higher than normal refuse and bio mass which is convenient for storage and transport.
- Its heating value is higher compared with bio mass and humidity is low.
This technology starts from separating refuse which cannot be burnt metal, glass and stone, harmful and recyclable garbage from the refuse. In some cases, magnetic separator is used to separate metal scraps from the refuse and Eddy Current Separator is used to separate aluminum. After that the refuse is fed to chopper to reduce size and to incinerator to reduce humidity by heat from steam or hot air. The refuse’s weight will decrease. Finally, the refuse is sent to pallet compressor to produce RDF which is appropriate in size and density to transport to sell as fuel. In some cases, CaO is added to the refuse during compression process to control and reduce toxic gases generated from burning.
Design of processes in transforming refuse to fuel depends on current refuse management. For example, if recyclable refuse (such as metal and glass) can be separated from the refuse before entering the process, the process may not need metal or glass separation activity.
Generally, separated garbage can be reused such as metal, aluminum and glass. And organic materials such as food scraps which are high in humidity can be fed to organic gas or soil conditioner production process. Moreover, refuse which is reduced in size is composed of paper, wood and plastic which can be directly burnt as ‘Coarse RDF (c-RDF)’ or dried and densified to produce ‘Densified RDF (d-RDF)’. Consideration of type of RDF produced depends on burning technology, location of plant, refuse and place of fuel use.
Composition of RDF depends on composition of refuse feedstock, storage method and processing system. Qualifications of the RDF are heating value, humidity value, ash volume and sulfur and chloride. Moreover, processing of refuse can reduce humidity causing the heating value to be higher.
Use of RDF is in the forms of electricity and heat which can be used on production site or somewhere else. Moreover, it can be used in co-firing to reduce use of coal in some industries such as cement industry. The combustors transforming RDF to energy are stoker, fluidized bed combustor, gasification combustor or pyrolysis .