A responsible approach to management of solid waste began in the latter part of the 19th century, when watertight cans were used to collect solid waste and in many areas of the United States sturdier vehicles were used to amass and transport solid waste at designated areas. A significant development took place when the city of London began the construction of the first refuse incinerator in the year 1874. By the beginning of the 20th century, 15% of American big cities had incinerating plants.
With the passage of time, the technology of waste management advanced and many more instruments came, like garbage grinders, compaction trucks, and the pneumatic pipe system. But disposing of waste in open fields created more pollution, jeopardising the health of living beings. A new system was created to overcome this problem, the sanitary landfill system. This system replaced the old incinerators and the dumping of waste in the open.
Nowadays, incinerators are made in such a way that they reduce the heat that escapes outside and have extensive air pollution control devices. Also, solid waste management plants are created for the purposes of recycling.
Solid Waste Characteristics
There are different kinds of solid wastes. These wastes may be from residential houses, commercial properties, industries, hospitals, etc. However, the main characteristic which distinguishes them is hazardous and non-hazardous waste. The hazardous wastes are collected in a specific way, then disposed or recycled. Even a minor mishandling may cause huge or grievous damage, so one has to be very careful.
The non-hazardous wastes have many more and common sources. At the individual level one can easily manage non-hazardous wastes. They should be segregated into wet and dry bins. The wet waste should be decomposed into manure form and dry waste should be used for recycling.
Garbage and rubbish components may also be recycled and used for other purposes, as they aren’t hazardous. Such trash accounts for about 20% of the municipal solid waste (MSW) in the USA. Such waste is managed with the Construction and Demolition (C&D) process in developed nations.
The form of the solid waste varies from nation to nation and region to region. America has very less waste of paper than Japan and Europe. India has more waste of plastics. The rate of wastes generated per person per day also varies. In America 2kg waste per person per day is generated, while in Canada it is 2.5kg per day per person. In several nations it is 0.5kg per person per day. In a few advanced nations, the figure is even lower.
A lot of waste is generated through food residues, or we can say wastes generated through houses and municipal waste. Such wastes should be collected and managed because they are compostable and can be easily decomposed, which will protect the environment.
Collection and Transportation
The solid waste coming from houses or municipal means or any other means must be collected in a hygienic way. However, this process is expensive in labour terms. For the collection of wastes, authorities should use advanced systems like pneumatic pipes and compactors. To compact and then collect in an easy way, we should use grinders.
For transportation, authorities should use trucks which have enclosed and compact capacity of 30 cubic metres. Also, loading can be done from both the front and rear sides. In many advanced nations, selected routes are used for the collection of regional wastes, but this becomes complex in cities which are congested or in congested areas. Such advanced technology in rural areas becomes very costly because these areas are low in population density and it needs lot of labour and work. The refuse collection should occur after small regular intervals as this garbage is degradable, so it emits foul air. Within these interval days if the refuse is reduced in size, then it will become easy to handle it.
A transfer station means a central facility which gets refuse from many vehicles which can be called primary vehicles. In many cities compact vehicles are used because of closed lids and these can unload by themselves. These are well equipped with ejector systems. In short we can say the vehicles are first emptied in the pit then the refuse or wastes are hoisted by machinery into a transfer station.
Treatment and Disposal
When solid or municipal wastes are collected, they are treated in order to minimise the size, so that they could be carried in an organised manner and in high quantity. It has benefits like reduced volume, weight, and segregation. In the process of reducing size and volume, many processes are involved, like:
Incineration: Though it can reduce the size and volume by the burning process, it is very noxious as it adds greenhouse gases in the atmosphere, so this burning is not a suitable way of reducing size. However, in new incinerators the wastes are reduced in size and volume by burning in a controlled furnace which doesn’t add greenhouse gases in the atmosphere. With this incineration process, the refuse gets 90% reduced in size, volume and weight, leaving behind only ash and residue which is collected at the bottom. The other part called as fly ash should be maintained in a balanced way within the incinerator. The incinerator should be guarded with high-quality emission control devices. Such devices should have modern equipment like electrostatic precipitator, gas scrubbers and many others.
Modern-day incinerators have receiving and burning equipments, which can burn the refuse in a controlled way and hold refuse in a storage pit and stropping area. Advanced incinerators also contain rectangular furnace, rotatory kilns, and other advanced technologies like vertical furnaces which maintain and control the refuse. These are made of refractory bricks which can withstand high temperature. Thus these furnaces are beneficial from an environmental perspective.
The combustion in these furnaces is grouped into processes of primary & secondary. In primary combustion the refuse is made dry by driving out moisture. in secondary combustion the remaining unburnt residues are oxidised and eliminated. In order to make both these processes effective, it requires enough oxygen. A continual supply of air can be maintained by making a natural draft through forced draft fans.
Composting: Organic waste is decomposable, so this can be separated and decomposed by the use of microbes. This can reduce the volume and size by about 50% and then can be used for manure. During this process both garbage and sludge can be processed.
Sorting & Shredding: The decomposable wastes are separated in the refuse on the basis of size, density, volume, etc, and are divided into glasses, metals and inorganic materials. This is done through physical separation or by the use of mechanical engineering on basis of magnetic properties or density. The shredding is done by hammering and rotatory methods, reducing the size and resulting in a uniform mass of material.
Sanitary Landfills: This is the most common method. An area is selected for the deposition of refuse which is far away from the community population. It should also be in a place from where the wind is not generally towards the community population. The pit shouldn’t be so deep as to get in contact with the water table. The landfill surfaces are capped with impermeable covers to prevent surface run-off and the bottom should be lined with plastic membranes, which will not allow secretion downwards. This system is reliable for the decomposition of wastes.