Characteristics of solid waste and Overview of solid waste generation and management techniques

Characteristics of solid waste

SOLID WASTE

Solid waste often called the third pollution after air and water pollution, is that the material which arises from the various human activities and which is usually discarded as unwanted or useless. Solid waste means the any garbage, bottles and sludge from a wastewater treatment plant, water supply treatment plant or air pollution controls facilities and other waste materials including solid, liquid, semi-solid, or contained gaseous material which is resulting from the industrial, commercial, mining and agricultural operations from community activities but does not included solid or other dissolved materials in domestic sewage, or solid or dissolved materials in irrigation return flows or industrial discharges.

The classification of solid waste is very broad and many classifications can be found. One of the classifications of solid waste is listed below:

Food waste (garbage)

Waste from the preparation, cooking and serving of food, market reuse, waste from the handling storage and sale of meat and vegetables are classified as food waste or garbage. Their sources are usually households, institutions and commercials such as hotel, stores, restaurants, markets, etc.

Rubbish

Rubbish includes combustible (primarily organic) such as paper, cardboard, cartons, wood, boxes, plastics, rags, cloths, bedding, leather, rubber, etc. and also includes noncombustible such as metal, tin cans, metal foils, dirt, stones, bricks, ceramics, crockery, etc.

Ashes and residue

They are the residue from fires used for cooking and for heating building, cinders, clinkers, and thermal power plants.

Bulky waste

Bulky waste includes large auto parts, tires, stoves, refrigerators and other large appliances furniture etc.

Street waste

They include paper, bottles, dirt, leaves, animal droppings, the content of litter, receptacles, dead animals, etc. Their sources are streets, sidewalks, alleys etc.

Pathological wastes

They are the human wastes and dead animals. The moisture content is 85% and there are 5% non-combustible solids. The heating value is around 2.5*10^6 J/kg.

Construction and demolition waste

They are lumber, roofing and sheathing scraps, crop residues, broken concrete, rubble, plaster, conduit, pipe, wire, insulation, etc. Their sources are construction and demolition sites, remodeling and repairing sites.

industrial waste

Solid waste resulting from industry processes and manufacturing operations, such as food processing wastes, boiler, house cinders, wood plastics and metal scraps and shaving etc. effluent treatment plant sludge of industries and sewage treatment plant sleds, etc. Their sources are factories, power plants, treatment plants, etc.

Hazardous waste

They are hazardous waste, pathological wastes, explosives, radioactive material, toxic waste, etc.

SOURCES OF SOLID WASTES

The sources of solid waste can be summarized as:

Residential sources

The residential sources are mostly societies and houses.

Commercial sources

Commercial sources include commercial institutes such as restaurants, hotels, etc.

Institutional sources

These sources include institutions such as schools, offices, etc.

Industrial sources

These sources include different industries.

SOLID WASTES IN NEPAL

Residential wastes

According to research carried out by Asian Development Bank, the per capita household solid waste generation rate was found to be vary from a minimum value of 75 g/capita/day (Triyuga) to a maximum value of 278 g/capita/day (Inaruwa). The amount of solid waste produced varied according to the net expenditure of the family. Thus, the urban areas produce more solid waste than rural areas.

Fig: Variation of composition of organic waste according to ecological region

COMMERCIAL AND INSTITUTIONAL WASTES

Table: Commercial and Institutional waste

Fig: Composition of commercial waste

The composition of commercial waste is summarized as:

Organic(43%)

Paper and paper product(23%)

Plastics(22%)

Glass(4%)

Metal(2%)

Textiles(2%)

Rubber and leather(1%)

Other(4%

IMPORTANCE

Solid wastes are the sources of pollution in the environment that has an adverse effect on the health of an individual and in the health of the environment if not disposed of properly and systematically. Thus to develop a proper disposal system of solid waste, it is very important to determine the type of solid waste produced the source from which it is produced. For example, from the statistics shown above, we know that the waste produced in the municipal areas in Nepal consists of a majority of organic waste. Thus, we can formulate plans and systems that are friendlier in the decomposition of the solid waste. And since the waste produced has the majority of organic waste, we can also introduce plants that make use of these organic waste to produce energy.

CONCLUSION

Thus, the majority of solid waste produced in municipal areas is from residential sources and consists of the majority of organic waste. The waste management technique in a majority of municipalities in Nepal are also not systematic and the majority of them practices roadside picking and disposing of in an open area which causes the major health problem. Thus, proper characteristics of the solid waste produced should be recognized and systematic solid waste management technique should be established likewise.

Aspects of SWM System

Storage:

Waste storage encompasses proper containers to store wastes and efficient transport of wastes without any way to transfer stations or disposal sites.

Containers:

- used for storage of wastes at the site of generation until they are collected.
- Desirable characteristics: low cost, size, weight, shape, resistance to corrosion, water tightness, strength, and durability.

- 100-200 m between each container (source: note)

Collection Vehicles:

- must be selected according to terrain, type, and density of waste generation points, route, and kind of material

e.g.: small scale, non-compactor trucks, and compactor

Collection:

Includes the gathering of wastes and transporting of wastes to transfer stations and/or disposal sites

Factors:

• Collection points
• Collection frequency
• Storage containers
• Collection crew
• Collection route
• Transfer station
• Transfer and Transport:

The transport of waste after collection, from the collection, sites to the processing area or dump site. It also includes the transport process from generation area up to the collection area

The transfer station is provided for separation of usable waste. This also serves as an intermediary between different collection sites and the common disposal site.

Processing:

Processing is done to achieve the best possible benefit from every functional element of the SWM system. The wastes that are considered suitable for further use, are processed to derive maximum economic value from them

Processing can also be done to facilitate disposal.

Various methods of processing are:

• Volume reduction or compaction
• Size reduction or shredding
• Component separation
• Drying

Recovery and Recycling:

Recycling is the process of utilizing the waste product as raw material for the new product. It can assist in reducing the amount of waste. It is done to prevent waste of potentially useful materials, reduce the consumption of the fresh raw materials, energy usage, air pollution (from incineration) and water pollution by decreasing the need for "conventional" waste disposal and lowering greenhouse gas emissions compared to plastic production.

Recovery is the process of extracting the usable part of waste in the form of energy, or material

Disposal:

Disposal is the final element in all the SWM systems. All types of waste, even after treatment needs to be disposed

Various disposal techniques are:

• Uncontrolled dumping or non-engineered disposal
• Sanitary landfill
• Composting
• Incineration
• Gasification
• Refuse-derived fuel (RDF)
• Pyrolysis

The disposal techniques are selected on the basis of the following criteria:

• Technical
• Institutional
• Financial
• Social
• Environmental

Factors Affecting SWM

• Quantity and Characteristics of Wastes:
  • One measure of a characteristic of waste is its density. A high density reflects a relatively high proportion of organic matter and moisture and lower levels of recycling.

• Climate and Seasonal Variations:
  • Higher temperature and humidity means faster decomposition. So the frequency of waste collection needs to be higher in high temperature and humid climates.

• Physical Characteristics of Urban Area:
  • The physical characteristics of an area like the accessibility of roads determine the appropriate mode of the method of SWM. The nature and size of roads, for example, will determine the nature of collection; hand carriage in a narrow road and large trucks in main roads.

• Cultural Constrains:
  • There is a tradition of caste for labor to be drawn from certain sections of the population. Social norms may override the rational solutions. People of so called higher class hesitate to work in the field of SWM.

• Management And Technical Resources:
  • The resources available at the disposal of the governing body such as available manpower, budget and other resources like dustbins, collector trucks determine the SWM system employed.

CURRENT SCENARIO

Waste Generation

• According to ADB, a survey conducted in 2012, in all 58 municipalities found that 317 grams per capita per day of waste was generated.
• According to the Environment Statistics of Nepal 2013 published by the Central Bureau of Statistics (CBS) for the fiscal year 2012-2013:

• Total amount of wastes generated by the 58 municipalities was around 670 metric tons per day
• KMC alone generated 457 metric tons of solid waste per day
• Of which, 63.2 percent is organic while the plastic, paper and glass constitute 10.8, 9 and 5.4 percent of the solid waste respectively
• After Kathmandu, the top five solid waste generators of the 58 municipalities are: Pokhara, Lalitpur, Kalaiya, Dharan and Butwal, which generate the 83, 65, 52.1, 50.2 and 47 metric tons of solid waste per day respectively
• Lowest quantities were generated at Waling, Dipayal, Triyuga, Ramgram and Baglung

• The data for the fiscal year 2006-2007 for KMC was 29.9 metric tons per day and for the fiscal year, 2009-2010 was 318.4 tons per day

Figure 1: Waste Generation

(Source: ENVIRONMENT STATISTICS OF NEPAL

Table 1: Comparison of Source of Waste in KMC

(Source: ENVIRONMENT STATISTICS OF NEPAL 2013

WASTE MANAGEMEN

• 30% of surveyed household in municipalities separate waste
• Collection efficiency ranges from 70 to 90 percent, for KMC 85%
• Collection modes: Container service, door-to-door collection, and roadside pickup from open piles or containers
• Transport modes:

• rickshaws, carts for primary collection
• Tractor for secondary collection
• Dump trucks for transport to disposal sites

• Transfer sites are not available in major municipalities except KMC, Lalitpur, and Madhyapur Thimi; transfer station for KMC and LSMC : Teku
• For Kathmandu and Lalitpur, a sanitary landfill site at Sisdol, Okharpauwa was constructed operated as a sanitary landfill site in the early stage of operation, although currently it is not operated as a sanitary landfill site.
• The household waste composition survey revealed that more than 25% of household waste and a much higher proportion of institutional and commercial waste could be either reused or recycled
• No formal system for recycling exists
• Informal and source recycling is present(scrap dealers)
• Composting is done in 30% of surveyed household

Figure 4: Types of Solid Waste Disposal Method in Municipalities of Nepal

(Source: Asian Development Ban

DISCUSSION AND CONCLUSION

The current methods of waste disposal are inefficient. The open dumping technique which is very common can make the waste a disease vector which transmits various types of disease and also shelter pests and rodents. This can also cause various types of pollution like air, soil, water, etc. The lack of recovery and recycling means a large volume of waste needs to be disposed and some potentially useful material is also lost in the waste. The current disposal technique of landfill site has also failed. The landfill site has been filled past its capacity and has been extended for temporary relief but the problem is set to persist if other concrete efforts are not made.

So a better system is required. It should incline with the 3R (reduce, reuse, recycle) principle to reduce generation and aid proper management of waste. Also to reduce the waste that is produced, segregation followed by proper disposal techniques tailed to each component should be applied, e.g.: bio-digestion for organic waste, incineration for inorganic waste. The system should however not contribute to further pollution (of another kind) e.g. incineration can cause air pollution. So, properly designed systems with proper pollution control measure must be employed.

References:
1. Mackenzie L. Davis & David A. Cornwell, “Introduction to Environmental Engineering”, McGraw Hill.
2. Gilbert M. Masters, Standford University, “Introduction to Environmental Engineering and Science”, Printice Hall.
3. Stephan Konz, Kansas State University, “Work design”, Grid Publishing Inc., Colombus, Ohio
4. C. S. Rao, “Environmental Pollution Control Engineering”, New age International (P) Limited, Publishers, India.