6 Waste collection – I

Dr. Yogalakshmi K. N

Objectives:

1.      To understand the concept of waste collection

2.      To study in detail about the various components of waste collection system

1.0 Solid waste

Waste is defined as any unwanted or unusable substance that is discarded after primary use. Wastes are normally generated as a result of human and animal activities. Urbanization and rapid advancements in industrialization has led to an increase in the production and consumption processes resulting in the generation of wastes from various sectors that include agricultural, commercial, domestic, industrial, institutional, social and from community activities. Over time, these wastes accumulate and can have real impacts on the health and the environment. Waste management is the only solution intended to reduce adverse effects of waste on health, the environment or aesthetics.

Waste based on its nature and properties are classified broadly into solid, liquid and gaseous waste. Solid waste is heterogeneous in nature with organic and inorganic matter. According to the source of generation and type they are classified as urban wastes, agricultural wastes, biomedical wastes, bulky waste, open area waste, radioactive wastes, e wastes and many more. The term refuse is also used for solid wastes. Examples of solid wastes include waste tires, septage, scrap metal, latex paints, furniture and toys, garbage, appliances and vehicles, oil and anti-freeze, empty aerosol cans, paint cans and compressed gas cylinders, construction and demolition debris, asbestos, plastics, styrofoam containers, bottles etc.

Management of solid waste is the crucial to avoid environmental and health hazards. Solid waste management is highly complex as it involves different steps, technologies and public. The steps involved in solid waste management include reduce waste generation, handling, storage, collection, segregation, transfer, transport, processing, treatment and disposal. The success of waste management depends on the public and the government. Both share equal responsibilities and they should work hand in hand to achieve proper waste management. However, the management element suffers from different issues. They include

• increasing waste generation due to population explosion economic status
• life style
• degree of industrialization and urbanization
• lack of awareness among individuals regarding the ill effects of waste on the individual health and environment
• lack of knowledge among individuals in handling the waste
• lack of understanding about the elements of waste management lack of strict regulations

2.0 Elements of waste management:

The functional elements of waste management include waste generation; handling and storage; collection; segregation; transfer and transport; processing, treatment and disposal

2.1 Waste generation: It is the first functional element of waste management. It is a process in which an individual decides or identifies materials that is of no use and should be disposed off from the source of generation. The understanding of an individual to separate them according to their nature is very important. In most of the developing and under developed countries, people do not segregate or separate the waste according to their nature; instead they are thrown off as comingled waste. Waste generation is increasing and has become uncontrollable. It varies among developed, developing and underdeveloped countries.

2.2 Waste handling and storage: The handling and separation of waste before it reaches the specific containers are taken care off in this element. The movement of waste from the source of generation to collection points is also a part of this element. This element is more prevalent in developed countries, where segregation or separation of waste at the source of generation is practiced. Apparently, this element is non-functional in developing and underdeveloped countries like India, Africa etc. As mentioned earlier, population explosion, increasing waste quantities, lack of knowledge, understanding of waste, lack of regulations, improper functioning of waste management system are the reasons for non-functioning of this element.

2.3 Waste collection: The waste is gathered from different locations and hauled to transfer stations, processing sites or disposal facilities. Waste collection differs for comingled and source separated wastes. Source separated wastes (i. e) biodegradables, recyclables and non recyclables are collected separately from different collection centre’s or containers and taken for further processing. The comingled waste is carried to transfer station for further separation and processing.

2.4 Waste transfer and transport: Transfer and transport includes two steps: the waste being collected in small containers and collection vehicles are transferred to big collection vehicles; and the waste transported to transfer stations, processing sites or disposal facilities. Transfer stations are intermediate facilities where the comingled waste is segregated, processed. It also serves as a waste treatment facility.

2.5 Waste Processing and treatment: Waste processing includes segregation of waste, treatment, volume and size reduction. This step occurs in the transfer stations, combustion facilities, material recovery sites and disposal sites. The waste is transformed through size and volume reduction, physical, chemical and biological treatment. The waste is subjected to chemical or biological treatment to reduce the toxicity of the waste. The waste processing sites also act as sites for energy recovery. The processing site holds facilities like incineration, gasification, pyrolysis, shredders and compactors, composting pits and many more.

2.6 Waste Disposal: Disposal is the final step in the waste management. Ultimately all solid waste ends in disposal site either directly or after some processing and treatment it ends in disposal sites. Most of the developing and under developed countries, dispose or dump the solid waste in an open land without any protection or environmental control. Such dumping is not safe and is called as open dumps or open dumping. Solid waste is also disposed off in water bodies e. g. Sea, ocean, lake, river etc. Sometimes they are also burned in open areas, the phenomenon termed as open burning. Developed countries are practicing a system of safe or controlled dumping called the landfill. Landfill is an engineered structure where the waste is safely disposed and contained. It does not cause nuisance to the public and environment.

3.0 Waste collection:

Waste collection is the major and crucial step in waste management process. It is defined as the collection or gathering of waste from the source of generation and haul them to the transfer stations, processing sites, disposal site or landfills. Hence, waste collection does not mean the gathering of waste alone. Waste collection differs for comingled and source separated wastes. Source separated wastes (i.e.) biodegradables, recyclables and non recyclables are collected separately from different collection centre’s or containers and taken for further processing. The comingled waste is carried to transfer station for further separation and processing. Waste collection is most difficult and complex in an urban environment because the generation of residential and commercial-industrial solid waste and recyclables takes place in every home, every apartment building, and every commercial and industrial facility, and in the streets, parks, and even vacant areas. Henceforth, the waste collection becomes complex with increasing waste quantity and diffused waste generation pattern. More diffuse is the waste collection, more is waste generation and more complex is waste collection. Waste collection is costly component of waste management. Around 50 to 70 percent of the total waste management cost is utilized for waste collection. The cost can be reduced if the waste collection is properly planned and managed. Waste collection depends on number of containers, collection vehicles, routes and collection frequency.

The collection of waste varies with the characteristics of the facilities, activities, or locations. Two types of collection services generally used include

Commingled (unseparated) wastes Source-separated wastes

3.1 Collection of commingled waste:

The residential dwellings are classified as low rise (below four stories), medium rise (from four to seven stories) and high rise (above seven stories). These dwellings accordingly have differences in the solid waste handling operations.

The residential collection services for low rise detached dwellings include (1) curb, (2) alley, (3) setout- setback, and (4) set out and (5) backyard carry. In case of curb service, the resident is supposed to place the containers which are to be emptied at curb on collection day and to return the empty containers to their storage location till next collection happens. Alleys include basic layout or pathways of any given residential area where the collection containers are placed. These alleys are used for placing the storage containers and facilitate collection of solid waste. In setout- setback collection service, the containers are set out in the property of resident and it is set back on emptying with the help of additional crew working in the conjunction with the collection crew. Collection crew is responsible for loading the collection vehicle. Setout service is similar to the setout- setback service except that residents is responsible to return the containers to their storage site. The collection of residential waste is also done manually by either direct lifting or carrying loaded containers to the collection vehicle for emptying it or rolling of loaded containers having wheels to the collection vehicle for mechanically emptying.

In case of low and medium rise apartments, curbside collection service is generally used. Usually the maintenance staff (watchman, servants) is responsible for manually or mechanically transporting the containers to the street for curbside collection. In high rise apartments, the commingled waste is usually bagged and placed by the tenants in waste chute system, used for the collection of waste at a centralized service location. The wastes are also in some case picked up by the building maintenance personnel from different floors and taken to the basement or service area. In commercial and industrial facilities, both, manual and mechanical collection of waste is used. The collection of waste is usually carried out in late evening and early morning hours in the commercial establishments because of traffic congestion during day.

3.2 Collection of wastes separated at the source

The separation of waste at the source is carried out for the recovery and reuse. There are three methods for the collection of the recyclable materials from the residential areas which include, (1) curbside collection using conventional and specially designed collection vehicles. (2) Incidental curbside collection by charitable organization. (3) Delivery by residents to drop- off and buyback centers. Drop off centres are places where the recyclables are dropped off in specific sites. This will facilitate collection of specific materials so that they can be recycled further. Buy back centre is one where the materials are bought for minimum price. Electronic wastes are disposed off in the buyback centre’s of respective companies.

In curbside system, the recyclables are separated at the source and collected separately from commingled waste at the curbside in the alley or at commercial facilities from low rise detached dwellings. Curbside program differs from community to community. In some programs, residents are required to separate different materials which are stored in their own containers and collected separately. Other programs use only one container to store comingled recyclables or two containers, one for paper and the other for heavy recyclables (glass, aluminum, and tin can). The non-containerized yard wastes are collected using claw and a modified vehicle. The waste collected is then emptied into a specially equipped compactor type collection vehicle with a wide receiving hopper. The collected yard wastes are usually taken to a compost facility. The streets are then swept once the wastes have been collected.

From low and medium rise apartments, two methods are used for the collection of source separated wastes. (1) Curbside collection with the help of conventional and specially designed mechanized collection vehicle. (2) Collection from designated storage areas with mechanizes collection vehicle.

In high rise apartments, the handling of commingled and source separated waste involves following methods.

(1) Recyclables and commingled wastes picked up by building maintenance personnel from different floors and taken to the basement or service area and placed in separate containers

(2) Recyclables and commingled wastes taken to the basement or service area by the occupants itself and placed in separate containers

(3) Recyclables wastes taken to the basement or service area and placed in separate containers and where available, other commingled waste is placed in specially designed waste chutes.

From commercial facilities, source separated materials are typically collected by private haulers. Recyclables are stored in separate containers. In large commercial facilities, baling equipment is used for paper and cardboard and can crusher for aluminum cans.

3.3 Components of waste collection:

As mentioned earlier waste collection is highly complex and costly process. It consists of the following components.

3.3.1 Collection points: Collection points are the sources from where the waste is generated or points where the waste is collected. These collection points can be located in residential, commercial of industrial area. The collection points determine the size of the crew, storage points and the time required for collection. The overall cost of waste collection is again determined by collection points.

3.3.2 Collection frequency: The rate at which the waste is collected from a collection is called as collection frequency. Collection frequency depends on many factors such as population, community, income group, life style and climatic conditions. In a hot humid climate, the waste collection must be frequent as this climate favor microbial activity resulting in faster decomposition of solid wastes. It also produces bad odour/foul smell and leachate (a watery liquid that oozes out from the waste). Henceforth this climate necessitates collection at least twice or thrice a week. This is applicable for putrescible material too. Frequent collection of putrescible waste will avoid health problems. Requirements of a locality are another factor that determines the collection frequency. Residential area requires frequent collection unlike the shops, institutions and industries. Likewise, urban areas generate more waste than rural areas and hence require frequent collection.

The requirement of containers too determines the collection frequency. According to the population and quantity of waste generation the number of containers should also be increased. Apparently open containers necessitate waste collection on daily basis unlike the sealed containers. Inappropriate estimation of waste generation and irregular waste collection increases the overall cost of the collection. Proper planning and segregation of waste at source will minimize the cost involved in waste collection.

3.3.3 Storage containers: The size and characteristics of storage container plays an essential role in waste collection. Selection of good container cansave collection energy, increase the speed of collection and reduce the crew size. The characteristics to be considered while selecting a container include

• Durable
• Easy to handle Economical
• Resistant to corrosion, weather and animals Covered to prevent entry of water
• Should not have sharp edges
• Less than 20 kg weight to facilitate easy emptying
• Avoid wooden containers (e.g., bamboo, rattan and wooden baskets) readily absorb and retain moisture and their surfaces are generally rough, irregular and difficult to cleanIn residential areas, where refuse is collected manually, standardized metal or plastic containers are used.
• When mechanized collection systems are used, containers are specifically designed to fit the truck-mounted loading mechanisms

3.3.4 Collection crew: The persons involved in collecting the waste from house to house; trucks and taking it to the transfer station or disposal site if termed as ‘collection crew’. The crew consists of 8-12 persons and headed by the supervisor. The size of the crew varies from community to community, region to region, amount of waste generation in a locality/ waste generation rate, frequency of waste collection, collection methods involved, space between the houses, size and type of collection vehicle and route characteristics. Labour and equipment costs also determine the crew size. The crew size increases when there is increase in the rate of waste generation. Less collection frequency also increases the crew size because the quantum of waste per individual stop will be high. The crew size has a great effect on collection costs which leads to

• Improper collection frequency
• Segregation of material at source
• Implementation of automation in collection

3.3.5 Collection routes: The route planned by collection crew to collect waste in a specific area is called as collection routing. A proper planning of the collection routes will decrease the overall cost in addition to labour cost, conserve energy by minimizing vehicle fuel consumption and reduce the working hours. The size of each route is decided based on

•      the amount of waste collected per stop,

•      distance between stops,

•      loading time

•      traffic conditions.

•      Barriers, such as railroad, embankments, rivers and roads with heavy traffic, can be considered to divide route territories.

All these factors determine the collection routing. Proper planning will improve efficiency of collection and decrease the collection cost. It will also help the supervisor to track the collection crew.

3.3.6 Transfer station: It is a centralised facility located between the collection and disposal site. It is also called as an intermediate station where waste from smaller collection vehicles are unloaded and re-loaded back into large vehicles for transport to a disposal or processing site. The transfer station also act as storage and processing station. Waste processing such as sorting, shredding, compacting, incineration, composting is done in transfer station. However, transfer stations involve additional capital costs of building transfer stations, extra labour and energy required for transferring wastes from collection truck to transfer station. The problems associated with transfer station are that it attract flies and other insect vectors and creates odours. Traffic and noise due to small and large collection vehicles, collectors, drivers, etc., invite the resentment of the communities living in the vicinity of transfer stations

4.0 Summary

• To summarize, in this module we have familiarized about
• Solid waste
• Elements of solid waste management
• definition and significance of waste collection
• Collection of commingled and source separated waste Components of waste collection

References

• George Tchobanoglous, Frank Kreith (2002) Handbook of Solid Waste Management, Second Edition, McGraw-Hill publication.
• TV Ramachandran (2009), ‘Management of Municipal Solid Waste’. Centre for Ecological
• Sciences, IISc Karnataka research foundation.
• www.nptel/Municipal solid waste management.com