Waste Management Definition
Waste management is the term used to describe the processes applied to deal with waste from its production until its final disposal.
Unfortunately, even in our days many people believe that waste management has to do only with technologies and plants.
However, in order a waste management system to be successful it requires appropriate planning and public participation, especially in the first steps.
To make a long story short, waste management consists of the following steps:
- Waste generation
- Collection and transportation
- Waste treatment and recycling
- Waste disposal.
All the waste management steps are further analyzed below, aiming to provide a better understanding of the waste management process.
Waste generation
Despite being ignored in most cases, waste generation is the starting point of any waste management system. More specifically, it is the quantity and the type of waste that a society generates which affect to a great extent the way it can be managed.
For example, societies that generate more organics require more often waste collection and need to focus on organic waste treatment methods such as composting or anaerobic digestion.
On the contrary, societies that generate more recyclables need to focus on the recovery of valuable materials, such as paper, plastics, metals, etc.
Waste collection and transportation
Waste collection refers to the all activities made to remove waste from generators. In most cases collection points have been determined in advance and bins have been placed.
Waste collection frequency depends on several parameters including waste generation rates, types of waste, capacity of bins installed and of the available collection equipment.
Most common waste collection schemes are curbside collection, drop off and door to door.
Following collection, waste is transported either directly or through a transfer station to its next destination.
Transfer stations are facilities used to store temporarily the waste collected prior being transported to a waste management facility. They are usually developed in case the facility is located at a long distance from the waste generators.
Their operation is quite simple. The waste collected is deposited into a container with high compaction. When full, the container is transported with bigger trucks to its next destination.
Aim of transfer stations is to reduce operational costs since fewer routes are conducted.
Waste treatment and recycling
Even though categorized in the third step of waste management just before waste disposal, treatment and recycling have distinct differences.
To begin with and as mentioned and above, recycling aims at recovering useful and valuable materials. Such materials are paper, plastics, metals, glass and wood. Main advantage of recycling is that it prevents depletion of raw materials, reduces emissions, saves valuable landfill space and creates jobs.
On the other side, waste treatment aims at either dealing with organic waste or at generating energy. Two are the main categories of waste treatment: a) biological waste treatment, b) thermal waste treatment.
Biological waste treatment
As defined by its name, biological treatment applies biological processes to “neutralize” organic waste and to prevent methane emissions from its decomposition. In brief, biological treatment includes:
- Composting is nothing more than a controlled aerobic decomposition of organic waste. Composting takes place naturally driven by the microorganisms present on the organic waste. Most common techniques include composting in windrows, in piles, and in vessel.
- Anaerobic digestion. In this method decomposition of organic waste takes place in lack of oxygen and in controlled conditions of temperature and pressure. Aim of the process is to generate methane and to use it for energy production. Following decomposition, the treated organic waste is still unstable and needs to be aerated in order to stabilize. Special reactors have been developed aiming to maximize methane production and to counterbalance the high cost of this technology.
Thermal waste treatment
In this type of treatment, heat is used to treat the waste. Aim of thermal waste treatment is firstly to reduce the volume of treated waste and secondly to recover energy from the treated waste. In addition, transfer costs are reduced and greenhouse emissions are decreased. The most common types of thermal treatment are presented briefly just below:
Incineration
Incineration is the most commonly used method to thermally treat waste and especially the municipal. More specifically, the waste is burnt in the presence of oxygen and it is converted into ash, water vapor, and gases (mainly carbon dioxide). Almost all modern facilities take advantage of the high temperature of the gases generated by the process and recover energy for electricity or heating.
Pyrolysis
Pyrolysis is a thermal process that can achieve similar if not the same results with the incineration. However, in this case decomposition of waste takes place in higher temperatures and with very little oxygen. In general pyrolysis is more expensive than incineration and it is more preferred to treat special types of waste such as tires, pesticides, etc.
Gasification
Similarly to pyrolysis, gasification is thermal treatment method that decomposes waste in high temperatures with limited amounts of oxygen or steam. As a result, carbon is converted to carbon monoxide and hydrogen, forming a mix of gases called syngas. Syngas is the product of the process and can be further burnt to product heat and electricity. Plasma arcs are usually used to ionize the gas and convert it to syngas. Main byproduct of gasification is an inert solid remnant called slag.
Open burning
Even though it is not considered a sound method to treat waste, open burning is still the main method to treat waste in developing countries or even in remote parts of the developed world. Despite reducing the volume of waste, no emission control takes place. Dioxins, polycyclic aromatic compounds, volatile organic compounds, etc. are among the substances emitted. Despite being a cheap method it must not be applied since it poses threats and pollutes heavily the environment.
Waste Disposal
Waste disposal refers to the burying of waste into the ground. According to the protection measures applied, waste disposal sites can be divided into sanitary landfills and uncontrolled dumpsites.
- Sanitary landfills are called the sites that meet the following criteria:
- The disposal area has been excavated;
- A lining system has been installed to protect the soil and the groundwater;
- A leachate collection and treatment system is in place;
- Operations follow a daily program;
- All waste is covered with a daily cover material;
- Disposed waste is compacted;
- Landfill gas is recovered and treated appropriately;
- After completion of operations the site is rehabilitated;
- Monitoring takes place for a certain period.
- Uncontrolled dumpsites are the sites that none or most of the above criteria are not met. Sadly, uncontrolled dumping is still the main practice in many parts of the developing world, posing a serious threat not only for the environment but for the residents living close to these sites.
