Frequently Asked Questions About Solid Waste

What is Municipal Solid Waste (MSW)?

To the layman municipal solid waste is rubbish, garbage, trash or refuse. The term municipal solid waste originates from that fact that traditionally all solid waste (i.e. not sewage) was collected by municipalities. Nowadays the trend is shifting towards waste collection by private companies, however the "municipal" reference remains in MSW.

Where does MSW come from?

MSW originates from households and businesses and comes about from discarding packaging of every day items, items that have reached the end of their useful life, unwanted items, disposable items and the like.

What is MSW made up of?

The composition of MSW is often broken down into the constituent "pure" materials: plastic, paper, cardboard, glass, metals, textile, organics, inert material (ceramic, cement) and others. The organic portion is typically also split into foodwaste (waste from food preparation, left over food, spoilt food) and garden waste (grass cutting, leaves, yard trimmings).

What other waste streams are there besides MSW?

Bulky waste is made up of large items, that are not thrown away routinely, such are furniture, large appliances, mattresses. Construction and demolition waste (C&D) originates from tearing down old buildings and construction new ones, this mostly made up of bricks and mortar, wood, glass and metal (pipes, cables). Medical waste originates from hospitals and is typically collected and treated separately. Hazardous waste contains substances containing heavy metals, toxins and other hazardous materials that mostly originates from industry. MSW can contain portions of the above waste streams as well.

What are the treatment options for MSW?

In the developing world virtually all MSW is landfilled as it is the lowest cost option. An advance was incineration to reduce the mass and recovery energy. Nowadays the trend is shifting to mechanical biological treatment to allow recycling of certain fractions.

What is landfilling?

Landfilling is a traditional waste disposal route, whereby the waste is dumped in a designated area, without prior sorting or extraction of any fraction. Landfills have advanced from unprepared pits to lined basins which capture leachate and prevent contamination of ground water. More advanced landfills are also capped to prevent rain penetration and sometimes landfill gas is extracted, this is often only flared, but sometimes used beneficially.

What are the problems with landfills?

Simply landfilling all waste is unsustainable by definition as nothing is reused, recycled or recovered. Greenhouse gas emissions from landfills (most methane decomposition of organics) are a major contributor to global green house gas emissions. Most landfills in developing countries are not lined thus ground water becomes contaminated, they are open and cause unpleasant odours, attract vermin and cause wind-born pollution.

What is incineration?

Incineration in the context of MSW means controlled thermal combustion of the waste in a furnace, typically the energy released is used beneficially to generate electricity via steam turbines. The main aim of incineration of MSW is the reduction of the mass of the waste, what remains is know as "bottoms ash" and is all the inert material (glass, metals, ceramics and rubble).

What is MBT?

MBT is short for "Mechanical Biological Treatment" and it is a waste treatment solution that employ mechanical and biological process. Mechanical steps are typically bag opening, screening, metals separation, wind-sifting and shredding. The biological process was traditionally aerobic treatment of the waste, such as composting, bio-drying or stabilisation. Nowadays an improved biological route is anaerobic digestion of the organics from MSW, the benefit being that the biogas contains useful energy, whereby aerobic processes consume energy.

What is a MRF?

"Material Recovery Facility" is what MRF stands for and it is a general description for facilities where waste is treated and some fractions of the waste recovered. Typically a MRF houses bag openers, screens, metal separators, manual or automatic sorting equipment. The extracted fractions are typically sent for recycling and/or RDF is produced.

What is RDF?

RDF stands for "Refuse derived fuel" and typically takes on the shape of a mix of combustible solid material (plastic foils & containers, paper, card, textiles) extracted from a waste stream. RDF is produced by removing moist and heavy materials from waste to be left with a highly energetic fuel. Cement kilns and other large industrial processes are typically the destinations of RDF.

What is recycling?

To most people recycling means substances that were disposed of are collected and re-introduced into a process to give the material a second life. Some countries and organisation define extracting energy (not a substance) from waste as recycling as well, for example incinerating waste and producing electricity is seen energetic recycling of waste.

What is separated waste collection?

There are various permutations of waste collection where all waste is not thrown into one bin, this practice is referred to as "source separation".

  • The "two bin" system typically refers to having one bin for dry and recyclable material (clean plastic foils & containers, paper, card, cans, glass), while the second bin is meant for organics and true waste, e.g. un-recyclable material (dirty/wet/oily plastic & paper) diapers, ceramics, textile, dust, etc).
  • The "three bin" system is similar to the two bin system, except that the organics are collected in a dedicated bin, allowing easier the beneficial use of the organics, for example by anaerobic digestion (biogas) or composting. These organics are referred to as "source separated organics" or SSO.
  • Glass and paper are materials that are sometimes collected separately, either by collection or having publicly available containers.