Waste comprises materials that are no longer needed, and thus are discarded. Waste can be classified as solid or liquid according to its form, and further categorised as hazardous and non-hazardous waste. Liquid waste includes municipal wastewater, storm water run-off and industrial wastewater discharge.
Solid waste includes household rubbish, which is also called municipal solid waste (MSW), industrial waste – for example, from agriculture – medical and electronics waste.
The treatment of solid waste is challenging because it may contain one of more contaminants (which may include heavy metals, explosive and flammable materials) and these must be dealt with before the waste can be treated.
Typical processes and associated gas detection issues
Biogas is produced when organic materials such as agricultural and food waste are broken down by bacteria in an oxygen-deficient environment. This is a process called anaerobic digestion. When the biogas has been captured, it can be used to produce heat and electricity for engines, microturbines and fuel cells. Clearly, biogas has high methane content as well as substantial H2S, and this generates multiple serious gas hazards.
In particular, there is elevated risk of:
Operators in a biogas plants must have personal gas detectors that detect and monitor flammable gas, oxygen and toxic gases like H2S and CO.
It is common to find flammable gas CH4 and toxic gases H2S, CO and NH3 in refuse bunkers. Refuse bunkers are built several metres underground and gas detectors are usually mounted high above them, which makes those detectors hard to service and calibrate.
In many cases, a sampling system is a practical solution as air samples can be brought to a convenient location and measured.
Leachate is a liquid that drains (leaches) from an area in which waste is collected, and it presents a range of gas hazards. These include the risk of flammable gas (explosion risk), H2S (poison, corrosion), ammonia (poison, corrosion), CO (poison) and adverse oxygen levels (suffocation).
Leachate pool and passageways leading to the leachate pool must be monitored for CH4, H2S, CO, NH3, O2 and CO2. Various gas detectors should be placed along routes to the leachate pool, with output connected to external control panels.
Detection of O2 and toxic gases SO2 and CO is vital in boiler house areas.
The flue gas from incineration is highly toxic, as it contains pollutants such as NO2, SO2, HCl and dioxin. NO2 and SO2 are major greenhouse gases, while HCL and dioxides are harmful to human health
It is usual to monitor oxygen and toxic CO in ash pits.