Odours can come from many different sources, but the typical kinds of odours EPA investigates are from industrial sources and premises such as sewage treatment facilities, abattoirs, animal renderers, landfills and composting facilities. Odour from domestic sources and some smaller commercial premises, such as shops and restaurants, should be referred to local council officers.

Compost and organic waste

Organic waste, especially municipal garden waste, is recycled into a number of organic products that are used to improve soil condition. Odour is released during the mixing and turning phases of composting. It is also a problem when organics start to decompose anaerobically (without oxygen). The process releases gases including carbon dioxide and organic sulphides.

In Victoria, garden waste is collected from residential houses and taken to transfer stations where litter is removed before the waste is mulched and consolidated. Odour can occur if the mulched waste is not transported to a compost facility before decomposition starts to occur. Mulched garden waste is then taken to EPA-licensed compost facilities where the waste is mixed with other organic wastes and further processed to form useful compost or soil conditioners.

Rubbish odours

Landfills that accept putrescible waste (for example municipal solid waste or household rubbish) have been known to create odour. These odours are created by the daily activities of adding new waste to a landfill and from the aerobic decay of organic waste exposed to air. The smell is often similar to that noticed from household rubbish bins.  

One way rubbish odour can be managed by landfill operators is to add a layer of compressed soil or earth on top of a day’s deposition of waste. The cover helps prevent interaction between waste and air, reducing odours and creating a firm base for vehicles to work on.

Landfill gas odours

Landfill gas is a mixture of gases produced as waste decays within landfills - a process known as methanogenesis. Landfill gas odour is different from rubbish odour as the process occurs anaerobically (without oxygen). There can be more than 500 types of gas produced by landfills but the mixture is mostly methane and carbon dioxide which are both odourless. Other gases present can include a range of sulphide gases. It is these gases that create the rotten rubbish smell of landfill gases. Waste can generate a significant amount of methane gas as it decomposes which can also be captured as a valuable energy source.

Anaerobic leachate

Landfill leachate is liquid that moves through or drains from a landfill. This liquid may either exist already in the landfill, or it may be created after rainwater mixes with the waste in the landfill.  Leachate may become anaerobic if it has been depleted of oxygen due to biological/chemical reactions. It is usually highly odorous and described as having an ammonia or sewage-type smell.

Part of landfill management requires collecting, containing and treating the leachate to protect surface and groundwater in areas near the landfill. The landfill liner system should include a leachate collection system that then drains into a leachate collection pond (or a sump). The leachate is then pumped from the sump and stored in ponds for aeration or treated and discharged into sewer for offsite disposal. The level of landfill leachate is monitored regularly to ensure compliance with the EPA licence, and leachate collection ponds are regularly tested for acceptable levels of contaminants.