During the wastewater treatment process, the most concentrated waste is separated from the remainder of the wastewater. This is then concentrated further and dried into a sludge product for disposal.
For every thousand tons of water processed, about one ton of sludge is produced. This sludge is transported to landfills where it slowly breaks down resulting in chemical leaching and the release of methane. Methane is 25% more potent than carbon in terms of global warming potential and landfills are one of the largest emitters globally of methane. For a midsize dyehouse, sludge disposal alone can result in over 6,000 tons of carbon emissions per year. Industry-wide, this amounts to 90 million tons of carbon emissions.