Definition of sludge in English:



  • 1Thick, soft, wet mud or a similar viscous mixture of liquid and solid components, especially the product of an industrial or refining process.

    ‘the dumping of sewage sludge’
    [count noun] ‘miscellaneous chemicals and treated sludges’
    • ‘Waste waters from direct and indirect cooling will be handled within the plant through a water re-circulation and treatment systems to remove sludges, steel scales and other residues, etc.’
    • ‘Incinerators are designed to destroy gases, liquids, solids, sludges, and slurries at high temperatures.’
    • ‘Food waste, process waste and non-hazardous sludges are some examples of waste streams where there are serious difficulties, Dr Kelly said.’
    • ‘The sewer system had a very low ceiling and much of the path was taken up by a stream of thick, black sludge that oozed sickeningly towards some central point.’
    • ‘A small town near Niagara Falls becomes a ghost town after industrial sludge from a leaking dump renders the area toxic.’
    • ‘Biliary sludge is a mixture of particulate matter and bile, and it may stimulate microlithiasis.’
    • ‘In addition, 132 million wet tonnes of agricultural wastes, effluent and sludges are generated in Ireland annually and are a major cause of harmful greenhouse emissions.’
    • ‘The second ground for refusal was that without a composting facility, the company could not deal with the residual sludge from the process.’
    • ‘Methods include in situ and ex situ treatment of contaminated soil, groundwater, industrial wastewater, sludges, soil slurries, marine oil spills, and vapour-phase effluvia.’
    • ‘However, this process is not selective, produces solid sludge for disposal, may have environmentally damaging effects of its own, and must be repeated to be effective.’
    • ‘If you put your waste down the disposal, it flows, along with household sewage, to a plant where it gets separated into thick sludge and treated wastewater.’
    • ‘Sewage, sludge, and mine waste are common sources of metals found in soils, but metals also occur naturally.’
    • ‘When they are 95 per cent dewatered, sludges are put into pellet form - superior for disposal purposes because in becoming pellets, nearly all of the pathogenic bacteria are killed.’
    • ‘It was important that the public were kept informed about the sludge plant proposal and it was vital that the sludges to be treated would be clearly set down.’
    • ‘Thus, the present invention advantageously avoids the production of tailings sludges caused by clay dispersion.’
    • ‘The black sludge from Venezuela is processed into a variety of petroleum products.’
    • ‘In future it will be necessary to pump this effluent, to aerate it and de-water surplus sludge from the treatment process.’
    • ‘Composted sludges are rich in slowly available nitrogen.’
    • ‘He dismissed as ‘scaremongering’ the claims that chemical and industrial sludges were being processed in the plant or that animal and body parts were being processed.’
    • ‘It now appeared to be the case that what was being treated was industrial waste when they were advised the plant was to treat sludge from sewage treatment plants.’
    mud, muck, mire, ooze, silt, alluvium, dirt, slime, slush, slurry
    sediment, lees, dregs, deposit, grounds, settlings, precipitate, residue
    gunk, crud, gloop, grunge, gook, goo
    gunge, grot
    guck, glop
    View synonyms
    1. 1.1Dirty oil, especially in the sump of an internal combustion engine.
      • ‘His already dirtied clothes were drenched in the sludge.’
      • ‘There were also at least six large oil spills, releasing an estimated 6 millions gallons of sludge, and over 300 smaller spills.’
      • ‘This sludge blocked fuel filters, carburettors and fuel-injection systems, leading to rough running and engine failures.’
      • ‘It's like dumping fresh oil on sludge and wondering why your engine isn't running better!’
      • ‘We became experts at disconnecting the fuel line at the carburetor, taking off the cap, blowing the sludge back into the pressurized tank, and reconnecting it for another five miles.’
      • ‘Picturesque coastal areas hit by the Prestige oil tanker spill were facing a fresh deluge of sludge yesterday, with fierce winds blowing slicks in from the Atlantic.’
      • ‘As an unforeseen consequence, oil contaminated with wax and sludge was poised to foul the new propeller governor and relief valve.’
      • ‘It's almost amusing, until one of them sinks into a pool of oily sludge and wings greased, struggles helplessly to get free as the others fly off.’
      • ‘And I'm sure my compressor will lock up with sludge soon.’
      • ‘Today, the accumulated amount of oil emulsions and sludge in the environment is estimated to be 1.2 billion tons.’
      • ‘With the trowel, I commenced scooping diesel oil sludge into the bucket.’
  • 2[usually as modifier] An unattractive muddy shade of brown or green.

    ‘a sludge green’
    • ‘Lunch is a revolting sludge burger in a pretty rustic restaurant, but Zoe thinks it's all marvellously delicious.’
    • ‘Her eyes were set upon the sight outside, it had snowed the other night and the street was coated in pure white snow, expect for the roadway which was compiled of a grey sludge due to the constant stream of traffic.’
    • ‘I can make do with that, if we mix it with a caffeine-sugar sludge combo.’
    • ‘But won't that just reduce everything to a nasty green/purple sludge?’
  • 3Sea ice newly formed in small pieces.


Early 17th century: of uncertain origin; compare with slush.