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.

    • ‘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.’
    • ‘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.’
    • ‘Composted sludges are rich in slowly available nitrogen.’
    • ‘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.’
    • ‘The second ground for refusal was that without a composting facility, the company could not deal with the residual sludge from the process.’
    • ‘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.’
    • ‘Food waste, process waste and non-hazardous sludges are some examples of waste streams where there are serious difficulties, Dr Kelly said.’
    • ‘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.’
    • ‘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.’
    • ‘A small town near Niagara Falls becomes a ghost town after industrial sludge from a leaking dump renders the area toxic.’
    • ‘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.’
    • ‘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.’
    • ‘The black sludge from Venezuela is processed into a variety of petroleum products.’
    • ‘Thus, the present invention advantageously avoids the production of tailings sludges caused by clay dispersion.’
    • ‘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.’
    • ‘Biliary sludge is a mixture of particulate matter and bile, and it may stimulate microlithiasis.’
    • ‘In future it will be necessary to pump this effluent, to aerate it and de-water surplus sludge from the treatment process.’
    • ‘Incinerators are designed to destroy gases, liquids, solids, sludges, and slurries at high temperatures.’
    • ‘Sewage, sludge, and mine waste are common sources of metals found in soils, but metals also occur naturally.’
    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.
      • ‘With the trowel, I commenced scooping diesel oil sludge into the bucket.’
      • ‘Today, the accumulated amount of oil emulsions and sludge in the environment is estimated to be 1.2 billion tons.’
      • ‘It's like dumping fresh oil on sludge and wondering why your engine isn't running better!’
      • ‘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.’
      • ‘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.’
      • ‘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.’
      • ‘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.’
      • ‘And I'm sure my compressor will lock up with sludge soon.’
      • ‘As an unforeseen consequence, oil contaminated with wax and sludge was poised to foul the new propeller governor and relief valve.’
      • ‘This sludge blocked fuel filters, carburettors and fuel-injection systems, leading to rough running and engine failures.’
    2. 1.2Sea ice newly formed in small pieces.


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