How to Vermicompost With Sewage Sludge

Written by patricia neill
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How to Vermicompost With Sewage Sludge
Worm castings make a terrific soil amendment. (Earthworms image by Ana Dudnic from

Using earthworms to compost sewage sludge has been around since the 1970s. The worms, usually red wrigglers or Eisenia fetida, eat and then excrete the sludge (also known as biosolids), which then ceases to smell. Applying treated sewage sludge directly on agricultural lands created problems as the sludge was still contaminated with disease-causing organisms. Further treatment by vermicomposting destroys these pathogens and results in an excellent soil amendment known as vermicastings.

Skill level:
Moderately Easy

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Things you need

  • Bins
  • Worm bedding
  • Food wastes
  • Sewage sludge
  • Red wriggler worms

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  1. 1

    Make worm bins from wood or plastic. Puncture some holes in the bottom for drainage. Bins should be no deeper than 18 inches, as worms feed on the surface. For drainage and air-circulation in the bin, raise the bin up on bricks or blocks and put plastic underneath to catch any draining liquids.

  2. 2

    Fill the bin with bedding for the worms -- shredded cardboard or newspaper, but skip the glossy, coloured paper -- and dead leaves. Consider adding some peat moss or loose soil as worms enjoy that environment.

  3. 3

    Purchase sewage sludge online or from your local water treatment plant. Some cities are now selling their treated biosolids as a soil conditioner. Mix the biosolids with the kitchen scraps or food waste in a 1:1 ratio. If you have two pounds of red wrigglers in your bin, you'll want to feed them one pound of biosolid/kitchen scraps a day.

  4. 4

    Purchase red wriggler worms, which are available online from a variety of suppliers. If there's a worm farm near you, get your supply locally. Worms will not only eat and provide the castings, they'll reproduce as well. Consider selling batches of your worms when your bin is looking overcrowded. Worms will reproduce every 21 days, and the young worms will be mature in another two months.

  5. 5

    Place the worms in the prepared bin or bins. You'll want a cover for the bins as worms prefer darkness, and the bedding should be slightly moist, like a rang-out sponge. Feed the worms a mix of the biosolid and the kitchen scraps, and add some grit like ground-up eggshells to help the worms digest their food. Avoid dairy foods or meats or fatty foods in the worm's feed. They'll do fine with vegetable and fruit scraps.

  6. 6

    Keep the temperature in the range of 12.8 to 25 degrees C. Don't let it get too cold or too hot or the worms will suffer.

  7. 7

    Prepare to remove the worm castings in about three to four months. To remove the castings and leave the worms behind, shine a bright light into the bin. The worms will move downward deeper into the bin. Use your hands to or a bowl shovel out the castings, making sure to put any worms in the vermiculture back into the bin.

  8. 8

    Use this rich fertiliser in potted plants, gardens, around trees or in flower gardens. Or bag it and sell it to fellow gardeners.

Tips and warnings

  • Check on your worms often to ensure the temperature and moisture in the bedding.
  • According to the University of Nebraska Coop Extension, worm castings "contain five times more nitrogen, seven times more phosphorus and 11 times more potassium" than ordinary soil.
  • Some environmentalists warn that treated sewage sludge may still contain heavy metals, pharmaceutical residues and other contaminants.
  • If you have cats, don't let them use the worm bin as a litter box -- their urine could kill your worms.

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