Treating sewage

Sewage Treatment Plants

Sewage treatment plants treat sewage from households, and trade waste from commercial and industrial customers. Wannon Water operates 18 sewage treatment plants to service 19 customer zones.

We operate different types of sewage treatment plants, from simple lagoon systems to activated sludge plants, depending on the type of waste they receive and the technology available at the time of construction. We also have a 'tertiary' plant in Hamilton which treats recycled water to a higher standard for industry.

For more about our sewage treatment plants, visit the Information Sheets page.

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How does sewage get to the plant?

Sewage from your bathroom, toilet, sinks and drains, and from industry, is collected in underground pipes. It then flows to larger pipes called sewers, which are generally situated along the back boundaries of properties.

Sewers generally slope downwards to allow the sewage to flow to the plant by gravity, or pumps and rising mains may be required to bring the sewage up from low level areas.

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Sewage treatment

Once the sewage reaches the plant, it is screened to remove any coarse material, such as sticks, rubble and rags. A special tank then removes grit, which can damage pumps and fill up valuable tank space if not removed.

A variety of treatment processes are then used at different sewage treatment plants, as detailed below (for more details, visit the Information Sheets page):

Biofiltration treatment

This includes four stages:

  1. Primary sedimentation - where sludge falls to the bottom;
  2. Trickling filters - that help remove bacteria from that sewage;
  3. Clarification - where sludge settles through gravity; and
  4. Sludge holding lagoon - allowing remaining particles to settle to the bottom.

Maturation pond system

Maturation ponds treat sewage with a clarifier, allowing sludge to settle to the bottom. Sewage is treated via trickling filters which help purify the water stream by using a rock bed. Lagoons are then used to aerate and settle the sludge with the use of UV rays and a maturation lagoon completing the process.

Reed-bed treatment

This provides a natural way to treat sewage, as bacteria, fungi, viruses and insects assist in neutralising pollutants in the water. Sewage is treated in lagoons then fed by gravity through artificial reed beds, which assist the treatment through the uptake of nutrients by plants and by capturing fine particles in rocks at the base of the beds.

Biological treatment

Sewage is mixed with activated sludge, allowing micro-organisms to assist the treatment. The sewage flows to activated sludge tanks, which involve aeration and settling periods, enabling solids to settle to the bottom. The treated effluent is decanted and the sludge is dried and transported for biosolids composting and reuse.

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How you can help

Industries assist Wannon Water by treating their sewage to remove significant pollution at the source.

You can also help the treatment process and the environment by: 

  • Using low phosphorous detergent
  • Not putting cotton buds, nappies, paints, oils, veggie scraps, Band Aids, pills, sanitary pads, etc. into the sewerage system.

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