Treatment

Wastewater from households, commercial premises, schools, hospitals and industry enter a network of wastewater pipes that all ultimately travel to a wastewater treatment facility. Hunter Water Corporation operates 17 wastewater treatment works (WWTW) at Burwood Beach, Belmont, Boulder Bay, Shortland, Dora Creek, Edgeworth, Toronto, Morpeth, Cessnock, Kurri Kurri, Kearsley, Paxton, Farley, Branxton, Raymond Terrace, Karuah and Tanilba Bay.

Our wastewater treatment processes rely on both biological processes and chemical processes to treat wastewater to an acceptable quality for discharge into local waterways or the ocean.
Many of our treatment plants supply treated, recycled water to local industries, golf courses, farms and woodlots. More information is available on recycled water here.

Our treatment processes differ at each site in small ways, but can be broadly split into:

1. Inlet works
2. Biological Treatment
3. Chemical Treatment
4. Biosolids Handling
5. Effluent disinfection (for inland WWTW)

Inlet Works

Wastewater received at the inlet works is screened by a mechanical process to remove all large (greater than 1.5 mm), non-biodegradable material, and all sand (or ‘grit’).

Approximately 30 cubic metres of screenings per week are removed at our inlet works screens. Screenings do not include faecal matter or toilet paper (they are dealt with under biosolid handlings) as the screenings mainly remove things that are not supposed to be discharged into the sewer system.

At most treatment plants, the inlet works is covered and odours are extracted and treated through a biological filter.

Biological Treatment

Suspended solids, dissolved organic matter, grease/oil, nitrogen and phosphorus are broken down by bacteria that grow naturally in a biological reactor.

As bacteria require oxygen to survive they consume the organic matter in the sewage. The oxygen is supplied to the bacteria by an aeration system in the reactor. Aeration systems normally consist of either:

• large propeller style blades on the reactor surface that violently stir air into the contents, or
• a set of porous diffusers on the floor of the reactor that are fed by air blowers.

The second stage of this process is a large settling tank (known as a clarifier) that allows the bacteria to gather together and settle to the floor, while the clear, treated effluent passes over weirs on the surface of the tank. The bacteria is then recycled back to the aerated reactor.

Chemical Treatment

Chemicals are added to help remove suspended solids and Phosphorus from sewage.

Biosolids Handling

The bacteria wasted from the process each day is known as biosolids. Despite the name, they are not necessarily solid. Depending on the type of wastewater treatment process used, biosolids usually have an extremely high water content (well over 90%), which means that the material is essentially liquid, and looks like murky water.

These biosolids are then stabilised by a process known as digestion. This process, involving further aeration, is necessary to minimise the odour producing potential of the biosolids when they are dewatered (which involves removing much liquid as possible) and used in land application projects. From the digestion process, the biosolids are dewatered, taking their water content from around 98% to around 80%. By this stage (at 80% water content), biosolids look much like garden soil. More information on Hunter Water’s biosolids programs can be found by contacting Hunter Water. 

Effluent disinfection

Inland treatment plans have effluent disinfection facilities that kill any bacteria or viruses remaining in the treated effluent after biological treatment. Either chlorination/dechlorination or UV light is used to disinfect effluent at Hunter Water’s inland treatment plants.