WASTEWATER

WHAT IS WASTEWATER?Wastewater from individual houses, units and businesses enters a network of wastewater pipes that all ultimately travel to a wastewater treatment facility, where it can be processed.

At our 17 wastewater treatment works we treat the wastewater before it is reused or discharged to rivers or oceans in accordance with strict licence conditions issued by the Department of Environment, Climate Change and Water.

Wastewater is therefore treated to a very high standard and clear effluent is discharged to waterways or reused where it is economically and environmentally beneficial.

HOW DO WE TREAT WASTEWATER?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.

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

Inlet works •Biological Treatment •Chemical Treatment •Biosolids Handling •Effluent disinfection (for inland •WWTW)

InlET WORkSWastewater received at the inlet works is screened by a mechanical process to remove all large (greater than 5mm), 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 by the biological treatment process) 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 TREATmEnTSuspended solids, organic matter, grease/oil, nitrogen and phosphorus are broken down by bacteria that grow naturally in a biological reactor.

The bacteria in the process consumes the organic matter in the sewage. The bacteria requires oxygen to survive and 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.

www.hunterwater.com.auFACTSHEET . ID . 002 . MAY09

HunTEr WATEr COrpOrATIOn IS COMMITTED TO prOTECTIng pEOplE’S HEAlTH AnD EnHAnCIng THE EnvIrOnMEnT

FAST FAcTS

ArOunD 9% OF EFFluEnT FrOM Our TrEATMEnT plAnTS IS rECYClED FOr IrrIgATIng gOlF COurSES, FArM lAnD AnD FOr InDuSTrY.

WE MAInTAIn An ExTEnSIvE SYSTEM TO TrAnSpOrT WASTEWATEr , WHICH InCluDES 4,477kM OF SEWEr MAIn SYSTEMS AnD 380 puMpIng STATIOnS, AS WEll AS 17 WASTEWATEr TrEATMEnT WOrkS

WASTEWATER

www.hunterwater.com.auFACTSHEET . ID . 002 . MAY09

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 TREATmEnTAt some inland plants, chemicals are added to help remove phosphorus from sewage.

BIOSOlIDS HAnDlIngThe bacteria and solids need to be wasted each day from the biological treatment process in order to maintain its treatment capacity.

The waste bacteria and solids 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.

EFFluEnT DISInFEcTIOn Inland treatment plans have effluent disinfection facilities that kill bacteria or viruses in the treated effluent after biological treatment.

The disinfection precess used includes, chlorination/dechlorination, uv light and ponding.

REcYclIng WASTEWATERA key objective in Hunter Water’s Environmental Management plan is the productive use of recycled water and biosolids where it is economically and environmentally feasible.

recycled water from our treatment plants is used by agriculture and industry, and we ensure that biosolids can be used wherever possible.

Hunter Water endeavours to find beneficial uses for biosolids – most biosolids from our plants are used for mine site rehabilitation.

EnvIROnmEnTAl SAFEguARDS FOR WASTEWATERThe Department of Environment, Climate Change and Water issues licences under the protection of the Environment Operations Act (1997) for Hunter Water’s wastewater pipe network and treatment systems.

The licences stipulate both quality and quantity conditions for discharge from each wastewater treatment works and are reviewed every three years under the legislation. The licences also specify operational controls and reporting for the pipe network and pump stations.