Gippsland Water's main objective is to ensure our discharges from our Wastewater Treatment Plants (WWTP) comply with Environment Protection Authority (EPA) discharge licence requirements.
The EPA is charged with the responsibility of monitoring Gippsland Water’s discharges and treatment processes. This discharge licence is to ensure our environmental resources are maintained through compliance with the State Environment Protection Policy (SEPP) for Victoria, which provides a legal framework for State and Local government agencies, businesses and communities to work together to protect and rehabilitate Victoria’s surface water environment.
The results of our annual wastewater monitoring program are reported to the EPA under the terms of our wastewater discharge licence agreements as part of our Annual Regulatory Reporting framework.
Overview of wastewater treatment processes
To ensure compliance with the EPA discharge licences, Gippsland Water employs physical, chemical and biological treatment of its wastewaters, since the role of a wastewater treatment plant is to reduce harmful contaminants and strength of the wastewater collected from homes and industry before it is released into the environment. There are several processes that can be employed to treat wastewater and many rely on nature’s bugs (ie: bacteria, protozoa, algae) to breakdown the solids and organic products in our wastewater.
Primary Treatment – is the removal of large solids, grit and oils from the wastewater entering the treatment plant by use of screens and gravity separation.
Secondary Treatment – is the biological process whereby a large population of microorganisms help convert organic material into other forms which can be easily separated into solids and clear liquid. These solids are settled out in settling tanks.
Tertiary Treatment – is the use of filters and /or disinfection of the clear liquid to reduce the other contaminants as well as pathogens, which are microorganisms that pose a risk to public health.
Due to the variety of treatment plants across the Gippsland Water region the treatment process may vary from plant to plant. To produce wastewater compliant with the EPA discharge licence, during the treatment process, wastewater passes through a number of stages that may include;
Pre-treatment
Flows and loadings are equalised prior to any treatment occurring to ensure the treatment process is not adversely affected by shock loads and volumes.
Screening - The wastewater is first passed through a coarse screen where large objects such as plastics, gravel and rags are collected on the mechanically cleaned screen and placed in the bin for collection and disposal. Screening protects pumps and equipment.
Grit Removal - The wastewater is aerated to increase the relative density of any fine sandy materials, seeds and heavy particulate matter (grit) which settles and accumulates in tanks and piping. The grit is then moved by a scraper and is discharged into a bin for disposal. Grit removal reduces abrasive wear and damage to mechanical equipment and prevents valuable tank space being wasted.
Secondary Treatment/Nutrient Removal (biological)
Secondary treatment processes use naturally occurring micro-organisms to remove most of the remaining suspended material, usually organic matter (measured as Biochemical Oxygen Demand, BOD) and other nutrients (phosphorus and nitrogen) from the water.
The process operates in distinct phases that can occur in separate tanks (in series) or within a single tank using biological processes or chemical precipitation.
Anaerobic – This involves the decomposition process using microorganisms to stabilize organic solids or biosolids, specifically microorganisms that live and reproduce in an environment containing no "free" or dissolved oxygen. Decomposition of solids produces biogas during this stage (carbon dioxide and methane).
Aerobic – This involves the use of bacterial processes occurring in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. Once there is a lack of organic matter, bacteria die and are used as food by other bacteria. Ammonia (a nitrogen compound) is converted to nitrate during this stage.
Anoxic – This involves a well mixed zone with little or no dissolved oxygen. This zone is part of the nitrogen removal process where nitrates produced in the aerobic zone are converted to nitrogen gas.
Nitrogen removal is achieved biologically by providing conditions suitable for the development of special microbes that are able to convert the various nitrogen compounds that are present in the sewage to nitrogen gas.
Phosphorus removal can be achieved biologically by providing conditions suitable for the development of special microbes that are able to remove dissolved phosphorus from the water by storing it within the microbial cells. The phosphorus is removed when the microbial cells that contain the excess amount of phosphorus are removed from the biological reactor tanks in a sludge by-product.
Phosphorus can also be removed by adding chemicals that react with dissolved phosphorus and form a precipitate that can be settled out of the water.
Sludge Removal
To prevent an excessive build-up of micro-organisms and other solid matter in the activated sludge tanks, solids must be regularly removed. The slurry of micro-organisms and other solid matter is referred to as “activated sludge.”
The excess activated sludge (waste activated sludge) is removed from the secondary treatment process and piped to either sludge lagoons or a belt press. Once it has been processed it is known as “biosolids”. Ultimately all biosolids are used in compost and then land applications.
Tertiary Filtration
This process is sometimes implemented after secondary treatment processes to further remove solids from the water. This can involve passing the water through a bed of sand/gravel, a Dissolved Air Floatation Filtration (DAFF) unit or through pores in a membrane (micro filtration).
Disinfection
Disinfection may occur after either secondary or tertiary treatment. The aim of disinfection is the removal, destruction or inactivation of pathogens (disease causing organisms) that may be present in the water. Typical disinfection processes are long term storage in ponds or ultra violet disinfection. |