The Eastern Treatment Plant is located approximately 35 km on the Southern region of Melbourne City. The treatment plant was initially a secondary treatment plant with a secondary treatment process of sewage. It was commissioned for operation in 1975, covering an area of 1000 hectares. Furthermore, it was upgraded into an advanced tertiary treatment plant in 2013 and it treats over 45 % of sewage in Melbourne. The following reflective journal will discuss the plant structure, how it works including the process of sewage treatment and its effects to the environment.
Construction of the newly upgraded plant involved installation of vital equipment in infrastructure such as ozone production and ozone injection buildings, ultraviolet light, biological media filters, chlorine contact basins, pump stations, pipelines and communication cables. In addition to that, the plant has internal access roads, treated water storage basins that are covered with ancillary tanks, storage facilities and chemical dosing tanks. The initial sewage treatment provided a Class C type of water but the upgrade improved it to a Class A. The recycled water is discharged to Boags Rocks. 5
How the plant works.
Sewage includes unwanted material that goes down from various places such as the laundry, the kitchen, toilet flush and bathroom sink. The following steps define the treatment process that is used at the Eastern Treatment Plant in Melbourne. Sewage in the plant undergoes three different treatment stages leading to a Class A quality of recycled water. The three stages include the primary, secondary and tertiary stages.
Sewage treatment process.
The primary treatment stage of effluent starts with filtration, large items such as cotton buds or rubbish are filtered from the sewage using fine screens. Next, the sewage is aerated which removes tiny particles such as sand. Finally, the primary process is completed with a sedimentation where a layer known as sludge is formed after large solid items sink to the bottom of tanks. The sludge is then pumped to larger tanks referred to as digesters where decomposition by bacteria takes place. 1
Secondary treatment of sewage entails the action of bacteria. Various types of bacteria co-exist and these include aerobic, anaerobic and facultative bacteria in that environment. The bacteria remove nutrients and breaks down organic substances in aeration tanks. The water flows though sedimentation tanks to allow for further settlement of sludge at the bottom of the tanks. Finally, clear water is formed at the top after sedimentation, this is known as the secondary effluent. The secondary effluent flows into holding ponds then to the tertiary stage of the sewage treatment process.
In the first step of the tertiary treatment stage, secondary treated effluent enters the advanced tertiary treatment plant using a pump station. The effluent is pumped by two steel pipes that are stainless, moreover, within the entrance of these two pipes, ozone gas is added. The tertiary treatment process of effluent begins with media filtration, which is done through ozone or biological methods to reduce odour, colour and suspended solids within the effluent. This filtration step is followed by secondary ozonation. Ozone is extracted from oxygen in the air by ozone generators. The next part of the process is disinfection using UV radiation and chlorine.
The third step is the biological media filtration where 32 concrete tanks that act as biological media filters allow the flow of treated water within them. The treated water flows to produce filtered water through the filtration method. The surface of the filter media has certain bacteria that enhance the water. In addition to that, the bacteria break down organic compounds and reduce the ammonia content in treated water. These stages form sludge that is removed through a backwash process, the sludge is thickened and sent to the available digesters that convert the sludge into biogas. Water used during backwash is further reused by sending it to the initial steps of the treatment process.
The fourth step involves water treatment in ozone for a second time, the water is then sent to concrete channels. The fifth step comprises of seven UV reactors that are used in disinfection using UV light. The final stage in the treatment process involves the use of chlorine to disinfect water hence ensuring that the water is completely treated. The treated water is finally passed on to an outfall pump station.
Effects of the plant to the environment.
The expansion project in Eastern Treatment Plant has led to environmental effects such as a higher quality of recycled water at the Boags Rocks it is eventually discharged, hence a substantial reduced impact on the marine environment. Moreover, there are more specific improvements in the water discharged into the marine environment that include reduced levels of oils, solids and grease deposited in the marine environment, improved disinfection of water and reduction in litter. In addition to that, other improvements include a reduced amount of water that is discharged into the marine environment, reduction in odour, water colour, foam and ammonia.
The amount of ammonia produced by the plant has had adverse effects to the marine environment. The plant has undertaken measures to reduce the levels of ammonia in the effluent through upgrading six tanks used in aeration at the secondary treatment process in order to achieve an 85% reduction in ammonia levels annually. The plant has further built four extra aeration tanks to reduce the levels of ammonia. Excess ammonia in the marine environment harms the organisms that live in that environment therefore the plant has undertaken measures to reduce the levels.
The Eastern Treatment Plant produces class A quality of water, a portion of it is used in the treatment process. The plant also supplies recycled water to customers who use it for non-drinking purposes such as firefighting, laundry use, watering sports grounds or gardens and irrigating various food crops. Recycling water reclaims water that has various uses and it satisfies most of the environmentally water demands. This recycled water meets the standards set by the Department of Health in Melbourne and it is approved to be safe for the non-drinking purposes.
Renewable energy is obtained though biogas. In the final treatment stage, methanogenic bacteria produce methane gas that is stored in large tanks. Methane gas runs seven generators that provide 40 % of electricity needs in the plant and it is used to run the heat pipes therefore, it saves on the electricity that would otherwise be imported from the grid. Moreover, it reduces the amount of methane gas produced to the environment, which is a major effect in reducing global warming through the reduction of greenhouse gases that deplete the ozone layer.
The Eastern Treatment plant has undergone an early upgrade to a tertiary treatment of sewage. The tertiary treatment process has led to many benefits such as improvement of the quality of recycled water and more benefits to the marine environemt. Furthermore, the plant has had its effect to the environment such as reduced odour, release of renewable energy from biogas, reduction in the levels of ammonia and treatment of sewage for better recycled products. The plant is an important factor in management of water in Melbourne.
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