Lithgow Sewage Treatment Plant

Plan

There are “two” treatment plants on this site. The “original” plant is a traditional trickling filtration treatment system, which was designed and constructed throughout NSW by Public Works from about the early 1930’s until the mid 1980’s, when it was constructed here. The new plant is a modern activated sludge treatment system, known as Intermittent Decanted Extended Aeration (IDEA). This was developed by NSW Public Works in the 1960’s and 1970’s and has been provided at about 170 locations in NSW. It is a well proven and economical treatment technology. The new plant does what the old plant can’t do, that is, remove nitrogen – as well as phosphorus – the two nutrients which, in combination, are responsible for algal blooms in receiving waterways, to a very high degree.

The plant has been designed to meet the needs of Lithgow for the next 30 years. It will serve the community well and protect the receiving environment. It is a major asset of which Council and the Lithgow community can be proud.

Sewage Treatment

Inlet

As the raw sewage enters the plant, it passes through the inlet works where gross solids and grit is removed. The screens catch large objects such as sticks and rags. Next the sewage flows through a grit chamber. Here it moves slowly, so that sand, gravel and other heavy material can settle. Separation of grit from other suspended material is aided by diffused air aeration.

IDEA (Intermittent Decanted Extended Aeration) biological reactors for the further treatment of a portion of the raw sewage, and of all the effluent discharged from the trickling filter plant, receive the flow from the trickling filters. These reactors include surface aeration and treated effluent decanting systems and achieve significant (ammonia and oxidized) nitrogen removal.

At the beginning of the treatment cycle, effluent has been decanted at the end of the previous cycle. Aeration begins and continues while influent wastewater increases the volume of mixed liquor for aeration. After a period aeration stops and is followed by a non-aeration sequence in which the mixed liquor is allowed to settle and anoxic processes can occur. Following the settlement/anoxic sequence, treated effluent is discharged.

Trickling Filters

Trickling filters reduce soluble and suspended organic load of the water. They have a solid support medium on which the biomass develops in a single pass irrigation process. Treatment is carried out by the biomass which is subsequently separated from the solid support and collected as sludge.

IDEA and Nutrient Removal

The IDEA tanks are sized to accommodate a flow 7 times the average dry weather flow without appreciable loss of effluent quality. An alum storage and dosing system for phosphorus removal is included as well as pH correction. The solid matter which has been removed from the sewage is concentrated and water is removed on a belt filter press.

There are “two” treatment plants on this site. The “original” plant is a traditional trickling filtration treatment system, which was designed and constructed throughout NSW by Public Works from about the early 1930’s until the mid 1980’s, when it was constructed here. The new plant is a modern activated sludge treatment system, known as Intermittent Decanted Extended Aeration (IDEA). This was developed by NSW Public Works in the 1960’s and 1970’s and has been provided at about 170 locations in NSW. It is a well proven and economical treatment technology. The new plant does what the old plant can’t do, that is, remove nitrogen – as well as phosphorus – the two nutrients which, in combination, are responsible for algal blooms in receiving waterways, to a very high degree.

Disinfection

Finally, chlorine is added as a disinfectant where ample contact time is allowed to kill bacteria before dechlorination and the next stage of treatment through the ultra-violet disinfection chamber. It is located at the end of the plant for further bacteria reduction and the removal of Crypto-sporidium and Giardia. This provides an additional barrier to assure disinfection before discharge to the environment or use as recycled water.

 Fact File

• 18 million litres of raw sewage daily maximum de­signed capacity
• 6 million litres of raw sewage received on average each day from Lithgow sewerage.
• 4 thousand litres of liquid trade waste received each day by tanker.
• 1 tonne of dry organic solids produced each day
• Lithgow STP is a relatively unique dual disinfection IDEA process.
• Achieves a level of treatment which satisfies best practice requirements for environmental protection

• Recycled water is used throughout the plant saving drinking water and is capable of supplying signifcant quantities via an off site distribution system.
• The process has a modern electrical control and monitoring system. This allows monitoring of the operation of every treatment unit and mechanical drive at the plant and to adjust operation remotely if required. The system also raises alarms should equipment malfunction