The problem
What was the problem that you experienced?
Morwell Waste Water Treatment Plant is an activated sludge plant with two treatment streams consisting of two activated sludge reactors connected to two secondary clarifiers running in parallel.
One of the main operational challenges is the routine cleaning of solids build up on the ‘V’ notch weirs and in the outlet channel of the clarifiers. This process is particularly time consuming as well as using lots of potable water and/or manual handling. During low seasonal flow, the weir overflow rate can be as little as <2L/s over a clarifier circumference of about 51 metres. This low flow allowed any suspended solids to build up in the grooves of the concrete and provided an environment for algae to grow easily. If the regular site operator is on leave, the cleaning process might not be completed as regularly due to the relief operator managing more than one site.
Historically, brushes were mounted to the scraper bridge to clean the top and side walls, with a brush mounted sled being dragged in the outlet channel. This method was never truly effective due to the imperfections in the concrete, and at times also
caused their own issues. If there was a surge in flow during a wet weather event, the sled would sometimes get stuck in the outlet of the clarifier, ‘fault out’ the scraper causing it to stop working and require a call out.
How did the problem impact you or your work situation?
The solids build-up on the weirs and outlet channel, as well as looking unpleasant, would eventually slough off in large clumps and block the clarifier outlet filter basket. These large clumps would also have the opportunity to be carried through to the UV system and reduce the effectiveness of the disinfection process.
Depending on the amount of build-up, the cleaning required could range from a hose down with potable water to, entering the outlet channel and manually scrubbing it out. A pressure wash is conducted several times a year to increase the time in-between cleans and reduce the need for a manual clean. Even the hose down takes a couple of hours for the operator to complete, cleaning both clarifiers, cleaning brushes and filter baskets, which requires bypassing treated effluent to the storage lagoons for a couple of hours.
Manual handling strains to some operators are a constant occurrence and the time required to complete the cleaning process takes the operator away from valuable plant operations.
How long had the problem been occurring?
The brushes have been modified many times over the years with varying degrees of success, and the cleaning process for the clarifiers was a standard procedure conducted at a number of sites across the business. If an operator not familiar with the site attempted the cleaning process, it would more often than not create issues downstream in the UV disinfection tank
The solution
How did you come up with the solution?
Initially, efforts concentrated on improving the existing brush system to make it more effective and reliable. Although the improved brushes and adjustments cleaned the walls better, this just increased the brush wear and cleaning requirements for the brushes, and therefore didn’t really make much of an improvement.
The next concept was to fabricate a spray system, which would be mounted to the scraper arm and clean the walls as it rotated around the clarifier. A pump was installed to draw the supernatant from the surface of the clarifier which would otherwise just be going over the weir anyway. This provided high-pressure cleaning and eliminated the need to use potable water. Through trial and error and in consulting with the workgroup, we came up with the current design.
Who helped work on the solution?
The idea along with its potential benefits was presented to my team leaders, and with some consultation was allocated a budget of $5000 to complete the project. I sought assistance from multiple electricians to solve the issue that arose with the existing electrical power supply to the clarifier and the limitations on which pump I could
use. Working with my fitter Jake, we put together our ideas and created a prototype. Multiple improvements have been made to optimise the spray system through trials and consulting with other operators within our team.
Describe the solution.
The solution was a spray system that is efficient and requires little routine maintenance. The pump is mounted under the walkway of the clarifier scraper
bridge. This allows for all the pipework and cables to be run out of the way whilst still allowing access to the spray system while the scraper bridge is still running. The hose from the pump to the spray manifold has a camlock fitting and all sections of the
manifold are screw fit allowing for easy removal for cleaning or maintenance. An inline filter prevents any solids picked up by the pump from blocking the spray nozzles and can easily be accessed for cleaning.
The spray system has been set up on an individual circuit breaker with built in timer, this allows for the system to be turned off separate to the scraper, and also allows for the operator to select on and off times to optimise and reduce power usage when not
required. All items are off the shelf and can easily be replaced for same day repair.
How has it helped you at work?
With the spray system up and running, cleaning by the operator is almost no longer
required. Routine visual inspections are carried out daily, and the filter is checked/
cleaned twice a week. This has reduced the time spent cleaning per week from 3-5
hour down to just 20 minutes. With more time spared for other plant related tasks
and less manual strain on the operator, the reduction in operator hours for cleaning
alone has covered the full cost of the project in less than 1 year.
No longer needing to bypass treated effluent, prevents around 300kL a week being sent to the storage lagoons which would take around a day to return back to be reprocessed. With the reduced flow being bypassed to the storage lagoons, the yearly lagoon pump energy consumption and run hours have dropped by 39%. Chemical usage has reduced by a combined average of around 100L per week over the year and potable water use for carrier water and cleaning has also reduced by around 150KL a year, saving our precious resource.
The UV system also has seen a reduction in cleaning requirements. A higher UVT means a better disinfection rate, reducing the risk to effluent quality and the environment. The time required to drain and clean the UV tank has reduced by 50%, large clumps no longer block the drain lines and build up on the UV sleeves has reduced requiring less water to clean. As less abrasive techniques are required for cleaning the UV sleeves, the risk to damaging the sleeves, or the lamps inside is also reduced. Morwell’s UV system requires custom built lamps and sleeves which take time to make, so a crack in a sleeve could cost $1200 just in parts to repair.
It’s a great piece of mind knowing that a small change has made a large impact on the operation of the plant. The specialised final effluent instruments are easier to clean,
and are found to be more accurate with small samples line blockages reduced.
From an environmental perspective, this minimises risk to Morwell Wetlands and Morwell River which the plant discharges into.
Suggest improvements, if time or financial limitations were not a factor.
Still continuing to modifying the spray manifold to allow for a better coverage and ease of cleaning. With the filter now installed it might be worth trying finer nozzles to improve the aesthetic appearance of the clarifier. Having a built in automated cleaning system might make it more viable for larger plants.
Any other comments?
This small, yet huge change makes the waste water technician’s life much easier and enables them to spend more time on system performance optimisation and other
operational activities. The reduced manual effort required for clarifier cleaning is a huge OH&S benefit and a big time saver.