The Problem
What was the problem that you experienced?
In the last few years, filling the Birregurra Raw Water Basins (2 No. approx. ~50ML each) during times of extreme weather has resulted in poor quality raw water being introduced into the basin. The raw water within the basins has had relatively high turbidity and organics which require additional disinfection at the Water Treatment Plant (WTP). This has led to increased disinfection by-product levels in the treated water, which, whilst well under the Australian Drinking Water Guidelines, were still a cause for concern.
To improve the raw water quality and reduce disinfection by-products in the treated water, we dosed liquid Poly Aluminium Chloride (PAC23) directly into the basin. It is common in the water industry to dose chemicals into large water storages directly from a boat (e.g. algaecide dosing). Our method involved driving a boat around the basin while pouring chemical out the side from a 15L drum. On average, we used around 400L of chemical per dose (equating to 27 no. drums per dose).
How did the problem impact you or your work situation?
Pouring chemical from a 15L drum out the side of the boat introduces a number of risks including chemical handling/spills, manual handling and poor mixing of the chemical in the raw water basin.
In order to get the PAC23 into the 15L drums, the team had to decant the chemical out of an IBC into each container individually. Whilst works were conducted under a Safe Work Method Statement with controls in place, this activity still carried chemical handling risks with PAC23, which is known to cause irritation to the skin, eyes and respiratory tract. The need to work with a number of chemical containers in the boat during the dosing activity also increased the risk of a chemical spill inside the boat during the works.
Major hazards that needed to be controlled during the dosing activity were the manual handling risk associated with having to load a number of drums into the boat (often walking across rock beaching with exposure to slips/trips/falls risks), having to lift and move the containers on the boat, and also reach out of the boat holding a container weighing approximately 20kg. Storing multiple containers of chemical in the boat also introduced an ergonomics risk when lifting and moving the containers in the boat, with the need to carefully manage the risk of destabilising the boat and sustaining a soft tissue injury due to poor ergonomics. With the need to carefully manage the risks of handling multiple chemical containers, manual handling and ergonomics, as well as the slower pour rate of only having one stream of chemical entering the water – the duration of the dosing activity was extended out – often taking us around 3-4 hours to complete.
Another issue was the inconsistent distribution of the chemical because the dose was being added in one large stream. To minimise the impact of this, we tried mixing it by pouring it under the boat and letting the engine mix it, but realistically we were unsure how effective or consistent this was.
How long had the problem been occurring?
This problem has only been occurring for the last few years. The inlet channel to the basin normally only allows transfer of high quality raw water from our West Barwon Reservoir. A number of extreme rainfall events in the past two years has resulted in uncontrolled overland flows (with high turbidity and organics) entering the inlet channel and flowing into the raw water basins.
The Solution
How did you come up with the solution?
There is currently a water supply augmentation project underway to connect Birregurra to the nearby Colac water supply. The basins and water treatment plant are planned to be decommissioned in the next 1-2 years as part of this project, so our solution needed to be cost effective and easy to install.
We tried using a handheld garden sprayer, but the flow was far too low, and it misted the chemical, meaning that the spraying activity could only be undertaken in times of low winds – making dosing activities wind-dependant.
We then came up with the idea of making something that could pump the chemical out of the containers into the water. Through a bit more thought and discussion with the workgroup, we came up with a solution.
Who helped work on the solution?
The Regional Network Operations team (Ben King, Dalkeith Mccallum Hanley, Tom Bennett, Ben McCallum and Wayne Neale) worked together to come up with the idea and layout of the final solution.
Describe the solution.
We made a boom spraying attachment to fit on the boat that would evenly spread the PAC23 throughout the basin. To design this, we knew that we needed it to be safe to use on a boat.
We settled on using a 12V Milwaukee stick pump, as it ran at only 4.6 meters head, which made it safer for operators to be near (less risk of a pipe burst and spill of chemical into the boat/onto an operator), had an ideal flow rate (34L/min), and ran on a small Milwaukee 12V battery that would not pose a hazard if it were to get wet.
We then recycled an old chemical tank from a previous site to hold the PAC23, taking into consideration the impact of the load on the boat. This allowed us to eliminate a significant amount of manual handling which was required to decant chemical from the IBC into the 15L drums and into the boat. Instead, the chemical storage tank in the boat could be filled directly from the IBC, by putting the same pump we use for dosing into the IBC, and pumping the PAC into the boat mounted tank using a long hose to fill the tank to a safe level.
The pump was connected to a regulating valve, and a boom at the front of the boat made out of 25mm PVC with 2mm holes drilled at 10cm spacings. This solution cost less than $500 in total.
How has it helped you at work?
This has removed all manual handling of PAC23 which had to be decanted into 15L containers, lifted in, and then poured out of the boat. It also means that operators can be further away from the chemical reducing the risk of possible exposure. Use of the drilled holes created a laminar flow so there was no gurgling, dripping or aeration of the chemical, meaning there was less risk of chemical splashing back at operators.
The spray boom gives a much better dispersion in the water as the 30 dosing points spray evenly across the water, instead of a singular stream. The use of the spray boom also resulted in significant time savings with the dosing works only taking around an hour, whereas it could take 3-4 hours when manually pouring out of the 15L containers directly into the basin.
Suggest improvements, if time or financial limitations were not a factor.
If we were to do this again, we would likely look into finding a way to lower the boom into the water to completely eliminate the chemical having any air exposure, further lowering the risks to the operations team in the boat.
Any other comments you would like to make?
Although this was made only temporarily for PAC23, this boom sprayer could be used for any array of chemicals which are commonly dosed from boats (e.g. algaecide) and will likely stay around as a tool that can be used again if required for algae, PAC, or other boat dosing situations.
These Milwaukee stick pumps are also useful for so much more in our day to day jobs, and prove to be an easy solution for quickly pumping out pits when it is not being used for dosing (saving significant time setting up other much larger/heavier pumps).