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The Wizard of Ox....idation

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The Wizard of Ox....idation

  1. 1. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 The Wizard of Ox The call came through early September 2014 during a stop off transit flight, “Fitzy are you prepared for a challenge, there’s a community in the Gulf that needs our help”. I detected an element of excitement in my colleague’s voice but would never had believed the challenges and learnings that were to develop from this one brief call. Georgetown is a small community in Far North Queensland boasting a population of approximately 250 residents. The town’s main industries are cattle, tourism and traditionally gold. The town is situated between Cairns and Normanton and is home to the Etheridge Shire Council. During 2014, Georgetown had been experiencing un-precented Iron and Manganese concentrations in their potable water supply persisting longer than any -previous event. Some believe this may have been a consequence of a string of failed consecutive wet seasons leading up to this point. The town’s water supply is via three shallow wells in the riverbed of the Etheridge River. The river is characterised by a predominantly dry river bed, low turbidity’s and higher metal concentration in the dry seasons, then a flooded bank-to- bank river with high turbidity’s, low metal concentrations in the wet season. The water is pumped from these wells at a flow rate of between 4.0 l/s- 14.0 l/s pending demand and was traditional just dosed with Sodium Hypochlorite for disinfection purposes. No other treatment was in place. Parameter Range Turbidity 1.0 – >25ntu Mn (total) 0.01 - 1.5mg/L Fe (total) <0.05 - ≥ 2.78mg/L pH 6.5 - 7.1 Temp 25 - 29°C Parameters of interest; Georgetown raw water With recent exceedances of the Australian Drinking Water Guidelines (ADWG) for both Aesthetic and Health values of Iron and Manganese, residents were calling on council to step in and take corrective action as this metallic tasting water and staining was not getting any better. The water had also appeared on QLD Health’s radar and had been tabled at State Parliament by this point. The town had not received any funding, nor budgeted for the development of a treatment plant prior to these unprecedented and sustained metal levels.
  2. 2. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 Manganese residual in the town’s internal pipework. A Sample of town water during a dirty water event. With a limited budget, high variability in water quality and the urgency that this matter presented it was time for us at Aeramix to work collaboratively with the Etheridge Shire Council to develop a customised solution. This solution was to originally be in the form of a temporary emergency treatment plant. Meanwhile in a neighbouring town; Richmond around 500km to the South West of Georgetown, Aeramix was in the process of working with this community to design and construct their first water treatment plant. Richmond had purchased second hand direct filtration treatment plant infrastructure in skid mounted configuration from Melbourne Water. Etheridge Shire and Richmond Shire were able to come to an agreement whereby Richmond supplied surplus treatment plant infrastructure to Etheridge. With that, the decision was made, Georgetown’s water woes were going to have to be addressed via a direct filtration process. It was then off to the lab for an intensive two week pilot scale testing regime to determine the exact nature and properties of the raw water source, how it reacted to various chemical and mechanical treatments and what results we were likely to be achieved under a direct filtration process. We extensively trailed various coagulants in a wide range of doses. Those included but were not limited to: Aluminium Chlorohydrate (ACH), Tanfloc, Poly Aluminium Chloride (PACL) and Ferric Chloride, before eventually settling on conventional Aluminium Sulphate. Although ACH offered quite admirable results, the
  3. 3. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 decision was made to utilise Aluminium Sulphate as it offered a robust floc that worked well within our raw water pH range, was available in a granular form (ideal for a remote town such as Georgetown where transport is charged on weight) and was already being utilised by the Shire in a neighbouring town’s treatment plant. Granular Activated Carbon was then trialled on coagulated raw water with admiral results. Next cab off the rank was oxidation to determine what could be done about the troublesome dissolved metals. Mechanical oxidation through aeration was our first attack. This was able to oxidise soluble Iron down to levels achieving compliance with standards in best case scenarios, however had little impact on Manganese. From these finding it was agreed that some form of chemical oxidation was needed as the results overall were not satisfactory, nor readily repeatable. Lab Scale Pilot investigations outback style. Just like coagulant selection a range of different oxidants were featured in the pilot study, all within a wide range of dosages. Sodium Hypochlorite (NaCLO) achieved acceptable results on the dissolved Iron constituent but didn’t come close to reining Manganese in to any level below the ADWG Aesthetic value of 0.1Mg/L, let alone the health value of 0.5mg/l. In previous jobs we have seen Manganese stain down to levels of 0.05mg/L so knew that we would have to achieve filtrate waters below this level to ensure client satisfaction. NaCl0 was soon ruled out as we reached for a chemical oxidant with a little more punch. Potassium Permanganate (KMnO4) did offer a higher oxidation rate yet was still unable achieve results below 0.1mg/L and with raw water manganese at this point fluctuating between 0.7-1.5 mg/L, it was unable to repeatedly achieve below 0.3mg/L treated water. With this it was back to the literature in search of a new direction.
  4. 4. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 One scientific journal of interest had focused on the effects organics within the water preventing some forms of Manganese from oxidating beyond a certain level. We utilised Activated Carbon as an organics pre-screen so see whether we were able remove some potentially interfering organics and thus increase the vulnerability of dissolved Manganese. This again proved fruitless and to make matters worse, by this point we had well and truly exceeded our expected chemical reagent usage and were running critically low on reagents to test for Free Chlorine, Iron and low range Manganese. With time running out and our laboratory reagent supplier 2,975 km’s away (thanks Google) it was time to get creative. Hours later we stood clutching our hats as a helicopter struggled against the breeze coming into land in Georgetown. In classic James Bond style we had been left no choice but to fly in reagents from one of our other job sites in Richmond, hand delivered by a pilot in a chopper without doors, usually reserved for mustering cattle on remote outback stations. Armed with more reagents we soldiered on to explore another trick we had up our sleeves; catalytic media. This media was specifically designed for the removal of Iron and Manganese. It was claimed to have a longer life span (doesn’t actually oxidise it’s self in the process) than conventional ‘greensand’ media whilst also providing elevated oxidation rates comparatively. After three days of intensive manipulation and monitoring, day and night we had finally activated our catalytic media and hit the Jackpot. Using NaCLO as the media’s required oxidant, we were able to strip both Manganese and Iron concentrations down to near undetectable levels.
  5. 5. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 Pilot Plant oxidation results Proceeding with the knowledge generated from the lab scale pilot plant findings we knew with confidence what would and wouldn’t work for this individual water source. Additionally we reviewed raw water data for the last few years so that we were aware of any patterns or worse case scenario’s likely to reappear in the future. Our experienced process engineer; Mark Samblebe and hydraulic engineer; Robert Hillgrove worked closely utilising findings of the pilot plant and the data review to decide upon the most effective treatment process design. The two settled on a Process and Instrumentation Diagram (P&ID) which featured two trains of filters (3 per train) with one floc vessel servicing both trains. The first train comprises of dual media, boasting granular activated carbon for the removal of turbidity, tastes, odours and organics that may compete for chlorine demand post Alum dosing. Water is then dosed with NaCLO before entering the second train of filter vessels, this time hosting the fine grade catalytic media specifically for dissolved metal removal. Treated water then leaves the second train and is dosed for sterilisation before making it’s way up to the town’s clear water tank. What started as a temporary emergency treatment plant grew into a permanent system designed to successfully treat both distinctively different seasons; the wet and dry whilst still utilising the same infrastructure in a strategic manner. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Manganese(mg/L) Oxidation/filtration method Treated water Mn (mg/L) under differnt methods of oxidation and filtration
  6. 6. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 Midway through the build phase. After a finalised P&ID was released we comprehensively tested the surplus second hand treatment infrastructure to ensure it would perform its required task and stand the test of time before even considering it for installation. The build phase was conducted in January 2015. It was a challenge constructing an exposed treatment plant in Northern Queensland during the summer contending with the constant elevated ambient temperatures as well as the storms which would come and go delivering up to 150mm of rain in a single shower.
  7. 7. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077 Another light shower on the way in, 41°C The Commissioning phase was conducted throughout February and surprise, surprise also had it’s set of challenges. Although the catalytic media we selected provided very good results, the activation phase however did require some patience and tricks to get it performing appropriately, but that’s a whole other story I’ll save for a future article. Overall we were very proud of the performance of the plant achieving a filtrate with turbidity’s as low as <0.1ntu, Iron <0.02mg/l and Manganese 0.002mg/l, delivering reliable and compliant water to Georgetown. From our experience in this project we have a few pertinent messages for others who may go down a similar path in the future:  The importance of automation- you don’t fully appreciate the merits (time, reliability, labour saving, monitoring capabilities) of automation until you work without it. If you can not fit it into your budget, design your system in a manner that enables retrofitting down the track if circumstances change.  Place a high value on Pilot Scale Investigations- they reveal secrets at the right time rather than when it is too late.  Harness the collective knowledge and resources of local personal- they are an invaluable resource
  8. 8. www.aeramix.com.au Head Office: 1 Stoney Way, Derrimut Victoria 3030 Regional Offices: Victoria Tasmania Suite C8, 50 Northways Rd, PO Box 440 Churchill 3842 Devonport 7310 1300 667 077  Involve local operators in all phases of the investigation and build after all they will be running the plant- it’s in their best interest to know it back the front and be across all aspects of troubleshooting.  Be prepared to innovate in remote areas- Water Treatment Equipment simply isn’t easily accessible in these areas. Our backwash tank was unable to be delivered on the roads to this location at the last minute so settling lagoons were designed and installed on the fly to compromise.  Know your enemy- research and liaise with those who have dealt with issues you may be facing before.  Design your systems to be able to cope with worse case scenarios

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