2016/17 – Bloomsbury (Queensland) Turbidity
2016/17: Bloomsbury (Queensland) – Turbidity 83.2 NTU (max), 7.18 NTU (av.)
Chlorine-resistant pathogen reduction: Where filtration alone is used as the water treatment
process to address identified risks from Cryptosporidium and Giardia, it is essential
that filtration is optimised and consequently the target for the turbidity of water leaving
individual filters should be less than 0.2 NTU, and should not exceed 0.5 NTU at any time
Disinfection: A turbidity of less than 1 NTU is desirable at the time of disinfection with
chlorine unless a higher value can be validated in a specific context.
Aesthetic: Based on aesthetic considerations, the turbidity should not exceed 5 NTU at the
consumer’s tap.
2020/21 – Bloomsbury (Queensland) – Chlorine
2020/21: Bloomsbury (Queensland) – Free Chlorine 9.7mg/L (max), 0.71mg/L (min)
2020/21: Bloomsbury (Queensland) – Total Chlorine 10.3mg/L (max), 0.73mg/L (min)
November 9 2020: Bloomsbury WTP was overdosing chlorine for a period on November 9, 2020 and as a result Bloomsbury Treated Water samples recorded total chlorine levels above the ADWG health guideline value of 5 mg/L.The overdosing incident was caused by an analyser fault likely associated with a power outage on November 8, 2020. Water treatment operators addressed the overdosing incident by making appropriate dosing and pump setting adjustments and releasing overdosed water as quickly as possible from the tanks at the WTP. SMS alarms and upper limit interlocks were set up in SCADA to prevent future overdose events.
GENERAL DESCRIPTION
Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion. Chlorine and hypochlorites are toxic to microorganisms and are used extensively as disinfectants for drinking water supplies. Chlorine is also used to disinfect sewage and wastewater, swimming pool water, in-plant supplies, and industrial cooling water.
Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. Water authorities may need to exceed the odour threshold value of 0.6 mg/L in order to maintain an effective disinfectant residual.
In the food industry, chlorine and hypochlorites are used for general sanitation and for odour control. Large amounts of chlorine are used in the production of industrial and domestic disinfectants and bleaches, and it is used in the synthesis of a large range of chemical compounds.
Free chlorine reacts with ammonia and certain nitrogen compounds to form combined chlorine. With ammonia, chlorine forms chloramines (monochloramine, dichloramine and nitrogen trichloride or trichloramine) (APHA 2012). Chloramines are used for disinfection but are weaker oxidising agents than free chlorine.
Free chlorine and combined chlorine may be present simultaneously (APHA 2012). The term totalchlorine refers to the sum of free chlorine and combined chlorine present in a sample.
Chlorine (Free) ADWG Guideline: 5mg/L (Chlorine in chloraminated supplies 4.1mg/L). Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion.
Chlorine (Total) ADWG Guideline 5mg/L (chloraminated supplies 4.1mg/L): The term total chlorine refers to the sum of free chlorine and combined chlorine present in a sample
Bloomsbury – (Queensland) – Hardness
2020/21: Bloomsbury (Queensland) – Hardness 202.5mg/L (max), 113.38mg/L (min)
GUIDELINE
“To minimise undesirable build‑up of scale in hot water systems, total hardness (as calcium
carbonate) in drinking water should not exceed 200 mg/L.
Hard water requires more soap than soft water to obtain a lather. It can also cause scale to form on hot water pipes and fittings. Hardness is caused primarily by the presence of calcium and magnesium ions, although other cations such as strontium, iron, manganese and barium can also contribute.”
Australian Drinking Water Guidelines 2011
Bloomsbury (Qld) – Chlorate Jul 2 2020 – March 2022
Chlorate (a parameter with no water quality criteria) was detected in Bloomsbury treated and Bloomsbury reticulation water samples (collected as part of the routine drinking water verification monitoring program) at levels above the Qld Health preferred guideline value of 800 µg/L. Incident investigation determined the source of the chlorate to be the sodium hypochlorite solution used for iron and manganese oxidation and disinfection at the Bloomsbury WTP. Chlorate is a natural break-down product of sodium hypochlorite and
concentrations are higher in older batches of chemical especially if they are exposed to heat or contain metals. The high chlorate levels at Bloomsbury are expected to be further exacerbated by the current WTP design which includes recirculation of chlorine dosed filtrate. Council reduced chlorate levels by cleaning out the raw water storge tank and continuing to empty and replace aged sodium hypochlorite solution stored at the WTP. In the long term, there will not be any potential for chlorate generation for the Bloomsbury water supply scheme as the WTP will be converted to chlorine gas for disinfection. This conversion is scheduled to be completed in January 2022. Since June 4, 2021 Council have been transferring treated water to the Bloomsbury scheme from other Council water supply schemes. This was prompted due to
raw water quality issues (high turbidity, iron and manganese) which made running the Bloomsbury WTP very difficult. At the time of reporting the WTP remains offline and 100% of water for the scheme is being sourced from other Council water supply schemes. Council are in the process of investigating alternative raw water sources / possible long-term connections to the Midge Point water supply scheme.
16/3/22: Bloomsbury (Queensland) Chlorate
Routine monitoring of the reticulation network at the Bloomsbury School sample point returned chlorate (a parameter with no water quality criteria) at levels above the Qld Health preferred guideline value of 800 µg/L. Due to a failure of the raw water groundwater bore at Bloomsbury, potable water has been transferred from Mackay since August 2021, averaging between 300 and 400 KL /month. After the exceedance occurred, additional water quality sampling of two treated water storage tanks on on 31 March 2022 identified there was ongoing impact from chlorate within the treatment tanks. The water in these tanks was removed and replaced with water transported from the Mackay scheme. Follow up sampling confirmed that this immediately reduced the overall chlorate levels in the treated water storage tanks. In
response to this incident, sodium hypochlorite at Bloomsbury is changed over monthly, ensuring the old sodium hypochlorite in storage is removed and the storage tank cleaned, before a delivery of fresh sodium hypochlorite is received.
Chlorite: ADWG Health 0.3mg/L.
Chlorite and chlorate are disinfection by-products of chlorine dioxide disinfection process.
“… industry are having serious problems meeting chlorite/chlorate limits that were proposed in the new Australian Drinking Water Guidelines, especially for disinfection in long distance pipelines that are dosed with sodium hyptochlorite” pers comm 18/5/11.
“Chlorite occurs in drinking water when chlorine dioxide is used for purification purposes. The
International Agency for Research on Cancer (IARC) has concluded that chlorite is not classifiable as carcinogenic to humans and is listed in the Group 3 category. Changes in red blood vessels due to oxidative stress are a major concern with excessive levels of Chlorite in drinking water. According to the US EPA, potential health problems for people drinking Chorite above safe drinking water guideline include: Anemia in infants and young children and nervous system effects.” https://water.epa.gov/drink/contaminants/index.cfm
“Chlorine dioxide (chlorite) is rarely used as a disinfectant in Australian reticulated supplies.
When used, the chlorite residual is generally maintained between 0.2mg/L and 0.4mg/L. It is
particularly effective inthe control of manganese-reducing bacteria. Few data are available on
chlorate levels in Australian water supplies….Chlorine dioxide, chlorite, and chlorate are all
absorbed rapidly by the gastrointestinal tract into blood plasma and distributed to the major
organs. All compounds appear to be rapidly metabolised. Chlorine dioxide has been shown to
impair neurobehavioural and neurological development in rats exposed before birth. Experimental studies with rats and monkeys exposed to chlorine dioxide in drinking water have shown some evidence of thyroid toxicity; however, because of the studies’ limitations, it is difficult to draw firm conclusions (WHO 2005) The primary concern with chlorite and chlorate is oxidative stress resulting in changes in red blood cells. This end point is seen in laboratory animals and, by analogy with chlorate, in humans exposed to high doses in poisoning incidents (WHO 2005).” Australian Drinking Water Guidelines – National Health and Medical Research Centre
“…Subchronic studies in animals (cats, mice, rats and monkeys) indicate that chlorite and chlorate cause haematological changes (osmotic fragility, oxidative stress, increase in mean corpuscular volume), stomach lesions and increased spleen and adrenal weights… Neurobehavioural effects (lowered auditory startle amplitude, decreased brain weight and decreased exploratory activity) are the most sensitive endpoints following oral exposure to chlorite…” https://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/chlorite-chlorate/indexeng.
php#sec10_1Guidelines for Canadian Drinking Water Quality.