What is eWQMS?

Emanti Management's Water Quality Management System (eWQMS) can be used to guide the tracking, reviewing and improving of water quality.

Aluminium

Pure aluminium is a silvery white, soft, light metal, resistant to corrosion. Although aluminium occurs naturally, aluminium is typically used as a coagulant in water treatment processes (alum - aluminium sulphate). This can result in increased concentrations of aluminium in the final water if optimal conditions for coagulation are not maintained.

Effect and possible implications of failure

  • Health

Prolonged exposure to aluminium has been implicated in chronic neurological disorders such as dialysis dementia and Alzheimer's disease.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <300 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 300 - 500 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • Source water has high aluminium (e.g. naturally occurring)
  • No process at the treatment plant to remove aluminium (e.g. no coagulation/flocculation, no oxidation, no reverse osmosis, no ion exchange)
  • No chemicals for aluminium removal (e.g. coagulants/flocculants not available)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring of residual aluminium and remedial intervention, no jar tests to optimise chemical dosages and ensure minimum aluminium concentrations, problem with process control/SCADA system)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged leading to ineffective settling and aluminium removal)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Antimony

Antimony is a silvery white metal of medium hardness that breaks easily. Antimony in high concentrations is rarely found in raw water sources.

Effect and possible implications of failure

  • Health

High concentrations of antimony can irritate eyes, skin and lungs, could lead to problems with the heart, and could result in diarrhoea, vomiting and stomach ulcers.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <10 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 10 - 50 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • No process at the treatment plant to remove antimony (e.g. no advanced coagulation/flocculation, no membrane process)
  • No chemicals for antimony removal (e.g. coagulants/flocculants not available)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged leading to ineffective settling and removal)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Arsenic

Arsenic is a greyish poisonous semi-metal.

Effect and possible implications of failure

  • Health

Arsenic poisoning is normally chronic, the predominant symptom being the presence of characteristic skin lesions. At high concentrations, arsenic can cause acute poisoning, with sensory loss in the peripheral nerves and gastrointestinal symptoms often occurring. Arsenic may be absorbed through the skin and cause health effects with bathing.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <10 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 10 - 50 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • Source water has high arsenic (e.g. pollution from mining activities, pollution from arsenic containing pesticides - in cattle dips)
  • No process at the treatment plant to remove arsenic (e.g. no coagulation/flocculation with ferric salts, no oxidation, no ion exchange)
  • No chemicals for arsenic removal (e.g. coagulants/flocculants not available)
  • Poor process control (e.g. ineffective chemical dosages, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged)
  • Poor design (e.g. inappropriate treatment plant, poor mixing, insufficient settling time)
  • Sabotage/vandalism

Cadmium

Cadmium is a soft metal, often found in galvanizing and used to protect metals from corrosion.

Effect and possible implications of failure

  • Health

Acute health effects from cadmium present as food poisoning-like symptoms (nausea, vomiting and diarrhoea), which is clinically indistinguishable from microbiological food poisoning. Chronic health effects include kidney damage and pain in the bone.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <5 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 5 - 10 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 6 months

Possible reason/s for failure

  • No cadmium removal process at the treatment plant (e.g. no conventional treatment)
  • No chemicals for cadmium removal (e.g. ferric salt flocculent not available, lime not available)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. pollution by galvanizing operations, infiltration or seepage)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Total Chromium

Chromium is a metal found in natural deposits as ores containing other elements. Chromium is used in the manufacture of metal alloys such as stainless steel and in the manufacture of paints, cement, paper, rubber, etc.

Effect and possible implications of failure

  • Health

Chromium has the potential to damage the nasal septum and cause skin ulcers, lung cancer and gastro-intestinal cancer from long term exposure. High concentrations may also impart an undesirable taste. The reduced forms of chromium (chromium (II) and chromium (III)) have much less toxicity indices than chromium (VI), and do not constitute as serious a health threat.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <100 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 100 - 500 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 3 months

Possible reason/s for failure

  • Source water has high chromium (e.g. no source protection near industries using chromium such as metal pickling and plating, leather, paints, dyes, explosives, ceramics and paper)
  • No process at the treatment plant to remove chromium (e.g. no reduction to trivalent form (with ferrous sulphate) followed by precipitation and flocculation (lime, alum or ferric salts), no reverse osmosis, no ion exchange)
  • No chemicals for chromium removal (e.g. coagulants/flocculants not available)
  • Membranes/resins require replacement (e.g. membrane life exhausted, breakthrough achieved)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industry)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged leading to ineffective settling, ineffective cleaning of membranes)
  • Poor design (e.g. poor mixing, insufficient settling time, inappropriate treatment system)
  • Sabotage/vandalism

Cobalt

Cobalt is a metal that occurs naturally in rocks, soil, etc. It is often used in the manufacture of alloys, magnets, catalysts for petroleum and chemical industries, pigments, etc.

Effect and possible implications of failure

  • Health

Exposure to high concentrations of cobalt through inhalation, ingestion, or contact with the skin can cause respiratory irritation, coughing, dyspnoea, fibrosis, asthma, pneumonia, and wheezing, cardiovascular effects, liver and kidney congestion, ocular effects, skin rashes, allergies and weight loss.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <500 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 500 - 1000 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • No cobalt removal process at the treatment plant (e.g. no precipitation with settling and filtration, no reverse osmosis)
  • No chemicals for cobalt removal (e.g. lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Copper

Copper is an orange coloured metal which is a good conductor of heat and electricity. A significant source of copper in domestic water arises from the dissolution of copper from plumbing systems in areas with soft or low pH waters, resulting in a blue-green appearance of the water. Stabilisation/pH adjustment to appropriate levels should alleviate such concerns.

Effect and possible implications of failure

  • Health

At relatively low concentrations copper imparts a strongly astringent taste to water and can give rise to staining of laundry, plumbing fittings and hair (blue-green discolouration). Ingestion of high concentrations of copper results in gastrointestinal disturbances and possible liver, kidney and red blood cell damage. However, owing to the extremely disagreeable taste of water with high copper concentrations, it is unlikely that such water would be consumed.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <1000 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 1000 - 2000 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • No stabilisation/pH adjustment process at water treatment plant (e.g. no lime dosing equipment, no limestone contactors)
  • No chemicals for stabilisation/pH adjustment (e.g. lime not available)
  • Incorrect/inappropriate chemicals for stabilisation (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, inconsistent dosing, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from other water sources)
  • Lack of maintenance (e.g. blocked lime dosers/limestone contactors)
  • Poor design (e.g. inappropriate treatment system)
  • Sabotage/vandalism

Cyanide

Cyanide is occasionally found in drinking-water, primarily as a result of industrial contamination.

Effect and possible implications of failure

  • Health

The acute toxicity of cyanides is high. In the short-term, cyanide can potentially cause rapid breathing, tremors and other neurological effects. In the long-term, cyanide can potentially cause weight loss, thyroid effects and nerve damage.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <50 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 50 - 70 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 week

Possible reason/s for failure

  • Source water has high cyanide (e.g. no source protection near problematic industries)
  • No process at the treatment plant to remove cyanide (e.g. no chlorination at high doses)
  • No chemicals for cyanide removal (e.g. chlorine not available)
  • Poor process control (e.g. chlorine dose too low, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industry into distribution network)
  • Lack of maintenance (e.g. chlorination system not maintained)
  • Poor design (e.g. inappropriate treatment system)
  • Sabotage/vandalism

Iron

In water, iron can be present as dissolved ferric iron, Fe(III) and ferrous iron, Fe(II) or as suspended iron hydroxides. Iron usually appears brown or black in colour due to oxidation on the surface of the metal. High concentrations of iron can be present in groundwaters (especially soft, acidic waters of the Cape). In addition, in areas where iron ductile pipes are used without adequate stabilisation, iron corrosion by-products may result.

Effect and possible implications of failure

  • Aesthetic
  • Operational

At the concentrations normally encountered in water, iron is predominantly an aesthetic concern as iron precipitates as insoluble ferric hydroxide which settles as a rust-coloured silt and is visible through staining of laundry, enamelled surfaces such as baths, hand basins, etc and walls. Health effects due to intake of excessive amounts of iron include acute poisoning in infants (massive concentrations) and chronic iron poisoning (haemochromatosis).

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <200 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 200 - 2000 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 7 years

Possible reason/s for failure

  • No iron removal process at water treatment plant (e.g. no aeration, no oxidation)
  • No stabilisation/pH adjustment process at water treatment plant (e.g. no lime dosing equipment, no limestone contactors)
  • No chemicals (e.g. oxidants such as chlorine, ozone and potassium permanganate not available, lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, inconsistent dosing, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from other water sources)
  • Lack of maintenance (e.g. blocked oxidant dosers/lime dosers/limestone contactors)
  • Poor design (e.g. inappropriate treatment system, poor mixing, insufficient settling time)
  • Sabotage/vandalism

Lead

Lead is a bluish-white, soft metal, which is highly malleable and ductile. It is also highly resistant to corrosion.

Effect and possible implications of failure

  • Health

At relatively low concentrations lead can cause neurological impairment in foetuses and young children. In adults, exposure to toxic concentrations of lead take the form of anaemia and lead colic, that is, acute episodes of abdominal pain.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <20 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 20 - 50 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 3 months

Possible reason/s for failure

  • Source water has high lead (e.g. no source protection near industries with battery, paint, alkyl lead manufacture)
  • No conventional treatment process at the treatment plant (e.g. no coagulation/flocculation with settling and filtration)
  • No chemicals for lead removal (e.g. alum, ferric salts and/or lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries, old lead pipes - should not be in use)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Manganese

Manganese is a metal common in soils and often associated with the dark tea-like colour of some water sources.

Effect and possible implications of failure

  • Aesthetic

Although manganese is essential for human and animals it is neurotoxic when consumed in excess amounts. Manganese is also associated with staining of laundry and with metallic tastes in waters. Manganese is also harmful to patients with kidney disease.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <100 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 100 - 1000 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 7 years

Possible reason/s for failure

  • No manganese removal process at water treatment plant (e.g. no oxidation, no green sand filter)
  • No stabilisation/pH adjustment process at water treatment plant (e.g. no lime dosing equipment, no limestone contactors)
  • No chemicals (e.g. oxidants such as potassium permanganate not available, lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, inconsistent dosing, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from other water sources)
  • Lack of maintenance (e.g. blocked oxidant dosers/lime dosers/limestone contactors)
  • Poor design (e.g. inappropriate treatment system, poor mixing, insufficient settling time, poorly sized filters)
  • Sabotage/vandalism

Mercury

Mercury is a rare heavy metal and concentrations thereof in the environment are normally very low. Higher concentrations of mercury may occur in water bodies subject to industrial pollution.

Effect and possible implications of failure

  • Health

Mercury serves no known beneficial physiological function in humans, and is a chronic neurotoxin. Poisoning takes the form of neurological and renal disturbances.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <1 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 1 - 5 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 3 months

Possible reason/s for failure

  • Source water has high mercury (e.g. no source protection near chloralkali industries, paint and fungicide industries, paper and pulp manufacture, discharge of medical wastes (dentistry, thermometers) and disposal of electrical equipment)
  • No mercury removal process at the treatment plant (e.g. no precipitation with settling and filtration, no activated carbon adsorption, no ion exchange)
  • No chemicals for mercury removal (e.g. alum, ferric salts, activated carbon not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no monitoring and remedial intervention, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged, ion exchange bed exhausted)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Nickel

Nickel is a naturally occurring silvery metal used in the manufacture of stainless steel and nickel alloys.

Effect and possible implications of failure

  • Health

Although evidence exists that inhaled nickel compounds and metallic nickel are carcinogenic, there is a lack of evidence of a carcinogenic risk from oral exposure to nickel.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <150 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 150 - 350 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • Source water has high nickel (e.g. no source protection near industries)
  • No conventional treatment process at the treatment plant (e.g. no coagulation/flocculation with settling and filtration)
  • No chemicals for nickel removal (e.g. alum, ferric salts and/or lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries, release of nickel from taps and fittings)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Selenium

Selenium is a semi-metallic element that is essential to human health at low concentrations.

Effect and possible implications of failure

  • Health

High intakes of selenium can cause liver damage and impairment of growth of nails and hair. Animals usually get selenium poisoning from their feed intake rather than from water.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <20 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 20 - 50 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • Source water has high selenium (e.g. no source protection near industries with glass, ceramic, ink, paint, plastics, rubber, alloy, etc manufacture)
  • No selenium removal process at the treatment plant (e.g. no coagulation and precipitation with lime or ferric chloride at pH > 8.5, no adsorption onto activated alumina at low pH levels)
  • No chemicals for selenium removal (e.g. ferric chloride and/or lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged, activated alumina bed exhausted)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

Vanadium

Vanadium is a white, soft, ductile metal, resistant to corrosion.

Effect and possible implications of failure

  • Health

Vanadium affects the metabolism of the amino acid cystine, resulting in a reduction of the concentration of coenzyme A. Symptoms of vanadium toxicity include conjunctivitis, rhinitis, a sore throat and a persistent cough. Exposure to high concentrations of vanadium can cause severe chronic bronchitis.

SANS 241 Standards

  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 3, Class I (recommended operational limit): <200 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 4, Class II (max. allowable for limit duration): 200 - 500 ug/L
  • SANS 241 Table 2 (Physical, organoleptic and chemical requirements) Column 5, Class II water consumption period, max: 1 year

Possible reason/s for failure

  • Source water has high vanadium (e.g. no source protection near industries with glassware, ceramic, textile, dye manufacture or chemical industries)
  • No vanadium removal process at the treatment plant (e.g. no coagulation and precipitation with lime or ferric chloride at pH 8.5 - 11.5, no ion exchange)
  • No chemicals for vanadium removal (e.g. ferric chloride and/or lime not available)
  • Incorrect/inappropriate chemicals (e.g. chemicals used not suitable for water type)
  • Poor process control (e.g. ineffective chemical dosages, no pH adjustment, no monitoring and remedial intervention, no jar tests to optimise chemical dosages, problem with process control/SCADA system)
  • Contamination (e.g. infiltration or seepage from industries)
  • Lack of maintenance (e.g. flocculation channels/sedimentation tanks not cleaned/de-sludged, ion exchange bed exhausted)
  • Poor design (e.g. poor mixing, insufficient settling time)
  • Sabotage/vandalism

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