Treatment PRINCIPLES

WATER TREATMENT PLANT combination of coagulation, remain are finer suspended PRINCIPLES , sedimentation, solids like clay particles. Wide Bay Water maintains and and disinfection. operates four plants The particles that remain after – Howard, Burgowan, Teddington COAGULATION the initial screening are extremely and Tiaro water treatment plants. Coagulation is the process small and take time to settle. All water treatment plants must of using chemicals to clump To assist settling, a coagulant hold a Development Approval very fine particles into larger is added to the water. The (Environmental Licence) that particles. This clumping makes chemical coagulant causes these contains specific conditions that it easier to separate the solids particles to be attracted to each the treatment plant must meet from the water by settling, other to form larger particles in protecting the environment. skimming, draining and/or of ‘floc’. These larger particles Legislation introduced by the filtering. Generally there are settle more quickly. Chemicals Queensland Government has made two key steps in coagulation: commonly used in coagulation it mandatory for water suppliers to initial screening and at our plants are Liquid Alum have risk-based quality management adding coagulant. or Aluminium Chlorohydrate. plans in place to protect the public from drinking unsafe water. WBW INITIAL1 SCREENING Commonly, the coagulation tank is one of the first water suppliers in WaterRaw2 (untreated) Treatment water Plantis Principlesis agitated as the coagulant is Queensland that has implemented withdrawn from a surface added. This encourages the the WideHACCP Bay (Hazard Water maintains Analysis and operates fourwater Water supply Treatment (such as Plants Lake Howard, Burgowan,water Teddington and coagulant and Tiaro to Water mix CriticalTreatment Control Plants. Point) All system Water Treatment for PlantsLenthall, must Maryhold a River Development or Tinana Approval (Environmentalthoroughly. Licence) This technique that contains specific all ourconditions water treatmentthat the Treatment plants. Plant mustCreek). meet in Theprotecting water the is pumped environment. Recent legislationis called ‘Flash changes Mixing’. introduced by the Queensland Government has made it mandatoryto a central for water treatment suppliers plant to have as a risk based quality management plans in place to Theprotect most widely the public applied from drinkingwater unsafe water.described Wide Bayabove. Water It is onescreened of the first water suppliers in Queensland that has treatmentimplemented process the – HACCP known system as for all ourto Water remove Treatment coarse Plants.solids like conventional treatment – is a weeds and other debris. What The most widely applied water treatment process – known as conventional treatment – is a combination of coagulation, flocculation, sedimentation, filtration and disinfection.

WATER SOURCE Coagulant added removal Chlorine added

Distribution

Flash mixer Flocculation Sedimentation Filtration Disinfection Clear water storage ConventionalCOAGULATION treatment

Coagulation is the process of using chemicals to clump very fine particles into larger particles. This clumping makes it easier to separate the solids from the water by settling, skimming, draining and/or filtering. Generally there are two key steps in coagulation: Initial screening and adding coagulant.

Initial screening

Raw (untreated) water is withdrawn from either a surface water supply (such as Lenthall Dam, Mary River and Tinana Creek). The water is pumped to a central treatment plant as described above. It is screened to remove coarse solids like weeds and other debris. What remain is finer suspended solids like clay particles.

Coagulation

The particles that remain after the initial screening are extremely small and take time to settle. To assist settling, a coagulant is added to the water. The chemical coagulant causes these particles to be attracted to each other to form larger particles of ‘floc’. These larger particles settle more quickly. Chemicals commonly used in coagulation are: Alum (aluminium sulphate), Ferric chloride and Ferric sulphate.

Commonly, the coagulation tank is agitated as the coagulant is added. This encourages the water and coagulant to mix thoroughly. This technique is called ‘Flash Mixing’.

FLOCCULATION

Once the coagulant is mixed in the water, the flocculation process begins. During this stage the water is gently passed through the flocculation tanks. The flocculation tanks use hydraulic or mechanical methods to encourage the particles to collide with other particles in the water to create a floc. Hydraulic flocculation tanks have a series of horizontal or vertical baffles. Mechanical flocculation tanks use reels, turbines or propellers to encourage the smaller floc from the flash mixer to bind with the floc.

As the small floc moves through the tank it collides with other small floc to create larger heavier floc particles. At this point chemical flocculants are added and the water is gently mixed to help the flow grow in size. The most common flocculant is a polymer. Also at this stage lime or soda ash may be added to treat the hardness of the water. Treatment PRINCIPLES

FLOCCULATION sedimentation and clarification RAPID MEDIA FILTER Once the coagulant is mixed processes are effective. In a typical rapid media filter in the water, the flocculation water moves vertically through process begins. During this A basic sedimentation process sand. There is also a layer of stage the water is gently passed involves a simple sedimentation activated carbon or anthracite through the flocculation tanks. tank. Flow enters from one side coal above the sand. The top The flocculation tanks use of the tank. As the water passes layer removes organic compounds hydraulic or mechanical methods through the tank the floc settles that can cause dangerous to encourage the particles to on the bottom of the tank to form disinfection by-products and those collide with other particles sludge. Chain driven scrapers with taste and odour problems. in the water to create a floc. are used to direct the sludge to The space between sand particles Hydraulic flocculation tanks have a draw-off point. The sludge is is larger than the smallest a series of horizontal or vertical collected in a hopper at the end suspended particles so most baffles. Mechanical flocculation of the tank where it is removed by particles pass through the surface tanks use reels, turbines or screw conveyors or pumped out. layers and are trapped in spaces propellers to encourage the or adhere to sand particles. smaller floc from the flash Some plants dewater the sludge mixer to bind with the floc. with a mechanical belt filter DISINFECTION press and send the water back Water is a universal solvent As the small floc moves through to the head of the plant. Others that can transport a wide the tank it collides with other direct the sludge to lagoons range of dissolved materials small floc to create larger heavier where the water evaporates and suspended particles. This floc particles. At this point leaving dried sludge. includes biological organisms chemical flocculants are added (pathogens). The disinfection and the water is gently mixed to SLUDGE BLANKET process is designed to make help the floc grow in size. The One form of sedimentation potable water safe for human most common flocculant is a process uses some form of consumption. To improve the polymer. Also at this stage lime upward flow settlement tank. quality and usability of the treated or soda ash may be added to These tanks are generally water it is disinfected as the last treat the hardness of the water. circular. Flow enters the bottom stage of the treatment process. of the tank. The water passes There are three main types of Once the coagulation and through the zone of suspended disinfection methods available: flocculation process is complete, sludge expanding it to form a the floc is ready to be taken thinc layer or ‘blanket’. Clear OZONE has powerful out. Removal of the floc water passes through the blanket disinfection properties but occurs in the sedimentation and overflows into decanting no lasting effect to protect and clarification process. channels. Sludge continuously the water once it enters enters a central hopper where the distribution system. SEDIMENTATION it is bled from the tank. The main aim of sedimentation ULTRAVIOLET RADIATION is to remove colloids and reduce FILTRATION is used widely in small turbidity. The velocity of the After separating most of the floc, plants but like Ozone water through the sedimentation the water is filtered as the final has no lasting effect. tanks is a key operating step in removing the remaining measure. It is directly related suspended particles and unsettled CHLORINATION is not as to the amount of time the water floc. Filters are classified as powerful as Ozone but it spends in the sedimentation either slow or rapid. They can has a lasting effect that tank. Having effective be operated using gravity or by limits bacterial growth in coagulation and flocculation pressure. The most common type the distribution network. processes will help ensure the of filter is a .

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