Process, SEQ Water (2016)
The flash tank: The water from the river flows to the flash mixer where it is mixed with caustic soda and alum chemicals. The rate of chemical used depends on some sediments and wastes contained in the water.
Flocculation chamber: In the flocculation chamber, smaller chemical particles undergo a gentle mixing process allowing them to mix and form large particles known as floccules made up of clay and silt. Floccules enter the sedimentation tank and settle at the bottom of the tank where they are separated and pumped out of the sedimentation tank through a vacuum process. The remaining water mixture goes to the next purifying stage.
The DAF (Dissolved Air Flotation): During the DAF process, pressurized steam saturated with air is blown into the tank to form fine bubbles. The bubbles rise from the bottom of the tank to the surface of the tank carrying fine flocculation particles that were left during the sedimentation process. Fine sand and rock filter beds found in the filtration tank helps get rid of fine particles. Moreover, mud sticking on the wall of the filtration tank is removed by pumping water into the tank to separate the mud from filtered water.
Several tests take place during the DAF process. These are:
The Turbidity test-Determines the level of suspended particles in water
pH test-Tests the level of acidity of water
The color test-Measures the presence of soluble organic matter.
The filtered water is mixed with chlorine and lime to disinfect and control the level of pH respectively. The treated water enters the pure water well and later pumped to reservation tanks. Water in the reservoir is mixed with chloramines disinfectant, a mixture of chlorine and ammonia, to prevent the growth of microorganisms in water.
The mud and waste water materials removed during the filtration process undergo a separate treatment process that occurs in a thickener and two circular tanks. When a mixture of waste water and mud is added into the tank, the mud sinks in the bottom layer while water forms the top layer. The floating water creates a lagoon where it is pumped towards the head of the treatment plant for processing. The remaining mud is emptied to the centrifuge machine.
In the case where water collected from the river contains a high volume of mud, the mixture is put in large drying pans placed under the sun where water evaporates leaving dried mud that is later spread over the land.
Formulas used in the design parameter:
Surface Area = Length* Width Eqn 1
Cross Sectional Area = urface Area*Height Eqn 2
Horizontal Velocity = FlowCross Sectional Area .. Eqn 3
Retention Time = VolumeFlow . Eqn 4
SLR = FlowSurface Area .. Eqn 5
Filtration Rate = FlowSurface Area . Eqn 6
Power Required = [G x (µ* volume)0.5)]2 Eqn 7
Flow rate at the treatment plant = 250 ML/Day (When two trains operate simultaneously)
Flow on a single train = 125ML/Day
Flow = 250 ML/Day = 250 x 103) / (24 x 3600) m3/s = 2.894 m3/s
Flow through a single train = = 2.8942 m3/s = 1.447 m3/s
The reduction of turbidity with the existing equipment in the plant may be achieved through increasing the operation efficiency of equipment, using meshes at the flocculation intake, and increasing sedimentation time.
Turbidity reduction may also be achieved through these changes done on the equipment:
Using basins with larger surface areas
Using technologically advanced equipment to increase drying efficiency of the sludge
Increasing the number of sludge drying beds
Changing to high-quality sludge thickener tanks, tube clarifying tanks and balancing tanks.
Using the hydrothermal oxidation process that helps improve the concentration of solids and decreased the volume of sludge waste by approximately 20 percent of the current volume.