Primary clarifier Primary clarifier are usually designed to

Primary clarifier

• Primary clarifier are usually designed to remove particles with settling rate of 0. 3 – 0. 7 mm/sec. • Two types of primary clarifiers • 1. rectangular • 2. circular.

Clarifier Loading Calculations Detention Time (DT) = Tank Volume, MG X 24 Flow into Tank, MGD Surface Overflow Rate (SOR) Flow, gallons/day = Surface Area, ft 2 gallons/day Weir Overflow Rate (WOR) = Flow, Length of Weir, ft Solids Loading = Solids, lbs/day Surface Area, ft 2

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Example 1: If a tank is 10 ft long and 5 ft wide, what is the surface area? SA, ft 2 = 10 ft X 5 ft = 50 ft 2

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Example 2: If a tank is 10 ft 6 inches long and 5 ft 9 inches wide, what is the surface area in sq. ft. ? NOT SA, ft 2 = 10. 6 ft X 5. 9 ft

Converting Inches to Feet 6 inches = 0. 5 ft 6 inches = 12 in/ft So: 10 ft 6 inches = 10. 5 ft 9 inches = 0. 75 ft 9 inches = 12 in/ft So: 5 ft 9 inches = 5. 75 ft

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Example 2: If a tank is 10 ft 6 inches long and 5 ft 9 inches wide, what is the surface area in sq. ft. ? SA, ft 2 = 10. 5 ft X 5. 75 ft = 60. 4 ft 2

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Work Calculations on Separate Paper Answers Given on Next Slides Practice 1: If a clarifier is 25 ft long and 9 ft wide, what is the surface area in sq. ft. ? Practice 2: If a clarifier is 22 ft 3 inches long and 7 ft 7 inches wide, what is the surface area in sq. ft. ?

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Practice 1: If a clarifier is 25 ft long and 9 ft wide, what is the surface area in sq. ft. ? SA, ft 2 = 25 ft X 9 ft = 225 ft 2

Surface Area Calculations Rectangles Surface Area, ft 2 = Length, ft X Width, ft Practice 2: If a clarifier is 22 ft 3 inches long and 7 ft 7 inches wide, what is the surface area in sq. ft. ?

1. 0 PRIMARY SEDIMENTATION TANKS Primary treatment traditionally implied a sedimentation process to separate the readily settleable and floatable solids from the wastewater. The primary sedimentation tank is where the flow velocity of the wastewater is reduced by plain sedimentation. The process commonly remove particles with a settling rate of 0. 3 to 0. 6 mm/s. The overflow rate of the primary sedimentation tanks ranges from 24. 5 to 49 m 3/m 2 d (1. 02 m/h to 2. 04 m/h) The detention time is the tank is usually 1 3 h (typically 2 hours)

Primary tank should removes: * 90 – 95% of settleable solids * 50 – 60% of total suspended solids * 25 – 35% of BOD 5 Laboratory analyses of settling column tests are commonly used to generate design information. The depth should not be less than 3. 0 m.

If waste activated sludge is returned to the primary clarifier, the design surface settling rate shall not exceed 41 m 3/(m 2 d). Weir loading rate should not exceed 250 m 3 per day linear meter (10 m 3/h/m)

1. 1 Rectangular Basin Design Basin dimensions are to be designed on the basic of surface overflow rate to determine the required basin surface area. An overflow rate of 36 m 3/(m 2 d) at average design flow is generally acceptable. The basin length to with ratio of 3: 1 is acceptable. Weir loading rates range from 250 to 273 m 3/(d. m) 1. 2 Circular Basin Design Inlet in circular or square basins are typically at the center and the flow is directed upward through a baffle that channels the wastewater (influent) toward the periphery of the tank. Inlet baffles are 10 20 percent of basin diameter and extend 0. 9 – 1. 8 m below the wastewater surface. A typical depth of sidwall of a circular tank is 3 m. The floor slope of the tank is typically 300 mm horizontal to 25 mm vertical.

• Circular tanks shall be no more than 50 m in diameter and the side water depth shall be at a minimum of 3. 0 m. Note: If weir loading exceeds 100 m 3/day/m at average flow, a multiple v notch weir must be used. Refer also to Clause 6. 3. 6 of MS 1228. 5. 8 Design of Biological Treatment Stage 5. 8. 1 Introduction Biological treatment is the heart of the treatment process. It is where the sewage is exposed to living organisms that remove dissolved and non settleable organic material remaining in the sewage. For reasons of long term whole life economics, ease of operation and maintenance, consistent effluent standards and standardisation, the following types of biological treat ment processes are recommended for use in Malaysia. • Conventional activated sludge system for PE > 20, 000 • Extended aeration activated sludge system for all PE

At least two DO meters shall be provided in each tank. The placement of these meters shall allow for easy removal, servicing and calibration. If mechanical aerators are used, a vented enclosure over the aerator shall be provided to minimise noise and aerosol. Aeration pipework shall typically be ductile iron or steel pipe with suitable protec tion. Galvanised steel or stainless steel shall be used for headers and drop pipes within the aeration tank. PVC pipes shall be restricted to the diffuser laterals and off takes. Tanks, preferably shall not be wider than 30 m for maintenance purposes, which is normally limited by the crane reach. Inlet gates shall be provided at the inlet section of the aeration tanks to isolate each tank. A sump for the drainage of each tank shall be provided. Table 5. 9 contains important design parameters.