Wastewater flow rates and BOD5 concentrations generated on a normal day from a residential area are presented in Table 1. Typical wastewater characteristics are given in Table 2. Additionally, the wastewater contains big particles such as plastic bottles, toilet paper, silt, gravel, and sand. Average water temperature throughout a year is in the range of 15 to 25 oC.
1 Water and Wastewater Treatment (300992 Autumn 2021) Assignment -2 Wastewater Treatment Process Design (Due 31 May 2021) Wastewater flow rates and BOD5 concentrations generated on a normal day from a residential area are presented in Table 1. Typical wastewater characteristics are given in Table 2. Additionally, the wastewater contains big particles such as plastic bottles, toilet paper, silt, gravel, and sand. Average water temperature throughout a year is in the range of 15 to 25 oC. Table 1: Details of wastewater flow rate and BOD5 on a normal day Time (h) Inflow (m3/sec) BOD5 (mg/L) Time ( h) Inflow (m3/sec) BOD5 (mg/L) 0:00 0.068 88.0 12:00 0.102 128 2:00 0.032 42.4 14:00 0.107 112 4:00 0.027 25.6 16:00 0.114 104 6:00 0.032 52.8 18:00 0.121 100 8:00 0.072 100 20:00 0.111 160 10:00 0.095 120 22:00 0.083 136 Table 2: Details of wastewater characteristics Parameters Concentrations Alkalinity as CaCO3 (mg/L) 100 pH 7.3 Suspended Solid (SS) (mg/L) 250 Settleable solids (ml/L) 250 Total dissolved solids (TDS) (mg/L) 510 Chloride (mg/L) 50 BOD5 (mg/L) ? (average BOD5 from Table 1) COD (mg/L) 425 Total organic carbon (mg/L) 160 Ammonia-N (mg/L) 40 Total Kjeldahl nitrogen (TKN) as N (mg/L) 45 2 Soluble PO4-P (mg/L) 10.5 Total PO4-P (mg/L) 13.5 3 Table 3: Details of unit processes, design parameters and design guidelines Unit process Design parameters Design guidelines Bar screen Cross-sectional area, height, number of screen Flow rate = peak flow, coarse screen =1.5-2.0 cm width, 4-5 cm clear spacing, 45o to the horizontal, channel width 0.90m Grit chamber Dimension: length, width and depth Flow rate = peak flow, horizontal velocity = 0.25 m/sec, water retention time = 1-2 min Equalization basin Volume Provide 30 % excess capacity for the equipment, use Table 1. Primary sedimentation tank Dimension: diameter, depth and, number of tank Flow rate = average flow rate, overflow rate = 30 - 50 m3/m2.d, hydraulic retention time = 1.5 - 2.5 h. Circular sedimentation tank, Diameter = 3 - 50 m and water depth = 3 - 5 m. Efficiency of primary sedimentation tank =70% Aeration tank Volume, quantity of air to be supplied in a day, quantity of sludge produced in day, check the F/M 90%BOD5 is soluble BOD given in Table 2, effluent standards = 25 mg/L BOD5 & 30 mg/L SS. BOD5 of the SS is 70 % of SS. Ks = 25-100 mg/L BOD5, µm= 1-8 d-1, kd = 0.01-0.30 d-1, Y = 0.4-0.8 mg VSS/mg BOD5 removed, MLVSS = 1500 – 2200 mg/L Secondary Sedimentation Tank Dimension: diameter, depth and, number of tanks MLSS = 2600 - 2900 mg/L, Diameter = 3- 50 m and water depth = 3 - 5 m. 40-50% of wastewater will be recirculated to the aeration tank. Follow attached the material Q1. Design unit processes (bar screen, grit chamber, equalization basin, primary sedimentation tank, aeration tank, and secondary sedimentation tank) using the water flow rates (Table 1), water characteristics (Table 2), design parameters and guidelines (Table 3). The flow rates and BOD5 given in Table 1 will be different for the individual. Multiply the flow rates and BOD5 given in Table 1 by (1+N*0.1). N is the last digit of your id number. List the assumptions you are using for your design. If need more data and information, please follow the reference book and list what additional assumptions you are using. (15 marks) Q2. Draw the flow diagram of the wastewater treatment plant designed in Q1 and mention the waste removal happen in each unit treatment process. (3 marks) Q3. Does this treatment process remove 90% of nitrogen? If not what are the unit treatment processes would you add and why explain with a flow diagram (4 marks). Q4. Assume the designed wastewater treatment plant remove only 15% of soluble PO4-P. However, before discharging the wastewater into natural water bodies 99% of PO4-P should be removed. If the wastewater treatment plant is going to dose FeCl3 for PO4-P removal, how much FeCl3 is required per day and how much chemical waste (sludge) will be generated in a day? List your assumptions. (3 marks) Secondary Sedimentation Tank-1 Secondary Sedimentation Tank-2