BKC3543 SECTION 1 SEM II/ 2014-2015

ASSIGNMENT 1DUE DATE: TUESDAY (7/4/2015 - 5.00 pm)1. A wastewater treatment plant discharges to a small stream. The characteristics of the wastewater and the characteristics of stream are given below:StreamWaste

Flow = 0.4 m3/s

BOD = 2.0 mg/L

DO = 90 % saturationTemperature = 24( C

k2= 0.45 d-1 Flow = 10,000 m3/dDO = 0 ms/L

Temperature = 21 (C

k1 = 0.23 d-1

Determine the maximum BOD5 (20(C) that can be discharge if a minimum of 4.0 mg/L of oxygen must be maintained in the stream.2. A dairy industry discharges a wastewater to a stream where the characteristics of the wastewater and the stream are shown as below:ParameterStreamWastewater

FlowBOD5 at 20 (C

DO

Temperature,(C

k1 at 20 (C

k2 at 20 (C19,000 m3/d2.0 mg/L

10.0 mg/L

10

-

0.55 d-11000 m3/d1250 mg/L

0 mg/L

50

0.35 d-1-

(a) If no treatment at all is given to the wastewater, what will be the lowest oxygen level in the stream as a result of the discharge?

(b) If the stream is a trout fishery and the stream standards require a minimum DO of 5.0 mg/L, what is the maximum BOD5 (20 (C) that can be discharged by the industry?

3. 200 mL water was collected from Klang river from the river stream. 2 mL of river water was diluted to 250 mL, aerated and seeded. The dissolved oxygen content was 7.6 mg/L initially. After 5 days, the dissolved oxygen content had dropped to 5.7 mg/L. A second sample was obtained 60 days later and retested using similar method. The initial dissolved oxygen was 7.5 mg/L and, after 5 days, dropped to 5.3 mg/L. What is the ultimate BOD for each of the samples? Which water sample was cleaner?4. The dilution factor for mixture of waste and water is 0.030. The DO of the mixture is initially 9.0 mg/L, and after 5 days it has dropped to 3.0 mg/L. The reaction rate constant k has been found to be 0.22 day-1.(a) What is the 5 day BOD of the waste?(b) What would be the ultimate BOD?(c) What would be the remaining oxygen demand after 5 days?(d) Based on your answer in (a) and (b), what would the 5 days BOD of this waste if the temperature is at 25(C?5. A wastewater treatment plant serving a city of 200,000 discharges 1.10 m3/s of treated effluent having an ultimate BOD of 50.0 mg/L into a stream that has a flow of 8.7 m3/s and a BOD of its own equal to 6.0 mg/L. The deoxygenation constant, kd is 0.20/day.(a) Assuming complete and instantaneous mixing, estimate the ultimate BOD of the river just downstream from the outfall.

(b) If the stream has a constant cross section, so that it flows at a fixed speed equal to 0.3 m/s, estimate the BOD remaining in the stream at a distance 30,000 m downstream.

6. A small water plant has a raw water inflow rate of 0.6 m3/s. Laboratory studies have shown that the flocculated slurry can be expected to have a uniform particle size (only one size), and it has been found through experimentation that all the particles settle at a rate of vs = 0.004 m/s. (This is unrealistic, of course). A proposed rectangular settling tank has an effective settling zone of L = 20 m, H = 3 m, and W = 6 m. Could 100% removal be expected?7. It has been determined that a community requires a maximum flow of 40 million L/day of water during 10 hour in a peak day, beginning 8 am and ending at 6 pm. During the remaining 14 hour, it needs a flow of 8 million liter/day. During the entire 24 hour, the water treatment plant is able to provide a constant flow of 24 million liter /day, which is pumped into the distribution system. How large must the elevated storage tank be to meet this peak demand?8. Determine the settling velocity of a spherical particle with a diameter of 100 m and a specific gravity of 2.3 in water at 25(C?

9. A settling column analysis is run on a type-1 suspension where the settling column is 2 meter tall. The initial concentration of the well-mixed sample is 650 mg/L. Results of the analysis are shown below:Time, min0587791114154250

Concentration remaining, mg/L65056041532521513052

What is the theoretical removal efficiency of the settling basins that receive this suspension if the loading rate of 2.4 10-2 m/min.10. A large stream flowing through a highly industrialized area must serve as a raw water supply for the community. The water is consistently turbid, has hardness in excess of 300 mg/L, and has refractory organics that are known precursors of trihalomethanes. Draw a schematic diagram of a treatment plant that should render this water potable. Identify all units, state their purpose and show the points of chemical addition. Identify all chemicals.