Assignment 1: Water Treatment Plant and Distribution System Design

Submission date: 03 October 2021 11:59 PM

A newly planned city wants to construct a drinking water treatment plant and distribution system. Use the information given at the end of the document to answer the following questions:

2. Design coagulation, flocculation, sedimentation, rapid sand filtration, and disinfection facilities.
4. Using the data on enhanced coagulation (Table 2) and TTHM and HAA5 yield data and propose modification to the design necessary if your treatment process cannot meet the new regulation that specifies a maximum 80 and 60 ppb of TTHM and HAA5, respectively.
6. Calculate the CT value achieved by your disinfection and compare with the table of values given in the lecture notes to understand whether the CT value is met by your dosing for primary disinfection.
8. Discuss other problems associated with dissolved organic carbon in water for primary disinfection and secondary disinfection. Why should bacterial regrowth be an issue in water distribution system and what parameters affect the regrowth? Compare the possibility of bacterial regrowth in chlorinated and chloraminated system. You will need to read journal articles on this.
10. Conceptually design a water treatment process for water:
    2. The river water has to be treated to remove dissolved solids to very low level to avoid solids deposition in boilers;
    4. List possible contaminants in stormwater from a car park that has to be used for gardening; and
    6. recycled water from secondary effluent that has to be treated for cooling tower in power plant and compare the benefits (economic/social/environmental) you would derive from using the recycled water instead of tap reticulated water.

DATA

Design capacity of the treatment plant is 0.2+0.02*86m³/s, with an initial demand expected to be 40% of the design capacity.

First customer is expected to receive water after 36 hr of disinfection and customer at the end of treatment system is expected to be approximately 10 days after the disinfection. Consider chlorine as the primary disinfectant and chloramine as a secondary disinfectant.

Water is assumed to travel the whole journey through pipes.

Source water quality (some of the data may not be needed for the assignment calculations):

Water temperature = 12 24^oC (Design for the maximum temperature)

Ca²⁺ - 95.20 mg/L

Mg²⁺ - 13.44 mg/L

Na⁺ - 25.76 mg/L

CO₂ 19.36 mg/L

HCO₃^- - 241.46 mg/L

SO₄^2- - 53.77 mg/L

Cl^- - 67.81 mg/L

DOC 4.5 mg/L

Turbidity 15 NTU

Total Coliforms = 10000 /100mL

Giardia = 20/L

A jar test conducted to understand the turbidity removal characteristics when turbidity was at 15 NTU showed the performance shown in Table 1.

Table 1

	1	2	3	4	5	6
pH Fe dose (mg/L) Settled water turbidity (NTU)	5.0 10 11	5.5 10 7	6.0 10 5.5	6.5 10 5.0	7.0 10 4.5	7.5 10 8

	1	2	3	4	5	6
pH Fe dose (mg/L) Settled water turbidity (NTU)	7.0 5.0 14	7.0 7 9.5	7.0 10 5.0	7.0 12 4.5	7.0 15 6.0	7.0 20 13

According to mEnCo program following final DOC was obtained at given doses for the water. Suggest how you would treat water by enhanced coagulation (i.e. define dose and pH) to get the final DOC necessary to achieve regulatory DBP requirements.

Assume the settlement characteristics of flocs is similar to that given in the first example of Powerpoint slides.

Filter bed is to be designed using the sand with the characteristics given in Table 3.

Table 3: Filter bed material characteristics.

US Standard Sieve No	Mass percent retained
8 12 16 20 30 40 50 70 100	0.03 0.05 0.32 6.70 22.90 40.00 26.20 3.70 0.10

Make reasonable assumptions as done in the examples for the class. While the complete filter bed should cater for future demand (the capacity), it should have the capability to handle the current demand by having few filters offline. Depth can be assumed to be 0.75 m, specific gravity of sand is 2.80, shape factor is 0.67, and specific porosity is 0.4+0.01*last two digits of your ID.

Mainly carry out calculation of head loss of the clean bed, number of beds, width x length etc. Indicate the position(s) of various elements of the filter bed. Also carry out the bed expansion calculation to determine the top position of the trove.

Chlorine decay characteristics can be explained by the first order reaction. The reaction rate, k_T, at any temperature (T^oC) can be described as

k_T = k₂₀*exp[-E/R(1/(273+T)-1/(273+20)].

where, k₂₀ is the reaction rate coefficient at 20^oC.

Chlorine decay rate (k₂₀) at 20^oC is given by 0.015*DOC+0.01 hr-1. The E/R value is found to be 8200 K^-1.

TTHM and HAA5 formation yields after chlorination are given as 25+5*(remainder if ID is divided by 5) and 10 +3*(remainder if ID is divided by 5) mg/mg chlorine reacted respectively. The final chloramine concentration has to be at least 0.4 mg/L at the customer tap.

Chloramine has the same yield of HAA5 as chlorine. However, TTHM yield is only 10% of TTHM yield of chlorine.

Chloramine decay characteristics could be approximately defined by the following relationship:

E/R value for chloramine is 6000 K^-1

Table 4: Chloramine decay rate at 20 ^oC in a water supply system

Total chlorine range	Total chloramine decay rate (h-1)
0-1.5 mg/L	0.01
1.5 2 mg/L	0.004
2-3.5 mg/L	0.002