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Environmental Engineering - Homework 6 Questions | CE 321, Assignments of Civil Engineering

Lafayette CollegeCivil Engineering

Material Type: Assignment; Class: Environmental Engineering; Subject: Civil Engineering; University: Lafayette College; Term: Fall 2008;

Typology: Assignments

Pre 2010

Uploaded on 08/18/2009

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DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING; LAFAYETTE COLLEGE
Homework Assignment 6, Due Oct 23, 2008
CE 321, Fall 2008
1. [Design Problem] A rectangular clarifier in a wastewater plant is to be designed to settle 2000
m3/day with a surface loading rate of 32 m3/day per m2. The tank is to be 2.4 m deep and 4 m
wide. How long should it be and what detention time would it have?
2. [Design Problem] A settling tank for a 2 MGD wastewater plant is to be designed to have a
surface loading rate of 800 gal/day per ft2. The tank must have a minimum retention time of 2 hrs
and must be at least 11 ft deep to allow proper settling of waste sludge. If the tank is circular,
what should its diameter and depth be?
3. Water containing 125 mg/L of suspended solids flows into a clarifier (settling tank) at 18,500
m3/day. The effluent from the top of the tank has no suspended solids. Solids are continuously
pumped from the bottom of the tank at a concentration of 8000 mg/L. What are the flow rates out
the top and bottom of the tank, assuming no accumulation of solids in the tank? What is the mass
of solids being removed from the tank per hour?
4. A wastewater contains a pollutant with an initial concentration of 1200 mg/L, which will be
treated in a batch reactor. The reaction is assumed to be first order, with a rate constant of -2.5
/day. Plot the concentration in the reactor for the first 2 days. How long will it take for
reductions of 75%, 90%, and 95% of the pollutant?
5. [Design Problem] For the wastewater of the previous problem, determine the HRT and
required volume for a CSTR for 90% removal and a flow rate of 0.05 m3/sec.
6. For a reaction order of 0, that is, rxn rate = -kC0 = -k, what is the difference in required
volumes for a constant flow rate for a CSTR vs. a PFR? (hint: assume steady-state, and find the
expressions for HRT)
7. [Design Problem] A wastewater flow of 1 MGD will be treated with 150,000-gal PFR
reactors. The reaction is first order, with a rate constant of 2.5 /day. How many PFRs connected
in series (one after the next) are necessary for reductions of 75%, 90%, and 95% of the pollutant?
How many must be connected in parallel (the total flow is split evenly between them), for the
same % reductions?

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DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING; LAFAYETTE COLLEGE

Homework Assignment 6, Due Oct 23, 2008 CE 321, Fall 2008

  1. [Design Problem] A rectangular clarifier in a wastewater plant is to be designed to settle 2000 m^3 /day with a surface loading rate of 32 m^3 /day per m^2. The tank is to be 2.4 m deep and 4 m wide. How long should it be and what detention time would it have?
  2. [Design Problem] A settling tank for a 2 MGD wastewater plant is to be designed to have a surface loading rate of 800 gal/day per ft 2. The tank must have a minimum retention time of 2 hrs and must be at least 11 ft deep to allow proper settling of waste sludge. If the tank is circular, what should its diameter and depth be?
  3. Water containing 125 mg/L of suspended solids flows into a clarifier (settling tank) at 18, m^3 /day. The effluent from the top of the tank has no suspended solids. Solids are continuously pumped from the bottom of the tank at a concentration of 8000 mg/L. What are the flow rates out the top and bottom of the tank, assuming no accumulation of solids in the tank? What is the mass of solids being removed from the tank per hour?
  4. A wastewater contains a pollutant with an initial concentration of 1200 mg/L, which will be treated in a batch reactor. The reaction is assumed to be first order, with a rate constant of -2. /day. Plot the concentration in the reactor for the first 2 days. How long will it take for reductions of 75%, 90%, and 95% of the pollutant?
  5. [Design Problem] For the wastewater of the previous problem, determine the HRT and required volume for a CSTR for 90% removal and a flow rate of 0.05 m^3 /sec.
  6. For a reaction order of 0, that is, rxn rate = -kC^0 =^ -k , what is the difference in required volumes for a constant flow rate for a CSTR vs. a PFR? (hint: assume steady-state, and find the expressions for HRT)
  7. [Design Problem] A wastewater flow of 1 MGD will be treated with 150,000-gal PFR reactors. The reaction is first order, with a rate constant of 2.5 /day. How many PFRs connected in series (one after the next) are necessary for reductions of 75%, 90%, and 95% of the pollutant? How many must be connected in parallel (the total flow is split evenly between them), for the same % reductions?