environmental chemistry

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Question 44552


Environmental Chemistry

Mass balance on a stream receiving waste. (+3.5 total) Let's revisit the BOD problem from the first homework. Instead of running a BOD5 experiment, an operator from the wastewater treatment plant provides you with the BOD5 and flowrate of the wastewater that spilled into the stream (BODWW =184.4 mg/L; Qww = 500 L/s). You find records that show the BOD5 and flowrate of the stream during normal conditions (BODS = 0.8 mg/L; Qs = 1000 L/s). Using this information, determine the BOD5 of the stream after the spill event, assuming steady state and no reaction. Begin by drawing and labeling a diagram of the system. (Answer: BOD5= 62 mg/L).

Question 44551


Environmental Chemistry

Batch reactor with first order reaction. (+4 total) A researcher is attempting to produce ethanol using an enzyme catalyzed batch reactor. The ethanol is produced from corn starch by first-order kinetics with a rate constant of 0.05 hr1. Assuming the concentration of ethanol initially is 1 mg/L,what will be the concentration of ethanol (in mg/L) after 24 hours? Assume the reactor stays at a constant volume and temperature. How long will it take to reach a concentration of 10 mg/L ethanol?(Answer: C = 3.32 mg/L; t=46 hr).

Question 44550


Environmental Chemistry

Half-life of a radioisotope. (+2.5 total) A lake in New Mexico was found to have radium-226concentrations of 50 pCi/L due to a nearby uranium mining operation. If no action is taken to remove the radium-226 from the lake, how long will it take to reach the federal limit of 5 pCi/L. Radium-226has a half-life of 1600 years. (Answer: 5,320 yrs).

Question 44548


Environmental Chemistry

1. Alkalinity. (+6 total) Prior to the industrial revolution, the concentration of bicarbonate and carbonate in the ocean was 110 mg/L and 14.7 mg/L, respectively, and the pH was 8.2.

a. Calculate the total alkalinity (in mg/L as CaCO3) of the ocean prior to the industrial revolution.

b. Today, the pH of the ocean is 8.1. Assuming that the concentration of bicarbonate and carbonate has stayed relatively constant, has the alkalinity of the ocean increased or decreased since the industrial revolution?

Question 40240


Environmental Chemistry

(a) What is meant by "Root Cause Analysis"?

marks)(b) One graphical method of Root Cause Analysis is Fault Tree Analysis. Detail the stepsneeded to undertake a Fault Tree Analysis.(7 marks)

(7 marks)(c) Figure 2 depicts a system for the treatment of a chemical plant effluent and its release to a watercourse.

Effluent material from the plant should normally be treated in treatment tanks 1 and 2 (each tank removes different toxic chemicals) and then safely released, via outlet 1, to the watercourse. However, both treatments can fail, under circumstances shown in Table 1.In an emergency, if the system becomes over-pressurised, an emergency pressure safety valve (PSV) will activate to prevent a dangerous explosion. In this emergency scenario waste released should be collected in an overflow tank. However, on days where factory output is 20% higher than average, the overflow tank level can be exceeded, and toxic material will flow through outlet 2 into the watercourse. Table 1 shows the frequency and duration of the unwanted events.

(i) Sketch a fault tree showing the scenarios that could lead to toxic material being released into the watercourse. You may assume that the high-output and the dangerous over-pressure condition are independent events.

(9 marks)(ii) Calculate the frequency, per year, of toxic material being released from Outlet 1?

(iii) Calculate the frequency, per year, of toxic material being released into the water course from either Outlet 1 or Outlet 2?(5 marks)

Question 40239


Environmental Chemistry

a) Using the thermal radiation equation below and your knowledge of solar flux calculate theflux emitted from a star with a temperature of 6200 K to 2.d.p. Assume the star is a perfectblack-body.

The Stefan-Boltzmann thermal radiation equation is: P = AɛoTªWhere

P= Power (W)

ASurface area (m²)

epsilon = Emissivity

sigma =The Stefan-Boltzmann constant is 5.67 x 10-8 W · m2 . K-4=

T = Temperature (K)

(i) Explain, in this context, what is represented by the term 4ttr2?

(ii) Explain, in this context, what is represented by the term a

(iii) Redraw the diagram depicting the Earth's atmosphere as a single layer above theearth and add labels and direction arrows for the resultant fluxes (W/m2) under thoseconditions.

(iv) Derive equations representing the temperature of the single atmospheric layer, and the temperature of the ground. State all the assumptions you have made.

Question 40238


Environmental Chemistry

a)Give examples of human-made methods for the clean-up of oil spills in water.

b)Detail and describe the chemical and physical processes that occur to oil when spilled in water.(0 morlke)

c)Describe how microbes can be used to aid in the clean-up following an oil slick.

Question 40237


Environmental Chemistry

An informal industry rule is to design occupied control rooms to withstand a 1-ton (907.18474 kg) blastof TNT at 100 ft (30.48 m).

a) What overpressure does this correspond to?

b) What quantity (in kg) of propane (C3H8) does this correspond to given that the energy of explosion for propane is 2043.1 kJ/mol, the molar mass of propane is 0.044 kg/mol and the energy of explosion of TNT is 4686 kJ/kg?

c) How far away (in m) from this 1-ton blast must a residential home be in order to receive no more than minor damage to house structures?

d) Estimate the length of the resulting flame if the equivalent propane gas is suddenly released(assume 1 s for the time of release) and ignites.ulu)

e) Calculate the total rate of release of energy by the flame.

(3 Marks)f) How close to the flame a person would need to be to experience skin burns given that skin burns requires an incident flux q of 100 kWm.2 for a 10-second exposure.(

Question 40236


Environmental Chemistry

The Immediately Dangerous to Life and Health (IDLH) concentration is defined as the concentration"that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed adverse health effects or prevent escape from such an environment." The IDLH implies a 30-min maximum exposure time. A table of transformation from percentage to Probits is given below:

a) The IDLH for chlorine gas is 10 ppm. Estimate the fraction of fatalities due to exposure at the IDLH for 30 min given that the Probit equation for chlorine deaths is:

P=-8.29+0.92 \times \operatorname{Ln}\left(C^{2.0} T\right)

where Cis the chlorine concentration in ppm and Tis the time exposure in minutes.

b) Estimate the maximum exposure or evacuation time to result in no more than 1% fatalities atthe IDLH level.

c) Define the parameters LC10, LC50 and LC90.

d) Determine the LC50 for a 10-minute exposure period.

e) Determine the LC10 for a 50-minute exposure period.

f) Give a definition of the threshold value limit (TLV). Specify the exposure that forms the basis of the definition of the TLV.13 Marks)

Question 40235


Environmental Chemistry

a) State the four main principles of engineering ethics.

b) State the three main methods used in accidents and loss statistics for measuring the effectiveness of safety programmes.

c) The UK Legislative structure is multi-layered. State the difference between Enabling Acts,Regulations or Statutory Instruments, Guidance Notes and Codes of Practice.

d) What is a source model? Give two examples of source models. What information can be obtained from source models?

e) Explain how liquid flow rate through a hole in a vessel is calculated. What are the main contributions to the overall pressure driving the fluid out of a vessel for an aperture of a given area?

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