Reference no: EM133331458

Case Study: Pentachlorophenol (PCP) is biocidal, and a priority pollutant widely used as a wood preservative. Wastewater from a new wood treatment facility that started using this compound but didn't tell anyone is combined and treated in a two-stage process in a nearby wastewater treatment plant. Wastewater containing 150 µg/L of PCP is generated at a rate of 0.3MGD (million gallons per day). The first treatment step is a typical settling basin which can remove PCP at a rate of 0.1 h-1in 2 hours. The remaining PCP along with the remaining CBOD, enters an activated sludge tank of 284 m3volume where CBOD is removed via biological oxidation. Laboratory studies on BOD removal in the activated sludge tanks have provided the following data.

time (hr) CBOD (mg/L)

1 12500

4 1987

6 456

7 287

11 18

The PCP decay rate is one-fifth lower than the CBOD decay rate based on specific analysis of PCP decay. 10% of the flow from the secondary clarifier returns to the activated sludge chamber. The effluent from the WWTP is discharged into the 640 m wide, 40 m deep Connecticut river that has an upstream flow of 65 MGD travels past a nearby community living 300 km downstream. The community draws water from this river. Based on the chemical nature of pentachlorophenol, it adsorbs to the sediment as it travels downstream, and the adsorption process is irreversible, resulting in a loss rate of about 0.01 d-1.

Questions:

1) For each of the control volumes of concern, draw the system, a control volume, and label all knowns and unknowns, inputs, outputs, sources or transformations.

2) What is the concentration of PCP leaving the wastewater treatment plant, in the effluent that discharges into the river?

3) Identify the regulations that apply to the contaminant in this scenario and state the specific regulation and the maximum concentration that should not be exceeded to protect aquatic life and human health.

4) What does the concentration profile look like in the stream as the effluent concentration travels downstream to the point where the community draws water. (Hint: Plot C vs. distance)

5) What are the possible risks posed by this contaminant to aquatic life and humans? Calculate what the increased cancer risk to a child living in this community would be due to the presence of PCP in the drinking water prior to treatment. State any assumptions.

6) Is the water safe for the community to drink with regards to PCP or must some treatment be installed? Given that this water would be used for drinking water, what are two different treatment options that could be installed for PCP treatment and explain how they work.

7) Research and explain one treatment process that could be installed or a modification of an existing treatment process at the WWTP to reduce the pentachlorophenol concentration in the effluent before discharging it into the river. Explain the process and why it works for this chemical.

8) The wastewater from the wood industry has been combining with the town's wastewater for months. As an environmental engineer and state regulator, you start to look into the history of the issue. Would you expect to see and data in the historical water quality reports that would suggest a concern? Going forward, to ensure that the community downstream is not further exposed and that they trust the treatment processes installed, what data would you collect and for how long? How would you communicate this to the community? How would you ensure this type of thing would be less likely to happen again?