CVEN 5534, Wastewater Treatment

Assignment 2, due Tuesday, Sept. 14.

Wastewater Characterization and Regulation

1. Wastewater Data (Influent and Effluent) for the City of Longmont, CO Wastewater Treatment

Plant (WWTP) is on the web page as a spreadsheet:

http://ceae.colorado.edu/~silverst/cven5534/notes. Use the spreadsheet data to:

a. Compare values for average daily flow, maximum month, average day (MMAD),

and maximum daily flow for the sampling period (Jan-Jun 2009).

b. Calculate ratios: Influent COD:TBOD, Effluent COD:TBOD, where TBOD includes

both soluble and particulate components.

i. The influent ratio is somewhat higher than typical values (see Composition table

in class notes for Characteristics on the web page). What might be an

explanation for that?

ii. The effluent ratio is much higher than the influent. Why do you think that is?

c. The WWTP discharges to the St. Vrain Creek, which is an ammonia-limited stream has

new water quality standards (WQS) for ammonia in 2011. (see WQS for St. Vrain Creek

in http://ceae.colorado.edu/~silverst/cven5534/notes)

i. Acute toxicity = 8.4 mg/L total ammonia nitrogen (NH3-N + NH4-N)

ii. Chronic toxicity = 0.06 mg/L NH3-N

The relationship NH3-N = 0.06 NH4-N can be used to estimate the allowable in-stream

concentration of NH4-N for chronic or acute WQS under the critical pH condition for St.

Vrain Creek (pH = 8.0).

Under low flow conditions the ratio of the base flow in St. Vrain Creek to the WWTP

flow is 0.54:1.

Given the Longmont WWTP performance in 2009, which standard, chronic or

acute, could impose the greatest changes to the discharge permit standard for total

ammonia-nitrogen? Considering dilution in St. Vrain Creek what might that new

standard be if the State tries to maintain WQS?

d. Currently the discharge permit for Longmont WWTP contains no limit on nitrate nitrogen

since the WQS for nitrate in the St. Vrain Creek is only limited by the agricultural

standard, 100 mg/L NO3-N. However, significant land development is occurring to the

east of Longmont, and there is a possibility that the drinking water standard for nitrate: 10

mg/L NO3-N may be added to WQS. If that should happen, estimate the potential

discharge standard for nitrate-nitrogen for the WWTP, considering the current

dilution factor for the plant.

e. The state is changing the in-stream WQS for recreational use from the old indicator, fecal

coliform bacteria (200 cells/100 ml) to a new indicator, E. coli, with a WQS of 126

cells/100 ml. Given the 2009 data, and a conversion factor of 0.63 E. coli/fecal

coliform cells, and the current dilution factor, will the plant meet the new WQS?

USGS has reported that a more reliable ratio if 0.77 E. coli/fecal coliform cells. Will

the WWTP be able to meet that standard?

2. Compare the merits of wastewater discharge permits based on technology-based limits versus

water quality based effluent limits. Consider factors such as: environmental impacts, cost,

social and political factors, ability to incorporate new science and new contaminants, and any

other aspects you think are important.