Determination of Biodegradation Rates for Ethanol Production Wastewater

Principal Investigator:

Timothy Ellis, tge@iastate.edu (other projects)

Project Status: In Progress

Start Date: 06/09/2003
End Date: 07/31/2003


Research Objective: Biodegradation rates of ethanol production wastewater were determined in this study using the extant respirometric technique. Four wastewater samples were tested at three temperatures using two different biomasses. Temperature alone was found to have a significant effect on biodegradation rates. The first-order, maximum specific substrate removal parameter was found and related to temperature through regression. A temperature coefficient was determined to be 1.044. Data scatter resulted in low confidence for effects determination and a low correlation coefficient squared for the temperature regression. At 0ºC, the first-order coefficient was extrapolated to be 0.080 L/(mg?hr).

The current ethanol plant was designed to be zero discharge and does not have wastewater treatment (Svatos, 2003). Due to higher than anticipated wastewater volumes and the stormwater generated on the site, there is a need for on-site wastewater treatment. Stanley Consultants, Inc. has been employed to design a treatment system for the combined ethanol wastewater and storm water. The following specifics describe the existing system (Svatos, 2003):

•There is a surge pond to collect bad batches and hold them for reprocessing
•A bad batch of wastewater can be as high as 14,000 mg/L as COD
•The evaporator condensate COD ranges from 2,000 - 8,000 mg/L.
•Stormwater runoff from their corn bunker has COD levels in the range of 2,000 - 7,000 mg/L.
•Boiler blowdown and iron filter backwash water will go to their lagoon system

The new system will consist of three aerated lagoons and a stilling basin. Each of the aerated lagoons will have a detention time of about 38 days. The design flow through the system will be 28,000 gpd (Svatos, 2003). The raw water source is groundwater with high sulfate and iron concentrations, 1,000 - 1,500 mg/L and 0.5 - 1.5 mg/L, respectively. The wastewater contains the known organic compounds ethanol, acetic acid, ketones, and fatty acids. The Iowa Department of Natural Resources will not permit the lagoon system without treatability testing to identify the COD removal rate coefficient for this wastewater.

Objectives
The objective of this research project was to determine the biodegradation rate of ethanol production wastewater using batch respirometric tests. Four samples were obtained from the ethanol plant and tested for their respirometric response. A range of temperatures were tested in order to quantify the temperature dependence of the biodegradation rate.

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