Section 4.    AGRICULTURAL WASTES
ANAEROBIC TREATMENT OF FUEL ALCOHOL WASTEWATER
BY SUSPENDED GROWTH ACTIVATED SLUDGE
Enos L. Stover, Associate Professor
Ganapathi Gomathinayagam, Graduate Student
Reinaldo Gonzalez, Graduate Student
Bioenvironmental and Water Resources Engineering
School of Civil Engineering
Oklahoma State University
Stillwater, Oklahoma 74078
INTRODUCTION
The wastewaters generated from fuel alcohol production processes are high strength wastewaters
that require the development of characterization and treatability information in order to determine
economical solutions for discharge, reuse and recycle alternatives. Treatability studies have been conducted with fuel alcohol wastewaters to develop the biological treatment kinetics required for design
of aerobic activated sludge systems. The results of these studies have been previously reported [1,2,3].
The aerobic process provides a treated effluent that can possibly be recycled back to the alcohol plant,
used for irrigation purposes, or discharged. A waste biological sludge is also produced that may be
dried and used as cattle feed with the grain solids and spent yeast solids.
Since this wastewater is a high strength wastewater, as indicated in Table I [1,2], anaerobic treatment should offer certain advantages over aerobic treatment. Sludge production would be significantly less with anaerobic treatment, but the sludge should still be suitable for cattle feed when dried
and mixed with the grain solids. No oxygen would be required and methane gas would be produced as
an additional by-product of anaerobic treatment for recycle directly back to the alcohol production
plant. Because of these anticipated advantages, batch and continuous flow anaerobic suspended
growth activated sludge studies were conducted at Oklahoma State University, and the results of these
studies are reported in this paper.
MATERIALS AND METHODS
Typical thin stillage or wastewater characteristics, as presented in Table I, were collected from the
Oklahoma State University Agricultural Engineer's 200,000 gallon per year capacity fuel alcohol
research facility and from the 3,000,000 gallon per year plant at Hydro, Oklahoma, for use in the
anaerobic activated sludge studies. These wastewaters were subjected to pretreatment by gravity settling, and the supernatant was then used in the biological treatment studies.
Bench-scale, complete mix, continuous flow anaerobic activated sludge systems were used in these
studies to evaluate the anaerobic treatability of the fuel alcohol wastewaters. These systems were
plexiglass with 7.2 liter mix tank reactor volumes and 3.5 liter settling compartment volumes. The
wastewaters were pumped from feed tanks to the mix tank reactors, and the treated effluents flowed
by gravity from the settling compartments to effluent collection tanks. The influent wastewater flow
rates were regulated and carefully controlled to provide the desired hydraulic retention times.
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