Anaerobic Treatment of Packing Plant Wastewater: A comparison study of the Anaerobic Sequencing Batch Reactor and the Static Granular Bed Reactor

Principal Investigator:

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

Other Authors: Kristin Mach Evans, Michael J. Roth, Ki Young Park, Jinyoung Jung

Project Status: In Progress

Start Date: 12/18/2000
End Date: 06/30/2003


Research Objective: The objectives of this research were to evaluate and compare the ability of the Anaerobic Sequencing Batch Reactor (ASBR) and the Static Granular Bed Reactor (SGBR) to provide satisfactory and cost-effective treatment of packinghouse wastewater from the Hormel Foods Corporation in Austin, Minnesota. Laboratory-scale (5 L) ASBR and SGBR systems were fed with the Hormel Foods wastewater and operated under different hydraulic retention times and organic loading rates in the Biotechnology Research Laboratories at Iowa State University. The results of the lab-scale study were used for comparison and evaluation of various configurations treating packinghouse wastewater. Full-scale design parameters, e.g., hydraulic retention time (HRT) and organic loading rate (OLR), were also developed for each system according to the experimental data.

The practical and engineering significance of this research was to demonstrate the possibilities of using a high rate anaerobic treatment process on the Hormel Foods wastewater. Since it was obtained prior to DAF treatment, the tested wastewater was at a higher COD and SS concentration than currently received at the anaerobic contact system in Austin. Therefore, the advantage of the ASBR or SGBR system would be to allow a higher organic loading rate to be treated in the existing digester volume. It is likely that the sedimentation (clarifier) tanks following the digesters would not be necessary with either the ASBR or SGBR system. Although sedimentation tanks were used in the laboratory study, their performance was not effectively evaluated due to the difficulties in size and scale effects at the laboratory volumes considered.

With respect to the differences between the ASBR and SGBR systems, it was clear that the SGBR offered significant advantages over the ASBR system. The SGBR had better effluent quality as evidenced by lower VFA, BOD5, COD, and TSS concentrations. The discrepancies in effluent quality became more dramatic as the HRT was decreased below 24 h. While stable SGBR operation was observed at HRTs as low as 8 h, the ASBR performance became erratic at the 18 h HRT. Lower HRTs were particularly problematic for the ASBR, and total failure occurred at the 8 h HRT. Therefore, an HRT of at least 24 h would be recommended for design purposes for the ASBR. The HRT design recommendation for the SGBR based on the laboratory study is not as obvious, since satisfactory performance was seen at all HRTs studied. Based on the performance results, a target design HRT of 14 to 18 h might be recommended. VFA concentrations began to increase slightly at the 12 h HRT, possibly indicating a change in the stress of the microbial population. The advantage of retrofitting the existing digesters to SGBRs at the Industrial Section Treatment Plant in Austin, MN would be the ability to achieve higher hydraulic and organic loadings, the production of higher quality effluent, the elimination of the sedimentation tanks, and the elimination of recycle pumping. The potential risk of such a retrofit, is that the technology has not been tried on a larger scale. Ongoing pilot plant testing at the Hormel Foods plant should help to remove this uncertainty.

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