On-site Pilot Demonstration of the Static Granular Bed Reactor

Principal Investigator:

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

Other Authors: Michael J. Roth

Project Status: In Progress

Start Date: 11/01/2002
End Date: 05/30/2003


Research Objective: Following successful laboratory testing at Iowa State University of Hormel Foods slaughterhouse wastewater using a high-rate anaerobic system known as the Static Granular Bed Reactor (SGBR), a pilot-scale SGBR system was operated at the Hormel Foods site in Austin, Minnesota. The on-site demonstration of this technology included operation of the system under various hydraulic retention times (HRTs) and organic loading rates (OLRs). Results from operation of the SGBR system were used to develop full-scale design parameters and recommendations. During this project a detailed characterization of the Hormel Foods slaughterhouse wastewater stream prior to pretreatment was also obtained.

Analytical testing showed excellent results for treatment of this wastestream using the SGBR. Results were consistent over a range of HRTs from 48 to 16-hours and a range of OLRs from 1.09 to 4.55 g COD/L•d, demonstrating the ability of the SGBR to be relatively unaffected by hydraulic and organic loading. Treatment efficiency during the study period ranged between 91.8- 96.1% total chemical oxygen demand (COD) removal.

This study demonstrated that rapid start-up (29 days) of the SGBR was possible with fairly consistent and high total COD removal efficiency (93.0 ± 1.4%). The SGBR was also able to achieve nearly identical treatment efficiencies following periods of time without sustained feeding to the system. As experienced in the laboratory comparison study, increased OLRs coupled with reduced HRTs only slightly affected performance of the SGBR. When compared to other high-rate anaerobic system treating slaughterhouse wastewater, the total COD removal efficiency of the SGBR system outperformed the systems investigated.

Limitations typically found in treating slaughterhouse wastewater were not experienced during this study using the SGBR system. High COD removal efficiencies, methane content (78.1-97.5%) in the biogas, and low effluent volatile fatty acids (16-25 mg/L as HAc) were evidence that no effects of inhibition from lipids and proteins occurred throughout the study. Accumulation of solid fractions of the influent wastewater was not apparent in the SGBR. Any accumulation that may have occurred did not negatively affect the performance and stability of the anaerobic process contrary to the suggestions by Ruiz et al. (1997). Suspended solids removal was excellent throughout the entire study.

Biomass yield was calculated by performing a COD balance for the system and ranged from 0.145-0.389 g VSS/g CODremoved. Biomass accumulation lead to increased headloss through the granule bed, and required biomass wasting from the system and the addition of an effluent pump to control the operating volume of the SGBR. Regular biomass wasting and/or “washing” was recommended to remove accumulated biomass from the system. Also, complete loss of structure was experienced when the granular biomass was subjected to excessive shear forces, compressive forces, and/or mechanical agitation through repeated pumping with a peristaltic pump. Pumps capable of minimizing these risks must be used to maintain the integrity of the granular biomass for use in the SGBR system.

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