Austin, Minnesota Wastewater Treatment Facility - Industrial Section Research Study

Principal Investigator:

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

Other Authors: Shaw-Ming Chao

Project Status: In Progress

Start Date: 08/02/1999
End Date: 07/31/2000


Research Objective: After the literature review and preliminary settling experiments were conducted, it was believed that the separators were overloaded with excess solids in the digester overflow. Rising sludge blankets occurring in the first-stage separators during the weekday operations provided evidence of the solids overloading condition.

As a result, the first recommended plant modification was to reduce the solids loading rate on the separators. This was achieved by decreasing the system SRT to lower the TSS concentration in the digester overflow and by operating the separators in parallel to increase the cross-sectional area for settling.

The new sludge wasting schedule to gradually reduce SRT was proposed and implemented in the middle of March 2000. Descending sludge blankets in the separators were observed after 4 weeks of operation. At the end of April 2000, the separator operation of subsystem #1 was converted from series to parallel. At that time, the sludge blankets depths in the separators have been maintained in the range of two to four feet through the week. Although the sludge blanket depth in the larger separators have risen as high as 8 to 10 ft due to some operation difficulties (pump malfunction, manual gate adjustments, etc.), the AC systems are still running with satisfactory performance (based on phone conversations with Jim Samuel at the Austin WWTF on 8/15/00 and 8/21/00).

At a relatively short SRT, the predominance of anaerobic filamentous bacteria in the AC digesters may become an issue. As a result, it was also recommended to convert the existing equalization tank to the first-stage selector followed by the two AC digesters in parallel after the new equalization tank is constructed.

From a kinetic standpoint, series digester operation can also achieve higher treatment efficiency than parallel operation due to the plug flow nature of tanks in series. In addition, adding settling aids into the digester overflow before it goes to the separators might provide a cost-efficient alternative to improve the treatment efficiency in terms of TSS removal. Two chemical suppliers (Philip Services Corporation and Water Tech Inc.) were brought in for jar tests. Each of them provided information on the settling aid with best performance and the cost of full-scale implementation. It is recommended that full-scale testing of settling aid addition be implemented after the effects of SRT and separator modifications on the AC system performance have been demonstrated.

Finally, it is recommended to conduct pilot studies on alternative processes treating the Hormel Foods wastewater for future plant expansion or remodeling. The objective of the pilot study is to evaluate 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 plant.

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