Iowa

Conversion to River Discharge

  • Client Undisclosed Animal Feed Supplements
  • Type Industrial
  • Services WWTP Improvements
  • Construction Cost $12 Million
  • Project Manager Mark Cramer, P.E.

CHALLENGE

An amino acids plant producing animal feed supplements desired to convert from a pretreatment facility to a direct discharger. The pretreatment plant was a plug flow activated sludge plant consisting of equalization, a three-zone aeration basin, a post aeration anoxic zone, a re-aeration basin, and a final clarifier prior to discharging to a neighboring wastewater treatment plant. It was determined that this plant could meet anticipated water quality based discharge limits by adding an anoxic zone upstream of aeration and recycle mixed liquor suspended solids (MLSS) back from the downstream end of aeration to enhance ammonia removal. However, the Corporation has higher standards in keeping with its goal of being known as a good environmental steward. Specifically, the new wastewater treatment plant was expected to meet discharge limits of 17 mg/L for BOD5 and 10 mg/L for total nitrogen; which could not be attained with this minor modification alone.

MBR Channels

MBR Channels

SOLUTION

Mark Cramer, P.E., now with FOX Engineering, was retained in 2008 to develop a Facilities Plan and consider potential design alternatives. After significant planning and a piloting period, membrane bioreactor (MBR) technology was determined to be the most effective means to achieving corporate effluent quality goals. To convert the treatment plant from a plug flow reactor to an MBR plant a preaeration anoxic zone was added and the existing reaeration basin was converted to three MBR channels and a sludge overflow channel. MLSS was to be recycled back from the third aeration zone, along with sludge recycled from the sludge overflow channel. One of the primary factors making MBR technology so effective is the ability to push higher concentrations of solids in the MLSS. However, increasing the MLSS concentration to 10,000 mg/L also depresses air transfer within the aeration zones. Consequently, the number of diffusers in aeration was increased substantially as well as adding an additional blower for this purpose. A separate building was constructed to house the pumps, chemical skids, and CIP equipment dedicated to the MBR system. The existing final clarifier was rendered moot by the MBR system, but was retained as an emergency sludge storage facility. Finally, a 4,000 ft. HDPE line was installed to convey effluent to an outfall structure constructed on the receiving stream to the north.

During the design and permitting process it was determined that this project would be subject to the new antidegradation rules that were adopted by the State in 2010 and under review by the EPA. Consequently, an Antidegradation Alternatives Analysis was prepared and became the first project to be approved under the new rules in the fall of 2010. The wastewater construction permit was attained in late 2010 and construction of the wastewater treatment plant commenced immediately. The plant began discharging to the river in late 2012.

OUTCOME

The MBR plant exceeded expectations with average BOD5 removals of 99.8 percent, TSS removals of 99.5 percent, and ammonia removals of 99.4 percent.

In 2014, FOX was hired to assist the owner in expanding the MBR plant. The new plant is generally a mirror of the treatment facility constructed in 2012. The Phase 2 expansion currently under construction entails doubling the tank capacity and adding sufficient equipment to increase the design capacity by 167 percent. Phase 3, at some future date, will add the remaining equipment to double current design capacity.

MBR prior to activation crop

MBR prior to activation

ONGOING

FOX continues to work with the industry on various projects that bring efficiency and improved performance to the industry.