Process Water Treatment Improvements

Arbre Farms

Arbre Farms updated its process water system to meet new MDEQ standards for BOD loading on agricultural fields. The new system has a better screening unit, a 4.5 acre lagoon with an innovative HDPE liner, and an efficient pumping system to reduce energy use.


Arbre Farms updated its process water system to meet new MDEQ standards for BOD loading on agricultural fields. The new system has a better screening unit, a 4.5 acre lagoon with an innovative HDPE liner, and an efficient pumping system to reduce energy use.

Background

Arbre Farms processes, freezes, and packages Michigan-grown fruits and vegetables. This process creates up to 3.8 million gallons per day of wash water, which carries large concentrations of organic materials and has a high BOD.

Arbre Farms formerly treated this water by filtering out some solids, storing it in a 1 million-gallon tank, and using it for irrigation on nearby crop fields. When the ground was frozen in winter, this water would pond on the surface or run off into the local stormwater system.

In 2010, the MDEQ instituted new rules regulating the amount of BOD that could be applied with irrigation water. The limit was set at 50 pounds of BOD per acre per day. Arbre Farms could not obtain a new MDEQ discharge permit without making changes to its system.

System Design

Arbre Farms hired Prein&Newhof and Production Solutions, LLC to design a system that would reduce its high BOD before irrigation and store process water between November 1 and April 1.

The improved system has four components:

  • Screening Unit – Process water flows through a new rotating screening unit capable of processing 3,000 gallons per minute. At 0.02 inches, the screen openings are four times smaller than the previous screens, producing significantly cleaner effluent. The screen is self-cleaning, using water from the lagoon. The unit housed in a new building designed to accommodate two screen, allowing for system expansion.
  • Ground Storage Tank – Filtered water flows into the existing 1-million-gallon tank, which was retrofitted with a wier box and discharge pipe near its top. This keeps water in the tank calm and allows larger particles to settle before water is used for irrigation or sent to the lagoon.
  • Lagoon – In the winter, water can be diverted to a 4.5-acre, 21-foot-deep concrete lagoon where it’s stored and treated anaerobically, reducing BOC loading by 50-70%. The lagoon can hold up to 22 million gallons, so Arbre Farms no longer has to irrigate frozen fields in the winter. The lagoon is lined with an double-layered HDPE liner, the first of its kind to be accepted by the MDEQ. Instruments monitor the area between the two liner walls to warn operators if the outer liner is leaking.
  • Pumping & Irrigation – P&N modified the pumping facility, allowing it to pump from either the ground storage tank or the lagoon. P&N also developing an operating plan to optimize pump efficiencies and electricity usage.
Challenges & Solutions

P&N designed and staged construction so it would not interfere with Arbre’s daily operations.

While building the new lagoon, Hallack Contracting used GPS-equipped grading equipment to properly place the controlled embankment fill. Hallack’s equipment synchronized digitally with P&N’s construction plans, saving a great deal of time during construction while maintaining excellent grade accuracy.

Sustainability

To keep electrical use low, the new process takes advantage of gravity wherever possible. P&N also devised an operating scheme that detailed how to sequence pump and disposal field use for optimal efficiency.

The screening unit is self-cleaning with a constant spray wash system that uses 130 gallons of water per minute. To meet this high demand, water is pumped from the lagoon, through a strainer that removes all particles larger than 400 microns, and to the screening unit. This was the only pump added to the treatment system by this project.

Contact

Matt Hulst, PE, (231) 798-0101

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