by Becky Larson

The wastewater from washing dairy milking equipment and the milking parlor after each milking contains milk waste, animal waste and cleaning products. This water can be problematic for dairy farmers without a suitable disposal method. The high oxygen demand and large amounts of nutrients, fats, oils and grease could pose an environmental risk if not taken care of properly.

In Michigan, disposal of dairy milking facility washwater is typically limited to lagoon storage and land application. This lack of treatment and disposal options has dairy farmers looking for alternatives.

In 2007, researchers at MSU investigated two aerobic treatment units — Nayadic and Multi-Flo — installed at the MSU Dairy Teaching and Research Facility to determine if they were capable of treating the washwater from the farm’s 150 cows. The goal was to reduce contaminants to a level at which the water would be suitable for reuse.

Each treatment unit was preceded by a 500-gallon settling tank and a dosing tank to provide flow control. Recirculation tanks diluted washwater prior to treatment. Each unit provided suspended growth, continuous aeration and constant mixing to maintain an environment suitable for the aerobic biological activity required to degrade the pollutants.

The Multi-Flo unit included physical solid-liquid separation via 30 filter socks within the unit. The Nayadic unit relied on a gravity-driven solid-liquid separation. Solid-liquid separation was a key feature in the design because a high solids concentration was the most significant variable in treatment performance.

Both systems successfully decreased the amounts of excess nutrients, fats, oils and grease, and oxygen demand. The Multi-Flo system reduced these pollutants to concentrations suitable for reuse in a first-flush scenario at a flow rate of 50 gallons per day for up to a month before becoming clogged with solids and malfunctioning. Treatment was not consistent for the entire period, however, and the treatment flow rate was not sufficient to keep up with washwater production. Extensive monthly maintenance, including minor repairs and cleanouts, was required to keep the system functioning.

Further investigation is warranted for the Multi-Flo unit, which appears to be particularly well-suited to a smaller farm with more vigorous solids management or a more extensive solid-liquid separation pretreatment.

Aerobic treatment units have the capability to treat dairy washwater and the potential to provide another viable disposal option for farmers, but further research is needed.