Five aerobic treatment units where installed to treat milkhouse wastewater. In the fall of 2002, two Biomicrobics FAST® systems and two NCS Nibbler® systems were installed at four dairy farms with between 50 to 125 cows. In the summer of 2003, a Pirana® unit was installed at a dairy milking 50 cows. The FAST® and Nibbler® units were designed with the surface discharge goal of 25 mg/L biochemical oxygen demand (BOD 5) while the target goal for Pirana® installation was a BOD 5 of 175 mg/L to be discharged through a drip distribution field. All of the systems included a primary treatment septic tank. System performance, design, management and economic aspects are being evaluated. Water flow data was collected on the five farms for over one year with water flow rates ranging from 636 to 2063 liters/day (L/d) (168 - 545 gallons per day (gpd)) or from 11.0 to 33.7 L/d/cow (3.1 - 8.9 gpd/cow). After primary treatment in a septic tank, effluent data has shown an averaged range of BOD 5 of 489- 3115 mg/L, chemical oxygen demand (COD) of 690-5080 mg/L, total suspended solids (TSS) of 218-1293 mg/L and Fats, Oils and Grease (FOG) of 89-1196 mg/L. The aerobic treatment units discharge levels for BODs, COD, TSS, and FOG ranged from a unit average value of 131-1584 mg/L, 256-2424 mg/L, 89-641 mg/L, and 12-267 mg/L, respectively. Equipment and installation cost ranged from $11,000 to $14,500. Challenges have arisen with higher than expected organic loading.