A combined composting operation benefits both Kearney, Nebraska and Double M Farms Inc. By mixing sludge cake from the city’s wastewater treatment plant with aerated manure from the farm’s feeding pens, Double M Farms reduces cattle stress, improves animal weight gain, and increases corn yields while helping the city cut material handling costs.
This partnership began in 1982 when Kearney was wasting sewage sludge at an abandoned air base. Area farmers were reluctant to use the untreated sludge on their fields due to the possibility of pathogens. Double M Farms was already composting manure but had difficulty removing the bottom layers from their feeding pens. This resulted in wet and muddy feedlots that negatively impacted cattle weight gain.
Professor Leon Chesnin suggested composting the sludge with the farm’s manure, a process that would destroy most viruses and pathogens. Kearney’s sludge had to be dried from 80-90% moisture to at least 60% moisture to be efficiently composted, and Double M’s manure was compatible and relatively dry.
To facilitate this, the city provided Double M Farms with $35,000 per year for the first 5 years and $24,000 per year after that to cover the cost of processing all of the city’s domestic sludge. Double M used the money to purchase a Brown Bear auger tractor for mixing and handling the compost. The Brown Bear had no trouble mixing all of the manure in the farm’s 14 pens, allowing them to maintain their desired 3,000 feeders per year.
The composting process involves mixing the manure and sludge on a 4-acre site on the farm property. The Brown Bear mixes and windrows the combined materials. The windrows are turned regularly to increase air content, speed up aerobic digestion, and eradicate viruses, pathogens, and weed seeds. The moisture content gradually reduces to 20% or less.
Once digestion is complete, the finished compost is stockpiled until it’s ready to be spread on Double M Farm’s fields. The application rate is approximately 3 tons per acre on their 3,000 acres of corn.
The results of this composting operation have been outstanding:
- The city of Kearney solved their sludge disposal problem with low and fixed costs, simplified budgeting, and no need for additional labor, machinery, or bulking agents.
- Soil and laboratory tests show no accumulation or effect of heavy metals in the receiving land or crops. The finished compost meets unrestricted 503 standards.
- Double M Farms maintained their cattle feeding program of 4,500 head per year.
- Soil organic content in the farm’s fields more than doubled.
- Water retention capacity improved substantially, reducing irrigation needs and pumping expenses.
- Composting makes all nutrients available to corn seedlings immediately, whereas raw manure has a one-year lag.
- Alternating years of compost application reduced salt and heavy metal accumulation to below EPA allowances.
- In-pen augering reduces manure moisture content, requiring fewer truckloads and less expense to move the material.
- The Brown Bear is also used for snow removal, keeping feed bunks open and providing dry areas for cattle.
Overall, the combined composting operation has been a success for both the city of Kearney and Double M Farms. The city has a cost-effective and environmentally sound way to dispose of its sludge, while the farm benefits from increased soil fertility, improved water retention, and healthier livestock.
