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AN ANAEROBIC BIOLOGICAL WASTE TREATMENT SYSTEM IS THE BEST AVENUE FOR A SUSTAINABLE DAIRY
MADISON, Wisconsin (October 4, 2007) – As environmental restrictions continue to tighten in the dairy industry, many producers are going to be faced with compliance levels that will seriously challenge the capabilities of their existing manure and wastewater treatment facilities, said Dr. Chuzhao Lin, Director of Research at Pro-Act Microbial, Warren, Rhode Island. Dr. Lin spoke at a media breakfast sponsored by Engineered Storage Products Company held Thursday at the 2007 World Dairy Expo in Madison, Wisconsin.
“There are regulatory, environmental, health and aesthetic reasons to treat animal waste,” said Dr. Lin. “As dairies become bigger, and communities grow into their backyard, there are greater concerns about odor, water quality and pathogens that become more difficult to address as dairies expand and produce more waste.”
Dr. Lin’s presentation outlined an “ideal” biotreatment system that deals with all these issues. Physical removal of solids through a solids separator is an important first step, but not enough – biological waste treatment is “Mother Nature’s way of cheaply dealing with biodegradable organics that produce odor,” she said. “Our goal is to remove solids, treat biodegradable organics, eliminate pathogens and remove nutrients for later use, ending up with good quality irrigation water so no nitrogen or phosphorus enters our streams.”
There are two major types of biological waste treatment – aerobic (bacteria needs oxygen to grow), and anaerobic (bacteria will not grow in the presence of oxygen). Aerobic treatment is sufficient for municipal wastewater treatment, but anaerobic is necessary to handle the significantly higher levels of organic matters found in dairy manure.
“Dairy waste is much more concentrated and harder to degrade,” Dr. Lin said. “Only about a third of the organic matter in the dairy manure can be digested in a short period of time. There are also high concentrations of nitrogen and phosphorus in the manure.”
The ideal dairy waste treatment system relies on anaerobic digestion in a multi-step process, Dr. Lin said. The biotreatment facility she presented (see graphic) is designed for a 2,000 cow dairy:
1. Manure is first flushed with biologically active lagoon water to an in-ground day tank (manure from scrape barns enters the day tank, and mixed in with an appropriate amount of lagoon water to approximate a flush system).
2. A separator removes solids containing nitrogen and phosphorus. The solids can be used for bedding after further treatment or turned into compost.
3. Effluent is pumped to an above-ground tank active with anaerobic microbes for digestion. The tank is covered to collect the methane by-product and to prevent this potent greenhouse gas from escaping into the atmosphere. The captured biogas is used to power a boiler that heats the contents of the tank to benefit the microbes. Sludge in the bottom of the tank is removed.
4. Top water from this tank is pumped to a second above-ground processing tank. This tank is not covered. A floating diffuser provides oxygen to the top layer to grow an aerobic odor cap that prevents odor from escaping; while anaerobic microbes digest manure wastes in the bottom layer. Bottom sludge is also removed here.
5. Finally, top water is pumped to a lagoon, outfitted with flush and irrigation pumps. By this stage, the water has low level nutrients. The lagoon also has a floating air diffuser that helps to produce a bacterial odor cap. Augmented microbial mix is added to the lagoon -- the microbes will circulate around the manure system through flushing to stabilize all of the anaerobic process throughout the system, and to help the performance of the solids separator.
The system meets dairy producers’ requirements of being economical and easy to use and maintain, according to Dr. Lin, or it wouldn’t be adopted and used. An advantage of this system is that it is possible to proceed in stages. For instance, a dairy can use microbes and a diffuser to tackle odor, solids, and nutrients first. Tanks can be added at a later time.
“Most larger dairies already have a separator and lagoon system,” Dr. Lin added. “We are suggesting adding one, possibly two above-ground tanks such as Slurrystores to complete the system and get the desired results.”
Anaerobic biotreatment requires less energy and feeder nutrients and produces methane for energy but much less biological sludge. However, starting an anaerobic biotreatment facility requires patience.
“It can take months to get started,” Dr. Lin warned. “Many producers take starter material from an anaerobic digester that is already working to reduce startup time to a few weeks.”
The system she recommends addresses the potential for odor and formation of corrosive gases, either physically by covering the tank, or by forming the biological odor cap, or both. By stabilizing the anaerobic treatment system, less hydrogen sulfide is produced. Using a solids separator to take out recalcitrant material prior to anaerobic digestion, allows only the relatively easier digested materials into the processing tank to circumvent the hydrolysis bottleneck and reduce the digestion time needed. Dairies that flush their barns will be able to benefit from the ideal treatment system.
Anaerobic systems are also temperature sensitive and slow down greatly in cold weather. In her system, methane-fueled boilers keep the tank warm enough so the microbes continue to thrive, even in northern climes.
It’s not possible for anaerobic digestion to remove nitrogen and phosphorus biologically, thus the need for physical removal in the separator first to capture these nutrients as solids before anaerobic treatment begins, Dr. Lin added.
Finally, anaerobic biotreatment can be fussy, Dr. Lin said. Anaerobic systems are prone to “upsets” and need a great amount of attention as compared to aerobic systems, so dairy producers unnecessarily abandon them.
“That is the role of the augmented microbes, to keep the anaerobic system active and stable,” Dr. Lin explained. “If we address traditional, well-known challenges of anaerobic biotreatment, we can maintain a wonderful dairy waste treatment system that captures nutrients for fertilization while keeping regulators satisfied, streams clear, odor contained and communities more accepting of our growing dairy operations.”
The Ideal Treatment System
Dr. Chuzhao Lin, Pro-Act Microbial
