Proposed Anaerobic Digester For Diamond D Dairy

About the Dairy

Aligned Digester Cooperative proposes to build an anaerobic digester at the Diamond D Dairy to treat the manure and flushwater that is produced by the dairy and today is stored in an anaerobic lagoon. The Diamond D Dairy currently maintains a herd of 3,800 milking cows, 380 dry cows, and 1,500 heifers. The milking cows are housed in freestalls and the other animals in open corrals. Manure from the entire herd is currently flushed using recycled water. Today, the flushwater and manure is currently stored in an anaerobic lagoon and periodically land applied.

About the Anaerobic Digester

To build the anaerobic digester, Aligned Digesters will construct a new lagoon measuring approximately 1,357 feet long by 115 feet wide with 13.7 million gallons of capacity. The new lagoon will then be covered with a plastic cover and outfitted with a piping system to collect the biogas produced. This digester will reduce the volatile solids in the flushwater, on average, by 85%. Treated wastewater will flow to the existing lagoon, which will be used to store the treated manure until it can be land-applied.

The biogas formed in the anaerobic digester will be captured by the HDPE cover installed over the lagoon. This gas, which is more than 50% methane, will be treated to remove most of the carbon dioxide, water, and other impurities. The processed gas will then be compressed and sold to compressed natural gas (CNG) fueling stations to be used as a renewable fuel for vehicles. The anaerobic digester project will not increase the scale of current operations at the dairy. However, the project will produce many benefits to the dairy and surrounding area:

• Anaerobic digesters reduce the odor of manure by removing most of the biological oxygen demand
• The process of anaerobic digestion improves manure’s value as a fertilizer by converting the nitrogen in the manure into a form that is more readily used by plants
• Anaerobic digesters eliminate many of the pathogens and weed seeds found in manure
• Anaerobic digesters reduce emissions of methane, a powerful greenhouse gas

What Is an Anaerobic Digester?

Anaerobic digestion is a naturally occurring process where microorganisms break down organic material, such as the carbohydrates in cow manure, in the absence of oxygen. The process results in a mixture of methane, carbon dioxide, and other gases that we call biogas. Anaerobic digesters can process many different kinds of organic waste and can be built using many different designs. All digesters:

• Collect organic waste material and feed it into the system
• Provide a closed vessel where microorganisms can break down the material without oxygen/ul
• Collect the biogas produced by the process; and
• Discharge the digester material for re-use or further processing.

A covered lagoon digester, such as the one proposed for Diamond D Dairy, uses a lined earthen lagoon as the digester vessel, and includes a synthetic membrane cover to keep air out of the system and collect biogas. Manure is piped into the lagoon from the dairy after the sand and other non-digestible solids are mechanically separated for composting. Digested manure (effluent) is pumped out of the digester into a storage lagoon until it can be applied to land as natural fertilizer.

Biogas collected from the covered lagoon is filtered and treated to remove hydrogen sulfide. Then the biogas can be used as a fuel to power an electric generator, or further processed for other applications such as making compressed natural gas to fuel vehicles. Biogas from anaerobic digesters is 100% renewable, providing a sustainable source of energy for decades to come.