Anaerobic Digestion

Unprocessed cow manure, a renewable resource, as well as food waste/grease trap waste are collected in a receiving pit at the digester site. The raw manure from the dairy and food waste from local food processors is mixed and heated to a temperature of 100 F. In the second stage of the anaerobic digester vessel, the methanogenic bacteria convert the volatile fatty acids into biogas, which consists primarily of methane (CH4, which is the same as natural gas) and CO2.

Evaluation of Co-Digestion

For a technical "Research Article" by the Department of Biological Systems Engineering, Washington State University, Pullman, and Michigan State University, East Lansing, describing how anaerobic digesters work, [click here]

Clean Renewable Energy

The methane biogas is collected and utilized for fuel in the combined heat and power genset. This genset is a commercially available, natural gas-fueled reciprocating engine modified to burn biogas. Electricity produced is sold to the local utility and utilized on the farm as a substitute for currently purchased power. Heat from a heat recovery system on the genset is used to heat the digester and excess hot water from the system is available to heat various dairy locations.

Utilization of Digested Solids

The digested manure and food waste is pumped from the effluent pit at the end of the anaerobic digester vessel to a solids separator. The mechanical separator separates the effluent digested waste stream into solid and liquid fractions. The solids are dewatered to approximately a 25% to 30% solid material. The separated solids, having the same odor and pathogen reduction characteristics as the liquid stream, are utilized by the dairy for animal bedding replacement. Utilization of the separated solids for bedding typically comprises 50-60% of the generated separated solids from a typical dairy. The residual 40-50% of non-utilized separated solids is sold to other dairies for bedding purposes, or to after-markets, such as nurseries and retailers, for soil amendment material.

Liquid Fertilizers

The liquid from the separator, now with the majority of the large solids removed, flows into the dairy's storage lagoon. A large advantage of the effluent from the anaerobic digester is that the nitrogen is converted to a more readily available form for the plant to make use of. Another benefit is the reduction of pathogens. With additional treatment, the amount of nitrogen and phosphorus may be further reduced.

Technical Details of our Digester

Our Anaerobic Digester System is a fully developed, proven, and patented digester design by DVO, Inc. Due to the combination of Andgar Corporation's diverse construction and project management experience with DVO, we have a strong team and dependable accountability. For a more detailed description of this technology visit Andgar Digesters.