Methane Digesters and Cogeneration - Producing Renewable Energy and Protecting the Environment

How Our Methane Digesters & Cogeneration Systems Work*

Methane digesters are anaerobic treatment lagoons covered with a gas-tight high-strength plastic (HDPE) fabric that produces methane-rich biogas through the anaerobic (without oxygen) digestion of manure or other agricultural waste. Our digester designs will work with either flush dairies, scrape dairies or other agricultural facilities.  In flush dairies, manure is flushed to a collection point where the large solids are removed and recycled.  The dairy manure wastewater is then sent in through the bottom of the digester were it is typically retained for a period of 40 to 60 days.  As the manure wastewater moves up in the digester, bacteria digest the waste and produce a methane rich gas known as biogas.  The biogas is typically about 60% to 80% methane or more. 


Anaerobic Digesters Work!

Strauss Anaerobic Digester

Background: A History of Biogas Production

Large Solids are Re-Usable as Fertilizer or Bedding

The large solids separated out can be dried or composted for use as fertilizer, as a soil amendment or as bedding. 

Digester Effluent Re-Usable as Liquid Fertilizer

After the dairy wastewater makes it way from the bottom of the digester to the top it will be ready for use as part of a comprehensive on-farm nutrient management system.  The digester effluent is a valuable natural liquid fertilizer containing nitrogen, phosphorous and potassium. 


Methane Digester/Cogeneration System Flow Diagram


Biogas Treatment & Monitoring for Engine/Microturbine Protection

Our exclusive biogas treatment and monitoring systems are designed to protect your engine or microturbine by improving the quality of the biogas (making it more like natural gas) and by monitoring the biogas fuel to prevent serious engine damage.  Untreated biogas contains  60% to 80% methane (CH4), carbon dioxide (CO2) and hydrogen sulphide (H2S).  Under certain circumstances, like frequent engine start and stops, relatively high moisture levels, etc. acids may be produced in the engine.  Presence of these acids, if unnoticed, will accelerate wear and possibly even corrode critical engine parts that could result in a major unplanned repair and downtime.

biogas treatment

Our system proactively treats the biogas to produce a fuel and engine/turbine pairing that should run for thousands of hours without any unplanned downtime.  In addition, we place electronic gas monitoring sensors throughout the gas treatment process leading up to the engine/turbine, so we are able to remotely monitor the methane, carbon dioxide, hydrogen sulphide, moisture level and biogas flow rates, etc. to identify potential problems early and reduce the possibly of an engine problem later.

Cogeneration - Electricity and Hot Water

Cogeneration refers to the simultaneous production of electricity from the generator and the production of heat from the engine or microturbine exhaust or cooling system.  Electricity is generally the primary output but the main byproduct, heat, can also be captured and used for food processing, water heating, steam production and many other uses.


Interconnection- Sending Electricity to the Grid or to the Farm

This portion of the system controls the flow of electricity either from "the Grid" to your farm or from your farm to "the Grid."  The electricity generator is connected to "the Grid" through a series of redundant electronic and manual interconnection relays, called switchgear, that is designed to prevent damage to "the Grid", the generator and to protect the safety of utility workers, farm workers and the general public.  Much effort goes into designing a safe and reliable switchgear and interconnection system.  We work with your utility provider to determine the best equipment to use based on your reliability needs,  blackout/brownout independence requirements (do you want your lights on even if "the Grid" goes out) and the unique characteristics of your Grid/utility connection and service capacity.  You will maintain a backup connection to the utility to provide electrical power to your farm for periods of system maintenance and to provide additional power during your peak usage typically during the summer.

We'll also help determine the right interconnection strategy (Rule 21, E-Bio Net Metering, Import/Export) for your operation and whether if you may be a candidate to sell your surplus power through our surplus power aggregation and wholesale program.  Through this program you may be able generate modest incremental revenue through the wholesale sale of your surplus power while you continue to generate per kilowatt hour tax credits.

Extended Warranty & Onsite Service, Repairs and Overhauls

We also offer optional extended "Repair or Replace" warranties and service agreements for up to three years where we'll perform all routine scheduled maintenance, perform major overhauls and provide all the parts, supplies and labor needed (the dairy/facility will be required to perform some very minor onsite inspections).  Systems that are located within the PG&E, SCE, or SDG&E service areas and that are applying for the $1500 per Kilowatt Self-Generation Rebate may choose to prepay some or all of the optional three year extended warranty or service agreement costs since these costs are eligible for reimbursement under the current Self-Generation rebate program.

Summary of Benefits of Methane Digesters and Cogeneration

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*Restrictions, limitations and eligibility requirements apply.  Offer may be withdrawn at any time.  Call for details and other terms and conditions.