Electrolytically-enhanced anaerobic digestion (eAD) for high yield biogas production (L-12143)

Biogas generation by anaerobic digestion (AD) of biodegradable waste is increasingly being viewed as a viable renewable energy source. However, the efficiency of biogas production is currently limited by a number of factors including the slow breakdown of complex organic waste and the presence of carbon dioxide and hydrogen sulfide byproducts in the biogas. These latter two components must be removed from the biogas before it can be used as fuel. These limitations are largely overcome by the incorporation of water electrolysis into the AD process, which enables a higher yield of biogas and greatly reduces the carbon dioxide and hydrogen sulfide. This enhanced process can be adapted to both new and existing anaerobic digesters, facilitating its implementation.

Applications

This electrolytically-enhanced biogas production process can be applied to AD waste management systems in general, including:

  • Wastewater & sewage treatment plants
  • Industrial waste (eg; food and forestry)
  • Agricultural and animal waste

Concept

Biogas produced by AD systems is rich in methane but usually contains substantial amounts of carbon dioxide (up to 50%) and small quantities of hydrogen sulfide (up to 1-3%). Although the amounts of hydrogen sulfide formed from sulfates in the feedstock are small, it is very toxic and negatively affects the microbial populations in the digester. This limits the rate of organic matter hydrolysis and thus biogas production. In addition, the biogas has to be refined to remove or greatly reduce both carbon dioxide and hydrogen sulfide if it is to be used as fuel.

Combining water electrolysis with anaerobic degradation of organic matter solves several issues facing biogas production, resulting in increased biogas quality, quantity and yield. The low power density used is sufficient to generate oxygen without harming microbial growth. The oxygen produced serves to oxidize hydrogen sulfide, effectively removing it from the biogas. The low oxygen levels also contribute to an increase in the rate of organic matter hydrolysis. Furthermore, hydrogen, the other electrolysis-generated reagent, reduces carbon dioxide into methane, resulting in an increased quantity and yield of higher quality biogas.

Benefits

Versatility

This process improvement can be applied to anaerobic digester systems in general, regardless of the nature or origin of the organic waste to be processed. It is ideally suited to systems dealing with more complex organic substrates where the normally slow anaerobic hydrolysis can be markedly enhanced by the low levels of oxygen produced by water electrolysis.

Ease of implementation

The electrolytic system can be incorporated into a new digester design or retrofitted to an existing unit in an external recirculating loop system. In addition, the cost of the electrodes themselves is limited since they can be made of carbon or stainless steel, avoiding the use of expensive noble metal catalysts.

Increased yield and quality of biogas

Both the oxygen and hydrogen produced by the electrolysis of water contribute to increased methane yield. Additionally, the proportion of carbon dioxide and hydrogen sulfide are greatly decreased, resulting in a higher quality biogas and reducing the need for expensive refining treatments.

Protection

Enhanced Production of Methane and Hydrogen from Organic Matter in an Anaerobic Reactor using Water Electrolysis (NRC no 12143).

Contact

Yves Quenneville
Telephone: 514-496-8507
Email: Yves.Quenneville@nrc-cnrc.gc.ca