Anaerobic digestion

Anaerobic digestion of liquid waste streams and sludges is a widely used and well developed technology for use in the reduction of solids and nutrients. It has not, however, been viewed as a means for generating significant energy to offset the energy used to treat waste streams.

Methane in the form of biogas has long been seen as a byproduct of the digestion process waste treatment systems in general and has frequently been flared as a means of disposal. Use of digestion as a means for waste treatment in the meat and dairy industries is still limited but gaining popularity – most of the resulting waste is washed into lagoons or used as compost/fertilizer, releasing any produced biogas .  Many municipal wastewater treatment plants use some of their digester produced biogas as a heat source to maintain digester temperatures in mesothermic and philiothermic systems. Only recently has biogas been gaining attention as a possible energy source for generating electricity.

Existing Digestion Systems

The CASCADE system provides the potential to drastically increase the energy yield and nutrient reduction from any nutrient rich waste stream by selecting methanogenic, hydrogenic and electrogenic bacteria present in the given waste stream, culturing them and injecting the culture into the waste stream. The beauty of this idea is that it can be retrofitted quickly and relatively inexpensively to most existing digestion systems. Every waste stream is unique, therefore the CASCADE solution for each system will be custom tailored to the operating parameters and biological characteristics involved. Basic elements such as culture storage and metered pumping can be somewhat standardized. The majority of existing systems have some means of capturing and handling methane based biogas and these can be reconfigured to handle increased production. Gas treatment systems may have to be installed to strip the biogases of moisture, siloxanes, hydrogen sulfide and other undesirable elements. Utlimate use of the gas as an energy source will require a means to store the treated gas and convert it to heat or electricity on demand.

CCE is also in the process of developing a Microbial Fuel Cell (MFC) for the direct generation of dc electricity from the metabolic activity of CASCADE selected electrogenic bacteria. MFC’s may become a stand alone treatment/production technology, however at present we are developing the technology as a downstream add on the existing digestion systems where they will act as polishing filters and late stage energy extraction devices.

Specifically Designed Systems

CCE is working to identify digester designs that give the CASCADE selected cultures the best conditions for producing maximum energy and optimal treatment levels at the fastest rate. Our lab in Nanjing will provide us with the facilities to test, modify and retest the most promising technologies so that we can make the most of any nutrient rich waste stream.