Re: GAS-L: MSW and Biosolids

[CAVM@aol.com]

In a message dated 4/1/2002 6:10:48 PM Central Standard Time, kchisholm@ca.inter.net writes:


> Dear Neal
>  
> OK.... what about "digesting the dirties", to produce biogas for high grade energy production, i.e., electricity, and then use the waste heat from the engine system, and the waste heat from residue incineration to serve the district heating needs?
>  
> Kevin Chisholm


Kevin, First of all let me say that you probably know a lot more about this than I do.  

Digestion is very appropriate in many situations, especially where the goals are well defined and meet the digestion potential.  Usually I think of this with odor control issues, wet biomass, non-combustables, etc.  For example, we usually advocate that dry biomass be combusted and wet biomass be digested.

However, in the case of biosolids, digestion may have already occurred in the municipal sewer plant so that wouldn't be much of an option.  But in any case, disposal of the digested material would still be an issue.  Thermophilic digestion has a good effect on pathogens but still biosolids are not very marketable from a public perception view point.

MSW is another story.  The MRF is an expensive and inefficient way to isolate organics.  It doesn't take much broken glass to render compost unusable for commercial purposes.  The effluent from an MSW digester has no chance of being a fertilizer ingredient, sorted or not.  MSW digestion might best take place in the landfill as landfill gas.  There is a company in Colorado that manufactures a machine called a Ranger, I think.  They advocate grinding the MSW as it is placed into the landfill to encourage more effective methane production from the landfill.

In small dairy and hog operations we recommend small, fixed film digesters.  For larger operations and for sites with many farms near each other we encourage a cooperative built combustion unit such as the Bioten, for electricity and heat production.

A farmers market or food processing plant might be a great place for a digester on site to produce power from the food waste.  Then the digested material is an organic fertilizer under the new USDA regs, as I understand them.

Regards,

Neal Van Milligen
Kentucky Enrichment Inc.
CAVM@AOL.com