Teru Talk Newsletter

Volume IV, Issue 1, January 6, 2014 

Teru Talk by Michael Theroux (pronounced "Terú")  

"If it's wet, keep it wet. If it's dry, keep it dry." That was the sage advice handed out by the EPA's long-standing AgStar program a number of years ago, providing core guidance for selection of technologies to convert waste liabilities to assets. That simple quip has held true a large part of the time for selection of the core waste conversion systems and methods. The concept combines a whole lot of science-based common sense - but don't bet the farm on it. Too much has changed; too many new approaches are proving the old ways no longer hold water.

In the last decade the variety of available systems for waste conversion and the number of functional reference projects to surface globally have both increased dramatically. Industrial and governmental would-be project owners have gone from a paucity of possible solutions to an overwhelming overload of detailed systems and methods information. Nay-sayers can always point to the failures, and there have been far more losses than gains. Clear-cut choices are not easily achieved and every waste conversion pathways is fraught with hazards. Accurate information remains awfully hard to come by (except of course in Teru Talk).

Waste can be deconstructed to constituent parts in any number of ways, using thermal energy, microbial digestion, chemical decomposition and kinetic force either alone or in combination. We whack something with enough energy, it tends to come apart. How much value we get out of any particular waste conversion process compared to the cost of the energy we use to break the bonds and separate the components largely determines the overall economics of the process. If you have to dry feedstock slurry before conversion, you expend energy twice when compared to "keeping it wet." If you need to turn dry biomass into slurry before wet fermentation, well, it would stand to reason you've just paid for two steps when one "keep it dry" stage might have been more cost-effective.

OK, all right - it's not that simple and every rule was only concocted to be broken. If "wet to wet, dry to dry" always held true, we wouldn't be seeing such success in use of feedstock pre-treatment, or so many new pre-treatment approaches entering the marketplace. Integrated use of engine heat for "tump drying" has become standard practice; busting woody biomass into a wood-sugar soup means a far greater range of feedstock has now become available. Process efficiency increases are to be garnered wherever more energy out is generated than energy put into the works, and incremental improvements add up over time.

It's all a balancing act, and engineering science provides ways to assess both the mass and the energy balance. We know that myriad conversion machines run; now let's tend to the individual systems and process trains, seeking mass and energy balance efficiencies, and see if we can make it all more cost-effective.