From BioCycle Magazine
August 2000, Page 33

INNOVATIONS UPDATE
THE SEARCH FOR BETTER BUGS AND BETTER MOUSETRAPS
Approaches to composting and other organics recycling technologies that employ innovative vessels, procedures, equipment and microorganisms.
Robert Rynk

The organics recycling industry sees a constant stream of new ideas, products, mechanisms, and systems — each attempting to improve the way organic residuals are handled, processed or turned into a value-added commodity. Some of these innovations seek to improve the process biology and biochemistry. Let’s call these “Better Bugs.” Others offer potential improvements to the physical, mechanical or combination of components that transform organic residuals. These fall in the category of “Better Mousetraps.”

Many of the Better Bugs and Mousetraps appear to hold promise while others are questionable. Nearly all of them are intriguing. It is interesting to observe how well these ideas work in practice or how a particular concept or product plays out in the marketplace — the ultimate proving ground. If even a few of the Better Bugs and Better Mousetraps are in fact better, then it is worth noting their comings and goings.

This article describes a selected cross section of some of the innovations that have come across my desk — as the technical editor of BioCycle — examples that I have found to be more interesting. They represent a snapshot of efforts to improve the state of the art, and suggest trends in the organics recycling industry. The Better Bugs and Better Mousetraps covered here primarily concern composting, but a few involve other organics recycling technologies. The article does not provide an assessment of the Better Bugs and Better Mousetraps covered, and it certainly does not intend any endorsement or criticism of them. Names of products and vendors are not directly mentioned.

BETTER BUGS

Ideas and products in the Better Bugs category attempt to affect the biological components and biochemistry of processes by altering the mix of microorganisms or enzymes present. After all, biology is the foundation of many, if not most, organics recycling systems.

Pyrophiles: The first example of Better Bugs involves pyrophilic organisms — bugs that can take the heat. This example is not actually a new product but the consequence of one. A relatively recent vertical silo-type in-vessel system is available that maintains the upper zone of the vessel at extremely high composting temperatures (160°F to 185°F or 70° to 85°C). These temperatures are well above the 140°F level considered the upper limit for healthy composting organisms.

However, the developers of this silo system suggest that this is advantageous, offering the following explanation: High temperatures enhance the decomposition of certain compounds, including fats, oils and waxes; the zone is inhabited by extreme-heat tolerant pyrophilic organisms; and these organisms contribute to the decomposition of the feedstocks. The pyrophilic zone is only a segment of the vessel. Like most silo-type reactors, a temperature gradient exists within the vessel. The coolest temperatures occur at the bottom where air is introduced and compost is removed. The highest temperatures are at the top where air exits and fresh feedstocks enter. Thus, after passing through the pyrophilic zone, materials are exposed to more conventional thermophilic temperatures and organisms as they move down the reactor.

Wood Workers: Woody materials are among the most abundant feedstocks and the most difficult to decompose. It simply takes a long time (more than a year) to transform woody feedstocks, with their lignin-bound carbon, into compost (not to be confused with raw wood mulch). In general, decomposing wood requires the help of fungi that can produce enzymes capable of degrading lignin. However, several companies are selling a special combination of microorganisms that reportedly turn woody materials into compost (or composted mulch) much faster then we are normally accustomed to waiting.

This set of bugs (most are bacteria in the Bacillus family) are promoted as having the ability to produce unique enzymes that are long lasting and particularly effective at breaking down carbon compounds. The explanation for their proficiency is that under stressed conditions, such as low oxygen levels, the selected bugs produce the desired enzymes. The enzymes make oxygen molecules available from the surrounding compounds when free oxygen from the air spaces is scarce.

While these microorganisms are purported to be more effective than the otherwise natural populations, they are not magical. It still takes on the order of two months to produce compost, and typical management practices are required, such as grinding wood to six-inches or minus, adding nitrogen (e.g. urea) and maintaining adequate moisture content. In addition, the solution of bugs plus water must be thoroughly mixed into the ground wood. A typical procedure is to grind, or double-grind, the wood feedstock and spray the bugs on the ground wood as it passes on the outlet conveyor. The ground wood is then stacked in passively aerated static piles to decompose until temperatures subside to near ambient levels. (Temperature monitoring also would be a good idea as the large pile size raises the possibility of spontaneous combustion.)

Several companies in various U.S. locations offer the same product, or offer their services using the product, as licensees of the product’s developer. Although these Better Bugs work on nearly any organic feedstock, the initial target applications appear to be yard trimmings, logging and landclearing debris, and other woody materials, in addition to bioremediation.

Composting Inoculants: Inoculants for composting are alive and kicking. Inoculation adds particular organisms at the start or during the process to make composting faster or less troublesome or to alter the compost product. The concept is not new. Based largely on research conducted over 30 years ago, current composting wisdom suggests that inoculants generally provide no advantage to the composting process. Both the feedstocks and the environment contain enough organisms to do the work just as fast and just as well, although exceptions occur with feedstocks, like food, that have been previously sterilized. At least, this is the conventional wisdom.

Despite convention, inoculation products for composting seem to be increasing and gaining interest. They are integral to several composting “philosophies,” including Advanced Composting Systems, Biodynamic Composting, Controlled Microbial Composting and Kyuesi Nature Farming. Furthermore, some credible composting facility operators say that they have observed differences when inoculants are used, although they may not consistently use them.

Given that research has shown no advantage, why are inoculants still being marketed and used? Proponents cite several possible reasons. First, the key research arguing against inoculation occurred over 30 years ago. In the meantime, proponents claim, better products and better ways of handling them have made inoculation more effective. In particular, turning machines that add water (with inoculants) while turning have improved distribution of the inoculated organisms plus improved conditions for their proliferation. There also is better guidance about composting recipes and conditions that sustain the inoculated organisms (e.g. including clay soil). Other proponents respond that the primary effect of inoculants is to improve the quality/characteristics of the compost product (e.g. texture, nutrient content, maturity), not the composting process. They argue that past research focused on the process and the product effects were neglected. Some advocates expect composting inoculants to become as well accepted as inoculants for farm silage, which also were once deemed unnecessary.

Even if composting inoculants have a positive effect, they certainly are not a requisite to producing good compost. Therefore, outside of the philosophical reasons for using inoculants, their prolonged use will depend on whether the perceived benefits are greater than the purchase and handling costs.

The more recent development concerning inoculation is adding specific organisms to compost, rather than the feedstocks. In most cases, compost is inoculated with specific beneficial organisms to improve its disease suppressive qualities, or make disease suppression more consistent. Once the compost cools to mesophilic temperatures and matures, it can serve as a carrier for disease suppressing microorganisms and also provides the organisms nutrients and a proper micro-environment.

Many of the added organisms are proprietary. Because of regulations that govern plant protection and microbial products, bringing inoculated compost to market takes time. Efforts to develop such products are continuing. They should emerge on the market within the next few years.

BETTER MOUSETRAPS

Better Mousetraps encompass products, practices, and systems that offer mechanical, chemical or structural innovations. They may include biological components but, unlike the Better Bugs, the innovations lie outside the biological processes. There are many Better Mousetraps promising superior, faster, or cheaper processing of organic residuals. Better Mousetraps are diverse and can be complicated. Some qualify as “black boxes” — systems that are somewhat mysterious because the supplier cannot or won’t reveal details of how they work. Therefore it is difficult to judge whether they are legitimate. The following examples are a small and selected sampling of current Better Mousetraps.

Micronized Compost: An example of a recent compost product innovation is micronized compost. It is a finely ground compost with a consistency similar to talcum powder. It is sold in bags, buckets and even jars. The small particle size of the compost makes it possible to carry and apply it with water. Thus, compost can be delivered through irrigation systems. The product also can be used to make compost teas at the application site, saving the cost of transporting water. Micronized compost has been called soluble compost, but it more likely a suspension of fine particles rather than a true solution, so periodic agitation is necessary.

The Better Mousetrap aspect of micronized compost is how it is made. The challenge is to grind compost to a small particle size without creating excessive heat that would kill the microorganisms. The manufacturing process is a guarded black box, but it appears that size reduction occurs with high velocity air movement, which also carries away heat. Suppliers of micronized compost cite laboratory tests showing that the product contains a greater density of microorganisms than the unprocessed product due to the increased surface area. Processing compost into micronized particles adds to the cost of the product, but it opens up new applications and market niches.

Pellets, Compost and Otherwise: While the micronizing process breaks compost particles apart to create a consistent product, pelletizing achieves uniform consistency by assembling small particles into larger ones. Because a consistent texture aids in transportation and application, pelletized compost is an emerging product, made possible by Better Mousetraps in forming pellets.

Various materials, from sawdust to biosolids, have been pelletized for many years, but the practice is relatively new for compost. Again, the challenge is to form compost pellets without heating the material to microbe-killing temperatures. The challenge is made more difficult because the compost must be reduced to small particles and dried before being formed into pellets. Typically, pellets are formed by extruding, compressing, rolling, tumbling or some other method of aggregating particles together, usually with the aid of a binder like molasses. Extruding and compressing create a lot of heat so some other form of aggregation, like tumbling, is more appropriate for forming compost pellets.

In addition to compost, there are other emerging pelletized soil fertility products derived from organic residues. In part, development is being driven by an overabundance of manure, poultry litter and biosolids. The Better Mousetraps associated with these products are in the various combinations of operations and processes used to manufacture them, including pelletizing, size reduction, drying, blending, and/or chemical stabilization.

Drums, Plus Boxes And Tunnels: For many years, rotating drum composting reactors have been used by backyard composters and at large mixed waste composting facilities. More recently, there has been a proliferation of rotating drum systems that suit applications between these extremes, such as farms and institutions that generate food residuals. At least four moderate-sized drum systems are available commercially. The drums represent Better Mousetraps because of their scale of operation and suitability to composting feedstocks at the point of generation. The development of these rotating drum systems follows the growing interest in composting manure and food residuals in contained environments that provide closer odor control.

Similarly, other contained composting systems, including aerated boxes and tunnels, also qualify as Better Mousetraps. Like drums, they contain the composting environment and its associated odors and make on-site composting of difficult feedstocks a possibility.

Most, but not all, rotating drum systems are characterized by very short retention times, typically less than five days. Some proponents claim this is sufficient time to produce usable compost, and some supply the results of maturity tests to support their claims. However, maturity tests can be misleading and much depends on how the compost is to be used. In general, such short retention times rarely produce a stable product suitable for general horticultural use. The composting periods typical of other aerated containers are longer than those associated with drums but often, they still fall short of producing mature compost. A secondary stage of composting or an extended curing phase is normally used. But, the drums and containers do produce a material that has been substantially decomposed and, therefore, has a much lower odor potential. Odor research has demonstrated that most odorous compounds are released early in the composting process. The material produced by a rotating drum or aerated container system can be finished by a less intensive and less expensive composting method like windrows or aerated piles with less risk of odors.

Oxygen Injection: One of the newer commercial rotating drum systems offers another innovative Better Mousetrap — oxygen injection. Rather than relying on air to deliver oxygen, this particular system, which is just entering the market, uses a pressure swing adsorption (PSA) oxygen generator to supply nearly pure oxygen to the materials in the reactor. Oxygen injection does not necessarily require a rotating drum, but an enclosed environmentally-controlled reactor is necessary to maintain the high oxygen atmosphere.

Does supplying nearly pure oxygen speed up the process? In some respects, the practice is doubtful. For forced aerated composting methods, it is well accepted that air flow rates are determined by the need for cooling rather than supplying oxygen to the process. In other words, if enough air is provided to keep the materials from overheating, there is more than enough oxygen available for aerobic decomposition. Thus, if the reactor must be cooled by exchanging air, injecting oxygen is unnecessary and the oxygen may be flushed out. It is possible that injecting oxygen has other effects such as improving diffusion of oxygen into the mass of materials (by increasing the oxygen gradient) or by altering the microbial population. In any case, the system’s developers say they are seeing faster composting rates plus other advantages in their pilot projects.

Passive Aeration: Recent developments in the composting industry suggest a renewed interest in passive aeration. Several new composting systems have chosen to supply air without fans, incorporating different twists that seek to make passive air exchange more reliable. Many innovations are evident in backyard and other small-scale applications, but even large-scale systems are trying Better Mousetraps for passive aeration. For instance, the vertical silo system discussed earlier is a passively aerated vessel. The high, pyrophilic temperatures at the top of the reactor increase the driving force for thermal convection. Another relatively new passively aerated silo system contains composting materials in a series of narrow wire mesh cages. Each cage is about four feet wide and separated from adjacent cages by an air channel. Therefore, material in the cages is at most only two feet from a fresh air source.

Although the Passively Aerated Windrow Systems (PAWS) of composting has been in use for many years, the basic approach continues to evolve. The original procedure used perforated pipes across the base of the windrow to draw in air by thermal convection. An adaptation of that approach replaced the pipes with a hollow concrete slab with slots on top to distribute air to the overlying materials. A more recent and simplifying modification eliminates the pipes and concrete slab, and relies only on a base of coarse organic materials, like wood chips, to distribute fresh air to the pile. This modification has been termed the Naturally Aerated Static Pile (NASP) method.

While passive aeration seems to be “hot,” the quest for Better Mousetraps is not limited to passive mechanisms. Innovations in forced aeration are occurring also — including better air distribution methods (plenums and orifices), improved control strategies and devices, cheaper valves, air recirculation and biofiltration. Similarly, Better Mousetraps continue to be developed for windrow turners and agitated beds with innovations that affect turning effectiveness, ease of transportation, the ability to add water, automated operation, and operator comfort.

Composting Appliances: In Japan, consumer products companies offer composting appliances intended to turn household food scraps, mixed with sawdust, into a usable soil amendment. Kitchen composting units have yet to rock the U.S. consumer market (although there is a food grinder promoted as a kitchen composting device). Some experts familiar with the Japanese composting appliances say these units are little more than grinders and dryers. After the processed mixture of food and sawdust becomes wet, it develops odors and flies just like raw food scraps. This is not surprising since converting food into something close to compost is difficult in the tight space and short time frame afforded by a household appliance. Nevertheless, the idea is appealing, given that home composting is the most cost-effective means of recycling household organic materials. Perhaps there is some merit to an appliance that can partially stabilize food and other household organic residues and make them less “icky” and less laborious to add to the backyard compost pile.

Many More Mousetraps: Many interesting attempts at creating Better Mousetraps for recycling organic residuals exist. A few additional examples include: aerobic fermentation (an oxymoron?) units that produce a stable soil amendment in a few days; a reactor that stabilizes or partially stabilizes manure using an electric current; steam treatment for preliminary breakdown and volume reduction; novel separation and size reduction techniques; and a variety of chemical treatment processes that stabilize or temporarily stabilize organic materials.

MORE TO COME

The Better Bugs and Better Mousetraps described in this article are interesting, but they are not necessarily better. It remains to be seen whether they will succeed technologically and economically.

The search for Better Bugs and Better Mousetraps is never exhausted. I have omitted many of the innovations that I am aware of and there are many more innovations of which I am unaware. Furthermore, because the search for Better Bugs and Better Mousetraps never stops, this article will be outdated soon. New Bugs and Mousetraps will emerge at conferences, in news releases, and in the pages of trade magazines and journals. Columns like BioCycle’s Industry News are a good place to hunt for them. We’ll be back in coming issues to report another round of developments.