Custom Biologicals, Inc.

TECHNICAL DISCUSSION #8

BioaugmentedComposting System

Biological considerations

In our experience, modern composting is best accomplished with Bioaugmentation, the timely addition of large numbers of selected microorganisms grown in the production laboratory. As a result of these studies, Custom Biologicals, Inc. has developed the product Custom SP #134.

In the natural process of composting, microorganisms break down organic matter and produce carbon dioxide, water, heat, and humus, the relatively stable organic end product. Under optimal conditions, this natural composting proceeds through three phases: 1) the mesophilic, or moderate-temperature phase, which lasts for a couple of days, 2) the thermophilic, or high-temperature phase, which can last from a few days to several months, and finally, 3) a several-month cooling and maturation phase.

Different communities of microorganisms predominate during the various composting phases. Initial decomposition is carried out by mesophilic microorganisms, which rapidly break down the soluble, readily degradable compounds. The heat they produce causes the compost temperature to rapidly rise.

As the temperature rises above about 40°C, the mesophilic microorganisms become less competitive and are slowly replaced by others that are thermophilic, or heat loving. At temperatures of 55°C and above, many microorganisms that are human or plant pathogens are destroyed. Because temperatures over about 65°C kill many forms of microbes and limit the rate of decomposition, compost managers use aeration and mixing to keep the temperature below this point.

During the thermophilic phase, high temperatures accelerate the breakdown of proteins, fats, and complex carbohydrates like cellulose and hemicellulose, the major structural molecules in plants. As the supply of these high-energy compounds becomes exhausted, the compost temperature gradually decreases and mesophilic microorganisms once again slowly take over for the final phase of "curing" or maturation of the remaining organic matter.

By its nature the process of natural composting is very inefficient and variable as it depends upon the sequential growth of several different microbial communities.   Long time periods are necessary for the correct population to grow from very small natural inoculums of organisms.  Until the proper concentration of the proper organisms is reached, very little composting activity is occurring.

The Custom Biologicals, Inc. Bioaugmented Composting System eliminates these long periods of lag time and inactivity as a very large population of selected microorganisms from each microbial community is added at the proper time and in the proper sequence using Custom SP #134.

Custom Biologicals, Inc., considers the following factors in its composting system:

1)                  Microbial population: All of the microorganisms in Custom SP#134 were selected for their ability to produce large amounts of extra cellular enzymes that degrade proteins, starches, lipids, and cellulose,

2)                  Nutrient concentrations:  A carbon: nitrogen ratio of 30:1 is maintained in the compost system. Phosphate and a variety of minerals are required and if the concentration is deficient these compounds are added.

3)                  Oxygen supply: Composting is an aerobic process and oxygen can be supplied on an as needed basis by turning the material or more efficiently by aerating the system.

4)                  Temperature should be controlled during the various phases in the range of 90 -140 degrees F.

5)                  Moisture content: should be controlled in the range of 40-60%

6)                  pH should be monitored closely

Monitoring and controlling the composting process in this manner realize a significant savings in time. In addition, a more standardized and safer compost product is produced.

Mechanical considerations

Custom Biologicals, Inc. believes that, if the biological aspects of composting are controlled as described above, the physical aspects can be easily varied on a site-specific basis. In addition to biological decomposition, three tasks are central to the design of a modern composting system: 1) collection, 2) contaminant separation, 3) sizing and mixing. The first of the preprocessing tasks, collection, largely determines the processing requirements of the remaining tasks because they must be tailored to the characteristics of the incoming waste. Separation processes at the composting facility generate recyclable and reject streams, usually at several places in the process. Size reduction increases the surface area of the organic wastes, enhancing opportunities for biological activity, while mixing ensures that nutrients, moisture and oxygen are adequate throughout the material. Many options for accomplishing these tasks are available, again on a site-specific basis.