Biological Augmentation or Bioaugmentation Technical Discussion
Bioremediation of Soil
In our experience, bioremediation is best accomplished with Biological Augmentation sometimes called Bioaugmentation. Biological augmentation is the addition of large numbers of specifically selected microbes grown in a production laboratory. In addition to biological augmentation, several physical and chemical parameters must be controlled in order to obtain optimal microbial growth and maximum degradation of soil contaminants.
The major factors that Custom Biologicals, Inc. (CustomBio) controls during biological augmentation are:
- Microbial population
- Nutrient concentration
- Oxygen supply
- Temperature and moisture content
- pH
Microbial Population
CustomBio has developed a synergistic group of microorganisms named Custom HC. The microorganisms digest both short and long chain hydrocarbons, heavy tarry types of oil and grease, coal tars, phenolic compounds chlorinated solvents and many other types of toxic chemicals.
The microbes in Custom HC are non-pathogenic and use the petroleum products or other chemicals in the soil for both a carbon source and an energy source. The convert the toxic chemicals to cell mass, carbon dioxide, and water.
With Bioaugmentation, a sufficient amount of Custom-HC is applied to the soil. Our studies have shown that this concentration insures that a sufficient population will be provided. It is not the intent to provide a ready-made population to immediately digest the contaminants, but rather to provide an inoculum that will insure rapid microbial growth. As the project progresses, the population of petrophilic microbes will show up to a 1000 fold increase as they digest the contaminants.
Tightly compacted soil may need additives to increase their permeability and the soil should be treated with either a shredding device or a vibrating screen to produce the smallest size particle possible.
In comparing Biological augmentation with natural degradation, the former greatly increases the rate of degradation. The microorganisms naturally present that degrade petroleum products are usually present only in the upper few inches of soil and in low concentrations. The dilution factor can be so large that it takes an excessively long time, if ever, to establish a working population of correct microorganisms.
Nutrient Concentrations
Nitrogen is needed for amino acid, purine and pyrimidine biosynthesis, and can be obtained by the microbes from either organic or inorganic sources. The most commonly used nitrogen sources in bioremediation are ammonia and nitrate. Many of the bacteria in Custom HC have two pathways for ammonia assimilation and which one is utilized depends on the ammonia concentration. We purposely keep the ammonia concentration high in order to allow the bacteria to use the most simple process.
When nitrate is utilizer as the nitrogen source, it is reduced to ammonia in a stepwise process. Nitrate is first reduce to nitrite by a molybdenum containing enzyme and then to ammonia. The average nitrogen level recommended is 50-100 mg/L and should be frequently monitored.
Phosphorus (in the form of phosphate) is utilized by microbes primarily to synthesize phospholipids and nucleic acids, RNA and DNA. A minimum of 50-100mg/L of phosphorus is recommended.
In addition to Nitrogen and phosphorus, a variety of minerals is universally required, such as potassium, calcium, magnesium, and iron. Many other elements are required only in trace amounts. These include zinc, copper, cobalt, manganese, and molybdenum. These metals function in enzymes or coenzymes.
Oxygen Supply
Utilization of aliphatic hydrocarbons by microorganisms is an aerobic process. The initial oxidation step of aliphatic hydrocarbons involves molecular oxygen as a reactant and one of the oxygen molecules is actually incorporated into the oxidized product.
The aromatic group of hydrocarbons can be viewed as derivatives of benzene. The breakdown of aromatic hydrocarbons involves the action of either oxygenases or mixed function oxygenases. These two reaction sequences both form catechol which can be degraded a number of ways leading to either acetyl CoA or TCA cycle intermediates. If the benzene ring contains added methyl groups or other constituents. these substituents may be attached before or after the ring is oxidized.
Very importantly, the oxygen concentration is the rate limiting factor in the biodegradation of petroleum based products. Microbial activity is most frequently limited by insufficient oxygen due to slow rates of diffusion into the interior layers of soil piles and the center of soil aggregates. Generally, the greater the mass of oxygen that can be distributed, the more rapid the cleanup. Effective application of biological augmentation can result in greatly accelerated cleanups.
Temperature and Moisture Control
The bacteria in Custom HC were all isolated from the soil and laboratory studies have shown that their optimal temperature for growth contaminant degradation is 28 degrees C. The temperature of the soil will be maintained as close to 28 as possible. Similar studies have shown that the soil moisture should be maintained at 15-25%.
pH
The microbes in Custom HC will achieve optimal results if the pH range is maintained between 6.5 and 8. Soils being treated using bioremediation should be monitored frequently and the pH should be manipulated to maintain soil within the optimal range.
Summary – Biological Bioaugmentation
Bioremediation of contaminated soils is best achieved using biological augmentation and Custom HC. For the most successful bioremediation, the oxygen and nutrient concentrations, as well as temperature and pH must be carefully controlled.
