Venturi Aeration, Inc.

Enzymes as Catalysts in Biological Reductions

OVERVIEW

The cells in all living organisms are chemical factories, however, only a few of the hundreds of compounds necessary for the operation of organisms are obtained from their diet. Most of the required compounds are synthesized within the cells, which means that the chemical reactions take place within the cells of the organism.

Nearly all of these synthesized reactions are catalyzed by enzymes, which are protein molecules that increase the rates of the chemical reactions within the cells of the organism without themselves undergoing any change. Without enzymes, organic life forms would not be possible.

Like all catalysts, enzymes do not change the position of equilibrium; i.e. enzymes cannot make a reaction take place that would not take place without them. What they do is increase the rate; they cause the reactions to take place faster. As catalysts,enzymes are remarkable in two respects:

1. They are extremely effective, increasing reaction rates by anywhere from 10⁹ to 10 ²⁰ times, and
2. They are extremely specific.

Every organism has many enzymes—more than 3000 in a single cell. Presumably, each chemical reaction has one enzyme that catalyzes it. This means that enzymes are very specific, each one speeding up only one reaction or class of reactions. For example, the enzyme urease catalyzes only the hydrolysis of urea and not that of other amides. Digestive enzymes, which also split proteins, are located within the organism’s digestive system.

Enzymes are classified into six major groups according to the type of reaction they catalyze:

1. Oxidoreductases: catalyze oxidations and reductions.
2. Transferases: catalyze the transfer of a group of atoms, such as CH₃, CH₃CO, or NH₂ from one molecule to another.
3. Hydrolyases: catalyze hydrolysis reactions.
4. Lyases: catalyze the addition of a group to a double bond or the removal of a group to create a double bond.
5. Isomerases: catalyze isomerization reactions.
6. Ligases (or synthetases): catalyze the joining of two molecules.

FACTORS AFFECTING ENZYMATIC ACTIVITY

Enzyme activity is a measure of how much reaction rates are increased. Factors that affect enzyme activity are: concentration, temperature, and pH.

Concentration:

If we keep the concentration of the substrate (the compound on which the enzyme works to speed up the reaction) constant and increase the concentration of the enzyme, the rate increases linearly. That is, if the enzyme is doubled, the rate also doubles.

Temperature:

Temperature affects enzyme activity because it changes the three-dimensional structure of the enzyme. In uncatalyzed reactions, the rate of activity usually increases as the temperature increases. The effect of temperature on enzyme-catalyzed reactions is different. When we start at a low temperature, an increase in temperature first causes an increase in reaction rate. Once an optimum temperature is reached, the substrate may then not fit properly onto the changed enzyme surface. Therefore the rate of reaction begins to decrease.

pH:

Since the pH of its environment changes the conformation of a protein, we can anticipate effects similar to those observed when the temperature is changed. Each enzyme operates best at a certain pH. Once again, within a narrow pH range, changes in enzyme activity are reversible. However, at pH extremes (either acidic or basic), enzymes are denatured irreversibly, and enzyme activity cannot be restored by changing back to the optimal pH.

As with any biological process oxidation enhances the metabolic digestion of organisms to accelerate their consumption of nutrients and foods. This is true for humans as well as microorganisms. Living cells are in a dynamic state, which means that compounds are constantly being synthesized and then broken down into smaller fragments. Hundreds of reactions are taking place. It is the total sum of all the chemical reactions involved in maintaining the dynamic state of the individual cell that is called metabolism. Metabolic reactions are divided into two groups:

1. those in which molecules are broken down to provide the energy needed by the cell and
2. those that synthesize the compounds needed by the cell. Two terms here are important.

The process of breaking down molecules to supply energy is called catabolism.

The process of building up molecules (synthesis) is anabolism.

There are two parts to the common catabolic pathway. This first is the citric acid cycle and the second is the oxidative phosphorylation pathway or the respiratory chain. It is the citric acid cycle that breaks down carbon molecules, and the carbon atoms are released in the form of carbon dioxide (CO₂), and the hydrogen atoms and special compounds in the cell pick up electrons. These special compounds are reduced of their hydrogen ions (H⁺) which are expelled outside the cell wall of the microorganism. In their drive to get back into the cell, the H⁺ ions form the energy, and once back in the cell they combine with Oxygen that picked up the electrons and produced water (H₂O). The enzymes that catalyze the common catabolic pathways in microorganisms are located in the cell, however external ions and molecules can penetrate the outer wall of the cell membrane to aid in reactions.

The reduced coenzymes in the citric acid cycle are end products. They carry hydrogen ions and electrons and thus the potential to yield energy when they combine with oxygen to form water.

4H⁺ + 4e^- + O₂ « 2H₂O

This simple exothermic reaction is carried out in many steps, all of which involve enzymes.

The protons that enter the cell membrane combine with electrons transported through the electron transport chain and combine with oxygen to form water. The net result of the various processes is that the oxygen respired by an organism combine with four H+ ions and four electrons to give two water molecules. The four H+ ions and four electrons come from molecules produced in the citric acid cycle. The functions of oxygen, therefore, are:

1. to oxidize the special compounds so that all these molecules can go back and participate in the citric acid cycle, and
2. to provide energy for the conversion of other compounds.

What does all this means for the animal-derived lagoon wastes?

Waste products from cattle and hogs have become a major concern for the environmental regulators. Waste streams contain various sulfur and nitrogen-containing molecules that have olfactory nuisance characteristics, in high concentrations, present a condition that can cause respiratory distress in the animals as well as humans. E.g. hydrogen sulfide and –mercaptans in high enough concentrations can cause edema and even death. Additionally, if these substances leak or leach into groundwater they create unhealthy conditions for biota. Regulators have been responding to nuisance complaints from residents near animal farms and even though their homes where built in proximity to an already existing hog farm or cattle ranch they still complain to the regulators to control both odors and impact from runoff. The situation presents a unique problem to the farmer because adding costs to address environmental issues raises his cost and reduces his margin, but there is help that is available.

Quellz:

Now there is a product called Quellz which is the result of five years of intensive field research. It is a proprietary blend of enzymes that are derived from the various classes of enzymes to catalyze the degradation of animal waste products (digestive and urine) into benign form to mitigate negative impact on the environment. Quellz addresses issues of odors emanating from sulfur-based (e.g. hydrogen sulfide) and nitrogen-based (e.g. urea-ammonia) compounds by catalyzing natural biological reactions. Enzymatic catalytic reactions (as shown above) involve the exchange of hydrogen ions, metabolism of cells, and environmental issues (pH, temperature, and concentration). Quellz works in a broader range of temperature and to greater extremes in pH than other enzyme products. The Quellz formulation also is highly concentrated and works best when diluted—as a minimum—one gallon to 75,000 gallons.

Adding Quellz to lagoons will assist in odor control and in the molecular reduction of ammonia and sulfur-containing substances by stimulating native bacteria and boosting their metabolism for enhanced digestion of carbon and assimilation of the hydrogen in to a form other than ammonia. Further, Quellz has been added to Shrimp farming and Aquaculture lagoons as a waste products clarifier.

Bioremediation:

In two recent field studies Quellz has been added along with bacteria and nutrients used in the degradation of hydrocarbon contaminated groundwater. It has been demonstrated that it increases the standard plate count (SPC) of facultative bacteria by 1000 times in an aerobic treatment system, and has degraded MTBE—a component in reformulated gasoline—up to 6000 times faster than conventional bioremedial methods including ORC-type compounds.

Extended Aeration:

In order for the enzymatically enhanced oxidation to occur there needs to be an abundant supply of dissolved oxygen (DO) and a neutral pH. Increasing the levels of dissolved oxygen in various wastewaters and sludges can be achieved by using the Venturi Aerator. Not only is the venturi aerator important for supplying dissolved oxygen it also conditions the wastewater in several ways. First, as microbial activity increases there is a release of carbon dioxide as a byproduct of microbial digestion. As carbon dioxide levels increase the pH of the wastewater will decrease.

pH = 6.35 + log (alkalinity/carbon dioxide)

This means that the Venturi Aerator is a mechanical means of non-chemical pH control.

It was discussed above that enzymes and microbes like to operate in a relatively neutral pH range. Using the venturi aerator ensures that a steady state pH will be maintained because the venturi aerator will strip carbon dioxide (CO2) while simultaneously adding dissolved oxygen (DO). Secondly, the microbial digestive activities can be exothermic, that is they may give off heat. Using the Venturi Aerator will continually aspirate ambient air into the liquid thereby regulating temperature of the liquid.

When adding an enzymatic formulation, like Quellz, the Venturi Aerator will allow for “equalization and mixing.” This is important because Quellz works best when it has a high surface area and is adequately mixed. The first zone of mixing is within the venturi Aerator itself, and the second zone of mixing takes place from the force of the kinetic discharge of the “treated” liquid from the discharge nozzle of the Venturi Aerator. By designing the system so that liquids are pulled from the bottom of a lagoon or tank—the most anoxic zone—into the Venturi Aerator, the greatest amount of dissolved oxygen can occur and well as cooling an non-chemical pH control. Many “first order reactions” occur within the venturi aerator’s mixing and oxidizing zone.

Another important feature of the Venturi Aerator is its ability to effectively oxidize hydrogen sulfide and –mercaptans into benign olfactory forms. E.g. H2S is converted in soluble SO4 and the H-S bond in the mercaptans is also oxidized. This reaction is reversible as oxygen is consumed by the microbes, therefore it is important to size the aeration system to maintain “residual DO” levels to be >1.0 mg/l, the Venturi Aerator will induce up to 7.5 mg/l of DO under most environmental conditions.

The combination of adding supplementary enzymes with the features of extended venturi aeration are a winning combination in solving the problems attributed to sulfur and nitrogen-containing substances associated with various wastewater liquids.

REFERENCES

Bailey, J.E., and Ollis, D.F., Biochemical Engineering Fundamentals, McGraw-Hill, New York, 1977.

Bettelheim, F.A., and March, J., Introduction to Organic and Biochemistry, 2^nd Ed., Harcourt Brace, New York, 1984.

McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill, New York, 1962.

Sawyer, C. N., and McCarty, P.L., Chemistry for Environmental Engineering, 3^rd edition., McGraw-Hill, New York, 1978.