High BOD, backup from filamentous bacteria growth overload, and bad odors at a wastewater treatment plant all signal that something is wrong — and encourage a quick solution. Rather than calling in a civil engineer to do a full plant redesign to keep up with the high treatment demand, biological treatments are opening up which provide a simple and cost-effective solution to handling heavy loads of organic material.

Biological treatment and natural attenuation treatment plant operators are already familiar with the natural biological processes that are used to degrade and remove organic waste substances from water during secondary treatment. Filter beds, lagoons, wetlands, activated sludge systems and membrane bioreactors all rely on natural biological treatment methods to help remove dissolved suspended solids from wastewater so the effluent can eventually be discharged into the environment as clean water.

Environments such as lagoons are a good example of biological treatment through natural attenuation (i.e., naturally occurring microorganisms treat contaminants as food). When the microorganisms sense this source of nearby “food,” they release enzymes that break the contaminants down into smaller particles, which can then be ingested and used for energy. The microbes release CO₂ and water back into the atmosphere as nontoxic byproducts.

The challenge of natural attenuation is that it can be a slow process. If the microbial population is not large enough to degrade the amount of contaminants in the environment, the result can be high BOD and bad odors. Sometimes this happens because of a drop in microorganisms through toxic shock, or because some other change in the environment disrupts the stability of the microorganism colony. It can also result from a sudden influx of extra contaminants.

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Microorganisms are natural enzyme factories that work to degrade contaminants and digest them as food. They release carbon dioxide and water as harmless byproducts.

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Bioaugmentation and biostimulation

In order to stabilize these imbalances and maintain a more efficient secondary treatment system, it is helpful for the treatment plant to conduct bioaugmentation and/or biostimulation to supplement the natural biological treatment process.

In bioaugmentation, the treatment plant adds additional microorganisms to the environment to speed up contaminant degradation. In biostimulation, nutrients are added to stimulate the growth and health of the microbial population — either those already present or those added as supplements. These strategies encourage a microbial population that is able to keep up with the amount of food (contaminants) present in the wastewater, leaving less organic material in the system to drive up biological oxygen demand and create discharge issues.

Matching the microorganism to the contaminant

The best bioaugmentation process is one in which the microorganisms are well matched to the contaminants and are complementary to each other. Every microorganism produces enzymes or a combination of enzymes that target a specific type of food the microbe can digest.

For example, microorganisms good at producing lipase will be good at degrading fatty contaminants. Microorganisms that specialize in amylase production will be good at degrading starches, and those that produce urease will be well suited to degrading urea into ammonia and carbon dioxide. Each microorganism has its own combination of specialty enzymes produced and should be chosen based on compatibility with the contaminants present in the wastewater treatment environment.

Having an appropriate blend of microorganisms is a more critical factor for effective treatment than applying a high dose of microorganisms to the wastewater. By combining the right organisms, a synergistic blend of microbes can be created for more efficient degradation that decreases BOD and COD, controls filamentous bacteria, and in the long run, decreases sludge.

A secondary priority is determining how many microbes to add. This can be discovered by testing the food/microorganism ratio. The ratio is calculated by multiplying BOD by influent flow rate and dividing by the volume of the reactor multiplied by reactor biomass. The ratio indicates how much waste breakdown is taking place. It must be kept within a narrow range to ensure efficient biodegradation.

Parameters for effective bioaugmentation

Once the most suitable bioremediation treatment has been determined, there are several other factors that should be monitored to ensure the best performance of the new microbial colony. In commercial bioremediation products, microbes are asleep until the presence of water and food wakes them up. It can take six hours to effectively activate the microbes, so mixing them with a small container of water is recommended in order to help the colony get established before adding them to the target wastewater treatment area.

Proper environmental conditions are also important. In order for microorganisms to work effectively, the wastewater environment must have a pH ranging from 5.5 to 9.5 and a temperature ranging from 10°C to 60°C (50°F - 140°F). Elements such as chlorine and heavy metals that could inhibit the performance of the microbes should be absent. Microorganisms in the wastewater must also have the right nutrients to ensure a healthy colony. This can be determined and adjusted according to the C:N:P (BOD₅: Total Nitrogen: Total Phosphate) ratio.

Short- and long-term treatment

A larger shock dose of microorganisms is usually needed to initially correct a system that has particularly high levels of BOD, odor or filamentous bacteria. Once these problems are under control, they can be prevented from happening again by applying a maintenance dose of microorganisms on a regular basis — usually once a week.

In the long run, regular bioaugmentation also reduces the amount of sludge in a lagoon system. This translates into cost savings, for example, where hauling of sludge every decade costs hundreds of thousands of dollars. If a treatment plant has the foresight to make a much smaller yearly investment in bioremediation, the long-term cost of sludge removal will drop substantially.

In the end, long- and short-term effects of bioremediation are significant and natural. Considering these benefits, could it be time to “bug” your system?

For more information on bioaugmentation, visit www.bionetix-international.com. 

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About the authors:
Diana Di Marco is Technical Sales Director at Bionetix International. She can be reached at ddmarco@bionetix.ca. Julie Holmquist is Content Writer at Cortec Corporation. She can be reached at jholmquist@cortecvci.com.