Bioaugmentation Aids Wastewater Systems
By Michael H. Foster, BS and Rob Whiteman, PhD
The practice of utilizing specific microorganisms to carry out chemical transformations has been applied in brewing, pharmaceutical and dairy industries. Microorganisms also are critical components in the treatment of municipal and industrial wastewaters.¹
In the treatment of wastewater, microorganisms (mainly bacteria) use the soluble organic matter in the waste stream as a food source. The bacteria consume the organic compounds and convert them into carbon dioxide, water and energy to produce new cells. Ultimately, the soluble pollutants are converted into insoluble biomass, which can be removed mechanically from the waste stream and sent to disposal.
Wastewater treatment plants come in many types and configurations, but this discussion will concentrate on aerobic treatment for industrial systems.
Two of the most common general categories of aerobic water treatment systems found in industrial plants are the once-through aerated lagoon system and the activated sludge system.
In aerobic treatment systems, aerobic bacteria utilize oxygen in the degradation of the organic compounds. Among these parameters must be controlled. Among these parameters, dissolved oxygen levels, pH and nutrient levels (ammonia and phosphorus) are the most critical. Classical control strategies have focused on monitoring and controlling the system parameters with little actual attention to the microorganisms themselves.
Bacteria are typically 1-2 um wide and 2-20 um long. Due to the small size, shape or morphology can be examined only by using a high power microscope (x1000) and staining techniques. The Gram Stain is the basic criteria used to categorize groups of bacteria as either gram positive of gram negative, indicating a fundamental variation in cell-wall structure. Bacteria also are categorized using other criteria such as:
* Use of oxygen in degrading organic matter (uses oxygen only – aerobic; can metabolize with or without oxygen – facultative; does not use oxygen – anaerobic);
* Use of carbon sources (organic – heterotrophic; carbon dioxide – autotrophic); and
* Optimum growth at different temperatures² (thermophiles – 55-75º C; mesophiles – 30-45º C; psychrophiles: obligate – 15-18º C, facultative – 25-30º C).
Most aerobic wastewater treatment systems operate in the temperature range of 10-40º C and therefore contain mainly mesophilic bacteria. These include both the gram positive types, such as Bacillus, and the gram negative types, such as Pseudomonas.
In addition, other microorganisms interact to transform organic matter into new biomass, carbon dioxide and water. Collectively, these microorganisms are called the biomass.
The biomass is the “workforce” of a waste treatment system. In a dynamic state of flux, different microbes are dying while others grow and become more dominant. Under adverse conditions such as toxic shock, certain bacterial populations may be reduced or eliminated, causing poor effluent quality. Examples of toxic shock would be black liquor spills in paper mills or a process upset in a chemical plant sending high levels of terpenes to the wastewater plant.
Historically, under such conditions, waste treatment plants have been slow to recover. National Pollution Discharge Elimination System (NPDES) permits often have been violated or the manufacturing process stopped to avoid the legal repercussions of NPDES permit violations.
The biological additives industry was started in the early 1960’s to address the problems of slow biomass recovery and to supplement lost bacterial populations. The application of this technology is termed bioaugmentation.
Defining the Terms
Frequently, the terms bioremediation and bioaugmentation are used interchangeably. Bioremediation will be defined here as the use of selected microorganisms to accomplish a biological cleanup of a specified contaminated area, such as soil or water; bioaugmentation will be defined as the application will be defined as the application of selected microorganisms to enhance the microbial populations of an operating waste treatment facility to improve water quality or lower operating costs. In other words, bioremediation deals with a definite project or area, while bioaugmentation involves working to improve a continuous process.
Bioaugmentation has been practiced since the early 1960’s. Because of frequent misapplication of additives or poor documentation of results, the technology has been regarded as less than scientific.
A prevailing belief has been that, over time, the proper microbes will populate the system and become acclimated to the influent. The approach assumes that the indigenous population introduced via routes such as windblown solids, rain water and the plant influent stream always will contain the best suited organisms. In reality, even though the natural population may develop into an acceptable one, there may be performance limitations that only can be overcome through the induction of superior strains of microorganisms.
In the aeration basin of a typical industrial waste treatment plant, one should expect to find numerous species or strains of bacteria. This bacterial diversity, as it is called, is necessary because some types of bacteria degrade different compounds more effectively and efficiently.
These bacteria generally are well suited to handle the contaminants in the waste influent and will become acclimated, over time, to provide the desired results, assuming a steady state of operation is approximated. Unfortunately, few industrial waste treatment plants ever achieve steady state. The influent characteristics may change drastically from week to week, or even day to day.
These variations may be due to production schedules of batch processes, chemical spills in the production plant, or incapable plant equipment. Many treatment plant biological populations never attain optimum numbers or diversity of species.
Without bioaugmentation, the indigenous population should consist of numerous types of organisms. Some of these organisms are more efficient and effective than others at degrading the various compounds and producing a settle able biomass. Figure 4 simplistically categorizes the biomass into Population A (desired indigenous organisms), and Population C (selected bioaugmentation organisms). The goal of the bioaugmentation program is to enhance the growth of Population A, establish the selected organisms of Population C, and minimize Population B.
There is the question of why bioaugmentation products must be fed continuously after the initial dosing of product. Due to system upsets and influent composition changes, a maintenance dosage is required to maintain the desired population diversity.
Proper monitoring of the system using statistical process control, combined with microbiological analysis techniques, will provide the information that the bioaugmentation consultant needs to maintain the desired population. By using microscopic analysis and advanced plating techniques, the consultant can correlate bacterial population characteristics with plant performance for a particular waste treatment system. Because every system is unique, the optimum population will vary from plant to plant.
Typical bioaugmentation products consist of blends of several strains of microorganisms, usually bacteria or fungi. The organisms are isolated from nature and are not genetically altered in any way. They are selected on the basis of accelerated reproduction rates and their ability to perform specific functions, such as good floc-forming capabilities to enhance settling or the ability to degrade specific compounds. The products are sold in a variety of forms, with dried organisms on a bran carrier and liquid products being the two most common.
Product selection for a particular application is based on a combination of laboratory treatability studies and field experience in similar applications. Plant samples of wastewater influent and aeration basin biomass are sent to the laboratory for product screening and treatability work.
Typically, one week is required to complete the laboratory work. In some cases, where the plant is in danger of permit violation, program implementation must begin prior to lab work completion. In these cases, the experience from similar application is critical in determining the initial course of action. The program implementation and utilized to make adjustments in the program, if necessary.
More Than Just Products
Successful bioaugmentation requires total system management. If the microbiological population can be viewed as a workforce, then the consultant or system manager is responsible for keeping the workforce productive.
The system manager must provide an acceptable work environment by controlling the key system parameters such as pH, temperature and oxygen levels. He must compensate them with nutrients to ensure good growth and a healthy population. He has to know to lay-off workers through wasting to keep the population young and vital. Finally, the successful system manager knows when to hire new workers to provide special skills not found in his workforce. Bioaugmentation is the mechanism to provide these skilled workers.
A critical part of the success of a bioaugmentation program is proper application. Because every system is unique, it is essential that products are properly applied. Bioaugmentation programs should be implemented with the help of surveying the total system, assessing the best solution to the problem and documenting the impact of the program. Simply dumping a product into the influent is not bioaugmentation.
The purpose of bioaugmentation is to facilitate a gradual shift in the microbial population, not to totally replace the existing biomass. The population shift must be accomplished in a planned and controlled manner to maintain the integrity of the microbial ecosystem. Over feeding the selected microorganisms could result in a biomass no better equipped to handle the broad range of compounds in the influent that the original population.
Proving The Results
The greatest difficulty in gaining acceptance of bioaugmentation as a valid technology is proving cause and effect of the addition of the specific organisms. Classical science would instruct the customer to run a controlled experiment in his plant, concurrent with the bioaugmentation program. In reality, this is rarely possible because a few waste plants have identical, separate, side by side systems to allow a rigorous head-to-head trial. Secondly, bioaugmentation is frequently a last ditch effect to save a system from “shutting down” and sending the plant into permit violation. Many times, in addition to bioaugmentation, other system parameters are changed, introducing new variables into the equation.
To effectively document the impact of the bioaugmentation program, plant data for several months prior to the program should be plotted and compared to the data after program implementation. For a bioaugmentation trial to be meaningful, the trial must be run three to five times the holding time for a once-through lagoon system, or four to six sludge ages (mean cell retention time) for an activated sludge system.
Figures 5 and 6 illustrate two examples of impact of bioaugmentation at two paper mill waste treatment plants. The paper mill in the first case was facing permit violations for BOD in the effluent. Figure 5 shows the improvement in BOD removal after the application of a bioaugmentation program. Within statistical significance, all operating variables, such as incoming BOD and flow, were constant before and after the application of the bioaugmentation program.
In the second example, the paper mill was experiencing both BOD and total suspended solids (TSS) excursions. To maintain TSS compliance, large amounts of polymer were being fed to the final clarifiers. Figure 6 shows the impact of the bioaugmentation program in reducing polymer usage. The graph shows the monthly cost of the bioaugmentation program to be one-half to one-sixth of total monthly cost of polymer for the nine months preceding program implementation.
These two cases provide excellent examples of the type of cause and effect documentation that can be demonstrated with proper data collection and analysis. In some cases, the program can be ceased to confirm the efficiency of the treatment. However, once the problem is solved, many users are reluctant to remove the program and risk system deterioration and possible permit violation.
Several areas where bioaugmentation has proven to be beneficial are discussed below.
ENHANCED BOD REMOVAL – Many systems, particularly once-through aerated lagoons, are being asked to provide results for the 1990s with technology from the 1960s and 1970s. It would cost millions in capital to upgrade these systems. By increasing the microbiology numbers and diversity via bioaugmentation, the desired results can be achieved. In the pulp and paper industry in the southeastern United States, improvement in BOD effluent levels of 30 percent have been documented.
IMPROVED SOLIDS SETTLING – An important step in biological waste treatment is solids removal, usually through settling in a lagoon or clarifier. Bacteria form a natural biopolymer that aid in settling. Toxic shocks and system changes can result in a bacterial population with little biopolymer and poor settling characteristics. The traditional approach of adding organic polymers or inorganic coagulants as settling aids can be effective but expensive. By inoculating the system with organisms known to be both resistant to the toxicity and excellent floc formers, polymer demand can be greatly reduced or eliminated.
Typically the cost of bioaugmentation is significantly less than polymer treatment. In addition, it provides an overall healthier biomass.
PREFERENTIAL DEGRADATION OF SPECIFIC COMPOUNDS – by adding selected organisms, low levels of particular compounds can be achieved that are not possible with the indigenous populations. Compounds such as phenols, chlorinated aromatics and aromatic hydrocarbons are but a few compounds that can be reduced with bioaugmentation.
IMPROVED NITRIFICATION – Many industrial waste plants have difficulty in achieving nitrification because of design limitations or toxic shocks. By regularly adding nitrifying bacteria, the proper population for ammonia removal can be maintained.
OTHER AREAS – Other areas where bioaugmentation offers benefits include odor reduction, oil and grease removal, rapid system start-up and improved tolerance to toxic shock. Additionally, research continues to explore new application areas for this evolving technology.
As environmental restrictions tighten, many industrial operators will be faced will compliance levels that will seriously challenge the capabilities of their existing wastewater treatment plants. In some cases, bioaugmentation will be a cost-effective, short-term or medium-term fix to keep them in compliance until system changes can be implemented. In other instances, bioaugmentation will be the long-term solution because of the lack of capital funds or expense of the mechanical solutions.
The concept of effectively managing the microbiological population of an aeration basin in a new one. It involves much more than introducing new organisms into the system. Total system management requires in-depth understanding of waste plant operation and design, in addition to environmental microbiology. By combining these two disciplines effectively, the wastewater manager can be provided with the optimum results for existing system.
¹Grady, CPL and Lim, HC, Biological Wastewater Treatment, Theory and application, pg 3.
²Stainer, RY; Doudoroff, M. and Adelberg, EA. The Microbial World, 3rd ed., Page 316.
Palermo, DR and Holzer, KA, TAPPI Environmental Conference, 1992 Proceedings, Vol.3, Page 881.
Whiteman, GR, TAPPI Environmental Conference, 1992.