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Bioaugmentation Aids
Wastewater Systems
As environmental
restrictions tighten, many industrial waste treatment plant operators face
compliance levels that will seriously challenge the capabilities off their plants.
Bioaugmentation may be a viable "fix" until solutions are available.
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 perameters,
disolved 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.
The Bacteria
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 settleable biomass. Figure 4
simplistically categorizes the biomass into Population A (desired indigenous organisms),
and Population C (selected bioaugmentation organisms). The goal of the bioaugmantation
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 continously 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.
The Products
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 specfic 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 serveying 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 exicting 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
equiped 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 bioaugentation 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 aexample, 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. Fiqure 6 shows the impact of the bioaugmantation 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 charicateristics. 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 compunds 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 NIRIFACATION - Many indusrial waste plants have difficulty in
achieving nitrification because of design limitations or toxic shocks. By regularly adding
nitrifying bacteria, the proper population for ammonia removel can be maintained.
OTHER AREAS - Other areas where bioaugnentation offers benefits include
odor resuction, 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.
Summary
As environmental restrictions tighten, many industrial operators will be faced will
compliance levels that will seriously shallenge the capabilities of their exsiting
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 exsisting system.
¹ Grady, CPL and Lim, HC, Biological Waatewater 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 Envornmental Conference, 1992 Proceedings, Vol.3, Page
881.
Whiteman, GR, TAPPI Environmental Conference, 1992. |
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