Bioaugmentation

Bioaugmentation or biomass enhancement is the addition of commercially prepared bacterial cultures to a wastewater treatment system to (1) increase the density of desired bacteria and their enzymes and (2) achieve a specific operational goal—for example, decrease sludge production or control malodor production. The addition of bacterial cultures increases the density of desired bacteria without significantly increasing the solids inventories and solids residence times of an activated sludge process or anaerobic digester. Sufficient addition of bioaugmentation products may enable an operator to decrease MLVSS concentration and MCRT. Decreases in MLVSS and MCRT help to control the undesired growth of filamentous organisms.

Treatment efficiency, permit compliance, and operational costs at a municipal wastewater treatment plant are influenced greatly by the enzymatic activities and abilities of a large population and diversity of coli-aerogens. Coli-aerogens are bacteria that inhabit the gastrointestinal tract of humans and enter wastewater treatment plant in fecal waste.

Examples of significant activities of coli-aerogens that are of important to waste-water treatment plants include:

• Nutrient and dissolved oxygen requirements

• Products obtained from the degradation of substrates

• Rates of degradation of the substrates

• Types of substrates that can be degraded

Examples of significant abilities of coli-aerogens that are of importance to waste-water treatment include

• Adverse conditions that are tolerated

• Competition with other organisms

• Floc-forming ability

• Temperature growth range

The activities and abilities of coli-aerogens are supported by a smaller population of several important genera of saprophytic and nitrifying bacteria that enter the treatment plant as soil and water organisms through inflow and infiltration (I/I). The saprophytic bacteria and their enzyme systems are more efficient in degrading a larger variety of substrates than the coli-aerogens. Also, many saprophytic bacteria have unique abilities that enable them to survive and remain active under harsh environmental or operational conditions that are not tolerated well by the coli-aerogens.

Saprophytic bacteria are primarily responsible for the degradation of organic compounds (substrates) in nature. However, saprophytic bacteria do not enter wastewater treatment plants in significant numbers and do not grow in large numbers in wastewater or sludge, due to the presence of very large numbers of coli-aerogens that enter wastewater treatment plants. Therefore, the efficient enzymatic activities and unique abilities of the saprophytic bacteria are "diluted" by the coli-aerogens. Due to the relatively small number of saprophytic bacteria in a wastewater treatment plant as compared to the large number of coli-aerogens, a wastewater treatment plant may experience difficulties in treating specific substrates, tolerating adverse conditions, or correcting an operational problem.

The addition of bioaugmentation products is to improve or correct treatment plant performance. The products or bacterial cultures used at a treatment plant are selected according to (l) the needs of the treatment plant and (2) the activities and abilities of the bacterial cultures to address the operational problem.

Bacterial cultures may be added to several locations at a wastewater treatment system (Table 5.1). The location for the addition of the bacterial cultures is selected according to the needs of the treatment system and the adjustment period of the bacteria.The adjustment period is the time required by the bacteria to produce their enzymes in a new environment such as the aeration time or anaerobic digester. The longer the adjustment time that is required, the greater the distance (detention time) from the treatment unit the bacteria are added.

Although bioaugmentation products are introduced to a specific location for use in a specific tank, the bacteria are transferred throughout the treatment plant—that

TABLE 5.1 Commonly Used Addition Points for Bioaugmentation Products

Lift station

Conveyance system Headworks

Primary clarifier influent Primary clarifier effluent Aeration tank influent is, activated sludge, aerobic digester, and anaerobic digester. Bacterial cultures are added to a treatment unit at an introductory dose and maintenance dose. If an introductory dose is used, the dose usually is >2ppm and may be applied for 2-4 weeks. In most cases the maintenance dose is approximately 2ppm and may be applied daily, weekly, or as needed.

Bioaugmented saprophytic bacteria do reproduce in wastewater treatment plants, but they cannot outnumber the coli-aerogens that continuously enter the process in very large numbers. Coli-aerogens are present in millions per milliliter of mixed liquor and billions per gram of floc particle. Saprophytic bacteria are added to a level where the impact of their activities and abilities can be observed.

Bioaugmented saprophytic bacteria are not pathogenic (disease-causing). However, the some preservatives that are used to arrest the growth of the bacteria during storage and shipping may cause an allergic reaction with some individuals. Therefore, appropriate protective clothing such as long sleeve uniforms or shirts, dust masks, and splash shields or eye goggles should be used when handling bioaugmentation products. Individuals who come in contact with the products should wash or shower.

Selected saprophytic bacteria are obtained from soil and water samples from a variety of habitats. They are screened to determine their enzymatic activities and abilities. Screening determines

• Efficiency and rate of degradation of organic compounds (substrates)

• Operational conditions that are tolerated

• Variety of organic compounds (substrates) that can be degraded

Saprophytic bacteria are grown to a relatively large population on a carbon source. Their growth is arrested through suspension, freeze-drying, or air-drying techniques, and the bacteria are packaged in liquid or dry forms.

Although there are numerous genera and species of saprophytic bacteria that are used for specific and general purposes, there are several common genera that are used in many bioaugmentation products (Table 5.2). In addition to saprophytic bacteria, nitrifying bacteria may be added used (Table 5.3) as well as fungi.

TABLE 5.2 Commonly Used Genera of Saprophytic Bacteria in Bioaugmentation Products

Genus

Enzymatic Activity

Aerobacter

Bacillus

Cellulomonas Pseudomonas

Rhodopseudomonas

In anaerobic digester, it coverts complex organic compounds into volatile fatty acids that are converted to methane. It increases gas production and decreases sludge production in anaerobic digester.

It produces a large number of exoenzymes that solubilize and degrade a large variety of carbohydrates, lipids, and proteins. It decreases sludge production.

It solubilizes and degrades cell wall material such as cellulose within vegetative tissue. It decreases sludge production.

It degrades difficult biodegradable compounds such as phenols and phenolic compounds. It decreases sludge production and reduces toxic upsets caused by phenols and phenolic compounds.

It degrades difficult biodegradable compounds. It decreases sludge production.

TABLE 5.3 Nitrifying Bacteria Used in Bioaugmentation Products

Genus Enzymatic Activity

Nitrobacter It converts nitrite (NO2-) to nitrate (NO3-), resulting in reduced nitrogenous loading to the receiving waters. It initiates or improves nitrification at low MLVSS concentration or cold temperature.

Nitrosomonas It converts ionized ammonia (NH4+) to nitrite (NO2-), resulting in reduced nitrogenous loading to the receiving waters. It initiates or improves nitrification at low MLVSS concentration or cold temperature.

Saprophytic bacteria can efficiently degrade readily degradable cBOD and difficult-to-degrade cBOD. Degradation is achieved through the use of unique enzyme systems and the production and release of exoenzymes (Figure 5.1). Exoen-zymes released by saprophytic bacteria diffuse through the floc particle and solu-bilize carbohydrates, lipids, and proteins that have been adsorbed to the floc particle. Once solubilized, the sugars (from carbohydrates), fatty acids (from lipids), and amino acids (from proteins) can be degraded further by not only the saprophytic bacteria but also the coli-aerogens. Also, many saprophytic bacteria can compete more effectively for available nutrients and dissolved oxygen in the bulk solution than many coli-aerogens and filamentous organisms. This effective competition for dissolved oxygen and nutrients helps to provide for acceptable wastewater treatment during marginal concentrations of dissolved oxygen and nutrients and may help to prevent the undesired growth of filamentous organisms.

An example of the ability of saprophytic bacteria to solubilize and degrade cBOD resulting in improved treatment plant performance (i.e., decreased sludge production) is the solubilization and degradation of cellulose (Figure 5.2). Cellulose is an insoluble polysaccharide or starch consisting of numerous units or mers (polymer) of glucose. The glucose units are held in an insoluble form due to the unique chemical bond between each glucose unit. Cellulose is found in plants and is not degraded by humans or the coli-aerogens in the gastrointestinal tract. Therefore, much cellulose is found in fecal waste. Cellulose is found in primary and secondary sludges at wastewater treatment plants. Cellulose makes up 8-15% of primary and secondary sludges.

Cellulomonas is a genus of bacteria having species that produce the exoenzyme cellulase. The enzyme is capable of breaking the unique chemical bonds between the glucose units in cellulose. However, Cellulomonas typically is not found in large numbers in the indigenous bacterial population of an activated sludge process, but Cellulomonas may be augmented to the process.

By adding Cellulomonas to the activated sludge process, cellulose is solubilized; that is, individual glucose units are separated from the starch and dissolve in the wastewater. Once in solution, glucose is absorbed and degraded by Cellulomonas and many other bacteria including coli-aerogens. The degradation of glucose results in the production of carbon dioxide, water, and new bacterial cells (sludge or MLVSS). Approximately 0.6 pound of cells or sludge and 0.4 pound of carbon dioxide and water are produced from each pound of glucose degraded. A pound of cellulose that is solubilized and degraded represents approximately 0.6 pound of cells or sludge wasted from the activated sludge process. A pound of cellulose that is not solubilized and degraded represents one pound of solids or sludge that is insoluble substrate insoluble substrate insoluble substrate insoluble substrate insoluble substrate insoluble substrate

insoluble substrate + endoenzymes soluble substrate insoluble substrate + endoenzymes soluble substrate

soluble substrate soluble substrate

FIGURE 5.1 Production and release of exoenzymes. When an insoluble substrate becomes adsorbed to the surface of an exoenzyme-producing bacterium (2), exoenzymes are produced within the cell (3). The exoenzymes are released by the bacterium (4) and "attack" the insoluble substrate. The attack upon the insoluble substrate results in the solublization of the substrate (5) and the production of soluble substrate (6). The soluble substrate then is absorbed by the exoenzyme-producing bacterium (7) and finally degraded by endoenzymes within the exoenzyme-producing bacterium.

FIGURE 5.1 Production and release of exoenzymes. When an insoluble substrate becomes adsorbed to the surface of an exoenzyme-producing bacterium (2), exoenzymes are produced within the cell (3). The exoenzymes are released by the bacterium (4) and "attack" the insoluble substrate. The attack upon the insoluble substrate results in the solublization of the substrate (5) and the production of soluble substrate (6). The soluble substrate then is absorbed by the exoenzyme-producing bacterium (7) and finally degraded by endoenzymes within the exoenzyme-producing bacterium.

wasted from the activated sludge process. The use of Cellulomonas to solubilize cellulose represents a reduction of approximately 40% in sludge production for cellulose. Cellulomonas added to the activated sludge process is transferred to the aerobic or anaerobic digester in secondary sludge. Cellulomonas continues to degrade cellulose in the aerobic or anaerobic digester.

Bioaugmentation products may be used to correct several operational problems or improve treatment efficiency (Table 5.4). Some applications of bioaugmentation products (e.g., decreased sludge production) may result in monetary savings to the wastewater treatment plant. Sulfur-containing malodorous compounds also can be degraded with appropriate bacterial cultures. For example, bacteria in the genera cellulose cellulose cellulose cellulose cellulose cellulose

cellulose+exoenzymes glucose glucose glucose

FIGURE 5.2 Degradation of cellulose. Cellulose is an insoluble starch molecule that consists of many units of glucose bonded together in chain-like fashion. When cellulose comes in contact with the bacterium Cellulomonas, cellulose is adsorbed to the surface of the bacterium (2). Once cellulose is absorbed, Cellulomonas produces the exoenzyme cellulase (3) that is released to the surface of the bacterium and "attacks" cellulose (4). Cellulase solublizies cellulose (5), and glucose is produced from the attack by cellulose (6). Soluble glucose is then absorbed by Cellulomonas (7) and is degraded by endoenzymes (8).

FIGURE 5.2 Degradation of cellulose. Cellulose is an insoluble starch molecule that consists of many units of glucose bonded together in chain-like fashion. When cellulose comes in contact with the bacterium Cellulomonas, cellulose is adsorbed to the surface of the bacterium (2). Once cellulose is absorbed, Cellulomonas produces the exoenzyme cellulase (3) that is released to the surface of the bacterium and "attacks" cellulose (4). Cellulase solublizies cellulose (5), and glucose is produced from the attack by cellulose (6). Soluble glucose is then absorbed by Cellulomonas (7) and is degraded by endoenzymes (8).

Thiobacillus and Hyphomicrobium can degrade methyl sulfide, dimethyl sulfide, and dimethyl disulfide.

Before adding bioaugmentation products, the following information should be reviewed in order to select and apply the appropriate bacterial cultures:

• Evaluate the treatment plant's existing conditions.

• Identify the specific conditions to be addressed with bioaugmentation products.

TABLE 5.4 Applications for Bioaugmentation Products

Application

Example

Control of foam production Control of malodors

Nitrification, cold weather

Reduce filamentous growth Reduce sludge production Increase digester gas production

Improve BOD and SS

removal efficiency Provide resistance to some forms of toxicity

Addition of bacterial cultures that produce enzymes that degrade lipids (lipase) or surfactants Addition of bacterial cultures (Pseudomonas) that degrade organic sulfur compounds before they are released to the atmosphere Addition of Nitrosomonas and Nitrobacter to the aeration tank to initiate or improve cold weather nitrification or addition of saprophytic bacteria to remove cBOD more quickly to prove longer time period for nitrification to occur Addition of sufficient saprophytic bacteria to reduce MLVSS

concentration and MCRT Addition of saprophytic bacteria to solubilize particulate and colloidal cBOD

Addition of facultative anaerobic and anaerobic bacteria to hydrolyze particulate and colloidal BOD and produce substrate (fatty acids) for methane-forming bacteria Addition of saprophytic bacteria that are more efficient and tolerant of existing operational condition Addition of saprophytic bacteria that can safely bioaccumulate heavy metals in slime and cell walls or can degrade organic toxicants

• Collect and review appropriate data for use in selecting appropriate bioaugmentation products.

• Review possible effects of bioaugmentation products upon indigenous biomass.

• Review storage and application procedures, including activation of bacterial cultures.

• Determine time period needed to observed the impact of bioaugmentation products.

• Determine tests or observations that indicate that the bioaugmentation products are working.

• Determine the costs for bioaugmentation products and any anticipated monetary savings.

Was this article helpful?

0 0
Losing Weight Without Starving

Losing Weight Without Starving

Tired of Trying To Loose Weight And It Never Works or You Have To Starve Yourself Well Here's A Weight Loss Plan That takes Care of Your Weight Problem And You Can Still Eat. In This Book, You’ll Learn How To Lose Weight And Not Feel Hungry! In An Easy Step-By-Step Process That Enables You To Feel Good About Loosing Weight As Well As Feeling Good Because Your Stomach Is Still Full.

Get My Free Ebook


Post a comment