steve deiters and dan scrogghs pollution control, inc

Steve Deiters and Dan Scrogghs Pollution Control, Inc. Florence, KY

order to meet all the required discharge parameters. With these steps in motion, the package biological Wastewater treatment plant moved from concept to reality. The package wastewater treatment plant was originally developed to meet the water pollution control demands and regulatory requirements for the treatment of comparatively small (10,000 to 700,000 gallons per day, gpd) domestic waste flows. It was in this application that the package treatment concept gained widespread use and acceptance.

Package wastewater treatment systems are typically installed in rapidly expanding areas and in diversified pockets of non-urban, residential developments. These are areas that either do not have access to the high volume publicly owned treatment works (POTW) found in large urban areas or where smaller systems prove to be more practical and economically feasible to install and operate. These wastewater treatment systems remove 95 percent or more of the organic contaminates present prior to discharge into a local water course.

The package wastewater treatment system provides the user with a readily available, cost-effective, and easy to operate aerobic biological wastewater treatment plant. These package plants allow for the development of areas, which previously would not have been considered for residential or commercial

development. They also permit remote industrial/commerciaI areas such as isolated manufacturing plants, mining and timber camps, and other facilities of this type to be more compatible with sensitive environments. These systems, since they are pre-engineered and fabricated from rectangular steel tanks, can be made available with very short lead times from conception, to fabrication, installation, and actual operation.

The package wastewater treatment system is viewed as a simple solution to the complex problem of meeting numerous agency-mandated treated wastewater discharge parameters. These wastewater treatment systems are readily accepted by the local regulatory agencies and have rapidly become the standard of comparison and performance for domestic wastewater treatment applications of flows of 100,000 gpd or less. As the shifting regulatory policy is placing greater emphasis on the pretreatment of industrial wastewater, prior to discharge to a POTW, the package wastewater treatment system concept takes on a new role.

These changing environmental policies have greatly expanded the potential applications for these systems to include not only domestic waste, but also industrial process wastewater. While these treatment systems provide effective treatment of domestic waste, they are also capable of treating

30 The National Environmental louvnal January/February 1994

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* . relatively low flows of high strength wastewater from industrial facilities using similar aerobic biological operating principles. The adaptation of this equipment from domestic to industrial wastewater treatment is done by altering the loading criteria and applying it for the removal of higher levels of contaminates in the industrial process wastewater streams.

Not only does the use of a package biological treatment plant provide a user-friendly vehicle for regulatory compliance, but it also can become a profit center for the industrial user. Installation and operation of these biological pretreatment systems by an industrial wastewater generator can significantly reduce the surcharges paid to a POTW for the discharge of a high strength (greater than 300 mg/l biological oxygen demand, BOD) industrial wastewater. These charges can be substantial since the concentration of the contaminants in the wastewater multiplied by the flow is the basis for the surcharge fees. The savings realized from surcharge reduction can positively affect the profitability of any industrial facility. This holds true even when the operational and personnel costs of the treatment plant are taken into account.

Basic ~~~~ ~~~~~~~~~S

The package biological wastewater treatment plant takes a naturally occurring biodegradation process and accelerates it. This process is consolidated into an efficient configuration in the form of a prefabricated package. The aerobic process converts organic contaminates into cell mass, water, and carbon dioxide. The conversion is done in a biological process similar to the breaking down of food. In fact a package wastewater treatment plant once operating could actually be considered an organism which exists for the sole purpose of consuming organics present in wastewater.The pretreatment of high strength/low flow wastewater in a package wastewater treatment system is similar to the method used for the complete treatment of domestic wastewater. The difference is that the strength of the industrial waste may be 10 to 15 times higher than its domestic counter- Dart. Conseauentlv certain desian factors must be considered to

accommodate this difference. Wastewater treatment is accomplished by creating an environment where microorganisms biologically decompose the soluble industrial organic contaminates in the wastewater.

Package treatment plants typically use variations of the activated sludge process known as extended aeration. Other variations available are contact stabilization, step aeration, complete mix, sequencing batch reactions (SBR), variable depth reactors (VDR), and hybrid fixed film/suspended growth reactors. Pack- age wastewater treatment plants use several basic steps to attain the desired effluent quality. First, the wastewater undergoes pre- liminary treatment where gross solids are physically removed or mascerated. The wastewater is then biologically activated by mixing the incoming nutrient-rich waste stream with an active biomass returned from the secondary side or aeration stage of the treatment system. Activation of the wastewater flow is followed by biological reduction in which the active biomass consumes the organic contaminants present in the wastewater and converts them to cell mass. This step is followed by gravity clarifi- cation in which the biomass is separated from the effluent stream and returned to the process activation step, while the clear effluent moves from the secondary treatment phase of the plant to the clarifier for solids removal. Subsequent to this step, the secondary treated effluent will be disinfected and or filtered prior to discharge. Surplus biomass generated by the conversion of soluble organics to insoluble cell mass can be wasted to an option- al aerobic digester where endogenous respiration takes place reducing the mass. This activity causes a further reduction in the biomass and requires only a portion of the material to be removed from the system and ultimately disposed.

Detailed operation of the package plant begins when the influent wastewater enters the package plant by passing through a comminution device or is delivered to the treatment plant via a grinder pump. This step provides for solids size reduction. Microorganisms can consume these precondi- tioned, smaller materials more readily. A bar screen for gross solids removal may be located on the influent side of the plant. This step, besides allowing the biological consumption

process to function more smoothly, helps to reduce the BOD by physically removing putresible solids prior to aeration.

Once the wastewater flow has entered the secondary treatment aeration chamber from the equalization tank, the untreated flow is intimately mixed with an active biomass, or return activated sludge (RAS). This mixing action manifests itself in the plant in a rolling of the entire contents of the aeration chamber which takes place along the entire length of the aeration chamber. This rolling mixing action is the result of air originating from diffusers located along one side of the bottom of the tank. This aeration driven mixing action insures that the incoming waste is kept in contact with the biomass and is ade- quately oxygenated so that efficient

Cutaway drawing of a typical pre-engineered and prefabricated package biological biodegradation can take place. wastewater treatment plant. The chambers are beveled on each

The National Environmental Journal January/February 1994 31

Five step biological treatment process utilized in package biological wastewater treatment plants.

side of the bottom to enhance the rolling motion of the water ‘

and eliminate any “dead zones” which may occur otherwise in the chamber. Oxygen transfer is achieved by diffused air passing through the wastewater. This provides sufficient oxygen to permit microorganisms to rapidly assimilate the organic contam-

based on organic load per cubic feet of the aeration chamber of

chamber can be as short as 4 hours or as long as 10 days, depending on the BOD loading and the degree of treatment required.

After the aeration treatment stage, the wastewater flows to the clarifier. Most clarifiers typically have a

inates present in the water. Sizing of the aeration chamber is

the treatment reactor. Hydraulic retention time in the aeration

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hopper bottom configuration, but circular clarifiers with a moving rake mechanism have also been used with these plants. The clarifiers are sized to provide a 2-4 hour retention time, based on an average 24-hour design flow retention and a surface loading rate between 600 to 1000 gpd/per square foot. During the liquid/solid separation process in this quiescence zone solids will float to the surface of the water or settle on the bottom of the clarifier for thickening prior to returning them to the head of the treatment plant.

Air lift pumps with adjustable pumping capabilities are used to return a predetermined amount of settled activated sludge to the aeration chamber on an ongoing basis. This is done to maintain the mixed liquor suspended solids (MLSS) at a level that will maximize the efficiency of the biological process. When neces- sary, excess sludge is wasted to an aerated sludge digestion tank as waste-activated sludge for additional treatment and storage prior to dewatering and ultimate disposal. A skimmer device with an airlift pump returns floatable solids and scum from the clarifier to the aeration chamber for further processing and continued biological reduction. If required, a third treatment can be accomplished by using a sand filter of some type. The treated water flows from the clarifier to the disinfection chamber to complete the treatment process.

The adaptation of activated sludge package

flow applications is fairly straightforward. As mentioned above, the flows feeding these special application package wastewater treatment plants are usually relatively low, but are high in BOD values. These two factors affect the sizing of the aeration chamber, air delivery system, sludge holding tank, and clarifiers significantly. Domestic waste is typically rated at 200 to 350 mg/l BOD, while industrial applications, depending on their origin, can very

plants to the treatment of industrial process ~~

CIRCLE 221 ON CARD FOR FREE INFO. easily have BOD loadings running 10 to 15

32 The National Environmental Journal January/February 1994

- times these levels or more. While these levels are extremely high, the treatment principles used to reduce them are the same as those found in traditional domestic wastewater treatment applications. Removal rates of 95 percent and more have been achieved.

Package treatment plants are typically sized based on an organic load per cubic volume of the bioreactor. This rate varies depending on the degree of treatment required, as well as the process used. For industrial pretreatment, the load would be 60 to 80 pounds BOD per 1,000 cubic feet of aeration volume prior to discharge to a sanitary sewer at a level of 300 mg/l. More stringent discharge guidelines may require either a revised loading rate or a second stage biological system loaded at 15 pounds BOD per 1000 cubic feet of aeration volume to achieve these levels. An aeration tank used to treat 30,000 gpd of domestic waste for stream discharge could also be used to treat 30,000 gpd of food process waste to sewer discharge limits. To achieve stream discharge limits for industrial wastes, the plant would have to be four times that size.

Because the oxygenation process is the heart of the biological reduction process, care should be taken to ensure that the required amount of oxygen is supplied. In addition to changes in the reactor volume, the aeration requirements must also change. The oxygen required by a treatment plant is a function of the amount of work it must do, and the work is defined as the amount of BOD that must be removed. Oxygen must be transferred into the system at a rate of at least 1 to 2 pounds oxygen delivered to the wastewater per pounds of BOD to be removed. The amount of oxygen required is estab- lished by using predetermined factoring criteria based on “clean water“ oxygen transfer efficiency against wastewater demands which take into account mass transfer coefficients, dissolved solids, water temperature, and altitude. This is a fairly sophisticated process that ensures that adequate oxygen is supplied to the wastewater in the system. The evalua- tion process is further complicated by taking into consideration the relative oxygen transfer efficiency of various diffuser types (coarse or fine bubble), as well as diffuser submergence, tank geometry, and diffuser density.

Another factor related to the sizing is the design of the aeration system to accomplish mixing. As a rule, if the system is sized based on oxygenation the mixing requirement is 15 SCFM per 1000 cubic feet of volume. However, oxygenation can be achieved by using relatively efficient diffusers with imputing enough oxygen transfer, but this cannot guarantee suspension of the MLSS.

Clarifier siting is normally based on a surface loading rate of gpd per square feet. Industrial wastewater process flow is affected by the high BOD and chemical oxygen demand (COD) ratings and usually requires the clarifier to be oversized slightly. Since the high levels of BOD/COD are being con- verted to a proportionately larger biomass, this results in larger sludge handling equipment. The design considerations and mechanical fabrication of these larger clarifiers are easily accomplished.

The fact that more sludge is being generated does affect the sludge dewatering and disposal capacity required for the installation. These dewatering requirements can be met at the site with the use of a number of dewatering devices, such as a belt filter, plate and frame filter press, or vacuum filter, or by using local agricultural land. The volume of sludge generated

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can be reduced using an aerobic digester.

Aside from the organic strength of the wastewater for treatdent purposes, the non- biodegradable constituents of the wastewater flow also must be considered. The pH of the water is an important factor when considering the ability of the biological process to function; the level should be between 6.0 and 9.0. In some cases, alkalinity is consumed by the biodegradation process; this is especially true in food process wastes where acid- forming bacteria may be present. The pH levels must also be evaluated to ensure that the proper materials of construction and coatings are used on the treatment tanks and auxiliary equipment. Due to process, maintenance, and cleanup activities, many industrial process installations may have tremendous swings in the pH

The treatment capabilities of the package biological treatment plant are expanded significantly with the proper selection of auxiliary equipment immediately upstream and downstream of the system.

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34 The National Environmental Journal January/February 1994

* *

. . c E “levels of the wastewater over a 24-hour to 7-day period. An equalization tank prior to the system can be used to buffer large swings in the pH and hydraulic surges.

Other contaminants, such as a heavy loading of suspended solids, FOG, light fraction hydrocarbons, dissolved metals, and other materials, may have to be removed from the wastewater flow in order for the biological treatment system to operate most efficiently. This can be achieved with the proper selection of auxiliary equipment prior to the biological treatment plant. These contaminants can be lowered significantly by using dissolved air flotation to remove gross amounts, with a concurrent reduction in the BOD loading. In some cases where the FOG and suspended solids loadings are extremely high and the flow is low, the entire stream can pass through a vacuum filter prior to biological treatment. Dissolved metals can be chemically precipitated and removed by gravity settling in a primary clarifier prior to the biological treatment phase.

The most widely used method of disinfection in these plants for the treatment of domestic wastes is chlorinization. Other industrial process applications and local regulations may necessitate the use of alternate methods of disinfection such as ultraviolet lights or ozone. Both of these disinfection tech- nologies are easily adaptable to package wastewater treatment plants.

~ ~ i c ~ 1 ~ ~ ~ ~ ~ ~ ~ 1

Industrial users made large capital investments in processing facilities and physical plants long before more stringent wastewater discharge guidelines were in place or had to be considered. The use of tailored equipment, such as pH adjustment systems, dissolved air flotation systems, vacuum filters and other equipment, in conjunction with package wastewater treatment plants, can vastly expand the viable applications for these types of wastewater treatment systems. The potential industrial users of this equipment are typically mature industries located in developed areas, with limited space for expansion, tight compliance time schedules, and categorical discharge limits.

Perhaps the most obvious area in which these units can be used is in food processing - dairies, yogurt manufacturers, egg processors and washers, cheese production facilities, candy manufacturers, meat processors, poultry preparation facilities, and others high in BOD and FOG loadings. Chemical plant streams with phenols and other organic chemicals in the wastewater stream also are likely candidates for this type of pretreatment. The treatment of landfill leachate and groundwa- ter remediation installations are rapidly emerging applications.

The adaptation of the concept of package wastewater treatment plants to the treatment of industrial process streams can be achieved with consideration of all the factors involved in design. If the proper physical and chemical treatment equipment is used upstream of the package plant, the capabilities of these aerobic biological treatment systems are expanded tremendously. These expanded capabilities offer solutions to process wastewater stream generators who are under pres- sure to find solutions in short order. The package wastewater treatment plant provides compact, user friendly, and cost- effective solutions. These systems provide both regulatory and operating cost relief for the user in a compressed time frame. All are factors that make a successful installation for

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steve deiters and dan scrogghs pollution control, inc

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