While Constructed Wetlands are most commonly stand-alone units, there are certain applications where the influent wastewater flow from the process plant has certain characteristics that could require additional or enhanced pretreatment in order to reduce the footprint of the constructed wetland. In those cases, a Venturi Aeration Oxygenator unit is used for pre-aeration to achieve reductions designed to reduce the toxicity and biological loadings of wastewater going into the Constructed Wetland. This reduces the overall capital cost of the total project, and increases performance of the combined system.

Pre-aeration of the influent wastewater in a separate aeration tank using a Venturi Aeration Oxygenator unit has many benefits for Constructed Wetland systems:

1. Dissolved Oxygen: The liquid being processed through the venturi aerator unit is saturated with dissolved oxygen (DO). The discharged liquid is highly oxygenated with DO levels ranging between 5.0 mg/l and 7.5 mg/l.

2. Mixing and Equalization: The discharge from the venturi aerator unit mixes and equalizes the influent liquids with the contents of the preaeration tank. Any solids are kept in suspension by circulating the tank contents at 2 fps.

3. Odor Control: Imbedded malodorous and corrosive hydrogen sulfide from organic material is readily oxidized into soluble SO4, a non-odorous form of sulfur.

4. BOD Reduction: Pre-aeration induces large amount of dissolved oxygen into the aeration tank to effect BOD5 reduction from nascent bacteria in the sanitary wastestream to levels at which the Constructed Wetland can be effective; this is usually < 800 mg/L.

5. Nitrification: With excess amounts of dissolved oxygen in the aeration tank, nitrification at pH levels >6.8 begin in the aeration tank enhancing the Constructed Wetland’s performance. The constructed wetland has both aerobic and anaerobic areas in the reeds to both nitrify and denitrify.

6. Floatation of FOG: Conditioning with the Venturi Aeration Oxygenator causes imbedded fats, oils and grease (FOG) to separate and float to prevent their migration into the Constructed Wetland system.

7. Temperature: The Venturi Aeration Oxygenator has the ability to reduce the temperature of the influent wastewater. In field tests on the Venturi Aeration Oxygenator device with septage, temperature reductions have been documented to range between 2° and 6° C in summer months in New England. Reducing elevated temperatures of the process liquid increases the solubility of dissolved oxygen, thus allowing for greater amounts of DO to achieve targeted biological reductions.

8. Non-chemical pH Control: As the nascent bacteria become active aerobically they produce carbon dioxide as a digestive byproduct. The increase in carbon dioxide lowers the pH. This acidity may stress micro-organism performance and reed viability. Since carbon dioxide is readily strippable with the venturi aerator device, a steady state pH can be maintained on the liquids being decanted into the Constructed Wetland.

9. Hydraulic Shear: Solids that migrate from the primary settling tank are conditioned in the venturi aeration device to increase their surface to enhance digestion.

10. Strips VOCs: The venturi aeration device protects the biomass and reed beds in the Constructed Wetland by stripping certain weak Henry’s Constant VOCs that may be present in cleaning chemicals or detergents that could cause degrade performance of the reed beds or even kill them.

There are many applications for Constructed Wetlands or Reed Beds, not all of them require pre-aeration. However in those cases where pre-aeration is required a computer model has been developed to calculate the desired amount of dissolved oxygen that would be needed in pre-aeration to achieve targeted reductions in BOD5 for the influent wastewater. The computer model can assist the consulting engineer in the proper sizing of the aeration tank and venturi aeration oxygenator device to ensure desired reductions are achieved for liquids decanted to the reed beds

Summary: The addition of a Venturi Aeration Oxygenator unit in a pre-aeration and equalization tank can greatly enhance the performance of the Constructed Wetland system allowing it to treat larger quantities of wastewater than could otherwise be achieved without adding additional expensive pretreatment equipment to treat the influent flow. This reduces overall project costs and increases efficiencies. Because of the many specific benefits listed above from pre-aeration, the Venturi Aeration Oxygenator should be utilized for preconditioning difficult wastestreams.

To control the usual high BOD5 associated with the supernatant, dilution with secondary sludge from the intermediate and final clarifiers can be utilized. Secondary sludge withdrawal from the final clarifier can be adjusted to obtain the desired BOD5 level of the treated supernatant. Dilution rates of 4:1 to 10:1 should be considered depending on the strength of the supernatant. The wetted volume of the supernatant aeration basin should be sized for a minimum of 60 minutes detention time of the combined influent. The venturi aeration process equipment should be sized to pump at least twice the maximum rate of the combined influent. To operate the system with a minimum of energy, the entire operation can be placed on inexpensive timers. Primary, intermediate and final clarifier sludge withdrawals and the venturi aeration equipment can all be synchronized to operate together with a minimum energy cost.

When properly designed and constructed, this supernatant treatment method will return to the headworks an odor free liquid high in dissolved oxygen (DO) and BOD in the same range of the raw influent sewage. The supernatant odors will be controlled throughout the entire plant.

In some designs the venturi aeration equipment can be installed at a septage receiving area for odor control and conditioning and when not in use for septage treatment, typically up to 14-16 hours per day, it can be used for supernatant aeration during non-septage receiving hours. Supernatant liquids extracted from plate and frame pressings can also be aerated using the venturi aeration equipment. This increases the flexibility of the equipment when it can be multi-tasked.

For additional information on the venturi aeration equipment or process please contact Venturi Aeration, Inc. at 800-439-2610.

This system was first developed in 1990 for use in a point-of-use system for stripping PCE out of water in a contaminated aquifer. While the venturi aerator strips the PCE, Radon and soluble carbon dioxide, there was originally no requirement to disinfect the influent air. Venturi Aeration, Inc. designed and recommended that the influent air be cleaned in order to prevent the introduction of airborne bacteria and airborne particulate into the drinking water.

The UV Air Disinfection Unit uses UV germicidal wavelength bulbs to disinfect the air being aspirated into the venturi aerator. The airflow through the UV unit is generated by the vacuum effect created by the venturi aerator itself. Detention times in the UV unit have been calculated to ensure the all the air is exposed to the UV light source to ensure complete disinfection.

Venturi Aeration, Inc. has made several changes to the unit through the ensuing years. The unit is now constructed in stainless steel and the internal baffles have been reconfigured to allow additional detention in the UV air disinfection chamber.

In addition to UV air disinfection, a fabric particulate filter traps any airborne particulate materials that could otherwise be introduced into the water through the venturi aerator. These fabric filters are disposable. The filter is exposed to the UV light to ensure that no bacteria grow on the filter.

Various Boards of Health have specified the following maintenance schedule for the UV Air Disinfection unit. 1. Annual change out of the UV bulbs, even if they have serviceable life, and 2. Quarterly change out of the particulate fabric filter, at a minimum or more frequently if feasible.

The enzymatic product Quellz® was added to the lagoon at a ratio of 1 gallon to 100,000 gallons of lagoon contents to determine its efficacy. The purpose of the full-scale field test was to evaluate the ability of Quellz® enzyme to 1. Abate ammonia (NH₃) and hydrogen sulfide (H₂S) odors, 2. Aid in water clarification, 3.Enhance decomposition of sludge, and 4. To reduce the volume of sludge in the lagoon. The lagoon has a depth of 21 ft.

Prior to adding the Quellz® enzymes to the lagoon several measurements where taken on July 5, 2000 to determine sludge levels and to make observations on water clarity. A survey team measured the depth of the sludge in the lagoon and developed a base profile:

Depth 0’ Surface ____________

5’ murky colored water

10’ dark colored water and thin viscous material

15’ sludge solids 20’ thick sludge solids

21’ bottom thick sludge solids

The sludge on the bottom of the lagoon was from the 21’ level up to the 15’-5″ level, and between 15’-5″ to 10’ the water was already becoming viscous.

Quellz® was added to the lagoon, and several qualitative observations were made. These initial tests were made without supplemental aeration, all activity for this initial testing was anaerobic, and there was no mechanical mixing.

On the morning of July 9th (after 4 days) the level of odors had significantly been reduced, but remained recognizable at lower threshold levels as predominately amine-type odors. No analytical instruments were used, just a three member odor panel.

On the morning of July 12 the level of odors off the lagoon were de minimus or unrecognizable.

By July 31 the odors remained abated and the lagoon had begun to experience “clarification” down to the 6’ level. The Quellz®, which had been added at one specific point in the lagoon, had migrated across the entire lagoon during the 3.5 weeks.

Depth 0’ Surface ____________

5’ clear liquid

10’ clear liquid

15’ murky colored water

19’ thin sludge solids at 19’ to 21’

20’ thin sludge solids

21’ bottom thin sludge solids

Sludge levels had been reduced 3’-5″ and changed in characteristic from thick solids difficult to stir to think sludge that was stirable with a long pole. Clarification has occurred down to the 10’ depth level.

The end use of this lagoon water is to spray irrigate it over the following crops: corn, soybean, and cotton. Nutrients were measured and TKN levels had minimal change.

A second test occurred concurrently in two hog barns. A dose of Quellz® was added directly into the 8’ x 8’ x 40’ pits under the slatted floor of the hog barn. The product was allowed to remain in the pit for four weeks before the pit’s contents were flushed into the central lagoon. Odors began to abate in four (4) days, and the sludge in the bottom of the pit began to liquefy. Typically, flushing the barn requires both labor and lots of wash-down water. However, in this case, the sludge in the pit flowed freely without clogging the pump or plugging the interconnecting pipes to the lagoon.

Because of the observed ability of Quellz® abate odors, the hog farmer asked to spray some of the material over the contents of his “dead box.” A one gallon concentrate was atomized and sprayed over the carcasses in the dead box. The odor abated in one hour and also reduced the number of flies in the dead box.

While sludge reduction and denitrification are traditionally an anaerobic process,a dual zone lagoon can be established to address both aerobic and anaerobic issues. In other studies, the Quellz® enzymes have been documented to significantly increase the number of colony forming units (CFU) to aid in digestion of organic materials, reduce BOD and control odors.

However, it does this 18 times more effectively with a venturi aerator component that is used to continually strip carbon dioxide (CO2) a byproduct of microbial digestive processes which naturally buffers pH for enhanced microbial digestion, and to provide high levels of dissolved oxygen (DO) for enhanced microbial colony propagation.

Other qualitative studies on Quellz® are taking place, e.g. adding it to fresh water shrimp farming for lagoon clarification, organics reduction, ammonia-nitrogen reduction and pH buffering; added to naturally occurring bacteria to degrade hydrocarbon contaminants in groundwater; treating odors from landfills and reducing toxicity of landfill leachate, and others.

For additional information on Quellz® enzymes, MSDS or Venturi Aerator units contact John M. Salonich at Venturi Aeration, Inc. 603-635-8239 or e-mail: johns@venturi-aeration.com

The Bioclere™ trickling filter consists of a bed of highly permeable media to which microorganisms are attached and through which wastewater is trickled. The Bioclere™ uses a patented plastic filter media in a randomly packed configuration. The influent wastewater is passed from the primary settling tank, where most of the solids are separated from the untreated waste. While the Bioclere™ is most commonly a stand-alone unit, there are applications where the influent wastewater flow from the primary settling tank has certain characteristics that would require additional or enhanced pretreatment. In those cases, a Venturi Aeration Oxygenator unit is used in a pre-aeration tank to achieve reductions designed to reduce the biological loading on the Bioclere™. This reduces the overall capital cost of the total project, and increases performance of the combined system.

Pre-aeration of the influent wastewater in a separate aeration tank using a Venturi Aeration Oxygenator unit has many benefits for Bioclere™ systems:

1. Dissolved Oxygen: The liquid being processed through the venturi aerator unit is saturated with dissolved oxygen (DO). The discharged liquid is highly oxygenated with DO levels ranging between 5.0 mg/l and 7.5 mg/l.

2. Mixing and Equalization: The discharge from the venturi aerator unit mixes and equalizes the influent liquids with the contents of the tank. Any solids are kept in suspension by circulating the tank contents at 2 fps using the velocity of the discharge.

3. Odor Control: Imbedded malodorous and corrosive hydrogen sulfide from organic material is readily oxidized into soluble SO4, a non-odorous form of sulfur.

4. BOD Reduction: Pre-aeration induces large amount of dissolved oxygen into the aeration tank to effect BOD5 reduction from nascent bacteria in the sanitary wastestream to levels at which the Bioclere™ can be effective; this is usually < 500 mg/L.

5. Nitrification: With excess amounts of dissolved oxygen in the aeration tank, nitrification begins in the aeration tank enhancing the Bioclere™ unit’s performance.

6. Flotation of FOG: Conditioning with the Venturi Aeration Oxygenator causes imbedded fats, oils and grease (FOG) to separate and float to prevent their migration into the Bioclere™ unit.

7. Temperature: The Venturi Aeration Oxygenator has the ability to reduce the temperature of the influent wastewater. In field tests of the Venturi Aeration Oxygenator device with septage, temperature reductions have been documented to range between 2° and 6° C in summer months. Reducing elevated temperatures of the process liquid increases the solubility of dissolved oxygen, thus allowing for greater amounts of DO to achieve targeted biological reductions.

8. Non-chemical pH Control: As the nascent bacteria become active aerobically they produce carbon dioxide as a digestive byproduct. The increase in carbon dioxide lowers the pH. This increase in acidity can stress micro-organism performance in the Bioclere™ unit. Since the venturi aerator concurrently strips carbon dioxide (CO2) while oxygenating the liquid, a steady state pH is maintained on the liquids being decanted into the Bioclere™ unit.

9. Hydraulic Shear: Solids that migrate from the primary settling tank are conditioned in the venturi aeration device to increase their surface to enhance digestion.

10. Strips VOCs: The venturi aeration device protects the biomass on the trickling filter media by stripping certain weak Henry’s Constant VOCs that are characteristic of cleaning chemicals or detergents that degrade bacterial activity in the Bioclere™ unit.

There are many applications for Bioclere™ units, not all of them require pre-aeration. However in those cases where pre-aeration is required, a computer model has been developed to calculate the desired amount of dissolved oxygen that would be needed in pre-aeration to achieve targeted reductions in BOD5 for the influent wastewater. The computer model can assist the consulting engineer in the proper sizing of the aeration tank and venturi aeration oxygenator device to ensure desired reductions are achieved.

The pre-aeration tank does not use a submersible pump to provide the recirculation of the liquids to the venturi aeration device, because 1. Submersible pumps are not designed for continuous operation, and 2. Submersible pumps would transfer their heat from operation into the liquid being treated thereby reducing the solubility of dissolved oxygen in the process wastewater.

Summary: The addition of a Venturi Aeration Oxygenator unit in a pre-aeration and equalization tank can greatly enhance the performance of the Bioclere™ system allowing it to treat larger quantities of wastewater than could otherwise be achieved without adding additional Bioclere™ units to split the influent flow. This reduces overall project costs and increases efficiencies. Because of the many specific benefits listed above from pre-aeration, the Venturi Aeration Oxygenator should be utilized for preconditioning difficult wastestreams. The Bioclere™ is a class 1 device that cleans wastewater well in excess of secondary treatment requirements. The Venturi-Aeration Oxygenator unit is the preferred pre-aeration device for difficult wastestreams.

Bioremediation is the process of using bacteria, nutrients, enzymes and other biological augmentation products, under controlled conditions, to metabolize organic compounds into carbon dioxide, water and energy for the replication of cells. The principal requirements crucial to the bioremediation process successes are, 1. an active, hydrocarbon or contaminant specific microorganism population, 2. a continuous supply of dissolved oxygen (DO), 3. frequent addition of nutrients (N, P, S, etc.), 4. micronutrients to support biological processes and 5. “conditioning” of their working environment for optimal digestion (pH, temperature, catalytic enzymes, colony concentrations, etc.).

Technology Transfer

While the venturi principle is several hundred years old, the modern venturi aeration process using the Venturi Aeration OxygenatorÔ was developed for municipal, industrial and agricultural wastewater as well as potable water applications to condition the liquids for various desired results. In wastewater applications the device is predominately used to transfer high levels of dissolved oxygen into wastewater for BOD reduction while stoichiometrically oxidizing organic contaminants into benign forms. While in drinking water applications the venturi aeration process has been used to strip weak Henry’s constant substances in order to non-chemically shift pH (viz. CO2), remove soluble radon gas, and strip VOCs (TCE, PCE, etc.) from contaminated aquifers.

pH = 6.3 + Log (alkalinity / carbon dioxide).

Stripping the CO₂ means a logarithmic increase in pH in relation to the nascent (natural) alkalinity. This feature is important to the enhanced bioremediation process.

Since the venturi aeration process is very effective for: adding dissolved oxygen into wastewater, simultaneously stripping partially soluble substances with weak Henry’s constants and developing a biomass– it should be considered for bioremediation.

These three features make it an ideal device for use in environmental bioremediation projects that require high levels of dissolved oxygen to achieve biological reduction (biodegradation) activities and maintain a steady state pH (stripping CO₂) environment in which these biological processes will occur.

Importance of Dissolved Oxygen and pH/ORP Adjustment in Microbial Degradation

As with most bioremediation projects, the rate of contaminant degradation is usually limited by the amount of available dissolved oxygen available to support the microorganisms’ metabolic activity and to a greater extent the pH of the liquid in which degradation occurs. It cannot be emphasized enough that even in the presence of high dissolved oxygen (DO) levels biological activity may slow down if the liquid becomes too acidic (pH < 5.8) from the respired CO₂ of the biological degradation process. ORP (Redox) readings shift from –150 to +200. This large change in ORP is a measure of the increased microbial activity that is occuring.

Note: the principal byproducts of microbial digestion are CO₂ and H₂O. Further, in geographical areas like the Northeast, groundwater is naturally acidic to begin with because of a lack of minerals which can “buffer” pH. Additionally, certain hydrocarbons because of their length, molecular weight, shape and other chemical properties may resist transport into the cell walls of the microorganisms, in these cases the addition of specific enzymes aid in catalyzing the necessary biological reactions.

Unique Design and Operation

The venturi aeration process in wastewater applications routinely will transfer up to 7.5 mg/l of dissolved oxygen into a liquid [20° C at sea level]. However, the Venturi Aerator device can be configured to “saturate” groundwater with dissolved oxygen. It is proprietary knowledge of how the Venturi Aerator can be configured that makes it unique among technologies for enhanced bioremediation. Groundwater extracted from the plume of contamination is pumped into the Venturi Aeration Bioremediation system where the Venturi Aerator adds dissolved oxygen, strips weak Henry’s constant substances and adjusts pH non-chemically, floats free phase product for recovery and supports the growth of a viable biomass. In this manner groundwater is “conditioned” ex situ in the Venturi Aeration Bioremediation Unit, and then is injected into the subsurface vadose zone and groundwater for biological reductions of residual hydrocarbons or chlorinated solvents in the soil and groundwater.

Multiple Functions:

The single Venturi Aerator configured for bioremediation accomplishes all the tasks achieved by an array of different environmental equipment frequently used for bioremediation, i.e.:

1. air sparger with compressor or blower,

2. air stripper tower or column,

3. diffused air floatation (DAF),

4. a fixed film bioreactor,

5. reciculating well, and

6. chemical treatment for pH adjustment

By having only one (1) venturi aeration system accomplish all these combined tasks its makes the capital costs for setting up a bioremediation system very cost effective, and because it is actually moving groundwater to the bioreactor component in a closed loop system it makes the process “dynamic.” Many passive or static bioremediation technologies, e.g. addition of bacteria, nutrients and peroxides, or ORC (oxygen release compounds) require longer periods of time to treat a site just because they are “static.” Additionally, it may eliminate the need for expensive activated carbon adsorbers and their frequent changeouts, transportation and the disposal or reactivation of spent carbon associated with pump and treat systems, depending on clean air emission requirements for the specific project. If there are significant amounts of free phase products present in the groundwater a small oil skimmer or oil/water separator can be added for free phase product recovery directly in the bioremediation unit.

Full Scale System Tested

In the first full-scale demonstration project of this system, the Venturi Aeration Bioremediation unit, was at a site with contaminated groundwater (diesel fuel and gasoline). It was positioned on the site so the various hoses could be moved around the plume of contamination as required to influence the entire plume. The system was connected to the existing wells that were part of on-going “passive” remedial activities. The environmental contractor had been adding hydrogen peroxide to all the monitoring wells and observation wells to provide as much DO as possible approximately every two weeks. The process of adding diluted 35% hydrogen peroxide, microorganisms and nutrients took two man days two times a month.

With the Venturi Aeration Bioremediation unit the influent line into the unit was connected to an existing 0.5 hp Grundfoss pump in a four (4″) recovery well on the down gradient side of the plume. Groundwater was extracted at a rate of 30 gpm, and the pump was put on a timer to allow the well to periodically recharge. The groundwater was pumped directly into the Venturi Aeration Unit that immediately stripped the carbon dioxide from the groundwater changing the pH non-chemically. The pH of the extracted groundwater was consistently in an acidic range of 5.6 to 5.8 and was shifted to a neutral range 7.2 to 7.4 without addition of any chemicals exclusively by stripping the carbon dioxide. This is extremely beneficial to the microorganisms.

Conditioned Groundwater

The Venturi Aerator unit added dissolved oxygen (DO) by discharging the aspirated liquid into a stilling well. The continuous flow forced the highly aerated liquids to migrate to the bottom of the stilling well where they were attached with fine micro bubbles. These micro bubbles allow residual amounts of free phase product to float where they could be removed. DO stratified in the Venturi Aerator Bioremediation unit, at the top of the tank it measured 16.0-18.0 mg/l, in the middle 10.0-12.0 mg/l, and at the bottom 3.5-4.0 mg/l. Conditioned groundwater with a pH of 7.4 and DO levels of 10.0-12.0 mg/l were then injected into the plume using a diaphragm pump. Because of the pulling action of the Grundfoss extraction pump and the pushing action of the diaphragm injection pump, groundwater moved through the plume every 1:20 minutes from the injection well to the extraction well. This time was measured by adding a non-toxic biodegradable food grade coloring to the injected groundwater and timing its movement through the groundwater by observing its extraction into the Venturi Aeration unit. At a flow rate of 30 gpm, 1,800 gph can be extracted, conditioned and reinjected (43,000 gpd). For this pilot test site it is estimated that a 100% turn of the groundwater in the plume was achieved every five (5) days. By causing a movement of the groundwater to the extraction well, extracted groundwater could be “conditioned” and treated ex-situ prior to reinjection in the upgradient injection wells with microorganisms and nutrients already added to the neutral pH liquids. Groundwater temperatures at this site are 14-17° C and depth to groundwater averages 22’5″.

Hydraulic Flow

At the full-scale pilot system after several days of operation, groundwater had migrated into the plume from the surrounding areas and the surrounding outlying observation wells were dry while the system was operating. This indicates that the groundwater had migrated to the extraction points aiding in “soil washing” and reducing chances for smear in the vadose zone.

Preventing Iron Fouling

This site also has free iron (Fe++) at 35 mg/l. Iron can foul well screens and other system components. By oxidizing the iron in the Venturi Aeration unit, iron is immobilized and does not reenter the groundwater to plug the slotted well screens. However, for those sites with higher levels of iron in groundwater, a Hydro-Cat Catalytic Ionizer can be added to the system to keep iron colloidal in order to prevent it from fouling system components. Iron scaling also is reversible using the Hydro-Cat Ionizer.

Enzyme Catalyzed Biodegradation

While no catalytic enzymes have been added to this pilot test site, they have been added to another hydrocarbon contaminated groundwater site in California where there were significant increases in metabolic reactions were directly attributable to the enzymatic activity. The field microbiologist calculates enzyme-catalyzed reduction rates have increased by almost 1000% based on SPC (standard plate count). The enzymes (QuellzÔ ) are protein-based substances that help catalyze these reactions. By attaching themselves to hydrocarbons, enzymes allow certain hydrocarbons that are ordinarily hydrophobic in nature to cross the cell walls (membranes) into the microorganism for degradation. Regardless of the amounts of DO used to enhance degradation, certain hydrophobic molecules, by nature, are unable to cross the cell membrane thereby leaving the molecule undegradable by biological processes. In these cases, enzymes help catalyze cellular transport of these hydrophobic molecules for degradation.

Summary

The Venturi Aeration treatment process for used for treating wastewater and potable water is directly transferable into the environmental field for enhanced bioremediation. One Venturi Aerator can take the place of several more pieces of expensive environmental cleanup equipment making the cost of remediation economical while more importantly accelerating the degradation of hydrocarbon and solvent contamination in both the saturated vadose zone and in groundwater. For hydrophobic hydrocarbons, adding catalytic enzymes helps catalyze beta-oxidative reductions that would not occur biologically, or would otherwise occur very slowly.

The effluent of the EQ tank is pumped from the pretreatment tank into a lift station operated by the town but located on Tannery property immediately adjacent to the EQ tank. Then the wastewater entering the lift station is pumped up a hill to a drop manhole in the center of the street at the main intersection of Town where it enters into a gravity flow line to the treatment plant 2 miles away. The problem with this treatment scenario occurs when the process wastewater enters the drop manhole. Because of the turbulence very large amounts of hydrogen sulfide gas are released in the manhole, which migrate into the surrounding residential area. Malodors linger for hours because the hydrogen sulfide concentrations are so high.

The local wastewater treatment plant personnel receive numerous complaints daily from residents about the odors at the intersection, and these odors are especially bad during warm summer days. The wastewater utility’s consulting engineer contacted Venturi Aeration, Inc. directly trying to determine what treatment could be accomplished in the lift station to prevent the release of hydrogen sulfide in the drop manhole.

When treatment plant personnel investigated the odor complaints they discovered that H₂S levels where “off the scales” of their H₂S gas detection analyzer, which only had a range scale of 0.5 to 100 ppm, the device would immediately “peg out.” Additionally, there were corrosion-related problems in that entire gravity flow line of the collection system associated with the release of the hydrogen sulfide gas in the drop manhole. Sections of concrete would fall into the sewer line and the line was caked with lime that the tannery used for pH adjustment. The Town has to jet clean this sewer line twice a year to remove the scale and they pass the cost for cleaning back to the Tannery in the form of a surcharge.

Solution:

Venturi aerators are frequently used in connection with lift stations to oxidize hydrogen sulfide odors into soluble SO₄. However, it became very apparent that the best location for a venturi aerator solution for odors was not in the Town’s lift station but rather to treat the Tannery process wastewater at the Tannery itself. The best location for treatment was in their pretreatment EQ tank prior to discharge to the lift station. Venturi Aeration, Inc. configured a system using a single venturi aerator that would:

1. Add sufficient dissolved oxygen to effectively oxidize hydrogen sulfide to eliminate odors at the drop manhole.

2. Reduce the temperature of the process wastewater to allow for the solubility of dissolved oxygen to transfer into the wastewater.

3. Accomplish mixing and equalization for the alkalinity being added to the tank for pH control.

4. Strip carbon dioxide to non-chemically reduce the amount of alkalinity being added for pH adjustment.

5. Eliminate the addition of the ferric chloride used for odor control.

6. Eliminate the blower, which exceeds OSHA PEL for noise.

Venturi Aeration, Inc. installed a Gorman-Rupp T-6 series pump (with modification) with a 3-phase, 40-hp motor to provide the pumping capacity to develop the required head to operate a venturi aerator Model VA-1100 at 20 psi. The venturi aerator was installed on the top of the EQ tank. The kinetic energy of the discharge from the venturi aerator is also used for mixing and equalization.

The venturi aerator aspirates 2.2 volumes of ambient air into one (1) volume of process wastewater to provide for both cooling the process wastewater and inducing oxygen transfer. Even though the temperature of the influent process wastewater is high 115°F (46°C), the venturi aerator reduces the temperature to 86°F (30°C). This is accomplished by the continuous recirculation of the contents of the equalization tank by aspirating ambient air into the wastewater. For every one volume of process wastewater 2.2 volumes of ambient air are mixed in the venturi aerator unit itself. There is a complete 100% turn of the contents every 2.3 hours. As the venturi aerator decreases the temperature of the process wastewater the solubility of dissolved oxygen increases achieving H₂S oxidation and allowing for sufficient residual DO to be present in the treated wastewater when it reaches the drop manhole. Having residual DO in the effluent prevents H₂S from reforming as the oxygen is onsumed in the sewer line.

There hasn’t been sufficient time to evaluate the venturi aerator’s impact on reducing lime scale in the gravity collection line due to the lower levels of lime addition for pH control. However, the basic fact that odor complaints from Town residents have stopped is testimony that the venturi aerator was the correct solution for the problem. Additionally, the Tannery has reduced both its chemical costs by reduced levels of hydrated lime and ferric chloride as well as labor costs.

Most importantly, Town residents now believe that the Tannery doesn’t “stink” anymore and that the Tannery heeded their numerous complaints to solve the odor problem that had persisted for years. The community relations value of the venturi aeration project was as important to the Tannery as were the savings since many of the workers at the Tannery live in the local Town.

Solution:

Kline’s was referred to Venturi Aeration, Inc. by their consulting engineer, Glace Associates, in Harrisburg, PA. Venturi staff members visited the site with the engineer and determined that only one (1) venturi aerator was required for each 100,000-gallon tank to achieve the desired odor control, to accomplish mixing and oxidation, and for BOD reduction.

Hydrogen sulfide molecules in septage that are pumped through the venturi aerator unit are immediately oxidized by the oxygen derived from ambient air. This is a first order chemical reaction. The venturi aerator provides 2.2 volumes of ambient air to one volume of liquid being processed. It transfers 20% of the available oxygen in the 2.2 volumes of ambient air into the liquid (20° C @ sea level). Further, the residual oxygen not used to oxidize H2S into soluble SO₄ is used to effect biological reductions of BOD. The Kline facility had been experiencing problems achieving their targeted BOD discharge permit limit, <200. Since the addition of the venturi aerators the facility has consistently experienced discharge levels <90 for BOD.

The kinetic energy of the discharge from the venturi aerators is used for mixing and equalization. The liquids are drawn into the venturi aerator from the bottom of the tank. The discharge is tangential to the sidewall of the tank causing the liquids in the tank to spin. Because of spinning solids migrate to the center of the tank where they are drawn back into the pump for resuspension and digestion in the treatment tank.

The addition of the venturi aerators in the EQ tanks has solved several operational problems for Kline’s. First, and most notable, is the lack of odor complaints from the neighbors in a nearby apartment complex. Second, it allows Kline’s to “eliminate” their hefty surcharges associated with discharges not in compliance with their permit, and third, it helps reduce operational costs.

The cells in all living organisms are chemical factories, however, only a few of the hundreds of compounds necessary for the operation of organisms are obtained from their diet. Most of the required compounds are synthesized within the cells, which means that the chemical reactions take place within the cells of the organism.

Nearly all of these synthesized reactions are catalyzed by enzymes, which are protein molecules that increase the rates of the chemical reactions within the cells of the organism without themselves undergoing any change. Without enzymes, organic life forms would not be possible.

Like all catalysts, enzymes do not change the position of equilibrium; i.e. enzymes cannot make a reaction take place that would not take place without them. What they do is increase the rate; they cause the reactions to take place faster. As catalysts,enzymes are remarkable in two respects:

1. They are extremely effective, increasing reaction rates by anywhere from 10⁹ to 10 ²⁰ times, and
2. They are extremely specific.

Every organism has many enzymes—more than 3000 in a single cell. Presumably, each chemical reaction has one enzyme that catalyzes it. This means that enzymes are very specific, each one speeding up only one reaction or class of reactions. For example, the enzyme urease catalyzes only the hydrolysis of urea and not that of other amides. Digestive enzymes, which also split proteins, are located within the organism’s digestive system.

Enzymes are classified into six major groups according to the type of reaction they catalyze:

1. Oxidoreductases: catalyze oxidations and reductions.
2. Transferases: catalyze the transfer of a group of atoms, such as CH₃, CH₃CO, or NH₂ from one molecule to another.
3. Hydrolyases: catalyze hydrolysis reactions.
4. Lyases: catalyze the addition of a group to a double bond or the removal of a group to create a double bond.
5. Isomerases: catalyze isomerization reactions.
6. Ligases (or synthetases): catalyze the joining of two molecules.

FACTORS AFFECTING ENZYMATIC ACTIVITY

Enzyme activity is a measure of how much reaction rates are increased. Factors that affect enzyme activity are: concentration, temperature, and pH.

Concentration:

If we keep the concentration of the substrate (the compound on which the enzyme works to speed up the reaction) constant and increase the concentration of the enzyme, the rate increases linearly. That is, if the enzyme is doubled, the rate also doubles.

Temperature:

Temperature affects enzyme activity because it changes the three-dimensional structure of the enzyme. In uncatalyzed reactions, the rate of activity usually increases as the temperature increases. The effect of temperature on enzyme-catalyzed reactions is different. When we start at a low temperature, an increase in temperature first causes an increase in reaction rate. Once an optimum temperature is reached, the substrate may then not fit properly onto the changed enzyme surface. Therefore the rate of reaction begins to decrease.

pH:

Since the pH of its environment changes the conformation of a protein, we can anticipate effects similar to those observed when the temperature is changed. Each enzyme operates best at a certain pH. Once again, within a narrow pH range, changes in enzyme activity are reversible. However, at pH extremes (either acidic or basic), enzymes are denatured irreversibly, and enzyme activity cannot be restored by changing back to the optimal pH.

As with any biological process oxidation enhances the metabolic digestion of organisms to accelerate their consumption of nutrients and foods. This is true for humans as well as microorganisms. Living cells are in a dynamic state, which means that compounds are constantly being synthesized and then broken down into smaller fragments. Hundreds of reactions are taking place. It is the total sum of all the chemical reactions involved in maintaining the dynamic state of the individual cell that is called metabolism. Metabolic reactions are divided into two groups:

1. those in which molecules are broken down to provide the energy needed by the cell and
2. those that synthesize the compounds needed by the cell. Two terms here are important.

The process of breaking down molecules to supply energy is called catabolism.

The process of building up molecules (synthesis) is anabolism.

There are two parts to the common catabolic pathway. This first is the citric acid cycle and the second is the oxidative phosphorylation pathway or the respiratory chain. It is the citric acid cycle that breaks down carbon molecules, and the carbon atoms are released in the form of carbon dioxide (CO₂), and the hydrogen atoms and special compounds in the cell pick up electrons. These special compounds are reduced of their hydrogen ions (H⁺) which are expelled outside the cell wall of the microorganism. In their drive to get back into the cell, the H⁺ ions form the energy, and once back in the cell they combine with Oxygen that picked up the electrons and produced water (H₂O). The enzymes that catalyze the common catabolic pathways in microorganisms are located in the cell, however external ions and molecules can penetrate the outer wall of the cell membrane to aid in reactions.

The reduced coenzymes in the citric acid cycle are end products. They carry hydrogen ions and electrons and thus the potential to yield energy when they combine with oxygen to form water.

4H⁺ + 4e^- + O₂ « 2H₂O

This simple exothermic reaction is carried out in many steps, all of which involve enzymes.

The protons that enter the cell membrane combine with electrons transported through the electron transport chain and combine with oxygen to form water. The net result of the various processes is that the oxygen respired by an organism combine with four H+ ions and four electrons to give two water molecules. The four H+ ions and four electrons come from molecules produced in the citric acid cycle. The functions of oxygen, therefore, are:

1. to oxidize the special compounds so that all these molecules can go back and participate in the citric acid cycle, and
2. to provide energy for the conversion of other compounds.

What does all this means for the animal-derived lagoon wastes?

Waste products from cattle and hogs have become a major concern for the environmental regulators. Waste streams contain various sulfur and nitrogen-containing molecules that have olfactory nuisance characteristics, in high concentrations, present a condition that can cause respiratory distress in the animals as well as humans. E.g. hydrogen sulfide and –mercaptans in high enough concentrations can cause edema and even death. Additionally, if these substances leak or leach into groundwater they create unhealthy conditions for biota. Regulators have been responding to nuisance complaints from residents near animal farms and even though their homes where built in proximity to an already existing hog farm or cattle ranch they still complain to the regulators to control both odors and impact from runoff. The situation presents a unique problem to the farmer because adding costs to address environmental issues raises his cost and reduces his margin, but there is help that is available.

Quellz:

Now there is a product called Quellz which is the result of five years of intensive field research. It is a proprietary blend of enzymes that are derived from the various classes of enzymes to catalyze the degradation of animal waste products (digestive and urine) into benign form to mitigate negative impact on the environment. Quellz addresses issues of odors emanating from sulfur-based (e.g. hydrogen sulfide) and nitrogen-based (e.g. urea-ammonia) compounds by catalyzing natural biological reactions. Enzymatic catalytic reactions (as shown above) involve the exchange of hydrogen ions, metabolism of cells, and environmental issues (pH, temperature, and concentration). Quellz works in a broader range of temperature and to greater extremes in pH than other enzyme products. The Quellz formulation also is highly concentrated and works best when diluted—as a minimum—one gallon to 75,000 gallons.

Adding Quellz to lagoons will assist in odor control and in the molecular reduction of ammonia and sulfur-containing substances by stimulating native bacteria and boosting their metabolism for enhanced digestion of carbon and assimilation of the hydrogen in to a form other than ammonia. Further, Quellz has been added to Shrimp farming and Aquaculture lagoons as a waste products clarifier.

Bioremediation:

In two recent field studies Quellz has been added along with bacteria and nutrients used in the degradation of hydrocarbon contaminated groundwater. It has been demonstrated that it increases the standard plate count (SPC) of facultative bacteria by 1000 times in an aerobic treatment system, and has degraded MTBE—a component in reformulated gasoline—up to 6000 times faster than conventional bioremedial methods including ORC-type compounds.

Extended Aeration:

In order for the enzymatically enhanced oxidation to occur there needs to be an abundant supply of dissolved oxygen (DO) and a neutral pH. Increasing the levels of dissolved oxygen in various wastewaters and sludges can be achieved by using the Venturi Aerator. Not only is the venturi aerator important for supplying dissolved oxygen it also conditions the wastewater in several ways. First, as microbial activity increases there is a release of carbon dioxide as a byproduct of microbial digestion. As carbon dioxide levels increase the pH of the wastewater will decrease.

pH = 6.35 + log (alkalinity/carbon dioxide)

This means that the Venturi Aerator is a mechanical means of non-chemical pH control.

It was discussed above that enzymes and microbes like to operate in a relatively neutral pH range. Using the venturi aerator ensures that a steady state pH will be maintained because the venturi aerator will strip carbon dioxide (CO2) while simultaneously adding dissolved oxygen (DO). Secondly, the microbial digestive activities can be exothermic, that is they may give off heat. Using the Venturi Aerator will continually aspirate ambient air into the liquid thereby regulating temperature of the liquid.

When adding an enzymatic formulation, like Quellz, the Venturi Aerator will allow for “equalization and mixing.” This is important because Quellz works best when it has a high surface area and is adequately mixed. The first zone of mixing is within the venturi Aerator itself, and the second zone of mixing takes place from the force of the kinetic discharge of the “treated” liquid from the discharge nozzle of the Venturi Aerator. By designing the system so that liquids are pulled from the bottom of a lagoon or tank—the most anoxic zone—into the Venturi Aerator, the greatest amount of dissolved oxygen can occur and well as cooling an non-chemical pH control. Many “first order reactions” occur within the venturi aerator’s mixing and oxidizing zone.

Another important feature of the Venturi Aerator is its ability to effectively oxidize hydrogen sulfide and –mercaptans into benign olfactory forms. E.g. H2S is converted in soluble SO4 and the H-S bond in the mercaptans is also oxidized. This reaction is reversible as oxygen is consumed by the microbes, therefore it is important to size the aeration system to maintain “residual DO” levels to be >1.0 mg/l, the Venturi Aerator will induce up to 7.5 mg/l of DO under most environmental conditions.

The combination of adding supplementary enzymes with the features of extended venturi aeration are a winning combination in solving the problems attributed to sulfur and nitrogen-containing substances associated with various wastewater liquids.

REFERENCES

Bailey, J.E., and Ollis, D.F., Biochemical Engineering Fundamentals, McGraw-Hill, New York, 1977.

Bettelheim, F.A., and March, J., Introduction to Organic and Biochemistry, 2^nd Ed., Harcourt Brace, New York, 1984.

McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill, New York, 1962.

Sawyer, C. N., and McCarty, P.L., Chemistry for Environmental Engineering, 3^rd edition., McGraw-Hill, New York, 1978.

Air flotation technology is a proven, reliable method for removing oil & grease (O&G) and suspended solids (TSS) from wastewater or contaminated groundwater. It is the process of using micro-sized bubbles of air to enhance the natural buoyancy of substances with low specific gravities to float them to the surface of the skimmer tank. Based on the specific gravity a know rise time can be computed to determine removal efficiency. Once liquids enter the skimmer section of the tank the O&G and floatable TSS can be effectively removed with a unique slimmer blade that ever so gently skims the surface of the quiescent tank.

Unlike other DAF systems which require polymers that increase treatment costs, diffusers that be prone to fouling with biofilm or from oil & grease, and noise from a compressor or blower. The venturi aerator DAF effect technology is totally external to the tank and uses a high efficiency water quality pump to accelerate the liquids through the venturi which causes a natural vacuum to aspirate ambient air into the wastewater. The air is intimately commingled with the wastewater entraining micro bubbles that are discharged into Venturi Aeration, Inc.’s unique stilling well design, allowing the liquids to be forced out the bottom of the tank. In doing so, not only are micro bubbles attached to oil & grease to cause them to float, but oxygen is transferred which can aid in biological reduction of BOD (biochemical oxygen demand). The Venturi DAF-Effect Oil Skimmer can also be used effectively for oil and grease with specific gravities >0.90.

The Venturi Aerator DAF Effect Oil Skimmer units are made from Stainless Steel components and can be equipment with standard ODP motors or EP (explosion proof) motors depending on their application and the environment. Units can be built in different sizes with different flow rates specific to a project’s requirements. HydroQuip, Inc. (North Attleboro, MA) has a license to manufacture and market the Venturi DAF-Effect Oil Skimmers for environmental and process applications. HydroQuip, Inc. can be reached at 508-695-3640.