Posts Tagged ‘odor control’

Floating Covers For Evaporation and Odor Control

November 11, 2010

Floating Cover Applications

Properly designed reservoir floating cover systems prevent fluid loss due to evaporation, reduce chemical demand and improve water quality by preventing contamination from bird droppings, airborne particulates, dead animals pollen and other pollutants.  Floating covers block off sunlight preventing algae bloom.  They also reduce the production of trialomethane (THM) type compounds such as chloroform from forming that result from the combining of organic substances with chlorine due to reductions in chlorine demand.  In anaerobic digester systems, floating covers are increasingly being used to capture organic gases and to reduce biological oxygen demand (BOD).

Floating cover systems were introduced over 30 years ago.  Many have provided a service life beyond 20 years.  When first introduced, materials and designs were not developed and in some cases had limited success. Today, with advancements in design and materials, floating covers offer the low cost quality solution of choice where water quality standards require potable water reservoirs be covered.

Floating cover applications range from anaerobic digestion covers for wastewater systems, to potable water reservoir covers for municipal drinking water applications.  In farming applications they have been successfully used with enzymes to capture methane gas that is used to fuel electricity producing generators that can satisfy 150% of a typical swine farm’s electrical power requirements.  This alternative generates renewable “green energy” from an otherwise polluting system that provides zero return on investment.  In agricultural and other water management applications, floating covers are increasing  being used for evaporation control and odor control.

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Part 2 of Biogas and Anaerobic Digestion

October 26, 2010

Biogas and Anaerobic Digestion | Covered Lagoon

A covered lagoon digester is a large anaerobic lagoon (not a manure storage pond or basin) with a long retention time and a high dilution factor.  Typically covered lagoons are used with flush manure management systems that discharge manure at 0.5 to 2 percent solids.  The in-ground, earth or lined lagoon is covered with a flexible or floating gas tight cover.  They are not heated and considered ambient temperature digesters.  Retention time is usually 30-45 days or longer depending on lagoon size.

In climates that have elevated year round temperatures, such as southern and western U.S., these digesters can produce stable, reduced odor, nutrient rich effluent for application on fields and crops; pathogen and weed seed reduction and; produce biogas for farm energy use.  Heat recovery from the biogas can be used to heat nurseries on swine farms and warm milking parlors on dairy farms.  Very large lagoons in hot climates may produce sufficient quantity, quality and consistency of gas to justify use in an engine generator.  In areas with cooler climates, waste digestion, odor control and gas production will be less consistent and the low quality gas may need to be flared off much of the year for odor control and greenhouse gas reduction.

Why Use Floating Covers?

October 12, 2010

Floating Cover Systems

Floating Cover Systems are successfully used in several commercial and municipal applications.  Some examples include:

  • evaporation and algae growth prevention
  • potable water protection from pollution and contamination
  • odor and emission control
  • biogas recovery for power generation or flaring
  • protection of birds and waterfowl from contact with hazardous liquids
  • remediation contamination

Why Use Floating Covers?

The best engineered floating cover systems cost 75% to 85% less than most every acceptable rigid roof structure.  A single floating cover can exceed over a million square feet / 93,000 square meters of surface area and be viable.  Saving of natural resources is another large factor that should be considered.

Floating cover systems prevent water loss due to evaporation; greatly reduce algae growth and treatment chemical demand resulting in improved water quality.  They also provide barriers against contamination by dead animals, airborne particles such as pollen and bird droppings.

In potable water contamination applications, another advantage is treatment chemical cost reduction and positive health impact as considerably less chlorine is required in covered reservoirs.  Using less chlorine in potable water enhances safety by reduced production of trihalomethane (TTHM) (a methane-derived compound that contains three halogen atoms, e.g. chloroform, formed especially during the chlorination of drinking water) type compounds like chloroform that result from the combining of organic substances with chlorine.

Floating Cover Systems have been used for about 35 years.  Service life’s of 20 years or more have been recorded in potable water applications.  Gas collecting floating cover systems can be expected to perform for about ten years.

Floating Cover Systems For Odor Control and Gas Collection

September 13, 2010

Odor Control | Gas Collection

Odor Control & Gas Collection Covers are specifically designed for each client utilizing a variety of material options.  Cover applications can be used with any type of gas collection from water basin and keep rain and snowmelt water separate from wastewater under the cover. Advantages of a cover include installation without site interruption, use on tanks or lagoons, elimination of rainwater ponding problems, elimination of gas ballooning, provides high buoyancy and rigidity, hatches can provide access to in-basin equipment, improved quality with pre-manufactured panels and are fabricated at IEC’s plant, so field welding is not required.

Modular Cover System comprised of a series of individual casings connected together to form a complete floating cover system.  Each individual casing consists of a panel of closed cell insulation encapsulated between two sheets of durable geomembrane.  The result is a unique floating cover system that provides insulation values ranging from R-2 to R-30; and is engineered and manufactured to specific dimensions/basin requirements.

The Modular Cover System offers the following advantages over conventional covers systems:

  • maintenance free
  • can be installed on tanks or lagoons
  • adepts to varying water levels
  • individual casings are removable
  • installed without site interruption
  • shorter installation time, no field welding required
  • installation requires less heavy equipment
  • eliminates rainwater ponding problems
  • eliminates gas ballooning
  • high buoyancy and rigidity
  • hatches can provide access to in-basin equipment

Floating Covers Eliminate Algae Growth and Reduce Odors

August 5, 2010

Floating covers eliminate algae growth and airborne contamination, and reduce odors, evaporation and thermal losses.  Covers may be modular or all-encapsulating.  The latter covers fully encapsulate the upper surface of the reservoir by being mechanically fixed and sealed around the perimeter.  They can be designed to allow for fluctuating water levels, rainwater drainage and routine access.

Floating Covers

Floating covers use flexible geomembranes to enclose the top of a pond.  Floating covers are commonly used for odor control, dilution and evaporation control, and in the containment of treated potable water.  A floating cover is an economical alternative to tanks and concrete vaults for water storage and is one of the few techniques available to cover very large volumes of water.

Floating covers are a unique use for geomembranes where an engineered membrane system is placed on top of the liquid in a pond.  This cover needs to move with changes in water level, resist movement in wind, collect precipitation, and resist damage from ice.

The Modular Cover System offers the following advantages over conventional covers systems:

  • maintenance free
  • can be installed on tanks or lagoons
  • adepts to varying water levels
  • individual casings are removable
  • installed without site interruption
  • shorter installation time, no field welding required
  • installation requires less heavy equipment
  • eliminates rainwater ponding problems
  • eliminates gas ballooning
  • high buoyancy and rigidity
  • hatches can provide access to in-basin equipment

Geosynthetics In Agricultural Applications

August 3, 2010

Agricultural Use Of Geosynthetics

Agricultural use of geosynthetics is one of the fastest growing market segments worldwide.  The earliest geosynthetics applications were for on farm use and some of the earliest specifications were directed at agricultural use of pond linings.  These early uses included the lining of ditches to help save valuable water as well as the lining of farm ponds and water harvesting catchments in the arid regions of the world.

Today, there is a wide variety of applications ranging from covered and uncovered ditch linings and ponds to protection of the groundwater and surface waters that are being polluted by animal waste.  The use of geosynthetics and in particular geomembranes on the farm has come a long way and has grown significantly in recent years, especially with more stringent governmental legislation as well as public awareness through programs such as those developed by the USDA/NRCS, U.S. EPA and governmental agencies in other countries.

Containment As A Requirement

Potable water sources are becoming more and more scarce and water is becoming more costly.  The requirement to provide a barrier against high rates of water seepage loss is already a reality in many more areas than just the arid and semiarid regions of the world.  And, just as water is important to conserve, it is even more important to environmentally protect surface and groundwater sources from pollution due to animal waste and the air we breathe from noxious gases and odors.  Again, containment with a reliable time proven method is a requirement, not just an option due to  environmental legislation in many parts of the world.

Shown here: Anaerobic digesters with waste lagoon

Geosynthetics will provide a reliable cost effective alternative to traditional compacted soil and clay liners that provide much less in seepage control, are highly variable in quality and may not be acceptable for design and regulatory compliance.  Although geomembranes are the primary type for use as a barrier or odor control cover, other geosynthetics are used in conjunction with geomembranes and include geotextiles, geo-composites, and geonets.

Animal Waste Lagoon Liners

Animal waste lagoons contribute to the pollution of ground and surface waters worldwide.  To control waste seepage, compacted earth linings as well as geosynthetics are utilized.  However, with the increasing concern over pollution and governmental legislation, the use of geosynthetics has been increasing very rapidly.  In particular, exposed geo-membranes, geo-membranes with soil cover and GCL’s with soil cover are currently being used.  In addition, geo-textiles and geo-net composites are utilized for protection / gas transmission.

Animal Waste Odor Control Covers

A growing number of scientists and public health officials have traced a variety of health problems to vast amounts of concentrated animal waste which emit toxic gases such as hydrogen sulfide and ammonia.  Odor control covers can be a low cost geomembrane or coated fabric or they can be a more expensive engineered floating geo-composite cover system dependent on the design and criticality of the containment.

Shown here: Irrigation canal

Water Conveyance
Geosynthetics and most notably geomembranes have been used for decades in preserving and transporting clean water for on farm use.  The conveyance of water in ditches, laterals and main canals for delivery to crops is as common as on farm water storage tanks and ponds.  However, water is becoming more and more scarce and more costly especially with the drought conditions in many parts of the World.  Seepage loss in canals and ditches can approach 30 to 50% but loss of valuable water can be eliminated with the use of geosynthetics as lining systems.  Both soil covered and exposed geomembranes are used extensively in the lining of both new and old canals that require rehabilitation.

In addition, old cracked concrete lined canals have lost their effectiveness over the years and are being replaced or repaired with geomembranes.  Water conveyance systems utilize other geosynthetics in conjunction with geomembranes such as protection geo-textiles, geocomposites and geo-grids.

Water Containment
Water containment in ponds and concrete tanks for on farm use is just as important as water conveyance in that seepage and loss of valuable water should be minimized, especially for remote ponds and tanks.  Soil covered geomembranes and GCL’s are used for the construction of new or the rehabilitation of old ponds.  Exposed geomembranes are used to re-line old stock water concrete tanks or to line

Anaerobic Digesters
Anaerobic digesters are used to rapidly decompose animal waste in a controlled environment thus allowing the recovery and use of methane-rich low Btu biogas.  Biogas is used to fuel combined heat and power (CHP) generators that produce on farm electricity, process heat and domestic hot water.  They are also a viable method of waste management due to the fact that both bottom lining systems as described above and flexible cover systems are used.  With every digester constructed, geosynthetics are used to either line the anaerobic lagoon or cover the lagoon for collection of biogas. The number of operating digesters is rapidly increasing worldwide as government funding is becoming available for farm installations.

Data provided with compliments http://www.geosyntheticssociety.org and R. Frobel.

Patented Design Floating Covers, Tank Systems, Storage Lagoon Covers and Liners

July 6, 2010

IEC, a company with 16 years experience designing, fabricating, and installing industrial cover and liner systems, designs its products to provide many years of lasting service in a variety of environments and applications.  Since 1993, the company has designed, fabricated and installed more than 250 projects involving odor control, gas collection, pond liner systems and tank liner systems.

IEC’s Odor Control & Gas Collection Covers are specifically designed for each client utilizing a variety of material options.  Cover applications can be used with any type of gas collection from water basin and keep rain and snowmelt water separate from wastewater under the cover. Advantages of a cover include installation without site interruption, use on tanks or lagoons, elimination of rainwater ponding problems, elimination of gas ballooning, provides high buoyancy and rigidity, hatches can provide access to in-basin equipment, improved quality with pre-manufactured panels and are fabricated at IEC’s plant, so field welding is not required.

IEC also has a patented Modular Cover System comprised of a series of individual casings connected together to form a complete floating cover system.  Each individual casing consists of a panel of closed cell insulation encapsulated between two sheets of durable geomembrane.  The result is a unique floating cover system that provides insulation values ranging from R-2 to R-30; and is engineered and manufactured to specific dimensions/basin requirements.

The Modular Cover System offers the following advantages over conventional covers systems:
• maintenance free
• can be installed on tanks or lagoons
• adepts to varying water levels
• individual casings are removable,
• installed without site interruption
• shorter installation time, no field welding required
• installation requires less heavy equipment
• eliminates rainwater ponding problems
• eliminates gas ballooning
• high buoyancy and rigidity
• hatches can provide access to in-basin equipment

Floating Cover Systems

June 8, 2010

Floating Cover Systems

Floating cover systems have been used successfully for nearly 30 years.  With current advancements in design and materials, floating covers offer a low cost alternative to traditional tanks, concrete vaults and fixed-cover systems used for liquid and semi-solid storage.  Applications for floating covers can be far reaching, but the primary objective of a properly designed cover is to either prevent the loss of characteristics desired for your containment effort, or to prevent the introduction of particulates and other characteristics that negatively affect the containment effort.

Floating cover designs fall into a few specific types.  Defined Sump, Tensioned and Modular are the more common designs.  A variety of geomembranes have proven effective in these system designs: HDPE, reinforced polypropylene and XR-5 are just a few.  Floating covers can be used for potable water storage, odor control, methane gas capture, heat loss prevention, deter algae growth, chemical containment, evaporation control, airborne contaminants and to prevent dilution.

Types of Anaerobic Digesters Part 1

June 1, 2010

Types Of Digesters

There are three basic digester designs. All of them can trap methane and reduce fecal coliform bacteria, but they differ in cost, climate suitability and the concentration of manure solids they can digest.

A covered lagoon digester, as the name suggests, consists of a manure storage lagoon with a cover.  The cover traps gas produced during decomposition of the manure.  This type of digester is the least expensive of the three.

Covering a manure storage lagoon is a simple form of digester technology suitable for liquid manure with less than 3-percent solids.  For this type of digester, an impermeable floating cover of industrial fabric covers all or part of the lagoon.  A concrete footing along the edge of the lagoon holds the cover in place with an airtight seal.  Methane produced in the lagoon collects under the cover.  A suction pipe extracts the gas for use.  Covered lagoon digesters require large lagoon volumes and a warm climate.  Covered lagoons have low capital cost, but these systems are not suitable for locations in cooler climates or locations where a high water table exists.

A complete mix digester converts organic waste to biogas in a heated tank above or below ground.  A mechanical or gas mixer keeps the solids in suspension.  Complete mix digesters are expensive to construct and cost more than plug-flow digesters to operate and maintain.

Complete mix digesters are suitable for larger manure volumes having solids concentration of 3 percent to 10 percent.  The reactor is a circular steel or poured concrete container.  During the digestion process, the manure slurry is continuously mixed to keep the solids in suspension.  Biogas accumulates at the top of the digester.  The biogas can be used as fuel for an engine-generator to produce electricity or as boiler fuel to produce steam.  Using waste heat from the engine or boiler to warm the slurry in the digester reduces retention time to less than 20 days.

Plug-flow digesters are suitable for ruminant animal manure that has a solids concentration of 11 percent to 13 percent.  A typical design for a plug-flow system includes a manure collection system, a mixing pit and the digester itself.  In the mixing pit, the addition of water adjusts the proportion of solids in the manure slurry to the optimal consistency.  The digester is a long, rectangular container, usually built below-grade, with an airtight, expandable cover.

New material added to the tank at one end pushes older material to the opposite end.  Coarse solids in ruminant manure form a viscous material as they are digested, limiting solids separation in the digester tank. As a result, the material flows through the tank in a “plug.”  Average retention time (the time a manure “plug” remains in the digester) is 20 to 30 days.

Anaerobic digestion of the manure slurry releases biogas as the material flows through the digester.  A flexible, impermeable cover on the digester traps the gas.  Pipes beneath the cover carry the biogas from the digester to an engine-generator set.

A plug-flow digester requires minimal maintenance.  Waste heat from the engine-generator can be used to heat the digester.  Inside the digester, suspended heating pipes allow hot water to circulate.  The hot water heats the digester to keep the slurry at 25°C to 40°C (77°F to 104°F), a temperature range suitable for methane-producing bacteria.  The hot water can come from recovered waste heat from an engine generator fueled with digester gas or from burning digester gas directly in a boiler.

There are three basic digester designs.  All of them can trap methane and reduce fecal coliform bacteria, but they differ in cost, climate suitability and the concentration of manure solids they can digest.

A covered lagoon digester, as the name suggests, consists of a manure storage lagoon with a cover.  The cover traps gas produced during decomposition of the manure.  This type of digester is the least expensive of the three.

Covering a manure storage lagoon is a simple form of digester technology suitable for liquid manure with less than 3-percent solids.  For this type of digester, an impermeable floating cover of industrial fabric covers all or part of the lagoon.  A concrete footing along the edge of the lagoon holds the cover in place with an airtight seal.  Methane produced in the lagoon collects under the cover.  A suction pipe extracts the gas for use. Covered lagoon digesters require large lagoon volumes and a warm climate.  Covered lagoons have low capital cost, but these systems are not suitable for locations in cooler climates or locations where a high water table exists.

A complete mix digester converts organic waste to biogas in a heated tank above or below ground.  A mechanical or gas mixer keeps the solids in suspension. Complete mix digesters are expensive to construct and cost more than plug-flow digesters to operate and maintain.

Complete mix digesters are suitable for larger manure volumes having solids concentration of 3 percent to 10 percent. The reactor is a circular steel or poured concrete container. During the digestion process, the manure slurry is continuously mixed to keep the solids in suspension. Biogas accumulates at the top of the digester. The biogas can be used as fuel for an engine-generator to produce electricity or as boiler fuel to produce steam. Using waste heat from the engine or boiler to warm the slurry in the digester reduces retention time to less than 20 days.

Plug-flow digesters are suitable for ruminant animal manure that has a solids concentration of 11 percent to 13 percent. A typical design for a plug-flow system includes a manure collection system, a mixing pit and the digester itself. In the mixing pit, the addition of water adjusts the proportion of solids in the manure slurry to the optimal consistency. The digester is a long, rectangular container, usually built below-grade, with an airtight, expandable cover.

New material added to the tank at one end pushes older material to the opposite end. Coarse solids in ruminant manure form a viscous material as they are digested, limiting solids separation in the digester tank. As a result, the material flows through the tank in a “plug.” Average retention time (the time a manure “plug” remains in the digester) is 20 to 30 days.

Anaerobic digestion of the manure slurry releases biogas as the material flows through the digester. A flexible, impermeable cover on the digester traps the gas. Pipes beneath the cover carry the biogas from the digester to an engine-generator set.

A plug-flow digester requires minimal maintenance. Waste heat from the engine-generator can be used to heat the digester. Inside the digester, suspended heating pipes allow hot water to circulate. The hot water heats the digester to keep the slurry at 25°C to 40°C (77°F to 104°F), a temperature range suitable for methane-producing bacteria. The hot water can come from recovered waste heat from an engine generator fueled with digester gas or from burning digester gas directly in a boiler.

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The Process of Anaerobic Digestion

The process of anaerobic digestion occurs in a sequence of stages involving distinct types of bacteria. Hydrolytic and fermentative bacteria first break down the carbohydrates, proteins and fats present in biomass feedstock into fatty acids, alcohol, carbon dioxide, hydrogen, ammonia and sulfides. This stage is called “hydrolysis” (or “liquefaction”).

Next, acetogenic (acid-forming) bacteria further digest the products of hydrolysis into acetic acid, hydrogen and carbon dioxide. Methanogenic (methane-forming) bacteria then convert these products into biogas.

The combustion of digester gas can supply useful energy in the form of hot air, hot water or steam. After filtering and drying, digester gas is suitable as fuel for an internal combustion engine, which, combined with a generator, can produce electricity. Future applications of digester gas may include electric power production from gas turbines or fuel cells. Digester gas can substitute for natural gas or propane in space heaters, refrigeration equipment, cooking stoves or other equipment. Compressed digester gas can be used as an alternative transportation fuel.

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Manure Digesters

Anaerobic digestion and power generation at the farm level began in the United States in the early 1970s. Several universities conducted basic digester research. In 1978, Cornell University built an early plug-flow digester designed with a capacity to digest the manure from 60 cows.

In the 1980s, new federal tax credits spurred the construction of about 120 plug-flow digesters in the United States. However, many of these systems failed because of poor design or faulty construction. Adverse publicity about system failures and operational problems meant that fewer anaerobic digesters were being built by the end of the decade. High digester cost and declining farm land values reduced the digester industry to a small number of suppliers.

The Tillamook Digester Facility (MEAD Project) began operation in 2003. The facility is located on a site once occupled by a Navy blimp hanger on property owned by the Port of Tillamook Bay. The facility consists of two 400,000-gallon digester cells. The facility uses the biogas to run two Caterpillar engines, each coupled to a 200 kilowatt generator. The facility sells its electric output to the Tillamook PUD. Manure is brought to the facility by truck from participating dairy farms in the Tillamook area.

Anaerobic Digesters For Lagoons Part 2

May 27, 2010

Anaerobic Digester Lagoon With Methane Gas Recovery

Anaerobic lagoons are perhaps the most trouble free, low maintenance systems available for treatment of animal waste. This is particularly true in the southern U.S.where winter temperatures are mild, permitting anaerobic digestion the year around.  The effluent from the digester is a valuable source of nitrogen for plants that can be field applied for improved crop production.  Placing a cover over the lagoon for collecting biogas virtually eliminates odor from the lagoon.  The collected biogas, a byproduct of the digestion process, is typically 60 to 70 percent methane that can be utilized as a valuable energy resource.  Limited experience indicates that odor from field application of effluent from two cell covered lagoons is much reduced from what might be expected when applying untreated or uncovered lagoon effluent.  A properly designed, constructed and operated anaerobic digester is a low maintenance system that is very forgiving and not likely to create emergency situations that can be expected with many alternative waste management systems.  Adding methane recovery to the anaerobic digester increases maintenance, but even in the event of failure of the gas collection system, it will not interrupt the waste stream and digestion process.  It is well suited to the livestock industry.