Archive for June, 2010

Floating Cover Applications

June 29, 2010

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

  • Evaporation and algae growth prevention
  • Odor and emission control
  • Biogas recovery for generation of flaring
  • Potable water protection from pollution and contamination
  • Protection of birds and waterfowl from contact with hazardous liquids

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.  Another factor that should be considered is the saving of natural resources.  These covers are intricate and complex projects that require a contractor with specialized knowledge and experienced crews.

Advertisements

Wastewater Lagoons

June 22, 2010

Lagoons

Wastewater lagoons have been used as a process for wastewater treatment for centuries.  In the 1920’s artificial ponds were designed and constructed to receive and stabilize wastewater.  By 1950, the use of ponds had become recognized as an economical wastewater treatment method for small municipalities and industries.  As of 1980, approximately 7,000 waste stabilization lagoons were in use in the U.S. Today, one third of all secondary wastewater treatment facilities include a pond system of one type or another.  Of these, just over 90% are for flows 1 MGD or less.  But ponds can be used for larger cities for wastewater treatment as well.  Some of the largest pond systems in this country are in Northern California, serving such cities as Sunnyvale (pop. 105,000), Modesto (pop. 150,000), Napa (pop. 175,000), and Stockton (pop. 275,000).

Floating tank covers can be custom designed for lagoon or tank applications.   Floating covers are a cost-effective alternative to many aluminum or fiberglass dome applications and do not require venting (non-gas-collection applications), recirculation or explosion proof equipment.  Tank covers can adapt to varying water levers and in-basin equipment.  They also install easily and quickly.

Bio Wastewater Treatment Part 2

June 17, 2010

Biological Wastewater Treatment Part 2

SELECTION CRITERIA

Biological-treatment technologies vary greatly in their strengths and weaknesses.  The following are application criteria, which are normally relevant in evaluating various biological treatment options for the CPI:

Bioassay/toxicity control — The ability to control and minimize the impact of toxic constituents in wastewater on indicating organisms when the treated water is released

BOD removal efficiency — The ability to remove biodegradable, organic com pounds

COD removal efficiency — The ability to remove chemically oxidizable substances that may or may not be biodegradable

O&M costs — The cost to operate and maintain the treatment method

Sludge production — The amount of residual biological solids generated by the bio logical-treatment process

Sludge disposal costs — The cost to collect, dewater and dispose of residual sludge from the treatment method, either on-site or off-site

Performance in winter and summer — The degree in which high or low ambient temperatures will affect biological treatment

Performance on high- and low-temperature water — The degree in which high and low wastewater temperature will affect biological treatment

Operator attention — The relative amount of time required to operate the biological treatment system

Upset recovery — The amount of time it takes for a treatment method to recover from upset conditions.  Upset conditions are defined as abnormal variations in the flow or characteristics of the wastewater, which can detrimentally affect a biological treatment system

Expandability — The ease of expanding the treatment capacity to accommodate either an overall plant expansion or an increase in loading

Nitrification Efficiency — The relative ease of converting ammonia contained in wastewater to nitrates

VOC containment — The relative ease with which the biological treatment equipment can be enclosed to contain and collect VOC emissions

VOC stripping potential — The relative ease with which the biological-treatment system will strip volatile organic compounds from the wastewater

Ease of installation — The total amount of time and labor required to install the treatment method

Energy efficiency — The amount of energy used by a treatment method

Ease of secondary containment — The ability and ease with which the treatment system can be provided with secondary containment in case of overflow, spills or leaks

Space requirements — The area required by the treatment method

The use of microorganisms to remove contaminants from wastewater is effective and widespread. To choose the right system from the many options offered, understand the various techniques available and evaluate them based on your requirements.

Bio Wastewater Treatment Part 1

June 15, 2010

Biological Wastewater Treatment

Biological treatment — the use of bacteria and other microorganisms to remove contaminants by assimilating them — has long been a mainstay of wastewater treatment in the chemical process industries (CPI).  Because they are effective and widely used, many bio logical-treatment options are available today.  They are, however, not all created equal, and the decision to install a biological-treatment system requires ample thought.  When considering biological wastewater treatment for a particular application, it is important to understand the sources of the wastewater generated, typical wastewater composition, discharge requirements, events and practices within a facility that can affect the quantity and quality of the wastewater, and pretreatment ramifications.  Consideration of these factors will allow you to maximize the benefits your plant gains from effective biological treatment.  Those benefits can include:

  • Low capital and operating costs compared to those of chemical-oxidation processes
  • True destruction of organics, versus mere phase separation, such as with air stripping or carbon adsorption
  • Oxidation of a wide variety of organic compounds
  • Removal of reduced inorganic com pounds, such as sulfides and ammonia, and total nitrogen removal possible through denitrification
  • Operational flexibility to handle a wide range of flows and wastewater characteristics
  • Reduction of aquatic toxicity

The use of microorganisms to remove contaminants from wastewater is effective and widespread.  To choose the right system from the many options offered, understand the various techniques available and evaluate them based on your requirements.

Biological Treatment Options

June 10, 2010

Biological Treatment Options

There are three basic categories of biological treatment: aerobic, anaerobic and anoxic.  Aerobic biological treatment, which may follow some form of pretreatment such as oil removal, involves contacting wastewater with microbes and oxygen in a reactor to optimize the growth and efficiency of the biomass.  The microorganisms act to catalyze the oxidation of biodegradable organics and other contaminants such as ammonia, generating innocuous by products such as carbon dioxide, water, and excess biomass (sludge).  Anaerobic (without oxygen) and anoxic (oxygen deficient) treatments are similar to aerobic treatment, but use microorganisms that do not require the addition of oxygen.  These microorganisms use the compounds other than oxygen to catalyze the oxidation of biodegradable organics and other contaminants, resulting in innocuous by-products.  The three individual types of biological-treatment technologies — aerobic, anaerobic or anoxic — can be run in combination or in sequence to offer greater levels of treatment.  Regardless of the type of system selected, one of the keys to effective biological treatment is to develop and maintain an acclimated, healthy biomass, sufficient in quantity to handle maximum flows and the or­ganic loads to be treated.  Maintaining the required population of “workers” in a bioreactor is accomplished in one of two general ways:

• Fixed film processes — microorgan­isms are held on a surface, the fixed film, which may be mobile or station­ary with wastewater flowing past the surface/media.  These processes are designed to actively contact the bio­film with the wastewater and with oxygen, when needed.

• Suspended growth processes — bio­mass is freely suspended in the wastewater and is mixed and can be aerated by a variety of devices that transfer oxygen to the bioreactor con­tents

It is also possible to combine both meth­ods in a single reactor for more effective treatment.

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 2

June 3, 2010

Anaerobic Digesters

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.

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.

Wastewater

Municipal sewage contains organic biomass solids, and many wastewater treatment plants use anaerobic digestion to reduce the volume of these solids.  Anaerobic digestion stabilizes sewage sludge and destroys pathogens.  Sludge digestion produces biogas containing 60-percent to 70-percent methane, with an energy content of about 600 Btu per cubic foot.

Most wastewater treatment plants that use anaerobic digesters burn the gas for heat to maintain digester temperatures and to heat building space.  Unused gas is burned off as waste but could be used for fuel in an engine-generator or fuel cell to produce electric power.

Landfill Gas

The same anaerobic digestion process that produces biogas from animal manure and wastewater occurs naturally underground in landfills.  Most landfill gas results from the decomposition of cellulose contained in municipal and industrial solid waste.  Unlike animal manure digesters, which control the anaerobic digestion process, the digestion occurring in landfills is an uncontrolled process of biomass decay.

The efficiency of the process depends on the waste composition and moisture content of the landfill, cover material, temperature and other factors.  The biogas released from landfills, commonly called “landfill gas,” is typically 50-percent methane, 45-percent carbon dioxide and 5-percent other gases.  The energy content of landfill gas is 400 to 550 Btu per cubic foot.

Capturing landfill gas before it escapes to the atmosphere allows for conversion to useful energy.  A landfill must be at least 40 feet deep and have at least one million tons of waste in place for landfill gas collection and power production to be technically feasible.

A landfill gas-to-energy system consists of a series of wells drilled into the landfill.  A piping system connects the wells and collects the gas.  Dryers remove moisture from the gas, and filters remove impurities.  The gas typically fuels an engine-generator set or gas turbine to produce electricity.

The gas also can fuel a boiler to produce heat or steam. Further gas cleanup improves biogas to pipeline quality, the equivalent of natural gas.  Reforming the gas to hydrogen would make possible the production of electricity using fuel cell technology.

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.

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

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.

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

http://www.oregon.gov/images/spacer.gif

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.