Anaerobic Digestion Makes Renewable Energy from Rubbish

Introduction

An Anaerobic Digestion system which is suitable for processing mixed (black bag) waste has been developed from technology first developed in Israel.

It recovers resources from waste while producing renewable energy and helping to reduce carbon emissions.

The ArrowBio process has been developed through a series of pilot and demonstration plants to a level ready to be used commercially in many countries, and is best described as a water-based mechanical biological treatment (MBT) facility, with energy recovery.

ArrowBio’s process has been developed in such a way that it can either be used as a stand-alone solution or in conjunction with other technologies. For example it can be built within sustainable energy parks to provide a source of energy for the park, as well as recycled materials for further processing.

The recycled materials are re-used as feedstock by the other businesses based within the park to create a variety of products.

Two Stage Anaerobic Digestor

ArrowBio sets out to fully recover and wash the recyclable elements of the waste, so it should be favoured by environmental groups which tend to object to alternative processes which handle mixed waste, like incineration, on the basis that the ability of incineration to handle mixed wastes reduces the necessity to separate and recycle, and that the flu gas can contain toxic chemicals. The argument is also that incineration makes it too easy to neglect recycling, so it should not be used. None of these objections apply to Anaerobic Digestion.

The process has at its core a two stage anaerobic digestor which has been optimized for better energy yield than competing systems, from every unit mass of organic matter processed.

Extracting the maximum available gas yield, is in fact a stated primary aim of the ArrowBio processs.

This is recognised as good policy environmentally, and of course the gas and, or electricity generates revenue, which helps to pay for the upkeep of the plant.

The process consists of two distinct yet integrated components: a “front-end” wet Materials Recovery Facility (MRF) and a “back-end” advanced anaerobic digestion system.

The wet MRF combines standard solid waste handling technology in combination with liquid and slurry pumping, water based processing facilitates, passive separation, and cleaning of recyclables and their automatic conveyance around the facility, while also suppressing odours and dust.

The wet MRF the action is cleans, and recovers, ferrous metals, non-ferrous metals and plastics separated by type.

These are then sorted into recycled materials of various grades that can be sold directly into the recycling market.

A “hydrocrusher” has also been successfully developed by ArrowBio which forms part of the wet (anaerobic) process. In effect the biodegradable waste is jetted with high pressure jets of water through a series of pipes. Food and paper is torn apart, greatly increasing the surface area available to biological action, while simultaneously suspending the organic chemicals in a watery solution.

Any waste that is not recoverable or that is not sent through the anaerobic digesters exits from the ArrowBio facility as a residue, and is normally present in only in minor quantities.

The first part of ArrowBio’s anaerobic digestion process is known as the acidogenic stage, and the second is a methanogenic stage. The biomass achieves optimum efficiency compared with single tank AD, and optimisation of pH levels, temperature and residence times is achieved automatically.

The plant has low emissions. The ArrowBio design needs no costly gas scrubbing stage, and the largely water borne technique does not produce the troublesome (dust, odour, etc) emissions experienced from other processes.

Recognition of the sustainability benefits of Anaerobic Digestion is rising fast. Find out more about this technology for the future at the Anaerobic Digestion web site, and more about the ArrowBio AD Process.

Read more about the AD process now. Visit the ArrowBio page at Anaerobic Digestion.Com. The AD Community.

Anaerobic Waste – How Anaerobic Digestion Works in Wastewater Treatment

Anaerobic Digestion

Anaerobic waste digestion happens in a closed reactor. Bacteria act upon the organic waste and release plenty of carbon dioxide and methane. The microbial community has only obligate anaerobic and facultative bacteria. As in aerobic chemohetrotrophic metabolism, initially the macromolecules are hydrolyzed. These products are then converted to volatile fatty acids (mainly acetic acid), and alcohols. The organisms responsible for these anaerobic waste reactions are popularly called acid formers.

They obtain energy through oxidation of organic compounds, but do not use oxygen as electron acceptor. Instead, another fragment of the substrate is reduced to anaerobic acids and alcohols through anaerobic processes. These are then metabolized by a second group of obligate anaerobic biomass (the methane formers), and converted to methane gas.

It is estimated that 60 to 70% of methane production in an anaerobic waste reaction is through conversion of acetic acid and the rest through carbon dioxide reduction by hydrogen.

The activities of the methane and acid producing groups of bacteria must be balanced as the former is sensitive to pH changes and works best in pH range 6.8 to 7.5.

Stabilization Ponds

Anaerobic waste stabilization ponds are large and shallow basins with residence times of 12 to 25 days. A variety of microorganisms inhabit such ponds participating in the anaerobic digestion of waste. In addition to the aerobic and anaerobic chemoheterotrophic organisms, a pond has a large variety of photoautotrophic life forms also. Green and blue-green algae are found in abundance in the top layers, maintaining a symbiotic relationship (I am ok, you are ok!) with the bacteria. At times the pond may also have a significant population of sulfur photosynthetic anaerobic waste water organisms.

About The Anaerobic Digestion Process

Containing and treating the wastes are essential in order that the treated waste mud is stable, the offensive smell is eliminated, the quantity of pathogenic bacteria is reduced, the mass and volume of sludge is cut off, and people can dewater and dry the mud.

Anaerobic digestion is the most common and useful method for treating waste water sledges nowadays. It is really a relatively stable process thanks to the ability to control, low operating costs and a useful production, a combustible gas, which can be used as a source of energy.

 

The advantages of this process:

 

The organic content of the sludges is significantly reduced by conversion into gaseous end-products; the obnoxious odour of the sludge is removed and the final digested sludge has a characteristic ‘tarry’ odour; fats and greases are broken down by the process; there is a significant reduction in the quality of pathogenic bacteria; there is a marked chemical change after digestion. The liquid fraction (supernatant) contains increased levels of ammonia as a result of the breakdown of organic nitrogen (proteins). This makes the digested sludge liquor potentially suitable for agricultural use; the biogas that is formed is a mixture of carbon dioxide (CO2) and methane (CH4) that can be used for digester heating or to generate power.

 

The disadvantages of this process:

 

A relatively high initial capital cost is involved, which tends to limit the process to medium to large size waste water works. The slow rate of bacterial growth requires long periods of time for start-up and limits the flexibility of the process to adjust to changing feed loads, temperatures and other environmental conditions. The process is prone to upsets if not regularly monitored and if corrective action is not taken in time.

 

Anaerobic digestion is a multi-stage biological waste treatment process whereby bacteria, in the absence of oxygen, decompose organic matter to carbon dioxide, methane and water. In this way, the waste sludge is stabilised and the obnoxious odour is removed. The process can, however be described adequately and simply as occurring in two stages, involving two different types of bacteria. The first stage, the organic material present in the feed sludge is converted into organic acids (also called volatile fatty acids) by acid forming bacteria. In the second stage, these organic acids serve as the substrate (food) for the strictly anaerobic methane-producing bacteria, which converts the acids into methane and carbon dioxide. The end result of the process is a well-established sludge in which 40 to 60% of the volatile solids are destroyed. Finally, a combustible gas consisting of 60 to 75% methane and the remainder largely being carbon dioxide.

 

The digestion process is continuous. Fresh feed sludge must be added continuously or at frequent intervals. The gas formed during digestion is removed continuously. In high-rate digestion, stabilised sludge is displaced from the digester during feeding. In low-rate digestion, sludge ‘supernatant’ is normally removed as the feed sludge is added, stabilised sludge is removed at less frequent intervals.

 

It is essential that the organic acids formed in the first stage of the waste treatment process are converted to methane at the same rate at which they are formed. If not, they accumulate and ultimately lower the pH, leading to inhibition of the second stage of the digestion process and digester failure. Temperature must be maintained within certain ranges – heating increases the activity of the anaerobic bacteria reducing the required digestion time. A pH of 7,0 to 7,5 is recommended to encourage the methane-producing stage. A correctly operating digester will have sufficient buffer capacity (alkalinity) introduced from the breakdown of organic matter.

 

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Anaerobic Waste – How Anaerobic Digestion Works in Wastewater Treatment

Anaerobic Digestion

Anaerobic waste digestion happens in a closed reactor. Bacteria act upon the organic waste and release plenty of carbon dioxide and methane. The microbial community has only obligate anaerobic and facultative bacteria. As in aerobic chemohetrotrophic metabolism, initially the macromolecules are hydrolyzed. These products are then converted to volatile fatty acids (mainly acetic acid), and alcohols. The organisms responsible for these anaerobic waste reactions are popularly called acid formers.

They obtain energy through oxidation of organic compounds, but do not use oxygen as electron acceptor. Instead, another fragment of the substrate is reduced to anaerobic acids and alcohols through anaerobic processes. These are then metabolized by a second group of obligate anaerobic biomass (the methane formers), and converted to methane gas.

It is estimated that 60 to 70% of methane production in an anaerobic waste reaction is through conversion of acetic acid and the rest through carbon dioxide reduction by hydrogen.

The activities of the methane and acid producing groups of bacteria must be balanced as the former is sensitive to pH changes and works best in pH range 6.8 to 7.5.

Stabilization Ponds

Anaerobic waste stabilization ponds are large and shallow basins with residence times of 12 to 25 days. A variety of microorganisms inhabit such ponds participating in the anaerobic digestion of waste. In addition to the aerobic and anaerobic chemoheterotrophic organisms, a pond has a large variety of photoautotrophic life forms also. Green and blue-green algae are found in abundance in the top layers, maintaining a symbiotic relationship (I am ok, you are ok!) with the bacteria.

At times the pond may also have a significant population of sulfur photosynthetic anaerobic waste water organisms.

Anaerobic Digestion Makes Renewable Energy from Rubbish

Introduction

An Anaerobic Digestion system which is suitable for processing mixed (black bag) waste has been developed from technology first developed in Israel.

It recovers resources from waste while producing renewable energy and helping to reduce carbon emissions.

The ArrowBio process has been developed through a series of pilot and demonstration plants to a level ready to be used commercially in many countries, and is best described as a water-based mechanical biological treatment (MBT) facility, with energy recovery.

ArrowBio’s process has been developed in such a way that it can either be used as a stand-alone solution or in conjunction with other technologies. For example it can be built within sustainable energy parks to provide a source of energy for the park, as well as recycled materials for further processing.

The recycled materials are re-used as feedstock by the other businesses based within the park to create a variety of products.

Two Stage Anaerobic Digestor

ArrowBio sets out to fully recover and wash the recyclable elements of the waste, so it should be favoured by environmental groups which tend to object to alternative processes which handle mixed waste, like incineration, on the basis that the ability of incineration to handle mixed wastes reduces the necessity to separate and recycle, and that the flu gas can contain toxic chemicals. The argument is also that incineration makes it too easy to neglect recycling, so it should not be used. None of these objections apply to Anaerobic Digestion.

The process has at its core a two stage anaerobic digestor which has been optimized for better energy yield than competing systems, from every unit mass of organic matter processed.

Extracting the maximum available gas yield, is in fact a stated primary aim of the ArrowBio processs.

This is recognised as good policy environmentally, and of course the gas and, or electricity generates revenue, which helps to pay for the upkeep of the plant.

The process consists of two distinct yet integrated components: a “front-end” wet Materials Recovery Facility (MRF) and a “back-end” advanced anaerobic digestion system.

The wet MRF combines standard solid waste handling technology in combination with liquid and slurry pumping, water based processing facilitates, passive separation, and cleaning of recyclables and their automatic conveyance around the facility, while also suppressing odours and dust.

The wet MRF the action is cleans, and recovers, ferrous metals, non-ferrous metals and plastics separated by type.

These are then sorted into recycled materials of various grades that can be sold directly into the recycling market.

A “hydrocrusher” has also been successfully developed by ArrowBio which forms part of the wet (anaerobic) process. In effect the biodegradable waste is jetted with high pressure jets of water through a series of pipes. Food and paper is torn apart, greatly increasing the surface area available to biological action, while simultaneously suspending the organic chemicals in a watery solution.

Any waste that is not recoverable or that is not sent through the anaerobic digesters exits from the ArrowBio facility as a residue, and is normally present in only in minor quantities.

The first part of ArrowBio’s anaerobic digestion process is known as the acidogenic stage, and the second is a methanogenic stage. The biomass achieves optimum efficiency compared with single tank AD, and optimisation of pH levels, temperature and residence times is achieved automatically.

The plant has low emissions. The ArrowBio design needs no costly gas scrubbing stage, and the largely water borne technique does not produce the troublesome (dust, odour, etc) emissions experienced from other processes.

Recognition of the sustainability benefits of Anaerobic Digestion is rising fast. Find out more about this technology for the future at the Anaerobic Digestion web site, and more about the ArrowBio AD Process.

Read more about the AD process now. Visit the ArrowBio page at Anaerobic Digestion.Com. The AD Community.

Aerobic dance. The background music is All Around The World by Zippers. ps I am not the maker of the footage. It was obtained from other place and I forget the original source of it. As for the music, I have tried to find but I can’t find the mp3 for it.
Video Rating: 4 / 5

About The Anaerobic Digestion Process

Containing and treating the wastes are essential in order that the treated waste mud is stable, the offensive smell is eliminated, the quantity of pathogenic bacteria is reduced, the mass and volume of sludge is cut off, and people can dewater and dry the mud.

Anaerobic digestion is the most common and useful method for treating waste water sledges nowadays. It is really a relatively stable process thanks to the ability to control, low operating costs and a useful production, a combustible gas, which can be used as a source of energy.

 

The advantages of this process:

 

The organic content of the sludges is significantly reduced by conversion into gaseous end-products; the obnoxious odour of the sludge is removed and the final digested sludge has a characteristic ‘tarry’ odour; fats and greases are broken down by the process; there is a significant reduction in the quality of pathogenic bacteria; there is a marked chemical change after digestion. The liquid fraction (supernatant) contains increased levels of ammonia as a result of the breakdown of organic nitrogen (proteins). This makes the digested sludge liquor potentially suitable for agricultural use; the biogas that is formed is a mixture of carbon dioxide (CO2) and methane (CH4) that can be used for digester heating or to generate power.

 

The disadvantages of this process:

 

A relatively high initial capital cost is involved, which tends to limit the process to medium to large size waste water works. The slow rate of bacterial growth requires long periods of time for start-up and limits the flexibility of the process to adjust to changing feed loads, temperatures and other environmental conditions. The process is prone to upsets if not regularly monitored and if corrective action is not taken in time.

 

Anaerobic digestion is a multi-stage biological waste treatment process whereby bacteria, in the absence of oxygen, decompose organic matter to carbon dioxide, methane and water. In this way, the waste sludge is stabilised and the obnoxious odour is removed. The process can, however be described adequately and simply as occurring in two stages, involving two different types of bacteria. The first stage, the organic material present in the feed sludge is converted into organic acids (also called volatile fatty acids) by acid forming bacteria. In the second stage, these organic acids serve as the substrate (food) for the strictly anaerobic methane-producing bacteria, which converts the acids into methane and carbon dioxide. The end result of the process is a well-established sludge in which 40 to 60% of the volatile solids are destroyed. Finally, a combustible gas consisting of 60 to 75% methane and the remainder largely being carbon dioxide.

 

The digestion process is continuous. Fresh feed sludge must be added continuously or at frequent intervals. The gas formed during digestion is removed continuously. In high-rate digestion, stabilised sludge is displaced from the digester during feeding. In low-rate digestion, sludge ‘supernatant’ is normally removed as the feed sludge is added, stabilised sludge is removed at less frequent intervals.

 

It is essential that the organic acids formed in the first stage of the waste treatment process are converted to methane at the same rate at which they are formed. If not, they accumulate and ultimately lower the pH, leading to inhibition of the second stage of the digestion process and digester failure. Temperature must be maintained within certain ranges – heating increases the activity of the anaerobic bacteria reducing the required digestion time. A pH of 7,0 to 7,5 is recommended to encourage the methane-producing stage. A correctly operating digester will have sufficient buffer capacity (alkalinity) introduced from the breakdown of organic matter.

 

Learn about how to do a high impact aerobic exercise from a fitness expert in this free exercise video on high and low impact aerobics. Expert: Andrea Austin Bio: Andrea Austin has been a Trainer for 8 years, and an Instructor for 20. Filmmaker: stuart murphy
Video Rating: 4 / 5

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