Sunday, November 28, 2010
The report, prepared by Progressive Energy and CNG Services, shows that unlike biomethane produced by anaerobic digestion Bio-SNG is formed by the conversion of thermally derived syngas into methane. Feedstocks can also include more durable materials such as woody biomass and wastes that are not broken down in traditional anaerobic digester plants.
It states that biomethane retains all the attributes of natural gas with the advantage that the fuel is renewable, which means there are substantial carbon dioxide savings. However, in order to achieve a step change in production capacity alternative approaches such as thermal routes are necessary.
Among the conclusions of the report are that implementation of Bio-SNG will only occur with the appropriate tax, incentive and legislative environment; and that it is likely the development of Bio-SNG facilities would require the developer to go upstream into the supply chain for both grown and waste derived fuels.
A process and technology review found that the major process operations required to produce Bio-SNG can be identified and assembled from existing technology suppliers; while a full lifecycle analysis of Bio-SNG production found that for many types of feedstock the savings of Bio-SNG compared with fossil fuel alternatives are as high as 90 per cent.
Source: The Green Car Website
View the original article here
Friday, November 12, 2010
A very popular idea currently gaining publicity is a very old concept: methane digestion. The methane given off during the decomposition of the manure is captured and burned, providing either heat or power, for electrical generation. These promise a minor revolution in small and medium scale energy generation from methane, with a scale smaller than wind turbines, but still significant in terms of national adjustments to high oil prices.
However, the digestion process has been criticized for being inefficient and unstable in operation. But, the technology of anaerobic digestion has been largely ignored until the last run on oil prices about 5 years ago (about 2003), when for the first time for as long as anyone can remember the oil price exceeded the production cost for fuel produced as methane by digestion.
Five years has been scarcely long enough for more than some half a dozen to one dozen AD plants to be designed, constructed and commissioned, in the UK for example. These should be considered to be a first generation of a new breed of reactors using this technology. This is a bit like the people who criticized the motor car for being slow while the law (in the UK certainly) required all automobiles to be preceded by a man holding a flag to warn pedestrians.
Many did criticize the automobile at that time, but do you want to do so for digestion, as I think that you will be looking as silly as those flag wavers were just ten years later, when the motor car became an established mode of transport.
There are many ways in which the efficiency of Anaerobic Digestion bio-reactors are being improved, and the first is by using sophisticated ultrasonic technology to break up the particles and so allow breakdown of a bigger proportion of the organic content.
In some of the other processes being developed the excess liquor from the process is used to re-wet incoming biowaste as it contains useful bacterial populations. This method can produce a faster reaction then the original start-up.
It is important because on-farm Digester (Anaerobic Digestion) projects can provide needed services to farmers; develop local, renewable electrical generation; enhance environmental quality; and generate income for the community.
Other researchers have identified the fact that if you have fluctuating temperatures, then you will not be able to establish an optimum microbial population. The digester stirring system must be efficient and operational at all times to ensure that the cold, newly introduced sludge, is mixed with the warm older solids and the bacteria. This sounds easy but in a large tank with a fairly viscous sludge mass it can be surprisingly onerous on the mixing technology.
Anaerobic digestion consists of a series of reactions which are catalyzed by a mixed group of bacteria and through which organic matter is converted in a step-wise fashion to methane and carbon dioxide. Polymers such as cellulose, hemicellulose, pectin, and starch are hydrolyzed to oligomers or monomers, which are then metabolized by fermentative bacteria with the production of hydrogen (H2), carbon dioxide (CO2), and volatile organic acids such as acetate, propionate, and butyrate. Clearly, this is a complex reaction which e can be greatly improved by better knowledge gained by further academic study which can now take place given the raised awareness and importance of this technique. This will most likely yet result in big advances in how man designs and runs its new digesters.
In the developing world another angle for them is selling carbon credits from the renewable energy created by anaerobic digestion on the worldwide market. Those credits should be a source of income for as well as providing a way to readily obtain seed capital for these projects from the banks.
However, the process also produces a solid and a liquid digestate in the slurry. The use of the process would not be sustainable without an environmentally safe method of disposal, and better still preferably a 'beneficial use' of the output from digestion.
The market for the digestion processing outputs is still undeveloped just about everywhere. However, there are some positive signs reported that the outputs will be genuinely useful, and indeed a source for additional revenue for the operators of these plants.
The adoption of manure digesters at animal operations is much more advanced in Europe than in the U.S. But, there are many successful AD plants in operation throughout the U.S.
Northern Concrete has one such installation and has reported on its digestion process. They have said that the feedstock (animal byproduct) goes into a holding area until it is ready to enter the digester. It sits in the digester for 22 days and is released as useful by-products like methane and a grassy sawdust-like product that can be used as fertilizer, animal bedding or after further processing for floor boards.
There is certainly other evidence of progress in selling AD outputs. Another operator (Pro-Gro Mixes of Tualatin, Ore.) is thought to have contracted to market the solids material or digested fiber to the wholesale nursery and landscape industries, reportedly. It is understood to be selling between 1,000 to 3,000 yards of digested fiber, under the FiberLife brand, per month in the Willamette Valley.
There is also potential for the methane to be burnt in efficient turbines, rather than today's ubiquitous reciprocating engines. Here the heat from turbine exhaust is used to maintain the optimum digester temperature and sustain bio-gas production. The resultant bio-gas is collected from one such system and cleaned, then used to fire the turbines. The results have reportedly been way above expectations, with a significant increase in production, higher yield and fewer rejects being recorded. The digester in question is thought to qualify as a small-power production facility, which means it follows a funding schedule, enabling projects to gain rapid approval.
Digestion can be considered for a wide variety of agricultural and industrial and commercial sites. From agricultural community scale Digesters to supermarkets with waste food, to municipal authorities with organic waste in their collected waste streams. All should now be considering the installation of digestion of one type of another. For more information visit the Digestion web site.
Wednesday, November 10, 2010
Certain components of the sludge may be advantageously utilised when the sludge is incorporated into agricultural land. In fact, as a result of the organic content and the presence of the nutrients and the trace elements essential for plant growth, sludge is generally valued as a soil conditioner. However, due to the presence of certain contaminants such as heavy metals, viable pathogenic and other organisms and complex organic compounds, careful consideration must be given to its potentially dangerous and hazardous properties when disposing of waste treatment sludge.
Waste-water sludge is classified into three types; (a) unstable with high odour and fly nuisance potential, contains a high content of pathogenic organisms - primary or raw sludge falls into this grouping, (b) stable with low odour and fly nuisance potential, has a reduced content of pathogenic organisms - humus, waste activated and anaerobically digested sludges fall into this grouping, (c) stable with insignificant odour and fly nuisance potential, contains insignificant numbers of pathogenic organisms - anaerobically digested sludge when preceded or followed by pasteurisation falls into this grouping, (d) as type c but with contents of specified elements below prescribed limits.
The purpose of describing the waste sludge in terms of the above classification and placing certain restrictions on the disposal of waste sludge is to minimise nuisances and the transmission of pathogenic organisms either directly to man or indirectly through the food chain, as well as protecting water resources and the environment from pollution.
As indicated above, waste-water sludge contains nutrients which can be used beneficially to improve the condition of the soil. Sludge helps to break up heavy clay soils and improves the moisture retaining ability of sandy soils. Although the nitrogen, phosphorus and potassium contents of waste sludges are low compared with the inorganic fertilisers, these nutrients are not leached out as quickly as those from inorganic fertilisers.
Sludges derived from domestic waste-water treatment contains trace elements and minor nutrients in relative concentrations that are of the same order as required by most crops. This means that provided reasonable spreading rates are used, one should not experience metal accumulation problems with domestic sludges. However, when industrial effluents are present in the waste-water, significant concentrations of metals and other undesirable constituents may be present in the sludge and it becomes most important to ensure that the spreading rate is such that undesirable concentrations of metals etc, do not accumulate in the soil.
Where waste sludge cannot be disposed as a soil conditioner, it may be desirable or even necessary to co-dispose the sludge in admixture with refuse on a sanitary landfill site. The co-disposal of refuse and secondary waste-water sludge (in particular digested sludge) in sanitary landfills is being practised in many parts of the world, especially in drier areas which have a perennial water deficit.
Although the utilisation of waste sludge to improve soils used for agricultural process provides an attractive means of disposing of the waste sludge, there are many factors to be considered to avoid creating a secondary waste pollution problem that may be very costly and time-consuming to rectify.
Michael Russell Your Independent guide to Waste Treatments [http://waste-treatments.com].
Tuesday, November 09, 2010
Anaerobic digestion is the most common method in use today for treating waste water sludges. Its attractiveness comes from it being a relatively stable process if properly controlled, with low operating costs and the production of a useful by-product, 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.
Your Independent guide to Waste Treatments [http://waste-treatments.com]
Friday, November 05, 2010
Junior DEFRA minister Lord Henley said he was in talks with the Department for Energy and Climate Change (DECC) to help improve Feed-in Tariff rates which are rewarded to those who set up renewable energy programmes.
"We have given a commitment that we will encourage anaerobic digestion."
Lord Henley also claimed the technology can offer farmers a wide range of benefits other than energy production.
In addition to reducing the amount of waste which is sent to the landfill, the bi-product of the anaerobic digestion process can be used as a fertiliser for crops.
Typical Guttridge equipment used in the anaerobic digestion industry includes; elevators – bucket elevators – valves
View the original article here
Thursday, November 04, 2010
North British Distillery will use the cash to part-fund a three-year £9m investment programme which could generate 33% of its energy needs from renewable sources.
The firm hopes to save between 9,000 and 10,000 tonnes of carbon dioxide emissions annually from the programme.
The £3m loan was provided by Lloyds Banking Group.
The programme includes the installation of a biogas boiler and gas engine that will enable North British to generate its own electricity via anaerobic digestion of its distillate residues.
David Rae, managing director of North British, said: "Our sustainable business strategy will enable North British to make savings in terms of energy costs whilst at the same time significantly reducing the environmental impact of our production process."
The distillery, which has been based in Edinburgh's West End since 1885, already recycles residual low-grade waste heat to heat classrooms at nearby Tynecastle High School.
The firm said the supply enabled the school to make significant energy savings and reduce its own carbon dioxide emissions by 500 tonnes per year.
Most the firm's whisky spirit is sold to other companies for blending purposes, with Famous Grouse, Johnnie Walker Black Label and J&B Rare among its customers.
View the original article here
Tuesday, November 02, 2010
According to the EPA, the Unites States generate over 30 million tons (27.2 million tonnes) of food waste every year, and recycles less than 3%.
As anaerobic bacteria digest our trash, they release carbon dioxide and methane gas, both of which seep out of the soil and into the air. As a result, landfills are one of the largest producers of methane, which has been proven to be a leading cause of global warming.
It takes an average of 30 years for organic waste to break down into stable compounds in your average landfill, in comparison, a well run composter will complete the job in as little as three weeks.
Brian Dick, CEO of Quest Recycling Services LLC and Matt Hedrick, EVP of Quest Recycling Services LLC were keynote speakers at Biocycle Tenth Annual Renewable Energy From Organics Recycling Conference in Des Moines, IA this month.
"The time is right" said Dick. "There are less than 200 operating anaerobic digesters in the United States currently and only a select few of those have the ability to process food waste. In contrast, Europe has thousands that have been successful for many years producing green power from food waste. The time to invest in this technology is now."
"We are excited to be in the fore front of this exciting emerging business that can reduce the amount of food waste in our landfills and provide a much need green power source", said Matt Hedrick.