Tuesday 01 December 2009
Build a Family Farm Biodigester for R500
Listen to Make a Difference by South African Band Tucan-Tucan
For expert advice on building biodigesters and agro-ecological farming contact Tarirai at the Forest-Vale Agro-Ecological Project
For farming systems to be sustainable there should be a close relationship among the different components that interact in the conversion of solar energy and soil nutrients into food of animal and plant origin for the benefit of both the consumer and the producer.
As a result of the increasing emphasis on the promotion of farming systems based on the sustainable use of natural resources, it is now appreciated that the biodigester should be considered in a much wider perspective and specifically in its potential role for the recycling of plant nutrients. This process has implications both as a means of reducing the dependence on inorganic fertilizers and for facilitating the production of foods and feeds of organic origin.
Read More Low-cost biodigesters as the epicenter of agro-ecological farming
The simplest and often most effective design for small farmers has no moving parts. Central to the operation and common to all manure plant designs' is an enclosed tank called a digester. This is an airtight tank which may be filled with raw organic waste and from which the final slurry and generated gas may be drawn. Differences in the design of these tanks are based primarily on the material to be fed to the generator, the cycle of fermentation desired and the temperatures under which the plant will operate.
Tanks designed for the digestion of liquid or suspended-solid waste (such as cow manure) may be filled and emptied with pipes and pumps. However, circulation through the digester may also be achieved without pumps by allowing old slurry to overflow the tank as fresh material is fed in by gravity. An advantage of the gravity system is its ability to handle bits of chopped vegetable matter which would clog pumps. This is quite desirable, since the vegetable waste provides more carbon than the nitrogen-rich animal manure.
Another advantage to this is that there are no moving parts, gravity plus the build up of gas pressure forces the digested slurry out the exit. This system can be operated with the fresh manure/organic feedstock feed in by wheelbarrow for the smaller farmer.
Installing a $50 biodigester in a trench.
a. Fertiliser
Fertilizer is an essential input for any crop. The slurry is rich in various plant nutrients such as nitrogen, phosphorous and potash. Well-fermented biogas slurry improves the physical, chemical and biological properties of the soil resulting qualitative as well as quantitative yield of food crops. Nitrogen remains in the effluent of biofertilizer from the slurry, while
some escapes as ammonia gas. When the effluent is dried, most of the nitrogen is lost.
Slurry from the biogas plant is more than a soil conditioner, which builds good soil texture,
provides and releases plant nutrients.
It was found that the slurry from anaerobic fermentation of a biogas digester improves the
physical and chemical properties of the soil. Since there are no more parasites and pathogens
in the slurry, it is highly recommended for use in farming. The economic value of the slurry
shows that investment can be gained back in three to four year's time if slurry is properly
used.
b. Feeding fish and animals
Other uses of the slurry include putting it into ponds as feed for algae, water hyacinth, fish or ducks; using it in hydroponics, where plants are grown in a nutrient rich solution on a gravel bed or even using it as feed supplement for pigs and chickens. The author conducted an experiment in feeding slurry (about 15%) to the fishpond and about 200 fishes were harvested at the end of the experiment.
c. Mushroom cultivation
The slurry coming from the plants can also be used for mushroom cultivation. The slurry mixed with powder of rice straw or wheat straw, water, lime, urea, calcium super phosphate, powder of maize when put in a plastic bag with some seeds of mushroom and keeping in a room temperature of about 22-25 degree Celsius will be ready for cultivation within about six
weeks. The author conducted this experiment in Butwal.
d. Earthworm cultivation
The byproduct received from mushroom cultivation can be used for feeding animals as well as for earthworm cultivation used for feeding chickens. This was observed at Sichuan
Province of China.
e. Other advantages
Environmental pollution control
Environmental sanitation
Drudgery reduction
Since biogas is a high quality fuel, it can be used for many purposes besides cooking and lighting, such as fuel for running dual fuel engine, for agro-processing, pumping water and for generating electricity. A brief description of each use is given below:
Since biogas is a high quality fuel, it can be used for many purposes besides cooking and lighting, such as fuel for running dual fuel engine, for agro-processing, pumping water and for generating electricity. A brief description of each use is given below:
a. Cooking
The main use of biogas, at present, is for domestic purposes, such as cooking and lighting. About one cubic foot of gas may be generated from one pound of cow manure. This is enough gas to cook a day's meals for 4-6 people.
Biogas can be used with suitably designed burners to give a clean, smokeless, blue flame, which is ideal for cooking. More than 87 percent of the people in Nepal use firewood for cooking. If the trend continues all forest will disappear in less than 25 years.
It is believed that biogas will help in reducing deforestation as majority of the biogas owners use the gas for cooking.
b. Lighting
Most of the Nepalese people in rural settlements use kerosene for lighting lamps. Nepal has no indigenous sources of kerosene. As such the country has to spend scarce foreign exchange and supplies are often unpredictable. Biogas owners especially in the hillswhere there is no electricity prefer the use of biogas facilities for lighting.
c. Operating dual fuel engines
Biogas is a high-grade fuel, which means that it can be used in internal combustion engines. It is more usual to use it in dual-fuel engines which are adopted diesel engines that still use 20-30 percent diesel along with 70-80 percent biogas to provide ignition.
About 70% of diesel requirement can be replaced by biogas for running dual fuel engines such as Kirloskar, Usha etc. These engines can be used as follows:
• For running agro-processing equipment
• For pumping water for irrigation
• For generating electricity
METHODS OF INCREASING GAS PRODUCTION IN COLD CLIMATES AND WINTER
MONTHS
There are various methods of increasing gas production in cold climates, especially in winter months. Some of them are described below.
Compost for Heat Generation
It is interesting to note that using a portion of the gas generated to heat the water is entirely feasible... the resulting enormously-increased rate of gas production more than compensates for the gas thus burned.
One of the most important factors affecting biogas is the temperature. The optimum temperature for methane producing bacteria is about 35 degree Celsius. When the slurry temperature is low, the gas production is greatly reduced. At 10 degree, the production of biogas more or less stops. Insulation of dome with compost is one of the best methods for
heat generation for smaller dome type biogas plants.
A compost pile can generate significant amount of heat from decomposition of organic materials such as agricultural residue, straw, grasses etc. Decomposition can be accelerated by the addition of water with effluent from the plant. The effect of compost for heat generation greatly varies with the height of the compost pile and the time it takes to decompose. The height should be not less than a meter or so. The compost should be piled on the
top of the plant for insulation.
This experiment was done in GGC office at Butwal in Oct. 1982, in a 10 cum dome plant.
The plant was daily fed with 60 kg of cow dung. Daily gas production, temperature of the slurry as well as compost was measured.
A similar 10 cum plant at Kalikanagar, near Butwal was used as control measuring daily gas production as well as temperature. It was also fed with equal amount of manure daily with that of the first plant. The slurry temperature inside the digester was 2.03 degree Celsius more in
the plant with compost. Similarly the gas production was increased by about 22.3%.
A similar experiment was conducted in Kathmandu, and the gas production was increased by about 51%. This shows that the effect of composting is more in cooler place (Kathmandu) than in warmer place (Butwal).
Thus compost is more than a fertilizer and more than a soil conditioner. Compost generates heat for the plants, but also builds good soil texture and structure, provides and releases plant nutrients, protects against drought and stops nutrient loss through leaching but also stimulates the growth of the plants.
Utilization of Waste heat from biogas power generation
A heat exchanger was applied in a 500 cf. steel drum plant at Bhutaha of Nawalparasi, the
gas of which was used in 7 HP engine for agro-processing on experimental basis. The gas production was increased by about 37% in winter, assuming that only 50% gas is produced in a similar plant of the same capacity without having heat exchanger.
A similar experiment was also conducted in R&D office of GGC at Butwal.
The engine installed was of water cooling system. One heat exchanger assembly is made up of concentric GI pipes connecting between the engine and heat exhaust silencer and uses waste heat from the exhaust gas to heat water. The other part of the heat exchanger was placed one foot above the digester base and heats the slurry in the digester. A valve can
adjust the amount of cooling water flowing through the engine. Maximum heat was generated when the water is flowing at the rate of 2 lit. /min. as the flow rate increased the temperature decreased and vice versa.
Thus using gas heat from an engine is one of the best ways to maximize biogas production in winter in large size plants, by increasing the temperature of the slurry.
Solar radiation
In this process the influent (gobar mixed with water) in the inlet can be warmed under the sun by covering with a plastic sheet and let the influent enter inside the digester at about 2-3 p.m.
This experiment was conducted at GGC R&D Unit at Butwal by the author. GGC experiences showed that this process could increase about 5-8% of the gas production.
Insulation with straw
Insulation can also be done with straw, rice husk and so on. Their thermal conductivity is 23 times lower than that of soil and condenses to run off leaving the insulation dry.
Similarly plastic sheets like polyethylene can be used as a cover over insulating materials to reduce the amount of materials required. As light penetrates the plastic, it is transformed into the longer heat waves. The heat enhances evaporation of moisture from the insulating material and ground below.
The gas can further be increased when cow or horse manure was mixed with other feeding materials such as poultry dropping, piggery and night soil.
It has long been known that pond plants produce high protein feed for dairy, beef, pigs and chickens.
Read more about pond plants as livestock feed
For expert advice on building biodigesters and agro-ecological farming contact Tarirai at the Forest-Vale Agro-Ecological Project
For farming systems to be sustainable there should be a close relationship among the different components that interact in the conversion of solar energy and soil nutrients into food of animal and plant origin for the benefit of both the consumer and the producer.
As a result of the increasing emphasis on the promotion of farming systems based on the sustainable use of natural resources, it is now appreciated that the biodigester should be considered in a much wider perspective and specifically in its potential role for the recycling of plant nutrients. This process has implications both as a means of reducing the dependence on inorganic fertilizers and for facilitating the production of foods and feeds of organic origin.
Read More Low-cost biodigesters as the epicenter of agro-ecological farming
The simplest and often most effective design for small farmers has no moving parts. Central to the operation and common to all manure plant designs' is an enclosed tank called a digester. This is an airtight tank which may be filled with raw organic waste and from which the final slurry and generated gas may be drawn. Differences in the design of these tanks are based primarily on the material to be fed to the generator, the cycle of fermentation desired and the temperatures under which the plant will operate.
Tanks designed for the digestion of liquid or suspended-solid waste (such as cow manure) may be filled and emptied with pipes and pumps. However, circulation through the digester may also be achieved without pumps by allowing old slurry to overflow the tank as fresh material is fed in by gravity. An advantage of the gravity system is its ability to handle bits of chopped vegetable matter which would clog pumps. This is quite desirable, since the vegetable waste provides more carbon than the nitrogen-rich animal manure.
Another advantage to this is that there are no moving parts, gravity plus the build up of gas pressure forces the digested slurry out the exit. This system can be operated with the fresh manure/organic feedstock feed in by wheelbarrow for the smaller farmer.
Installing a $50 biodigester in a trench.
Uses of Bio-slurry
a. Fertiliser
Fertilizer is an essential input for any crop. The slurry is rich in various plant nutrients such as nitrogen, phosphorous and potash. Well-fermented biogas slurry improves the physical, chemical and biological properties of the soil resulting qualitative as well as quantitative yield of food crops. Nitrogen remains in the effluent of biofertilizer from the slurry, while
some escapes as ammonia gas. When the effluent is dried, most of the nitrogen is lost.
Slurry from the biogas plant is more than a soil conditioner, which builds good soil texture,
provides and releases plant nutrients.
It was found that the slurry from anaerobic fermentation of a biogas digester improves the
physical and chemical properties of the soil. Since there are no more parasites and pathogens
in the slurry, it is highly recommended for use in farming. The economic value of the slurry
shows that investment can be gained back in three to four year's time if slurry is properly
used.
b. Feeding fish and animals
Other uses of the slurry include putting it into ponds as feed for algae, water hyacinth, fish or ducks; using it in hydroponics, where plants are grown in a nutrient rich solution on a gravel bed or even using it as feed supplement for pigs and chickens. The author conducted an experiment in feeding slurry (about 15%) to the fishpond and about 200 fishes were harvested at the end of the experiment.
c. Mushroom cultivation
The slurry coming from the plants can also be used for mushroom cultivation. The slurry mixed with powder of rice straw or wheat straw, water, lime, urea, calcium super phosphate, powder of maize when put in a plastic bag with some seeds of mushroom and keeping in a room temperature of about 22-25 degree Celsius will be ready for cultivation within about six
weeks. The author conducted this experiment in Butwal.
d. Earthworm cultivation
The byproduct received from mushroom cultivation can be used for feeding animals as well as for earthworm cultivation used for feeding chickens. This was observed at Sichuan
Province of China.
e. Other advantages
Environmental pollution control
Environmental sanitation
Drudgery reduction
Since biogas is a high quality fuel, it can be used for many purposes besides cooking and lighting, such as fuel for running dual fuel engine, for agro-processing, pumping water and for generating electricity. A brief description of each use is given below:
Uses of biogas
Since biogas is a high quality fuel, it can be used for many purposes besides cooking and lighting, such as fuel for running dual fuel engine, for agro-processing, pumping water and for generating electricity. A brief description of each use is given below:
a. Cooking
The main use of biogas, at present, is for domestic purposes, such as cooking and lighting. About one cubic foot of gas may be generated from one pound of cow manure. This is enough gas to cook a day's meals for 4-6 people.
Biogas can be used with suitably designed burners to give a clean, smokeless, blue flame, which is ideal for cooking. More than 87 percent of the people in Nepal use firewood for cooking. If the trend continues all forest will disappear in less than 25 years.
It is believed that biogas will help in reducing deforestation as majority of the biogas owners use the gas for cooking.
b. Lighting
Most of the Nepalese people in rural settlements use kerosene for lighting lamps. Nepal has no indigenous sources of kerosene. As such the country has to spend scarce foreign exchange and supplies are often unpredictable. Biogas owners especially in the hillswhere there is no electricity prefer the use of biogas facilities for lighting.
c. Operating dual fuel engines
Biogas is a high-grade fuel, which means that it can be used in internal combustion engines. It is more usual to use it in dual-fuel engines which are adopted diesel engines that still use 20-30 percent diesel along with 70-80 percent biogas to provide ignition.
About 70% of diesel requirement can be replaced by biogas for running dual fuel engines such as Kirloskar, Usha etc. These engines can be used as follows:
• For running agro-processing equipment
• For pumping water for irrigation
• For generating electricity
METHODS OF INCREASING GAS PRODUCTION IN COLD CLIMATES AND WINTER
MONTHS
There are various methods of increasing gas production in cold climates, especially in winter months. Some of them are described below.
Compost for Heat Generation
It is interesting to note that using a portion of the gas generated to heat the water is entirely feasible... the resulting enormously-increased rate of gas production more than compensates for the gas thus burned.
One of the most important factors affecting biogas is the temperature. The optimum temperature for methane producing bacteria is about 35 degree Celsius. When the slurry temperature is low, the gas production is greatly reduced. At 10 degree, the production of biogas more or less stops. Insulation of dome with compost is one of the best methods for
heat generation for smaller dome type biogas plants.
A compost pile can generate significant amount of heat from decomposition of organic materials such as agricultural residue, straw, grasses etc. Decomposition can be accelerated by the addition of water with effluent from the plant. The effect of compost for heat generation greatly varies with the height of the compost pile and the time it takes to decompose. The height should be not less than a meter or so. The compost should be piled on the
top of the plant for insulation.
This experiment was done in GGC office at Butwal in Oct. 1982, in a 10 cum dome plant.
The plant was daily fed with 60 kg of cow dung. Daily gas production, temperature of the slurry as well as compost was measured.
A similar 10 cum plant at Kalikanagar, near Butwal was used as control measuring daily gas production as well as temperature. It was also fed with equal amount of manure daily with that of the first plant. The slurry temperature inside the digester was 2.03 degree Celsius more in
the plant with compost. Similarly the gas production was increased by about 22.3%.
A similar experiment was conducted in Kathmandu, and the gas production was increased by about 51%. This shows that the effect of composting is more in cooler place (Kathmandu) than in warmer place (Butwal).
Thus compost is more than a fertilizer and more than a soil conditioner. Compost generates heat for the plants, but also builds good soil texture and structure, provides and releases plant nutrients, protects against drought and stops nutrient loss through leaching but also stimulates the growth of the plants.
Utilization of Waste heat from biogas power generation
A heat exchanger was applied in a 500 cf. steel drum plant at Bhutaha of Nawalparasi, the
gas of which was used in 7 HP engine for agro-processing on experimental basis. The gas production was increased by about 37% in winter, assuming that only 50% gas is produced in a similar plant of the same capacity without having heat exchanger.
A similar experiment was also conducted in R&D office of GGC at Butwal.
The engine installed was of water cooling system. One heat exchanger assembly is made up of concentric GI pipes connecting between the engine and heat exhaust silencer and uses waste heat from the exhaust gas to heat water. The other part of the heat exchanger was placed one foot above the digester base and heats the slurry in the digester. A valve can
adjust the amount of cooling water flowing through the engine. Maximum heat was generated when the water is flowing at the rate of 2 lit. /min. as the flow rate increased the temperature decreased and vice versa.
Thus using gas heat from an engine is one of the best ways to maximize biogas production in winter in large size plants, by increasing the temperature of the slurry.
Solar radiation
In this process the influent (gobar mixed with water) in the inlet can be warmed under the sun by covering with a plastic sheet and let the influent enter inside the digester at about 2-3 p.m.
This experiment was conducted at GGC R&D Unit at Butwal by the author. GGC experiences showed that this process could increase about 5-8% of the gas production.
Insulation with straw
Insulation can also be done with straw, rice husk and so on. Their thermal conductivity is 23 times lower than that of soil and condenses to run off leaving the insulation dry.
Similarly plastic sheets like polyethylene can be used as a cover over insulating materials to reduce the amount of materials required. As light penetrates the plastic, it is transformed into the longer heat waves. The heat enhances evaporation of moisture from the insulating material and ground below.
The gas can further be increased when cow or horse manure was mixed with other feeding materials such as poultry dropping, piggery and night soil.
Biodigester effluent versus manure, from pigs or cattle, as fertilizer for duckweed
It has long been known that pond plants produce high protein feed for dairy, beef, pigs and chickens.
- With the same input of nitrogen, plant nutrients derived from biodigester effluent support higher concentrations of crude protein in duckweed, than nutrients from raw manure.
- Root length of duckweed is inversely related with protein content and is therefore an excellent indicator of the protein status of the plant.
Read more about pond plants as livestock feed
Subscribe to Posts [Atom]
Post a Comment