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A well functioning plant can bring several benefits to its owner, society and environment in general.

Money saving:
• money, earlier spent on fuel and electricity can be saved;
• Money earlier spent on purchasing fertilizer and weed killers.

Opportunity of receiving additional income:
• you can sell biogas and biofertiliser;
• you receive additional income with increased due to application of biofertiliser yield of agricultural plants;
• you receive additional money due to faster growth and weight gain of animals by adding digested slurry to their fodder.

Short payback period:
• biogas plant with heating system of any capacity has a payback period of no longer than a year of operation;
• risk of respiratory and eye illnesses is reduced due to purification of air through lowering the volume of openly stored organic waste;
• epidemiologic situation is improved through extermination of some microorganisms contained in waste;
• health is improved due to consumption of ecologically pure agricultural products grown with application of ecologically pure fertilizer.

Saving of time, storage place and woman labor:
• time, earlier spent on tending to stoves using coal and firewood is saved;
• time, earlier spent on gathering, transportation, drying of firewood and storage space taken up by pressed dung, coal, firewood and so on;
• time, earlier spent on weeding is saved due to lesser content of weed seeds in biofertiliser compared to normal manure, as seeds die in the process of digestion [13].

Environmental benefits:
• decrease in methane (greenhouse gas) emissions to the atmosphere created by open storage of manure;
• decrease in emissions of carbon dioxide and combustion products of coal, firewood and other fuel types;
• decrease of air pollution by nitrogen compounds that have unpleasant smell;
• decrease of water resource pollution by manure sewage;
• forest conservation;
• decrease in use of chemical fertilizers.

Individual households judge the profitability of biogas plants primarily from the monetary surplus gained from utilizing biogas and bio-fertilizer in relation to the cost of the plants. The following effects, to be documented and provided with a monetary value, should be listed as benefits:
• expenditure saved by the substitution of other energy sources with biogas. If applicable, income from the sale of biogas;
• expenditure saved by the substitution of mineral fertilizers with bio-fertilizer. Increased
• yield by using bio-fertilizer. If applicable, income from the sale of bio-fertilizer;
• crop yield increase due to application of fertilizer;
• income from fertilizer sales;
• time saved for collecting and preparing previously used fuel materials (if applicable),
• time saved for work in the stable and for spreading manure (if this time can be used to generate income).

Monetary equivalents of individual benefits
The economic evaluation of the individual benefits of biogas plants is relatively simple if the users cover their energy and fertilizer demands by purchasing fuel and fertilizers. Monetary benefits from biogas plants for enterprises and big farms should be quite reliably calculable.
In contrast, it is more difficult to calculate monetary equivalent of benefits for small-sized biogas plants in rural area of Kyrgyzstan as mostly traditional fuels and fertilizers like wood, harvest residues and cow dung are used. The monetary benefits can be calculated through economy of traditional fuel, the monetary value for bio-fertilizer through the expected increase in crop yields, and income from biofertilizer sales.
The main problem in the economic evaluation is to allocate a suitable monetary value to the
non-commercial fuels which have so far no market prices. But even if the particular household does not purchase the required traditional fuel, it’s value can be calculated with the help of fuel prices on the local market. In case no prices for traditional fuels can be established the monetary value of biogas can be determined by comparing its calorific value with other energy sources. Traditional energy sources used by the household are calculated and savings from substituting them with biogas is determined.
Example 10. A family of 5-6 people is using 12 10-liter propane balloons (120 kg or 262 m3 of propane) and 2,5 tons of coal per year. Then for substitution of these energy sources with biogas it will be necessary 262х1,84 = 482 m3 of biogas and 2 500х1,1 = 2 750 m3 of biogas, in total 3 232 m3 of biogas per year, or around 9 m3 of biogas per day.
From the table 21 it can be seen that with substitution of propane for biogas the savings will amount to 3 000 som. Substitution of 2,5 tons of coal that costs 1,8 som per kg, around 4500 som per year can be saved. Overall savings will amount to 7 500 som per year.
Economic benefits from using biofertilizer can be calculated by cost and benefit analysis of previously used fertilizers, increase in crop yields and income from selling fertilizer.

Increased crop yields
The effect of increase in crop yields should not be neglected. Data on crop increase after application of biofertilizer differs from 10 to 30%, but exact forecasts are difficult due to influence of many other factors.

Table 21. Comparison of biogas (70% methane content) and other energy sources [19]
Energy source Calorific value of fuel per unit, kW Calorific value of fuel per unit, MJ Price of fuel unit, som Fuel equivalent of 1 m3 of biogas Biogas equivalent per fuel unit
Diesel/kerosene, liters 10 36 19,5 0,69 liter 1,44 m3
Benzene, liters 8.5 30 25 0,82 liter 1,28 m3
Fuel wood, kg 4.5 16,2 8 1,5 kg 0,65 m3
Dried dung, kg 5 18 0,15 1,4 kg 0,7 m3
Dry vegetation waste, kg 4.5 16,2 – 1,5 kg 0,65 m3
Solid coal, kg 7,7 27,6 1,8 0,9 kg 1,1 m3
Natural gas, m3 9,3 kW/m3 33,5 3,1 0,75 m3 1,34 m3
Propane in balloons, m3 12,8 kW/m3 46 13 0,54 m3 1,84 m3
Electricity, kW 1 3,6 1 6,9 kW 0,14 m3
Biogas, м3 7 25 2,8 1 m3 1 m3

Тable 22. Increase in crop yields after application of biofertilizer
Type of plants Standard yield,
Centners/hectare Price, som/centners Yield increase, % Additional yield, centners/hectare Income, som
Wheat 23-25 450 10 2,3-2,5 1035 – 1125
Barley 18-20 500 10 1,8-2 900 – 1000
Lucerne 40-100 350 10 4-10 1400 – 3500
Corn 50-80 350 10 5-8 1750 – 2800
Beetroot 200-400 120 10 20-40 2400 – 4800
Cotton 25-30 4000 10 2,5-3 10000-12000
Potatoes 180-200 1000 10 18-20 18000 – 20000
Beans 20-25 2000 10 2 – 2,5 4000 – 5000
Apples 250-300 2000 10 25-30 50000 – 60000

Comparative cost of biofertilizer
Biofertilizer is not only effective but also quite cheap – substitution of mineral fertilizers with biofertilizer leads to savings of around 1 750 som per hectare of fertilized soil.

Table 23. Comparison of biofertilizer and other fertilizers [4]
Fertilizer Application norm, kg/hectare Price, som/kg Overall cost, som/hectare
Mineral fertilizer 300 16 4800
Manure 20000 0,15 3000
Biofertilizer 3000 0,5 1500

Monetary equivalent of biofertilizer
Benefits from biofertilizer are added up from the savings from substitution of mineral fertilizer calculated earlier and increase in yields of agricultural crops.
Example 11. Household grows wheat on 100 hectares of land and spending 480 000 som per year on mineral fertilizers. Substituting mineral fertilizer with purchased biofertilizer household will spend only 150 000 som, saving 330 000 som per year, and digesting organic waste on their own biogas plant savings will amount to 420 000 som per year. Increase in crop yields by 10% will bring additional income equal to 112 500 som per year.