|
MEKARN Conference 2010 |
Responding to the challenges posed by global warming and the declining availability of most of non-renewable resources will require a paradigm shift in the practice of agriculture and in the role of live stock within the farming system. Farming systems should aim at maximizing plant biomass production from locally available diversified resources, processing of the biomass on farm to provide food, feed and energy and recycling of all waste materials.
The approach that is the subject of this paper is that the production of food/feed can be combined with the generation of electricity, thus ensuring sovereignty in food and energy for families in rural areas. The concept that facilitates this approach is the fractionation of biomass into edible (for food-feed) and inedible cell wall material, the latter being converted into a combustible gas by gasification, the gas in turn being the source of fuel for internal combustion engines driving electrical generators. The cell contents and related structures are sources of digestible carbohydrates, oil and protein which are used as human food and/or animal feed. An important byproduct from this process is “biochar” (65% carbon- 35% ash) that is both a sink for carbon, as well as a valuable amendment for the typically acid soils in tropical latitudes. The overall balance of these activities results in a farming system in which the carbon footprint is negative.
The appropriate production and utilization of biochar is in integrated farming systems that ensure food and fuel sovereignty without conflict. The principles are: (i) multi-strata cropping in systems which maximize capture of solar energy and provide substrates for production of food and fuel; (ii) a live stock component which facilitates recycling of high moisture organic waste through biodigesters to produce fertilizer and cooking gas; (iii) gasifiers to produce a combustible gas and biochar; and (iv) feed-in tariffs (FIT) for electricity derived from renewable resources.
In the TOSOLY ecological farm in Colombia on 4 ha (sugar cane 2 ha, forage trees1 ha, New Cocoyam [Xanthosoma sagittifolium] 1 ha, with average population of 60 pigs and 50 goats), the substrates for energy are: 24 tonnes dry bagasse, 12 tonnes dry forage tree stems, 3650 m3 biogas from 30 m3 of tubular polyethylene biodigesters and 2920 Kwh form solar voltaic panels (capacity 1 KW). The annual energy production is 37920 KWh (2920 solar electricity, 5500 biogas, 20000 producer gas) with an estimated EROEI >7. Energy demand is 7000 KWh (living quarters 3650, machinery 1850, electric van 1500). Annual surplus is 3920 KWh, which with an FIT of USD 0.50/KWh would give an income of USD 15 000. The annual ecological balance is: 3.6 tonnes of biochar equivalent to 8.4 tonnes of carbon dioxide sequestered, 1095 m3 liquid biodigester effluent (548 kg organic N), 1000 m3 of rain water harvested from roof tops, a negative carbon foot print and food produced organically.
Lessons learned are the need for rural-based support systems for construction and maintenance of equipment producing renewable energy, and advantages of small scale production systems, which facilitate animal traction and efficient recycling of wastes. Future strategies should include national rebalancing of payments/taxes to compensate rural areas that produce food and energy from renewable resources (eg: by FIT for electricity) for consumption in the towns.
Key words: Biodigesters, carbon sequestration, climate change, feed-in tariffs, gasification, greenhouse gases, live stock, recycling, rural development