With the world generating millions of agricultural waste every DAY, a logical question that arises is: How best can we turn this waste into value?
A related question is: If biofuels are produced from plants, can we make biofuels from agricultural waste too?
Agricultural waste represents a diverse set of biomass waste. These could be stuff like rice husk from rice mills, bagasse from sugar mills, stalks of cotton, mustard, sugarcane and a lot more from farms, and the like.
The properties of biomass – calorific value, ash content, moisture content, sulphur content, size of biomass, bulk density etc. – could vary depending on the source.
Based on the biomass properties, and with the current technology, it is optimal to process specific types of waste biomass for specific biofuels:
- Biodiesel (a direct substitute for diesel) – Biodiesel can be derived from biomass rich in oil / lipid content. Only in select cases can biomass rich in oil content be considered waste biomass, but one such example is specific algae strains that are rich in oil but are currently used for food or other industrial uses. Since 2005, a small sector of scientific and industrial research has been devoted to research for obtaining biodiesel from algae in an economically viable manner.
- Ethanol (a substitute for gasoline/petrol) – Ethanol has been conventionally obtained from food crops such as corn and sugarcane. Increasingly however, biomass waste are being used for this purpose. Recent advances in what is called as Cellulosic Ethanol are also attempting to obtain ethanol from of a variety of plant and agri waste rich in cellulose – corn cobs, bagasse, tree barks, wood chips, saw dust…
- Charcoal – Many woody agri or crop waste (coconut shell is a prime example) when processed using pyrolysis give us charcoal, a fuel rich in calorific value. Some of the prominent agri waste used today for charcoal production include wood chips, coconut shells, ground nut shells etc.
- Biogas – If one were to consider wet, starchy stuff like garden waste and kitchen waste, these can be fed to biodigesters to generate biogas.
- Some emerging technologies can convert a wide variety of agri waste to a range of liquid and gaseous fuels similar in composition to the fossil based fuels we all know so well (gasoline, diesel, LPG, natural gas, furnace oil…)
One of the senior industry professionals I am acquainted with has devoted almost two decades of his career to developing innovative technologies to derive a range of biofuels from all sorts of agricultural waste. Every time I have had a session with him on his accomplishments, my head used to spin – there were so many combinations he had tried for starting materials and end products! His speciality however seems to be the route where he takes an agri waste, converts it into an intermediate product called the Synthetic Gas (a mixture of CO and H2, mainly), and uses this gas to (almost magically) produce a host of fuels similar to the petro-fuels we use every day.
The area he works in is indeed fascinating, though economics are quite vague at this stage for most of these emerging technologies.