Alternative Use of Almond Hulls and Shells – One person’s trash is another person’s treasure?
Background The Australian almond industry has long been aware of the looming significant increase in kernel production, with greater than 80,000 tonnes expected by 2015. Whilst kernel production has received a lot of attention, the so called waste (i.e. hulls and shells) has received little fanfare, even though it accounts for 70% of the harvested weight meaning over 280,000 tonnes of hull and shell will be produced in 2015. In Australia, the hull and shell is sold between $0 to $35/tonne to freight companies who then transport and on sell the product to dairies and feedlots. The final price paid by the animal handlers is a lot more than that received by the almond industry; however, the majority of the money covers the freight. The scope to further increase the quantity sold or value obtained in the Australian market is limited. Customers are located too far from the almond industry, the hull and shell in its natural form has a low bulk density making freight expensive, and the almond hull and shell makes up only 5-10% of the animal’s diet with grain the main competitor. These challenges were clearly evident during the 2011 harvest with hullers and shellers having difficulty clearing their stockpiles in readiness for the 2012 harvest. In comparison, the hull and shell is quite valuable in California as the animal handlers are commonly direct neighbours and as such, the freight is minimal. The hull and shell is a valuable commodity and attracts prices greater than US$130/US ton with the majority of this paid to the huller and
subsidise hulling and shelling costs.
sheller. For many Californian almond growers there is no charge for hulling and shelling as this is covered from the sale of the waste. Almond hulling and shelling costs in Australia are estimated at approximately $0.30/kg and in a study conducted by Pocock (2007) cracking was calculated as 15% of an almond orchard’s costs or nearly $1,000/ha (assuming a 3.2 t/ha yield). Cracking was ranked as the second most expensive cost, behind unallocated labour; and more expensive than fertiliser, irrigation, harvest and bee hive rental. Since 2007 there have been considerable fluctuations and increases in water and fertiliser costs, but it is estimated the cracking is still one of the most expensive operations. Not only is hulling and shelling expensive, but growing the hull and shell is also expensive. For example, approximately 60% of the annual fertiliser applications (or approximately 100 kg/ha and 200 kg/ ha of nitrogen and potassium applications, respectively) ends up in the hull and shell. This equates to over $20,000,000 of nitrogen and potassium fertilisers assuming UAN and potassium sulphate would need to be applied to replace (i.e. fertilisation), one for one, just these two elements (Table 1). The hull and shell also contains other nutrients such as phosphorus, calcium, magnesium, zinc etc. The associated chemical and physical properties of hull and shell provide a great opportunity for alternative uses such as bioenergy, biochar, compost etc that could
Bioenergy Bioenergy is defined 1 as renewable energy made available from materials derived from biological sources or biomass (e.g. almond hulls, shells and prunings). In 2009, the Australian government implemented the Renewable Energy Target (RET) scheme, which is designed to deliver on the Government’s commitment to ensure 20% of Australia’s electricity supply (equivalent to Australia’s current household use) will come from renewable sources by 2020. Bioenergy is the subject of considerable interest and activity worldwide, but is also a very complex topic. I would like to highlight just a few exciting areas of relevance to the almond industry. The waste could undergo pyrolysis or gasification (without combustion) to create a synthetic gas. This gas can then be burned directly in a gas engine/turbine or used to produce methanol or converted into a synthetic fuel. This energy source could then be used to power hulling and shelling facilities, aeration/dehydration facilities etc with the remaining energy sold to the “grid”. Portable pyrolysis units are in development overseas. It is estimated by 2015, the quantity of almond hull and shell produced by the entire industry could have the energy potential to deliver approximately 1,000,000GJ of electricity per annum, or the equivalent of potentially $8,000,000 per year of carbon off-sets at $23 per tonne or the carbon equivalent of 25,000 houses or 81,000 cars. Biochar In the process of pyrolysis, a product called biochar is produced as a “waste” stream. This so called waste is a material that could sequest carbon (to be confirmed) and be used to increase orchard soil fertility. Another version of pyrolysis also has the ability to produce activated carbon, a sought after product in water filtration.