Agricultural waste is a part of life for farms of every size and type, but the solutions for managing this waste are as varied as farms themselves. Any opportunity to turn waste into a valuable commodity is enticing, which is why many farms have explored the feasibility of implementing an on-site digester. However, before making this investment, it’s essential that farmers understand how digesters work, and the advantages and drawbacks of digesters as a solution for the management of crop waste.
Two types of farm-based digesters
Biodigesters are one agricultural waste option that large farms have put to use, and that smaller farms may be considering. Before deciding if this solution is right for you, it’s important to understand that there are two distinct types of biodigesters.
An anaerobic digester is a sealed tank in which organic waste is deposited. Over the course of about a month, that waste breaks down in a process that does not use oxygen. Byproducts of the decomposition process include digestate (the liquid and solid waste left after digestion) and biogas.
This biogas, largely made up of the greenhouse gas (GHG) methane, is one reason that farms are adopting anaerobic digesters. Methane, the second most abundant GHG, accounts for approximately 20% of global GHG emissions.
Over a 20-year period, methane has a global warming potential that is 84 to 87 times greater than carbon dioxide.
By installing a biogas recovery system alongside their digester, agricultural operators can potentially capture this damaging GHG and instead convert the biogas to heat or electricity for use on the farm or to sell back to the grid.
Aerobic biodigesters, on the other hand, break down organic waste in an oxygen-rich process. This sealed equipment tends to be smaller – in some cases, small enough to be located within a kitchen or food production area. The byproducts of aerobic biodigesters include carbon dioxide and grey water that can be disposed down the drain or used for landscape irrigation.
The potential to capture biogas certainly sounds promising, but it comes with some major caveats. Understanding the drawbacks of the anaerobic digester has tipped many farms to invest in aerobic biodigesters as a more environmentally friendly solution for crop waste management.
Maximizing efficiency of farm-based digesters
Dairy farms in Vermont and California that have explored the feasibility of using biodigesters to manage manure are finding these solutions are more effective when paired with food waste. As Modern Farmer explains, cow manure alone is not efficient enough to fuel traditional biodigesters, as the waste has already been twice processed by the cow.
Farmers are finding it requires approximately 5,000 cows to feed a biodigester with manure alone and generate a reasonable return on the costly biodigester investment.
The Environmental Protection Agency further reports that different methods of managing manure and housing their animals may lead to pretreatment or other modifications before they are able to send their waste to the digester.
For an anaerobic biodigester to generate enough biogas for use on smaller farms, farmers will find they must provide additional fuel sources. Farms that have turned to food waste often find themselves growing crops specifically to feed their biodigester. Another option may potentially be to partner with other farms in search of better crop waste management solutions or food prep organizations.
Drawbacks to farm-based anaerobic digesters
The need for additional food is only one of the drawbacks to anaerobic digesters. Farmers producing more biogas than needed at a given time may have to flare off excess gas, an additional impact on climate change.
Moreover, as Modern Farmer reports, many digesters stop operation over time due to maintenance costs as high as half a million dollars, problematic designs, and difficulty securing enough food waste for sustainable operation.
Vermont’s well-established Cow Power program is one example of how promising digester programs can lose their appeal over time.
Over the last decade, seven of the state’s digesters have stopped operation. Yale Carbon Containment Lab researchers’ analysis of the EPA’s AgSTAR database have found that since the push to adopt agricultural digesters in the 2000s, at least 37 digesters nationwide have been abandoned and a number of currently active projects are at risk of going offline.
A better, more scalable digester solution
The bottom line is that even large farms are finding that anaerobic digesters aren’t truly feasible solutions for agricultural waste management. Aerobic digesters, however, may make sense for many small farms. These environmentally friendly solutions can easily scale with growth and adapt to process the amount of food waste generated over slow and busy seasons.
Rather than contributing to carbon emissions, LFC biodigesters from Power Knot allow farmers to sustainably manage crop waste. These units are available in sizes capable of handling as much as 6,000 kg (13,200 lbs) of organic waste each day. When paired with the SBT bin tipper, biodigesters can significantly minimize the labor impacts of managing the approximately 20 billion pounds of produce lost on farms every year.
To discover how a biodigester might help simplify crop waste management on your farm, contact Power Knot.