Quantalux Blog

News, events, observations, industrial and otherwise, from a Quantalux point-of-view.

Food Waste - A Practical Guide

Many municipalities and companies are trying to figure out how to responsibly dispose of the over 34 million tons of food waste that is generated each year. (This is roughly 15% of the total landfill volume in the US.) The current option of landfilling leaves much to be desired: the natural decomposition of organic matter results in increased methane emissions, and leachate can migrate to the ground water.

Landfills certainly have their place for trash disposal, but when it comes to food waste, most people ask “Can’t we do better?” After all, food waste is high in water, and also has a high bioenergy content. Dumping it into the ground is, frankly, a short-sighted solution.

In our work to improve biodigester systems, we’ve studied the issue of food-waste quite a bit. We learned that there are all kinds of food waste. Food waste comes from the food that is left over after meals at homes and restaurants, but food waste can also be generated from food production facilities. In addition, there are other greasy, oily types of food waste that are left over from cooking and processing (so called Fats, Oils and Greases, or FOG). Some waste is liquid, some is nearly solid, and many times the food waste is combined with other materials like paper napkins or straws.

Based on our studies, we’ve developed some practical guidelines for food waste.

1) Biodigestion and composting are complementary processes, not competitors.

Different types of food waste need to be processed differently. For food waste from restaurants or homes, composting is the best option because of the paper and plastic that is mixed in with the organic material. Conversely, food waste with a higher liquid content (from food processors or breweries) is best processed in biodigesters. The same is true for FOG because the fats and greases have very high intrinsic energy content during biodigestion. Neither liquid waste nor FOG is a good candidate for composting.

2) Regulations matter

States such as Massachusetts have enacted organic waste bans to decrease the amount of food waste that is landfilled. Companies generating more than one ton of waste per month are required to find more sustainable options for disposal. Surprisingly, there was little opposition to the Massachusetts Organics Ban, which probably mirrors the public’s increasing desire to see more sustainable business practices.

Vermont and Connecticut, and cities such as Seattle, San Francisco and Portland have also banned landfill disposal of food waste from large commercial food waste generators.

Regulations are important in order to assure a steady stream of material to the biodigester. A guaranteed supply of food waste allows the digester owner to receive financing in order to invest in maintenance, improvements and renewable energy generation. The good news is that once the digester is built, disposal costs are often less than at landfills.

Interestingly, locations with Organics Bans have seen many entrepreneurs working to provide new technology for biodigestion. This is good news for any state seeking to have more high-tech job growth.

3) Size matters

The old saying “Go big or go home” definitely holds true for biodigesters. Our studies looked at biodigester systems from small to large, and also looked at the economic viability as a function of size. Without question, larger systems were more viable, which is not surprising since biodigestion is just like any other biological process where economies-of-scale hold. One driving issue with biodigestion is the need for good monitoring and maintenance, and in order to pay skilled personnel adequately, a certain scale for the biodigester is needed. While automatic monitoring may someday make small digesters viable, today’s biodigesters rely on a human’s knowledge and expertise to operate smoothly.

4) Leverage existing digesters

Finally, our studies showed that the capital cost of building a digester was a tremendous barrier. The availability of food waste alone is not sufficient to justify construction. However, when food waste is combined with manure or sewage sludge, biodigestion becomes very appealing for two reasons. First, the biological process itself is improved. The combination of high energy food waste and manure/sludge is nearly perfect for stable biogas production. Second, the existing biodigester facility earns tipping fees from the incoming feedstocks, providing diversified income. Both benefits make the overall digester facility much more financially stable.

There are approximately 550 biodigesters at existing wastewater treatment plants in the US, and approximately 200 agricultural digesters. All of these facilities are the ideal candidates for disposing of food waste, resulting in renewable energy production and smaller landfills.

In short, our staff remains committed to the notion that biodigestion is a great solution for food waste processing, but only under certain conditions. The four points above show that by following some practical guidelines, successful biodigesters can be part of our country’s food waste disposal solution.

Earlier in this blog, we asked “Can’t we do better?”. The answer is a definite YES.

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