Putting food waste to use

Each week, 1 million tons of food waste are unsustainably incinerated or landfilled, which contributes to the release of extremely harmful pollutants into the planet’s atmosphere.

Alternatively, anaerobic digestion (AD) technology has a 30-year history of success in sustainably recycling food waste at scale. Organics recycling practices, such as AD, are proving to be the most sustainable, effective way to remedy the landfill and incineration crisis.

In short, AD is a process in which organic materials are broken down naturally by microorganisms in the absence of oxygen. Food waste is placed into an anaerobic digester, and the microorganisms transform it into biogas and an organic matter known as digestate. The process itself is incredibly involved and requires a great deal of expertise. Digestate, the final output of the AD process, is an organic, nutrient-rich soil amendment that can be used alone or mixed to create topsoil that provides nutrients for growing more food.

Organics recycling is a viable way to effectively use unrecoverable food and organic waste through methods such as converting organic waste to fertilizer for use in agriculture, which aids in water retention, prevents soil erosion and improves the soil’s nutrient content. The process also helps to preserve landfill space by repurposing leftover food that would otherwise be disposed of in a landfill. Since landfill sites are a growing concern for countries worldwide, finding strategies to reduce the amount of waste disposed of in this manner is critical to developing a healthier planet.

AD also can contribute to conserving electricity as recycling food waste in AD facilities produces biogas and allows for energy generation.

Arguably the most significant advantage of processing organic waste in recycling facilities is that it minimizes the emission of gases such as methane and carbon dioxide.

Preparing the material

Prior to the production of digestate, extensive preparation is necessary, even before introducing organic content into the digester. The focus must be on the materials introduced, aiming for a consistent and balanced mixture to produce high-quality digestate. Ensuring the right balance is crucial and helps achieve the sustainability and circularity goals associated with AD.

An ideal “diet” for AD systems can be compared with that of humans. Rather than taking in strictly protein or only fats, balance is key. For example, if a digester is only given high-protein content, it will not be able to digest the material effectively. High-protein content alone will result in the elevation of ammonia, hindering microbial growth and making it difficult to break down other contents, thereby reducing digestate quality. Digestate like this could be unusable or much more complex and costly to work with.

This high-protein example is one of many situations that highlight the importance of balancing organic content. Problems could arise if the materials were strictly fats or sugars, as well. The key is to find a heterogenous mixture on a consistent basis.

Another aspect of preparation is the ease of working with the organic content. Is the material easily or quickly broken down? Does it require additional substances to aid in its decomposition? For example, agricultural crop waste—straw, stems, stalks—can be broken down but could need other materials or processes to facilitate its digestion.

While balance is essential, solubility also plays a crucial role. Organic content that is more soluble could be easier to convert quickly to biogas. It not only can significantly enhance the operation’s effectiveness and sustainability but also provides balance to material with slower conversion rates.

Many people devote their careers to improving the planet through the practice of AD. While their tasks and responsibilities vary from day to day, some aspects of the job stay reasonably consistent. Analyzing organic content is a vital part of their work. Diving into the technical work of “microbe farmers,” there are many factors to consider when it comes to analyzing organic content.

On a daily basis, they monitor pH, chemical oxygen demand (COD), FOSTAC (acidity and alkalinity), ammonia, sulfur, sodium, magnesium and calcium, to name a few. If any issues are suspected, a much more in-depth analysis will take place to unearth the root of the problem.

Experts also perform a proximate analysis, measuring the incoming feedstock for protein, fat, starch, sugar, ash content, dry matter and fibers—both neutral-detergent and acid-detergent. This analysis is used in biogas estimating and provides insight into the overall interaction of feedstocks within the digesters.

This process emphasizes the importance of proper front-end balance before introducing organic content into the digester because it directly affects the overall operation.

Forty percent of all food grown and produced in the world goes to waste via land application, landfills and incinerators. When this food decomposes, it creates methane, a greenhouse gas that is up to 80 percent more potent than carbon dioxide.

Organics recycling, like AD, not only conserves energy but reduces air and water pollution, greenhouse gasses and the depletion of natural resources, contributing to a healthier, more sustainable environment—providing hope for the future.

The author is chief operating officer for Bioenergy Devco, Annapolis, Maryland, and can be reached at cmckiernan@bioenergydevco.com.