Sustainable Technology Institute (STI) is a small business and research center that has created a novel concept that involves anaerobically digesting food waste and using the digestate product as the nutrient for urban hydroponic vegetable cultivation. Although scientists have studied the use of digestate as an alternative fertilizer in hydroponic gardening and found the synergy between the two fields a feasible alternative to buying commercial fertilizer, no evidence has been found of this taking place on a commercial level. Furthermore, the concept that this synergy takes place in an urban environment where local food waste is digested into fertilizer and used to grow vegetables that are sold to the very restaurants that are donating the food waste in a closed loop process is particularly a novel concept. Further research will take place at STI’s eco-park, where this concept will be tested and economically analyzed, with the intention of providing a model that developing countries and other developed urban cities can utilize.

STI is located in Richmond, Virginia started as a renewable energy, building energy efficiency, and agricultural training center and eco-park. The company also performs renewable energy installations and provides consulting to local non-profit organizations, businesses, and government bodies in all fields involving energy efficiency and sustainability. The company’s new location on nearly one acre located in the inner city of Richmond has led to new developments in the field of urban agricultural research, which so far has taken place through funding provided by STI.
Because of cheap fossil fuel prices in the U.S. and a lack of regulating and deterring the irresponsible disposal of organic waste into landfills, there have been only a few digesters constructed in the U.S. where food waste is the primary feedstock. Most U.S. digesters are used on farms for manure processing, where odor reduction and modest electricity generation are the primary reasons for adopting the practice of anaerobic digestion process. In Europe, food waste is commonly used as a primary feedstock, but regulations on disposal of food waste is the primary reason for this and costs of shipping the food waste and the created fertilizer create a situation where the practice is sustainable, but not profitable. Developing countries commonly practice anaerobic digestion of food waste on a small scale and the gas is generally used for cooking and the digestate is used onsite for gardening. If residents of developing countries could transport their food waste to an area where digestion and hydroponic vegetable growing is taking place, they could dispose of their waste responsibly and take vegetables home in the same trip. Also needed jobs could be created for the local population.

STI has two newly built 24X50’ greenhouses at its headquarters in the inner city of Richmond and the growing space is currently being retrofitted with hydroponic garden beds. A large solar-thermal heated thermophilic anaerobic digester was recently built and the methane gas generated is currently heating STI’s warehouse and office space. Connections with local restaurants are being made with the intention of streamlining and economizing the food waste collection process. The hope is to cut down on fossil fuel inputs by delivering vegetables to the restaurants and picking up the food waste and waste vegetable oil in the same trip.

The few organization in the U.S. who have created operations where the anaerobic digestion of food waste takes place generally use the methane onsite for heating and electricity generation. However, the digestate fertilizer created in the process generally is dewatered and shipped, creating a situation where fossil fuel use for shipping makes the process less efficient on the level of sustainability. By eliminating the need for centrifuging the water and using the digestate as a tea fed to an onsite hydroponic garden, no fossils fuels are used to fuel the centrifuge or the trucks that would typically be used to transport the fertilizer for use at a different location.

Thermophilic digestion and need of destroying pathogens and smaller size tank
Empower is replicating this design for third world countries.
In an effort to promote closed-loop sustainable concepts, STI has also stepped outside the scope of profit oriented endeavors to team with a number of NPO’s including Empower, Shalom Farms, TEENS, and Tricycle Gardens.