As Stahlbush Island Farms planned the launch of North America's first -of its- kind Biogas Facility, they recognized that they had an opportunity to make the facility truly unique. Digesters are renewable energy plants that convert waste products - manure or food waste - into electricity through anaerobic digestion. In other words, they turn waste into revenue generating power; in the case of Stahlbush, enough electricity to power 1,100 homes
But digesters themselves produce a high volume, difficult-to-process waste stream that is normally disposed of by land spreading, in this case up to 40,000 gallons per day. In Oregon, land spreading can take place only during a few dry months out of the year because of concern of run-off and contamination of nearby waterways. The storage and hauling of the constant waste stream is both burdensome and expensive.
But Stahlbush saw this problem as an opportunity. If the waste stream could be concentrated, not only would the hauling and storage issues be minimized and fresh water reclaimed, but the resulting concentrated product would qualify as a high-value organic fertilizer - and could replace the expensive fertilizer that they were already buying to feed their crops.
In other words, the already green technology of their anaerobic digester would instantly become twice as green, and doubly profitable. The idea appealed to Stahlbush both as a commercial business, and a farming operation committed to sustainable farming practices.
Digester waste streams are very high in solids, making traditional separation technologies useless for concentrating the stream. So Stahlbush turned to Hydration Technology Innovations whose proprietary Forward Osmosis technology has proven itself in other challenging applications such as the concentration of landfill leachate.
De-watering, or concentrating, a digester waste stream is extremely challenging. On one hand, a concentrated waste stream is rich in nutrients and has value as an Organic fertilizer. Retaining those nutrients in the concentrate is critical, but requires very tight separation technology. On the other hand, the waste stream is very high in solids and quickly fouls traditional filtration processes that are tight enough to retain the nitrogen, phosphorous, potassium and other desirable components.
HTI's forward osmosis systems are ideally designed for this type of challenge. Instead of hydraulic pressure, the process uses salt brine on one side of a membrane. When the waste stream is introduced on the other side of the membrane, the salt pulls water from the waste stream by osmosis. Because hydraulic pressure is not required, the process is extremely resistant to fouling or clogging. Forward osmosis removes 75 - 90% of the water from the waste stream, and the membrane is tight enough to retain the nutrients. The diluted salt brine is then reconcentrated using standard Reverse Osmosis technology, recovering the brine for re-use and generating clean water for use in the food plant or disposal.
HTI's Forward Osmosis concentration system has been piloted extensively, and a full scale operating plant is expected to be operational by fall of 2010. When it is, instead of buying expensive Organic fertilizer, Stahlbush will be making it themselves, transforming what was once problematic waste into a valuable resource and furthering the Stahlbush goal of sustainable farming.
The Forward Osmosis Solution is capable of treating this wastewater and generating two products. The first product is clean water that can be reused in the food processing plant or discharged to the environment. The second is an organic fertilizer that has significant commercial value. With current organic fertilizer prices, the fertilizer byproduct alone could pay for or dramatically reduce the operation cost of the digester.
Even modest-sized farms (approx. 4,000 acres) can generate two megawatts of electricity from food waste digesters, which is enough electricity to power up to 2,000 homes. By producing a high-value Organic fertilizer as a byproduct in an energy efficient operation and reducing the overall costs of treating the waste stream, forward osmosis adds a major contribution to making the digester plant economically viable, and thus a real alternative energy source.