he examines the contents of a series of glass jars. one is full of little brown pellets. the other contains a dark brown liquid and is labeled “raw digestate – non-hazardous.”

“we’re trying to produce sustainable fertilizers,”  explains edalati, a graduate student in the university of california, davis, department of biological and agricultural engineering.

edalati said that each kind of fertilizer has its benefits and its drawbacks. the liquid form can be applied through drip irrigation, a farming method in which the plant roots are slowly watered via small tubes; however, it contains very little nitrogen – in many cases, not even 1 percent. the pellets, on the other hand, contain up to 5 percent nitrogen but cannot be applied through the ease of drip. 

plants need nitrogen to thrive. they use it to make chlorophyll, a compound that aids them in photosynthesis.

“soils need organic matter returned to them to support the soil microbiology that helps in crop cultivation,” edalati says. the fertilizer he is creating helps provide that.

these fertilizers are the byproduct of the renewable energy anaerobic biodigester (read), which make up the four giant silos that tower in the sun behind edalati. the vision behind read is to break down organic waste and produce a recycled product that can be used in farming and agriculture. it can hold up to 50 tons of organic waste like food and manure.

the concept for read was invented by ruihong zhang, ph.d., of the uc davis department of biological and agricultural engineering. she is also the chief technology advisor to cleanworld, a private company with which uc davis partnered to produce the machine.

“the digester is basically a vertical hammer mill,” zhang says, referring to a machine that crushes and shreds material through the repeated blows of little hammers.

read is composed of four tanks. three of them are for breaking up and pulverizing waste. the digester first separates any plastic that does not belong. it then grinds the food waste and organic material into a paste, which is pumped into the first tank.

“the first tank has bacteria that break food waste down into organic acid,” zhang says. “then (it) goes into the second tank, which has high density microbes that convert organic matter into gas.”

the fourth tank is where the digestate, or leftover organic matter, is stored.

“the leftovers have all the nutrients,” zhang says.

zhang developed this technology 10 years ago at uc davis and was able to turn the plans into action with the help of cleanworld, which specializes in biodigesters.  the university took over full operation of the digester in early 2018, with zhang as a liaison between cleanworld and uc davis, and is now investing more into the operation.

it’s also an easy way for local restaurants, farms and communities to dispose of waste for between $35 and $52 per ton.

uc davis is a non-profit, but zhang says her operation “is a full business model.”

“economically, we’re not getting any money back,” she says. “we got funding from [the] state to create these. it’s not about money, it’s about the show and tell, and making it work.”

even though zhang and her team are not making money, that’s not to say others couldn’t.

“this is a great example of taking the technology forward and making a commercial business,” she says.

zhang and her team give the fertilizer they make to area farms who then report the results back to them. a 2-year-long study on digestate fertilized tomatoes yielded results comparable to tomatoes fertilized with uan-32, a popular synthetic fertilizer, which is 32% nitrogen.

“yields for the digestate fertilizers were equal to the uan-32 and even higher in the case of the digestate concentrate,” edalati says. “the digestate fertilized tomatoes had higher soluble sugar content than the uan-32 tomatoes.

“uan-32 is good for providing nitrogen, but does not give you anything else. plants also need more than just nitrogen. digestate can provide that.”

zhang and her team want to ship the digestate farther than they are currently able to.

“the digestate is valuable, but transporting it is not necessarily economically viable,” edalati says of the liquid fertilizer. “the pellets would be one way to be able to transport nutrients far away at a cheaper cost.”

the difficulty lies in nitrogen content. the liquid digestate is 5% to 6% nitrogen – an essential component to fertilizer – whereas the pellet form is only 0.1 percent to 0.3 percent nitrogen. “you’d have to transfer a lot more of this to get the same amount of nitrogen,” edalati says.

neither, though, compare to uan-32, the popular synthetic commercial fertilizer.

“you can literally apply a couple hundred milliliters of uan-32 versus hundreds of gallons of (digestate),” edalati says. “that’s the challenge.”

thankfully, though, they have a virtually endless supply of test material while they work out how to make their fertilizer more nitrogen-rich.

“ice cream, muscle milk, tomato paste and cut tomatoes from campbell’s,” he says with a laugh, listing some of the more frequent items from which he’s made fertilizer. “all of those used to go to a landfill. now they come here.”

“coffee, too,” zhang adds. “we put a lot of coffee in here. maybe those bacteria love it and get energized.”

a new pilot-scale controlled environment high rise farm (cehrf) system on clarkson university’s campus is enabling faculty and students to research and explore new technologies for integrating food production and energy recovery from waste.

a three-year research project developed by engineering students has culminated in the construction and implementation of a pilot-scale greenhouse on clarkson’s campus that utilizes innovative energy efficient technologies for the year-round production of leafy green vegetables.

related idea: the climate-friendly gardener

the 650 sq. ft. greenhouse is designed to grow produce year-round in northern climates limited by cold and dark winters. its internal heating, led lighting, and water and plant growth systems are designed to maximize plant growth while limiting fossil fuel energy inputs. the state-of-art aeroponic growing system uses only a small fraction of the water and nutrient inputs required by other greenhouse growing operations.

“this pilot scale system is a prototype for controlled environment high-rise farming (cehrf), which promotes the production of vegetables in cold climates and urban settings thereby reducing the energy we currently consume shipping produce around the world,” says susan powers, spence professor of sustainable environmental systems.

the interdisciplinary project was originally conceived by clarkson physics student daegan gonyer ’09, now a graduate student in engineering science. student teams raised phase i and phase ii funding for the project in 2009 and 2010 from the epa through their people, prosperity and the planet (p3) student design competition for sustainability they also conducted laboratory and feasibility studies and did all of the design, construction and operation aspects of the greenhouse and its systems.

earlier this year, gonyer and two fellow graduate students sean bonnell and shaun jones started their own business, blue sphere industries, inc., to further develop the technologies and construct larger scale systems. the company has already received awards in several business plan design competition.

a zero-waste integrated system
the cehrf system uses a biomass-solar thermal heating system and an anaerobic digester for cafeteria waste to create a closed-loop, energy efficient and zero-waste system that contributes to clarkson’s sustainability efforts. collectively, these coupled systems represent an approach to maximize mass and energy efficiencies as the “waste” resources (heat, plant matter, nutrient rich digester effluent, co2) are shared among the building facilities.

clarkson’s anaerobic digester system consists of three 1,400 gallon anaerobic mixed reactors, a combined heat and power system, heaters, and a grinding system. the self-contained anaerobic food digester and combined heat and power unit, which is valued at approximately $300,000, was donated by feed resource recovery. it is currently being implemented to manage some of clarkson university’s food waste. approximately 200 lpd (650 pounds per day) of cafeteria waste are ground up and fed to the pilot digester system. “the net result will be a reduction in the volume of solid waste sent to a landfill, generation of heat and power, and discharge of a nutrient rich effluent that can be used in the greenhouse and on campus grounds,” said powers.

auxiliary heat for the digester and greenhouse is provided by a wood pellet boiler and solar thermal heating system. act bioenergy of schenectady, n.y., supplied this self-contained, integrated heating system that combines a 20kw wood pellet boiler with 2kw solar-thermal heating panels and integrated hot water storage and control system. the unit is fitted with a solar thermal system that can provide free hot water for six months of the year and the pellet boiler will provide the bulk of the hot water during the winter season.

research and educational opportunities
the integrated food-waste-energy system provides ample opportunities for project-based and hands-on learning, as well as research experiences for students. the systems have already been integrated into several senior capstone projects and directed study research efforts for student learning. a grant from the dominion foundation will help with data collection from this integrated system for use in classroom activities.