BioCycle December 2011, Vol. 52, No. 12, p. 34
With space constraints for on-site composting, research study evaluates a food dehydration machine, and the potential to use the output as a soil amendment on campus.
Joe Rasmussen and Briana Bergstrom
As an urban university without the space needed to easily have a traditional on-site composting operation, Loyola Marymount University (LMU) in West Los Angeles, California is challenged to find other ways to handle its food waste in an environmentally, socially and economically sound manner. The university also was interested in reducing the amount of water used on campus and being able to generate more of its own fertilizers and soil amendments.
LMU’s preconsumer food waste was being hauled to a landfill. A team, consisting of faculty and students, Facilities Management, Dining Services and Campus Sustainability representatives, decided to conduct research and implement programs that most appropriately recycle campus food waste streams. One option evaluated was volume reduction via dehydrating food waste.
One of the first steps in the research process was to quantify the amount of food waste generated. The LMU Dining Services staff conducted a two-week audit in the main dining hall. Preconsumer food waste generated by the kitchen was weighed on a large digital scale and measurements were recorded in a log. The data showed that the kitchen generated just over 1,000 lbs/week of food waste which was put into a trash compactor located on the kitchen’s dock.
In June 2010, LMU purchased a food dehydration machine. The unit, the Somat eCorect, uses a combination of turbines and 200°F heat to physically break down the scraps coming out of the kitchen, drain them of their water, and reduce the volume by 80 to 90 percent. Feedstocks such as pineapple tops, banana peels and browning lettuce are loaded in the top of the system. The final product is ejected after an 18-hour cycle, consisting of a dark, dry, mulch-like material.
LMU immediately saw a savings in hauling costs and a reduction in what is landfilled by using the eCorect. But due to its interest in producing a soil amendment for landscaping on campus, LMU decided to evaluate the suitability of dehydrated food waste (DFW). A review of the literature found very little information on this topic, including its physical and chemical properties. Companies marketing the units claim that the material can be used as a soil amendment. Others suggest mixing the DFW with landscaping mulch and using it in commercial and home garden applications. Questions such as whether DFW needs to undergo further processing such as composting, and if so, for how long and under what conditions, led LMU to initiate a research project. Moreover, if the material cannot be used on LMU’s grounds, then further research needs to be done to evaluate DFW’s suitability for anaerobic digestion.
Ultimately, LMU wanted to mix the DFW with mulch already used on campus grounds. The study tested four mixtures: DFW only; 1 DFW:1 mulch; 1 DFW:3 mulch; and all mulch. Treatments were contained in plastic boxes fitted with screens for ventilation. Three replicates of each mixture were used. The mixtures were thoroughly mixed, stored at room temperature, and rehydrated weekly over the course of six weeks to an appropriate moisture level according to the “squeeze test” outlined in Woods End Laboratories, Inc.’s compost testing methods.
Mixtures were tested and observed once weekly for the following variables: temperature, pH, fungal growth, CO2 and volatile ammonia (NH3). These variables were chosen based on their usefulness as indicators of compost stability and maturity as well as their ability to provide a basic understanding of the chemical changes occurring within the mixtures. Temperature of each mixture was measured using a REOTEMP compost thermometer inserted into the middle of the mixtures; pH was measured using the electrometric pH determination for compost methods outlined in the Test Methods for the Examination of Composting and Compost (TMECC).
Without a more exact way to measure fungal growth, a visual estimation was made based on a percent-coverage rating system: 0=no fungus; 1=very minimal fungus (< 10%); 2=minimal fungus (10-25%); 3=low fungus (25-49%); 4= moderate fungus (50-75%), 5= high fungus (75-100%); photo documentation was taken weekly. A Solvita Compost Emission Test Kit measured CO2 and NH3 to derive a maturity level. This test was conducted in the beginning of the study and again after the six week study period. Averages were taken of all replicates.
A nutrient analysis of the DFW indicated extremely high N-P-K of DFW. Nitrate was 277 ppm, phosphorus was 2,094 ppm and potassium was 12,760. By comparison, levels in mulch were: N=0.3 ppm; P=79 ppm and K=857 ppm.
RESULTS AND IMPLICATIONS
Temperature results from the study indicated that mixture 1, which contained only DFW, showed a spike in temperature during week 2, followed by a steep decline until it began to rise again in week 4. Mixtures 2 and 3, which included different ratios of both DFW and mulch, showed similar patterns of increase during the first two weeks followed by a decrease until another rise in week 4. Mixture 4, including only mulch, showed a decrease in temperature until a rise was measured in week 4.
Results from the pH test indicated starting pH levels that were very low (acidic) for mixtures 1, 2 and 3 (3.48, 3.99, and 4.24 respectively), while mixture 4 (mulch only) showed a more neutral pH of 6.35. All mixtures showed a similar upward trend in pH that began to level off after the second week. Interestingly, mixtures 1, 2 and 3 leveled off between 6.50 and 6.80, while mixture 4 became basic and leveled off at a pH of 8.23. Visual estimations of fungal growth showed that mixtures 1, 2 and 3 (all containing some ratio of DFW) experienced a steep rise in fungal growth over the first two to three weeks; all three reached high fungus coverage (between 75-100% coverage). These mixtures then all experienced similar steep declines in fungal growth, indicating a dying off. Interestingly, mixture 4 (mulch only) experienced no fungal growth over the six-week study period, confirming the source of fungal growth was indeed the DFW.
Initial testing for CO2 and NH3 showed average maturity index levels of 8, 7.17, 5.83, and 5.50 for mixtures 1, 2, 3 and 4, respectively. Final testing showed average maturity index levels of 4.33, 5.00, 5.17 and 6.33 for mixtures 1, 2, 3, and 4, respectively. According to the Solvita maturity range, materials in the 4 and 5 range are considered “active compost”; 6 represents a material that is in the “curing” stage.
Ultimately, the study revealed that the unprocessed dehydrated food waste samples were not suitable as a soil amendment on LMU’s campus. Rehydration of DFW produced large quantities of fungus, an outcome not acceptable on LMU’s grounds. Although dehydrated, the material is not decomposed to a stable state. This is a key distinction. While dehydrating LMU’s preconsumer food waste is a good first step towards sustainability, further processing of this material is needed before it is suitable to be used as a soil amendment or for another purpose.
Field trials indicated that DFW can be added to active compost piles and degrade successfully without rapid fungal growth. Identifying a way to process large quantities of DFW through addition to active composting piles is LMU’s next step in determining how to use this nutrient-rich material on-site. Additionally, a pilot project to explore the potential of anaerobic digestion of DFW will be a study to explore as a next step. LMU has been working with the City of Los Angeles Hyperion Waste Water Treatment Plant to consider the dynamics involved with adding dehydrated food waste to anaerobic digesters. For the latter, a pilot test must be conducted to determine whether or not this material is suitable for anaerobic digestion.
Dr. Joe Rasmussen is the Sustainability Manager at Loyola Marymount University. Briana Bergstrom was an LMU student at the time this research was conducted, as well as a sustainability intern working part time for LMU Facilities Management.
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BioCycle December 2011, Vol. 52, No. 12, p. 34