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DEVELOPMENT OF A METHOD TO CONVERT GREEN AND ANIMAL WASTES TO A USEFUL AGRICULTURAL PRODUCT WITH POSSIBLE ALTERNATIVE FUEL USE
Impact/Purpose:
, Biology, and Chemistry curricula. If successful, the college will employ the technology for use on our 200-acre farm.
, Biology, and Chemistry curricula. If successful, the college will employ the technology for use on our 200-acre farm.Challenge Area: EPA-G2007-P3-Z1 – Agriculture
We propose that a product composed of animal and green wastes will have application as an agricultural resource and/or a carbon neutral energy source. Green waste will be prepared to serve as a binder to produce a solid product when combined with animal wastes. A laboratory scale project will research methods to produce this product and test its performance as a soil amendment and as a solid fuel. Use of the product will reduce solid waste, improve water quality and provide an alternative energy source.
This project will: characterize the properties of green and animal wastes, develop methods to blend them into a product that will be nutrient-rich soil amendment and/or a fuel source, and test mixtures of the two wastes to determine the proportions yielding the best properties for use as a soil amendment or fuel.
This product represents a new approach toward waste use that combines two problem wastes to form a multiuse product that is clean and simple to produce. Previous treatment of these wastes by composting, biodigestion or pyrolysis are single use, more complex and produce unwanted byproducts.
The nutrient value of the product when used as a soil amendment will reduce the need for fertilizers which are derived from oil and reduce the impact of animal waste on our water supply. If used as a fuel, the product will not increase the levels of greenhouse gasses as it is carbon neutral since its carbon is derived from the atmosphere.
Green and animal wastes will be analyzed for nutrient and contaminant content. Test plantings will be used to compare the product to commercial fertilizers and unamended soil and its use as an alternative fuel will be tested using a bomb calorimeter.
Students gain experience in developing and conducting a research project. This sustainable technology will be integrated into the Environmental Science, Agriculture
Description:
Initially, we thought that we would shred the green waste to use as a binder for the animal manure to produce a material useful as a fuel or soil amendment. Our first experiments in mixing the materials revealed that manure was, instead, better used as a binder for the green waste and there was no need to process green waste to increase its absorbency.
Energy Product: Measurement of the energy content of manure, green waste, and various mixes of the two were essentially the same (4,000 to 6,000 BTU/lb) and approximate the energy content of the lignite coal (4,000 to 8,000 BTU/lb) used extensively to generate electricity in the U.S. Briquettes made from mixtures of manure and green waste burned easily and completely providing a fire fuel for use in developing countries to replace the wood presently used for cooking and heating.
Fuels used in power plants must have a moisture content that is less than 40%. The moisture content of our raw green waste varied between 35% and 58% depending on how long it was stored out doors to dry and that of our manure was higher, varying from 60% to 80%. This indicates that some drying would be required for a finished fuel product.
Discussions with Phil Reese, director of CalBiomass, Inc., the advocacy group for California’s biomass power industry revealed some unanticipated problems. First, manure has been found to have excessive amounts of chlorides that corrode boiler mechanisms when manure is used as a sole source of fuel in power plants. Second, considering disposal costs, biofuels must have less than 10% ash content to be of practical use in power plants. Presently, the biofuel plants in California use only wood which has an ash content of 4% or less. We determined the ash content of our manure (39%) and green waste (44%) and found it to exceed this maximum allowable value. Considering these findings it was, therefore, concluded that we would restrict or eliminate manure used in the fuel to obtain acceptable chloride levels and would have to further investigate the green waste to determine the origin of the abundant ash components.
We sieved the green waste to produce different size fractions and determined the ash content of each fraction. We found that the bulk of the ash was in fact silt sized mineral grains in the fine fraction and small pebbles in the coarsest fraction. These were picked up by the equipment (e.g. lawnmowers, rakes, brooms) used to produce and collect the green waste. The mineral content of the ash was highest in the fine fractions while the coarse fraction consisted mostly of vegetation and left little mineral residue in the ash. When green waste is processed at the collection yard, the large chunks of wood (e.g. limbs, stumps, roots etc,) are removed before the raw waste is ground to mulch for storage. This woody material constitutes 20%-30% of the volume of raw green waste and is dumped in landfills. Consequently, it was not included in the green waste we collected. This material, however, should be useful as biofuel with acceptable ash and chloride characteristics to be useful as a fuel for electrical generation. Based on the information obtained in Phase I, we propose that the coarse fraction of processed green waste and the woody components normally landfilled can be combined to form an acceptable fuel for power plant use.
Agricultural Product: It was necessary to determine if municipal green waste contains herbicides used for weed control that would preclude its use as a soil amendment. To test this, a germination test using radish seeds was performed comparing our stock shredded green waste to Miracle Grow® potting soil as a control. Twice as many seeds sprouted in the green waste compared to potting soil and it was concluded that the green waste is free of herbicides and can be used for agricultural purposes.
To determine the fertility of a green waste/manure soil amendment, a growth experiment was conducted using radishes as a test plant. Soil was obtained from the orchard at Pierce College and prepared as follows: Flat 1 unamended soil, Flat 2 soil amended with commercial fertilizer, Flat 3 soil amended with green waste only, Flat 4 soil amended with a mixture of green waste and manure. Fifty radish seeds were planted in each flat.
The results were surprising. The growth of plants in the stock green waste and manure/green waste mix was much slower than those in the raw soil and soil amended with commercial fertilizer. A search of the literature revealed that this is an expected result. When using raw green waste or manure as a soil amendment, it takes time for the soil microbes (bacteria, yeast, fungi) community to grow large enough to begin the breakdown of these added organic materials. During this period, the growing colonies of soil microbiota extract the nitrogen they need for growth from the soil and since the added organics are not yet decaying, existing stocks of soil nitrogen are depleted. When the microbial populations are fully developed and begin the decay process, nitrogen release is continuous and plant growth is enhanced. Once microbial colonies are established organic amendments can be added continuously to provide a substrate for further decay and nutrient release.
To confirm that this was the cause of the inhibited growth we observed, the soil of each bin was tested for nitrogen. No detectable nitrogen was found in the bins containing green waste and the manure/green waste mix while the soil in the other bins showed excellent nitrogen content. To further demonstrate that the slow growth was actually due to nitrogen deficiency, urea (a nitrogen rich fertilizer) was sprinkled over the first two rows of plants in the bin with the manure/green waste mix that showed the slowest growth. Growth improved significantly in the rows to which urea was added.
Project Period for Phase II: 09/2008 to 05/2009
Proposed Phase II Objectives and Strategies:
Use of manure combined with green waste provides no problem for its use a fire fuel in developing countries. However, for use in commercial power plants we must insure that our energy product has the proper moisture content and ash levels, minimal chloride content and will yield enough energy to be a viable fuel. We will collect samples of the woody components not examined in Phase I and mix it with the coarse green waste fraction to produce a storage pile on the Pierce farm. We will collect moisture and temperature data on this pile to determine the best strategy to dry the materials. Samples will be collected at regular interval for determination of energy content (BTU/lb), ash content, and chloride levels during the drying process. The ash will be further analyzed for environmental contaminants that might affect disposal strategies.
The finer green waste fractions will be combined with manure to product the agricultural product. The literature records two possible solutions to the nitrogen depletion problem encountered in Phase I: 1) spike the waste material with a nitrogen supplement until the microbial populations are developed or 2) compost the soil amendment for the period of time necessary to allow microbial populations to develop before application. Amendments will be prepared according to both methods and growth experiments using radishes will be conducted to determine their effectiveness and determine which method will be best used for commercial production of the product. To confirm product safety, levels of potential pathogens and environmental contaminants and to confirm product utility, quantitative nutrient levels will be determined for green waste, manure and the composted and spiked mixed product.
After proving the concept, Dave Hare of Ecologics, Inc. will initiate steps to use our findings to produce the energy and agricultural product at his green waste processing and storage yard in Moorpark, California. He will approach California power plants that use biofuels to establish contracts to supply them with fuel. In addition, he will use his established relationships with California growers to have them test the agricultural product and, if satisfied, use it on their farms.