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Location Mexico City, Mexico
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Lots of methane gas production harnessed for use and removal from atmosphere
Effluent from biodigester
Using the methane for cooking

Biodigesters are a technology used to help small farmers treat animal and human waste, while providing fertilizer with reduced pathogens for safer crop consumption and gas for their stove, boilers, and electricity generation. The result is a reduction in fuel wood consumption, deforestation, and air pollutants in the home. (Eaton, 2009)(Soeurn, 1994)(Natural Research Council, 1998) Though biogas utilization has been extensively studied, the fertilizer quality has not. (Eaton, 2009) Due to the plant nutrients in biol and a growing organic food movement worldwide there is increasing interest in biol as a fertilizer. (Eaton, 2009) (Kean, 2001) Our study will sample effluent from biodigesters (biol), in Mexico, from a variety of different animals and feed and test the pH, temperature, nitrogen, total ammonia (NH3 + NH4), phosphorous, potassium, calcium, magnesium, and coliforms. (Rosas, 1984) Our study will find how stable the different nutrients in the biol are in comparison to alternative fertilizers and how safe the crops are for consumption after application. We will also do our testing in conjunction with surveys in order to find how different animals and feed are better matches for the different crops in Mexico, how farmers are already using the biol and their satisfaction with it, and how the biogas production relates to fertilizer quality. Lastly since some farmers may not need to use the biol for 4 to 6 months after it's produced, we will test to see how the biol degrades and changes over time as it is stored and the changes after dehydration and rehydration as for the transportation of biosolids.

Background[edit | edit source]

High population density, climatic changes, and increasing human consumption of resources are depleting soil fertility worldwide. (Thy et al, 2003) (Ding Jieyi et al, 1984). At the same time, increased fertilizer use and animal rearing has led to biological and chemical leaching and run off into waterways, in turn killing fish and plants and posing health issues to humans.(Environmental Protection Agency, 2000) In order to boost soil fertility and reduce the harmful effects of manure or fertilizer runoff into waterways, an integrated system of farming that treats and uses the animal waste for application as a fertilizer could help reduce the loss of nutrients from the soil, reduce erosion and salinity problems, as well as reduce contamination of water resources. (Preston et al, 1996)

In Mexico city untreated domestic waste water is often used as a fertilizing agent leading to the contamination of salts and heavy metals in the soil as well as unsafe levels of pathogens on the crops. (Rosas, 1984) Meanwhile, manure from backyard farms, known colloquially as traspatios, empty directly into the waterway in some areas of Mexico City causing water contamination and eutrophication. Biodigesters capture and store animal waste in an anaerobic environment and after 20- 30 days the processed effluent, known as biol has reduced pathogens for crops, can increase fertility of the soil, reducing pollutants in the water and environment. (Eaton, 2009) (Kean, 2001)(Bui Xuan)

One study has shown that the use of biodigester effluence can increase crop yield by 69%. (Kean, 2001) Another study comparing equal amounts of total nitrogen in urea to biodigester effluence found that biol was a superior fertilizer producing increased crop yield (in biomass) by over 16%. (Kean, 2001) It's also been shown that adding fertilizing agents like biol can increase the protein content of crops. (Rodríguez, 1996) Additionally, another study found that organic fertilizers experienced lower nitrate- nitrogen leaching by 4.4 to 5.6% in comparison to conventional fertilizers. (Kramer et al, 2006)

The element Nitrogen exists in all life, and its circulation in the living universe and throughout nature forms a complex web known as the Nitrogen Cycle, the form nitrogen takes in this cycle may mean it is available to plants or that it leaches or vaporizes into the air. Biodigesters work by creating an anaerobic environment, which is able to break down organically bound nitrogen, as found in manure, into ammonia- N. Ammonia can either be converted into ammonium or nitrite (and then nitrate). (NMED, 2007) Ammonium attaches to soil particles and doesn't leach (or percolate past the soil) or denitrify (convert to Nitrogen gases). However ammonium does turn into nitrate through nitrification by bacterial organisms in the soil. Nitrates do easily leach and denitrify. (Sawyer, 2008) Bacteria doing the nitrification into nitrites and nitrates require free dissolved oxygen to do their work, thus in the anaerobic biodigester it is unlikely that there will be much conversion from ammonia or ammonium to nitrites or nitrates. (Sawyer, 2008)(NMED, 2007) Instead, ammonium accumulation increases in flooded environments similar to our biol, thus we expect to see high ammonium concentrations and low nitrate concentrations in the biol. We will compare the concentrations of ammonium, ammonia, and nitrates as it changes over time being stored at room temperature over several months in order to see how stable the nitrogen is in the biol.

Methods[edit | edit source]

For each test site, we will collect one sample from the untreated waste waiting in the registro and one sample of fresh biol that comes out when applying pressure on the biodigester bag. We will place the samples on ice, and get the bacteria tests incubating within 6 hours of collection. After initial testing of the fresh biol we will leave it unrefrigerated in order to analyze the changes and degradation of biol, over a period of months. Since different growers use the biol at different times we will test how well the biol stores over time in liquid form. While avocado tree growers may not use the biol for 4 to 6 months until the trees are flowering, others may only wait a month or less before applying it on their corn crops, thus we will test after 1, 2, 4, and 6 months. (Davenport) Also since some farms are located far from the animals and biodigester we will test how the biol changes after dehydration and rehydration as done for transporting biosolids. (Crush, 2006) We will be testing for pH, temperature of the biol, temperature outside, nitrate, total ammonia (NH3 + NH4), phosphorous, potassium, magnesium, and calcium. These represent major indicators for stimulation of plant growth or an indicator of the stability of the nutrients in the biol (especially in relation to ammonia and ammonium levels). We will coordinate our lab research with standardized site visit questionnaires for families asking: what types of animals are used and what are they fed, if biogas is being produced and how much, if they use the biol for fertilizer and for which types of crops, how long they wait before using the biol, and other observations including their satisfaction with the biodigester. This will help us understand how biogas production relates to fertilizer quality, how different animals and feeds affect the fertilizer quality, and how farmers are already using the fertilizer and their satisfaction with it.

Goals[edit | edit source]

  • Understand overall biol fertilizer quality when it is fresh out of the biodigester
  • Measure the stability of the nutrients in the fertilizer in comparison to other commonly used fertilizers
  • Find the level of reduction in coliform levels from the fresh manure to the biol, both proportionally (percentage reduced) and quantitatively (CFU's)
  • Compare:
  • How waste from different animals changes the fertilizer quality
  • How waste from different feed changes the fertilizer quality
  • Which crops are better suited to which biol types from the different animals and feed
  • How farmers are already using the fertilizer and their satisfaction with it.
  • How well the biol stores over time in liquid form
  • How the biol changes after dehydration and rehydration as done for transporting biosolids
  • How biogas production relates to fertilizer quality

Sample sites[edit | edit source]

  1. Intake registro with fresh mixed fecal material
  2. Salida for biol (or biodigester effluent), after giving the 'masaje' push on biodigester bag until fresh biol comes out into your sample container.

Sample size[edit | edit source]

18 different systems, 2 samples each tested 5 times over a period of 6 months

Process[edit | edit source]

  • use a 500ml sterile container to take a sample from the fresh manure mix in the registro
  • label the sample MR (manure from registro) and write the date on the sample
  • place another 500ml sterile container under the effluent exit pipe to take a sample from the fresh biol of the biodigester
  • ask someone to slightly step on the biodigester to get fresh biol into the sample, this is important for us to know the time the biol leaves the bag in order to know how the effluent changes and degrades over time.
  • label the sample FB (fresh biol) and write the date on the sample

In the Field Testing[edit | edit source]

  • Before leaving the site take the temperature reading of the outside environment and write the time
  • Also take the temperature reading of the fresh biol after it comes out into the sample container
  • Check the pH of the biol using the pH strips
  • and check the Dissolved Oxygen of the biol using the DO meter
  • cap both samples and place them in an ice box
  • then ask the following questions

Survey Questions[edit | edit source]

  • What kind of animals do you have_________________________________________________
  • How many animals__________________________________________________________________
  • What do you feed your animals______________________________________________________(new)
  • What is the loading rate of the biodigester kg/L
  • Is biogas being produced?
  • How much biogas is being produced?
  • Do you use the biogas?
  • Do you use the biol for fertilizer?_____________________________________________________________
  • For what types of crops do you use the fertilizer?___________________________________________
  • How long do you wait before applying the biol?_____________________________________________
  • How satisfied are you with the fertilizer? 1 very satisfied- 5 not happy with it at all__________________________________________________________________________________________________

Back in the Lab Testing[edit | edit source]

  • When returning to the lab place the samples in a refrigerator if you are not testing right away
  • Test for nitrogen, total ammonia (NH3, NH4), phosphorous, potassium, calcium, magnesium, and coliforms, both total and fecal by following the cholorimeter manual.
  • for information on expected concentrations and their significance check out Fertilizer quality parameters for testing
  • after the initial testing of the fresh biol, leave out samples (unrefridgerated and lids off), this will tell us how biol degrades over time. We will construct a small overhang roof outside for the biol to remain under during this time.
  • retest the same samples after 1 month, 2 months, 4 months, and 6 months.

References[edit | edit source]

  • Crush J.R., Sarathchandra J.R., and Donnison A. Effect of plant growth on dehydration rates and microbial populations in sewage biosolids, Bioresource Technology. Vol. 97, no. 18. Dec 2006, Pg 2447-2452
  • Bui Xuan, An. The Role of Low-cost Plastic Tube Biodigesters in Integrated Farming Systems in Vietnam. Livestock Feed Resources within Integrated Farming Systems. Pg 277-294.http://www.fao.org/ag/againfo/resources/documents/frg/conf96pdf/an.pdf
  • Davenport, T.L. Avocado Flowering, Hort. Reviews 8: 257-289
  • Ding Jieyi and Han Yujin. Comparative studies on the effects of fresh pig manure and anaerobically fermented pig manure upon fish farming, 1984 p: 288-296.
  • Environmental Protection Agency. 2000. National Water Quality Inventory: Water Quality Assessments. Ch. 2 Rivers and Streams. http://water.epa.gov/lawsregs/guidance/cwa/305b/upload/2002_09_10_305b_2000report_chp2.pdf
  • Kean, Sophea and T R Preston. Comparison of biodigester effluent and urea as fertilizer for water spinach vegetable. Livestock Research for Rural Development 13 (6) 2001.
  • Kramer, Sasha B.; Reganold, John; Glover, Jerry; Bohannan, Brendan; and Mooney, Harold. Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils. The National Academy of Sciences of the USA. January, 2006.
  • Natural Research Council, 1981. Food, fuel and fertilizer from organic wastes. Report of an ad hoc panel of the Advisory Committee on Technology Innovation, Board on Science and Technology for International Development, National Research Council, Washington, DC.
  • NMED, New Mexico Environment Department. Wastewater Systems Certification Study Manual. Surface Water Quality Bureau. November, 2007. http://web.archive.org/web/20130502201459/http://www.nmenv.state.nm.us/swqb/FOT/WastewaterStudyManual/13.pdf
  • Preston T R and Rodriguez L. Recent developments in the recycling of livestock excreta; an essential feature of sustainable farming systems in the tropics. 1996. http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/recycle/default.htm
  • Rodríguez, Lylian and Preston, T. R. Use of effluent from low-cost plastic biodigesters as fertilizer for duck weed ponds. Livestock Research for Rural Development. Vol 8. No 2. July 1996.
  • Rosas I., Baez A., and Coutino M. Bacteriological Quality of Crops Irrigated with Wastewater in the Xochimilco Plots, Mexico City, Mexico. Applied and Environmental Microbiology. American Society for Microbiology. May, 1984, Vol. 47, No. 5. pg. 1074-1079.
  • Sawyer, John. Surface Waters: Ammonium is Not Ammonia. Iowa State University,Department of Agronomy. 4/21/2008. http://www.extension.iastate.edu/CropNews/2008/0421JohnSawyer.htm
  • Soeurn, Than. Low cost biodigesters in Cambodia. Proc. National Seminar-workshop in sustainable Livestock Prod. on local feed resources. Agric. Pub. House Ho Chi Minh, 1994. pg.109-112.
  • Thy, S., Preston T.R., and Ly, J. Effect of retention time on gas production and fertilizer value of biodigester effluent. Livestock Research for Rural Development 15 (7) 2003.
  • Yunez-Naude, Antonio. MEXICO'S BASIC- CROPS SUBSECTOR: STRUCTURE AND COMPETITION UNDER FREE TRADE. Farm Foundation, Agricultural and Food Policy Systems Information Workshops. Series Structural Change as a Source of Trade Disputes Under NAFTA; Proceedings of the 7th Agricultural and Food Policy Systems Information Workshop - 2001.
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