IV SIMPÓSIO INTERNACIONAL DE TECNOLOGIAS E TRATAMENTO DE RESÍDUOS ECOS DE VENEZA 9 a 11 de NOVEMBRO de 2011 Rio de Janeiro - RJ POTENTIAL OF BIOGAS GENERATION THROUGH CO-DIGESTION OF MSW, SEWAGE SLUDGE AND GLYCEROL Ingrid Alves, MSc. PhD Student COPPE/UFRJ ingalves@yahoo.com.br
1. Introduction 1.1 Anaerobic Digestion Anaerobic digestion is a biochemical degradation of complex organic matter into simple organic compounds and dissolved nutrients, mediated by microorganisms in an oxygen-free environment. At the end of the process, the organic matter is degraded into carbon dioxide (CO 2 ), methane (CH 4 ), ammonia, hydrogen sulfide and the mixture of gases is known as biogas. 1.2 Co-digestion Mixture of selected substrates, with balance of several parameters, involving qualitative and quantitative characteristics of the waste from different sources. In addition to higher yields of biogas, due to positive synergistic effects on microorganisms, there are other benefits of co-digestion:
-dilution of toxic substances coming from any of the substrates involved - improved nutrient balance - reducing micro and macronutrient deficiency - improving process stability - the use of a co substrate can also help to establish the required moisture contents of the digester feed. Better handling and digestibility can be achieved by mixing solid waste with diluted waste or seawage. - in addition, economic advantages can be significant, derived from the fact of sharing equipment. 1.3 Biodiesel, Glycerol and Sewage Sludge Biodiesel is a fuel produced from vegetable oils and animal fats. In Brazil, the addition of 2% biodiesel (B2) with diesel has been mandatory since January 2008, increasing to 5% (B5) in 2013. Glycerol (propane-1,2,3-triol) is a co-product of biodiesel production equivalent to 12% of biodiesel produced, making it a waste worldwide.
Some chemical and pharmaceutical applications of glycerol (polyurethane synthesis, lubricants, solvents, biosurfactant, organic acids, etc.). Require the purification step (high cost), reinforcing the need to develop new applications. Regarding the sewage in Brazil, only 60% is collected, of which only 40% is treated. It is estimated that about 1 million people expected to generate about 150 tons of sludge / day. Thus, the co-digestion is presented as a viable alternative for reducing the duration of treatment of sewage. MSW and glycerol can be used in different proportions by tests that allow assessment of biogas generation from the biodegradation of such compounds.
2. BMP Test - Biochemical Methane Potential 2.1 Experimental Stage Small fraction of solid waste was previously cut and crushed, placed in a glass jar and inoculated with a fraction of anaerobic digester sludge (50 ml) of sewage treatment plants (WWTP). Anaerobic conditions are kept by recirculating a gas mixture (CO 2 /N 2 ) inside the bottle. Then, they are incubated (37 C) for 60 days. For each sample, the tests are performed in triplicate. BMP tests were carried out: - Binary mixture (Sludge + Glycerol) - Ternary mixture (Sludge + Glycerol + MSW - organic fraction)
a b c Figure 1. (a) recirculation of the mixture (N 2 /CO 2 ) in bottles (b) Closure of the bottle and putting the manometer, (c) bottles incubated (37 C).
2.2 Data Analysis The temperature data are collected by reading a thermometer placed in the laboratory. The atmospheric pressure data are obtained on the site of the National Institute of Meteorology - INMET (www.inmet.gov.br) The calculations of the volume of biogas generated in the BMP test bottles are obtained through daily monitoring (pressure and temperature) of each jar as well as atmospheric pressures and temperatures. The volume of biogas accumulated (NmL) is calculated and corrected to Standard Temperature and Pressure - STP.
3. BMP Test Results Co-digestion Sewage Sludge + Glycerol Test 1: 5, 10 and 15% Co-digestion Sewage Sludge + Glycerol Test 2: 0,85 to 35%
Co-digestion Sewage Sludge + Glycerol + MSW (organic fraction) Test 1: 5, 10 and 15% Co-digestion Sewage Sludge + Glycerol + MSW (organic fraction) Test 2: 10, 15 and 20%
4. Discussion and Conclusion Tests using Sewage Sludge + Glycerol showed that the mixture with 15% glycerol increased about 78% the yield of biogas accelerating the anaerobic digestion process that almost stabilizes at 20% of the time. Tests using Sewage Sludge + Glycerol + MSW (organic fraction) showed an increase in the yield of biogas on average 85%. The results presented indicate the viability of the process and benefits of applying this technique on a commercial scale, since it allows use in a wide application (several digesters); increased the decomposition rate; increased supply of biogas; reducing the size of reactors and their investment.
Ingrid Alves, MSc. PhD Student COPPE/UFRJ ingalves@yahoo.com.br