Production of Biogas from Organic Solid Waste in Thermophilic Phase

Transcription

1 Production of Biogas from Organic Solid Waste in Thermophilic Phase Derbal Kerroum*, Bencheikh-Lehocine Mossaab, Meniai Abdeslam Hassen. Laboratoire de l ingénierie des procédés de l environnement (LIPE) Département de Chimie Industrielle, Faculté des Sciences de l Ingénieurs, Université Mentouri, Constantine Constantine, Algérie, derbal_kerroum@yahoo.fr These last years there is an increasing world request on energy biodegradable and organic waste, such as animals waste, agricultural waste, municipal organic waste, etc., for the production of biogas. To satisfy these request, this research come in order to study and to estimate the biogas produced by the anaerobic co-digestion process of municipal organic waste in thermophilic conditions (Temperature =55 C), in order to increase the volume of biogas produced. This work is carried out in an anaerobic completely mixed digester of 500 litter volume. The digester is feed daily with a mixed substrate of biodegradable solid waste and activated sludge from a wastewater treatment plant. During the experimentation period, the analysis concerning the measurement of the digester stability parameters - total solids (TS), total volatile solids (TVS), total kjeldhal nitrogen (TKN), volatile fatty acids (VFA), ph, ammonia nitrogen (NH + 4), total and soluble chemical oxygen demand (COD), volume of biogas production and its composition, total and partial alkalinity, total phosphorus (Ptot) was made. The results obtained during this study, show that the quantity of biogas produced is significant in comparison with that obtained in Co-digestion of solids waste under mesophilic condition. Thus in this study the average specific gas production (SGP) is about 0.51 m 3 /kgtvs, this is a good result with in comparison to the results obtained in mesophilic co-digestion where the SGP is 0.31 m 3 /kgtvs. 1. Introduction Important quantities of organic solid wastes are continuously generated and must be treated. Different processes may be used for their treatment but in the present study an anaerobic digestion of these solid materials is used for biogas production, providing then an energy source (Bolzonella et al., 2002). This process is even getting economically more attractive, when considering the current cost of energy, particularly when treating industrial waste with high percentage of biodegradable matter (Koutrouli et al., 2009). In the literature, several studies on the anaerobic co-digestion process are reported where the influence of different parameters such as mixing velocity, temperature, ph, etc., are investigated (Vavilin et al., 2002). Other studies were concerned with the use of different solid wastes, one can cite the use of organic solid wastes with or without wastewater treatment plant sludge by (Kayhanian and Rich, 1995) and (Bolzonella et al.

2 2005), cheese whey by (Erguder et al., 2001), agro-industrial wastewaters by (Demirer et al., 2000), grey water from vacuum toilets by (Feng et al., 2006), manure by (Kaparaju et al., 2009), olive mill waste by (Fezzani and Bencheikh, 2009), etc. The objective of the present work is the monitoring of the thermophilic anaerobic codigestion process of mixtures of municipal solid wastes mixed with sludge obtained from the wastewater treatment plant. 2. Experimental Experimental data were obtained from the monitoring of anaerobic digestion of sludge waste obtained from wastewater treatment plant, carried out in a pilot digester, under thermophilic conditions (T = 55 C). The reactor was continuously stirred (CSTR), without recycling. It is daily fed with 22.5 L of a substrate (19.1L sludge waste + over 3 kg of solid wastes) and a hydraulic loading rate of 1.8 kg TVS/m 3 /d to maintain a hydraulic retention time (HRT) of 23 days, during all the experimental phase. Daily influent and effluent analyses were made for ph, TS, TVS, TVFA, biogas volume and it composition, partial alkalinity (TA) and total alkalinity (TAC), NH + 4. Other analyses were made two or three times a week, like COD, TKN and Ptot. Analyses of COD, TS, TVS, ph, NH + 4, TKN and Ptot were performed according to the standard methods for the examination of water and wastewater (1998). TVFA were analysed by gas chromatography equipped with flame ionization detector (FID) and a capillary column (15 m in length and a diameter of 0.53 mm), with hydrogen as carrier gas (APHA, 1998). The biogas composition is obtained using a portable gas analyzer (Geotechnical Instrument, MOD. GA2000). It is also able to detect and measure the concentration of hydrogen sulphide in the biogas within a range of 1 to 5000 ppm. For the measurement of produced gas volume a hydraulic gas flow meter (Ritter) was used. Typical characteristics of influent feed are shown in Table 1. Table1: Typical characteristics of influent substrate Parameters Average min max Std. Dev. Nr. of Samples ph NH 4 (mgn/l) TKN (waste) (mgn/gts) COD (waste) (mgcod/gts) Ptot (waste) (mgp/gts) TKN (sludge) (mgn/gts) COD (sludge) (mgcod/gts) Ptot (sludge) (mgp/gts) TS (waste) (g/l) TVS (waste) (g/l) TVS (waste) (%TS) TS (sludge) (g/l) TVS (sludge) (g/l) TVS (sludge) (%TS)

3 3. Results and discussion The obtained results concerning the above mentioned parameters are presented in the following sections, for the steady state conditions. 3.1 ph in digester The ph is an important parameter which gives information on the anaerobic digestion process, as shown in Figure 1 where its variation is from 7.5-8, close to the range of (6.5-8), reported in the literature (Bolzonella et al., 2003). This can explain the significant production of bicarbonate due to the temperature elevation. ph in digester Figure1: ph profile in the digester 3.2 Solids and volatile solids in the digester Figure 2 shows that these two parameters are stable indicating a good operation of the digester. TS and TVS (gts/l) 60,00 50,00 40,00 30,00 20,00 10,00 0, TS TVS Figure2: TS and TVS concentration in digester

4 3.3 Alkalinity in the digester Figure 3 shows slight varaiations of alkalinity at each ph values of 4 and 6 in the digester, and hence an almost constant difference between the two corresponding curves, indicating a stability of the process. Alkalinity (mg CaCO3/l) Alkalinity (ph=6) Alkalinity (ph=4) Figure 3: Alkalinity concentration in the digester 3.4 VFA in digester The values of the volatile fatty acids concentrations in the digester have a direct influence on its operation., and hence the quality and the volume of the produced biogas. Figure 4 shows a variation between 10 and 100 mg COD/L an acceptable range according to the literature. 120 VFA (mgcod/l) Figure 4: VFA concentration in digester 3.5 Biogas volume and composition Figure 5a shows a reduction followed by an increase in biogas production, due to the variation of the various control parameters process. This is not critical for the process, and can be self controlled since the biogas volume variation is related to the influent rupture or composition variation. In this case, a particular increase in organic loading rate (OLR) was considered in order to increase the treated waste volume. Figure 5b

5 presents the biogas composition (methane and carbon dioxide), where it can be noted that the percentages are about 61 and 39 %. Biogas flow (m3/day) 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 a 0 Biogas composition (%) 70,0 60,0 50,0 40,0 30,0 20,0 10,0 b 0, CH4, % CO2, % Figure 5: Biogas production (a) and it composition (b) 3.6 Gas production rate The variations of gas production rate (GPR) in the digester are shown in Figure 6 where the average production rate of gas is about 0.96 m 3 / m 3 d, with peaks of 1.61 m 3 / m 3 *d indicating an increase in waste treatment capacity. 2,00 GPR (m3/m3.day) 1,50 1,00 0,50 0,00 Figure 6: Gas production rate (GPR) 4. Conclusion The analyses of the substrate (organic waste + sludge waste), showed that they are very rich in organic biodegradable matter which can be converted into biogas by means of the anaerobic co-digestion process. The analysis carried out on the effluent showed the quality of the treatment as well as an acceptable conversion of the substrate to biogas in thermophilic phase. The analysis of produced biogas showed that the percentage of biomethane is 62%. The average specific gas production (SGP) is about 0.51 m 3 /kgtvs, whereas under mesophilic conditions the value of the SGP was 0.31 m 3 /kgtvs. Which shows that the increase of temperature from 35 to 55 C results in almost a doubling the SGP. It would be an interesting idea to evaluate the energy balance when increasing the temperature.

6 Moreover, different substrates could be used to evaluate gas production and classified with their SGP. References Bolzonella D., Pavan P., Battistoni P. and Cecchi F., 2005, Mesophilic anaerobic digestion of waste activated sludge, influence of the solid retention time in the wastewater treatment process, Process Biochemistry, 40, Bolzonella D., Battistoni P., Mata-Alvarez J. and Cecchi F., 2003, Anaerobic digestion of organic solid wastes: process behaviour in transient conditions, Water Sciences and Technology, 48 (4), 1-8. Bolzonella D., Innocenti L., Batitistoni P. and Cecchi F., 2002, The AF-BNR-SCP process application at Treviso wastewater treatment plant: results of the activated sludge model N 2 simulation and mass balances, AIDIC conference series, Vol. 5, Elsevier Ed., Demirer G. N., Metin D., Erguder T.H., Guven E., Ugurlu O. and Tezel U., 2000, Anaerobic treatability and biogas production potential studies of different agroindustrial wastewater in turkey, Biodegradation Netherlands, 11, Erguder T.H., Tezel U., Guven E. and Demirer G.N., 2001, Anaerobic Biotransformation and methane generation potential of cheese whey in batch and UASB reactors, Waste Management, 21, Feng, Y., Behrendt, J., Wendland, C. and Otterpohl, R., 2006, Parameters analysis and discussion of the anaerobic digestion model No.1 (ADM1), Water Science & Technology, 54 (4), Fezzani B. and Bencheikh R., 2009, Anaerobic co-digestion of olive mill wastewater with olive mill solid waste in a tubular digester at mesophilic temperature, Bioresource Technology Journal, 162, Kaparaju P., Ellegaard L. and Angelidaki I., 2009, Optimisation of biogas production from manure through serial digestion: Lab-scale and pilot-scale studies, Bioresource Technology Journal, 100, Kayhanian M. and Rich D., 1995, Pilot-scale high solids thermophilic anaerobic digestion of municipal solid waste with an emphasis on nutriment requirements, Biomass and Bioenergy, 8 (6), Koutrouli E.C., Kalfas H., Gavala N.H., Skiadas I.V., Stamatelatou K. and Lyberatos G., 2009, Hydrogen and methane production through two-stage mesophilic anaerobic digestion of olive pulp, Bioresource Technology Journal, 100, Standard Methods for the Examination of Water and Wastewater, 20 th edition, APHA, AWWA, WPCF, USA, (1998). Vavilin V.A., Sergy V.R., Ljudmila Y.L., Spyros G.P. and Morton A.B., 2003, Distributed Model of Solid Waste Anaerobic Digestion: Effect of leachate recirculation and ph adjustment, Biotechnology and Bioengineering, 81 (1),