School of Energy and Environment Science, Yunnan Normal University, Kunming , Yunnan, China

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1 2016 International Conference on Energy Development and Environmental Protection (EDEP 2016) ISBN: Biogas Production from Lettuce Leaf by Mesophilic Fermentation Cheng GUO a, Qiang WANG, Xing-Ling ZHAO, Chang-Mei WANG, Jing LIU, Hong YANG, Fang YIN b,*, Wu-Di ZHANG c,* School of Energy and Environment Science, Yunnan Normal University, Kunming , Yunnan, China a chengguo1993@outlook.com, b yf709@sina.com, c wootichang@163.com * Corresponding author Keywords: Lettuce Leaf, Biogas Production, Potential. Abstract. The experiment on potential of biogas production with lettuce leaf was conducted under the condition of mesophilic (30 C) batch fermentation. The consequence pointed out that the experimental group generated 1219 ml net biogas in 15 days. Moreover, the production rate of lettuce leaf was 700 ml/g TS and 852 ml/g VS. Introduction Lettuce leaf is seen commonly and widely, especially in the vegetable base. In recent years, people s demands for vegetable have been growing. At the same time, a large number of poor quality vegetables in production and procession become solid waste which will pollute the environment if not handled. For example, there are approximately 60~180 million tons vegetable wastes in Songming County, Yunnan Province every year. To make the utilization of the vegetable wastes, this experiment used lettuce leaf as raw material for anaerobic fermentation to probe its biogas production potential. Experimental Materials and Methods Materials Fermentation Materials. Fermentation material was unwanted lettuce leaf at vegetable base of Songming County, Yunnan Province. The determination value of TS and VS was 7.92%, 82.12% respectively. Fermentation Inoculums. The inoculums were pig manure enriched for a long time and the determination value of TS% and VS% was 15.24%, 79.91% respectively. Experimental Equipment. Experimental equipment mainly consisted of fermentation bottle, gas storage bottle, metering bottle and thermostatic water bath pot, as shown in Fig. 1.

2 Figure 1. Experimental equipment for biogas fermentation. Methods Pretreatment for Raw Material. Lettuce leaf was cut up by a knife and its length was nearly 1 mm. Experiment project (1)The experiment was made by batch fermentation craft in 30 C. At the same situation, both experimental groups and control groups were designed for 3 repeated experiments. TS value of fermentation liquid is 5%, inoculums 30%. (2)Composition of fermentation liquid Experimental groups: 120 g pig manure + 22 g lettuce leaf + water = 400 ml; Control groups: 120 g pig manure + water = 400 ml. (3)Character of fermentation liquid Experimental groups: TS = 6.25%, VS = 82.71%, ph = 6.5. Control groups: TS = 1.13%, VS = 67.20%, ph = 6.0. Determination item & Methods (1) TS (Total Solids): Keep the sample in the draught drying cabinet (105±5 C) to constant weight, and calculate the TS [1]. (2) VS (Volatile Solids): Burning the dried sample above in the muffle furnace (550±20 C) to constant weight, and calculate the VS[1]. (3) ph: ph precise test paper in the range of 5.5 ~ 9.0. (4) Biogas Production: Reading the scale on metering bottle at nine o clock p.m. every day. (5) Methane Content: Using the FULI GC9790 II type gas chromatography to determine it from the biogas. Experimental Consequence & Discussion Gas Yields & Analysis Daily Gas Yields. In the Fig. 2, it revealed the gas yields variation as fermenting.

3 Figure 2. Net gas yield curves. In the Fig. 2, it can be seen that the gas yields achieved 216 ml on the 1st day and through the determination of gas chromatography, methane content in the gas reached 24.26%. Therefore, the gas disabled from lighting [1]. On the next day, the yields decreased to 144 ml. But, the 3rd day saw the yields 199 ml that was the peak value later on. After the 3rd day, the gas yields basically tended to drop. From 4th to 10th day, gas can be burned with color of blue continuously and the methane content of gas in 4th, 10th was 57.20%, 61.13% respectively. The experimental group did not produced gas any more when fermentation time was near 15th. We can conclude that the fermentation on lettuce leaf activated fast and its period was short. Accumulated Gas Yields. In the Fig. 3, it revealed the variation of accumulated gas yields and gas yields rate as experimental group fermenting.

4 Figure 3. Accumulated gas yield & Gas yield rate curves. From the Fig. 3, we can see a trend that accumulated gas yields increased mostly from fast speed to slow speed. As well as, accumulated gas yields took up more than 80% of the number of gases in the 7th day. Thus, HRT (Hydraulic Retention Time) in the biogas engineering is able to be designed for 7 days. Biogas Production Potential. Biogas production potential of lettuce leaf can be obtained by counting on the basis of the characteristic of fermentation materials, fermentation time and fermentation volume. Consequences were presented as Table 1. Table 1. The biogas generation potential of lettuce leaf. Raw materials Net gas yields/ml Rate of gas generation of tank volume/(ml/ ml d) Rate of gas generation/[ml/g](ts) Rate of gas generation/[ml/g](vs) Lettuce leaf Control group generated 108 ml gas. From Table 1, we can see the rate of gas generation (TS & VS) of lettuce leaf was 700 ml/g and 852 ml/g separately. Li et al had made experiment of the study of biogas fermentation on the leaf of lettuce whose rate of gas generation (VS) had been 809 ml/g [2]. Compared with her result, this experiment is higher than that, for which the reason that the temperature is upper than her 24.5 C account more likely. Comparison of Gas Generation Potential with Other Fermentation Substrates. To evaluate gas generation potential of lettuce leaf comprehensively, a comparison with other fermentation substrates can be displayed in following Table 2.

5 Table 2. Potential for biogas generation from various materials. Fermentation substrates Biogas yields(ml/g TS) References Lettuce Leaf Baby Cabbage 258 [3] Corncob 768 [4] Blue Grass 457 [5] Spinach Leaf Stalk 313 [6] Weeds-Eupatorium 245 [7] Dry Haulm 748 [8] Significantly, what can be seen from Table 2 is that lettuce leaf surpasses baby cabbage, blue grass, spinach leaf stalk, weeds-eupatorium in biogas yields (TS). However, the biogas yields (TS) of lettuce leaf is inferior to corncob and dry haulm. Synthetically, lettuce leaf is capable of being called a worthy sort of raw material for fermenting. Conclusions The lettuce leaf can generate biogas in 30 C. The rate of biogas generation of TS and VS is 700 ml/g, 852 ml/g alone. So lettuce leaf is well utilized to fermenting and generating biogas. In order to enhance biogas yields and quality further, it is indispensable to research fermentation parameters. Acknowledgements This work was supported by the Specialized Research Fund for the Doctoral Program of Higher Education ( ), the National Science Foundation of China ( ), the Yunnan Province Key Project Foundation (2014FA030), the Yunnan Province New Energy Major Projects (2015ZB001, 2015ZB005), the Yunnan Province International Science and Technology Correspondent (2015IA022), Yunnan Rural Energy Engineering Key Laboratory Fund (2015), Collaborative Innovation Center of Research and Development of Renewable Energy in the Southwest Area ( ). References [1] W.D. Zhang, H.C. Song, F. Yin, et al. Biogas Fermentation & Comprehensive Utilization. Kunming: Yunnan Science Press, 2004, pp [2] L.L, W.D. Zhang, F. Yin, et al. The study of biogas fermentation on the leaf of lettuce. Human Agricultural Machinery, 2007, no.7, pp [3] Y. Zhang, J.X. Wang, W.H. Feng, et al. Laboratory Scale and Pilot Scale Test on Biogas Production of Baby Cabbage Waste. China Biogas, 2015, no.33 (5), pp [4] X.J. Wang, G.K. Zeng, S.Q. Liu. Study on Biogas Fermentation of Corncob. Anhui Agricultural Science Bulle, 2006, no. 12(10), pp [5] L. Qiu, X.M. Wang, Y.Q Qiu, et al. Experiment on Anaerobic Fermentation with Lawn Waste for Eco-campus. China Biogas, 2009, no. (5), pp

6 [6] Y. Mao, W.D. Zhang. Experimental Study on Potential of Biogas Fermentation with Spinach leaf stalk. Agriculture & Technology, 2004, no. (2), pp [7] W.D Zhang. The Utilization of Malignant Poisonous Weeds-Eupatorium. Yunnan Forestry Science and Technology, 1996, no. (1), p. 78. [8] G.W. Cheng, Z.Q Zhu L.N. Hu, et al. Research about Biogas Fermentation of Various Common Agricultural Organic Residues. Research of Agriculture Modernization, 2009, no. 30 (2), pp