Nội dung

Hóa học & Kỹ thuật môi trường IMPACTS OF INOCULUM TO SUBSTRATE RATIO ON METHANE POTENTIAL OF ORGANIC WASTE FROM ANIMAL HUSBANDRY AND GREEN WASTE Pham Thi Mai Chi, Vo Ngoc Trang, Nguyen Thanh Phong* Abstract: The study investigated biochemical methane potential (BMP) of four different substrates from pig slurry (PS), cow slurry (CS), water hyacinth (WH) and water lettuce (pistia stratiotes) (WL). The experiments were conducted using anaerobic sludge from household biogas digester with different ratios of substrate to inoculum (S/I). The substrates were used as PS only, CS only, WH only, WL only, PS-CS mixture, PS-WH mixture, PS-WL mixture, CS-WH mixture, CS-WL mixture, WH-WL mixture. Research involved investigation of the effects of parameters such as temperature (35, 45, and 55oC), substrate to inoculum ratio (S/I: 0.5, 2.0, 4.0, and 6.0 as g DM substrate/g DM inoculated). The results showed that the high cumulative methane production were obtained for CS-WL and PS mixtures at an S/I ratio 0.5g DM/ g DM mixture (as 41L methane/kg DM and 33L methane/kg DM respectively) at 30oC. Results illustrated that CS-WL mixture can be used as suitable substrates for biogas digester. Keywords: Anaerobic, Water hyacinth, Water lettuce, Pig slurry, Cow slurry, Biogas, Methane. 1. INTRODUCTION Due to agricultural development, abundant organic waste is produced. Organic waste comes mainly from agricultural residue, manure of livestock and household waste. Biodegradable waste accounted more than 80% of the total [1]. In fact, the agricultural waste and biowaste are not collected and treated correctly. Most of them landfilled or just disposed of at local dumpsites. Consequently, the environment is getting polluted more and more. Anaerobic digestion has a potential for treatment of organic waste [2] and can therefore be a solution for this kind of pollution. The digestion is enhanced by the tropical climatic conditions and by existence of lots of waste [1]. Anaerobic digestion is a complex biological process in which organic materials are decomposed in the absence of oxygen. Biogas and digestate are produced in the process [3]. Anaerobic digestion deserves more and more interest because it has many benefits such as treating organic waste, recovering heat and producing energy [4,5]. Additionally, anaerobic digestion can reduce total amount of waste to landfills. There are some studies in tropical countries showed that anaerobic digestion is an appropriate method to generate energy in the Mekong Delta (henceforth MD) [1,6,7]. Looking into the real conditions of the tropical countries, among the organic waste treatment method uses, anaerobic digestion could potentially be used as an important method to treat and to recover energy from organic waste. Biogas is considered one of the cheapest renewable energies in rural areas in developing countries. Production of biogas would not only save fuel but also be beneficial for integrated farming systems by converting agriculture and household residues to an improved fertilizer for crops or ponds for fish and water plants. Other benefits of bio-digestion include the reduction of manure smell, elimination of smoke when cooking and the alleviation of pathogens and thereby improving hygiene on farms [8]. 46 P. T. M. Chi, V. N. Trang, N. T. Phong, “Impacts of inoculum to … and green waste.” Nghiên cứu khoa học công nghệ The study examined the mixing ratio, temperature on methane generation from different organic substances (water hyacinth, water lettuce, pig manure and cow manure) to find out factors affecting biogas and methane production. 2. MATERIALS AND METHODS The study was conducted to measure Bio-Methane Potential (BMP) of four different substrates from pig slurry (PS), cow slurry (CS), water hyacinth (WH) and water lettuce (pistia stratiotes) (WL) between March and May in 2017. The substrates were used as PS only, CS only, WH only, WL only, PS-CS mixture, PSWH mixture, PS-WL mixture, CS-WH mixture, CS-WL mixture, WH-WL mixture. The experiments were conducted using anaerobic sludge from household biogas digester with different ratios of inoculum to substrate (S/I: 0.5, 2.0, 4.0 and 6.0) dry matter (DM) (g DM substrate/g DM inoculum). The schematic of experiment is shown in figure 1. Water hyacinth (WH) is an aquatic plant native to South America. One of the fastest growing plants known, WH is developing considerably in South-eastern region in Vietnam. And water lettuce (WL) is also an aquatic plant which its native distribution is uncertain. WL is quite developing in the same area of WH’s region. Biogas sludge collected from household biogas digester with DM of 16.5% was used as inoculum. The second experiment was to invest the effect of different temperatures (30°C (room temperature), 45°C, and 55°C). Figure 1. Schematic of a simplified test for Bio-Methane Potential (BMP). 2.1. Batch Digester Start-up and Experimental Design The BMP test was performed in three glass bottles of 500ml each. The first bottle was partially filled with substrate and inoculum according to the fixed ratio of 0.5, 2.0, 4.0 and 6.0 (g DM inoculum to substrate (S/I)). Tap water was added up to ensure the moisture of substrate for anaerobic digestion. For ratio S/I 2.0, 4.0 and 6.0, the amount of tap water is poured into each bottle which is 20ml, 40ml and 60ml in turn. pH was measured before starting and after ending the experiment. The input of pH ranged from 6.2 to 5.8 and the output one was between 6.5 to 5.5. Tạp chí Nghiên cứu KH&CN quân sự, Số Đặc san NĐMT, 09 - 2017 47 Hóa học & Kỹ thuật môi trường The bottle was sealed with a thick gumming cap. The bottle was connected by capillary tube to the second glass bottle which was inverted and containing an 2% alkaline solution (NaOH). The capillary tube was equipped on both ends with a needle to pierce the thick gumming cap to enable gas transfer through the two connected bottles. Daily methane production was monitored measuring the volume of alkaline solution displaced from the measure bottle and collected in a third 500mL glass bottle. The displaced liquid was measured daily by a cylinder (Fig. 1). The CO2 contained in the biogas was dissolved in the alkaline solution; therefore, it did not affect the volumetric methane measurements. Temperature and pH in each BMP bottle were monitored at the beginning and the end of the experiment with a TFK 325 thermometer and a pH meter (Martini, Rumania). All bottles were shaken once a day for 30 second by hand. The bottles were immersed up to two third height in hot water, kept at a constant temperature of 45 ±1°C and 55±1°C by WNP 45 submersible heater (Memmert, Germany). For the experiment of 30±1°C, the bottles were set up in the room temperatures (ranged from 29 to 31±1°C). Triplicate analyses was performed for each sample. DM contents were measured according to Standard Methods [9]. The DM was determined by drying the samples at 105°C until the weight was unvarying. The percentage of DM content was calculated in relation to the initial weight. 2.2. Substrates Collection and Preparation Cow Slurry and Pig Slurry were collected from a household farm in Can Duoc District, Long An Province, Vietnam; whereas, water hyacinth and water lecture were also collected from a canal in Can Duoc District, Long An Province, Vietnam. Inoculum (biogas digestate) was collected from biogas digesters in a pig farms in Long An. All materials were collected and transferred to laboratory in Quang Trung Software City, District 12, Ho Chi Minh City within the day. Experiments were then carried out the following day. All materials were measured for dry matter (DM) before starting the fermentation. 3. RESULTS AND DISCUSSION 3.1. The Effects of Different Substrates on Biochemical Methane Potentials Cumulative methane production from Pig Slurry (PS), Cow Slurry (CS), Water Lettuce (WL) and Water Hyacinth (WH) is showed in Fig. 2. Methane production was measured under controlled conditions for 28 days. The highest methane yield was 33L CH4/kg DM from PS. Methane production of PS was increased sharply during the first 5 days; whereas WH produced CH4 after 4 days. The difference could be explained by the fact that PS was stored in the pig farm before collection for the experiment. In fact, hydrolysis (the first period happens in anaerobic digestion process) was taken place in the storage tank. WH was collected fresh, so the hydrolysis was take place first in the bottle, while PS was experienced the hydrolysis in the pig farm before. The methane production of CS, WL and WH were 25.8, 25.6 and 7.7 L CH4/kg DM substrate, respectively. 48 P. T. M. Chi, V. N. Trang, N. T. Phong, “Impacts of inoculum to … and green waste.” Nghiên cứu khoa học công nghệ Methane production of PS in this paper was 33L CH4/kg DM. This result is one third lower than that reported by other authors [10]. The differences could be explained by the fact that previous studies were added micronutrients (Na2CO3 powder to prevent a critical drop in pH), whereas this study only measured the input and output of pH. All bottles were shaken once a day for only 30 second by hand and kept them in 30oC±1oC, which was lower than previous study [10] 5oC. 40 Methane (L/kg DM substrate) Pig Slurry 30 Cow Slurry Water Lettuce 20 10 Water Hyacinth 0 0 5 10 15 20 25 30 Duration (day) Figure 2. Cumulative methane production from Pig Slurry (PS), Cow Slurry (CS), Water Lettuce (WL) and Water Hyacinth (WH). Results of the experiment showed that the highest CH4 production was at the ratio of 0.5 g DM Substrate/Inoculum. The higher the ration, the lower was methane production. The highest BMPs were measured as 40 L CH4/kg DM at an S/I ratio of 0.5g. At the ratios of 4 and 6 g DM S/I CH4 production was very low during the first days and increased slowly after 20 days. pH of these cases were very low (4 to 5). The methanotrophic bacteria was inhibited; therefore, methane production was very low. Methane (L/kg DM substrate) 50 0.5g DM Substrate/Inocculum A1CB1 (0.5 S/I) B1CB1 (2 S/I) C1CB1 (4 S/I) D1CB1 (6 S/I) 40 30 2g DM Substrate/Inocculum 20 4g DM Substrate/Inocculum 10 6g Substrate/Inocculum 0 0 5 10 15 20 25 30 Duration (day) Figure 3. Cumulative methane production in samples A1CB1, B1CB1, C1CB1, D1CD1 at 0.5, 2.0, 4.0, and 6.0 g DM substrate/g DM inoculum (S/I). Tạp chí Nghiên cứu KH&CN quân sự, Số Đặc san NĐMT, 09 - 2017 49 Hóa học & Kỹ thuật môi trường 3.2. The Effects of Temperature on Biochemical Methane Potentials The study investigated the effects of different temperature (30, 45 and 55oC) on methane yields of mixture cow slurry (CS) and water lettuce (WL). Fig. 4A illustrates the cumulative methane production in these samples (CS+WL) respectively at 30°C, 45°C, and 55°C. The methane productions at 30°C, 45°C, and 55°C were 41, 25 and 1 L CH4/ kg DM substrates, respectively (Fig. 4B). The results showed the highest methane yields at 30°C; whereas, the lowest methane yield was at 55oC. In contrast to this result, high temperature pushes methane production was reported by another study [11]. The advantage range for temperatures was 50 to 65oC, which reached the peak of methane production. The effect of temperature on the process of anaerobic digestion was different. The results were in line with a previous study [11]. The study showed that temperature has an effect on seaweed biomass, which 35oC condition yielded the highest methane. In addition, at temperature of 45 and 55oC methane production declined by 23.3% and 39.7%, respectively [12]. Methane (L/kg DM substrate) 50 30oC 45oC 55oC 40 30oC 30 A 45oC 20 10 55oC 0 0 5 10 15 20 25 30 Duration (day) 50 B 30oC Methane (L/Kg DM) 40 30 45oC 20 10 55oC 0 A1CB-35A A1CB-45A A1CB-55A Figure 4. A: Cumulative methane productions at 30, 45 and 55oC; B: methane production at 30, 45 and 55oC. 50 P. T. M. Chi, V. N. Trang, N. T. Phong, “Impacts of inoculum to … and green waste.” Nghiên cứu khoa học công nghệ 4. CONCLUSIONS The effects of S/I ratio and temperature on biochemical methane potential were studied. For this purpose, pig slurry (PS), cow slurry (CS), water hyacinth (WH) and water lettuce (pistia stratiotes) (WL), mixture of PS-CS, PS-WH, PS-WL, CSWH, CS-WL and WH-WL were investigated to determine the highest BMP depending on varying environmental and operating parameters. Results showed that CS + WL as substrates had the highest BMPs at 30°C and an S/I ratio of 0.5 g DM substrate/ g DM inoculum, suggesting that a mixture of CS-WL can be used for biogas production under anaerobic conditions with high efficiencies. REFERENCES [1]. Nguyen Phuc Thanh, Yasuhiro Matsui, Takeshi Fujiwara. 2010. “Household solid waste generation and characteristics in a Mekong Delta city”, Vietnam. Journal of Environmental Management, 91, pp. 2307-2321. [2]. Bolzonella D., P. P., Mace S. and Cecchi F. 2003. “Dry anaerobic digestion of differently sorted organic municipal solid waste: a full-scale experience”. Bio-resource Technology, 86, pp. 123-129. [3]. Duerr, M., Gair, S., Cruden, A. and McDonald, J. 2007. “Hydrogen and electrical energy from organic waste treatment”. International Journal of Hydrogen Energy, 32, 705-709. [4]. Gregor D. Zupancic, Natasa Uranjek-Zevart, Milenko Ros. 2008. “Full-scale anaerobic co-digestion of organic waste and municipal sludge”, Science Direct. Biomass and Bioenergy (2008) 162– 167. [5]. Barth, J. 2006. “Status of organic waste recycling in the EU”. First Baltic Biowaste Conference 2006. [6]. Nguyen Vo Chau Ngan and Fricke Klaus. 2012a. “Improving the biogas application in the Mekong Delta of Vietnam by using agricultural waste as an additional input material”. Journal of Engineering Technology and Education. International Conference on Green Technology and Sustainable Development. [7]. Nguyen Vo Chau Ngan and Fricke Klaus. 2012b. “Energy recovery from anaerobic co-digestion with pig manure and spent mushroom compost in the Mekong Delta”. J. Viet. Env. 2012. Vol. 3, No. 1, pp. 4-9. [8]. Bui Xuan An. 2002. “Experiences in biogas technology development in Vietnam agriculture and rural areas”. Proc. Intl. seminar in biogas technology for rural-mountainous development and urban areas, Hanoi, Vietnam, Jan/2002. [9]. Laskri N, Hamdaoui O and Nedjah N. 2015. Journal of clean energy technologies, Vol.3, No.3, pp.181-184. [10]. Giovanni Esposito, Luigi Frunzo, Flavia Liotta, Antonio Panico and Francesco Pirozzi. 2012. “Bio-Methane potential tests to measure the biogas production from the digestion and co-digestion of complex organic substrate”, 5, pp. 1-8. Tạp chí Nghiên cứu KH&CN quân sự, Số Đặc san NĐMT, 09 - 2017 51 Hóa học & Kỹ thuật môi trường [11]. V. H. Varel, A. G. Hashimoto and Y. R. Chen. 1980. “Effect of temperature and retention time on methane production from beef cattle waste”, Vol. 40, No. 2, pp. 217-222. [12]. Carlos Vanegas, John Bartlett. 2013. “Anaerobic digestion of Laminaria digitata: The effect of temperature on biogas production and composition”. Vol. 4, pp. 509-515. TÓM TẮT SỰ ẢNH HƯỞNG CỦA TỶ LỆ CHẤT MỒI VÀ CHẤT NỀN ĐẾN KHẢ NĂNG SINH KHÍ MÊ TAN CỦA CHẤT THẢI CHĂN NUÔI VÀ THỰC VẬT Nghiên cứu thực hiện nhằm đánh giá tiềm năng sinh khí mê tan (BMP) của bốn chất nền khác nhau từ phân heo (PS), phân bò (CS), lục bình (WH) và bèo tai tượng (pistia stratiotes) (WL). Các thí nghiệm đã được tiến hành bằng việc sử dụng bùn thải từ hầm biogas trong hộ gia đình để làm chất mồi với các tỷ lệ phối trộn khác nhau với các chất nền (S/I). Các chất nền chỉ được sử dụng như PS, CS, WH, WL, hỗn hợp PS-CS, hỗn hợp PS-WH, hỗn hợp PS-WL, hỗn hợp CS-WH, hỗn hợp CS-WL, hỗn hợp WH-WL. Các nghiên cứu điều tra các ảnh hưởng của các thông số như nhiệt độ (35, 45, và 55oC), tỷ lệ phối trộn của chất nền với bùn từ hầm ủ (S/I = 0.5, 2.0, 4.0 và 6.0 là g DM chất nền/g DM bùn biogas). Kết quả cho thấy hỗn hợp CS-WL và PS sinh khí cao nhất ở tỷ lệ phối trộn S/I là 0,5g DM/g DM (41L khí mê tan/kg DM và 33L mê tan/kg DM) ở 30oC. Kết quả cho thấy rằng hỗn hợp CS-WL có thể được sử dụng làm chất nền phù hợp cho máy hầm biogas. Từ khóa: Kỵ khí, Lục bình, Bèo tai tượng, Phân heo, Phân bò, Biogas, Mê tan. Received date, 07th July, 2017 Revised manuscript, 28thAug, 2017 Published, 15thSep, 2017 Author affiliations: Department of Environmental Engineering, Hoa Sen University, 8 Nguyen Van Trang, District 1, HCMC, Vietnam. * Email : phong.nguyenthanh@hoasen.edu.vn. 52 P. T. M. Chi, V. N. Trang, N. T. Phong, “Impacts of inoculum to … and green waste.”