BIOGAS PROCTION FROM ANAEROBIC CO-DIGESTION OF COW DUNG AND ORGANIC WASTES (NAPIER PAK CHONG I AND FOOD WASTE) IN THAILAND: TEMPERATURE EFFECT ON BIOGAS PRODUCT

Biogas production has been attracting increasing at tention as a biofuel of the future because biogas t echnology not only constitutes a biofuel source, but also can be applied in the various environmental pollutants . Anaerobic digestion of high solid slurries (such as food wast e and cow dung) is typically performed in continuou sly reactor (by force substrate flow) to avoid problems with a thick floating layer or large amounts of sediments. Temperature also seems to have profound influence o the biogas production. The objective of the study was to identify the optimum biogas production for anaerobi c co-digestion of cow dung and organic wastes (napierpakchong I and food waste). Influence of tem p rature (psyhrophilic temperature 25°C and thermop lilic temperature 45°C) and active biogas process on sing le substrate (food waste feed) and co-digestion of cow dung and organic wastes (napierpakchong I and food waste ) was used, within the reactor was studies in 1.80 cm high over a 45 day. Results showed that best digestion w as achieved when digested of cow dung, napierpakcho ng I and food waste) on 1:1:1 and thermoplilic temperatu re. Maximum biogas production (R4), biogas yield, m ethane content and %VS reduction was found that 70 L/day, 70 L/VS feed, 65 and 80%, respectively. The result showed that the biogas production increased progressively withhigher temperature.The increased in biogas prod uction in thermophilic temperature and psyhrophilic temperatu re could be up 28.01 and 26%, respectively. The bio gas yield increased 12.5% of co-digestion system, which compared to thermophilic temperature and psyhrophi lic temperature (R4 and R2). This behavior might be due to the higher degradability. Therefore, temperatur e of digester can be used effectively as an operating st rategy to optimize biogas production.


INTRODUCTION
Thailand is full of suitable areas for agriculture and plantation. Therefore, Thailand's agricultural products are enough for domestic consumption. Moreover, Thailand also has sufficient agricultural products for exportation. Most energy used in Thailand is from oil that is mostly imported from other countries. When AJES Science Publications comparing the price of Thai exported agricultural products with the price of imported oil, it is found that exported agricultural products are cheaper than the price of imported oil. As a result, if there is any change of agricultural products by dividing some areas for planting products that is sufficient domestic consumption and some areas for planting some alternative energy plants for domestic consumption, it will be the solution for creating Thailand's balance of trade. Agriculture has the potential for replacing some of the purchased energy in the form of fossil fuels, commercial fertilizer and field produced animal feed with bioenergy and organic fertilizer and animal feed from on-site renewable biomass in order to economically and environmentally sustain it self (Ghaly and Hattab, 2012). Most Thai people live in the capital city and big cities of each region contributing areas of high population density resulting in high level of consumption. Consequently, there is a consecutive problem on large amount of waste and food scrapes leading to the problem of waste and food scrapes management of big cities' municipality. The solution that is mostly used to solve this problem is landfill requiring the areas for processing bringing pollution to residents who live nearby such areas in case of poor management. For Thailand's agricultural development, there is a research and development of Giant King Grass (Napier Pak Chong I) plantation for animal husbandry in the areas of Pak Chong district, NakhonRatchasima province. This kind of grass is grown easily and able to be bred well and rapidly. Cutting can breed it and its tillering stage is generated automatically without new growing. As a result, it can be harvested at least 7 years with the average productivity of 40-80 tons/rai/year. Energy consumption increases rapidly because of high economic development speed rate of Thailand. Biogas is seen as an important source of energy to meet the electricity demands for small towns and rural areas. Biogas is produced by Anaerobic Digestion (AD) of organic feedstock, the most common being animal wastes and crop residues, dedicated energy crops, domestic food waste and Municipal Solid Waste (MSW); the integrated process included feedstock supply and pretreatment and use of digestate. Biogas consist of 50-70% Methane (CH 4 ), 25-45% Carbon Dioxide (CO 2 ), 2-7% Water (H 2 O) at 20-40°C, 2-5% Nitrogen (N 2 ), 0-2% Oxygen (O 2 ) and less than 1% Hydrogen (H 2 ), 0-1% Ammonia (NH 3 ) and 0-6000 ppm Hydrogen Sulphide (H 2 S) (Akbulut, 2012). Anaerobic of manure, alone or in a mixture of manure and others organic wastes, is widely used today. A number of full-scale anaerobic mesophilic and thermophilic digesters for biogas production have been developed in Thailand. Temperature and the type of raw material are two of most important parameters in anaerobic digestion. The anaerobic digestion is, of course strongly affected by the type of raw material and both the methane yield and the possible reduction of the solid content depends on the composition of the waste material (Alvarez and Lidén, 2009).
Anaerobic digestion can be complete at psyhrophilic (10-25°C), mesophilic (30-40°C) or thermophilic (50-60°C) temperature and can occur under hydraulic flow regimes being Batch Reactor (BR), Sequencing Bath Reactor (SBR) or Continuous Flow Reactors (CFR). Continuous flow bioreactors are operated as a Plug Flow Reactor (PFR) or as a Completely Stirred Tank Reactor (CSTR). Both CFR types are operated at constant volume, which means that as substrate is fed into the bioreactor an equivalent and is more prone to biomass washout and bioreactor failure than sequencing bath reactors (Massé et al., 2011). Compared to orther biological treatment process, the advantages of biogas plants are varied; (i) economically attractive investment, (ii) easily operated and safe installation, (iii) production of renewable electricity and heat resulting in a reduction of CO 2 emissions (iv) reduction of methane emissions from manure storage, (v) improvement of fertilizing qualities of manure (Akbulut, 2012), (vi) production of usable biogas that is about 60-80% methane with a fuel value of 17-23.9 MJ/m 3 , (vii) the digested residue is almost odorless with reduced solids content, (viii) the inorganic nutrients are conserved in the digestion process resulting in the enhancement of the fertilizer value of the digested sludge and (viiii) pathogenic microorganisms such as Salmonella Sp. and Brucella Sp. as well as weed seeds are destroyed during the anaerobic digestion process (Ghaly and Hattab, 2011).
Co-digestion of mixed substrates offers many advantages, including ecological, technology and economic benefits compared to digesting a single substrate (Brown and Li, 2013). According to Brown and Li (2013), digestion of more than one substrate in the same digester, which food waste collected from restaurants, which was found to have a C/N ratio of 15, could be added to balance the C/N ratio of yard waste. The final mixture of liquid AD effluent, yard waste and food waste should have a C/N ratio in range 20-30 for optimum microbial performance.
From the problem of big cities regarding large amount of waste and food scraps resulting in agricultural sector, there is the development of grass growing in Pak Chong district. This is the concept of energy research and development by fermenting Napier Pak Chong 1 AJES Science Publications (NPC) with food waste scrapes to obtain biogas energy. In this research, biogas was produced first by single digestion of Napier Pak Chong 1 (NPC) and then by codigestion of NPC and food waste and the amount of biogas and methane content produced were compared was obtained from continuous anaerobic digester. A series of experiments were carried out under psyhrophilic (25°C) and thermophilic (45°C) condition using continuously tank reactors.  (Satoto et al., 2010). The most important characteristics of three substrates for anaerobic codigestion experiments are presented in Table 1.

Experimental Method
The organics wastes were anaerobically digested for the determination of biogas production potential, as shown in Fig. 1. Four different batches of experiments were conducted in the study and all of reactors were operated in parallel. 872 L continues batch digesters were used in the small scale. In Reactor 1 (R1) contained 100 % of food waste and Reactor 2 (R2) mixture contained 1:1 of napierpakchong I: Food waste, base on Volatile Solids (VS) 30% of food waste and 70% of napierpakchong I, respectively, which R1 and R2 were carried out on digestion at psyhrophilic (25°C) for 45 days.    In reactor 3 (R3) contained 100% of food waste and reactor 4(R4) mixture contained 1:1of napierpakchong I: Food waste, base on Volatile Solids (VS) 30% of food waste and 70% of napierpakchong 1, respectively, which R3 and R4 were carried out on digestion at thermophilic (45°C) for 45 days. In each digestion, the first day started with water about 593 L and then added 2 kg day −1 of inoculum (cow dung) was used. The TS and VS of the inoculum used were 299.33 and 11,400 mg L −1 , respectively. Schematic experimental biogas fermentation set up and digester are presented, as shown in Fig. 2 and 3.
Daily gas production was measured by using water displacement method and corrected for Standard Temperature and Pressure (STP). During the digestion period, the reactors were automatic mixed each day prior to gas measurement to maintain intimate contact between the microorganisms and the substrate. Daily gas production was recorded and corrected for STP and the biogas composition was measured by Portable gas analyzer (BIOGAS 5000). Daily pressure differences were converted into biogas volumes using the following

Analytical Methods
The measurements of Total Solids (TS), Volatile Solids (VS), Total Kjeldhal Nitrogen (TKN), Ammonia Nitrogen (NH 3 ), volatile suspendedsolid and suspended solid of for characterization of organics waste (food waste and napierpakchong I) and inoculum (cow dung) were conducted according to the procedures outlined in Standard Methods (Hamed and Zhang, 2012). Analyzes of Carbon (C), Nitrogen (N) and Hydrogen (H) for substrate were carried out using CHNS/O analyzer. The measurement of pH was conducted using a pH-meter.

Characteristics of Raw Material
Temperature plays a critical role in the anaerobic codigestion. The temperature for anaerobic co-digestion of napierpakchonk I, food waste and inoculum cow dung is psyhrophilic temperature (25°C) and thermophilic temperature (45°C) for 45 days. Along with temperature, the appropriate balance of nutrients is very important for the anaerobic digestion of napierpakchong I and food waste. The advantage of co-digestion with animal dung is that optimum C/N ratios are established without adding chemical and higher methane yield and biogas production are the result.
Napier pakchong I have a low content of nitrogen, which results in relatively high C/N ratios and typical C/N ratios values of substrate are shown in Table 2 and Fig. 4. The napierpakchong I and food waste used in both digesters (R2 and R4) had a C/N ratio of 35 and 16, respectively. Therefore, the nutrient balance in the digesters is dependent upon the addition of an inoculum (cow dung), which relatively high content of nitrogen and the temperature for digestion. The cow dung used in the digesters had a C/N ratio of 24. The initial mixtures napierpakchong I, food waste and cow dung resulted in an overall C/N ratio of 25 in R2 and R4. This resulted indicates that the C/N ratios for R2 (for psyhrophilic temperature) and R4 (thermophilic temperature) for is near the optimum range (25-30) (Mijung et al., 2012).

Effect of Temperature on Biogas Production and Methane Content
The measured values of biogas production are shown in Fig. 5 and Table 3. The highest average biogas production was observed to be 70 L day −1 in R4, while the biogas production for R3, R2 and R1 were about 52, 35 and 25.9 L day −1 , respectively. In particular, effect on temperature it was found that the temperature of the R4, R3, R2 and R1were maximum at 45.3, 44.8, 26.7 and 25.3°C, respectively. It can also be seen that for the digesters operated at thermophilic temperature, the biogas product increased until about day 16 and then gradually leveled off thereafter (R3 and R4), which was readily biodegradable, whilefor the digesters operated at psyhrophilic temperature the biogas production increased until day 20 and then gradually leveled off (R1), except R2 there are the tend of biogas production similarly of thermophilic temperature condition, which increased until day 16, due to it had mixtures of napierpakchong I, food waste and cow dung resulted in an overall C/N ratio of 25. This resulted indicates that the C/N ratios for R2 (although operated at psyhrophilic temperature) for is near the optinum range (25-30).  Gas production obtained in R1 (food waste 100% at psyhrophilic temperature (25°C)), R2 (co-digestion of napierpakchong I, food waste and cow dung; 1:1:1 at psyhrophilic temperature (25°C)), R3 (food waste 100% at thermophilic temperature (45°C)) Fig. 6. Methane content obtained in R1 (food waste 100% at psyhrophilic temperature (25°C)), R2 (co-digestion of napierpakchong I, food waste and cow dung; 1:1:1 at psyhrophilic temperature (25°C)), R3 (food waste 100% at thermophilic temperature (45°C)) AJES

Science Publications
Several other authors reported an improvement of biogas productivity of anaerobic digesters by supplementing the main substrate with readily digestible co-substrates, which in this research observed that the addition of nepierpakchong I to digestion highest biogas production of R2 (psyhrophilic temperature) and R4 (thermophilic temperature) increased 26 and 28.01%, respectively. To compare highest biogas production of R1 and R3 (same substrate and difference temperature), this substrate were found increased 48.09%, whilecompare highest biogas production of R2 and R4 (same substrate and difference temperature), this substrate were found increased 49.50%. The reason of biogas production different, which there were similar substrates due to the higher degradability with higher temperature.
The measured values of biogas composition are shown in Fig. 6 and Table 4. Each data point is average of duplicate measurement for each reactor. In terms of Methane (CH 4 ) content, the highest methane composition of biogas was 65% in R4, while R3, R2 and R1 were observed to be 63, 61 and 58%, respectively Methane productions as well as VS removal efficiency for the different operating condition.
It is not surprising that the methane production of codigestion system and higher temperature was higher than those of the single digestion system because the OLRs of co-digestion system were set to be approximately equal to the sum of the single system digestion (Panyadee et al., 2013). The highest VS reduction was observed to be 80, 78, 70 and 68% for R4, R3, R2 and R1, respectively (Fig.  7). Probably, higher VS conversions might have been achieved for R4. A C/N ratio 25 seemed to perform better during thermophilic anaerobic co-digestion of napier pak chong I, food waste and cow dung.
Biogas yield of the digestion are shown in Fig. 8. The biogas yield increased 12.5% of co-digestion system, which compared to thermophilic temperature and psyhrophilic temperature (R4 and R2).

Fig. 7.
Volatile solid reduction obtained in R1 (food waste 100% at psyhrophilic temperature (25°C)), R2 (co-digestion of napierpakchong I, food waste and cow dung; 1:1:1 at psyhrophilic temperature (25°C)), R3 (food waste 100% at thermophilic temperature (45°C)) Fig. 8. Biogas yield obtained in R1 (food waste 100% at psyhrophilic temperature (25°C)), R2 (co-digestion of napierpakchong I, food waste and cow dung; 1:1:1 at psyhrophilic temperature (25°C)), R3 (food waste 100% at thermophilic temperature (45°C) and R4 (co-digestion of napierpakchong I, food waste and cow dung; 1:1:1 at at thermophilic temperature (45°C)) Table 3. Gas production in food waste and co-digestion of napier pak chong I, food waste and cow dung under psyhrophilic temperature (25°C) and thermophilic temperature (45°C) Gas Production (L/day)  It can also be seen that the lower biogas yield at R1 (digested of food waste at psyhrophilic temperature) indicated there was an inhibition of methaogenic bacteria. Biogas yield were lower when operating under psyhrophilic temperature condition 52 L/VS feed (R1) and 59 L/VS feed (R2) compared to 65 L/VS feed (R3) and 70 L/VS feed (R4), respectively, at thermophilic temperature for single food waste and co-digestion feed of napierpakchong I, food waste and cow dung. This behavior might be due to the higher degradability. From all results, it has been found that the biogas quality parameter in all digester is shown in Table 5.

DISCUSSION
Even through anaerobic digestion of organic substrates is a well-developed technology, some new technical problems in the anaerobic process occur when new substrates are used. It has been found that codigestion of various material often gives a higher methane production and biogas yield than digestion of a single material. The process of bio-methanation is very sensitive to changes in temperature. The degree of sensitivity, in turn, is dependent on the temperature range. Brief fluctuations not exceeding ±1°C/h may be regarded as still un-inhibitory with respect to the process of fermentation. The temperature fluctuations between day and night are no great problem for plants built underground, since the temperature of the earth below a depth of one meter is practically constant. The graph below indicates the gas production per kg of substrate in relation to the retention time. The researches indicate that different substrate and different temperatures produce different conditions. In this results, examined the anaerobic digestion of food waste and combined food waste, napierpakchong I and cow dung at psyhrophilic temperature (about 25.3 and 26.7°C) and thermophilic temperature (about 44.8 and 45.3°C), finding that the thermophilic reactor produced higher biogas production, methane content, biogas yield and VS reduction than the psyhrophilic reactor. The results demonstrate that biogas production, methane content and biogas yield are influenced by temperature for single and co-digestion anaerobic digestion. It was found that the suitable raw material ratio ofnapierpakchong 1, food waste and cow dung for biogas production is 1:1:1:1. For maximum biogas and methane production and appropriate Carbon to Nitrogen (C:N) ratio must be followed 25. There were higher methane content, biogas yield and biogas product along with digester onthermophilic temperature than digester onpsyhrophilic temperature that higher %VS reduction, mainly due to high biogas activity. Therefore, the present results in practice suggest that biogas production can be optimized if a digester with thermophilic condition and co digestion can be used effectively as a means of cell and solid material retention within the reactor.

CONCLUSION
The study reveals that food waste, napierpakchong I and cow dung have a good potential as an energy source in Thailand. The results showed that operating s continuously reactor at thermophilic temperature condition could optimize the biogas production from codigestion. Napier pakchong I addition to food waste and cow dung digesters improves biogas production on psyhrophilic and thermophilic temperature condition. Best results were obtained when carried out on food waste, napierpakchong I and cow dung on the ratio 1:1:1 atthermophilic temperature condition for 45 days. The increased in biogas production in thermophilicand psyhrophilic temperature condition could be up 28.01 and 26%, respectively, compared to single feed (food waste only and co-digestion). The biogas production from R4 (co-digestion of food waste, napierpakchong I and cow dung 45.3°C in 45 days) was found to be 70