IMPROVEMENT OF ANAEROBIC DIGESTION OF RICE STRAW USING WET – MILLING PRETREATMENT APPROACH

Assiut University web-site: www.aun.edu.eg

IMPROVEMENT OF ANAEROBIC DIGESTION OF RICE STRAW USING WET – MILLING PRETREATMENT APPROACH

NAGHAM ELSAIDY1; FATMA ABOUELENIEN1 and YUTAKA NAKASHIMADA2
1 Department of Hygiene and Preventive Medicine, Faculty of Vet. Med., Kafr Elshiekh University, Kafr Elshiekh Governorate-33156, Egypt.
2 Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Kagamiyama 1-3-1, Higashi- Hiroshima

Received 22 December 2015; Accepted 20 January 2016

ABSTRACT

As rice production continues to rise in order to provide a stable food source for over half of the world’s population, so rice straw will continue to be an abundant and accessible agricultural waste. Rice straw is a widely available lignocellulosic waste with potential for energy recovery through anaerobic digestion. Lignin slows the hydrolysis phase, resulting in low methane recovery and long digestion periods. Pretreatment with wet milling was tested in contrast with grinding rice straw and control one without rice straw, as a technique for enhancing the anaerobic digestion. Two mixtures were used, M1 containing grinded rice straw and M2 containing wet milled rice straw and the both were inoculated with seed sludge and kept under thermophilic conditions (55°C) with dry fermentation (total solids, TS%) over 20. Control vials were used with only seed sludge. Two batch cultures lasted for 35 days for each. The results showed that wet milling seems to enhance methane production from rice straw with maximum production of 1493.98 ml/g-vs compared with 387.7 ml/g-vs from grinded one. Methane percentage was ranged from 48 to 55%. Acetate production was low ranged from 0.74 to 0.93mM/kg mixture which meant success of methane production. Thermophilic condition was used at 55°C which in contrast to previous study enhance the degradation. Methane potential from grinded rice straw, wet milled rice straw, and glucose as reference was 234, 230, and 338 l/kg vs respectively.

Keywords: Dry anaerobic-digestion, Methane production, Rice straw, Wet-Milling, Pretreatment, Thermophilic.

INTRODUCTION

Rice is the most important staple food consumed daily by at least half of the world’s population, including all Asian countries, most of West and North Africa, some countries in East and Central Africa (Sreepada and Vijayalaxmi, 2013). The Food and Agriculture Organization of the United Nations (FAO) estimated that a total of 679 million tons of rice were produced in 2009 (FAOSTAT, 2011), which equates to approximately 916 million tons of rice straw available for energy production (Kadam et al., 2000).

Egypt has a large rural population whose major energy source was biofuel (crop residue and fuel wood). However, rapid economic development has increased rural access to commercial energy, and the use of biofuel is decreasing. As a result, crop residue is not in such high demand as fuel, so it is increasingly burned in the crop fields (El Saidy, 2011).

Corresponding author: Dr. Nagham Elsaidy
E-mail address: nagham.elsaidy@yahoo.com
Present address: Department of Hygiene and Preventive Medicine, Faculty of Vet Med., Kafr Elshiekh University, Kafr Elshiekh Governorate-33156, Egypt.
The issue that contributed to formation of smoke cloud over Egypt that always in parallel to the period of rice straw burning by farmers in the delta Governorates especially Dakahlya, Sharkia, and Kalyobia (Moussa and Abdelkhalek 2007) in a phenomenon called (Black cloud). Akmal et al. (2011) estimated the amount of rice straw produced annually in Egypt by 3.5 million tons.

A major problem with burning of rice straw in the fields is the incomplete combustion of the burning nature which result in emission of large amounts of smoke and other pollutants into the atmosphere, including toxic gases (Co2, carbon monoxide (CO), volatile organic compound (VOC), fine/inhalable particles and carcinogenic polycyclic aromatic hydrocarbons as recorded by (Kim Oanh et al., 2005), which accelerates increase in atmospheric temperature and can cause global warming. In addition to their effects on ambient air hygiene it poses a public health hazard as the smoke from biomass burning has been shown to be potentially toxic (Kim Oanh et al., 2002). Due to health and environmental concerns, many countries have imposed new regulations restricting field burning activities (Mansaray et al., 1999). Therefore, there were a lot of trials suggested several alternatives methods of rice straw uses instead of its burning. Van Nguu (2000) mentioned that the most traditional uses of rice byproducts includes straw and hull were used for energy, animal feed, building materials and paper production. Mansour et al. (2007) suggested recycling of rice straw with a mixture of cement not only forms a sustainable low cost building material, but could also reduce air pollution. In addition to these benefits, the straw could act as a thermal insulation material for the unpleasant Egyptian weather. Another potential use of rice biomass for energy production can be utilized worldwide; even in the developing countries is the conversion of rice residues into the clean-burning fuel through anaerobic digestion. The issue which represents an important trend for Egypt, in the present time where Egypt is facing a high population growth rate, rising fuel costs and much need for clean fuel sources for generation of heat and /or electricity. During the anaerobic digestion process, microorganisms convert biomass into biogas, a mixture of methane and carbon dioxide with trace amount of other gases like carbon monoxide and hydrogen, in the absence of oxygen (Ondrej and Dagmar, 2013). The produced biogas can be used as fuel to generate heat and/or electricity. Furthermore, the digestate can be used as a good organic fertilizer (Chandra et al., 2012). The most important challenges and limitations in the process of converting rice straw to biogas are mainly related with high Carbon/Nitrogen (C/N) ratio or low hydrolysis performance and digestibility because of high lignin content and its complex, stable and recalcitrant lignocellulosic structure (Chen and Lei, 2008). Therefore, it needs a further balance of nutrients and destructive pretreatments. Pretreatment is a key process for accomplishing efficient enzymatic hydrolysis of lignocellulosic biomass, and it has been subject of many studies (Sun and Cheng, 2002; Mosier et al., 2005; Alvira et al., 2010). Among the pretreatment methods used wet milling method is described as an energy saving pretreatment method (Endo et al., 2008 and Hideno et al., 2009). The advantages of this pretreatment method were include its environmental-friendly nature given only water that used as a carrier; it is effective for enzymatic hydrolysis, and has a low energy consumption compared with conventional ball milling (Hideno et al., 2009; Yanagida et al., 2009). As little research has been conducted to examine the effect of direct biogasification of rice straw under anaerobic condition which is still important and promising, especially in rural areas of developing countries. So the objective of this study was to assess the availability of direct anaerobic digestion of rice straw with anaerobic sludge, and to examine the effect of wet milling pretreatment on methane yield and biogasification characteristics of rice straw during semi-continuous batch culture under thermophilic condition.

MATERIALS AND METHODS

1. Seed sludge
The seed thermophilic methanogenic sludge used in the study was collected from a wastewater treatment center in Hiroshima, Japan. The digested excess sludge referred to as sludge in this article is a digested sludge obtained after the fermentation of methane by thermophilic anaerobic digestion of excess activated sludge (Nishio and Nakashimada, 2007). This sludge was anaerobically incubated at 55°C for 60 days in the laboratory to achieve complete consumption of the substrate, in order to be used as inoculum or seed sludge. The sludge was stored at the refrigerator with -4oC before use and its Characteristics were summarized in Table 1.

2. Biomass used in the study
2.1 Rice straw
Rice straw used in this study was collected from field at Fukushima prefecture; in Japan in 2013. The air dried rice straw was cut into small pieces and further milled to powder, by grinding with a hammer mill and fraction passed 250μm mesh. Its Characteristics were summarized in Table 1.

2.2 Treated Rice straw
Rice straw was treated with a wet-milling method, using a bead mill with 4L of volume (LME4, Tsukuba, Japan), to accelerate methane production that was developed by Ohtuka and Nakamura in Forestry and Forest Products Research Institute, Japan (Hideno et al., 2009). Its character was summarized in Table 1.

3 Batch Experimental design
3.1 First batch
3.1.a Mixture 1 (M1) using Grinded rice straw
Mixture 1 (M1) was used to measure methane production from grinded rice straw, 80g of the seed sludge was mixed with 4g rice straw, 1g NaHCO3 and 16g Milli Q water. The mixture was filled into 700 ml anaerobic vials. The headspace of the bottle was filled with nitrogen gas to achieve anaerobic condition and the anaerobic vials were statically set at the incubator with 55°C. Simultaneously, the control culture without rice straw was also carried out. The triplicate culture was performed for each experiment. The character, conditions, ratios and experimental setup of M1 are illustrated in table 2. TS and VS of M1 content were illustrated in table 3. (Abouelenien et al., 2010).

3.1.b Mixture 2 (M2) using treated rice straw
Mixture 2 (M2) was used to measure methane production from rice straw treated with wet-milling method, 80g of the seed sludge was mixed with 20g treated rice straw and 1g NaHCO3. The mixture was filled into 700 ml anaerobic vials. The headspace of the bottle was filled with nitrogen gas to achieve anaerobic condition and the bottle was statically set at the incubator with 55oC. Simultaneously, the control culture without rice straw was also carried out. The triplicate cultures were performed for each experiment. The characters, conditions, ratios and experimental setup of M2 were illustrated in table 2. TS % and VS% of M2 content were illustrated in table 3. (Abouelenien et al., 2010).

3.2 2nd batch
3.2.a Mixture 1 (M1) using Grinded rice straw
At the end of first batch which was reached when gas production stopped, the anaerobic vials were opened and 20g of the first batch M1 was mixed with 1g grinded rice straw and 4 ml Milli-Q water. The mixture was filled into 500 ml anaerobic vials of total volume. The headspace of the bottle was filled with nitrogen gas to achieve anaerobic condition and the bottle was statically set at the incubator with 55°C. Simultaneously, the control culture without rice straw was also carried out. The triplicate cultures were performed for each experiment (Abouelenien et al., 2009).

3.2.b Mixture 2 (M2) using treated rice straw
At the end of the first batch which reached when gas production stopped, the anaerobic vials were opened and 20g of the first batch M2 was mixed with, 5 g pretreated rice straw.

The mixture was filled into the bottle with 500ml of total volume. The headspace of the bottle was filled with nitrogen gas to achieve anaerobic condition and the bottle was statically set at the incubator with 55oC. Simultaneously, the control culture without rice straw was also carried out. The triplicate culture was performed for each experiment. (Abouelenien et al., 2009).

4. Analytical methods
Fermentation samples (ca. 0.3 g wet weight) were withdrawn into 2-ml plastic tubes and suspended with 1.2 ml deionized water. The suspension was centrifuged at 3,000 rpm for 10 min at 4 °C, and the clear supernatant was used for measurement of VFAs. VFAs were measured using High Performance Liquid Chromatograph (Shimadzu, Kyoto, Japan) that was equipped with Aminex HPX-87H Column, 300mm x 7.8mm (Bio-Rad, Tokyo, Japan). The column temperature was 65 °C. The flow rate was 0.8 ml min -1 for 0.005 M H2SO4 solution, used as a mobile phase. Total solids (TS) and Volatile solid (VS), were measured in accordance with the standard methods (APHA, 1998). To measure total solids in the organic matter, the sample was put on the glass filter (GS-25、ADVANTEC, 47mm) and dried more than 24 h at 80oC and weighted. Then, the dried sample was treated at 600oC for 3h, and then weighted to measure volatile solids (APHA, 1998).

Gas production was measured periodically by displacement of saturated aqueous NaCl in a graduated cylinder. The compositions of CH4, H2, and CO2 were determined by a gas chromatograph (GC-8A, Shimadzu) with a thermal conductivity detector equipped with a glass column (2m x 3 mm) packed with unibeads C 60/80 (Shimadzu) at 140°C. Argon was used as the carrier gas at a pressure of 100kPa. (APHA, 1998).

Calculation of methane potential
Methane production was calculated as the volume of methane produced per unit weight of straw TS or VS loaded. The cumulative methane production by the stems and leaves of each variety was fitted with the modified Gompertz equation using the solver function in Microsoft Excel:

.(Feng et al., 2013)

Where M is the cumulative methane production (ml), t is the incubation time (days), λ is the lag phase (days), P is the methane production potential (ml), Rm is the methane production rate (ml/d) and e is the exponential index.

RESULTS

The substrate characterization, composition, and concentrations in grinded rice straw, wet-milled rice straw and seed sludge, were shown in Tables 1 and 3. On a dry matter (TS) basis, wet milled rice straw contained higher VS than Grinded rice straw and seed sludge; the VS % content of wet milled rice straw was 87%, compared to that of grinded rice straw that was 85%.

The course of daily biogas production was illustrated in Fig.1 with peak of production observed in the 3rd day of first batch for all treatments. With highest amount obtained from Wet-milled pretreated rice straw (M2), 240 ml/g-VS/d followed by grinded (M1), 132.2 ml/g-VS/d, and finally control (59.9 ml/g-VS/d). While in the 2nd batch there were two peaks of biogas production from both M1 and M2, the first peak observed in 1st day, (the 36th day of the total course), with 161,5 and 899.47 ml/g-vs/day from M1 and M2 respectively. The 2nd peak was reached at 12th d (48th day of the total course) with 228 and 806 ml/g-vs/d from M1 and M2 respectively. Additionally it was observed that in the 2 batches gas production was higher in the beginning of each batch and then decreased toward the end of the batch with higher biogas yield in the 2nd batch than the first.

The results of cumulative biogas yield were illustrated in Fig. 2a for Grinded, pretreated and control, the highest amount was obtained from M2 in both 1st and 2nd batches, with values of 860 and 3267 ml/g-vs respectively.

The methane content was measured every day, and the average methane content in each group was 55.4, 48 % and 24% for M2, M1 and control respectively. The other components of biogas were Carbon dioxide, Hydrogen and Nitrogen. Fig2.b illustrated the cumulative methane production from all mixtures during 1st and 2nd batches under thermophilic (55C°) conditions. Highest cumulative methane was obtained at the end of the 2nd batch from M2 (1493.98 ml/g-vs), with about 4 times as that obtained from M1 (387.7 ml/g-vs).

The changes in water content, total solid percentage (TS %) and Volatile solid percentage (VS%) during Anaerobic Digestion of rice Straw from M1 and M2 in initial and final of 1st and 2nd batch were illustrated in table 5. TS% was decreased from 20.9 to 20% and from 18.9 to 16.3% in initial and final of 1st and 2nd batches of M1, and from 20.4 to 19.7% and from 19.5 to 19.2% in initial and final of 1st and 2nd batch of M2 respectively. On the other hand VS% was decreased from 65 to 57.73% and from 77.8 to 67.17 % of M1 1st and 2nd batch respectively, and from 66.9 to 64.3% of M2 1st and 2nd batch respectively.

Table. 6 illustrated the potential methane production from grinded, wet milled, and glucose as reference was 234, 230, and 338 l/kg vs respectively.

Figures caption

Fig. 1: Daily biogas production from dry anaerobic digestion by repeated batch culture of M1 Containing Grinded rice straw or M2 containing pretreated rice straw (by wet milling). Seed sludge was used as inoculum. Fermentation temperatures were 55 °C (thermophilic). Duration of batch I was 35 days; batch II was 35 days (fixed culture time).

Fig. 2 (a,b): Cumulative biogas and Methane production from dry anaerobic digestion by repeated batch culture of M1 Containing Grinded rice straw or M2 containing pretreated rice straw (by wet milling). Seed sludge was used as inoculum. Fermentation temperature was 55 °C (thermophilic). Duration of batch I was 35 days; batch II was 35 days (fixed culture time).

Table 1: Characteristic of rice straw and seed sludge used in the present study.
Parameter Rice straw Rice straw treated with a wet-mill Seed sludge
Total Solids, % (w/w） 98.3 82.7 78.5
Volatile Solids, (g/g-TS) 0.85 0.87 0.857

Table 2: Rice straw pretreatment conditions and Experimental setup that used in the present study.
Mixture Pretreatment condition seed sludge: Rice straw (volume basis) Temperature
(C)
M1 Grinded alone 4 : 1 55
M2 Wet milling 4 : 1 55
Control - 1: 0 55

M1: Mixture was used to measure methane production from grinded rice straw.
M2: Mixture was used to measure methane production from rice straw treated with wet-milling method.

Table 3: Feed substrate characteristics in the present study.
Mixture Pretreatment condition TS% VS% of TS
M1 Grinded alone 20.9 65.01
M2 Wet milling 20.4 64%
Control - 17.45 60.6

Methane Yield (L/Kg VS added) Type of pretreatment Digestion Temp (°C) Time period (d) References
46 Cut (1cm) 35 92 Mussoline et al. (2013)
231 Codigestion with pig waste water 35 189 Mussoline et al. (2012)
302-340 Cut (1cm), Codigestion with pig waste water & paper Mill Sludge 35 92 Mussoline et al. (2013)
195 Cut (50-100 mm) 40 40 Dinuccia et al. 2010
280 Cut (3-5) 22 120 Lei et al. 2010
215 Pulverized 35 120 El-shinnawi et al. 1989
190 2% NH3 35 24 Zhang and zhang 1999
198 Cut (25mm) + 2% NH3 35 24 Zhang and zhang 1999
245 Ground (25mm), 2% NH3, preheated to 110C 35 24 Zhang and zhang 1999
273 Cut/ pre-digested with biogas sludge for 46 hrs 26-28 146 Sun et al. 1987
224# Cut/ delignified 30 63 Ghosh (1999)
328# Cut/ delignified/white rot fungi 30 63 Ghosh (1999)
296# Cut/ delignified/brown rot fungi 30 63 Ghosh (1999)
240 Cut/ white rot fungi 18-28 (Ambient) 89 Lianhua et al. (2010)
93 Milled/white rot fungi 25 59 Lianhua et al. (2010)
124 Milled/white rot fungi 35 59 Lianhua et al. (2010)
388 Grinded Rice straw 55 71 Current study
1494 Wet milling Rice straw 55 71 Current study
M1: Mixture was used to measure methane production from grinded rice straw.
M2: Mixture was used to measure methane production from rice straw treated with wet-milling method.
TS %: Total solids %
VS%: Volatile solids %

Table 4: Methane Yields (in terms of VS) from Anaerobic Digestion of Rice Straw

VS%: Volatile solids %
Grinded rice straw Wet milling
1st batch 2 nd batch 1st batch 2nd batch
Initial final Initial final Initial final Initial final
Water content 79.1 79.97 81.07 83.7 79.6 80.3 80.5 80.8
TS% 20.9 20.03 18.93 16.3 20.4 19.7 19.2 19.5
VS% 65.01 57.73 67.17 77.8 64 59 66.9 64.27
Table 5: Changes in water content, TS% and VS% and during anaerobic digestion of rice straw with different experimental conditions.

TS %: Total solids %
VS%: Volatile solids %

Table 6: Properties of methane production of tested biomass.

Biomass Methane potential
(ml/g-VS) Max. methane production rate
（ml/g-VS/d） Delay time
(d)
Grinded rice straw 234 44 2.8
Grinded rice straw with wet-milling 230 38 2.2
Glucose（as a reference） 338 40.4 3.6
VS%: Volatile solids %

DISCUSSION

Two semi continuous batch cultures were conducted to evaluate the process of anaerobic digestion of rice straw. The whole duration of biogas production lasted 35 days for each batch. The biogas production increased rapidly in the initial time and then decreased by the end of each batch in all mixtures. The methane percentages (55.4, 48 % and 24% for M2, M1 and control respectively) were lower than that obtained by Abouelenien et al. (2010) and Magbanua et al. (2001). As protein rich substrates such as Poultry manure, hog wastes and sewage sludge produced higher methane percentage than that obtained from carbohydrate as the main component of rice straw is complex carbohydrate in the form of cellulose, hemicellulose and lignin (Angelidaki and Sanders 2004).

The rice straw as a substrate with high lignin content, inappropriate C/N ratio, and high total solids content can be easily anaerobically digested only when it is pretreated (Cundr and Haladová; 2014). Wet milled pretreated rice straw (M2) showed highest biogas and methane yield if compared with control and grinded rice straw (M1), this could be explained as follow; rice straw is a lignocellulose containing primary cellulose and hemi-cellulose which is difficult to degrade using conventional anaerobic digestion processes. The degradation of lignocelluloses into biogas is a complicated process, since lignocelluloses have a recalcitrant structure which is naturally designed to prevent enzymatic degradation (Demirel and Scherer; 2011 and Niu et al., 2013). Lignocellulose formed in a compact and crystalline structure and often contain a high amount of lignin. In order to permit degradation of these materials in an anaerobic digester, the structure has to open up and/or the lignin has to be degraded or removed. Pretreatment of rice straw by mechanical size reduction and/or wet milling improves its digestion (Zhang and Zhang, 1999; Sun and Cheng, 2002; Mosier et al., 2005 and Alvira et al., 2010). In the current study the produced methane was much higher than that produced from previous work as illustrated in table 4.

Anaerobic digestion was performed under dry condition with TS % of 20.9 and 20.4 for M1 and M2 respectively (table 3). Using thermophilic (55°C) condition of incubation as a new technique. Dry anaerobic digestion (water content 75%) has some benefits of using smaller reactor size and smaller wastewater treatment facility than those of conventional processes (Abouelenien et al., 2009). Rice straw as a carbon rich substrate In contrast to organic nitrogen rich substrates, with which anaerobic digestion in dry condition proceeded at a lower efficiency due to the accumulation of ammonia (Koster and Lettinga 1984; Heinrichs et al., 1990; Krylova et al., 1997; Sung and Liu 2003), and will not show this problem. Temperature played an important role in determining both biogas yield and kinetics (Contreras et al., 2012). Thermophilic temperature will enhance the degradation of rice straw and improve the anaerobic digestion by methanogenic bacteria in the sludge (Buhr and Andrews 1977).

The C/N ratio of rice straw is very high which is not appropriate for anaerobic bacteria, (Forster-Carneiro et al., 2007). To adjust the C/N to the preferred range 15–30 (Li et al., 2013), sludge was added to rice straw. In the current study TS% of both mixtures were decreased by anaerobic digestion as illustrated in table 5. Also reduction in VS was observed in both mixtures after first and second batch.

VFA was measured at the initial and final of first and second batch, only acetate and propionate were detected in trace amounts. Acetate was detected in trace amounts not exceed the range of 0.74-0.93mM/kg-mixture. And this meant that all amounts of acetate produced were rapidly converted to methane and no acetate accumulation was observed. In all mixtures better performance of anaerobic digestion was observed in 2nd batch than the first one (table 5 and fig 2 a,b). This could be explained through the process of acclimatization which occurred to methanogens in seed sludge for the degradation of rice straw (Demirci and Demirer, 2004).

The decreased TS % and consequently VS % of M1 and M2 in 1st and 2nd batch (Table 5) indicated the degradation of rice straw organic matter to methane during the anaerobic digestion under different experimental conditions in the current study. This results were in compatible with that obtained by Contreras et al. (2012) and Cunderand Haladova (2014).

The Methane potential (MP) has been widely used to determine the methane yield of organic substrates in specific conditions (Owen et al., 1979; Nallathambi, 1997; 2004; Luna-delRisco et al., 2011). The methane potential, however, of untreated rice straw is on the lower end when compared to other agricultural biomasses and agro-industrial by-products. Several studies have been conducted to determine the ultimate methane yield of rice straw with various inocula, and the results range from 92 to 404 L/kg of VS added at ambient and mesophilic temperatures, (Dinuccio et al., 2010; Lei et al., 2010 and Lianhua et al., 2010). There is considerable variation in methane yield of straw depending on the type of pretreatment, if any, and the digestion conditions (Moller et al., 2004). The values of potential methane production from grinded, wet milled, and glucose as reference was 234, 230, and 338 l/kg vs respectively which located in the range that mentioned in the previous studies (Table. 6).

CONCLUSION

One of the major challenges with the digestion of rice straw is the lignocellulosic structure that makes bacterial decomposition difficult. Wet milling was seemed to enhance methane production from rice straw with maximum production of 1493.98 ml/g-vs compared with 387.7 ml/g-vs from grinded one. Methane percentage was ranged from 48 to 55%. Acetate production was low and ranged from 0.74 to 0.93mM/kg mixture which was meant success of methane production. Thermophilic condition was used at 55°C which in contrast to previous study enhance the degradation. Methane potential from grinded, wet milled, and glucose as reference was 234, 230, and 338 l/kg vs respectively.

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تحسين الهضم اللاهوائي لقش الأرز باستخدام تقنية الطحن الرطب کمعالجة قبلية لزيادة معدل انتاج غاز الميثان
کمصدر للوقود الحيوي

نغم الصعيدى ، فاطمه ابو العينين ، يوتاکا ناکاشيمادا

E-mail: nagham.elsaidy@yahoo.com Assiut University web-site: www.aun.edu.eg

يستمر انتاج الارز بالارتفاع من اجل توفير مصدر غذاء مستقر لاکثر من نصف سکان العالم. وما زال قش الارز من اکثر المخلفات الزراعية وفرة وسهولة في الحصول عليها وهو من اکثر المواد اللجنوسيلوزية انتشارا ووفرة من حيث امکانية الحصول علي الطاقة منها من خلال الهضم اللاهوائي. ولکن وجود اللجنين يساهم بشکل کبير في ابطاء عملية التحلل مما يؤدي الي انخفاض معدل انتاج الميثان ويطيل من فترات عملية الهضم لقش الارز. وفي هذا البحث تم اختبار معالجة قش الارز بالطحن الرطب کاسلوب لتعزيز عملية الهضم اللاهوائي ومقارنتة باسلوب الطحن الجاف فقط لقش الارز مع وجود التجربة الحاکمة بدون قش ارز واستخدام الحماة فقط. وتم استخدام اثنين من الخلائط M1 حيث تحتوي علي قش الارز الجاف المطحون فقط وM2 تحتوي غلي قش الارز المعامل بالطحن الرطب وکلا منهم تم اضافة الحماة لة کمصدر للبکتريا المصنعة لغاز الميثان وتم ابقائهما تحت الظروف الحرارية العالية عند ه ه درجة مئوية تحت ظروف التخمر الجاف حيث يحتوي علي مجموع المواد الصلبة اکثر من۲٠% وقد استمرت التجربة ه۳ يوم واجريت علي مرحلتين من التخمر. اظهرت النتائج ان الطحن الرطب لقش الارز ساهم بشکل کبير في عملية انتاج غاز الميثان من قش الارز حيث وصل الي 1493مل/جم من المواد الصلبة المتطايرة مقارنة باسلوب الطحن الجاف فقط لقش الارز الذي اعطي غاز الميثان بمعدل 387,7مل /جم مواد صالبة متطايرة وقد تراوحت نسبة الميثان الناتجة خلال هذا البحث من 48-55% وکما تراوحت نسبة الاسيتات من 0.74-0.93 مليمولار/کجم من الخليط مما يعني نجاح انتاج غاز الميثان ولقد اظهرت الظروف الحرارية عند 55 درجة مئوية علي خلاف الدرسات السابقة انها عززت من انتاج غاز الميثان حيث ان الکمية القياسية المتوقعة لانتاج الميثان من قش الارز الجاف المطحون وفش الارز المعامل بالطحن الرطب والجلوکوز کمرجع هو 234, 230 و 338 لتر/کجم من المواد الصلبة المتطاير علي التوالي.