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Anaerobic Digestion of Mixed Dried Fallen Leaves by Mixing with Cow Dung

MA Rouf
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh.

MS Islam
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh.

T Rabeya
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh.

Ak Mondal
Institute of Fuel Research and Development, Bangladesh Council of Scientific and Industrial Research, Dhanmondi, Dhaka-1205, Bangladesh.

Abstract/ Executive Summary:

An investigation was carried out for the production of biogas from dry fallen leaves. The sample was collected from BCSIR campus of Dhaka in winter. The substrate was mixed leaves mainly mahogany (75%), eucalyptus (10 %) and rain tree (15 %) leaves. The study was carried out by whole leaves and crushed leaves directly followed by aerobic pretreatment at 8% total solid (TS) concentration. The raw materials were fed into two liter capacity glass bottle bio digester on batch basis for 60 days at ambient temperature. Different proportion of substrate and cow dung were mixed to get the optimum mix for maximum yield of biogas. The biogas reactor containing 6% crushed and pretreated leaves mixed with 2% cow dung (on 8% TS basis) gave maximum (0.199 l/g) biogas yield. The biogas yield from leaves without pretreatment was found to be too low (0.0106 l/g) for 8%. The COD reduction, VS reduction and methane composition of two biogas reactors have been determined where biogas yield were relatively higher. The maximum methane content of the biogas was found to be about 69.3%.

Keywords: Anaerobic digestion; Biogas; Volatile solids (VS); COD reduction; Pretreatment

Location: BCSIR campus, Dhaka

Start Date: 00-00-2015

End Date: 00-00-2015

Program Area: Resource Development and Management

Non-commodity: Performance

Objectives:

1.To characterize the substrate, optimize the biogas generation and study the biogas composition, to examine the performance of biogas unit set up by using leaves.

Methodology:

Collection of sample and pretreatment methods - The dried leaves sample was collected from BCSIR campus of Dhaka in winter. The substrate was mixed leaves mainly mahogany (75%), eucalyptus (10 %) and rain tree (15 %) leaves. The sample was grounded by a grinder. Both the whole leaves and grounded leaves were pretreated in aerobic condition for 10 days by adding effluent from stable biogas digester. Analysis of sample - Moisture content and ash content were estimated by gravimetric method by drying at 105º C and by complete combustion at 800º C. Calorific value was determined according to IS: 1350 (part 4) 197 by bomb calorimeter. Total solids (TS) were estimated by subtracting the moisture content from 100% and volatile solids (VS) were estimated according to the procedure recommended in IS: 10158-1982 by heating at 600º C for two hours in a furnace. Carbon and nitrogen contents in the sample were determined with the help of a C-N-H-S analyzer (Thermo Fischer Scientific, FLASH-2000) with TCD detector. Helium gas was used as carrier gas at 250 kPa and 140 ml/min, furnace and oven temperatures were 900º C and 65º C respectively. Chemical oxygen demand (COD) of the sample was estimated by oxidizing the sample with potassium dichromate then
titrating with ferrous ammonium sulphate using ferroin indicator. pH of the sample slurry was recorded using digital pH meter (HANNA,HI 98208) nd gas composition was determined by gas chromatograph (Thermo Fischer Scientific, Trace GC Ultra with TCD detector). Helium gas was used as carrier gas at 900 kPa and 10.5 ml/min, Oven and detector temperatures were 80º C and 180º C respectively. Experimental set up for anaerobic digestion in the laboratory The sample was fed into two liter capacity wide mouthed glass bottle on batch basis for 60 days at ambient temperature. Volume of the substrate in the glass bottle was one liter. It was inoculated (10% inoculums) with the sludge collected from an anaerobic plant based on cow dung. Seven anaerobic reactors were set up containing different proportion of substrate and cow dung on the basis of 8% TS. The total gas production was measured by water displacement method at an interval of 24 hours. Contents of the bottle were mixed manually after every gas measurement. Daily gas production was recorded. The conditions of the seven biogas reactors were as follows:
Reactor1 (R1): 8% whole leaves without cow dung
Reactor 2 (R2): 6% whole leaves + 2% cow dung
Reactor 3 (R3): 4% whole leaves + 4% cow dung
Reactor 4 (R4): 8% pretreated whole leaves without cow dung
Reactor 5 (R5): 8% pretreated ground leaves without cow dung
Reactor 6 (R6): 6% ground pretreated leaves + 2% cow dung
Reactor 7 (R7): 4% pretreated ground leaves + 4 % cow dung

Source of Information: Bangladesh J. Sci. Ind. Res. 50(3), 163-168, 2015; ISSN 0304-9809 eISSN 2224-7157

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/bjsir.v50i3.25579

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The organic content of the sample is very high (about 88% volatile solids), which are biodegradable. But the C/N ratio of the sample is much higher (40:1). So mixing of cow dung with the substrate is very important to achieve optimum C/N ratio and also to stabilize the biogas digester. The yield of biogas for pretreated leaves is much higher than non-pretreated leaves. The optimum mixing condition for biogas generation from mixed dried grinded leaves is 6% leaves and 2% cow dung. The specific biogas yield for optimum mixing condition is 0.0199 l/g where the methane content is 69.3%. The percentage of VS and COD reduction is 35.33 and 35.89 respectively. The anaerobic digestion of fallen dried leaves in forest area can be used for biogas generation. The generation of biogas from leaves will benefit us in three ways: clean fuel, nutrient rich biofertilizer and hygienic environment.

Knowledge Management: Journal, Online Circulation