Studies on Biogas Production using withered Flowers as a Substrate

 

Lakshmi C, Vijayalakshmi S*

CO₂ Research and Green Technologies Centre, VIT University, Vellore-14

 

ABSTRACT:

Preliminary study on withered flowers as substrate for biogas production has been carried out using anaerobic digestion. Three experimental sets have been conducted by varying the substrate to inoculum concentration such as 2:1, 1:1 and 1:2.  Digester has been designed with an outer and inner cylinder of 500 and 300 liters capacity respectively. Substrate concentrations were also varied as 5, 7, 9, 10, 11 and 12% to analyze the amount o biogas produced per kg of substrate. Results showed that 7% of substrate concentration to be optimum for biogas production. The yield of biogas was also found to be higher with less digestion time period. Flowers which are available in plenty which was thrown in garbage after a few days can be used efficiently as a source for energy production. This concept can also be seen as waste to energy to enhance the sustainability of the environment.

 

 

 

1. INTRODUCTION:

For the treatment of wastes, anaerobic digestion technology has been used for the production of biogas which results in the generation of electricity and heat¹. Bio-gas is considered to be one of the alternative sources for fossil fuel usage. The major component in biogas is methane (50-70%), carbon dioxide (20-40%) and traces of other gases such as nitrogen, hydrogen, ammonia, hydrogen sulphide, water vapour etc².The biochemical process for bio-gas production is:

 

(C₆H₁₀ O₅)n  + nH₂O  ---->    n (C₆ H₁₂ O₆)  Hydrolysis

n(C₆ H₁₂ O₆)            ---->   n CH₃ COOH  Acetogenesis

3nCH₃ COOH         ---->                  n CH₄ + CO₂Methanogenesis

 

Biogas residue can also be utilized as a biofertilizer since it contains essential elements such as nitrogen and phosphorus which is eco-friendly and doesn’t affect the nature of the soil³.

 

 

The process parameters is not same for the all the raw material used for biogas production, it depends on the chemical composition of the species, growth and age of the particular substrate⁴. Types of wastes for biogas production is animal wastes^5,6,7, industrial wastes⁸, food processing wastes⁹, plant residues^10,11etc. Previous work with flower and vegetable waste has been done to determine the biogas production yield which results in higher yield with minimum digestion period^{12, 13, 14, 15}.

 

Presently in Bangalore, tons of flower waste is being generated daily in temples, marriage halls, function halls, markets, residential area at festivals and tons are from temples, tons from function halls, tons are from houses, tons are from markets.The waste generated in temples is presently piled at one place and then disposed off in water bodies or dumped on land to decay which causes several environmental problems such as water, soil pollution etc. The aim of this workis to determine the biogas yield by using flower waste as a raw material.

 

2. MATERIALS AND METHODS:

2.1 Substrate and Inoculum:

Flower wastes (Chrysanthemum) were collected from temples in Bangalore (Fig 1). The wastes were dried in hot air oven at 105^◦C until moisture content appeared to be 0 for the feedstock preparation. Further, the dried wastes were grinded into fine powder. Inoculum used was fresh cow dung which was mixed with water at 1:1 ratio and filtered.

 

2.2 Digester design:

The digester was made of M.S steel material which was wrapped in black polythene bags to keep out light. The gas drum consists of 2.5 mm steel sheets in the sides and 2 mm sheets in the top and welded-in braces. The designed model consists of two cylinders, an outerand inner cylinder with 500 and 300 liters capacity respectively.The outer cylinder is provided with an inlet and an outlet. The  inletto introduce the flower waste andoutlet is to clean the cylinder, which was fitted with pressure gauge to measure thedevelopment of pressure and a valve to collect and store the produced biogas. Finally, the model had ensured for leak proof. To avoid rusting, the digesterwas painted and coated (Fig. 2).Outer cylinder and the central pipe were fabricated to a height of 1300mm and 1200mm respectively.

 

2.3 Experimental procedures:

2.3.1 Experimental set no: 1

Initially digester filled with 100kg of cow dung and 50 kg of flower waste (2:1) in 50 litres of water. Methane was observed around 40 – 50 %.

 

2.3.2 Experimental set no: 2

In second set up sample were filled to digester about 100kg of cow dung and 100 kgof flower waste (1:1) in 100 litres of water. Methane was observed around 50 – 55 %.

 

2.3.3 Experimental set no: 3

In third set up sample were filled to digester about 100kg of cow dung and 225 kg of flower waste (1:2) in 150 litres of water (not at once daily 10 litre with flowerwaste ). Methane was observed around 60 – 65 %.

 

2.4 Effect of substrate concentration:

Effect of substrate concentration was studied in detail with six different variations like 5, 7, 9, 10, 11 and 12%. Amount of gas produced per kg of substrate at all these combination have been analyzed.

 

Digital Pressure Guage: 

The pressure of the biogas in the digester was checked using digital pressure gauge, for every24 hours.

 

Statistical Analysis:

Observed daily biogas production is calculated using STP condition. STP refers to 273.15K and 1 atm pressure. 

Po Vo T/P V To = n/n1

 

Po = standard pressure.

P = pressure of biogas observed

Vo = volume of 1 mole gas at STP(22.414lit)

V = volume of gas collected(700ml).

To = standard temperature.

T= room temperature(26-36C)

n = 1mole.

n1 = moles of gas.

 

The amount of biogas produced per kg of substrate was calculated. The biogas produced per kg of dried substrate was calculated first and from the moisture content of each substrate, the biogas produced per kg of original substrate was calculated using standard formula.

 

3. RESULTS:

3.1 Characterization of Flower waste:

The flower wastes were collected from temples in Bangalore. It was dried and grounded into fine powder and analyzed for various parameters which were listed in Table 1.

 

Table 1: Basic characteristic analysis of collected flower waste

 

3.2 Moisture Content:

Moisture content was measured for all the three experimental set up.

The moisture content ranges between 70 to 80% for all the three set of experiments. Set 3 at day 3 shows higher moisture content of 76.5%. At day 1 irrespective of experimental sets shows lesser moisture content varies from 71 to 72%.

 

3.3 Experimental Procedures:

The variation of inoculum with flower waste in varied proportions i,e 2:1, 1: 1, 1: 2 were analyzed and showed that 1:2 is found to be the most effective composition (Fig 1).

 

Fig. 1: Rate of production of biogas at different inoculum to flower waste concentration

3.4 Production of Biogas:

The amount of biogas produced and amount of biogas produced per kg of substrate at different substrate concentrations were given in Table 2. Maximum biogas production was seen in 8^th day.

 

Table 2: Amount of biogas produced and amount of biogas produced per kg of substrate at different substrate concentrations

Days	pH	Temperature (°C)	Pressure Developed from Biogas (kg/cm2)
			5%		7.5%		9%
			Amount of gas	Amount of gas/kg of substrate	Amount of gas	Amount of gas/kg of substrate	Amount of gas	Amount of gas/kg of substrate
1	6.4	28	0	0	0	0	0	0
2	6.0	27	0.02	12.9	0.02	15.30	0.11	71.0
3	5.8	27	0.03	25.8	0.04	30.61	0.16	103.7
4	5.0	27	08	57.9	09	68.88	25	62.0
5	5.2	27	0.12	77.0	12	91.84	0.37	239.8
6	4.9	27	0.12	77.5	0.12	91.84	0.43	278.7
7	4.9	28	0.12	77.5	0.12	91.84	0.48	311.2
8	5.2	27	0.12	84.0	0.13	99.49	0.51	329.5
9	4.9	28	0.12	84.0	0.13	99.49	0.47	304.7
10	5.0	28	0.10	77.5	0.12	91.84	0.42	271.3
11	4.8	28	07	64.6	0.10	76.53	0.36	2.6
12	4.9	27	0.01	51.6	0.08	61.22	0.31	232.6
13	5.0	28	0	12.9	0.02	15.30	0.18	200.3

 

Table 2..... continued

Days	pH	Temperature (0C)	Pressure Developed from Biogas (kg/cm2)
			10%	11%		12.5%
			Amount of gas	Amount of gas/kg of substrate	Amount of gas	Amount of gas/kg of substrate	Amount of gas	Amount of gas/kg of substrate
1	6.4	28	0	0	0	0	0	0
2	6.0	27	0.07	45.2	0.12	77.5	0.02	12.9
3	5.8	27	0.18	116.7	0.17	110.2	0.04	25.9
4	5.0	27	27	175.0	29	188.0	0.8	51.8
5	5.2	27	0.35	226.9	0.27	175.0	0.12	77.8
6	4.9	27	0.44	285.2	0.26	168.5	0.18	116.7
7	4.9	28	0.46	298.2	0.26	168.5	0.2	129.6
8	5.2	27	0.46	297.2	0.25	161.5	0.2	129.2
9	4.9	28	0.46	298.2	0.19	123.1	0.1	64.8
10	5.0	28	0.44	284.3	0.15	96.9	0.18	116.3
11	4.8	28	00	258.4	0.12	77.5	0.14	90.4
12	4.9	27	0.36	232.6	0.09	58.1	0.07	45.2
13	5.0	28	0.20	129.6	0.01	6.4	0.03	19.4

 

 

Fig. 2 Graphical representation of amount of gas produced per kg of substrate for 13 days.

The above graph shows the amount of biogas produced by the digestion in the anaerobic tank. This shows that the production of biogas is more in 7% substrate, followed by 9% and 10%. This shows that 7% substrate is more efficient in producing biogas.

 

4. CONCLUSIONS:

The biogas production of good quality varies on the size of the material, mixing equipment, percentage of solid waste mixed with inoculum, loading rate, hydraulic retention time temp, distraction of volatile solid waste. The biogas production from the lab scale model was found to be 60% consisting of methane and remaining part by gases such has H₂S and CO₂ etc. Constant monitoring of biogas on daily basis showed the gas production by increase in pressure from 0 Kg/cm² to 0.51 Kg/cm². The different proportions of flower waste introduced was 5%,7%,9%, 10%,11% and 12%. The pressure from 7% of flower waste with cow dung showed a pressure up to 0.51Kg/cm2. The variation of innoculum as cowdung with flowerwaste in varied proportions i,e 2(cow dung ):1(flower waste),1(cow dung); 1 (flower waste),1(cow dung): 2(flower waste) showed results as the most effective composition was found to be 1:2. The presence of methane was found to be 60 to 65% in this proportion. IT shows that flower waste as substrate is a good source of production of biogas.

 

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Accepted on 09.08.2017        © RJPT All right reserved

Research J. Pharm. and Tech 2017; 10(12): 4223-4226.