production of biogas and biomanure from the textile-processing residue, willow-dust, by dry...

Agricultural Wastes 16 (1986) 295-302

Production of Biogas and Biomanure from the Textile- Processing Residue, Willow-Dust, by Dry Anaerobic

Fermentation

R. H. Ba lasubramanya , V. G. K h a n d e p a r k a r & V. Sunda ram

Microbiology/Biochemistry Department, Cotton Technological Research Laboratory (ICAR), Matunga, Bombay 400 019, India

ABSTRACT

Willow-dust is one of the solid cellulosic textile mill wastes available in large quantities. A batch fermentation method to process this material for the production of biogas and biomanure has been previously standardised. This process involves an initial aerobic fermentation of willow-dust treated with sodium hydroxide (1% w/w) and inoculated with slurry from anaerobically digested willow-dust followed by anaerobic fermentation with a substrate to liquid ratio of l :6. With a 100 kg capacity biogasplant 17 m 3 of biogas could be generated in 30 days. The spent slurry served as a good manure. The present work showed that it was possible to produce biogas as effectively as before with a substrate to liquid ratio of l : l.5. The process was further improved by replacing most of the sodium hydroxide with lime to obtain an agriculturally suitable biomanure without affecting the biogas yield.

INTRODUCTION

In India, considerable work has been done and a technology developed for biogas production which is primarily dependent on cattle waste where the Total Solids is adjusted to 8 ~o (Acharya, 1935; Desai & Biswas, 1945; Desai, 1951; Patel, 1951; Idnani & Varadarajan, 1974; Sathinathan, 1975; Singh & Gupta, 1977; Goswami, 1978). The biogas generated from this waste is popularly known as Gobar Gas. However, the technology

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296 R. H. Balasubramanya, V. G. Khandeparkar, V. Sundaram

involving fermentation of other waste materials with higher solid contents has not been developed to the same extent.

The textile industry, which consumes considerable electrical and thermal energy, generates large amounts of solid waste materials such as willow-dust, sweepings, weaving rubbish, etc. It is estimated that the total amount of willow-dust generated in textile mills in India is about 30 000-33 000 tonnes per year (Bhide, 1974).

This Laboratory has already established that biogas can be produced from willow-dust by a batch fermentation process with a solid to liquid ratio of 1:6 (Balasubramanya et al., 1981). This process consumes half the amount of water used by Gobar gas plants in the existing plug-flow digesters. It was, therefore, thought worthwhile to reduce the amount of water further to accommodate more fermentable material in unit space and also to obtain a readily usable biomanure. Apart from this, in places where water is scarce, the technology becomes much more meaningful and practicable.

METHODS

Substrate

Willow-dust obtained from one of the textile mills in Bombay was used in all the fermentation studies.

Analytical methods

Moisture was determined by drying the samples to a constant weight at 105 °C. The loss of Volatile Solids was determined by first carbonising the samples and then heating in a muffle furnace at 600 °C for 4 h. pH was measured by suspending the sample in distilled water (1:I0). Total nitrogen was determined by the micro-Kjeldahl method of Perrin (1953). Ammoniacal nitrogen was determined by the method of Jackson (1960). The substrate to liquid ratio was calculated from the percentage of Volatile Solids and the amount of liquid.

Batch fermentation

Bench-scale studies Willow-dust (2"5 kg) was mixed with 3.75 litres of water containing 0-1 sodium hydroxide (w/w), 1.5 ~ lime (w/w) and 15 ~ slurry (as below) (v/w)

Digestion of cotton-processing waste 297

as inoculum and placed in plastic buckets of 10-1itres capacity and allowed to ferment aerobically for 3 days. Thereafter, the material was mixed again with 10 ~ of slurry from batches of anaerobically digested willow-dust as inoculum and transferred to a 10-1itre capacity bottle. The bottle was closed with a one holed rubber bung which was connected by means of a glass tube to a wash bottle as an air trap. This, in turn, was connected to a 10-1itre capacity aspirator bottle to collect the gas by downward displacement of water. The bench-scale studies were carried out along with the experimental plant studies.

Experimental plant studies Willow-dust (200 kg) was mixed with 300 litres of water containing 200 g of sodium hydroxide, 1.5 kg of calcium hydroxide and 15 ~ of digested slurry from the previously fermented batches and heaped to a height of about 30 cm and left in the open for 72 h for aerobic fermentation. A polythene sheet was placed over the material to avoid excessive evaporative loss of water. Thereafter, the material was mixed with 10 inoculum of spent slurry as before and charged to a batch anaerobic digester of 0.7 m 3 capacity. The gas generated was collected over water in a floating gas holder. The assembly was described earlier by Khandeparkar et al. (1981).

Gas analysis Carbon dioxide and methane were determined with an Orsat apparatus every 24 h to the end of the fermentation period. Carbon monoxide and hydrogen sulphide were observed to be only in traces and hence were not taken into account for analysis. Methane and CO 2 production was converted to NTP for use in calculating material losses.

Changes occurring during aerobic and dry anaerobic fermentation Samples were withdrawn daily for 3 days from the aerobically fermenting willow-dust in one of the sets of the bench-scale studies for the estimation of moisture, pH, total nitrogen, ammoniacal nitrogen, loss of Volatile Solids and for the calculation of substrate to liquid ratio. To observe the changes occurring during anaerobic fermentation, a series of bottles of 3- litres capacity were charged with 500 g of willow-dust (previously mixed with NaOH, lime, inoculum and aerobically fermented and then further inoculated as before) and one set was removed every 7 days for various analyses.


RESULTS AND DISCUSSION

Animal excreta is the substrate most widely used for the production of biogas. It contains considerable amounts of vegetable fibres that have already undergone both biochemical and mechanical changes in the animal's digestive tract and requires the least pretreatment prior to methane generation. Willow-dust differs from animal excreta in physical form, particle size, etc., although closely resembling it in its chemical composition (nitrogen, 1.5 %; cellulose, 26 %; hemicellulose, 16 %; ether extractives, 5 %; lignin, 16 % and ash, 10 %, including sand) and it needs some pretreatment for the purpose of producing biogas. A process involving an initial aerobic fermentation of willow-dust treated with dilute sodium hydroxide followed by anaerobic fermentation with a substrate to liquid ratio 1:6 was developed by Balasubramanya et al (1981). With a 100 kg experimental biogas plant 17 m 3 of biogas could be generated in 30 days. The spent slurry was a good biomanure (Khandeparkar et al., 1981).

This process requires large amounts of water which might become a

TABLE 1 Changes Occurring During Aerobic and Dry Anaerobic Fermentation of Willow-Dust

Incubation Loss of pH Total NH4-N Loss of Substrate period water nitrogen (%) Volatile to liquid (days) (%) (%) Solids ratio

(%)

0 - - 8.1 1.71 0.36 - - 1:1-5 1" 3-7 7.9 1.71 0.39 2-3 1:1.5 2 a 5-10 7.5 2.30 0.19 3-5 1:1.6 3" 10--15 7.2 2-53 0.16 5-8 1:1.5 b 7 c - - 7.0 2.40 0.15 6 1 : 1.6

14 1 7.1 2.30 0.16 30 1:2.0 21 7 7.1 2.16 0-19 45 1:2.6 28 8 7.1 2.09 0.26 46 1:2.6 35 12 7.1 2.00 0.25 49 1:2-8 42 11 7.0 2.00 0.20 50 1:2-9

a 1-3, aerobic fermentation. bAdjusted with inoculum.

7-42, anaerobic fermentation. (Results from the bench-scale trials).


constraint in places where water is scarce. An attempt was, therefore, made to reduce the amount of water in the process.

The changes occurring during aerobic and dry anaerobic fermentation of willow-dust are given in Table 1. There was about 10 ~-15 ~o loss of moisture during the aerobic fermentation. This was compensated for by adding appropriate amounts of water in the inoculum for the anaerobic digestion. The pH remained around neutrality throughout the anaerobic fermentation. There was a considerable increase in the percentage of total nitrogen during the initial aerobic fermentation but this remained more or less constant during anaerobic fermentation.

The results of bench-scale and experimental plant trials are given in Figs 1 and 2, respectively. Biogas production started after 1 week as compared with 10 days in the earlier process (Balasubramanya et al, 1983). In experiments where 10-1itre bottles contained 2.5 kg willow-dust (substrate to liquid ratio, 1:1.5), two prominent peaks for biogas, one around 5 days and another around 25 days as compared with 15 days and 30 days in the earlier process (Balasubramanya et al., 1983), were observed (Fig. 1). This indicates that pretreatment with low concentrations of NaOH with lime, followed by the addition of small amounts of water, alters the additional first peak to a great extent without significantly affecting the normal major second peak. Although two such peaks were observed in the experimental plant studies using 200 kg of

30

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20

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Fig. 1.

0 10 20 30 40 50 Time ( days )

Daily production of biogas from willow-dust. (Results from trials with 2.5 kg bench-scale digester).


1600

1200

800

o ~ 4OO

F ig . 2.

- m e t h Q n e

• f , ~ ~ - biogGs

. ~ . - - -mox. temp • ~ -m!° t_e~,L..~

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150 ~

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Production of biogas from willow-dust. (Results from trials with 200kg experimental plant).

willow-dust (Fig. 2), they were not so pronounced. This pattern was not observed in the earlier process where the substrate to liquid ratio was maintained at 1:6 (Khandeparkar et al., 1981).

The first peaks shown could be formed by biogas production from organic acids produced during the aerobic fermentation of the willow- dust (Figs 1 and 2). The major gas production would arise from the cellulosic willow-dust. Degradation of cellulose is inherently slow and, in the present case, compaction of the dust due to the small amount of water present could have reduced the surface area of particles available to hydrolytic bacteria (Price & Cheremisinoff, 1981). In addition to the first peak, 40 m 3 of biogas was obtained in 30 days and another 12 m 3 in the subsequent 15 days from 140 kg of Volatile Solids of willow-dust, making the entire process viable for a total period of 45 days, unlike the earlier process where it was economically viable for only 30 days.

Although it has been reported that increasing the density of solid wastes decreases the rate of gas production, in the present investigation it was observed that the rate of gas production did not alter even when the substrate to liquid ratio was reduced to 1 : 1-5. However, the gas production declined when the solid to liquid ratio was further reduced to 1 : 1.25 and 1 : 1.00 and hence the experimental solid to liquid ratio was restricted to 1:1.5.

In the fermentation of cattle waste with different solids content, it has been reported that methane production proceeded only up to 32~ , although hydrolytic bacteria functioned normally to 60 % Total Solids.


Jewell et al., (1981) reported that, in the case of wheat straw and corn stover with an initial Volatile Solids content of 28~ , 9 0 ~ of the biodegradable fraction was converted to methane in about 200 days. However, fermentation proceeded in the case of willow-dust at a Volatile Solids content of 53 ~ . It has been reported that ammonia nitrogen at concentrations exceeding 3000 mg litre-1 becomes toxic at pHs greater than 7.4 (Cheremisinoff & Morresi, 1976). Hobson & Shaw (1976) observed that the methane-producing bacterium Methanobacterium formicicum was inhibited by high concentrations of ammonium. The smooth functioning of the methanogenesis in the present investigation, even at a Volatile Solids content of 53 ~o, could be due to the steady pH of around 7-0 and an ammoniacal nitrogen content in the range 1500-2600mgkg -1 of the fermenting material, which is below the reported toxic limit values.

In the experimental plant 200 kg of willow-dust left 110 kg dry weight of residue after anaerobic digestion. The organic matter loss could be approximately equated with biogas production.

The biomanure obtained after fermentation can be directly used for plants (Balasubramanya et al., 1982), unlike the spent slurry from Gobar gas plants which requires dewatering for immediate use or sun-drying. During this process, nutrients are lost either through evaporation or percolation. The replacement of most of the sodium hydroxide with lime during the aerobic fermentation of willow-dust gave an agriculturally suitable biomanure. The bulk density of the material at the end of the fermentation was 0.846 as against an initial value of 0-626.

Thus, the dry anaerobic fermentation of willow-dust consumes less water, accommodates more fermentable material in the unit space, produces more gas and leaves behind a good quality of readily usable biomanure.

REFERENCES

Acharya, C. N. (1935). Studies on the anaerobic decomposition of plant materials. Biochem. J., 29, 528-41.

Balasubramanya, R. H., Khandeparkar, V. G., Betrabet, S. M. & Sundaram, V. (1981). Production of biogas from willow-dust by a batch fermentation process. J. Text. Assn., 42, 145-9.

Balasubramanya, R. H., Khandeparkar, V. G. & Sundaram, V. (1982). Utilisation of willow-dust through anaerobic fermentation for the production of biogas and biomanure. Eng. Des., 11, 31-3.


Balasubramanya, R. H., Khandeparkar, V. G. & Sundaram, V. (1983). Biogas from willow-dust by dry fermentation. Indian Soc. Cotton Imp. J., 8, 93-4.

Bhide, A. D. (1974). Compost from blow-room dust. Compost Sci., 15, 5. Cheremisinoff, P. N. & Morresi, A. C. (1976). Energy from solid wastes. Marcell

Decker, New York. Desai, B. P. (1951). Combustible gas from cattle dung. Poona agric. Coll. Mag.,

42, 74-82. Desai, S. V. & Biswas, S. C. (1945). Manure and Gas Production by Anaerobic

Fermentation of Organic' Wastes. Indian Fmg., 6, 67-8. Goswami, K. P. (1978). Proc. India/FAO/Norway, Seminar on the

Development of the Complementary use of Mineral Fertilizers and Organic Materials in India, Ministry of Agriculture and Irrigation, Dept. Agri. (Fert. Divn.), Krishi Bhavan, New Delhi.

Hobson, P. N. & Shaw, B. G. (1976). Inhibition of methane production by Methanobacterium formicicum. Water Res., 9, 649-52.

Idnani, M. A. & Varadarajan, S. (1974). Fuel gas and manure by anaerobic fermentation of organic materials. Tech. Bull. No. 46, ICAR, New Delhi, 60.

Jackson, M. L. (1960). Soil chemical analysis. Prentice Hall, Inc., Englewood Cliffs, NJ.

Jewell, W. J., Dell'orto, S., Fanfori, K. J., Fast, S., Jackson, D. & Kabrick, R. M. (1981). Dry anaerobic methane fermentation. Paper presented at the Biogas and Alcohol Fuels Seminar at Chicago, Illinois, 13 March, 1981.

Khandeparkar, V. G., Balasubramanya, R. H., Ganesan, S. & Sundaram, V. (1981). Biogas from willow-dust. Indian Cotton Mills Fed. J., 18, 5-9.

Patel, J. J. (1951). Digestion of waste organic matter by production of methane and organic fertilizer and a new economic apparatus for small scale digestion (Gramlaxmi). Poona agric. Coll. Mag., 42, 150-9.

Perrin, C. G. (1953). Rapid modified procedure for the determination of Kjeldahl nitrogen. Anal. Chem., 25, 968-71.

Price, E. C. & Cheremisinoff, P. N. (1981). Biogas production and utilization, Ann Arbor Science Publishers Inc., Michigan, 16.

Sathinathan, M. A. (1975). Biogas--Achievement and challenges. Assoc. of Voluntary Agencies and Rural Development, New Delhi, 192.

Singh, R. B. & Gupta, B. K. (1977). Proc. Symp. held at Hindustan Lever Research Centre, Bombay, April. In: Perspectives in industrial microbiology. (Kalle, G. P., Freitas, Y. M. & Tamhane, D. V. (Eds)), 38-61.

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