Rene,able Ener#p Vol. 3. No. I, pp. 45~.7, 1993 0960 1481/93 $6.{}0+.00 Printed in Great Britain. Pcrgamon Press Lid

M E T H A N O G E N E S I S OF WATER HYACINTH IN THE PRESENCE OF BORON C O M P O U N D S

S. K. SINGH, AMARIKA SINGH* and G. N. PANDEY

Applied Chemistry Section, Department of Applied Sciences and Humanities, Institute of Engineering and Technology, Sitapur Road, Lucknow-20, India

(Received 6 December 1991 ; accepted 4 Mareh 1992)

Abstract--Cowdung, human excreta, distillery effluents etc. are used for biogas generation in India. The addition of various boron compounds at different concentrations was made to study its effect on the cumulative gas production rate. A retention time of 15 days in a small batch digester was used. Additions of borax, boron hydride, boric and borozol were made at appropriate levels. The addition of such compounds affected the methanogenesis and increased gas generation.

INTRODUCTION

Water hyacinth is used as a feed material in biogas generation [1,2]. It has been reported that the rate of gas production is greater and gas evolution starts earlier when water hyacinth supplements cattle manure in biomethanogenesis [3]. 66% of the volatile solids were reduced and gas yield was 7.73 ml/g of volatile solid destroyed when sewage sludge was added to water hyacinth slurry [4]. A mixture of water hyacinth and cattle manure also increases biogas generation without affecting C H 4 content, calorific value and pH of the slurry. The optimum con- centration of this weed is 20%, measured in terms of dry matter content. The effect of sodium nitrate, urea, calcium compounds etc. on methane generation has been examined by several scientists. It was found that, on addition of NaNO3, the gas production increased from 50 L/kg to 150 L/kg of wet biomass. The meth- ane content was found to be 71%, whereas this value was 69 70% if calcium compounds were used as addi- tives in biogas generation. It was also observed that on the addition of 0.5 g/L of urea, the rate of gas production increased; but at higher concentrations i.e. about 1 g/L, it decreased.

MATERIALS AND METHODS

1 L of slurry containing various solid concen- trations, for example, 500 g, 200 g and 100 g of total solid per kg was taken separately into an airtight batch digester. The cumulative gas production was measured for up to 32 days by a simple water dis-

* Author to whom correspondence should be addressed.

placement technique, which is shown in Fig. 1. The temperature of the digester was controlled by fibre wools as well as thermocole. The innoculum was added to feed material in the appropriate ratio while making a slurry of chopped water hyacinth. A control run without boron compounds added at the beginning was conducted at ambient temperature (an average of 32C).

The feed material used in the digester was pretreated with sodium hypo-iodide. The optimum con- centration of sodium hypo-iode used was 200 mg for 1 kg of biomass in 2 L water. Pretreatment increases the breakdown of the lignin network. When cattle dung was added to water hyacinth in the ratio of 1:1, gas production increased.

RESULTS AND DISCUSSION

The effect of boron compounds on methanogenesis of water hyacinth was studied. The cumulative gas produced in litre per unit weight in kg of dry solids for different experiments was measured as a function of time, and is shown in Fig. 2. Results are expressed as total biogas production per kg of total solid added. It was seen that the addition of borax 0.2 g/L gave an increase in cumulative gas evolution from 4.7 to 13.9 L gas kg ~ dry solid for a retention period of 17 days. The addition of 1 g of borax to another digester containing fresh feed material further increased the cumulative gas production, up to 18.21 L.

Borax was added at the initial stage of mixing. After its addition, an acclimatization period of 13 days was need before the cumulative gas evolution rate exceeded the control run. Addition of borax increases

45

46 S.K. SINGH et al.

THERMOMETER-,~

INLET

CERAMIC D]DESTEI~ -=

GAS COLLECTING CHAMBER ~ ~ I--GAS SAMPLER

=I= : t GAS o u ' r t E T = i ; - - - - -

"i" ING

Fig. 1. Diagrammatic representation of digester assembly.

the manurial effect of slurry. It was seen that an increase in quantity of water hyacinth from 250 g to 750 g wet weight per litre, resulted in a nearly 10-fold increase in gas evolution at the end of 30 days. The gas production was increased (up to 19%) when pre- treated water hyacinth was used as slurry.

In another experiment, water hyacinth slurry was digested with 0.2 g of diborane. The gas generation increased by an appreciable volume. The cumulative gas production was nearly 390 L/kg t of dry solids.

On addition of both borax and diborone, the total biogas production was increased, and the proportion

o

II01

500

400

300

z o o

100

1.. .~e 2 • Dibortme compound / / . ~ 2 • Borax compound

70 g Water hyacinth 500 ml water

/

~ _ • •'--* = 300 g Water hyacinth " 5 0 0 ml water

I P ~ > ~ T ~ . , , I , I , I , I

0 8 16 24 32 40

Time in days

Fig. 2. Effect of addition of additives on cumulative gas production rate.

Methanogenesis of water hyacinth 47

of methane increased with respect to CO2. Methane content of the biogas was measured using an orsat apparatus as 7(~7 ! %.

In Fig. 2, line 2 represents the increase in cumulative gas production, due to pretreated water hyacinth, whereas lines 3 and 4 represent the increase due to the addition of borax and diborone compounds to water hyacinth, respectively.

The minimum amount of borax, 0.2 g/L, was required to give an increase in gas production.

CONCLUSION

The addition of boron compounds increases biogas production from water hyacinth. These compounds act as catalysts in the process of methanogenesis. The exact mechanism of this is under investigation. More- over, by the addition of such compounds converted

the organic compounds of water hyacinth mostly into biogas : CH4 and CO,.

Acknowledgements--The authors are grateful to Dr S. S. Yadav, Bioenergy Specialist, NEDA, Lucknow, for his valu- able suggestions. One of us (SKS) is also thankful to the Non- Conventional Energy Development Agency, Government of U.P., Lucknow for providing financial assistance and JRF award.

REFERENCES

I. B. R. Guha, T. K. Bandopadhya and K. K.Chaudhary, Khadi Gramodyog 22, 483. Khadi and Village Industries Commission, Gramodaya, Bombay (1976).

2. P. Deshpande, S. Sarnaik, S. H. Godbole and P. M. Wagle, Current Science 48, 490. Current Science Associ- ation, Indian Academy of Sciences, Bangalore (1979).

3. D. R. Randey, S. Sarnaik and S. H. Godbole, in Proc. Golden Jubilee Symt). on Renewable Sources ~?f Ener.qy, National Academy of Science, New Delhi (1980).

4. K. K. Chin and T. N. Goh, in Symp. Enerqyjkom Biomass and Wastes (Edited by Klass, D. I. and Waterman, W. W.). Institute of Gas Technology, Chicago (1978).