JOURNAL OF FERMENTATION AND BIOENGINEERING VOI. 70, NO. 5, 343-344. 1990

N O T E S

Effect of Agricultural and Other Wastes on Anaerobic Digestion of Water Hyacinth-Cattle Dung D A T T A M A D A M W A R , * VIKRAM PATEL, AND A N A M I P A T E L

Department of Biosciences, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India

Received 17 March 1990/Accepted 14 September 1990

In order to improve the anaerobic digestion of water hyacinth-cattle dung with enriched methane content, the effect of various easily available residues, such as Polyalthia longifolia (Sonn.) Thw. leaves, Azadirachta indica A. Juss. leaves, eucalyptus leaves, sugarcane bagasse, banana stem, poultry waste, cheese whey, algal powder (Enteromorpha sp.) and sugarcane filtercake have been studied. Among the residues tested, sugarcane bagasse, banana stem. poultry waste, cheese whey and algal powder showed more than 100% increase in gas production with 5 to 10% higher methane content.

Water hyacinth (WH) has a high product ivi ty coupled with an excellent pol lutant removal and methane genera- t ion potent ial that makes it amenable to uti l ization in in- tegrated pol lu t ion-control and energy-conversion systems in rural areas. Cattle dung (CD) has so far been the major resource for biogas product ion (1-3). In recent years W H has come to be used as a replacement for CD, mainly due to the limited availabil i ty of the latter (4-6). In practice, however, a problem arises due to the nature of the organic content in this material; it has a reputat ion for poor process stability. Our studies have shown that W H : CD used in the ratio of 7 : 3 on a dry weight basis gives a high produc- tion of biogas with enriched methane content . However, if anaerobic digestion can be made still more efficient and therefore more economical ly attractive, farmers will be more apt to adopt this process. One possible approach would be to increase the availabil i ty of hydrogen donors f rom easily digestible volatile solids. This would divert more carboxylated intermediates into methane rather than CO2 (7). Therefore, in an effort to improve the gas produc- tion and its methane content so as to enrich its fuel value, the effect of various easily available residues have been studied.

Sugarcane filtercake from a sugar factory, Palaj , India; cheese whey from Amul , India; and CD, WH, agricultural and other wastes obtained from Vidyanagar , Gujara t , India were used in biogas product ion by anaerobic bio- conversion.

Several bench-scale anaerobic digesters were used. Each vessel consisted of a 10l glass reaction bott le, having a working volume of 6 l and containing 7%o of total solids (TS) (mixture of W H : CD, 7 : 3 w/w). The digesters were intermit tent ly stirred (120 rpm) with a magnetic stirrer and mainta ined at 37_+ 1 °C in a thermostat . Gas was collected and measured by displacement of an acidified saturated salt solution, making due corrections for a tmospheric pressure and temperature . The digesters were fed on a semi-continuous basis: once per day with a mixture of W H (dried at 60°C and powdered to 50 mesh) and CD in the rat io of 7 : 3 (w/w) and TS of 7O/oo (w/v), and a loading

--Corresponding author.

343

rate of 8.75 g TS/I of diges ter /d , which our studies found to be most suitable. Pr ior to feeding, an equal quant i ty of sludge was withdrawn from the bo t tom of the digester. Residues were incorpora ted with feed sludge.

Fresh digester was always started by preparing a mixture of powdered W H and CD in the ratio of 7 : 3 (w/w) to give a final TS concentrat ion 7O/oo (w/v), and using 10% in- oculum from a running biogas digester of the same type.

Feed and effluent slurry were routinely analysed for pH, volatile acids, BOD, COD, TS, volatile solids, lignin, cel- lulose and hemicellulose as per s tandard procedures (8- 11).

A trend of enhanced gas product ion with increased a- mount of algal powder (Enteromorpha sp.) is evident from Fig. 1. Maximum enhancement (of over 100~) was achieved with the addi t ion of 30°/00 (w/w) of TS. In addi t ion to in- creasing total gas product ion, algal powder was responsi- ble for higher methane content in the digester gas, with as much as 70°f00 methane being present in the total gas as com- pared to 64~00 in the control without algal powder .

Process stability, as evidenced by lower volatile acids, consistently increased with increased levels of algal powder (Fig. 1). Volatile acid concentrat ion ranged f rom 1.3 g/l in the digester with no algae to 1.1 g/l in the algal-dosed digester. This indicates that volatile acids were consumed at a faster rate than in the control experiments where no algal powder was used. From Fig. l , it seems that the pres- ence of algal powder in a suitable p ropor t ion along with W H - C D boosts the methane-forming step of the digestion process, by making the substrate easily utilizable. This may be because of a suitable carbon to nitrogen ratio and easily digestible materials, but further study is required to explain this phenomenon.

Process performance can also be judged by BOD and COD values. As shown in Fig. 1, addi t ion of algal powder gave low values of BOD and COD, indicating greater bio- degradat ion. It was found that there was 81% COD re- moval in a 30~00 (w/w of TS) algal powder-dosed digester in compar ison to the control without additive where the COD reduction was 6 2 ~ in 8 d.

Studies with other residues like sugarcane bagasse, banana stem, poul t ry waste, cheese whey and sugarcane

344 MADAMWAR ET AL. J. FERMENT. BIOENG.,

/

7 0 - 2"~ , / : ~ . ~ 2 6 136 18

66- 2.0 22 i32

52- -..~ 1.5 ~ 8 ~ j281

o c: "~ l I I I I I i l L I l 1 I l

ta

: ° ' /2: f'' l ° 59 • • :~ : =~ lZ, 12z, JlO

57 ' 05 I0 0

16

] 4

~2 C

2'o ~'o o'o 8~ ~ 2~ 4~ 6o 8~ ~ 2'o ~'o 6'o 8~ Woste added ( ' / , ,w/w ofTS )

FIG. 1. Enhancement of anaerobic digestion of water hyacinth-cattle dung in presence of (a) algal powder, (b) poultry waste, (c) banana stem, (d) cheese whey, (e) sugarcane bagasse, (f) sugarcane filter cake. Symbols: O, gas production; <, methane content; ~, BOD; v, COD; ~, volatile acids. Operational conditions: temperature, 37°C; RT, 8 d; loading rate (WH : CD, 7 : 3, w/w), 8.75 g TS/l of digester/d.

f i l tercake also showed increased gas p roduc t i on with higher me thane con ten t (Fig. 1), indica t ing that the add i t ion o f easily digestible mater ia l enhances the convers ion efficiency. A d d i t i o n o f these residues were also respons ib le for low values o f B O D , C O D and vola t i le acids as c o m p a r e d to the con t ro l wi thou t residue, indicat ing higher b iodeg rada t i on and increased process stabil i ty. In all cases, C O D remova l was m u c h higher than in the con t ro l wi thou t addi t ive over 8 d. Thus a mix ture o f W H , CD and agr icul tura l or o ther waste such as algae, sugarcane bagasse, b a n a n a stem, pou l t ry waste and cheese whey could be used to increase the po ten t ia l o f exist ing digesters and to avo id the load on one par t icu lar substrate , especial ly CD.

Cheese whey has a very low p H , and when it is loaded into the digester it reduces the p H significantly and there- fore the process pe r fo rmance . H o w e v e r , this p r o b l e m can be o v e r c o m e by neut ra l iz ing cheese whey before loading.

A d d i t i o n o f o ther wastes such as Polyalthia Iongifolia (Sonn. ) Thw. leaves, Azadirachta indica A. Juss leaves, and eucalyptus leaves, was found to be de t r imen ta l to the digesters (data not shown) . This may be because o f their chemica l na ture , and the presence o f substances which can ei ther inhibi t the g rowth o f digester mic roorgan i sms or may kill them. Eucalyptus and Azadirachta indica leaves are k n o w n to con ta in an t imic rob ia l substances. Thei r presence in the W H - C D anaerob ic digester caused a r educ t ion in gas p r o d u c t i o n with low me thane content . They were also re- sponsib le for high values o f B O D , C O D and volat i le acids, suggest ing lesser degrada t ion o f organic ma t t e r and low process stabil i ty. H o w e v e r , they can still be used in anaero- bic digest ion with some modi f ica t ion , such as pre- t reat - ment , to i m p r o v e their digestibil i ty, t hough this needs m o r e study.

Thanks are due to the DNES, New Delhi, India for financial sup- port.

REFERENCES

1. Madmwar, D. B. and Mithai, B. M.: Effect of pectin on anaero- bic digestion of cattle dung. Biotechnol. Bioeng., 28, 624-626 (1986).

2. Varel, V. H., Hashimoto, A. G., and Chen, Y. R.: Effect of tem- perature and retention time on methane production from beef cat- tle waste. Appl. Environ. Microbiol., 40, 217-222 (1980).

3. Malik, R. K., Tauro, P., and Dahiya, D. S.: Effect of delignifica- tion pretreatment and selective enrichment on methane produc- tion from cattle waste. Biotechnol. Bioeng., 33, 924-926 (1989).

4. Saraswat, N. and Kbanna, P.: Methane recovery from water hyacinth through anaerobic activated sludge process. Biotechnol. Bioeng., 828, 240-246 (1986).

5. Obeid, M.: Utilization of water hyacinth-introduction, p. 101- 103. In Obeid, M. (ed.) Aquatic weeds in the Sudan. Natl. Conn. Res., Sudan, and U.S. Natl. Acad. Sci., Washington, D.C. (1975).

6. Walverton, B.C. and McDonald, R.C.: Don't waste water weeds. New Scientist (USA), 71, (1913), 318-329 (1976).

7. Gbose, T. K. and Mukhopadhyay, S. N.: Some basic engineering considerations to maximise bioenergy production. Ind. Chem. Engr., 18 (4), 12-16 (1976).

8. American Public Health Association: Standard methods for the examination of water and waste water, 14th ed. American Public Health Association Inc., Washington, D.C. (1975).

9. Deschatelets, L. and Yu, K. C.: A simple pentose assay for bio- mass conversion studies. Appl. Microbiol. Biotechnol., 24, 379- 385 (1986).

10. Updegraffs, D. M.: Semi-microdetermination of cellulose in bio- logical materials. Anal. Chem., 32, 420-425 (1969).

11. Goering, H.K. and van Soest, P .J . : Forage Fiber Analysis Agricultural Hand Book Nr. 379, Agriculture Research Service US Dpt. Agriculture (1970).