Organic Waste Recycling

Aquatic weeds and their utilization 329

produced quickly and had higher methane content (69.2%) at 36°C than at 25°C
(59.9%). In the same study, Wolverton et al. (1975) noted that the rate of
methane production is higher in plants contaminated with nickel and cadmium
than in uncontaminated plants.

Table 7.3. Production of volatile fatty acids and methane from laboratory fermentation of
cattle dung + water hyacinth (1:1 mixing ratio) (Gopal and Sharma 1981).

Duration

(days)

pH Temp. (°C) Volatile fatty acid Average

gas

production

(L/day)

Methane

(%)

1-4 7.0-

7.5

30 Acetic, propionic and

butyric acids

0.95 0

5-13 6.5 27-30 Acetic, propionic and

butyric acids and

ethanol on 7th day

1.22 3-8

14-28 6.5-7.0 26-29 Acetic, propionic,

butyric, isobutyric,

valeric and isovaleric

acids

0.81 10-60

29-49 7.0 27-28 Propionic acid

isovaleric acids

6.01 57-62

50-60 8.0 26-28 4.31 60-64

1-60 8.0-8.5 26-28 From cattle dung

alone, acetic,

propionic, acid and

butyric acids

3.81 50-60

The use of dried water hyacinth as fuel in Indian villages is common. Gopal
and Sharma (1981) reported that in 1931, Sen and Chatterjee were the first to
demonstrate the possibility of using water hyacinth for generation of power
alcohol and fuel gas. They described three methods of utilizing the plant. In one
of the methods the plant is saccharified by acid digestion and subsequent
fermentation, yielding 100 kg potassium chloride, 50 L ethanol and 200 kg
residual fibre of 8,100 kJ calorific value. In another method the plant is gasified
by air and steam to produce 1,150 m^3 of gas (equivalent to 150 kJ/m^3 ), 40-52 kg
ammonium sulphate and 100 kg potassium chloride. The gas obtained at 800 °C
comprises of 16.6% hydrogen, 4.8% methane, 4.1% carbon dioxide, 21.7%
carbon monoxide, and 52.8% nitrogen. The third method employs bacterial
fermentation, which produces 750 m^3 gases with a calorific value of 22,750
kJ/m^3. It comprises of 22% carbon dioxide, 52% methane and 25% hydrogen.