97. Vermiculture and vermicomposting of non-toxic organic solid waste applications in aquaculture.
Aquacultural Engineering section, Agricultural and Food Engineering Dept., Indian Institute of Technology, Kharagpur 721 302
Waste: a misplaced resource :
The scope and potential for recycling
of a variety of waste resources is vast. Waste recycling can bring
tremendous benefits to the society in the long run. In addition,
there are the benefits of a cleaner environment and a healthier
habitat to live in. Once a waste is recycled or made use of, it
becomes a valuable resource, rather a form of wealth. The potential
for waste recycling in aquaculture, agriculture, horticulture,
forestry etc. is so large and basically user as well as eco-friendly,
that the term waste itself could in most cases be done away with.
Waste recycling - benefits
Proper recycling of wastes creates a lot
of simultaneous benefits e.g. i) supplying essential plant nutrients,
ii) improving soil physical properties, iii) reducing their accumulation
at or near the sites of production, iv) reducing health hazards,
v) providing employment and income to many, vi) improving environment
quality which also includes the quality of human life, apart from
quality of water, soil, air etc. and vii) illustrates that man
is not just a waste generator but also its wise utilizer and manager.
Vermiculture and Vermicomposting
Recently interest has been shown in the development of ecofriendly novel processes which are based upon the utilization of biological systems. One such system involves the culture of earthworms (vermiculture) for the stabilization of a variety of organic solid wastes (vermicomposting). The key role of earthworms in improving soil fertility is well known since long(Darwin, 1881; Chandana, 1981; Kale and Krishnamoorthy, 1981). Earthworms feed on any organic waste, consume two to five times their body weight and after using 5-10% of the feedstock for their growth, excrete the mucus coated undigested matter as wormcasts. Wormcasts consist of organic matter that has undergone physical and chemical breakdown through the activity of the muscular gizzard which grinds the material to a particle size of 1-2 micron. The nutrients present in the wormcast are readily soluble in water for the uptake of plants (Bhawalkar and Bhawalkar, 1993). Vermicasting is a rich source of macro and micronutrients, vitamins, enzymes, antibiotics, growth hormones and immobilised microflora.
Vermicompost refers to an organic manure produced by earthworms. It is a mixture of worm castings (faecal excretions), organic material including humus, live earthworms, their cocoons and other organisms. Vermicomposting is an appropriate technique for the disposal of non-toxic solid and liquid organic wastes. It helps in cost effective and efficient recycling of animal wastes (poultry, horse, piggery excreta and cattle dung), agricultural residues and industrial wastes using low energy (Jambhekar,1992).
The main steps of vermicomposting are described below:
1. Selection of earthworm: Earthworm which is native to the local soil and vermicompost may be used.
2. Size of Pit : Any convenient dimension such as 2m X 1m X 1m may be prepared. This can hold 10 -40 thousand worms giving one tonne manure per month.
3. Preparation of vermibed: A layer (15 -20 cm thick) of good loamy soil above a thin layer (5 cm) of broken bricks and sand should be made. This layer is inhabited by earthworms.
4. Inoculation of earthworms: About one hundred earthworms are introduced as an optimum inoculating density into a compost pit of about 2m X 1m X 1m, provided with a vermibed.
5. Organic layering: It is done on the vermibed with fresh cattle dung. The compost pit is then layered to about 5 cm with dry leaves or hay. Moisture content of the pit without flooding is maintained through the addition of water.
6. Wet organic layering: It is done after four weeks with moist/green organic waste which can be spread over it to a thickness of 5 cm. This practice can be repeated every 3-4 days. Mixing of wastes periodically without disturbing the vermibed ensure proper vermicomposting. Wet layering with organic wastes can be repeated till the compost pit is nearly full.
7. Harvesting of vermicompost: At maturation, the moisture content is brought down by stopping the addition of water for 3-4 days. This ensures drying of compost and migration or worms into the vermibed. The mature compost, a fine loose granular mass is removed out from the pit, sieved, dried and packed.
8. Rate of application: Mature vermicompost is recommended @5t/ha.
(Source: Ismail, 1994)
Nutrient content of vermicompost :
The nutrient status of vermicompost (prepared
by two species of earthworm) and farm yard manure (FYM) is shown
in the table below for comparison.
Parameters Eisenia foetida Perionyx excavatus FYM
pH 7.40 7.00 7.20
Organic Carbon (%) 27.43 30.31 12.20
Total nitrogen (%) 0.60 0.66 0.55
Total phosphate(%) 1.34 1.93 0.75
Total potassium(%) 0.40 0.42 2.30
C: N ratio 45.70 45.90 24.40
(Source : Shinde et al, 1992).
Firstly, there are appreciable differences
in the nutrient content of vermicomposts produced by different
species of earthworms. Vermicompost is thus not a single, standard
material or product. On an average, vermicompost contained more
C and P than FYM, it had less K and micronutrients than FYM and
both had comparable contents of N. Vermicomposts generally had
wide C:N ratio as compared to FYM. On the whole vermicompost cannot
be described as being nutritionally superior to other organic
manures but the unique way in which it is produced, even right
in the field and at low cost makes it very attractive for practical
application (Gaur and Singh, 1995).
Applications of vermiculture and vermicomposting in aquaculture
The most common method of solid waste disposal is land spreading which causes pollution of soil as well as surface and ground water resulting in mortality of aquatic organisms. Vermicomposting of wastes controls the pollution of soil and water, thus ensures the survivality and growth of fish, prawn and other aquatic organisms. The application of vermicastings which is a high grade organic fertilizer, to the aquaculture ponds reduces the input cost making the aquaculture production process more profitable and it also helps in controlling the harmful effects of chemical fertilizer application. Deolalikar and Mitra (1996) have used vermicompost prepared from paper mill solid waste for fertilizing aquacultural tanks and found an increase in net primary productivity from 32.08 to 220.83 mgC/m /h. Vermicompost application also showed better growth of rohu fish (Labeo rohita) when compared with other commercially available organic manures (Deolalikar and Mitra, 1997). There is an increasing demand for protein-rich raw materials in fish and other animal feed industry. Fish meal is the main protein component of fish feed. Earthworm is generally used as bait by the anglers. But large scale vermiculture has the potential of supplying earthworm meal as a substitute of fish meal. The earthworm meal contains all the essential amino acids required in fish feed. The methionine and lysine availability are higher than that of fish meal.
The chemical compositions of earthworm,
Eisenia foetida and two other protein sources are compared
in the table below (values expresed as a dry matter basis, expressed
Composition Earthworm meal Fish meal Blood meal
Protein 67.68 66.00 80.00
Fat 5.15 8.00 1.50
Fibre 0.71 1.00 1.00
Phosphorous 0.88 2.40 0.25
Calcium 0.55 4.00 0.30
(Source : Reinecke and Alberts, 1987)
Vermicomposting technology is applicable to the rural as well as the urban society. It not only helps in commercial aquafarming but also acts as a convenient source of earthworm for growing ornamental fishes in aquarium. Thus vermicomposting can be included as a component of sustainable life-style. Application of vermiculture and vermicomposting in aquaculture is ecofriendly and bioethically acceptable.
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