Bioaugmentation technology for cereal waste management
- Sunita Gaind

Bioaugmentation, a remediation technology, refers to the use of specific microorganisms that possess the trait to accelerate the processing of biodegradable wastes that other wise take a much longer time to decompose. These microorganisms convert waste in to more useful non polluting product in a shorter time. As the chemical composition of agricultural residues varies, it may be necessary to use multiple microbial cultures or consortia for bio-augmentation. The process of degradation is brought about by a number of enzymes and no single culture possesses all the enzymes in optimum level. Therefore, mixed inoculum has always been more effective in degrading diverse substrates compared to single inoculum.

Need for effective waste management
Globally 998 million tones of agriculture waste are produced every year. Total amount of crop residue produced in India is estimated at 350 x 106 kg yr-1, of which wheat residue constitutes about 27% and that of rice about 51 %. Management of the voluminous paddy straw is a major challenge, as it is considered to be a poor feed for the animals due to its high silica content. More over, its high lignin content makes it less vulnerable to microbial attack. Therefore, it is generally managed by burning in the field it self, resulting in huge losses of N (up to 80%), P (25%), K (21%) and S (4-60%), thereby depriving the soils of its organic matter. A rice-wheat sequence that yields 7 t ha-1 of rice paddy and 4 t ha-1 of wheat removes more than 300 kg ha-1 N and K along with 30 kg ha-1 P from the soil. Effective management of cereal waste in the current scenario is an important issue that needs specific attention. Some eco-friendly, low cost, easily adoptable residue management strategies that can replenish the soil of its nutrients need to be provided. This may not only save these natural resources being wasted but may protect the soil from further impoverishment due to consistent use of chemical fertilizers and also return the soil its lost share of organic matter. Composting of cereal waste is the most sought out option.
Composting: It is a solid state oxidative transformation of biodegradable material into a stable product by diverse group of microorganisms under controlled conditions of temperature and moisture.
Pre requisites for microbial biodegradation

The success of composting process depends upon the conditions conducive for the
decomposition of substrates

ï'˜ C/N ratio of decomposable substrates. A C: N ratio of 50:1 is desirable to initiate degradation and can be achieved by amending the primary substrate with material containing high nitrogen as poultry manure, grass clipping, farm yard manure, cow dung etc.
ï'˜ Shredding of substrates to pieces of 6-8 cm is desired
ï'˜ Amendments with minerals like P and S in the form of rock phosphate and pyrite.
ï'˜ Moisture: 55-65 % of moisture content of substrate mixture is generally considered optimum to start with. Excess moisture favors anaerobic conditions and results in putrefaction
ï'˜ Aeration: In the early stages of composting air requirements is more. Therefore, turning at fortnightly intervals is preferred.
ï'˜ Temperature: The operating temperatures to maximize
1. Sanitization (> 55 o C)
2. Stabilization (45-55o C)
3. Maturation (35-40o C)

Microorganisms involved in acceleration of cereal waste composting
Use of composting inoculants of cellulolytic and lignolytic microorganisms capable of hydrolyzing lignin bound cellulose is effective to expedite the process of decomposition and the compost gets ready within 3 months depending upon the substrates.
Most of the mesophillic fungi found effective in accelerating decomposition are

Trichoderma viride, Trichoderma, reesei, Trichrus spiralis, Paecilomyces spp, Penicillium spp, Phanerochatae chrysosporium, Aspergillus awamori, Aspergillus niger.

Some thermophgillic fungi found effective in augmenting the process of cereal waste decomposition are Aspergillus nidulans, Scytalidium thermophilum, Humicola sp.

Action of microorganisms: Cellulolytic and lignolytic fungi play an important role in the decomposition of crop wastes. The microorganisms involved in the process of decomposition derive their energy and carbon requirement from decomposition of carbonaceous materials. The living organisms under aerobic conditions, utilize oxygen, decompose organic matter and assimilate some of the carbon, nitrogen, phosphorus and sulphur along with other nutrients for synthesis of cell protoplasm. Greater amount of carbon is assimilated than nitrogen. The oxidation of carbon to carbon dioxide results in the release of exothermic energy and temperature of the substrate mixture rises to 55-60o C during thermophilic phase. Some spore forming bacteria develop at this temperature. When the temperature falls down to ambient, mesophilic bacteria and fungi become active.

- Sugars, Celluloses, hemicelluloses (CH2O) x + x O2 → x CO2 + x H2O + E

- Proteins (organic nitrogen) → NH3 → NO2 - → NO3 - + E

- Organic sulphur (S) + O2→ SO4--

- Organic phosphates (Phytin and Lecithin) → H3PO4 → Calcium phosphate

Compost production: Prepare the substrate mixture by mixing cereal straw with nitrogen rich substrate in quantity to bring down the C/N ratio of substrate to 50:1 to prevent immobilization of nitrogen. Add 1-2 % low grade rock phosphate (w/w). Besides, phosphorous, it is a source of calcium and micronutrients. Bone meal can also be used; it contains 9-11% P and 2-4% N. Basic slag provides calcium, magnesium and trace nutrients and small amount of phosphorous. Banana residues that contain about 1-1.5% phosphorous on an ash basis can be another alternative to rock phosphate. Fill the contents in 1m3 pit. Moisten the substrates with water to maintain moisture content of 60-65 %. Inoculate the content with mixed fungal cultures inoculum (A. nidulans, T. viride and P. chrysosporium) raised in broth or solid medium. Mix the content thoroughly. Keep turning at fortnightly interval. Compost will be ready with in three months depending upon the substrates used.

The enhancement of nutritive values and reduction in volume of agricultural wastes using fungal consortium is an eco-friendly low cost technology that can be easily adopted by farming communities to convert their farm waste into value added product. The compost so prepared is most suited for organic agriculture.

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