The pulp and paper industry is one of the oldest and major industries in India. There are more than 60 large industrial units which manufacture paper and allied products. Most of the paper producing units in India is integrated pulp and paper mills. These units utilize different cellulosic materials like wood, bamboo and biogases as raw materials in the pulp mills. There are few mills which produce only pulp.
Paper industry is one of the largest water consuming industries. Manufacture of writing paper requires large quantities of water and a bulk of it is discharged as waste water. As such the paper mills are almost invariably located near or along a water course.
The water course provides raw water and in many cases receives wastewater also. The pulp and paper waste contain very high COD and color, the presence of lignin with waste is obtained from the raw cellulosic materials and are not easily biodegradable.
The volume characteristics of the pulp and paper mill wastes depends on the type of manufacturing process adopted and the extent of water employed in the plant. In pulp making phase, the chipped cellulosic raw materials are digested with different chemicals in one tank under high temperature and pressure. This process loosens the cellulose fiber and dissolves the lignin, resin and other non- cellulosic materials.
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The lignin is solublised via degradation or derivatisation to free fibers for the manufacture of paper and other products. The Kraft process of pulping uses sodium sulphate, sodium hydroxide and sodium supplied as digesting chemicals. Other methods of pulp making known as sulphite process uses magnesium or calcium bisulphate and sulphuric acid as the digester chemicals whereas the alkali process of pulp making uses lime or sodium hydroxide in digester.
The spent liquor produced by the above process of digestion is known as ‘Black liquor’. It is not only very rich in lignin content but also contain a large amount of unutilised chemicals. Rivers and streams receiving this effluent are generally characterized by a black colour and frothy surface. The volume of the waste depends mainly on the process of manufacture. It has been observed that a well operated a well managed integrated pulp and paper mill employed Kraft process for pulping produces a waste volume in the rate the 225-320 m3 per tonne of paper manufactured.
Crude pulp mill wastes or partially treated wastes cause very serious problem in India, when discharged into the stream. This pollution extends over a long stretch. Sometimes as long as 80 km. A toxic effect induced upon the flora and fauna of the stream due to sulphites and phenols in the waste. The fine fibres often clog the water intake screen in the downstream side.
Conventional biological treatment systems are effective in removing the suspended solids and BOD to the permissible level but colour and COD remains at higher level, utilization of lignin bearing coloured paper mill waste for crop irrigation is worth trying Khambatta and Ketkan studied cultivation of sugar cane, paddy, wheat, vegetable and fruits using paper and pulp mill effluent for irrigation. Rajannan and Oblisami reported increased rice yields by using paper mill sludge as fertilizer and conditioner. Prasad and Jamaladdin studied the effect of using treated pulp and paper mill effluent in irrigation and its effect on plants, soil and nodulation.