Introduction

POLLUTION DUE TO INDUSTRIAL WASTES
  • Population explosion and rapid industrial development for the essential commodities have led to formation of various contaminants in the environment. During the last five decades xenobiotic compounds have been increasingly added to the environment by industrial activities. Some of them are highly toxic, recalcitrant, and have higher bio-accumulating and biomagnifications properties.
  • The following are the major industries which pollute the environment.
  • Pulp and paper are manufactured from wood, non-wood fibres and recycled fibres. The primary raw material used in paper manufacturing is cellulose fibre, which constitutes 50% of wood. The pulp and paper industry is both huge and small in size, technically diverse, operate on a wide variety of manufacturing processes on a large number fibre types. There are two main pulping methods, mechanical and chemical. The yield of the pulp by mechanical process is as high as 90-95%, but the quality fo the pulp is of low grade, highly colorued, and contains short fibres. In the chemical process, the wood chips are cooked with appropriate chemicals in an aqueous solution, at an elevated temperature and pressure so as to break the chips into a fibrous mass. The yield of the pulp by this process is about 40-50% of the original wood material. Chemical pulping is carried out in two media: alkaline and acidic.
  • Paper mill effluent is a white colorued effluent noted for low pH value and high suspended solids. BOD and COD values are not so high. It also contains filler size material and pigments.
  • Impact on air quality is an important concern of the pulp and paper industry, even though it is not often the most dangerous for human health. Odour, smoke, vapour and dust are emissions that people recognize immediately as characteristic of a pulp mill. Hydrogen Sulphide, Methyl Mercaptan, Dimethyl Sulphide and Dimethyl Disulphide. Total Reduced Sulphur (TRS) emissions, Sox and NOx emissions are different compounds which are a major source of odour and main factors of air pollution.
  • Hazardous material in the pulp and paper industries can fall into two different risk classes, such as first: inflammable, corrosive, reactive, toxic, pathogenic, mutagenic, and second: general hazards associated with industrial facilities like electrical, structural, mechanical or general conditions like ergonomy, temperature, noise and oxygen deficiency which can lead to accidents. The effluent, even upon dilution by the receiving waters, can cause adverse effects on the reproduction and behaviour of aquatic organisms. The effluents from pulp mill using bleaching were identified as a priority for the assessment of their effect on human health and environment.

Control

Treatment of Air Pollutants

  • Electrostatic precipitators, thermal precipitators and bioscrabbers are used for the removal of air pollutants from pulp and paper mills.
  • Wet scrubbers are applied to provide a more effective removal of fine particles, in the size range of 0.1 to 2.0 m radius from an exhaust gas stream.

Treatment of Waste Water

  • One of the main constraints on effluent discharge from the pulp and paper mill industry is its brown or black colour due to the dissolved lignin based compounds derived from the blow – heat condensate, pulp-Decker washing, chlorine and alkali bleach waste, black liquid spillage and foul evaporator condensate.
  • The waste water should be treated and discharged.
Last modified: Wednesday, 17 August 2011, 5:51 AM