ACIDIFICATION AND ALUM COAGULATION STUDIES ON BLACK LIQUOR

Abstract

Multifold increase in production of industrial goods has overstrained the assimilative. capacity of our waters, land and atmosphere. Pulp and -Paper industry is one such ever expanding• industry. law materials shortage and depleting forest cover his influenced the technologists to encourage the agriculture residue based small paper mills (SPM) of capacities less than 10000 tonnes per annum (IPA). A number of them has come up in western U.P. and Gujarat. Due to financial instability these SI'M are unable to install. a full scale chemical recovery unit, and as such they discharge very high concentrations of -pollutants such as COD, BOD, Colour and Total Solids into the natural water courses or land. Integrated methods for removal of COD, ROD, Colour and Total Solids for small paper mills have not been much explored. The methods tried and suggested are numerous, but none of them are found to be successful in case of small paper mills. In the present study reduction in the pollution parameters of l‘lack Liquor from small paper mills by acidification has been investigated, by lowering the• pH of the black liquor to the value of 2,0, 2.5, 3.0, 3.5, 4.5 and 5.5. Percentage removal of COD, Colour and Total Solids have been observed in the range of 40-5596, 90-9996 and 10-50% due to precipitation and sludge blanket formations. Further studies were conducted on alum coagulation at p11.5.5, 6.0, 6.5 and 7.0. Reduction • in COD, Colour and Total Solids were obServed in the range of 40-80%, 30-97% and 5-6596. Cost analysis indicates that the acid precipitation treatment varies in cost as a function of removal percentage of COD, Colour and Total Solids arid the alum coagulation cost is much lower than acid precipitation.