Control of sulphite pulping wastes in the United States.

Abstract

Statistics indicate that US capacities for acid and neutral suiphite pulping are presently at about the same level, running about 10000 short tons daily for each type of pulp. It is projected that acid suiphite will remain at about this level over the next ten years while the production of neutral suiphite will probably double. Most of the spent liquor from the operating mills is burned with or without chemical recovery. For acid sulphite liquor handling systems magnesium and ammonia base are employed to about an equal degree, there being only one sodium base mill. Neutral sulphite liquor recovery systems are either the Institute of Paper Chemistry Process or the Mead process. Most liquor incineration systems employ the fluidized bed furnace. An effort is being made to adapt this unit for magnesium base liquor incorporating chemical recovery. Effluents from acid suiphite mills employing chemical recovery contain about 20 per cent of the original BOD load. Biological treatment in the forms of the activated sludge process and the aerated stabilization basin have been applied in full scale to treat the effluents from both magnesium and ammonia base operations, producing BOD reductions averaging in excess of 85 per cent. The manufacture of by-products continues to consume around 10 per cent of the acid liquor, some being marketed as crude evaporate and the remainder converted to speciality chemicals. The number of companies involved in this business is decreasing. Neutral sulphite effluents are treated by various means. When associated with kraft operations the liquor is invariably diverted to the kraft recovery system as make-up. Remaining effluent is generally treated with the other mill discharges by clarification and biological oxidation. Three mills use land disposal and the same number discharge to the treatment systems of large municipalities. One mill recovers formic and acetic acids from the liquor and sells the remaining raffinate to a kraft mill. At the present time the United States has the capacity for producing somewhat over 21000 short tons daily of acid and neutral sulphite pulps. While manufacture of the former has been declining in recent years, the latter has steadily increased and at present the capacity for producing neutral suiphite semi-chemical pulp exceeds that for acid sulphite by approximately 1500 short tons daily. Projections indicate that acid suiphite capacity will probably