Technical Bulletin No. 0090: Evaluation of Bio-oxidation Pilot Plant Studies at Pulp and Paper Mills

It is a characteristic of most pulp and mill effluents that a large portion of the Bio-chemical Oxygen Demand (BOD) fraction of these wastes is in a soluble or finely divided form. Recirculation and internal reuse of these waters, while resulting in reduction of solids losses, does not significantly decrease the absolute quantities of soluble oxygen demand substances which are discharged. Similarly, the various forms of primary treatment employed In the industry –flotation, sedimentation (with or without chemical coagulation) and filtration – remove, at best, only about a third of the BOD, This percentage may be as low as 10 – 15% in more concentrated effluents resulting from chemical pulping or where a high degree of recirculation is practiced. The excessive discharge of BOD to streams is objectionable for several reasons. Oxygen is but very slightly soluble in water; at 20°C only about 75 pounds of oxygen is dissolved in a million gallons of water. When this saturation level is dropped much below 4% through the oxidation of waste materials fish life is endangered. The complete depletion of dissolved oxygen results in anaerobic decomposition, the by-products of which include compounds having noxious odors. Most state water pollution agencies, therefore, have regulations of one type or another which limit the allowable BOD discharged at a particular location. Some states are requiring an advanced degree of treatment without specific regard to stream condition but as part of a general improvement program. In other locales, individual situations of excessive BOD loadings or low seasonal flows have made secondary treatment mandatory. It is becoming increasingly frequent for the regulatory agencies to make approval of new mills or expansion contingent upon a high degree of waste treatment.