A four-year pilot plant program was carried out to investigate the technical and economic feasibility of treating unbleached kraft pulp and paper mill effluent for reuse. Preliminary laboratory studies and cost estimates indicated that the following treatment sequences should be investigated in the pilot plant; (1) Primary clarification, carbon adsorption; (2) lime treatment, carbon adsorption; (3) primary clarification, bio-oxidation, carbon adsorption. Water of reusable quality can be provided from unbleached kraft effluent by several combinations of treatment utilizing activated carbon. Unbleached pulping effluents typically contain about 1000 color units, 250 mg/1 TOC, and 250 mg/1 BOD. Reusable water quality as defined in this study is 100 color units and 100 mg/1 TOC. The most economical treatment is the microlime-carbon process that utilizes low dosages of lime and clarification followed by carbon adsorption in down-flow granular carbon beds. Capital cost for treatment by the process of 9.6 mgd of unbleached kraft effluent from an 800-ton-per-day mill was estimated to be approximately $6.7 millions. Operating costs, inclusive of capital depreciation, were extimated to be $0.30 per 1000 gal and $3.58 per pulp-ton, including credit for the reused water.

"Grant No. 12040 EJU; program element 1BB037; ROAP/TASK 21 AZX/027." Report prepared by St. Regis Paper Company, Research and Development Center, Pensacola, Florida. Includes bibliographical references (pages 166-169).