Anaerobic treatment of condensates: Trial at a kraft pulp and paper mill

The Domtar Papers pulp and paper mill in Windsor, Quebec, Canada, investiga ted the potential for anaerobic treatment of contaminated kraft mill conden sates. The objectives of this project were to assess the technical feasibil ity of replacing the steam stripper with anaerobic treatment, to provide ba sic information for the design of an anaerobic treatment process for conden sates, and to provide information on treated condensate quality for eventua l reuse. The project involved extensive chemical characterization of conden sates, followed by treatability tests. The tests included laboratory bench- scale tests and onsite pilot testing using direct feed from the process. Ch aracterization showed that the organic content of the condensates was essen tially methanol, as expected, but that foul evaporator condensates had high sulfide contents. It was found that undiluted foul condensates at the Wind sor mill are toxic to the anaerobic biomass because of these high concentra tions of sulfides. Treatment of combined condensates is possible at an appr oximate volumetric loading of 10 to 12 g/L.d chemical oxygen demand (COD) w ith good production of biogas (0.35 L/g of COD removed) and excellent metha nol removal (better than 95%). The biogas produced is of excellent fuel qua lity with close to 90% methane, but with a high sulfide content (close to 4 %).