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

The Domtar Papers pulp and paper mill in Windsor, Quebec, Canada, investigated the potential for anaerobic treatment of contaminated kraft mill condensates. The objectives of this project were to assess the technical feasibility of replacing the steam stripper with anaerobic treatment, to provide basic information for the design of an anaerobic treatment process for condensates, and to provide information on treated condensate quality for eventual reuse. The project involved extensive chemical characterization of condensates, followed by treatability tests. The tests included laboratory bench-scale tests and onsite pilot testing using direct feed from the process. Characterization showed that the organic content of the condensates was essentially methanol, as expected, but that foul evaporator condensates had high sulfide contents. It was found that undiluted foul condensates at the Windsor mill are toxic to the anaerobic biomass because of these high concentrations of sulfides. Treatment of combined condensates is possible at an approximate volumetric loading of 10 to 12 g/L.d chemical oxygen demand (COD) with good production of biogas (0.35 L/g of COD removed) and excellent methanol removal (better than 95%). The biogas produced is of excellent fuel quality with close to 90% methane, but with a high sulfide content (close to 4%).