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Keywords:

  • anaerobic digestion;
  • biogas production;
  • activated sludge;
  • biological treatment;
  • pulp and paper wastewater

The pulp and paper industry produces a large quantity of wastewater containing recalcitrant organic compounds. In this study, a pilot-scale anaerobic–aerobic sequential system was employed to treat four different waste streams produced in a kraft pulp and paper mill. The system consisted of a 2.3 m3 packed-bed anaerobic digester and a completely mixed activated sludge process. Under the applied organic loading rate to the anaerobic digester (0.2 to 4.8 kg-COD m−3 d−1), a COD removal efficiency of 50–65% was achieved. After the anaerobic treatment, the BOD/COD ratio of the effluent was low (0.12 ± 0.03), suggesting that additional pretreatment is necessary for the digester effluent to be further polished aerobically. Combined with the aerobic treatment, the overall COD removal efficiency was up to 70% for the substrates evaluated. Air purging before feeding sulfide-containing substrate was shown to be effective for removing sulfide toxicity in the digester. Kinetic analysis showed that the pseudo-first-order degradation rate constants of the evaluated substrates are 0.28–0.46 d−1 in the anaerobic digester, with a methane production yield of 0.22–0.34 m3-CH4 kg-COD−1 at standard temperature and pressure (0°C, 1 atm). These values are comparable to those found for other industrial substrates, indicating that an anaerobic process is a sound treatment alternative for the evaluated waste streams. The quality of biogas produced by the substrates was excellent, containing ∼80% of methane. The application of anaerobic treatment has the potential of significantly improving the energy footprint of the pulp and paper industry. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 359–368, 2014