Pilot‐scale sequential anaerobic–aerobic biological treatment of waste streams from a paper mill

Abstract

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