Methane potentials of the Swedish pulp and paper industry – A screening of wastewater effluents

Abstract

With the final aim of reducing the energy consumption and increase the methane production at Swedish pulp and paper mills, the methane potential of 62 wastewater effluents from ten processes at seven pulp and/or paper mills (A-G) was determined in anaerobic batch digestion assays. This mapping is a first step towards an energy efficient and more sustainable utilization of the effluents by anaerobic digestion, and will be followed up by tests in lab-scale and pilot-scale reactors. Five of the mills produce kraft pulp (KP), one thermo-mechanical pulp (TMP), two chemical thermo-mechanical pulp (CTMP) and two neutral sulfite semichemical (NSSC) pulp. Both elemental and total chlorine free (ECF and TCF, respectively) bleaching processes were included. The effluents included material from wood rooms, cooking and oxygen delignification, bleaching (often both acid-and alkali effluents), drying and paper/board machinery as well as total effluents before and after sedimentation.The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940 NmL CH 4 per g TOC) among the effluents. For the KP-mills, methane yields above 50% were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10-15% of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60% of the theoretical potential.The TMP mill (A) gave the best average yield with all 6 effluents ranging 40-65% of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40% while three of the six effluents at mill G (CTMP) yielded 45-50%.

Anaerobic co-digestion of acetate-rich with lignin-rich wastewater and the effect of hydrotalcite addition

“…It can be observed that R1 had the highest yield (324 mL CH 4 / gCOD) which is attributed to the higher VFA content (acetic acid) available in the EC substrate. Similar results for NSSC evaporator condensates ranging from 140 to 340 mL CH 4 /gCOD were found in other studies (Meyer and Edwards, 2014;Ekstrand et al, 2013;Arshad and Hashim, 2012). A common setback of easily degradable substrates is the possible accumulation of intermediate products through the anaerobic degradation pathway.…”

“…Methanogenic bacteria can directly convert acetic acid into methane and carbon dioxide avoiding the initial hydrolysis step which is the ratelimiting step in the anaerobic digestion process. Different studies have investigated the anaerobic treatment of evaporator condensate (Ekstrand et al, 2013;Silva et al, 2009;Ferguson and Benjamin, 1985) and found that in spite of a general good running of the anaerobic digestion of this substrate, by itself it may cause inhibition and stability problems. Silva et al (2009) also recognized that anaerobic treatment when an external carbon source is added to the reactor, specifically at high organic loads (2 kg COD/m 3 d À1 or higher) was beneficial and achieved a steady state of COD evolution.…”

Wastewater Treatment and Reclamation: A Review of Pulp and Paper Industry Practices and Opportunities

“…20. Due to the value of methane as a fuel, and perhaps also the importance of avoiding its release into the atmosphere (Weiland 2010), much research has been devoted to its generation during anaerobic treatment of P&P mill wastewater (Maat and Habets 1987;Korczak et al 1991;Minami et al 1991;Sierraalvarez et al 1991;Vidal et al 1997;Kortekaas et al 1998;Ahn and Forster 2002;Buzzini and Pires 2007;Yilmaz et al 2008;Tabatabaei et al 2010;Lin et al 2011;Saha et al 2011;Elliott and Mahmood 2012;Bayr et al 2013;Ekstrand et al 2013;Hagelqvist 2013;Hassan et al 2014;Meyer and Edwards 2014;Larsson et al 2015). …”

Anaerobic digestion of pulp and paper mill wastes – An overview of the developments and improvement opportunities

“…This is a very important issue because the kraft wood pulping efflu ent is alkaline [142] which may lead to the failure of the system. Moreover, the ECF acidic effluents from the KP mills have been shown to be very toxic to the AD microorganisms [143] and this can directly affect the methane production from such effluents. Gao et al (2010) [111] indicated that although a pH shock of 8.0 had no important adverse effects on the performance of a SAnMBR in terms of COD removal, biogas production and membrane filtra tion, the long lasting negative effects of pH shocks of 9.1 and 10.0 were significant.…”