High-rate anaerobic co-digestion of kraft mill fibre sludge and activated sludge by CSTRs with sludge recirculation

Abstract

Kraft fibre sludge from the pulp and paper industry constitutes a new, widely available substrate for the biogas production industry, with high methane potential. In this study, anaerobic digestion of kraft fibre sludge was examined by applying continuously stirred tank reactors (CSTR) with sludge recirculation. Two lab-scale reactors (4L) were run for 800days, one on fibre sludge (R1), and the other on fibre sludge and activated sludge (R2). Additions of Mg, K and S stabilized reactor performance. Furthermore, the Ca:Mg ratio was important, and a stable process was achieved at a ratio below 16:1. Foaming was abated by short but frequent mixing. Co-digestion of fibre sludge and activated sludge resulted in more robust conditions, and high-rate operation at stable conditions was achieved at an organic loading rate of 4g volatile solids (VS)L(-1)day(-1), a hydraulic retention time of 4days and a methane production of 230±10NmL per g VS.

Viscosity dynamics and the production of extracellular polymeric substances and soluble microbial products during anaerobic digestion of pulp and paper mill wastewater sludges

“…Two lab-scale CSTRs (R1 and R2) with working volumes of 4 L were operated for 800 days at 37 °C, as described by [26]. The substrates used were fibre sludge from the primary clarification and activated sludge from the secondary treatment of two kraft pulp and paper mills.…”

“…pH was controlled by additions of Ca(OH) 2 , and from day 49, part of the Ca(OH) 2 was replaced by MgO to increase the concentration of magnesium in the reactors. For details on the feeding procedures, see Ekstrand et al [26]. Nitrogen and phosphorus were supplied at a ratio of 350:5:1 for COD:N:P, where COD is the chemical oxygen demand of the substrate.…”

“…The samples for extraction of EPS/SMP were kept frozen at − 20 °C until time of analysis, when they were thawed at + 4 °C over-night. TS, volatile solids (VS), pH and volatile fatty acids (VFA) were determined as described by [26]. Elemental analysis was carried out once a month for the reactor sludge samples and for every new delivery of substrate by Eurofins Environment Testing Sweden AB.…”

Anaerobic Process

“…The energy conversion efficiencies raised from 4.6-6.6% after the first stage to 57-70.9% after the second stage. Kraft fiber sludge co-digestion with activated sludge was studied by Ekstrand et al (2016). Obtained from pulp and paper industry, Kraft fiber sludge has high potential for biomethane production.…”

Influence of Pre-Hydrolysis on Sewage Treatment in an Up-Flow Anaerobic Sludge BLANKET (UASB) Reactor: A Review

“…However, this efficiency comes at high capital and operational costs, as well as advanced technology requirements [1,2]. High-rate anaerobic digestion biotechnology has proven to be an excellent process and is considered by many authors to be the core of sustainable waste management techniques [1,[3][4][5][6][7].…”