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

Abstract

The production processes of the pulp and paper industry often run in campaigns, leading to large variations in the composition of wastewaters and waste sludges. During anaerobic digestion (AD) of these wastes, the viscosity or the production of extracellular polymeric substances (EPS) and soluble microbial products (SMP) may be affected, with the risk of foam formation, inefficient digester mixing or poor sludge dewaterability. The aim of this study was to investigate how viscosity and production of EPS and SMP during long-term AD of pulp and paper mill sludge is affected by changes in organic loading rate (OLR) and hydraulic retention time (HRT). Two mesophilic lab-scale continuous stirred tank reactors (CSTRs) were operated for 800 days (R1 and R2), initially digesting only fibre sludge, then co-digesting fibre sludge and activated sludge. The HRT was lowered, followed by an increase in the OLR. Reactor fluids were sampled once a month for rheological characterization and analysis of EPS and SMP. The production of the protein fraction of SMP was positively correlated to the OLR, implicating reduced effluent qualities at high OLR. EPS formation correlated with the magnesium content, and during sulphate deficiency, the production of EPS and SMP increased. At high levels of EPS and SMP, there was an increase in viscosity of the anaerobic sludges, and dewatering efficiency was reduced. In addition, increased viscosity and/or the production of EPS and SMP were important factors in sludge bulking and foam formation in the CSTRs. Sludge bulking was avoided by more frequent stirring.

Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why?

“…K, Mg, and Mn) could be identified in the biogas plants. Both cations and EPS have previously been found to increase viscosity, as the cations bridge and strengthen the polymer network, thus affecting the viscosity accordingly [56][57][58]. In line with this, there was a positive correlation of viscosity to arabinose (likely in the form of plant polysaccharides) at both investigated shear rates, with the highest content of arabinose being seen in AW1, followed by AW2 and AWM (Additional file 1).…”

“…The extraction and quantification of extracellular polymeric substances (EPS) and soluble microbial products (SMP) was performed as described by Frølund et al [64], with the modifications described by Ekstrand et al [56]. EPS and SMP were then quantified as protein (i.e.…”

“…Rheological characterization of all digestates and post-digestates was performed in triplicate at 37 ± 0.2, 38 ± 0.2, 42 ± 0.2, or 55 ± 0.2 °C, corresponding to the operational temperatures of the digesters and postdigesters at the plants (Table 2). The analyses were performed using a shear rate-controlled Searle-type rotational rheometer, as described by Ekstrand et al [56]. In short, a three-step protocol was implemented in which the shear rate was (1) increased linearly from 0 to 800/s over a period of 800 s; (2) maintained constant at 800/s for 300 s, and (3) decreased linearly from 800 to 0/s over a period of 800 s. Due to the often non-Newtonian character (i.e.…”

Ultrasound-Assisted Extracellular Polymeric Substance Removal from the Diatom Navicula sp.: A Route to Functional Polysaccharides and More Efficient Algal Biorefineries

“…Furthermore, this layer contributes to extending the effective hydrodynamic volume occupied by the cells, which would be expected to increase the viscosity of cell slurries. Consistent with this idea, the viscosity of anaerobic bacterial sludges is observed to be increased with an increase in the EPS content.…”

“…Apart from the effect on the viscosity, the presence of these polymers is also expected to affect the ability to remove water from the suspensions. This in turn affects the separation efficiency when concentrating the cells using compressional processes such as filtration and centrifugation . Disintegrating or detaching the EPS from the particle surface is expected to reduce the water holding capacity of the suspension and improve dewaterability .…”