Granular Sludge Bed Processes in Anaerobic Digestion of Particle-Rich Substrates

Abstract

Granular sludge bed (GSB) anaerobic digestion (AD) is a well-established method for efficient wastewater treatment, limited, however, by the wastewater particle content. This review is carried out to investigate how and to what extent feed particles influence GSB to evaluate the applicability of GSB to various types of slurries that are abundantly available. Sludge bed microorganisms evidently have mechanisms to retain feed particles for digestion. Disintegration and hydrolysis of such particulates are often the rate-limiting steps in AD. GSB running on particle-rich substrates and factors that affect these processes are stdied especially. Disintegration and hydrolysis models are therefore reviewed. How particles may influence other key processes within GSB is also discussed. Based on this, limitations and strategies for effective digestion of particle-rich substrates in high-rate AD reactors are evaluated. some of the main challenges associated with high-rate anaerobic digestion of particle-rich substrates with special emphasis on manure as a substrate, due to its abundance. Most high-rate AD processes in operation depend on granular sludge to retain sufficient active biomass. Granules are formed by the aggregation of microorganisms that develop into dense masses with sedimentation velocity high enough to avoid washout even under high hydraulic load [7]. It is observed that UASB reactors treating particle-rich manure slurries also accumulates suspended solids from the feed, forming an additional suspended fraction together with the granules [8,9]. The influence of such solids on AD is not understood well, leading some experts to claim that granular sludge bed (GSB) processes may not be appropriate for particle-rich substrates. [10]. It appears, however, that a significant fraction of feed particles can be digested and enhance methane production [11]. This review was undertaken to investigate to what extent and how sludge bed high-rate AD can be used to treat particle-rich substrates. We aim to find more evidence for particle digestion in granular sludge beds, identify process limitations, and find appropriate kinetic models in order to establish design criteria for such processes. There is little directly relevant literature on the topic, limiting this review to mainly indirectly relevant literature. The review covers particle-rich substrates characteristics; particle disintegration and hydrolysis, including models for such; physical characteristics of granular sludge; sludge bed reactor designs and observations of particle effects.

Effect of Intermittent Aeration in a Hybrid Vertical Anaerobic Biofilm Reactor (HyVAB) for Reject Water Treatment

“…The measured reject water UBOD = 90 mg/L confirms this, as does the observed lack of biogas production. Measured ORP was between −330 and −360 mV, and observed granular sludge morphology via the stereomicroscope ( Figure 10B) shows the appropriate conditions for biomethane production prevailed [25], but methane levels remained below saturation. Measured nitrogen species concentrations in the aerobic part of the HyVAB reactor and influent ammonium concentrations are given in Figure 8.…”

Enhancing energy recovery from aquaculture residual materials: a focus on anaerobic digestion of African catfish (Clarias gariepinus) sediment sludge

“…In UASB and related reactors, however, co-digestion with substrates rich in solids is only possible with a very high technical effort. Upstream hydrolysis and separation processes would be conceivable (Tassew et al, 2019). This study examines to what extent the widely used Continuous Stirred Tank Reactor (CSTR) reactor type can be used for African catfish RAS sludge.…”