Rheology and Microbiology of Sludge from a Thermophilic Aerobic Membrane Reactor

Abstract

A thermophilic aerobic membrane reactor (TAMR) treating high-strength COD liquid wastes was submitted to an integrated investigation, with the aim of characterizing the biomass and its rheological behaviour. These processes are still scarcely adopted, also because the knowledge of their biology as well as of the physical-chemical properties of the sludge needs to be improved. In this paper, samples of mixed liquor were taken from a TAMR and submitted to fluorescent in situ hybridization for the identification and quantification of main bacterial groups. Measurements were also targeted at flocs features, filamentous bacteria, and microfauna, in order to characterize the sludge. The studied rheological properties were selected as they influence significantly the performances of membrane bioreactors (MBR) and, in particular, of the TAMR systems that operate under thermophilic conditions (i.e., around 50 ∘ C) with high MLSS concentrations (up to 200 gTS L −1 ). The proper description of the rheological behaviour of sludge represents a useful and fundamental aspect that allows characterizing the hydrodynamics of sludge suspension devoted to the optimization of the related processes. Therefore, in this study, the effects on the sludge rheology produced by the biomass concentration, pH, temperature, and aeration were analysed.

Numerical Analysis of a Full-Scale Thermophilic Biological System and Investigation of Nitrate and Ammonia Fates

“…subject of a publication by Abbà et al [33], despite the large time interval between the two measurements, we note the continued absence of nitrifying bacteria. Figure 6 The biomass of this plant proves to be quite peculiar, given the particular process conditions that lead to the development of minute flocs and a bacterial community whose populations are present in different percentages compared to conventional activated sludge.…”

“…In any case, no AOB (Ammonia Oxidizing Bacteria), NOB (Nitrite Oxidizing Bacteria), and anammox bacteria were identified. If we compare the results with the results of the analysis carried out on samples from the same AWTP plant, which was the subject of a publication by Abbà et al [33], despite the large time interval between the two measurements, we note the continued absence of nitrifying bacteria. Figure 6 displays a picture of the flocs, which have a diameter always lower than 150 µm and are quite dense, without any bone of filaments, as previously highlighted.…”

A Review on the Rheological Behavior of Organic Waste for CFD Modeling of Flows in Anaerobic Reactors

“…The study showed that the apparent viscosity, the yield stress and the fluid consistency increased with the TS concentration increase [76]. Abbà et al (2017) evaluated the rheology and microbiology of sludge from a thermophilic aerobic membrane reactor [77]. The Hershel-Bulkley model fitted with experimental data [77].…”

Review of rheological behaviour of sewage sludge and its importance in the management of wastewater treatment plants

“…Testing a secondary sludge, they found that both the threshold stress and the plastic viscosity were positive correlated with pH increases up to 7, highlighting that the best cohesion of the flocs and occurred in acidic conditions with pH between 6 and 7 (Dollet & Baudu 2000). Abbà et al (2017) and Collivignarelli et al (2019c) studied the effect of TSS content on rheological behaviour showing that the sludge derived from a Thermophilic Aerobic Membrane Reactor (TAMR), with 150 g TSS /L exhibited shear-thickening (dilatant) behaviour. When TSS increase up to 190 g/L, the interactions between the sludge particles were expected to be even more intense and therefore a non-zero yield stress was observed.…”

“…Moreover, the thermally treated sludge exhibited gel-like, viscoelastic characteristics similar to untreated sludge (Hii et al 2017). Abbà et al (2017) studied the rheological properties of the sludge derived from a Thermophilic Aerobic Treatment Reactor (TAMR), that is an innovative membrane bioreactor (MBR) treatment that works around 50 °C. Also in this case, the most important parameter that affect the rheological behaviour is the TSS concentrations (in this case up to 200 g/L).…”