Estimation of thermal energy released by thermophilic biota during sludge minimization in a fluidized bed reactor: Influence of anoxic conditions

Thermophilic biological fluidized bed reactors operating in aerobic/anoxic alternate conditions proved to be a feasible solution for sewage sludge minimization. However, to date, no data about energy released by thermo-philic biota (ThBio) are available in literature. This work aims to estimate specific thermal energy released by ThBio highlighting the influence of daily anoxic conditions. A pilot-scale reactor (1 m3) was fed continuously with mesophilic sewage sludge and monitored for more than four months and a thermophysical model was applied to estimate thermal energy released by ThBio (kT,biota and kT,COD). Results suggested that the increase of daily anoxic time stimulated COD removal (92.7 +/- 1.3 % vs. 81.3 +/- 4.9 %, with 6 h and 0 h of daily anoxic time, respectively). The thermal energy released by ThBio was strictly dependent on anoxic conditions. In fact, increasing anoxic conditions from 0 h d-1 to 6 h d 1, kT,biota and kT,COD reduced from 1.8 & PLUSMN; 1.3 Mcal kg17S1 kg(-1) COD and 26.6 & PLUSMN; 13.7 Mcal kg(-1)COD to 0.5 +/- 0.1 Mcal kg17S1 kgjD and 15.6 & PLUSMN; 4.2 Mcal kgjD, respectively. Although, biological mechanism responsible of this behaviour is not completely clear, this work can serve as reference for future studies about the optimization of conditions to maximize thermal energy release from ThBio during organic substance degradation alternate aerobic/anoxic, in view of subsequent energy recovery

Influence of Heavy Metals on the Rheology of a Thermophilic Biological Sludge for nutrients Recovery: Effect of Iron, Copper, and Aluminium on Fluid Consistency

Currently, thermophilic membrane biological reactors (TMBRs) are used to treat industrial wastewaters and biological sewage sludge with the aim of nutrients recovery. The performance of the biological process is strongly influenced by rheological behaviour of the thermophilic biological sludge (TBS) inside the reactor. Considering the high concentration of heavy metals in matrices fed to the reactors, this work aims to evaluate the influence of heavy metal types and concentration on rheological properties of TBS. Sludge has been extracted from a full-scale TMBR and conditioned with Fe3+, Cu-2(+), and Al-3(+). Rheological measures have been conducted and constants k and n of Herschel-Bulkley model were used to define the rheological properties of TBS. Rheological properties of high consistency TBS (0.06 <= k(0) < 0.2 and 0.6 <= n(0) < 0.8) were not significantly affected by the conditioning with Fe3+, Cu-2(+), and Al-3(+). In case of TBS with initial low consistency (0.02 <= k(0) < 0.06) and behaviour more similar to Newtonian fluids (0.8 <= n(0) < 1), Fe3+ and Al3+ determined a significant increase in consistency. On the contrary, the addition of Cu2+ reduced k of conditioned TBS with a lower impact on the distance for Newtonian behaviour (n). This work demonstrates the strong influence of Fe3+, Cu2+, and Al3+ on the rheological properties of TBS depending on the initial consistency of the sludge, and the types and dosage of heavy metals