Municipal wastewater was amended with organic garbage leachates at a concentration around 700 mgCODsoluble/L and fed to three different anaerobic systems to compare their performance: a down flow fluidized bed (DFFB), an expanded granular sludge bed (EGSB) and a zeolite-packed anaerobic filter reactor (ZPF). The DFFB and EGSB reactors were operated at HRT of 6 and 4 h and the ZPF reactor at 12 and 36 h. Organic loads rate for the DFFB reactor were 2.3±0.9 and 4.8±1.8 gCOD/L·d, with removal efficiencies around 40% and a methane productivity of 0.2±0.03 L/Lreactor·d. For the EGSB reactor, organic loads tested were 2.1±0.9 and 4.3±1.3 gCOD/L·d, removal efficiencies attained were of 77.6±12.7% and 84.4±4.9%, respectively at both conditions and total suspended solids were removed in 54.6±19.3%, while methane productivity at 4 h HRT was of 1.29±0.4 L/Lreactor·d. The ZPF reactor was operated at lower organic loading rates, 1.4±0.27 and 0.42±0.13 gCOD/L·d and attained removal efficiencies of 48±18% and 83±8%, respectively, reaching a methane productivity of 0.21±0.09 and 0.12±0.04 L/Lreactor·d, 83±8.0% of total suspended solids were retained in the reactor and as HRT was increased ammonium concentrations increased in 39%. Specific methanogenic activity in all systems was around 0.2 gCOD-CH4/gVSS d.

The cheese industry produces residues, such as acid cheese whey; this by-product has a high organic-matter concentration and other nutrients that are severe environmental contaminants. The aim of this study was to evaluate the acidogenesis/methanogenesis of acid cheese whey with short Hydraulic Retention Times (HRT) in Hybrid-UASB reactors, following the organic matter, ammonia, and orthophosphate evolution. The acidogenic reactor was operated at HRT of 0.5 days, while for the methanogenic reactor, ranged from 1‒2 days; both reactors were operated in series. Results show that the overall HRT of 1.5 days allowed optimal removal (89‒96.8%) with organic loading rates between 2.5 and 10.7 g COD/L-d, while at 14.2‒24.9 g COD/L-d best results were found at 2.5 days of overall HRT. Highest methane productivity ranged from 0.99‒1.15 L_CH4/L_Reactor-d (0.238‒0.308 L_CH4/g COD_degraded). Ammonia formation was only significant in methanogenesis (85 mg/L), while orthophosphates showed no change throughout all the process. In conclusion Hybrid-UASB reactors operated at short HRT were suitable for the acidogenesis/methanogenesis of this wastewater. Furthermore, methane can be used for energy generation, and ammonia and orthophosphate might be employed for the development of high value-added products.

Down-flow fluidization is an attractive unit operation because it allows having a smooth circulation of the fluid and the solid support material as well as an uninterrupted and controlled operation of the fluid. In addition, since the solid support material is less dense than the fluid, the pump energy consumption required for bed expansion is smaller in comparison with upward fluidization. Momentum transport in fluidized beds is usually modeled by macroscopic models, which are expressed in terms of effective-medium coefficients, by making analogies with transport in porous media. In practice, it is desirable to derive these models and to predict the involved coefficients in a reliable manner. For this reason, in this work we derive a macroscopic model for the hydrodynamics of down-flow fluidization, using the method of volume averaging obtaining a model with the form of Darcy’s law with a correction in the relative velocity of the fluid to the solid. A salient feature of the model is that it allows predicting the apparent permeability coefficient in different geometries, and under different transport conditions. Also, the average model obtained can be used for both types of fluidization, because it is not restricted by the flow direction.