Nitrogen removal from poultry slaughterhouse wastewater in anaerobic-anoxic-aerobic combined reactor: Integrated effect of recirculation rate and hydraulic retention time.

The aim of this work was to assess the nitrogen removal from slaughterhouse wastewater in an anaerobic-anoxic-aerobic combined reactor, evaluating the integrated effect of recirculation rate and hydraulic retention time. The recirculation of the liquid phase from the aerobic zone to the anoxic zone was applied to promote the denitrification through the use of endogenous electron donors. Three recirculation rates (R: 0.5, 1 and 2) and three hydraulic retention times (14, 11 and 8 h) were applied. The operation of the reactor was divided into 3 steps (I, II, and III) according to the factors evaluated (recirculation rate and HRT), to achieve operational conditions that would allow satisfactory performance in the different compartments of the reactor. During the experiment the reactor was fed with average total nitrogen (TN) and chemical oxygen demand (COD) of 65 mg L-1 and 580 mg L-1, respectively. The denitrification efficiency (theoretical) and kinetics parameters for COD decay were calculated. The highest performance was verified in the Step III (R = 2) and HRT of 11 h with NH4+ and TN removals of 84% and 65%, respectively. The TN removal efficiency (65%) was considered satisfactory, since the theoretical denitrification efficiency expected for this condition (R = 2) is 67%, without addition of an external carbon source. The lowest nitrification efficiency values were obtained in HRT of 8 h in the Step I and II (R = 0.5 and 1, respectively), indicating that the nitrification time (3 h - aerobic phase) may be the limiting factor in this HRT. The COD removal efficiency was high in all assays (>95%). The values of the kinetic degradation constants of organic matter were close for all recirculation rates, and the highest values were recorded for the HRT of 8 h and R = 1 and R = 2 (-0.48 and -0.43, respectively).

The application of an innovative continuous multiple tube reactor as a strategy to control the specific organic loading rate for biohydrogen production by dark fermentation.

Biohydrogen production in fixed-bed reactors often leads to unstable and decreasing patterns because the excessive accumulation of biomass in the bed negatively affects the specific organic loading rate (SOLR) applied to the reactor. In this context, an innovative reactor configuration, i.e., the continuous multiple tube reactor (CMTR), was assessed in an attempt to better control the SOLR for biohydrogen production. The CMTR provides a continuous discharge of biomass, preventing the accumulation of solids in the long-term. Sucrose was used as the carbon source and mesophilic temperature conditions (25°C) were applied in three continuous assays. The reactor showed better performance when support material was placed in the outlet chamber to enhance biomass retention within the reactor. Although the SOLR could not be effectively controlled, reaching values usually higher than 10gsucroseg(-1)VSSd(-1), the volumetric hydrogen production and molar hydrogen production rates peaked, respectively, at 1470mLH2L(-1)d(-1) and 45mmolH2d(-1), indicating that the CMTR was a suitable configuration for biohydrogen production.