A mathematical model was used to evaluate the effect of the aeration pattern and ammonium concentration in a partial nitritation-anammox sequencing batch reactor with granular and flocculent sludge. In the tested conditions, model results indicate that most of the aerobic ammonium oxidation potential would occur in the bulk liquid, with 70% of the ammonium-oxidizing bacteria (AOB) biomass in suspension rather than in granules. The simulated granular sludge consisted predominantly of anammox bacteria with AOB present in the outer layer of the granule (50 μm AOB layer, accounting for 3% of the granule weight). Simulation results indicated that when granules do not contain any AOB, the amount of granular biomass required to achieve the same level of nitrogen removal would strongly increase (in the simulated conditions, by a factor of three) due to anammox inhibition by oxygen. This underlines the importance of a small fraction of AOB present in the granular anammox sludge. The aeration pattern had an important impact on the nitrogen removal: a better performance was suggested for continuous aeration (90% N-removal) than for intermittent aeration (68-84% N-removal). Anammox inhibition during the periods of high oxygen concentration was identified as the main reason for the lower nitrogen removal in the intermittently aerated system. With increasing oxygen concentration, a higher residual (effluent) ammonium concentration was needed to assure nitrite-oxidizing bacteria repression in the system. This study contributes to further understand the complexity of a reactor with both granular and flocculent sludge and the impact of operation conditions on reactor performance.

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Tequila vinasses represent an acidic, highly concentrated pollutant effluent generated during the distillation step of Tequila production. Although acidogenesis of Tequila vinasses has been reported for some reactor configurations, a characterization of the bacteria present during this metabolic process is lacking in the literature. Hydraulic retention times (HRT) between 36 and 6 h and organic loading rates (OLR) from 5 to 30 g COD L−1 d−1 were assessed in a UASB reactor fed with Tequila vinasses. Results showed that OLR excerted a stronger effect (p ≤ 0.0001) on parameters such as gas production rate, pH, and acidity than HRT. While it was clear that shorter HRT were related to higher volatile fatty acid production levels. Figures above 2 Lgas Lreactor−1 d−1 (where “gas” could be a mixture of methane and hydrogen) were attained only with an OLR as high as 30 g COD L−1 d−1. Bacterial identification of a sludge sample at the end of the experiment revealed that acid-tolerant microorganisms that remained in the reactor were exclusively affiliated to the Clostridium genera, being the first report of organisms identification for Tequila vinasses acidogenesis. These findings are relevant to the field of biotechnology since acidogenesis of Tequila vinasses using identified and studied microorganism abilities (i.e. Clostridium strains) presents the opportunity of optimizing processes intended for different metabolites production (butanol, volatile fatty acids, hydrogen, solvents).

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This paper assesses the economics of heat recovery from biological wastewater treatment plants (WWTPs) treating concentrated wastewater, as higher concentrations result in higher heat generation in the treatment basin. A heat balance model has been applied to calculate the amount of recoverable heat from the system and the effect of the heat extraction capacity on the economics of a heat pump installation, evaluated using the internal rate of return. A sensitivity analysis has been performed to evaluate the effect of several parameters on the economics of heat recovery in this type of WWTP: the electricity price, the price of the fuel substituted by heating savings, the investment costs, the coefficient of performance (COP) and the amount of heat extracted from the system. It was calculated that the heat pump capacity has to be high enough to recover a significant amount of heat, but low enough to improve the economics of the system. The economic performance of the system is very dependent on the energy prices of both electrical power to run the heat pump and the fuel (heat) cost substituted by the heat pump.