In this study single-chamber microbial electrolysis cells (MECs) were applied to treat cheese whey (CW), an industrial by-product, and recover H gas. Firstly, this substrate was fed directly to the MEC to get the initial feedback about its H generation potential. The results indicated that the direct application of CW requires an adequate pH control to realize bioelectrohydrogenesis and avoid operational failure due to the loss of bioanode activity. In the second part of the study, the effluents of anaerobic (methanogenic) digester and hydrogenogenic (dark fermentative H-producing) reactor utilizing the CW were tested in the MEC process (representing the concept of a two-stage technology). It turned out that the residue of the methanogenic reactor - with its relatively lower carbohydrate- and higher volatile fatty acid contents - was more suitable to produce hydrogen bioelectrochemically. The MEC operated with the dark fermentation effluent, containing a high portion of carbohydrates and low amount of organic acids, produced significant amount of undesired methane simultaneously with H. Overall, the best MEC behavior was attained using the effluent of the methanogenic reactor and therefore, considering a two-stage system, methanogenesis is an advisable pretreatment step for the acidic CW to enhance the H formation in complementary microbial electrohydrogenesis.

BACKGROUND: Centrate treatment using microalgal-bacterial processes might be limited by the hydraulic retention time (HRT) required to achieve satisfactory chemical oxygen demand (COD) and nutrients removal. Moreover, the poor settling of microalgal biomass still limits the technical and economic performance of microalgal-bacterial processes. In this work, the performance of microalgal-bacterial aggregates (MABAs) supplied with flue gas was investigated as an effective strategy to improve the treatment of centrate from anaerobic digestion of winery wastewater. RESULTS: MABAs supplied with flue gas achieved maximum soluble COD, N-NO 3− , P-PO 4 3− and N-NH 4 + removal efficiencies of 95%, 94%, 100%, and 100%, respectively, in five-fold centrate dilution within 7 days of operation. Centrate turbidity or its components did not hinder the performance of the MABAs under the conditions tested and no aggregates were formed in controls without MABAs inoculation. The mean diameter of the MABAs after centrate treatment was the same or even larger than that of the aggregates of the inoculum. Scanning electron microscopy analyses showed that the liquid medium composition influenced the structure and the type of microalgae cells established in the MABAs. CONCLUSION: MABAs-based centrate treatment supported by flue gas is a promising technology for improving COD and nutrients removal from centrate as well as further biomass harvesting.

La cinética microbiana y enzimática son factores importantes durante la degradación aerobia de la fracción orgánica de los residuos sólidos urbanos, estas dependen principalmente de la temperatura de incubación y las tasas de aireación. El objetivo de esta investigación fue evaluar el proceso de degradación aerobia, por múltiples variables y su combinación para comprender las interacciones entre las tasas de aireación en la degradación aerobia y sus respuestas. Las tasas de aireación se fijaron en 0.032, 0.064, 0.125, 0.251 y 0.392 L de aire húmedo kg-1 min-1 a 35 °C con inóculo. La actividad microbiana se evaluó de forma indirecta por medio de la respirometria; es decir, la generación de CO2 y el consumo de O2. Las actividades enzimáticas extracelulares (es decir, pectinasas, celulasas, xilanasas y proteasas) se cuantificaron mediante la liberación de los azúcares reductores. Los diferentes ensayos se realizaron en la Universidad Autónoma Metropolitana Unidad Iztapalapa en septiembre de 2019. Encontrando una fuerte relación positiva entre la actividad enzimática xilanasa y pectinasa con la pérdida de peso en seco, junto con el aumento de las actividades celulasas y xilanasas a mayores tasas de aireación.