Parametric optimization of domestic wastewater treatment in an activated sludge sequencing batch reactor using response surface methodology.

In this work, the parametric optimization of real domestic wastewater treated in an activated sludge sequencing batch reactor (SBR) was performed by means of the response surface methodology (RSM). The influences of influent organic matter concentration as chemical oxygen demand (CODinf), biomass concentration (Xs) and aeration time (t) on the COD, organic matter removal efficiency as COD (η) and sludge volume index (SVI) were determined to evaluate the performance of activated sludge SBR. The results showed that organic matter efficiency and maximum SVI were obtained at a t of 12 h, 300 mg L-1 of CODinf and 2000 mg L-1 of Xs. The SBR-activated sludge exhibited a η of 73% and an SVI of 119 mL g-1. Both values indicated a very good performance. Furthermore, the COD of the effluent under these conditions complied with Mexican regulations for wastewater discharged into water bodies.

Biohydrogen, biomethane and bioelectricity as crucial components of biorefinery of organic wastes: a review.

Biohydrogen is a sustainable form of energy as it can be produced from organic waste through fermentation processes involving dark fermentation and photofermentation. Very often biohydrogen is included as a part of biorefinery approaches, which reclaim organic wastes that are abundant sources of renewable and low cost substrate that can be efficiently fermented by microorganisms. The aim of this work was to critically assess selected bioenergy alternatives from organic solid waste, such as biohydrogen and bioelectricity, to evaluate their relative advantages and disadvantages in the context of biorefineries, and finally to indicate the trends for future research and development. Biorefining is the sustainable processing of biomass into a spectrum of marketable products, which means: energy, materials, chemicals, food and feed. Dark fermentation of organic wastes could be the beach-head of complete biorefineries that generate biohydrogen as a first step and could significantly influence the future of solid waste management. Series systems show a better efficiency than one-stage process regarding substrate conversion to hydrogen and bioenergy. The dark fermentation also produces fermented by-products (fatty acids and solvents), so there is an opportunity for further combining with other processes that yield more bioenergy. Photoheterotrophic fermentation is one of them: photosynthetic heterotrophs, such as non-sulfur purple bacteria, can thrive on the simple organic substances produced in dark fermentation and light, to give more H2. Effluents from photoheterotrophic fermentation and digestates can be processed in microbial fuel cells for bioelectricity production and methanogenic digestion for methane generation, thus integrating a diverse block of bioenergies. Several digestates from bioenergies could be used for bioproducts generation, such as cellulolytic enzymes and saccharification processes, leading to ethanol fermentation (another bioenergy), thus completing the inverse cascade. Finally, biohydrogen, biomethane and bioelectricity could contribute to significant improvements for solid organic waste management in agricultural regions, as well as in urban areas.

The influence of total solids content and initial pH on batch biohydrogen production by solid substrate fermentation of agroindustrial wastes.

Hydrogen is a valuable clean energy source, and its production by biological processes is attractive and environmentally sound and friendly. In México 5 million tons/yr of agroindustrial wastes are generated; these residues are rich in fermentable organic matter that can be used for hydrogen production. On the other hand, batch, intermittently vented, solid substrate fermentation of organic waste has attracted interest in the last 10 years. Thus the objective of our work was to determine the effect of initial total solids content and initial pH on H2 production in batch fermentation of a substrate that consisted of a mixture of sugarcane bagasse, pineapple peelings, and waste activated sludge. The experiment was a response surface based on 2(2) factorial with central and axial points with initial TS (15-35%) and initial pH (6.5-7.5) as factors. Fermentation was carried out at 35 °C, with intermittent venting of minireactors and periodic flushing with inert N2 gas. Up to 5 cycles of H2 production were observed; the best treatment in our work showed cumulative H2 productions (ca. 3 mmol H2/gds) with 18% and 6.65 initial TS and pH, respectively. There was a significant effect of TS on production of hydrogen, the latter decreased with initial TS increase from 18% onwards. Cumulative H2 productions achieved in this work were higher than those reported for organic fraction of municipal solid waste (OFMSW) and mixtures of OFMSW and fruit peels waste from fruit juice industry, using the same process. Specific energetic potential due to H2 in our work was attractive and fell in the high side of the range of reported results in the open literature. Batch dark fermentation of agrowastes as practiced in our work could be useful for future biorefineries that generate biohydrogen as a first step and could influence the management of this type of agricultural wastes in México and other countries and regions as well.

Resistencia a la exposición al oxígeno de lodos anaerobios suspendidos / Oxygen exposure resistance in suspended anaerobic sludge

La tolerancia al oxígeno de una biomasa anaerobia suspendida en presencia o ausencia de un sustrato primario (sacarosa) se evaluó en términos de la recuperación de la actividad metanogénica aceticlástica especial (AME) de la biomasa anaerobia y un índice de inhibición 50 por ciento (II50) asociado a la AME. Incubada en presencia de sacarosa. La biomasa anaerobia suspendida mostró resistencia a la exposición al oxígeno; la recuperación de la AME fue >45 por ciento para [O²] iniciales <20 por ciento en el espacio gaseoso, y de 10 a 12 por ciento para [O²] iniciales >20 por ciento en el espacio gaseoso. Cuando fue incubada son fuente, la biomasa suspendida fue mucho más inhibida después de la exposición al oxígeno para [O²] iniciales >20 por ciento. El efecto inhibitorio fue descrito por un II50 elevado /28,6) en contraste con un bajo II50 (5,9) cuando se incubó en presencia de sacarosa. La tolerancia de la biomasa suspendida en este trabajo parece ser del mismo orden de la biomasa anaerobia inmovilizada (gránulos anaerobios) en condiciones de incubación en presencia de sustrato: los II50 fueron 5,9 para todos anaerobios suspendidos (sacarosa) y 5,3 y 2,4 para todos granulares incubados con acetato etanol, respectivamente. La respiración aerobia heterótrofa de los lodos anaerobio floculentos incubados con sacarosa fue cerca de 4 veces mayor que la respiración basal, y la inhibición de la AME descrita por el II50 parece seguir una relación inversa con la respiración aerobia heterótrofa. La relación inversa entre II50 y respiración aerobia heterótrofa se ajustó para datos de todos granulares en la literatura y todos floculentos de este trabajo, y sigue un modelo semi-empírico general, con un coeficiente de correlación de 0,82. Esta relación parece reforzar que uno de los mecanismos principales de protección de los consorcios anaerobios contra la inhibición por oxígeno es la respiración aerobia heterótrofa