Bioprospecting of wild type ethanologenic yeast for ethanol fuel production from wastewater-grown microalgae.

BACKGROUND: Wild-type yeasts have been successfully used to obtain food products, yet their full potential as fermenting microorganisms for large-scale ethanol fuel production has to be determined. In this study, wild-type ethanologenic yeasts isolated from a secondary effluent were assessed for their capability to ferment saccharified microalgae sugars. RESULTS: Yeast species in wastewater were identified sequencing the Internal Transcribed Spacers 1 and 2 regions of the ribosomal cluster. Concurrently, microalgae biomass sugars were saccharified via acid hydrolysis, producing 5.0 ± 0.3 g L-1 of fermentable sugars. Glucose consumption and ethanol production of yeasts in hydrolyzed-microalgae liquor were tested at different initial sugar concentrations and fermentation time. The predominant ethanologenic yeast species was identified as Candida sp., and glucose consumption for this strain and S. cerevisiae achieved 75% and 87% of the initial concentration at optimal conditions, respectively. Relatively similar ethanol yields were determined for both species, achieving 0.45 ± 0.05 (S. cerevisiae) and 0.46 ± 0.05 g ethanol per g glucose (Candida sp.). CONCLUSION: Overall, the results provide a first insight of the fermentation capacities of specific wild-type Candida species, and their potential role in ethanol industries seeking to improve their cost-efficiency.

Harvesting microalgae using ozone-air flotation for recovery of biomass, lipids, carbohydrates, and proteins.

The objective of this research was to study a novel ozone-air flotation microalgae harvesting method and evaluate its effect on the recovery of biomass and biocomponents (lipids, carbohydrates, proteins). Best processing conditions were established using a response surface methodology (RSM). Microalgae separation and biocomponent recovery were evaluated according to changes in gas concentration (13, 18 and 25 mgO3/L), ozone dose (0.04, 0.09 and 0.16 mg O3/mg biomass) and airflow rate (0.5, 1.0 and 1.5 L/min). More than 95% of the biomass was recovered from wastewater at an ozone-air combination of 0.09 mgO3/mg biomass and 1.5 L air/min. Using ozone-air represented a reduction of 59% in the ozone dose compared to the flotation process solely using ozone (0.22 mgO3/mg biomass). In addition, there was an improved yield in the recovery of all microalgae biocomponents. A maximum yield of 0.18 mg lipids/mg biomass was achieved at: 0.16 mg O3/mg biomass, 25 mg gas O3/L and 1.5 L air/min. In conclusion, combining the use of ozone-air for separation of microalgae reduces ozone requirement and enhances lipids and proteins post-extraction.

Development of bioplastics from a microalgae consortium from wastewater.

Nowadays, as the world population is in need of creating alternative materials that can replace conventional plastics, microalgae biomass may be identified as a viable source for producing more environmentally friendly materials. Scenedesmus sp and Desmodesmus sp are the main components (~80%) of a microalgae consortium (MC) that first has been used to remove Nitrogen and Phosphorus from wastewater. The potential to develop bioplastic materials from MC considering its relatively high protein content (~48%) has been assessed in the present manuscript, using as a reference a commercial biomass rich an Arthrospira specie (AM) also present in the studied consortium. Bioplastics were obtained through injection moulding of blends obtained after mixing with different amounts of glycerol, and eventually characterized using Dynamic Mechanical Thermal Analysis (DMTA), water immersion and tensile tests. All bioplastics displayed a glass transition temperature around 60 °C, showing a thermoplastic behavior which is less pronounced in the CM based bioplastics. This would imply a greater thermal resistance of bioplastics produced from the biomass harvested in wastewater. Moreover, these bioplastics showed a lower ability to absorb water when immersed, due to the lower deformability displayed in the tensile tests. The mechanical properties of all samples, independently of the nature of the biomass, were improved when the presence of the biomass was higher. Therefore, results here presented prove the potential of valorisation of microalgae consortia used in the effective treatment of wastewater through the development of bioplastic materials.

Final opportunity to rehabilitate an urban river as a water source for Mexico City.

The aim of this study was to evaluate the amount and quality of water in the Magdalena-Eslava river system and to propose alternatives for sustainable water use. The system is the last urban river in the vicinity of Mexico City that supplies surface water to the urban area. Historical flow data were analyzed (1973-2010), along with the physicochemical and bacteriological attributes, documenting the evolution of these variables over the course of five years (2008-2012) in both dry and rainy seasons. The analyses show that the flow regime has been significantly altered. The physicochemical variables show significant differences between the natural area, where the river originates, and the urban area, where the river receives untreated wastewater. Nutrient and conductivity concentrations in the river were equivalent to domestic wastewater. Fecal pollution indicators and various pathogens were present in elevated densities, demonstrating a threat to the population living near the river. Estimates of the value of the water lost as a result of mixing clean and contaminated water are presented. This urban river should be rehabilitated as a sustainability practice, and if possible, these efforts should be replicated in other areas. Because of the public health issues and in view of the population exposure where the river flows through the city, the river should be improved aesthetically and should be treated to allow its ecosystem services to recover. This river represents an iconic case for Mexico City because it connects the natural and urban areas in a socio-ecological system that can potentially provide clean water for human consumption. Contaminated water could be treated and reused for irrigation in one of the green areas of the city. Wastewater treatment plants and the operation of the existing purification plants are urgent priorities that could lead to better, more sustainable water use practices in Mexico City.