José Zavala-Loría

A two-stage culture process using Chlorella vulgaris for urban wastewater nutrient removal and enhanced algal lipid accumulation under photoautotrophic and mixotrophic conditions

Microalgae such as Chlorella vulgaris contain sufficient fatty acids to suggest their use as feedstocks for biodiesel production. Their capacity to remove nitrogen, phosphate, and other nutrients from a culture medium makes them a potentially useful element in urban wastewater treatment systems. A two-stage process was used to grow Chlorella vulgaris under mixotrophic and autotrophic conditions in artificial wastewater and urban wastewater media. Growth rate, nutrient removal, and lipids accumulation were quantified. Initially, the media were nitrogen-enriched (90 mg−1; Stage I), and then nitrogen limited (30, 20, and 10 mg l−1; Stage II). Growth was not inhibited under either of the culture conditions, and nitrogen uptake rates were above 90%. Total organic carbon removal was higher (56.2%–86%) under mixotrophic conditions than under photoautotrophic conditions (15.2%–69%). Lipids productivity was 2.7 times higher under mixotrophic conditions and nitrogen limitation than under photoautotrophic conditions...

Variation on the Fluxes of Nutrients in an Urban Lagoon by Seasonal Effects and Human Activities

This document to examine the changes occurred in the flux of nutrients and NEM during dry season and rainy + north wind season in the Caleta system located within the Terminos lagoon natural reserve which presents negative impacts caused by discharges of urban wastewater. Salinity, dissolved oxygen, chlorophyll a, nitrogen and phosphorus were monitored during nine months considering the dry, rainy and north wind season. Storms caused sediment disturbances which increased the amount of nutrients into the Caleta system as well as the phytoplankton production (25 mg m-3). The system shows longer times of water renovation during the summer (21 d) unlike (6 d) during the rainy + north wind season. On one hand, the ΔDIP values during dry season (0.0049 μmol m-2 d-1), establishes the system as producer and exporter of DIP into the ocean; on the other hand, the ΔDIP during rainy + north wind seasons (-0.0039 μmol m-2 d-1) suggests the importation of phosphorus from the ocean. Likewise, the system exports DIN (0.0031 μmol m-2 d-1) during the summer and imports DIN (-0.0048 μmol m-2 d-1), during the rainy + north wind seasons. The negative values of fixation-denitrification and NEM during the summer turn the system into a nitrogen sink. Seasonal changes were present in the system, dominated by heterotrophic NEM during summer with higher nitrogen fixation; while an autotrophic NEM dominated during winter.

Productivity and Biodiesel Quality of Fatty Acids Contents from Scenedesmus obliquus in Domestic Wastewater Using Phototrophic and Mixotrophic Cultivation Systems

RESEARCH ARTICLE Productivity and Biodiesel Quality of Fatty Acids

Batch Distillation: Thermodynamic Efficiency

The batch distillation is a separation processes that requires great amounts of energy. Due to high energy costs, the study of energy consumption is of great interest in this process (Zavala et al. 2007). According to Luyben (1990), the energy consumption increases when operation occurs in a batch manner. Determining how efficient is the heat transfer under specific conditions and to modify them in order to find how efficient the heat is used, is an important task.