Leopoldo Mendoza-Espinosa

Growth and nutrient removal in free and immobilized green algae in batch and semi-continuous cultures treating real wastewater

Two species of microalgae growing as immobilized and free-cells were compared to test its ability to remove N and P in batch cultures of urban wastewater. The best microalgae-cell growth configuration was selected to be tested in bioreactor operated in semi-continuous mode. Scenedesmus obliquus showed a higher N and P uptake rate in urban wastewater than Chlorella vulgaris. When tested in semi-continuous mode and with the re-calcification of beads, S. obliquus was more effective in removing N and P for longer periods (181 h) than batch cultures; fecal coliforms removal was good (95%) although the final concentration was still unsuitable for discharge to natural water bodies. Protein and lipids content analysis suggest that, from a practical point of view, immobilized systems could facilitate the separation of the biomass from the treated wastewater although in terms of nutritional value of the biomass, immobilized systems do not represent an advantage over free-cell systems.

A comparison of floating and sunken media biological aerated filters for nitrification

The versatility of the biological aerated filter (BAF) has made it an important process in wastewater treatment. These submerged three-phase fixed media reactors have been used in a wide variety of applications in wastewater treatment, such as primary treatment (solids removal), secondary treatment (COD and BOD removal), and tertiary treatment (nitrification). The aim of this work was to investigate the biological start-up of two such reactors to remove suspended solids (SS), total COD (tCOD) and ammonia, one containing a sunken medium (relative density 1·05) and the other containing a floating medium (relative density 0·92), both identical in shape and size. The reactors (0·054 m3 media) were run in parallel in upflow mode using secondary effluent as the process liquid at a flowrate of 0·2 dm3 min−1 and air: liquid ratio of 10:1. Overall, floating media performed better than sunken media for SS, tCOD and ammonia removal, probably due to the compression of the bed due to the buoyancy force of the media and the flow of air and liquid acting upwards. Bed compression improved solids removal and appeared to have promoted the growth of bacteria. Temperature had a greater impact on nitrification than on carbonaceous matter removal. The floating medium reactor was more resistant to low temperature shocks than the sunken medium reactor but the latter showed a faster recovery time as temperature increased. Although the backwashing frequency used was satisfactory, performance may have improved if the backwashing had been carried out only when reactor performance began to decline. Nitrification was shown to follow a reaction rate between zero and half order. Thus, ammonia removal was generally independent of ammonia concentration and more affected by the presence of carbonaceous matter.

Virtues of simple hydro-economic optimization: Baja California, Mexico.

This paper uses simple hydro-economic optimization to investigate a wide range of regional water system management options for northern Baja California, Mexico. Hydro-economic optimization models, even with parsimonious model formulations, enable investigation of promising water management portfolios for supplying water to agricultural, environmental and urban users. CALVIN, a generalized hydro-economic model, is used in a case study of Baja California. This drought-prone region faces significant challenges to supply water to agriculture and its fast growing border cities. Water management portfolios include water markets, wastewater reuse, seawater desalination and infrastructure expansions. Water markets provide the flexibility to meet future urban demands; however conveyance capacity limits their use. Wastewater reuse and conveyance expansions are economically promising. At current costs desalination is currently uneconomical for Baja California compared to other alternatives. Even simple hydro-economic models suggest ways to increase efficiency of water management in water scarce areas, and provide an economic basis for evaluating long-term water management solutions.

The effect of reclaimed wastewater on the quality and growth of grapevines.

The effect of the use of treated wastewater on the growth of cabernet sauvignon and merlot grapes from the Guadalupe Valley, Mexico was evaluated. Secondary advanced effluent was used to irrigate the grapevines at a rate of 66 L/vine/week. Wastewater quality results confirmed that all parameters complied with Mexican legislation for crop irrigation as well as reuse in activities in which the public would be in direct or indirect contact with the reclaimed water. Results showed that the number of leaves per shoot and the overall biomass increased in plants irrigated with wastewater and grape production per plant was 20% higher. The concentration of carbohydrates, organic acids and pH were similar in grapes from vines irrigated with wastewater to those irrigated with groundwater. Throughout the experiment, no fecal coliform bacteria were detected in the cultivated grapes. The wastewater caused an increase in the biomass of the grapevines and there was no presence of microbial indicators in the final product so a higher wine production could be achieved without an increase in health risk related problems. If 200 L/s of reclaimed wastewater would be returned to be used for grapevine irrigation in Valle de Guadalupe (the same amount that is currently being sent as drinking water to Ensenada), assuming an irrigation application of 6,000-7.500 m3/ha/year, approximately 837-1046 hectares (ha) of grapevines could be irrigated. Part of ongoing research includes an economical analysis of the best options for Ensenada and the Valle de Guadalupe in order to establish the optimum volume of water to be returned, the cost of its transportation, as well as the cost of irrigation.

Organic and Hydraulic Shock Loadings on a Biological Aerated Filter

The performance of a biological aerated filter (BAF) during short-term (60 min) organic and hydraulic shock loads was investigated. The BAF used for the present experiment was not capable of absorbing high peak organic shock loads when the organic loads were increased from a normal load of 1.2–1.4 kg soluble chemical oxygen demand (sCOD) m−3 d−1 to shock loads between 5.1– 7.3 kg sCOD m−3 d−1, based on empty bed volumes. Nevertheless, the effect on the biomass was limited as normal performance resumed very quickly. Increases in the hydraulic velocity from 0.7–1.0 m h−1 to 1.5–2.9 m h−1 had little effect on BAF performance in terms of soluble COD removal. Yet, sCOD effluent concentrations of <55 mg l−1 (~22 mg l−1 biochemical oxygen demand) were always achieved. The recovery of the reactor in both cases was fast, resuming normal performance within 60 min after the application of the shock load.

A Process Model to Evaluate the Performance of a Biological Aerated Filter

The biological aerated filter (BAF) is a three-phase reactor for waste water treatment that uses granular medium for biomass support. The parameter values from a process model for soluble COD were used to evaluate the impact of the medium characteristics and the process configuration on the performance of the BAF. In terms of reactor performance, the flow direction was more important than the medium characteristics. The results confirmed the applicability of the model.

Multi-tiered approach utilizing microbial source tracking and human associated-IMS/ATP for surveillance of human fecal contamination in Baja California, Mexico

As both the need for reuse of reclaimed wastewater and the burden placed on existing wastewater treatment plants increase, so does the need for methods that can reliably, rapidly and economically identify human-associated contamination. A survey of surface water quality was conducted in Baja California, Mexico where inadequate infrastructure or its inefficient operation leads to poor water quality. The HF183 and Bacteroides thetaiotaomicron (B. theta) human-associated gene markers were detected in 84% and 82% of samples collected during dry weather, illustrating evidence of widespread human fecal contamination. In addition, an inversely-coupled (Inv-IMS/ATP) viability-based assay for detection of B. theta was developed and applied for rapid detection and screening of human-associated fecal contamination. The Inv-IMS/ATP assay was able to effectively differentiate between surface waters impacted with human fecal contamination, and B. theta levels measured by Inv-IMS/ATP were highly correlated with HF183 and B. theta human marker measurements (r = 0.76; r = 0.82) in complex surface water samples. In areas with widespread human fecal contamination and limited access to more expensive methods, a multi-pronged approach utilizing a combination of methods including the Inv-IMS/ATP assay for rapid evaluation and screening of surface water quality alongside human-associated genetic markers may improve risk assessment and surveillance capabilities.