J. Ruiz

Comparing the use of different domestic wastewaters for coupling microalgal production and nutrient removal.

The streams from municipal wastewater treatment plants (WWTP) have been considered a valuable medium for mass cultivation of algal biomass. The aim of this work is to test and compare the performance of Chlorella vulgaris on several streams from five stages, from two different WWTP. The results showed biomass yields ranging from 39 to 195mg dry-weightl(-1)days(-1). The best performance as biomass production was obtained with the centrate (effluent from drying the anaerobic sludge). After testing a wide range of N/P ratios with centrate, the highest productivity and growth rates were obtained with the original N/P ratio (2.0) of this stream. The highest removal rates were of 9.8 (N) and 3.0 (P) mgl(-1)days(-1), in the centrate. Finally, this research also suggests that microalgal production seems to be a promising process when coupled to wastewater treatment.

Performance of a flat panel reactor in the continuous culture of microalgae in urban wastewater: Prediction from a batch experiment

A laboratory-scale flat panel photobioreactor was operated for the continuous growth of Scenedesmus obliquus and consequent removal of nutrients in wastewater. This study develops a simple model by which biomass values in continuous operation can be predicted from kinetic growth parameters obtained from a shorter batch experiment. Based on this study, biomass concentrations and productivities in continuous operation can be successfully predicted as a function of the specific hydraulic retention time (HRT) assumed. Considerable biomass production and nutrient uptake from wastewater were achieved in the experiment. Optimum operating conditions for the reactor depend on the particular objective: the maximization of biomass production and carbon dioxide biofixation involves a HRT of 2 μ(-1) (specific growth rate), whereas efficient nutrient removal involves a HRT as close as possible to μ(-1) (as long as discharges comply fully with the parameters set); alternatively biomass intended for biodiesel or biogas production would involve a HRT > 2 μ(-1).

Effect of nitrogen and phosphorus concentration on their removal kinetic in treated urban wastewater by Chlorella vulgaris.

This study evaluates the feasibility of removing nutrients by the microalgae Chlorella vulgaris, using urban wastewater as culture medium, namely the effluent subjected to secondary biological treatment in a wastewater treatment plant (WWTP). For this, laboratory experiments were performed in batch cultures to study the effect of initial nitrogen and phosphorus concentrations on growth and reduction of nutrient performance of C. vulgaris. The microalga was cultivated in enriched wastewater containing different phosphorus (1.3– 143.5 mg · L−1 P-PO3− 4), ammonium (5.8–226.8 mg · L−1 N–NH+ 4) and nitrate (1.5– 198.3 mg · L−1 N–NO− 3) concentrations. The nutrient removal and growth kinetics have been studied: maximum productivity of 0.95 g SS · L−1 · day−1, minimum yield factor for cells on substrate (Y) of 11.51 g cells · g nitrogen−1 and 0.04 g cells · g phosphorus−1 were observed. The results suggested that C. vulgaris has a high potential to reduce nutrients in secondary WWTP effluents.

Photobiotreatment model (PhBT): a kinetic model for microalgae biomass growth and nutrient removal in wastewater

This article proposes a kinetic model for wastewater photobiotreatment with microalgae (the PhBT model). The PhBT model for nutrient uptake, coupled with the Verhulst growth model, is a simple and useful tool to describe batch experiments of nutrient removal by microalgae. The model has been validated with experiments of Chlorella vulgaris (C. vulgaris) grown in wastewater and different synthetic media. The model provided information about nitrogen and phosphorus limitation and their luxury uptake during the test. Productivity observed in synthetic medium (0.17 g SS L−1 d−1) was similar to that obtained in nutrient enriched wastewater (0.15 g SS L−1 d−1). Biomass productivity of this alga in wastewater and the efficient nutrient removal suggested that C. vulgaris could be cultured in wastewater for biomass production while nutrients are reduced from this stream.

PHOTOBIOTREATMENT: INFLUENCE OF NITROGEN AND PHOSPHORUS RATIO IN WASTEWATER ON GROWTH KINETICS OF SCENEDESMUS OBLIQUUS

Nitrogen and phosphorus concentration in the effluent of a wastewater treatment plant can vary significantly, which could affect the growth kinetic and chemical composition of microalgae when cultivated in this medium. The aim of this work was to study the rate of growth, nutrient removal and carbon dioxide biofixation as well as biomass composition of Scenedesmus obliquus (S. obliquus) when it is cultivated in wastewater at different nitrogen and phosphorus ratio, from 1:1 to 35:1. A more homogeneous method for calculating productivities in batch reactors was proposed. The proper N:P ratio for achieving optimum batch biomass productivity ranged between 9 and 13 (263 and 322 mg L−1 d−1 respectively). This was also the ratio range for achieving a total N and P removal. Above and below this range (9–13) the maximum biomass concentration changed, instead of the specific growth rate.The maximum carbon dioxide biofixation rate was achieved at N:P ratio between 13 and 22 (553 and 557 mg CO2 L−1 d−1 respectively). Lipid and crude protein content, both depend on the aging culture, reaching the maximum lipid content (34%) at the lowest N:P (1:1) and the maximum crude protein content (34.2%) at the highest N:P (35:1).

Influence of light presence and biomass concentration on nutrient kinetic removal from urban wastewater by Scenedesmus obliquus

This work was aimed at studying the effect of light-darkness and high-low biomass concentrations in the feasibility of removing nitrogen and phosphorus from urban treated wastewater by the microalga Scenedesmus obliquus. Laboratory experiments were conducted in batch, where microalgae were cultured under different initial biomass concentrations (150 and 1500mgSSl(-1)) and light conditions (dark or illuminated). Nutrient uptake was more dependent on internal nutrient content of the biomass than on light presence or biomass concentration. When a maximum nitrogen or phosphorus content in the biomass was reached (around 8% and 2%, respectively), the removal of that nutrient was almost stopped. Biomass concentration affected more than light presence on the nutrient removal rate, increasing significantly with its increase. Light was only required to remove nutrients when the maximum nutrient storage capacity of the cells was reached and further growth was therefore needed. Residence times to maintain a stable biomass concentration, avoiding the washout of the reactor, were much higher than those needed to remove the nutrients from the wastewater. This ability to remove nutrients in the absence of light could lead to new configurations of reactors aimed to wastewater treatment.

Chlorella stigmatophora for urban wastewater nutrient removal and CO2 abatement.

Batch experiments were performed to study biomass growth rate, nutrient removal and carbon dioxide bio-fixation of the marine microalgae Chlorella stigmatophora. Four different cultures at different salinities were tested: wastewater (WW), synthetic wastewater (SWW), seawater (SW) and diluted seawater (DSW). Experimental results showed that Chlorella stigmatophora grew satisfactorily in all culture media, except in SWW where inhibition occurred. In all cases, biomass experimental data were fitted to the Verlhust Logistic model (R2 > 0.982, p ≤ 0.05). Maximum biomass productivity (Pbmax ) and CO2 biofixation (PvCO2) were reached in the WW medium, 1.146 g SS·L−1·day−1 and 2.324 g CO2·L−1·day−1 respectively. The order of maximum specific growth rates (μmax) was WW >DSW>SW. In order to compare nitrogen and phosphorous removal kinetics, an estimation of the time required to reach the most restrictive concentration of total N and P in effluents as defined in the Directive 98/1565/CE (10 mg ΣN·L−1 (T10( N)) and 1 mg ΣP·L−1 (T1(P) ) was performed. In the WW test T10( N) and T1(P) needed were of 45.15 and 32.27 hours respectively and at the end of the experimental the removal was in both 100%.

Wastewater treatment and biodiesel production by Scenedesmus obliquus in a two-stage cultivation process.

The microalga Scenedesmus obliquus was cultured in two cultivation stages: (1) in batch with real wastewater; (2) maintaining the stationary phase with different conditions of CO2, light and salinity according to a factorial design in order to improve the lipid content. The presence of the three factors increased lipid content from 35.8% to 49% at the end of the second stage; CO2 presence presented the highest direct effect increasing lipid content followed by light presence and salt presence. The ω-3 fatty acids content increased with CO2 and light presence acting in isolation, nevertheless, when both factors acted together the interaction effect was negative. The ω-3 eicosapentaenoic acid content of the oil from S. obliquus slightly exceeded the 1% maximum to be used as biodiesel source (EU normative). Therefore, it is suggested the blend with other oils or the selective extraction of the ω-3 fatty acids from S. obliquus oil.

Vibrations inside buildings due to subway railway traffic. Experimental validation of a comprehensive prediction model

The present paper focuses on the experimental validation of a numerical approach previously proposed by the authors for the prediction of vibrations inside buildings due to railway traffic in tunnels. The numerical model is based on the concept of dynamic substructuring and is composed by three autonomous models to simulate the following main parts of the problem: i) generation of vibrations (train-track interaction); ii) propagation of vibrations (track-tunnel-ground system); iii) reception of vibrations (building coupled to the ground). The experimental validation consists in the comparison between the results predicted by the proposed numerical model and the measurements performed inside a building due to the railway traffic in a shallow tunnel located in Madrid. Apart from the brief description of the numerical model and of the case study, the main options and simplifications adopted on the numerical modeling strategy are discussed. The balance adopted between accuracy and simplicity of the numerical approach proved to be a path to follow in order to transfer knowledge to engineering practice. Finally, the comparison between numerical and experimental results allowed finding a good agreement between both, fact that ensures the ability of the proposed modeling strategy to deal with real engineering practical problems.

Optimization of pilot high rate algal ponds for simultaneous nutrient removal and lipids production

Special attention is required to the removal of nitrogen and phosphorous in treated wastewaters. Although, there are a wide range of techniques commercially available for nutrient up-take, these processes entail high investment and operational costs. In the other hand, microalgae growth can simultaneously remove inorganic constituents of wastewater and produce energy rich biomass. Among all the cultivation technologies, High Rate Algae Ponds (HRAPs), are accepted as the most appropriate system. However, the optimization of the operation that maximizes the productivity, nutrient removal and lipid content in the biomass generated has not been established. In this study, the effect of two levels of depth and the addition of CO2 were evaluated. Batch essays were used for the calculation of the kinetic parameters of microbial growth that determine the optimum conditions for continuous operation. Nutrient removal and lipid content of the biomass generated were analyzed. The best conditions were found at depth of 0.3m with CO2 addition (biomass productivity of 26.2gTSSm-2d-1 and a lipid productivity of 6.0glipidsm-2d-1) in continuous mode. The concentration of nutrients was in all cases below discharge limits established by the most restrictive regulation for wastewater discharge.