De aguas residuales a productos de valor: curvando la línea hacia la economía circular

El tratamiento de aguas residuales es una plataforma idónea para basar el desarrollo tecnológico enfocado al cambio de modelo productivo de economía circular. En este sistema moderno todos sus elementos excedentes se transforman en materia prima, que es incorporada de nuevo al sistema, lo cual implica potencialmente un concepto de emisión cero. Se hace un repaso de alternativas y proyectos desarrollados. Recientemente han surgido varias alternativas de tratamiento de aguas residuales basadas en este concepto de economía circular y desde el enfoque de biorrefinería

Urban wastewater treatment by seven species of microalgae and an algal bloom: Biomass production, N and P removal kinetics and harvestability

This study evaluates the capacity of seven species and a Bloom of microalgae to grow in urban wastewater. Nutrient removal kinetics and biomass harvesting by means of centrifugation and coagulation–flocculation-sedimentation have been also tested. Results show that the best biomass productivities ranged from between 118 and 108 mgSS L−1 d−1 for the Bloom (Bl) and Scenedesmus obliquus (Sco). Regarding nutrient removal, microalgae were able to remove the total dissolved phosphorus and nitrogen concentrations by more than 80% and 87% respectively, depending on the species tested. The final total dissolved concentration of nitrogen and phosphorus in the culture media complies with the European Commission Directive 98/15/CE on urban wastewater treatment. Regarding harvesting, the results of coagulation–flocculation sedimentation using a 60 mg L−1 dose of Ferric chloride were similar between species, exceeding the biomass removal efficiency by more than 90%. The results of centrifugation (time required to remove 90% of solids at 1000 rpm) were not similar between species, with the shortest time being 2.9 min for Sco, followed by the bloom (7.25 min). An overall analysis suggested that the natural bloom and Scenedesmus obliquus seem to be the best candidates to grow in pre-treated wastewater, according to their biomass production, nutrient removal capability and harvestability

Cinéticas de crecimiento y consumo de nutrientes de microalgas en aguas residuales urbanas con diferentes niveles de tratamiento

El objetivo principal de este trabajo ha sido el estudio de la velocidad de crecimiento y de consumo de nitrógeno y fósforo de un bloom de microalgas cultivadas en aguas residuales urbanas con diferente nivel y tipología de tratamiento. Para ello se han cultivado las microalgas por duplicado en discontinuo bajo condiciones controladas de temperatura, luz y aireación, en cuatro medios de ensayo, consistentes en cuatro aguas residuales: (1) salida de pretratamiento; (2) efluente de decantación secundaria; (3) efluente de un reactor anaerobio de flujo ascendente denominado UASB (Upflow Anaerobic Sludge Blanket), y finalmente, (4) mezcla de efluente del UASB y agua de secundario, todas de la misma estación depuradora de aguas residuales urbanas. La modelización cinética para el análisis de resultados con los modelos de Verhulst y el Photobiotreatment model indica una evolución temporal diferente de la concentración de biomasa, N y P total disuelto, respectivamente, en los diferentes medios de ensayo. La productividad es mayor en los ensayos con agua procedente del biorreactor UASB (0.094 g SS l-1 d-1). En este medio de cultivo, la velocidad de eliminación del nitrógeno no presenta diferencia con el resto de aguas residuales utilizadas en el ensayo, mientras que en el caso del fósforo, la eliminación es la menor de entre todos los medios estudiados

Capability of different microalgae species for phytoremediation processes: Wastewater tertiary treatment, CO2 bio-fixation and low cost biofuels production.

Scenedesmus obliquus, Chlorella vulgaris, Chlorella kessleri and a natural Bloom were cultivated in batch experiments, under controlled conditions, in urban wastewater (WW) and synthetic wastewater (SW) under 5% CO2 in air, with the object of estimating their capacity for nutrient removal, carbon dioxide biofixation, and generation of valuable biomass. In both culture media, the Bloom (Bl) and Scenedesmus (Sc) showed higher final biomass concentration (dried weight, dw) than the other species; the maximum yield obtained was 1950 ± 243 mg L−1 for Bl and the minimum 821 ± 88 mg L−1 for Cv, both in synthetic wastewater. Maximum specific growth rate values do not show significant differences between any of the 4 strains tested (p ≤ 0.05), nor between the 2 culture media. A new homogeneous method of calculating productivities has been proposed. Nitrogen removal in all the reactors was higher than 90%, except for BlSW (79%), and for phosphorus, the removal was higher than 98% in all trials. Maximum CO2 consumption rates reached were 424.4 and 436.7 mg L−1 d−1 for ScSW and ScWW respectively

Factorial analysis of the biokinetic growth parameters and CO2 fixation rate of Chlorella vulgaris and Botryococcus braunii in wastewater and synthetic medium

Microalgae strains, Botryococcus braunii and Chlorella vulgaris were cultured in urban wastewater as monoalgal cultures and together in co-cultures; the same experiments were performed in synthetic growth medium to establish comparisons between both media. A fully crossed factorial design was used to design and carry out the experiment, resulting in 18 tests, and this procedure allowed the development of regression models that defined experimental factors and their interactions. Results indicated that both strains were able to grow in wastewater, but productivities in this medium were halved respective to those obtained in the synthetic medium. Specific growth rates presented higher values in wastewater than in synthetic medium. B. braunii was the most productive strain, but when both strains were grown together in co-cultures C. vulgaris dominated the reactor. The use of microalgae in wastewater treatment systems demonstrates to minimize anthropogenic environmental pollution load and to generate valuable biomass

Performance evaluation of a control strategy for photosynthetic biogas upgrading in a semi-industrial scale photobioreactor

Producción CientíficaThe validation of a control strategy for biogas upgrading via light-driven CO2 consumption by microalgae and H2S oxidation by oxidizing bacteria using the oxygen photosynthetically generated was performed in a semi-industrial scale (9.6 m3) photobioreactor. The control system was able to support CO2 concentrations lower than 2% with O2 contents ≤ 1% regardless of the pH in the cultivation broth (ranging from 9.05 to 9.50). Moreover, the control system was efficient to cope with variations in biogas flowrate from 143 to 420 L h−1, resulting in a biomethane composition of CO2 95.5%, O2 < 1% and no H2S. Despite the poor robustness of this technology against failures in biogas and liquid supply (CH4 concentration of 67.5 and 70.9% after 2 h of biogas or liquid stoppage, respectively), the control system was capable of restoring biomethane quality in less than 2 h when biogas or liquid supply was resumed.Junta de Castilla y León y Programa Europeo FEDER (CLU 2017-09) y (UIC 071).European Union’s Horizon 2020 research and innovation programme under grant agreement No. 68924

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

Effect of ph control by means of flue gas addition on three different photo-bioreactors treating urban wastewater in long-term operation.

Effect of pH control with flue gas has been studied in two high rate algal ponds (HRAPs), one with a carbonation sump station (HRAP + S), and a tubular airlift photobioreactor (TPBR) treating urban wastewater. Flue gas, from 1600 MW combined cycle plant, addition (4–5% volume CO2) not only increased biomass productivity but also improved efficiency of total nitrogen removal (TNRE) and total phosphorus removal (TPRE). The differences between the HRAP and HRAP + S were significant at all the flue gas injection flow rates tested. HRAP + S reached maximum TNRE, TPRE and biomass productivity (92.15 ± 1.45%, 95.10 ± 0.84% and 19.77 ± 0.38 g m−2 d−1, respectively) at a flow rate of 15 L min−1, while the HRAP reached similar productivity levels at 20 L min−1. TPBR showed an initial lower carbon limitation than HRAP and HRAP + S, but nevertheless a strong inhibition was observed in TPBR at the end of the test. Flue gas addition promotes the production of biomass with less nitrogen reserves and consequently with higher lipid content because of the nutrient limitation stress

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

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