Saúl Blanco

Long-term operation of high rate algal ponds for the bioremediation of piggery wastewaters at high loading rates.

The performance of two 464-L high rate algal ponds (HRAPs) treating 20- and 10-folds diluted swine manure at 10 days of hydraulic residence time was evaluated under continental climatic conditions in Castilla y Leon (Spain) from January to October. Under optimum environmental conditions (from July to September), both HRAPs supported a stable and efficient carbon and nitrogen oxidation performance, with average COD and TKN removal efficiencies of 76+/-11% and 88+/-6%, respectively, and biomass productivities ranging from 21 to 28 g/m(2)d. Nitrification was identified as the main TKN removal mechanism at dissolved oxygen concentrations higher than 2mg/L (accounting for 80-86% of the TKN removed from January to May and for 54% from July to September). On the other hand, empirical evidences of a simultaneous nitrification-denitrification process were found at dissolved oxygen concentrations lower than 0.5mg/L (high organic loading rates). However, despite the achievement of excellent COD and nitrogen oxidation performance, phosphorous removal efficiencies lower than 10% were recorded in both HRAPs probably due to the high buffer capacity of the piggery wastewater treated (absence of abiotic pH-mediated PO(4)(3-) precipitation). Finally, a detailed monitorization of the dynamics of microalgae population revealed that the combination of moderate temperatures/solar irradiances and high organic loading rates, prevailing during late spring and summer, supported higher microalgae diversities than those found during winter conditions.

A comparative evaluation of microalgae for the degradation of piggery wastewater under photosynthetic oxygenation

Two green microalgae (Scenedesmus obliquus and Chlorella sorokiniana), one cyanobacterium (Spirulina platensis), one euglenophyt (Euglena viridis) and two microalgae consortia were evaluated for their ability to support carbon, nitrogen and phosphorous removal in symbiosis with activated sludge bacteria during the biodegradation of four and eight times diluted piggery wastewater in batch tests. C. sorokiniana and E. viridis were capable of supporting the biodegradation of four and eight times diluted wastewater. On the other hand, while S. obliquus and the consortia isolated from a swine manure stabilization pond were only able to grow in eight times diluted wastewater, S. platensis and the consortium isolated from a high rate algal pond treating swine manure were totally inhibited regardless of the dilution applied. TOC removal efficiencies (RE) ranging from 42% to 55% and NH(4)(+)-RE from 21% to 39% were recorded in the tests exhibiting photosynthetic oxygenation. The similar oxygen production rates exhibited by the tested microalgae under autotrophic conditions (from 116 to 133mgO(2)L(-1)d(-1)) suggested that factors other than the photosynthetic oxygenation potential governed piggery wastewater biodegradation. Microalgal tolerance towards NH(3) was hypothesized as the key selection criterion. Further studies in a continuous algal-bacterial photobioreactor inoculated with C. sorokiniana, S. obliquus and S. platensis showed that C. sorokiniana, the species showing the highest NH(3)-tolerance, rapidly outcompeted the rest of the microalgae during the biodegradation of eight times diluted wastewater, achieving TOC and NH(4)(+)-RE comparable to those recorded in the batch biodegradation tests.

Distribution, ecology and nuisance effects of the freshwater invasive diatom Didymosphenia geminata (Lyngbye) M. Schmidt: a literature review.

Abstract: The diatom Didymosphenia geminata (Lyngbye) M.Schmidt has been commonly considered a taxon restricted to pristine habitats in mountainous areas of circumboreal regions. Recent studies show that it has a broader distribution and ecological amplitude. This shift seems to have occurred recently, as it now forms large growths in rivers within its native geographical area (North America, Europe) but also mass developments have recently appeared in New Zealand, where it is considered an aggressive invasive species with dramatic ecological and economic impacts. This nuisance organism grows attached in streambeds and may impact freshwater fish and aquatic plants and insects, causing severe disturbance in food webs. This paper investigates the historic and current biogeographic range of this invasive species (and varieties) based on 1000 citations collected mainly from the scientific literature. The locations where this diatom has appeared, including both fossil and recent records, are presented in world distribution maps. Our results confirm that the native range of D. geminata is almost restricted to the Holarctic region, though its distribution area is broader than usually reported in the literature. The ecological profile of this alga, along with its nuisance effects, is also discussed. Excessive growths do not only appear in areas where this species is presumably exotic. Contrarily to general statement, reports of mass developments of D. geminata date back to the 19th century. World references to D. geminata have increased exponentially during the last decades; however; with respect to the whole diatom literature during the XIX and XX centuries, the relative frequency of citations has decreased progressively.

Influence of flue gas sparging on the performance of high rate algae ponds treating agro-industrial wastewaters.

The influence of flue gas sparging (7% CO(2)) on the performance of two 465 L High-Rate Algal Ponds (HRAPs) treating diluted swine manure at 10 days of hydraulic retention time was evaluated under continental climatic conditions (Castilla y León, Spain). COD, NH(4)(+), and PO(4)(3-) removal efficiencies were not significantly affected by flue gas input (at 2.2 and 5.5 L min(-1)), which suggests that CO(2) sparging does not compromise wastewater treatment in HRAPs. In this particular study, COD and NH(4)(+) removal efficiencies of 56+/-31% (near to maximum swine manure biodegradability) and 98+/-1%, respectively, were consistently maintained, regardless of the environmental and operational conditions. CO(2) sparging resulted however in lower pH values (approximately 2 units lower) and an enhanced NH(4)(+) nitrification (higher NO(3)(-) and NO(2)(-) concentrations) compared to the system operated in the absence of flue gas supply. Biomass concentration was only higher (approximately 30% than in the control HRAP) when flue gases were supplied at 5.5 L min(-1), probably due to the fact that the higher irradiances and temperatures prevailing within this experimental period resulted in an inorganic carbon-limited scenario in the control HRAP. Therefore, it can be concluded that CO(2) assimilation would be ultimately dependent on the occurrence of inorganic carbon limitation and will never occur in light, COD or nutrients-limited scenarios.

Influence of Biogas Flow Rate on Biomass Composition During the Optimization of Biogas Upgrading in Microalgal-Bacterial Processes

The influence of biogas flow rate (0, 0.3, 0.6, and 1.2 m(3) m(-2) h(-1)) on the elemental and macromolecular composition of the algal-bacterial biomass produced from biogas upgrading in a 180 L photobioreactor interconnected to a 2.5 L external bubbled absorption column was investigated using diluted anaerobically digested vinasse as cultivation medium. The influence of the external liquid recirculation/biogas ratio (0.5 < L/G < 67) on the removal of CO2 and H2S, and on the concentrations of O2 and N2 in the upgraded biogas, was also evaluated. A L/G ratio of 10 was considered optimum to support CO2 and H2S removals of 80% and 100%, respectively, at all biogas flow rates tested. Biomass productivity increased at increasing biogas flow rate, with a maximum of 12 ± 1 g m(-2) d(-1) at 1.2 m(3) m(-2) h(-1), while the C, N, and P biomass content remained constant at 49 ± 2%, 9 ± 0%, and 1 ± 0%, respectively, over the 175 days of experimentation. The high carbohydrate contents (60-76%), inversely correlated to biogas flow rates, would allow the production of ≈100 L of ethanol per 1000 m(3) of biogas upgraded under a biorefinery process approach.

Consistency in Diatom Response to Metal-Contaminated Environments

Diatoms play a key role in the functioning of streams, and their sensitivity to many environmental factors has led to the development of numerous diatom-based indices used in water quality assessment. Although diatom-based monitoring of metal contamination is not currently included in water quality monitoring programs, the effects of metals on diatom communities have been studied in many polluted watersheds as well as in laboratory experiments, underlying their high potential for metal contamination assessment. Here, we review the response of diatoms to metal pollution from individual level (e.g. size, growth form, and morphological abnormalities) to community structure (replacement of sensitive species by tolerant ones). These potential effects are then tested using a large, multi-country database combining diatom and metal information. Metal contamination proved to be a strong driver of the community structure, and enabled for the identification of tolerant species like Cocconeis placentula var. euglypta, Eolimna minima, Fragilaria gracilis, Nitzschia sociabilis, Pinnularia parvulissima, and Surirella angusta. Among the traits tested, diatom cell size and the occurrence of diatom deformities were found to be good indicators of high metal contamination. This work provides a basis for further use of diatoms as indicators of metal pollution.

Are biotic indices sensitive to river toxicants? A comparison of metrics based on diatoms and macro-invertebrates.

Biotic indices based on macro-invertebrates and diatoms are frequently used to diagnose ecological quality in watercourses, but few published works have assessed their effectiveness as biomonitors of the concentration of micropollutants. A biological survey performed at 188 sites in the basin of the River Duero in north-western Spain. Nineteen diatom and six macro-invertebrate indices were calculated and compared with the concentrations of 37 different toxicants by means of a correlation analysis. Several chemical variables analysed correlated significantly with at least one biotic index. Sládeceks diatom index and the number of macro-invertebrate families exhibited particularly high correlation coefficients. Methods based on macro-invertebrates performed better in detecting biocides, while diatom indices showed stronger correlations with potentially toxic elements such as heavy metals. All biotic indices, and particularly diatom indices, were especially sensitive to the concentration of fats and oils and trichloroethene.

Identification versus counting protocols as sources of uncertainty in diatom-based ecological status assessments

In 2009, seventeen analysts participated in a pan-European diatom ring-test (intercalibration), analyzing nine samples from seven countries following the European standard EN 14407. The objective of this exercise was to agree on practical conventions on diatom identification to facilitate future intercalibration work and to assess the extent to which national differences in sample analysis (counting protocol and identification conventions) contribute to variability in EU-level comparisons of diatom-based methods. Differences in the reported taxa lists were large, but not a major source of variation in values of a common metric (the phytobenthos Intercalibration Common Metric, ICM). Therefore, every country can apply its own identification conventions for national assessments, and still be fairly confident that the ICM reflects the national classification of its streams. Part of the index variation was due to differences in counting protocols and care should be taken when handling broken valves, girdle views and small taxa. More work at both national and European level is needed to provide a harmonized way of using diatoms for ecological status assessments in the future.

Evaluation of wastewater treatment in a novel anoxic-aerobic algal-bacterial photobioreactor with biomass recycling through carbon and nitrogen mass balances.

Algal-bacterial symbiosis, implemented in an innovative anoxic-aerobic photobioreactor configuration with biomass recycling, supported an efficient removal of total organic carbon (86-90%), inorganic carbon (57-98%) and total nitrogen (68-79%) during synthetic wastewater treatment at a hydraulic and sludge retention times of 2 days and 20 days, respectively. The availability of inorganic carbon in the photobioreactor, determined by its supply in the wastewater and microalgae activity, governed the extent of nitrogen removal by assimilation or nitrification-denitrification. Unexpectedly, nitrate production was negligible despite the high dissolved oxygen concentrations, denitrification being only based on nitrite reduction. Biomass recycling resulted in the enrichment of rapidly settling algal flocs, which supported effluent total suspended solid concentrations below the European Union maximum discharge limits. Finally, the maximum nitrous oxide emissions recorded were far below the emission factors reported for wastewater treatment plants, confirming the environmental sustainability of this innovative photobioreactor in terms of global warming impact.

Protease cell wall degradation of Chlorella vulgaris: Effect on methane production

In order to optimize the enzymatic dosage and microalgae biomass loads subjected to enzymatic hydrolysis prior anaerobic digestion of Chlorella vulgaris, organic matter solubilisation and methane production were investigated. Experimental data using protease dosage of 0.585 AU g DW(-1) showed that increasing biomass loads up to 65 g L(-1) did not affect markedly the hydrolysis efficiency (51%). Enzymatically pretreated biomasses subjected to anaerobic digestion enhanced methane production by 50-70%. The attempt of decreasing the enzymatic dosages revealed diminished hydrolysis efficiency concomitantly with a decreased methane production enhancement. In agreement with the good results observed for organic matter conversion into biogas, total nitrogen mineralization was attained for enzymatically pretreated biomass. Despite the high protein content of the biomass and the biocatalyst used in the present study no ammonia inhibition was detected.