Mineralogical evidence of unfavorable geochemical interactions between urban runoff pollutants and filter materials in low-impact systems.

We report on the geochemical interactions between a synthetic urban runoff (SUR) and the minerals of materials used in a multi-layered column filter (soil, sand, gravel, and tezontle) at the laboratory scale, which mimicked an unvegetated low-impact development (LID) system. After five 8 h infiltration cycles using the SUR, the average concentrations of Pb and Mn decreased slightly at the column outlet, as did HCO3-, SO42-, and Na+, whereas Mg increased and Cl-, Ca2+, and K+ were only detected at the outlet. The filter materials were comprised of silicates, Mn-bearing oxides (hausmannite and manganite), carbonates (calcite), chlorides (sylvite), and sulfates (anglesite, lanarkite, barite, and epsomite). PHREEQC modeling allowed the identification of the geochemical processes that occurred in the filter. The results showed the removal capacity of the filter materials through the formation of secondary minerals such as rhodochrosite (MnCO3) and the over-saturation of anglesite (PbSO4), and also showed that they may mobilize ions from the upper to the interior layers (as Mg2+ from epsomite, MgSO4·7H2O, and Ba2+ from barite, BaSO4). We highlight the importance of knowing the geological nature of filter materials used in LID systems because they may lead to the geogenic mobilization of toxic contaminants to the environment.

Effect of photocatalytic Fe2O3 nanoparticles on urban runoff pollutant removal by permeable concrete.

Permeable pavements are an efficient urban runoff (UR) management solution that also improve water quality. In this work, a photocatalytic layer of Fe2O3 nanoparticles (NP) was incorporated into permeable concrete to evaluate its impact on the removal of several microbiological (Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, and Enterococcus faecalis) and physicochemical (N-NH4+, N-NO3-, phenol, PO43-, Fe, Mn, and Pb) pollutants. First, permeable concrete samples were created with sufficient compressive strength and hydraulic conductivity for light traffic. The test samples were then coated with a mixture containing either 3% or 5% Fe2O3 NP by cement weight. Control samples were prepared without NP. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy analyses showed that the nanoparticles remained unaltered on the concrete's surface. Synthetic URs simulating the microbiological or physicochemical composition of real UR were applied to the samples to evaluate their pollutant removal efficiencies. The depollution performances of the test (with 3% and 5% Fe2O3 NP) and control samples were statistically compared. The test samples (3% NP, 5% NP, and the controls) significantly modified (p < 0.05) most of the measured variables (i.e., the concentrations of E. coli, A. hydrophila, PO43-, Fe, Mn, and Pb) in the synthetic URs. Unexpectedly, the test samples (with 3% or 5% Fe2O3 NP) did not significantly remove (p > 0.05) some pollutants prone to oxidation, such as phenol or ammonium. However, the 5% NP sample significantly enhanced Mn removal. In general, the decontamination performances of the concrete samples with Fe2O3 NP were not influenced by the nanoparticles; thus, they did not appear to add value to the generated permeable concrete. Nevertheless, our results indicate the considerable benefits of implementing permeable concrete to improve the quality of UR.

Effectiveness of rabbit manure biofertilizer in barley crop yield.

The quality of biofertilizers is usually assessed only in terms of the amount of nutrients that they supply to the crops and their lack of viable pathogens and phytotoxicity. The goal of this study was to determine the effectiveness of a liquid biofertilizer obtained from rabbit manure in terms of presence of pathogens, phytotoxicity, and its effect on the grain yield and other agronomic traits of barley (Hordeum vulgare L.). Environmental effects of the biofertilizer were also evaluated by following its influence on selected soil parameters. We applied the biofertilizer at five combinations of doses and timings each and in two application modes (foliar or direct soil application) within a randomized complete block design with three replicates and using a chemical fertilizer as control. The agronomic traits evaluated were plant height, root length, dry weight, and number of leaves and stems at three growth stages: tillering, jointing, and flowering. The effectiveness of the biofertilizer was significantly modified by the mode of application, the growth stage of the crop, and the dose of biofertilizer applied. The results showed that the foliar application of the biofertilizer at the tillering stage produced the highest increase in grain yield (59.7 %, p < 0.10). The use of the biofertilizer caused significant changes in soil, particularly concerning pH, EC, Ca, Zn, Mg, and Mn. It is our view that the production and use of biofertilizers are a reliable alternative to deal with a solid waste problem while food security is increased.

Resistance and inactivation kinetics of bacterial strains isolated from the non-chlorinated and chlorinated effluents of a WWTP.

The microbiological quality of water from a wastewater treatment plant that uses sodium hypochlorite as a disinfectant was assessed. Mesophilic aerobic bacteria were not removed efficiently. This fact allowed for the isolation of several bacterial strains from the effluents. Molecular identification indicated that the strains were related to Aeromonas hydrophila, Escherichia coli (three strains), Enterobacter cloacae, Kluyvera cryocrescens (three strains), Kluyvera intermedia, Citrobacter freundii (two strains), Bacillus sp. and Enterobacter sp. The first five strains, which were isolated from the non-chlorinated effluent, were used to test resistance to chlorine disinfection using three sets of variables: disinfectant concentration (8, 20 and 30 mg·L(-1)), contact time (0, 15 and 30 min) and water temperature (20, 25 and 30 °C). The results demonstrated that the strains have independent responses to experimental conditions and that the most efficient treatment was an 8 mg·L(-1) dose of disinfectant at a temperature of 20 °C for 30 min. The other eight strains, which were isolated from the chlorinated effluent, were used to analyze inactivation kinetics using the disinfectant at a dose of 15 mg·L(-1) with various retention times (0, 10, 20, 30, 60 and 90 min). The results indicated that during the inactivation process, there was no relationship between removal percentage and retention time and that the strains have no common response to the treatments.

Chlorine disinfection of Pseudomonas aeruginosa, total coliforms, Escherichia coli and Enterococcus faecalis: revisiting reclaimed water regulations.

Pathogenic organisms can be transmitted orally through drinking water or through skin and mucosae by both direct and indirect contact, and their presence in water thus has a negative impact on public health. In wastewater treatment plants (WWTP), water is disinfected to inactivate pathogens. The quantification of several microbial indicators in aquatic systems is required to estimate the biological quality of such systems. So far, coliform bacteria have been used as traditional indicators world-wide. This study has assessed the resistance of total coliforms, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis to three dosages of sodium hypochlorite (NaClO) at two exposure times. The bacteria were isolated from secondary effluents of a WWTP located in Hidalgo, Mexico. The results show that the number of colony-forming units of all studied bacterial types decreased when both the NaClO concentration and exposure times increased. However, they were not eliminated. The inclusion of the species Pseudomonas aeruginosa in regulations for treated wastewater quality as a new indicator is highly recommended due to its importance as an opportunistic pathogen. The detection of this species along with the traditional organisms could be particulary significant for reclaimed water to be used with direct human contact.

Standardization of activated sludge for biodegradation tests.

Activated sludges are an inoculum source commonly used in biodegradation studies, as wastewater treatment facilities constitute an entry point to the environment for many chemicals. In this paper, the main issues relating to the use of activated sludge in biodegradability tests are presented. Special attention is also devoted to discussing the factors affecting both the activity of the microbial communities and the test results. After a short survey of the state of the art of microbiology of activated sludge, the paper focuses on the methods used to reduce the variations in the diversity, quality and quantity of these communities. Finally, use of surrogates as reference materials in biodegradability tests is discussed.

Model-based design of different fedbatch strategies for phenol degradation in acclimatized activated sludge cultures.

Microbial degradation of phenol was studied using batch and fedbatch cultures of acclimatized activated sludge under a wide range of phenol (0-793 mg l(-1)) and biomass (0.74-6.7 g l(-1)) initial concentrations. As cell growth continued after total phenol removal, the production and later consumption of a main metabolic intermediate was considered the step governing the biodegradation kinetics. A model that takes explicitly into account the kinetics of the intermediate was developed by introducing a specific growth rate model associated with its consumption and the incorporation of a dual-substrate inhibitory effect on phenol degradation. Biomass growth and phenol removal were adequately predicted in all the cultures. Moreover, the model-based design of the fedbatch feeding strategies allowed driving separately the phenol degradation under substrate-limitation and substrate-inhibition modes. A sensitivity analysis was also performed in order to establish the importance of the parameters in the accuracy of model predictions.

A method for measuring the anoxic biodegradability under denitrifying conditions.

A test for assessing the anoxic biodegradability of organic compounds under denitrifying conditions is proposed. The method is based on the recovery and quantification of the CO2 produced, which is evidence of complete biodegradation of the test compound (added as the sole carbon source). The tests were carried out in a mineral medium, with nitrate as electron acceptor. Whole lake sediments, sediment extracts and a commercial inoculum were assayed as a possible inoculum source by means of glucose biodegradability tests. It was found that the sediment extracts constitute a suitable and environmentally-relevant inoculum source, since they add non-significant amounts of carbon to the tests. Two xenobiotic compounds, namely, aniline and phenol, were tested in the aforementioned conditions as well as in a standard aerobic biodegradability test. Both aniline and phenol attained a biodegradation level higher than 60% in a short time period (<28 days) and thus can be considered as readily biodegradable in denitrifying environments. Nevertheless, the kinetics obtained in the anoxic test were slower than in aerobic conditions, and even suggested the accumulation of intermediate metabolites in the case of phenol. The results of this study indicate that the fate of xenobiotic compounds under anoxic conditions differs from that observed in an oxic environment, and therefore it should be considered by standard biodegradability testing procedures.

Inocula from activated sludge for ready biodegradability testing: homogenization by preconditioning.

The use of activated sludge as inoculum source in ready biodegradability tests (RBT) suffers from several drawbacks related to the heterogeneity of these communities. In this work, the ability of a 7-day aeration period in a mineral medium to homogenize the characteristics of various activated sludges, as suggested by some RBT, was studied. The biodegradation potential of three activated sludge supernatants obtained from different wastewater treatment plants was assessed in terms of cultivable cell density, dehydrogenasic activity and a profile of hydrolytic enzymes. After the preconditioning, the homogenization of these characteristics in the supernatants was observed, as well as a decrease. When preconditioned inocula were used in acetate RBT, the biodegradation kinetics were homogenized. However, some preconditioned supernatants lost their ability to degrade an easily-assimilable xenobiotic compound (aniline) during the observation period, showing the effect of inoculum preconditioning on the behavior of complex bacterial communities, specialist populations (e.g. aniline degraders) being more sensitive than generalist populations (e.g. acetate degraders). These results show that preconditioning cannot be an optional inoculum pretreatment in RBT, and emphasize the importance of further studies focusing on inoculum homogenization.

Pruebas normalizadas para la evaluación de la biodegradabilidad de sustancias químicas. una revisión

La biodegradabilidad es una propiedad de las sustancias químicas que determina su persistencia ambiental. Diversos organismos han estandarizado métodos para la evaluación de esta propiedad, entre los que destacan, por su amplio uso a nivel internacional, las pruebas de la Organización para la Cooperación y el Desarrollo Económico (OCDE). En este trabajo se presenta una descripción general de estas pruebas, y se discuten sus principales ventajas e inconvenientes. Para tal efecto, se utiliza la estructura propuesta por dicha organización, que distingue tres niveles sucesivos de ensayo: las pruebas de biodegradabilidad inmediata, de biodegradabilidad intrínseca y de simulación. La complejidad de las condiciones experimentales empleadas aumenta en el mismo orden, por lo que dicho esquema permite evaluar a bajo costo el potencial de biodegradación de cualquier molécula orgánica. En este artículo se sugieren algunas mejoras a los métodos, tales como la aplicación de modelos cinéticos para la expresión de los resultados y el uso de la sustancia de prueba como fuente de N, P o S. Se revisan en particular las pruebas de simulación, que permiten conocer el comportamiento de las sustancias en medios naturales o industriales específicos, y se destaca la importancia de normalizar nuevos métodos de simulación y de optimizar los existentes para hacerlos más accesibles a los posibles usuarios. Entre los medios naturales susceptibles de ser normalizados destacan los anóxicos en presencia de distintos aceptores externos de electrones (i.e., nitratos, sulfatos o hierro). Finalmente, se presentan aplicaciones recientes de estas pruebas, así como algunas áreas de investigación futura.

As knowledge of the biodegradability of organic compounds is essential to determine their environmental fate, several standardized biodegradability tests have been proposed by regulatory agencies. This paper presents an overview of the most commonly used standardized methods for biodegradability assessment of chemicals, those of the Organization for Economic Cooperation and Development (OECD). A general description is given of these tests and of their most important advantages and disadvantages. The tests presentation follows the OECD strategy, which classifies the assays in three successive levels: ready, inherent and simulation tests. Since experimental complexity increases in the same order, this strategy permits the biodegradability assessment of any organic compound in a cost-effective way. Some improvements to the tests are suggested, such as the application of kinetic models for the expression of test results and the use of the test compound as a source of N, P or S. The simulation tests, which allow the study of the behavior of chemicals in specific natural or industrial environments, are reviewed. The need of both new simulation methods and the optimization of available ones in order to extend their use is emphasized. A relevant simulation test to be standardized is the anoxic medium with external electron acceptors (i.e., nitrates, sulfates or iron). Finally, some recent applications of these tests as well as some proposals for future research in the field are presented.

A biodegradabilidade é uma propriedade das substâncias químicas que determina sua persistência ambiental. Diversos organismos tem estandardizado métodos para a avaliação desta propriedade, entre os que destacam, por seu amplo uso a nível internacional, as provas da Organização para a Cooperação e o Desenvolvimento Econômico (OCDE). Neste trabalho apresenta-se uma descrição geral destas provas, e discutem-se suas principais vantagens e inconvenientes. Para tal efeito, utiliza-se a estrutura proposta por dita organização, que distingue três níveis sucessivos de ensaios: as provas de biodegradabilidade imediata, de biodegradabilidade intrínseca e de simulação. A complexidade das condições experimentais empregadas aumenta na mesma ordem, pelo que dito esquema permite avaliar a baixo custo o potencial de biodegradação de qualquer molécula orgânica. Neste artigo se sugerem algumas melhoras aos métodos, tais como a aplicação de modelos cinéticos para a expressão dos resultados e o uso da substância de prova como fonte de N, P ou S. Revisam-se em particular as provas de simulação, que permitem conhecer o comportamento das substâncias em meios naturais ou industriais específicos, e se destaca a importância de normalizar novos métodos de simulação e de melhorar os existentes para fazê-los mais acessíveis aos possíveis usuários. Entre os meios naturais susceptíveis de ser normalizados destacam os anóxicos na presença de distintos aceptores externos de elétrons (i.e., nitratos, sulfatos ou ferro). Finalmente, se apresentam aplicações recentes destas provas, assim como algumas áreas de investigação futura.