Kinetic modelling of a diesel-polluted clayey soil bioremediation process

A mathematical model is proposed to describe a diesel-polluted clayey soil bioremediation process. The reaction system under study was considered a completely mixed closed batch reactor, which initially contacted a soil matrix polluted with diesel hydrocarbons, an aqueous liquid-specific culture medium and a microbial inoculation. The model coupled the mass transfer phenomena and the distribution of hydrocarbons among four phases (solid, S; water, A; non-aqueous liquid, NAPL; and air, V) with Monod kinetics. In the first step, the model simulating abiotic conditions was used to estimate only the mass transfer coefficients. In the second step, the model including both mass transfer and biodegradation phenomena was used to estimate the biological kinetic and stoichiometric parameters. In both situations, the model predictions were validated with experimental data that corresponded to previous research by the same authors. A correct fit between the model predictions and the experimental data was observed because the modelling curves captured the major trends for the diesel distribution in each phase. The model parameters were compared to different previously reported values found in the literature. Pearson correlation coefficients were used to show the reproducibility level of the model.Se propone un modelo matemático para describir un proceso de biorremediación de suelos arcillosos contaminados con diesel. El sistema de reacción en estudio se consideró un reactor discontinuo cerrado completamente mixto, que inicialmente entró en contacto con una matriz de suelo contaminada con hidrocarburos diesel, un medio de cultivo específico líquido acuoso y una inoculación microbiana. El modelo acopló los fenómenos de transferencia de masa y la distribución de hidrocarburos entre cuatro fases (sólido, S; agua, A; líquido no acuoso, NAPL; y aire, V) con la cinética de Monod. En el primer paso, se utilizó el modelo que simula las condiciones abióticas para estimar solo los coeficientes de transferencia de masa. En el segundo paso, se utilizó el modelo que incluía tanto la transferencia de masa como los fenómenos de biodegradación para estimar los parámetros biológicos cinéticos y estequiométricos. En ambas situaciones, las predicciones del modelo fueron validadas con datos experimentales que correspondían a investigaciones previas de los mismos autores. Se observó un ajuste correcto entre las predicciones del modelo y los datos experimentales porque las curvas de modelado capturaron las principales tendencias para la distribución del diesel en cada fase. Los parámetros del modelo se compararon con diferentes valores reportados previamente encontrados en la literatura. Se utilizaron coeficientes de correlación de Pearson para mostrar el nivel de reproducibilidad del modelo

Disinfection of urine by conductive-diamond 1 electrochemical oxidation

This work focuses on the application of electrolysis with diamond anodes for the disinfection of urine. To do this, a synthetic human urine was polluted with Escherichia coli and Pseudomonas aeruginosa and then, it was electrolyzed at current densities within the range 0–100 A m−2. Results show that it is possible to disinfect completely the effluent even at applied electric charges lower than 2 kAh m−3, regardless the current density applied. This good performance is related to the production of powerful oxidants from the oxidation of the ions present in synthetic urine. Likewise, these species also react with the organics contained in urine (urea, creatinine and uric acid), favoring their degradation. The process efficiency for both microorganisms and organics is higher when working at low current densities. The removal of organics leads to the release of significant amounts of nitrogen in the form of nitrate which are later electroreduced to ammonium, that, in turn, reacts with the electrogenerated hypochlorite, favoring the production of chloramines (which can also contribute to the disinfection process). Regarding the mineralization, TOC removal higher than 90% can be achieved but higher applied electric charges than those required for disinfection have to be applied (around 30 kAh m−3)

Understanding the influence of the bioaerosol source on the distribution of airborne bacteria in hospital indoor air

The composition and concentration of airborne microorganisms in hospital indoor air has been reported to contain airborne bacteria and fungi concentrations ranged 101–103 CFU/m3 in inpatients facilities which mostly exceed recommendations from the World Health Organization (WHO). In this work, a deeper knowledge of the performance of airborne microorganisms would allow improving the designs of the air-conditioning installations to restrict hospital-acquired infections (HAIs). A solution containing Escherichia coli (E. coli) as a model of airborne bacteria was nebulized using the Collison nebulizer to simulate bioaerosols in various hospital areas such as patients’ rooms or bathrooms. Results showed that the bioaerosol source had a significant influence on the airborne bacteria concentrations since 4.00 102, 6.84 103 and 1.39 104 CFU mL−1 were monitored during the aerosolization for 10 min of urine, saliva and urban wastewater, respectively. These results may be explained considering the quite narrow distribution profile of drop sizes around 1.10–1.29 μm obtained for urban wastewater, with much vaster distribution profiles during the aerosolization of urine or saliva. The airborne bacteria concentration may increase up to 107 CFU mL−1 for longer sampling times and higher aerosolization pressures, causing several cell damages. The cell membrane damage index (ID) can vary from 0 to 1, depending on the genomic DNA releases from bacteria. In fact, the ID of E. coli was more than two times higher (0.33 vs. 0.72) when increasing the pressure of air flow was applied from 1 to 2 bar. Finally, the ventilation air flow also affected the distribution of bioaerosols due to its direct relationship with the relative humidity of indoor air. Specifically, the airborne bacteria concentration diminished almost below 3-logs by applying more than 10 L min−1 during the aerosolization of urine due to their inactivation by an increase in their osmotic pressure.La composición y concentración de los microorganismos transportados por el aire en el interior de los hospitales contiene concentraciones de bacterias y hongos que oscilan entre 101 y 103 UFC/m3 en los centros de hospitalización, que en la mayoría de los casos superan las recomendaciones de la Organización Mundial de la Salud (OMS). En este trabajo, un conocimiento más profundo del comportamiento de los microorganismos transportados por el aire permitiría mejorar los diseños de las instalaciones de aire acondicionado para restringir las infecciones adquiridas en el hospital (HAI). Se nebulizó una solución que contenía Escherichia coli (E. coli) como modelo de bacteria aerotransportada utilizando el nebulizador Collison para simular bioaerosoles en diversas áreas hospitalarias, como las habitaciones o los baños de los pacientes. Los resultados mostraron que la fuente del bioaerosol tenía una influencia significativa en las concentraciones de bacterias aerotransportadas, ya que se monitorizaron 4,00 102, 6,84 103 y 1,39 104 UFC mL-1 durante la aerosolización durante 10 minutos de orina, saliva y aguas residuales urbanas, respectivamente. Estos resultados pueden explicarse considerando el perfil de distribución bastante estrecho de tamaños de gota alrededor de 1,10-1,29 μm obtenido para las aguas residuales urbanas, con perfiles de distribución mucho más amplios durante la aerosolización de orina o saliva. La concentración de bacterias en el aire puede aumentar hasta 107 UFC mL-1 para tiempos de muestreo más largos y presiones de aerosolización más altas, causando varios daños celulares. El índice de daño de la membrana celular (ID) puede variar de 0 a 1, dependiendo de la liberación de ADN genómico de las bacterias. De hecho, el ID de E. coli fue más de dos veces superior (0,33 frente a 0,72) al aumentar la presión del flujo de aire de 1 a 2 bares. Por último, el flujo de aire de ventilación también afectó a la distribución de los bioaerosoles debido a su relación directa con la humedad relativa del aire interior. Concretamente, la concentración de bacterias en el aire disminuyó casi por debajo de 3 logs al aplicar más de 10 L min-1 durante la aerosolización de la orina debido a su inactivación por un aumento de su presión osmótica

Environmental applications of electrochemical technology. What is needed to enable full-scale applications?

In recent years, thousands of scientific articles have considered the application of electrochemical technologies to remediate environmental problems ranging from the treatment of polluted soils to the removal of hazardous species from industrial liquid wastes. New research topics continue to emerge. Despite such research efforts, the technology readiness level (TRL) for many of those technologies remains very low; although most are considered promising, many are far from being introduced as efficient processes into the market. Important barriers need to be overcome to reach high TRLs. Some of these are scientific or technological and generate the opportunity for critical, applied research. Others are related to the lack of components in the value chain of the technology and generate opportunities for entrepreneurs to benefit from an improvement in the TRL. In this short review, a brief description of the current state of the most relevant technologies which are still in low TRL is carried out, highlighting barriers that must be removed to achieve full-scale applications in industry

Electrochemical Technologies to Decrease the Chemical Risk of Hospital Wastewater and Urine

The inefficiency of conventional biological processes to remove pharmaceutical compounds (PhCs) in wastewater is leading to their accumulation in aquatic environments. These compounds are characterized by high toxicity, high antibiotic activity and low biodegradability, and their presence is causing serious environmental risks. Because much of the PhCs consumed by humans are excreted in the urine, hospital effluents have been considered one of the main routes of entry of PhCs into the environment. In this work, a critical review of the technologies employed for the removal of PhCs in hospital wastewater was carried out. This review provides an overview of the current state of the developed technologies for decreasing the chemical risks associated with the presence of PhCs in hospital wastewater or urine in the last years, including conventional treatments (filtration, adsorption, or biological processes), advanced oxidation processes (AOPs) and electrochemical advanced oxidation processes (EAOPs).La ineficiencia de los procesos biológicos convencionales para eliminar los compuestos farmacéuticos (PhC) de las aguas residuales está provocando su acumulación en los medios acuáticos. Estos compuestos se caracterizan por una alta toxicidad, alta actividad antibiótica y baja biodegradabilidad, y su presencia está provocando graves riesgos ambientales. Debido a que gran parte de los PhC consumidos por los seres humanos se excretan en la orina, los efluentes hospitalarios se han considerado una de las principales vías de entrada de PhC al medio ambiente. En este trabajo se realizó una revisión crítica de las tecnologías empleadas para la remoción de PhCs en aguas residuales hospitalarias. Esta revisión proporciona una visión general del estado actual de las tecnologías desarrolladas para disminuir los riesgos químicos asociados con la presencia de PhC en las aguas residuales hospitalarias o en la orina en los últimos años

The Role of the Anode Material in Selective Penicillin G Oxidation in Urine

In this work, the removal of antibiotic penicillin G by electrolysis with boron doped diamond (BDD) and mixed metal oxide (MMO) anodes in urine media is evaluated. First, electrolysis in different water matrices (sulfate, chloride and urine) were carried out with diamond anodes to shed light on the contribution of mediated mechanisms. Results showed that penicillin G was completely removed by electrolysis for electric charges below 5 Ahdm 3 , regardless of the water matrix and the current density applied (10-100 mAcm 2 ). Then, the influence of the anode material was evaluated for the degradation of penicillin G in urine media. A complete removal of the antibiotic was attained, regardless of the tested anode material, although the BDD anode was found to be more efficient than MMO. Results also showed that, at the current charges in which the antibiotic is depleted, the removal of other organics was much lower and the formation of chlorates was negligible, especially operating at low current densities. Because of this selective oxidation of the pharmaceutical compound, electrolysis can be proposed to be used as a pretreatment technology for later and cheaper biological treatment

Enhancement of UV disinfection of urine matrixes by electrochemical oxidation

This work focuses on the removal of antibiotic-resistant bacteria (ARB) contained in hospital urines by UV disinfection enhanced by electrochemical oxidation to overcome the limitations of both single processes in the disinfection of this type of effluents. UV disinfection, electrolysis, and photoelectrolysis of synthetic hospital urine intensified with K. pneumoniae were studied. The influence of the current density and the anode material was assessed on the disinfection performance of combined processes and the resulting synergies and/or antagonisms of coupling both technologies were also evaluated. Results show that the population of bacteria contained in hospital urine is only reduced by 3 orders of magnitude during UV disinfection. Electrolysis leads to complete disinfection of hospital urine when working at 50 A m−2 using Boron Doped Diamond (BDD) and Mixed Metal Oxides (MMO) as anodes. The coupling of electrolysis to the UV disinfection process leads to the highest disinfection rates, attaining a complete removal of ARB for all the current densities and anode materials tested. The use of MMO anodes leads to higher synergies than BDD electrodes. Results confirm that UV disinfection can be enhanced by electrolysis for the removal of ARB in urine, considering both technical and economic aspects

Innovative photoelectrochemical cell for the removal of CHCs from soil washing wastes

This work presents a novel photoelectrochemical cell concept for the treatment of soil washing effluents polluted with chlorinated hydrocarbons (CHCs). This cell combines the use of low current densities and the direct irradiation of UV light to the electrodes and the bulk, being easy to be scaled up. To evaluate its performance, the treatment of a soil washing effluent polluted with clofibric acid (~50 mg dm−3) was carried out. The prototype evaluated was equipped with two boron doped diamond (BDD) plates as anodes, two stainless steel (SS) plates as cathodes and a UV lamp located at the bottom. Results show that it was possible to attain a complete abatement and mineralization of the organochlorinated compound at applied electric charges lower than 5 Ah dm−3, regardless the irradiation of UV light. Nevertheless, the removal rate was higher during photoelectrolysis, specially at the beginning of the treatment, which indicates important advantages for the removal of aromatic compounds. In addition, the toxicity of the effluent was dramatically reduced at the end of the process. These results point out the high performance of the novel photoelectrochemical reactor proposed for the complete remediation of soils polluted with CHCs

Disinfection of urines using an electro-ozonizer

In this work, the disinfection of urines polluted with Klebsiella pneumoniae (K. pneumoniae) using a commercial electro-ozonizer is described. The device consists of a membrane-electrode assembly flow cell that specially promotes the electrochemical generation of ozone. Results show that a complete disinfection is attained in less than 180 min when working at current intensities higher than 0.5 A. The higher the current intensity, the higher the disinfection rate. Furthermore, the use of an electro-ozonizer for treating diluted urines leads to higher disinfection efficiencies. Ozone and chlorine-based disinfectants (hypochlorite and chloramines) were identified as the main oxidant species involved in killing bacteria. The combined effect of all disinfectants promotes higher removal efficiencies in comparison with the single effect of ozone evaluated in a urine matrix without chlorides, being more remarkable at lower current intensities. The crystal violet assay showed that cell wall is damaged by the electrogenerated oxidants and it is more remarkable by the combined effect of ozone and chlorine disinfectants when increasing the current intensity. Finally, the degradation of total proteins and genetic material (DNA) were also monitored and related to the oxidants produced during the electrochemical process

Removal of antibiotic resistant bacteria by electrolysis with diamond anodes: A pretreatment or a tertiary treatment?

In the present work, the influence of the water matrix on the removal of antibiotic resistant bacteria during the electro-disinfection with diamond anodes was studied, paying special attention to the disinfection efficiency and the prevention of the formation of hazardous disinfection by-products. This will allow to evaluate if electrolysis is more suitable as pretreatment of the main pollution source or as tertiary treatment of urban wastewater. To do this, electrolysis of synthetic wastewater rich in ammonium (simulating the effluent of an oxidation pond) and hospital urine intensified with three different bacteria (E. faecalis, K. pneumoniae, and E. coli) were carried out. Results show that the disinfection efficiency is higher in the synthetic wastewater for all the bacteria tested, but chlorate is formed as disinfection by-product. Electrogenerated hypochlorite and chloramines are the main responsible species for bacteria depletion. Presence of organics (urea, creatinine and uric acid) as additional ammonia precursors in hospital urine leads to the well-known breakpoint reaction with electrogenerated active chlorine, yielding an increasing concentration of chloramines. This helps to prevent the formation of chlorate in hospital urine because hypochlorite is mainly wasted in the oxidation of organics and the formation of chloramines. These results are of a great significance because they indicate that antibiotic resistant bacteria can be efficiently removed in complex matrixes without the formation of hazardous chlorine by-products if it is carried out as a pretreatment before discharge to WWTP