Activity control in nitrifying biofilms: application of respirometric tests

Nitrification is the biological oxidation of ammonia to nitrate via nitrite. These reactions are performed by aerobic autotrophic microorganisms, commonly known as nitrifiers. The nitrifiers are generally constituted of ammonia oxidizing bacteria and nitrite oxidizing bacteria. They are very sensitive to environmental factors, namely the pH, which has its optimum value in the range of 7.5 to 8.5 (Sharma end Ahlert, 1977) A simple method, the respiration rate measurement, has been extensively used in literature to characterize microbial populations in suspended cultures (Kristensen et al., 1992, Nowak and Svardal, 1993) and to monitor the nitrification performance of immobilized nitrifiers (Nakamura et al., 1995) and nitrifying activated sludge processes (Surmacz-Gorska et al., 1996). Respiration refers to reactions that use oxygen as an electron acceptor. The aim of the present study is to characterize the functional microorganism groups of a nitrifying biofilm using a simple microbial activity measurement, the respiration rate, and to use this information to identify disturbances that have an impact on process performance

Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor

The influence of dissolved oxygen concentration on the nitrification kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary effluent as feed water. The nitrifi- cation kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusion-reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fitting the diffusion-reaction model to the experimental results was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nitri fication kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5-2 gO2/gN-NH4+ for both laboratory and pilot scale reactors. The volumetric oxygen mass transfer coefficient (kLa) determined in the laboratory scale reactor was 0.017 sˉ¹ for a superficial air velocity of 0.02 m sˉ¹, and the one determined in the pilot scale reactor was 0.040 sˉ¹ for a superficial air velocity of 0.031 m sˉ¹. The kLa for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI, project 2/2.1/Bio/37/94.INTERREG

Water reuse for irrigated agriculture in Jordan: challenges of soil sustainability and the role of management strategies

Reclaimed water provides an important contribution to the water balance in water-scarce Jordan, but the quality of this water presents both benefits and challenges. Careful management of reclaimed water is required to maximize the nutrient benefits while minimizing the salinity risks. This work uses a multi-disciplinary research approach to show that soil response to irrigation with reclaimed water is a function of the management strategies adopted on the farm by the water user. The adoption of management methods to maintain soil productivity can be seen to be a result of farmers’ awareness to potentially plant-toxic ions in the irrigation water (70% of Jordan Valley farmers identified salinization as a hazard from irrigation with reclaimed water). However, the work also suggests that farmers’ management capacity is affected by the institutional management of water. About a third (35%) of farmers in the Jordan Valley claimed that their ability to manage salinization was limited by water shortages. Organizational interviews revealed that institutional awareness of soil management challenges was quite high (34% of interviewees described salinization as a risk from water reuse), but strategies to address this challenge at the institutional level require greater development

Salen Mn Complexes Mitigate Radiation Injury in Normal Tissues

Salen Mn complexes, including EUK-134, EUK-189 and a newer cyclized analog EUK-207, are synthetic SOD/catalase mimetics that have beneficial effects in many models of oxidative stress. As oxidative stress is implicated in some forms of delayed radiation injury, we are investigating whether these compounds can mitigate injury to normal tissues caused by ionizing radiation. This review describes some of this research, focusing on several tissues of therapeutic interest, namely kidney, lung, skin, and oral mucosa. These studies have demonstrated suppression of delayed radiation injury in animals treated with EUK-189 and/or EUK-207. While an antioxidant mechanism of action is postulated, it is likely that the mechanisms of radiation mitigation by these compounds in vivo are complex and may differ in the various target tissues. Indicators of oxidative stress are increased in lung and skin radiation injury models, and suppressed by salen Mn complexes. The role of oxidative stress in the renal injury model is unclear, though EUK-207 does mitigate. In certain experimental models, salen Mn complexes have shown “mito-protective” properties, that is, attenuating mitochondrial injury. Consistent with this, EUK-134 suppresses effects of ionizing radiation on mitochondrial function in rat astrocyte cultures. In summary, salen Mn complexes could be useful to mitigate delayed radiation injury to normal tissues following radiation therapy, accidental exposure, or radiological terrorism. Optimization of their mode of delivery and other key pharmaceutical properties, and increasing understanding of their mechanism(s) of action as radiation mitigators, are key issues for future study

On fatigue behavior of two spring steels. Part I: Wöhler curves and fractured surfaces

Symmetric fatigue in two spring steels is investigated in three groups of specimens. One of the groups (Steel EN10270-1SH/ DIN 17223C – C 0.82%, Mn 0.76%, Si 0.26%) has experienced rotating-bending fatigue in air, and the other two groups (Steel BS250A53/ DIN 55Si7 – C 0.56%, Mn 0.81%, Si 1.85%), torsion fatigue in-air and corrosion environment. Fatigue life-time data are obtained for both spring steels, and their corresponding Wöhler curves plotted and mathematically described. Surface short fatigue cracks are observed from origin to fracture by using acetate-foil replication technique, and their length, a, measured at the corresponding number of fatigue cycles, N. Those data are presented in plots “Crack lengths, a – Cycles, N” and a comparison made between both the steels. The fractured surfaces of all specimens have been studied and analyzed by the scanning-electron microscopy method

On fatigue behaviour of two spring steels. Part II: Mathematical models

Symmetric fatigue in two spring steels is investigated in three groups of specimens. One of the groups (Steel EN10270-1SH/ DIN 17223C – C 0.82%, Mn 0.76%, Si 0.26%) has experienced rotating-bending fatigue in air, and the other two groups (Steel BS250A53/ DIN 55Si7 – C 0.56%, Mn 0.81%, Si 1.85%), torsion fatigue in-air and corrosion environment. All experiments include testing to fracture, applying acetate-foil replication technique, replica monitoring of short crack surface growth, length measuring of propagating cracks, a, at the corresponding number of fatigue cycles, N. Data obtained from replica monitoring are presented in plots “Crack lengths, a – Cycles, N”, and used for calculating fatigue crack growth rates, da/dN, and graphical presentations “Crack growth rates, da/dN – Crack lengths, a”. A mathematical description of da/dN – a is presented by introducing a parabolic-linear model in different versions for each of the steels. The model versions are verified through comparing the experimental fatigue lifetimes with those calculated by the proposed model version

The Intrinsic Fractions and Radio Properties of Low Ionization Broad Absorption Line Quasars

Low-ionization (MgII, FeII, FeIII) broad absorption line quasars (LoBALs) probe a relatively obscured quasar population, and could be at an early evolutionary stage for quasars. We study the intrinsic fractions of LoBALs using the SDSS, 2MASS, and FIRST surveys. We find that the LoBAL fractions of the near infra-red (NIR) and radio samples are approximately 5--7 times higher than those measured in the optical sample. This suggests that the fractions measured in the NIR and radio bands are closer to the intrinsic fractions of the populations, and that the optical fractions are significantly biased due to obscuration effects, similar to high-ionization broad absorption line quasars (HiBALs). We also find that the LoBAL fractions decrease with increasing radio luminosities, again, similar to HiBALs. In addition, we find tentative evidence for high fractions of LoBALs at high NIR luminosities, especially for FeLoBALs with a fraction of ~18 per cent at M_K_s < -31 mag. This population of NIR luminous LoBALs may be at an early evolutionary stage of quasar evolution. We use a two-component model of LoBALs including a pure geometric component and a luminosity dependent component at high NIR luminosities, and obtain better fits than those from a pure geometric model. Therefore, the LoBAL population can be modelled as a hybrid of both the geometric and evolutionary models, where the geometric component constitutes 3.4\pm0.3, 5.8\pm0.4, and 1.5\pm0.3 per cent of the quasar population for BI-LoBALs, AI-LoBALs, and FeLoBALs, respectively. Considering a population of obscured quasars that do not enter the SDSS survey, which could have a much higher LoBAL fraction, we expect that intrinsic fraction of LoBALs could be even higher.Comment: 10 pages, 6 figures, submitted to MNRA

Impacto del estrés oxidativo sobre las lesiones cutáneas causadas por radiaciones ionizantes

RESUMEN Los efectos inducidos por exposición de manera accidental o terapéutica a dosis de radiaciones ionizantes inducen varios eventos celulares que afectan el proceso de cicatrización de la piel, y tiene gran impacto en la prognosis y supervivencia de individuos afectados. La información existente sobre los efectos nocivos por altas exposiciones a radiaciones proviene a partir de los accidentes ocurridos por las bombas atómicas en Hiroshima y Nagasaki produciendo problemas de salud por leucemias y linfomas en los sobrevivientes. El síndrome de radiación aguda (SRA) generalmente inicia durante las dos horas inmediatas posteriores a la exposición, y la severidad de las lesiones depende de la dosis y del tiempo de exposición. El desarrollo de las lesiones por el daño como efectos tardíos a exposiciones por radiaciones es más complejo y determina no únicamente el daño al parénquima celular sino también se presentan daños en el tejido vascular y en otros tejidos de soporte. Al menos parcialmente estos eventos se presentan a consecuencia del estrés oxidativo generado por el excesivo incremento de especies reactivas del oxígeno (EROs). Se han estado estudiando componentes comerciales como blancos potenciales para la prevención de los daños causados por radiaciones en piel que tienen una amplia actividad contra múltiples citocinas involucradas en los procesos de la lesión cutánea y por otro lado se están estudiando fármacos que reaccionan con los radicales libres o indirectamente inhiben la expresión de las enzimas que generan la producción de EROs o bien aumentan la expresión de enzimas antioxidantes intracelulares