Risk assessment of bioaccessible arsenic and cadmium exposure through rice consumption in local residents of the Mae Tao Sub-district,Northwestern Thailand

Environmental Geochemistry and Health - Consumption of contaminated rice is a toxin exposure route in Asian populations. Since total concentrations generally overestimate health risks, the...     

Enhancement of simultaneous nitrogen and phosphorus removal using intermittent aeration mechanism

Biological nutrient removal grows into complicated scenario due to the microbial consortium shift and kinetic competition between phosphorus (P)-accumulating and nitrogen (N)-removing microorganisms. In this study, three sequential batch reactors with constant operational conditions except aeration patterns at 6 h cycle periods were tested. Intermittent aeration was applied to develop a robust nutrient removal system aimed to achieve high energy saving and removal efficiency. The results showed higher correspondence of P-uptake, polymeric substance synthesis and glycogen degradation in intermittent-aeration with longer interval periods compared to continuous-aeration. Increasing the intermittent-aeration duration from 25 to 50 min, resulted in higher process performance where the system exhibited approximately 30% higher nutrient removal. This study indicated that nutrient removal strongly depends on reaction phase configuration representing the importance of aeration pattern. The microbial community examined the variation in abundance of bacterial groups in suspended sludge, where the 50 min intermittent aeration, favored the growth of P-accumulating organisms and nitrogen removal microbial groups, indicating the complications related to nutrient removal systems. Successful intermittently aerated process with high capability of simple implementation to conventional systems by elemental retrofitting, is applicable for upgrading wastewater treatment plants. With aeration as a major operational cost, this process is a promising approach to potentially remove nutrients in high competence, in distinction to optimizing cost-efficacy of the system.     

Le biotope dans le milieu marin

Ecological models taking into consideration a single or a few parameters rather than the distributional pattern of biotopes will probably prove to be over-simplified. In the oceans, large-scale biotopic patterns are remarkably regular, and this allows the concept of homology used in morphology to be applied also to biotopes. Isothermal deep uniform waters are homologous throughout all water structures, as are partly upper isothermal layers. The “permanent thermocline” in the tropics has no homologues in subpolar water-structures, where the intermediate layer is divided into cold and warm layers. Consequently, in tropical communities, some macroplankters. undertake extensive diel vertical migrations through the “permanent thermocline” and can benefit from the McLaren effect. Few such migrators exist in subpolar waters. The lower limit of phytoplankton is the second or third stability maximum and, therefore, the biotopes of phytocenes are not strictly homologous with each other. The areal distribution of biotopes can be described using the model of a deformation field; here, the two major types of biotopes are those of large-scale gyres and neutral cols. Regarding species with discontinuous ranges, one has to discover whether or not their isolated populations live in homologous parts of the deformation field. Bottom communities live in homologous biotopes if homologous water masses contact the bottom. More strict homology exists between similar “trophic zones” (in the sense used by Sokolova, 1966) within each water mass. Nekton and migratory benthos (such as tuna, Kamtchatka king-crab or several flatfish species) live only in biotopic complexes possessing varying trophic and/or thermal conditions. In the uniformly homogeneous deep waters there is neither nekton nor migratory benthos.