Effect of feeding strategy and COD/sulfate ratio on the removal of sulfate in an AnSBBR with recirculation of the liquid phase

The objective of this work was to analyze the effect of the interaction between feeding strategy and COD/sulfate ratio on the removal efficiency of sulfate and organic matter from a synthetic wastewater. An anaerobic sequencing batch reactor with recirculation of the liquid phase and containing immobilized biomass on polyurethane foam (AnSBBR) was used. The AnSBBR with a total volume of 3.7 L, treated 2.0 L synthetic wastewater in 8-h cycles at 30 ± 1 °C and was inoculated with anaerobic biomass from a UASB. Two feeding strategies were assessed: (a) batch and (b) batch followed by fed-batch. In strategy (a) the reactor was fed in 10 min with 2 L wastewater containing sulfate and carbon sources. In strategy (b) 1.2 L wastewater (containing only the sulfate source) was fed during the first 10 min of the cycle and the remaining 0.8 L (containing only the carbon source) in 240 min. The COD/sulfate ratios assessed were 1 and 3. Based on these values and on the concentrations of organic matter (0.5–11.25 gCOD/L) and sulfate (0.5 and 2.5 gSO₄^2?/L), the sulfate and organic matter loading rates applied equaled 1.5 and 4.5 gSO₄^2?/L d for sulfate and 1.5, 4.5 and 13.5 gCOD/L d for organic matter. After stabilization of the system time profiles were run of monitored parameters (COD, sulfate, sulfide and sulfite). In general, the reactor showed to be robust for use in the anaerobic treatment of wastewaters containing sulfate. Gradual feeding (strategy b) of the carbon source favored sulfate reduction, resulting in sulfate removal efficiencies of 84–98% and organic matter removal efficiencies of 48–95%. The best results were observed under COD/sulfate ratio equal to 1 (loading rates of 1.5 and 4.5 gSO₄^2?/L d for sulfate, and 1.5 and 4.5 gCOD/L d for organic matter). When COD/sulfate ratio was 3 (loading rates of 1.5 and 4.5 gSO₄^2?/L d for sulfate, and 4.5 and 13.5 gCOD/L d for organic matter) the effect of feed mode became less significant. These results show that the strategy batch followed by fed-batch is more advantageous for COD/sulfate ratios near the stoichiometric value (0.67) and higher organic matter and sulfate concentrations.     

Mineralization of integrated gasification combined-cycle power-station wastewater effluent by a photo-fenton process

The aim of this work was to study the mineralization of wastewater effluent from an integrated-gasification combined-cycle (IGCC) power station sited in Spain to meet the requirements of future environmental legislation. This study was done in a pilot plant using a homogeneous photo-Fenton oxidation process with continuous addition of H₂O₂ and air to the system.The mineralization process was found to follow pseudo-first-order kinetics. Experimental kinetic constants were fitted using neural networks (NNs). The NNs model reproduced the experimental data to within a 90% confidence level and allowed the simulation of the process for any values of the parameters within the experimental range studied. At the optimum conditions (H₂O₂ flow rate = 120 mL/h, [Fe(II)] = 7.6 mg/L, pH = 3.75 and air flow rate = 1 m³/h), a 90% mineralization was achieved in 150 min.Determination of the hydrogen peroxide consumed and remaining in the water revealed that 1.2 mol of H₂O₂ was consumed per each mol of total organic carbon removed from solution. This result confirmed that an excess of dissolved H₂O₂ was needed to achieve high mineralization rates, so continuous addition of peroxide is recommended for industrial application of this process.Air flow slightly improved the mineralization rate due to the formation of peroxo-organic radicals which enhanced the oxidation process.     

Affordability of residential water tariffs: Alternative measurement and explanatory factors in southern Spain

Using information on a basic or “lifeline” level of domestic water use obtained from a water demand function based on a Stone–Geary utility function, a minimum water threshold of 128 m³ per household per year was estimated in a sample of municipalities in Southern Spain. As a second objective, water affordability indexes were then calculated that relate the cost of such lifeline to average municipal income levels. The analysis of the factors behind the differences in that ratio across Andalusian municipalities shows that the relative cost of purchasing the lifeline appears inversely related to average income levels, revealing an element of regressivity in the component of water tariffs affecting the least superfluous part of the household’s consumption. The main policy recommendation would involve redesigning water tariffs in order to improve access for lower income households to an amount of water sufficient to cover their basic needs. The proposed methodology could be applied to other geographical areas, both from developed and from developing countries, in order to analyze the degree of progressivity of the water tariffs currently in effect and in order to guide the design of more equitable regulatory policies.     

Experience,but not distance,influences the recruitment precision in the stingless bee <Emphasis Type="Italic">Scaptotrigona mexicana</Emphasis>

Recruitment precision, i.e. the proportion of recruits that reach an advertised food source, is a crucial adaptation of social bees to their environment. Studies with honeybees showed that recruitment precision is not a fixed feature, but it may be enhanced by factors like experience and distance. However, little is known regarding the recruitment precision of stingless bees. Hence, in this study, we examined the effects of experience and spatial distance on the precision of the food communication system of the stingless bee Scaptotrigona mexicana. We conducted the experiments by training bees to a three-dimensional artificial patch at several distances from the colony. We recorded the choices of individual recruited foragers, either being newcomers (foragers without experience with the advertised food source) or experienced (foragers that had previously visited the feeder). We found that the average precision of newcomers (95.6 ± 2.61%) was significantly higher than that of experienced bees (80.2 ± 1.12%). While this might seem counter-intuitive on first sight, this “loss” of precision can be explained by the tendency of experienced recruits to explore nearby areas to find new rewarding food sources after they had initially learned the exact location of the food source. Increasing the distance from the colony had no significant effect on the precision of the foraging bees. Thus, our data show that experience, but not the distance of the food source, affected the patch precision of S. mexicana foragers.     

Partial relaxation of enzyme-product binding by refolding of the growing chain in autocatalytic RNA replication

Helpful advice and discussions with Prof. M. Eigen are gratefully acknowledged. A conversation with Dr. Chr. Biebricher proved most useful.     

A rare case of de novo structural rearrangement of X chromosome diagnosed by amniocentesis

A dicentric X chromosome was found in a female fetus during cytogenetic studies performed on amniotic cells. Blood samples from the parents showed normal karyotypes and the pregnancy was terminated. The mechanism for the formation of this ‘de novo’ rearrangement is discussed.     

Intrauterine left chamber myocardial infarction of the heart and hydrops fetalis in the recipient fetus due to twin-to-twin transfusion syndrome

A rare complication of twin-to-twin transfusion syndrome (TTTS) is described: myocardial infarction of the recipient fetus. Myocardial infarction and hydrops are considered to be consequences of hypertension in the recipient. No other organs were affected. Pathological signs of intrauterine hypertension were estimated by the thickness of vessel walls and signs of hypertrophied myocardial cells. In the heart of the recipient fetus there was a chronic myocardial infarction near the apex cordis on the anterior wall with an aneurysm 4×5 mm in diameter. Diagnosis was based on light microscopic examination. The poor myocardial systolic function resulted in hydrops. Since the mother was administered β sympathomimetics in therapeutic doses the contribution of the drug to the myocardial infarction is uncertain, but we would like to suggest this as a possible adverse effect in TTTS. The present case is the first reported myocardial infarction in connection with the syndrome. Copyright © 2002 John Wiley & Sons, Ltd.     

Preimplantation genetic diagnosis using FISH for carriers of Robertsonian translocations: the Portuguese experience

Preimplantation genetic diagnosis (PGD) is an alternative to prenatal diagnosis for couples at risk of transmitting genetic disorders to their offspring. We present a fluorescence in situ hybridization (FISH) analysis of embryos obtained after seven PGD cycles in six couples with Robertsonian translocations and male factor infertility: 4 der(13;14), 1 der(14;21) and 1 der(15;21). Of 74 metaphase II (MII) injected oocytes, 61 (82.4%) fertilized normally and cleaved. Of these, 37/61 (60.7%) embryos were of high morphological quality with ≥6 blastomeres. After biopsy of 44 embryos at day 3 of development, seven degenerated, seven arrested in development and 30/44 (68.2%) evolved, of which 25/30 (83.3%) reached the morula/blastocyst stage. Analysis of biopsied blastomeres showed 23/44 (52.3%) of normal/balanced embryos, of which 15 (11 at the morula/blastocyst stage) were transferred in six cycles. One term pregnancy was achieved, which ended by cesarean section at 37 weeks of gestation, giving birth to two healthy newborn. Analysis of 49 embryos (excluding 12 inconclusive cases) showed a predominance of alternate segregation (38/49, 77.6%) over adjacent segregation (7/49, 14.3%), with one (2%) being a polyploid mosaic and three (6.1%) chaotic. Copyright © 2002 John Wiley & Sons, Ltd.     

Silvery mole-rats (<Emphasis Type="Italic">Heliophobius argenteocinereus</Emphasis>, Bathyergidae) change their burrow architecture seasonally

Little is known about seasonal changes in burrowing activity and burrow architecture in subterranean African mole-rats (Bathyergidae, Rodentia). The solitary genus Heliophobius is the least known genus of this family. We examined burrow systems of the silvery mole-rat ( Heliophobius argenteocinereus) in Malawi in two periods of the dry season. Burrow pattern was influenced by the time of the year, becoming more reticulated at the peak of the dry season when soil was dry and hard. Overall digging activity did not cease during the dry season; yet burrowing strategy changed and the soil was deposited in tunnels rather than transported to mounds. The length of burrow systems was correlated with the body mass of the respective occupants. In spite of their solitary habits – and contrary to the prediction of the aridity food-distribution hypothesis – silvery mole-rats are able to occupy poor habitats with low food supply.