Simultaneous nitrification–denitrification of wastewater: effect of zeolite as a support in sequential batch reactor with step-feed strategy

One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m³/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.     

Human impacts on Laguna de Bay, Philippines and management strategies for their mitigation

Laguna de Bay is the largest lake in the Philippines bordering metropolitan Manila, the nation's capital and the industrial hub of the country. As a multiple-use resource the lake is of prime importance for its fisheries, as a transport route and as a water source for the cooling of industrial plants and for irrigation. The lake is also envisaged to supply the domestic water needs of the basin in the year 2000. With rapid urbanization, industrial development and deforestation of its watershed, Laguna de Bay has been stressed with sedimentation, overexploitation of its fisheries and pollution. Various management strategies have been adopted by government to address such human impacts. Among the major programs are the installation of a hydraulic control structure, implementation of a zoning and management plan and the formulation of a master plan. There is need for an integrated approach for the management of the Laguna de Bay basin for its sustainable development.     

A study of the variability of the Delta Scuti-stars

A total of 321 observations of the Delta Scuti star BD –6°4932, obtained in 1968 by Hall and Mallama (1970), are analyzed. We find four frequencies which represent the light curves satisfactorily.The three periods:P ₁=0 _. ^d 240,P ₃=0 _. ^d 182 andP ₄=0 _. ^d 114 seem to correspond to the radial modes of pulsation withK=0, 1, and 3, respectively. The last periodP ₂=0 _. ^d 220 can be related to a non-radial mode.     

Chlorophylla of size-fractionated phytoplankton at a temporary hypersaline lake

The size-fractionated distribution of chlorophylla was studied in a temporary hypersaline lake situated in the south of Spain during an annual hydrological cycle characterized by low levels of rainfall. The contribution of each size class to the total chlorophylla concentration indicates that ultraplankton (size class <5m) was the most important fraction of phytoplankton biomass during this year.     

A study of the variability of the Delta Scuti stars

More than 1700 photmetricV observations of the Delta Scuti HR 2557, obtained at the Merate Observatory during the two periods: 1979–80 and 1981, are analyzed. In spite of the fact that the sets of frequencies for the two periods are similar, the interpretation of these oscillations is far to be satisfactory. The lowest frequencies can be reasonably interpreted as corresponding to the lowest radial modes. Unfortunately, nothing can be said about the highest frequencies.     

Development and validation of sinkhole susceptibility models in mantled karst settings. A case study from the Ebro valley evaporite karst (NE Spain)

A preliminary sinkhole susceptibility analysis has been carried out in a stretch 50 km² in area of the Ebro valley alluvial evaporite karst (NE Spain). A spatial database consisting of a sinkhole layer and 27 thematic layers related to causal factors was constructed and implemented in a GIS. Three types of sinkholes were differentiated on the basis of their markedly different morphometry and geomorphic distribution: large subsidence depressions (24), large collapse sinkholes (23), and small cover-collapse sinkholes (447). The susceptibility models were produced analysing the statistical relationships between the mapped sinkholes and a set of conditioning factors using the Favourability Functions approach. The statistical analyses indicate that the best models are obtained with 6 conditioning factors out of the 27 available ones and that different factors and processes are involved in the generation of each type of sinkhole. The validation of two models by means of a random-split strategy shows that reasonably good predictions on the spatial distribution of future dolines may be produced with this approach; around 75% of the sinkholes of the validation sample occur on the 10% of the pixels with the highest susceptibility and about 45% of the area can be considered as safe.     

Precessing collimated outflows in the planetary nebula IC 4846

We present [N  ii ] and H α images and high-resolution long-slit spectra of the planetary nebula IC 4846, which reveal, for the first time, its complex structure and the existence of collimated outflows. The object consists of a moderately elongated shell, two (and probably three) pairs of collimated bipolar outflows at different orientations, and an attached circular shell. One of the collimated pairs is constituted by two curved, extended filaments the properties of which indicate a high-velocity, bipolar precessing jet. A difference of ≃10 km s⁻¹ is found between the systemic velocity of the precessing jets and the centroid velocity of the nebula, as recently reported for Hu 2-1. We propose that this difference is as a result of orbital motion of the ejection source in a binary central star. The orbital separation of 30 au and period 100 yr estimated for the binary are similar to those in Hu 2-1, linking the central stars of both planetary nebulae to interacting binaries. Extraordinary similarities also exist between IC 4846 and the bewildering planetary nebula NGC 6543, suggesting a similar formation history for both objects.     

Understanding Effectiveness in its Broader Context: Assessing Case Study Methodologies for Evaluating Collaborative Conservation Governance

Abstract

Collaborative forms of governance are increasingly favored in conservation and potentially offer a range of practical and outcome-based benefits. However, tools for critically assessing whether and how collaboration enhances the attainment of conservation objectives are lagging behind the enthusiasm. We use a framework that considers effectiveness in relation to capacity of key actors and institutions to achieve outcomes and respond to emergent problems, robustness over time (i.e. adapting to changes while still achieving objectives), context-specific drivers of change, and the structure of networks and institutions to assess common approaches for evaluating effectiveness. Network analysis performs well in terms of structure, while action research and the diagnostic method offer deep insights into capacity and context. Scenario planning performs well in understanding robustness and context but performs better when combined with a diagnostic. The evaluation reveals important insights for approaching and standardizing investigations of collaborative governance regimes and their effectiveness.