Simple model of sludge thickening process in secondary settlers

In wastewater treatment plants （WWTPs）, a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, us = aXb （ a =0.9925SSFI3.5, b = - 3.5411n（ SS VI3.5 ） ＋12.973）, describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.

Numerical simulation of flow characteristics in settler of flash furnace

A computational fluid dynamics （CFD） simulation was carried out with CFX4,3 to investigate the melt flow and temperature distributions in the settler of a flash furnace. Sixteen cases of one slag tap hole adopted with one matte tap hole （1-to-l） and one slag tap hole adopted with two matte tap holes （1-to-2） operation modes were modelled. The simulation results show that the melt flows are similar in both two operation modes, but evident circulations can be found in the case of the 1-to-2 operation mode. The combination modes of the slag and matte tap holes are found to have a significant effect on the temperature distributions of the melt. The melt temperature is more uniform in the case of the 1-to-2 mode. Selection of a matte tap hole farther away from the inlet is more conducive to achieve a uniform distribution of the melt temperature in the settler in nractical tannine oneration

Four Rare and Unusual Dedications From Areas of Viminacium and Nais

In the areas of Viminacium and Nais four rare and unusual votive dedications were identified.These are the dedications Deus Aeternus,Dii Angeli,Hero(Viminacium),and Atta(Naissus).The dedications Deus Aeternus and Dii Angeli may perhaps indicate Christianity,while the dedications Hero and Atta may indicate settlers of Greek origin.The dedication to goddess Atta could have been made by a freed man,since her cult was to an extent related to the cult of Heracles who,thanks to his loyal service to Omphale,where he was to repent his sins,was freed from slavery,and thus was also a protector of freed man.Main methodological approach in this paper is the analysis of cults as well as their backgrounds as conditions for their realisation.Until now for the territory of Serbia there was not corpus of analyzing cults.There is only corpus of grave and votive monuments for the territory of Serbia with very rare and sporadic comments of cult.So,the main topic of this article is analyzing of cults.It includes the main meaning of the cult,dateing of monuments and historical and archeological backgrounds of the cults.At the same time it was the main method in the analyzing of the mentioned votive monuments.By this method as the result appeared the dateing of the monuments and improvement of existing Greek settlers.At the same time there were the main research questions which should be ensolved.For ensolved the dateing of the monuments was used the system of analyzing syllabic formulae and for the improvement of existing Greek settlers the method of“healty mind”and connections of analogies.As a result the dateing of monuments of Deus Aeternus,Dii Angeli,and Hero was early 2-nd century,and for Atta from the beginning of 2-nd to the end of 3-rd century.

An experimental study of immiscible liquid–liquid dispersions in a pump–mixer of mixer–settler

Drop size distribution(DSD) or mean droplet size(d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d32/D = 0.13(1 + 5.9φ)We-0.6. Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d32/D = C3(1 + C4φ)We-0.6. For the surfactant system and extraction system, the prediction models met a general model as d32/D = bφnWe-0.6.

Computational fluid dynamics(CFD) simulation of effect of baffles on separation in mixer settler

The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baffles in a mechanically agitated vessel is to ensure even distribution,reduce settler turbulence,promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid,thus,greatly improving the mixing of liquid.The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing.However,excessive baffling would interrupt liquid mixing and lengthen the mixing time.Computational fluid dynamics(CFD) provides a tool for determining detailed information on fluid flow(hydrodynamics) which is necessary for modeling subprocesses in mixer settler.A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles,density and impeller speed.CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.

Structural optimization of a settler via CFD simulation in a mixer-settler

This work is aimed at optimizing a settler structure in a mixer-settler.Two different aspects have been considered.Firstly,the flowcharacteristics of a settler have been examined by computational fluid dynamics(CFD)simulation with various agitation speeds of the mixer,as well as organic phase volume fractions ranging from 0.075 to 0.6.The aqueous and organic phase turbulent flow fields were measured by particle image velocimetry(PIV)technique to verify the CFD simulation.Two organic phases with different physical properties were assessed in the CFD simulation to simulate the liquid-liquid systems related to rare earth element extraction,i.e.,0.072 mol·L^-1 P507/kerosene and 1.8 mol·L^-1 P507/kerosene.Secondly,the CFD simulation was carried out in a settler equipped with baffles.The effects of number and location of the baffle in the settler on flow features and entrainments of the aqueous and organic outlet were analyzed.Meanwhile,different settler/mixer volume ratios were also examined.By analyses and comparisons,an optimal design for settler was proposed.CFD can provide a significant guidance to better mixer-settler design.

Performance of a novel vertical-flow settler: a comparative study

By increasing particle concentration and G value （root-mean-square velocity gradient） to enhance flocculation, a novel vertical-flow settler was designed to increase sedimentation effectiveness, and to simultaneously improve operational stabilization. Due to the gradual decrease in upward flow-rate of raw water, a floes blanket would form and suspend in the middle section of the settler, not at the bottom as in a conventional clarifier. Enough large floes, resulted from flocculation or fltration, would continuously settle out of the floes blanket, and simultaneously, the floes in raw water or those forming above the blanket would ceaselessly enter the floes blanket. As a result, the floes concentration in the blanket could keep a dynamic balance. The hydrodynamic shear in the blanket was improved by flow separation, which was induced by the abrupt change in flow channel. Due to the floes blanket and improved hydrodynamic shear, flocculation would be enhanced, which was helpful for removing fine particles in raw water. A comparative study showed that the novel vertical-flow settler had a much better performance in the removal of the particles in raw water than a conventional one, when they treated kaolin suspensions of different concentrations （500, 100 and 50 mg/L, respectively） coagulated by polyaluminum chloride（PAC1） at the up-flow rates of 1 and 2 mm/s, respectively.

The Influence of Geometry on the Fluid Dynamics of Continuous Settler

Settlers are broadly used by industries for separating components with different densities, because they show operational facilities and high efficiency. As they use the action of gravity, they can treat great quantities of effluents with lower energy expenditure. However, the performance of the settler depends on the streamlines inside the equipment, which, in turn, are influenced by the characteristics of the suspended solids, the geometry, and dimensions of the tank. In this paper, the effect of the settler geometry properties on the hydrodynamic in a vertical circular cylindrical tank was investigated. The evaluated parameters were the feed pipe design, the dimensions of the piece of equipment, and the structure of settler bottom. The numerical simulations were performed using the package ANSYS-CFX 16.0. It was considered a turbulent, isothermal, and stationary flow. The Euler-Euler multiphase model and BSL-RSM model turbulence were applied. The recirculation zones were influenced by the separation tank geometrical form. The modification of the feed pipe in the original project reduced the mixture inside the feedwell. The increase of the sedimentation tank diameter improved the performance of water and solid separation, elevating the efficiency by 10.48%, whilst the increase of the tank depth reduced the separation efficiency by 16.72%, in comparison to the original project.

Spanning tree trajectory optimization in the galaxy space

The 10th edition of the Global Trajectory Optimization Competition considered the problem of the galaxy settlement wherein competitors from all over the world were expected to design the trajectories of different settler vessels to maximize the given multi-faceted merit function.The synthesis methods used by the winning team,led jointly by the National University of Defense Technology(NUDT)and Xi’an Satellite Control Center(XSCC),are described along with a greedy search method and the improved solution obtained by University of Jena.Specifically,we presented a layout-first topology-second approach that allows an efficient settlement tree search guided by the pre-specified ideal spatial distribution.We also explained how the problem of constructing settlement trees can be modeled as the widely studied minimum spanning tree problem.Furthermore,University of Jena explored the possibility that a greedy search can generate even better settlement trees,based on the same initial conditions,when compared to that of the winning solution.

Analysis of floc morphology in a continuous-flow flocculation and sedimentation reactor

The floc morphology was investigated in a continuous-flow reactor, in order to understand the evolution of flocs in practical flocculation and sedimentation processes in water utilities. Kaolin-humic acid suspension was used as the test water, and polyaluminum chloride was chosen as the coagulant. An in-situ recognition system was applied to analyze the floc size, boundary fractal dimension, and eccentricity ratios. Particle numbers and turbidity were also determined in the sedimentation stage. At a coagulant dose of 1 mg/L as Al, the average floc size increased from 62 to 78 μm and the boundary fractal dimension was around 1.14, suggesting that flocs were compact and continuously grew during the entire flocculation process. However, with the dose increased to 5 mg/L, the average floc size decreased and stabilized at around 65 μm, with the fractal dimension of 1.20. It can be concluded that the excess coagulant doses resulted in the formation of chain-shaped, lower density, and more branched structure flocs, thereby restricting flocs’ further growth in the subsequent flocculation. Floc morphology analysis suggested that charge neutralization dominated in the initial flocculation stage, then the bridge and sweep mechanisms were dominant in the subsequent flocculation. In addition, compared with the traditional inclined plate settler, a novel V-shaped plate settler introduced in this study had an advantage in small size floc（less than 5 μm） removal. The V-shaped region could promote aggregate restructuring and re-flocculation; therefore, the V-shaped plate settler provides an alternative method for sedimentation.

Extraction separation of rare earth with a novel USE extractor

The extraction separation of rare earth with a new USE extractor,using kerosene solution of HEH(EHP) as an extractant was studied.In single stage extractor experiment,the stage efficiencies of the USE extractor were measured.A six-stage USE extractor experiment of separating La and Ce,and funnel cascade experiment of the same process parameters were made.The experimental results showed that the USE extractor had high stage efficiencies,small basal area and big throughput capacity per unit volume coupled with improved operating environment.

Neoliberal Multiculturalism and Western Exceptionalism： The Cultural Politics of the West

The tradition of the west defines its modernity as a radical rupture with endless possibilities for egalitarian futures; yet western modernity was rooted in the genocide of indigenous populations, transatlantic racial slavery and colonialism. Moreover, as the war on terror demonstrates, racial/gender violence continues to be linked to the formation of western identity, culture and politics in the early twenty-first century. This paper examines how the histories of race and coloniality feature in the contemporary formation of the west, with a particular focus on US nationalism and Canadian multiculturalism. These nation-states are most often defined as antithetical, with the latter confirming that western society has transcended its originary racial/colonial politics. I begin with a brief discussion of the reformation of the west in the mid-twentieth century as the USA became the dominant western power. I then move to compare the contemporary national politics of the USA and Canada to highlight the divergence and convergence in their ddineation of their identity and values. My study demonstrates that although the white supremacist discourse that presently constitutes US nationalism is at variance with the multi- culturalism that shapes Canadian identity, these discourses can be defined as twin aspects of the racial/colonial politics that continue to give meaning to the idea of the west.

Enactments of Identity in the New Zealand Short Story

New Zealand, as a nation, has been in existence for less than two cen- turies-whether one dates its assumption of sovereignty to the 1835 Declaration of Independence by the Confederation of United Tribes, the 1840 Treaty of Waitangi between Maori and the British Crown, or its attainment of Dominion status in 1907. The question of a separate cultural identity for this post-colonial, multi-cultural country has therefore always been a complex one, and one which has had a strong influence on much of our artistic expression to date： particularly, perhaps because of its inherent tendency towards the self-analysis only really possible within language, literature. The fact that our most famous locally born writer to date, Katherine Mansfield, specialised in the short story has certainly helped to establish that as a vital genre here. This paper accordingly takes four successive anthologies of local short fiction--Frank Sargeson＇s Speaking for Ourselves （1945）, Michael Morris- sey＇s The New Fiction （1985）, Warwick Bennett and Patrick Hudson＇s Rutherford＇s Dreams （1995）, and Tina Shaw and Jack Ross＇s Myth of the twenty-firstCentury （2006）--and attempts to characterise their respective, overlapping visions of New Zealand identity by conducting a close reading of a representative story from each of them. The essay concludes with a call for a new anthology which might attempt to give expression to this series of gradual erosions of our initial cultural certainties into something more adequate to the realities of our place in the world, both geo- graphically and culturally.