Laboratory Testing of Sulfamethoxazole and its Metabolite Acetyl‐Sulfamethoxazole in Soil

The fate of ¹⁴C‐labeled sulfamethoxazole and acetyl‐sulfamethoxazole in soil has been investigated with special respect to possible entry routes of human and veterinary pharmaceuticals into soil environments. Therefore, the stability of the test substances was monitored first in sewage sludge and bovine manure. Within the incubation period of 72 d, 1% at maximum of the initially applied radiotracers was released as ¹⁴C‐carbon dioxide while ?75% was transferred to non‐extractable residues that were operationally defined by the ethyl acetate extraction. Test‐sludge and test‐manure samples with defined aged residues were prepared and, supplementary to standard solutions, applied to silty‐clay soil samples. After standard and test‐sludge application, soil/water distribution coefficients of K_d < 5 L kg^–1 were determined revealing both test substances as potential leachers. In contrast, the sorption of sulfamethoxazole increased after test‐manure application (K_d > 10 L kg^–1). In the long‐term degradability tests, the metabolic fate of both test substances was characterized by the continuous decrease of extractable residues, resulting in disappearance times of DT₉₀ ? 33 d, and the increase of non‐extractable residues. Mineralization reached 11% at maximum. Thereby, the dynamics of these processes differed whether the test substances were applied via standard, test‐sludge or test‐manure application. This fact emphasized the relevance of entry route specific matrix effects on the fate of both test substances in soil.     

The Effects of Nutrients on Natural Organic Matter (NOM) Removal in Biological Activated Carbon (BAC) Filtration

Effective biodegradation of organic compounds is one of the major objectives while optimizing biological drinking water treatment processes. Enhancing the biological activated carbon (BAC) filter performance with nutrient addition was studied using chemically pre-treated and ozonated lake water. Three parallel pilot-scale biofilters were operated: one with phosphorus addition, one with a mixture of inorganic nutrients addition, and one as a reference. The addition of nutrients had no statistically significant influence on the natural organic matter (NOM) removal when monitored by total organic carbon (TOC), UV absorbance, and assimilable organic carbon (AOC). However, the addition of nutrients significantly increased the heterotrophic plate count (HPC) bacteria of the filter effluent, while the adenosine triphosphate (ATP) analysis of the attached bacteria did not show any increase in BAC filters. It seemed that in BAC filters the bacterial growth was limited by phosphorus, but the increased bacteria could not attach themselves during the relatively short acclimatization period.     

Study on the particle breakage of ballast based on a GPU accelerated discrete element method

Breakage of particles will have greatly influence on mechanical behavior of granular material(GM)under external loads,such as ballast,rockfill and sand.The discrete element method(DEM)is one of the most popular methods for simulating GM as each particle is represented on its own.To study breakage mechanism of particle breakage,a cohesive contact mode is developed based on the GPU accelerated DEM code-Blaze-DEM.A database of the 3D geometry model of rock blocks is established based on the 3D scanning method.And an agglomerate describing the rock block with a series of non-overlapping spherical particles is used to build the DEM numerical model of a railway ballast sample,which is used to the DEM oedometric test to study the particles’breakage characteristics of the sample under external load.Furthermore,to obtain the meso-mechanical parameters used in DEM,a black-analysis method is used based on the laboratory tests of the rock sample.Based on the DEM numerical tests,the particle breakage process and mechanisms of the railway ballast are studied.All results show that the developed code can better used for large scale simulation of the particle breakage analysis of granular material.     

Scouring of a granular bed by dam break: Experimental study and numerical simulation by a VOF-LPT coupling

The first part of the research reported here consists of an experimental campaign to study the scouring of a granular bed(glass beads, sand) induced by a dam break in an open channel. Two configurations are considered: with and without cylinders. In the second part of this study, the volume of fluid method coupled with the shear stress transport turbulent model and the lagrangian particle tracking method is used to simulate the local scour processes. The four-way coupling is realized by consider...     

Numerical simulations of flow motion and deposition characteristics of granular debris flows

Flow motion and deposition characteristics of debris flows are of concern regarding land use planning and management. A simple model for the prediction of mentioned characteristics has been developed, incorporating a friction–collision rheological model. It demonstrated to be able to satisfactorily simulate the two-dimensional behavior of laboratory results and the one-dimensional behavior of two real debris-flow events. The numerical results show that the topography of the channel bed, the yield stress level of the debris flows, and the inflow pattern have significant influence on the simulated flow motion and deposition characteristics of debris flows. In addition, the predicted run-out distance has been compared with analytical solutions and field observations. The model could be employed for the preliminary evaluation of one-dimensional run-out distance of granular debris flows provided that the volume of the debris involved in the initial mobilization is assumed.     

Fabric evolution in a numerical direct shear test

This paper presents a three-dimensional discrete element study on the mechanical behaviour and fabric changes of elongated particle assemblages in a direct shear test. Assemblages with elongated particles are prepared under different preparation methods: random placing and deposition. Particles are generated inside a direct shear box with arbitrary orientations in the random placing method. In the deposition approach, two directions of deposition are used: perpendicular and parallel to the shear direction. Assemblages formed by different methods give significantly different initial particle orientations. Different dilatancy responses and shear strengths are resulted upon shearing. Change in fabric along the shear plane is noticeable and the magnitude of such rotation depends highly on the initial particle orientation.     

Modelling the pre-failure instabilities of sand

A simple incremental model describing the pre-failure behaviour of granular soils is presented. The model describes both the dry/fully drained and undrained response. It takes into account an initial anisotropy of soil and an initial state defined as either contractive or dilative. A physically sound definition of loading/unloading is assumed, which differs from elasto-plastic approaches. The model is based on extensive empirical data and gives predictions conformable with experimental results. It also describes pre-failure instabilities of granular soils, both dry/fully drained and undrained. The Hill’s criterion was used to examine stability. It was shown that this condition can be formulated either in terms of the effective stresses or by the total stresses. In the extreme cases of either dry/fully drained or undrained conditions, these alternative formulations are equivalent. This is not so in the case of partial drainage of pore water and associated volumetric deformations as well as pore pressure changes. The model describes the pre-failure instabilities well, and additionally allows for analytical derivation of the instability line. It was shown that the second order work, appearing in the Hill’s condition, is equivalent to the entropy source.     

Rheologic evolution of low-grade metasedimentary rocks and granite across a large strike-slip fault zone: A case study of the Kellyland fault zone,Maine, USA

We examine a large strike-slip fault zone that juxtaposes low-grade clastic metasedimentary rocks with coarse-grained granite near the brittle-ductile transition. The load-bearing matrixes in granite-derived ultramylonites and pelite and wacke metasedimentary intervals are texturally similar, and all deformed by diffusion-assisted granular flow. Granite underwent rapid strengthening as the pluton cooled followed by rapid weakening driven by brittle grain-size reduction and mixing that catalyzed ultramylonite formation. The textural and mineralogical similarity of pelitic intervals across the zone indicates they experienced little textural and reaction weakening. Wacke intervals record progressive textural and reaction weakening in an open system. Quartz recrystallized grain sizes in granite-derived ultramylonites record ∼2-times more differential stress than those in metasedimentary rocks in the interior of the zone. The relative weakness of metasedimentary rocks is correlated with fluid influx that likely enhanced diffusion and grain-boundary sliding in pelitic and wacke intervals and catalyzed textural and reaction weakening in wacke intervals. The lack of evidence for fluid and ionic communication with granitic rocks indicates that fluid movement was restricted to foliation-parallel pathways within single rock units. This localized fluid influx is the best explanation for the strength contrasts between texturally similar fault rocks deformed by similar mechanisms.     

Das Entwässerungsverhalten von Klärschlamm in Gegenwart von Polyelektrolyten

Dewatering Behaviour of Sludge in the Presence of Polyelectrolytes Interactions of sludge particles with well defined synthetic polyelectrolytes of different charge, molecular mass, and molecular geometry were investigated by means of zeta- and streaming potential measurements and polyelectrolyte titrations. Different mechanisms of flocculation were discussed with regard to the dewatering behaviour of the sludge. In dependence on the flocculation procedure (cationic monoflocculation, anionic-cationic, and cationicanionic dual flocculation) as well as on the chain length and branching of the polyelectrolytes used, different mechanisms of sludge dewatering were discussed: Polyanions are not adsorbed on the sludge particles and lead to a decline of the dewatering results. Linear short chain polycations result in a flocculation after surface charge neutralization of the particles according to a patch mechanism. Long chain linear polycations cause a bridging of the particles leading to a flocculation without charge neutralization of the aggregates formed. With branched polycations, a flocculation according to a patch mechanism is observed. These polycations form sludge particle aggregates which are surface charge neutralized at the flocculation point. In anionic-cationic dual flocculations using long chain polycations, an inclusion flocculation due to polyanion-polycation complex formation is the predominating mechanism. The cationic-anionic dual flocculation with complete covering of the particles with polycations in the first step can be discussed by a patch mechanism quite similar to an anionic monoflocculation of cationic particles. By knowing the mechanism of interaction for a given flocculation agent, an optimal sludge dewatering procedure can be predicted.     

散粒体斜坡注浆固坡工程防治技术实验研究

目前,国内外对散粒体斜坡的防治措施研究甚少。笔者推荐注浆固坡工程防治技术,具有以动制动特点。本文通过室外注浆物理模拟实验,得出注浆后固结体形态有舌形、灵芝形、柱形、长倒锥形、短倒锥形,其有效半径分别是46.3cm、26cm、21.4cm、16.5cm、40cm、29.4cm。结合现场颗粒取样筛分实验,研究了散粒体堆积结构对注浆固坡措施的影响,提出颗粒间孔隙比的影响最为主要,并通过计算机优化回归得出注浆量及浆液扩散半径的公式;最后对固结体进行直剪试验,得出注浆后的散粒体强度增加,说明了注浆固坡工程的可行性和合理性。这对散粒体斜坡坡体实施注浆加固工程具有重大的参考价值。