Presence Of Silt Research Articles

Influence of physical, biological cohesions, oil and grease on the incipient sediment motion in sewerage pipes

Sediment with varying sizes is transported through runoff, finding ways into sewerage pipes and deposited at low-velocity sections. As wastewater is high in organic content, biofilm formed on the deposited sediment, cementing the deposition and resulting in difficulties in the removal from pipes. High concentration of oil and grease in domestic wastewater promotes strengthening the cementing process of the deposited sediment. The presence of silt in the sediment distribution promotes physical cohesion, whereas biofilm through Extracellular Polymeric Substances (EPS) provides microbial cohesion. Thus, this study attempts to investigate the incipient sediment motion of sediment mixture with a different fraction of fine sand-silt, presence of biofilm through variation of EPS concentration, 0–0.1% and percentage of oil and grease (O&G) at 0–10%. The analysis showed that physical cohesion is more critical than microbial cohesion, with the presence of O&G posing the least significant on the changes of incipient sediment motion.

CESSATION OF A SUBTROPICAL GLASS RAMP DURING THE PERMIAN CHERT EVENT: MURDOCK MOUNTAIN FORMATION, WESTERN U.S.A.

ABSTRACT The Murdock Mountain Formation crops out across northern Utah and Nevada as part of the Park City Group; a unit within the greater Phosphoria Rock Complex. The Murdock Mountain is a hundreds-meters-thick section of mixed chert, dolomite, and siltstone. This unit is the southernmost expression of the widespread Permian Chert Event and offers unique views of sedimentology and paleoecology during this event. Previous researchers have described shallow-water facies dominated by biosiliceous sedimentary production as glass ramps. This framework has been speculatively applied by others to the units of the Park City Group in northern Utah and Nevada. In this study, we test whether the glass ramp depositional framework accurately represents the strata of the Murdock Mountain Formation. We use stratigraphic, hand sample, and thin section data to describe the sedimentological character of the Murdock Mountain Formation and the overlying Gerster Limestone. Four chert facies and one carbonate facies are recognized based upon the presence of silt, sponge spicules, carbonate bioclasts, and evaporites. The Murdock Mountain Formation shares many characteristics with other reported glass ramp localities. We interpret the transition from chert to carbonate-rich strata as an alternation between stable states with silica-producing fauna dominating the Murdock Mountain and carbonate-producing fauna dominating the Gerster. The takeover of biosiliceous deposition by carbonate highlights the termination of a glass ramp and the onset of a carbonate ramp regime.

Experimental Investigation and Statistical Analysis of Low Frequency RFID System

In today’s era RFID system plays a key role in the field of asset tracking but its maximum read range or detectability may get degraded due to the challenges which are being provided by varying atmospheric conditions. So, to study the effect of these challenging atmospheric conditions, experimental investigation and statistical analysis of RFID system detectability has been carried out. Varying surrounding temperature, humidity and the presence of soil layer thickness in between RFID reader and tag and its five different grain sizes were considered as input parameters. All these observations were carried out for three different soils i.e. sandy soil, Silt and clay. Execution of test was carried out according to the MINITAB 17 tool. According to ANOVA analysis as well as from interaction plot it was found that soil layer thickness have more impact on RFID system read range and R2 value was found to be 96.91%, 99.64% and 99.78% for RRSS, RRS and RRC respectively. Composite desirability of optimization was found to be 0.8425. Optimum values of process parameters Temperature, Soil Layer Thickness, Relative Humidity and Soil Grain Size were found to be 303.3°K, 2.5 cm, 40.1 %, 1.92 mm respectively. Best values of responses were found to be 10.94 cm for (Read Range in presence of Clay); 11.02 cm (Read Range in presence of Silt) and 10.97 cm (Read Range in presence of Sandy Soil).

Sorption and desorption behavior of residual antidepressants and caffeine in freshwater sediment and sewage sludge

The use of antidepressants is widespread in modern times. Thus, they present a potential risk for ecosystems due to occurrence in domestic sewage containing unaltered metabolites and structures, even after the treatment plants have processed the sewage. The current research investigated the sorption and desorption of antidepressants (citalopram, venlafaxine, fluoxetine, sertraline, and amitriptyline) and caffeine from freshwater sediment and sewage sludge. The samples of freshwater sediment were collected in a river spring in an area with few anthropogenic sources of pollution and samples of sewage sludge were taken from stabilization ponds of a sewage treatment. The matrices were mainly composed of organic fractions, sediment of humic nature, and aliphatic biomolecules in sludges. The presence of silt and clay in the sediment proved to be important for the sorption process when compared to the flocs and colloidal structure of the sludge. The kinetic study indicated pseudo-first order behavior. The Freundlich isotherm was satisfactorily used in the interpretation of sorption and desorption for all analytes and matrices. The high percentages obtained for desorption suggest analyte mobility, which is more intense in the sludge than in the sediment since each matrix has a different composition. It can be considered that the information obtained here reinforces the ecotoxicological concern with respect to pharmacological residues in the environment, as processes of retention by sorption in the sludge and the sediment have been confirmed, as well as the preferential partition of some analytes by the aqueous phase.

Origin and characterization of clay deposits in the Dupi Tila Formation of the Bengal Basin, Bangladesh

Clay is one of the most important minerals having both geological and industrial significance. Clay lenses in the Dupi Tila Formation of the Bengal Basin have been investigated to characterize and determine their origin in terms of geological environment. Clay samples have been collected from the fresh cropped surface from the areas of Dupigaon (Jaintiapur Clay), Birisiri (Bijoypur Clay), and Bandarban (Bandarban Clay) in Bangladesh. Characterizations of the clay deposits have been carried out by field investigation, scanning electron microscope (SEM), X-ray diffraction (XRD), laser particle size analysis techniques, and X-ray fluorescence (XRF). Field investigation shows that clays are white, yellowish to variegated in color with a thickness of 15 cm to about 4 m, and moderately soft. The X-ray diffraction analysis reveals that kaolinite is the predominant clay mineral in all samples with minor amounts of quartz and feldspar. SEM analysis indicates that abundant tiny disc and irregular shape of kaolinite crystals are mixed with sparse gathers of K-feldspar and detrital quartz grains. The presence of silt in all the clay samples has been verified by the gran size ranges from laser particle size analysis. The grittiness is the result of the deposition of silt considering the highest percentage in Bandarban and Bijoypur and lowers in Jaintiapur. The XRF analysis shows that SiO2 (68–75%) is the most abundant among major oxides, Al2O3 and Fe2O3 come next, along with the lower percentage of MnO, MgO, CaO, Na2O, K2O, TiO2, P2O5, and SO3. The average concentration of different trace elements has been ranging from 3 to 430 ppm. Several geochemical indices suggest that the sediments might be derived from the Shillong plateau and the Himalayas in the north and the Naga-Lushai-China Hill-Arakan Yoma mobile belt in the northeast, which are highly weathered sedimentary terrains. Provenance studies and elemental ratio supports the evidence of the felsic origin of the studied sample. The Chemical Index of Alteration (CIA) value of 93% indicates the occurrence of significant weathering in different sediment recycling phases. From the results of the aforementioned analyses, it is clear that clay lenses in the Dupi Tila Formation are in-situ in origin and parent materials are detrital rather than authigenic nature confirmed by the presence of detrital quartz and reviewing the depositional environment, which gives us the insights of the geological condition of that time as well as the possible mode of sediment transportation.

Polycyclic Aromatic Hydrocarbons in the Bottom Sediments of the River – Sea Mixing Zone on the Example of the River Chernaya and the Sevastopol Bay (the Black Sea)

Purpose. The study is aimed at determining concentrations of the polycyclic aromatic hydrocarbons (PAHs) and at revealing their pattern distribution in the bottom sediments of the "river – sea" contact zone on the example of the Sevastopol Bay and the river Chernaya. Methods and Results. Granulometric composition of the bottom sediments was determined by the decantation and dispersion method. Identification and quantitative determination of PAHs were carried out by the high performance liquid chromatography method. The total PAHs content in the bottom sediments of the area under study varied from 12 to 670 ng/g of dry weight. The pollutant content was minimum in the river site beyond the geochemical barrier. In the area where the river Chernaya flows into the Sevastopol Bay, the PAHs content was 121 ng/g. The highest PAHs content was revealed in the Sevastopol Bay bottom sediments, more precisely, in 1.5 km southwest of the river Chernaya flowing into the bay. 14 PAHs were identified in the estuary zone of the river, 4 of them (naphthalene, 2-methylnaphthalene, fluorene, anthracene) were in the trace amounts. The maximum concentration (99%) of silty material was observed in the Sevastopol Bay water area. The silt fractions were distributed as follows: 20% – aleuritic-pelite fraction, 79% – pelitic-aleurite fraction. Directly in the area of the river inflow into the bay, accumulation of the sand fraction (7%) and the maximum portion of pelitic silts were noted. Conclusions. The recorded values of PAHs corresponded to the natural non-toxic levels. PAHs identified in the bottom sediments of the river estuary zone are of the mixed, predominantly petrogenic origin. The obtained data show that in the conditions of the "river – sea" contact zone, the PAHs accumulation in general and their individual fractions were governed mainly by presence of silt in the bottom sediments.

Politsiklicheskiye aromaticheskiye uglevodorody v donnykh otlozheniyakh zony smesheniya reka – more na primere reki Chernoy i Sevastopol'skoy bukhty (Chernoye more)

Purpose. The study is aimed at determining concentrations of the polycyclic aromatic hydrocarbons (PAHs) and at revealing their pattern distribution in the bottom sediments of the "river – sea" contact zone on the example of the Sevastopol Bay and the river Chernaya. Methods and Results. Granulometric composition of the bottom sediments was determined by the decantation and dispersion method. Identification and quantitative determination of PAHs were carried out by the high performance liquid chromatography method. The total PAHs content in the bottom sediments of the area under study varied from 12 to 670 ng/g of dry weight. The pollutant content was minimum in the river site beyond the geochemical barrier. In the area where the river Chernaya flows into the Sevastopol Bay, the PAHs content was 121 ng/g. The highest PAHs content was revealed in the Sevastopol Bay bottom sediments, more precisely, in 1.5 km southwest of the river Chernaya flowing into the bay. 14 PAHs were identified in the estuary zone of the river, 4 of them (naphthalene, 2-methylnaphthalene, fluorene, anthracene) were in the trace amounts. The maximum concentration (99%) of silty material was observed in the Sevastopol Bay water area. The silt fractions were distributed as follows: 20% – aleuritic-pelite fraction, 79% – pelitic-aleurite fraction. Directly in the area of the river inflow into the bay, accumulation of the sand fraction (7%) and the maximum portion of pelitic silts were noted. Conclusions. The recorded values of PAHs corresponded to the natural non-toxic levels. PAHs identified in the bottom sediments of the river estuary zone are of the mixed, predominantly petrogenic origin. The obtained data show that in the conditions of the "river – sea" contact zone, the PAHs accumulation in general and their individual fractions were governed mainly by presence of silt in the bottom sediments

Changes in runoff and sediment load of the Huangfuchuan River following a water and soil conservation project

In this study, we analyzed changes in the water and sediment properties in the Yellow River during the flood season, which is the period with the largest runoff yield and sediment load in this river. The aim of this study was to understand the impact of water and soil conservation measures during this crucial season, and we focused on the Huangfuchuan drainage basin as the study region. We analyzed factors including the precipitation, runoff and sediment yield, and suspended sediment grain-size distribution during each of the flood seasons in 1986 to 1990 (P1) and 2006 to 2010 (P2). The results showed that most of the precipitation during the flood season was concentrated in the southeastern part of the basin. The mean flood season precipitation was similar in the two periods, with 260.1 mm and 256.9 mm in P1 and P2, respectively, but the frequency of floods in the basin decreased by 59.4% during P2. Compared with P1, the mean flood volume, sediment load, and duration during P2 decreased by 52.17%, 68.57%, and 1.52%, respectively. The composition of the sediments in the Huangfuchuan drainage basin was dominated by the presence of silts, which represented 61.2% and 96.6% of the total sediments in P1 and P2, respectively. The results obtained in this study demonstrate that the water and sediment conditions in the Huangfuchuan drainage basin during the flood season have improved over time, with a more homogeneous suspended sediment composition, more concentrated water and sediment processes, and decreases in the flood frequency, volume, and sediment transport. Our results indicate the effectiveness of river basin regulation, and they may be used as a reference for treatment of the main sediment production areas in the Yellow River.

Evaluación de la estabilidad de taludes en cárcavas, Huasca de Ocampo, Hidalgo, México.

In Santo Domingo, Huasca de Ocampo, Hidalgo, changes in the use of soil, the topographic and geomorphological conditions and the increase of runoffs, promote the formation of gullies in agricultural areas, causing the loss of soil fertility and a reduction of agricultural land. The objective of our research was to identify the main topographic features and physical/mechanical properties of the soil that cause a sidewall retreat of gullies (AV); determination was performed through principal component analysis (PCA) and multiple linear regression (MLR). The AV varied from 0.04 to 0.17 m yr‑1 with a mean value of 0.092 m yr-1. The most important variables in the PCA were: height, slope, orientation, vertical and horizontal curvature, transversal slope, ridge thickness, bulk density (0 to 5 and 5 to 10 cm), penetration resistance (2.5, 5 and 10 cm), hydraulic conductivity, shrinkage index, plasticity index, 0.25, 0.15 and 0.075 mm particles, cohesion and soil erodibility factor. The best linear regression explanatory model presented a f it value of 84.02% using four variables (particles of 0.15 and 0.075 mm, slope and ridge thickness). The AV is influenced by the presence of silt and clay in the regolith and soil surface (ridge), which are vulnerable to wetting and drying processes that boost the formation of cracks and disaggregation of the components of ridge and slope, reducing the soil’s resistance to erosion and causing headward erosion and instability in the gully slopes.

Farm-scale variations in soil color as influenced by organic matter and iron oxides in Japanese paddy fields

ABSTRACT To understand how soil color is influenced by soil components at the farm scale, we evaluated spatial variation in soil color and related soil properties in Japanese paddy fields. After harvest of rice, 246 surface soil samples were collected in 10-m grids from five contiguous irrigated paddy fields, each with an area of about 0.5 ha. The samples were analyzed to determine color parameters (L*, a*, and b*), and contents of total C, total N, Fe oxides, sand, and loss-on-ignition. The results obtained were modeled and mapped geostatistically. All color parameters indicated strong spatial dependence with long ranges (>85 m). In contrast, total C and N showed short ranges (about 40 m). The contents of Fe oxides, sand, and loss-on-ignition showed intermediate ranges (50–85 m). The ranges of these properties and their distribution patterns suggested that the contents of total C and N were influenced by long-term application of manure and that sand content was influenced by topography and past land consolidation. Further soil color analysis after removal of organic matter or silt plus clay particles revealed that soil organic matter, texture, and Fe oxides affected soil color parameters in a complex manner. Prediction of total C from soil darkness was hindered by the presence of silt plus clay particles containing Fe oxides. On the other hand, citrate-dithionite extractable Fe was estimated accurately from the b* value (yellowness), which can be useful for predicting the occurrence of akiochi (autumn decline) disease of rice at the farm scale.

Kriteria Pergerakan Ambang Sedimen bagi Campuran Sedimen Jelekit Biologi

Shields diagram is used as the main source to determine the incipient motion of sediment. However, incipient sediment motion in the Shields diagram was developed based on non-cohesive sediment where the parameter influencing the motion of cohesive and non-cohesive sediments are different. Therefore, this study attempts to investigate the incipient sediment motion for biological extracellular polymeric substance (EPS) influenced by a cohesive sediment mixture. Percentage of silt with a median grain size of 28μm (which acts as the cohesive material) and fine sand with of 150μm were varied as 10:90, 20:80, 40:60, and 50:50, which formed the cohesive sediment mixture. Two different concentrations of EPS 0.02% (which denotes as low concentration) and 0.1% (as high concentration) were well mixed with the sediment mixture. This study utilised Xanthan gum, which acts as a substitution for EPS. The experiments were conducted in a laboratory flume and the threshold criterion for sediment motion was obtained through observation. The critical Shields parameter θ_c was calculated using the critical shear velocity and root-mean-square horizontal velocity (representing turbulent fluctuations) when few of the particles on the bed was observed to move. Obvious finding from this study is the presence of EPS clearly influence the threshold criteria based on the higher value obtained at sediment mixture with 0.1% compared to the values found for the 0.02% EPS sediment mixture. The values of the critical Shields parameter were monotonously increased as the percentage of silt in the sediment mixture increases. The presence of silt in the sediment mixture increases the sediment stability signifying more hydrodynamic forces are required for the particles to be entrained. The critical Shields parameter obtained based on the critical shear velocity and turbulent fluctuations posed similar trend as described in the well-established Shields curve indicating that the velocity scale used to describe the incipient sediment motion is not a decisive factor.

ELECTRICAL RESESTIVITY INVESTIGATION FOR GROUNDWATER OF THREE VILLAGES IN SUMEL DISTRICT-DUHOK CITY NORTH OF IRAQ

A geophysical Electrical survey was conducted by applying Electrical Resistivity Sounding (VES) in three different villages located in Sumel district, which are belongs to Duhok city within the southern limb of Baikher anticline in northern of Iraq, in order to investigate the groundwater to dig wells for drinking and agriculture purposes which didn’t have available wells in villages. The survey involved sixteen vertical electrical sounding (VES) points along three profiles using a schlumberger array to investigate the subsurface aquifer of the area as well as evaluation of the groundwater aquifer characteristics in the regions. The depth of the penetration in the current study reached more than (150) m. The electric resistivity values ranged between (10-70) Ω.m. It has been recognize three geoelectrical zones at different depths in the three study areas. The first zone have electric resistivity values ranged between (20-50) Ω.m, which represented the recent deposits with the presence clay in some areas. The second zone have electric resistivity values ranged between (11-17) Ω.m, which represented a layer of sandstone of multiple sizes and saturated with groundwater, the third zone have electric resistivity values ranged between (22-55) Ω.m , which represented layers of claystone with the presence of silt in some depths. it has been observe the existence of a semi-confined groundwater aquifer due to the presence of permeable layers of sandstone and in most of the regions it is surrounded by impermeable layers of claystone rocks, and it has been determined the level of groundwater in the study areas. According to this information it has been dig the wells in those areas and found the water in depths very close from that it is reached in the vertical electrical sounding.

Suspended clays and silts: Are they independent or dependent fractions when it comes to settling in a turbulent suspension?

This research examines whether or not mixes of clay and silt in a turbulent suspension act and settle independent of each other. More specifically, we examine the following three questions: (1) does the presence of silt in suspension alter the size of mud flocs relative to those from a pure clay suspension of equivalent concentration? (2) can silt particles become bound inside clay flocs?; and (3) if silt is bound within flocs, how does this change the settling properties of the clay and silt mixture? These questions are explored through a series of laboratory experiments in which: (a) images of flocs and silt particles within the turbulent suspension are used to measure their size distribution as a function of time; and (b) the settling velocity of the individual aggregates from each of the suspensions are measured in a settling column. The experiments use pure clay, pure silt, and two different mixture ratios of silt and clay. The results show three primary conclusions. First, the presence of silt has no significant impact on floc size. Second, most of the silt in suspension became bound up within the floc aggregates. And third, the bound silt within the flocs increased the floc settling velocity by at least 50%. These results have potential implications for the modeling of suspended mud mixtures in rivers, estuaries, and turbidity currents.

SEDIMENTOS DE FUNDO E EM SUSPENSÃO NO CORREDOR FLUVIAL DO RIO PARAGUAI, PANTANAL NORTE MATO-GROSSENSE, BRASIL

To understand the variation of solid and liquid discharges during flood and drought periods, the present study aimed to analyze the types of sediments transported on the Paraguay River - the upstream in the city of Caceres (MT). The methodology consisted of collections of bottom and suspended sediments, flow monitoring and laboratory analysis with pipetting/screening and evaporation. The flow values ranged from 615,12 m³/s-1 to 135,74 m³/s-1 on the Paraguay River and from 62,28 m³/s-1 to 0,71 m³/s-1 at the entrance of the Long Bay with 56,61 m³/s-1at the exit of the Long Bay. Concerning to the average depth it was recorded a maximum of 4.73 and minimum of 0.10m. The bottom sediments showed higher sand volume (concentration above 70 %) with the presence of silt and clay. The volume of suspended solids on the Paraguay River ranged from 15412.44 tons/ day and 2111.02 tons/day. It was registered 1076.08 tons/day and 978.22 tons/day of suspended solids at the entrance and the exit of the channel of the morphological feature in the rainy season. It should be emphasized that the results of flow were higher than the historical average (1966-2002) and the values of the bottom sediments were similar to those obtained by Silva et al. (2008). The study proved relevance for the particle size characterization of the bottom sediments, and estimate of the quantity of suspended solids carried by the Paraguay River to morphological features of the floodplain. Key words: seasonality, siltation, channel abandonment.

Experimental evaluation of shear strength behaviour of plastic and non-plastic silts

Silt is available in many parts of the world in combination with sands and clays. However, due to lack of clear understanding of its engineering behaviour, most of the time it is interpreted in terms of either sands or clays. Structures that are usually built on silty soils are designed to take into account design procedures developed for sandy or clayey soils. Presence of silts in combination with varying amount of sand and clays produces silt that is either plastic or non-plastic in nature. Silt is available in and around the Delhi region, in a majority mixture along with fine sands, which is non-plastic in nature. On the other hand silty deposits found in offshore Bombay High region are found in abundance along with significant amounts of clays and are termed as plastic silts. In this paper a comparison of the stress-strain behaviour of plastic and non-plastic silts is carried out under triaxial compression loading during both drained and undrained conditions. Two representative samples each from Delhi and Bombay High regions were considered for this comparison and results of stress-strain under four sets of confining pressure are discussed in detail. It is observed from this study that behaviour of silts is mainly dependent on the composition and structure of the resultant soil matrix. It is concluded from the results that shear strength parameters as well as volume change/pore pressure response of silty soils is dominated by the constituent soil present along with the silt. It is seen from the comparative behaviour of non-plastic and plastic silts that the presence of sand and clays has a governing effect on pore pressure development and the resultant friction angle. The study also corroborated that the nature of silt is transitional both in the case of plastic and non-plastic forms.

Influence of Clay and Silt Proportions on Cement-Treated Fine-Grained Soil

AbstractNatural clay usually contains some silt, which is also a fine-grained soil. The proportion of silt in clay varies depending on the source, and the presence of silt in clay affects the reaction between the soil and cement. The purpose of this research was to study the relationship between the proportions of silt and clay in fine-grained soil and the engineering properties of the fine-grained soil after being stabilized with cement. Six types of fine-grained soils were used in this study: a natural clay and five synthetic clays with various proportions of bentonite and kaolinite. The six clays were mixed with silt in the following silt-to-clay proportions: 0∶100, 15∶85, 30∶70, and 45∶55. Cement was added to the synthetic clays in amounts corresponding to 7.5 and 15% of the dry weight of the soil, and the samples were cured for 28 days. Cement was added to the natural clay in amounts corresponding to 7.5, 15, and 20% of the dry weight of the soil, and samples were cured for 7 and 28 days. The results...

Evaluation of the liquefaction potential through dissipation measurement in PCPT

This paper discusses the interpretation of the pore water dissipation curves obtained during a piezocone test with the prime objective of determining the seismic behaviour of fine-grained soil. The pore pressure dissipation approach was attempted to perform a faster diagnosis of liquefiability of fine-grained soils where the ground water table is almost at the surface. Furthermore, because non-plastic silts are very difficult to sample for laboratory testing, such an in situ measurement appears to be the only realistic method for the purpose. Most of the dissipation tests were conducted by using the u 2 filter on the neck of the probe, and the others were performed by using the u 1 filter where the piezometer is located on the cone tip. Penetration was arrested at depths where the presence of silts had been detected by previous sounding and drilling, and t 50 , t 90 and t 100 were determined analytically. The results indicate that t 90 values have a notable potential for diagnosing a potential for liquefaction. This was demonstrated by a t 90 of 300 s or less for liquefiable layers, whereas considerably longer periods are required for non-liquefiable silts similar to clays. This feature is illustrated by the presentation of several types of dissipation curves.

Effect of algae- and silt concentration on clearance- and growth rate of the razor clam Ensis directus, Conrad

Laboratory experiments were carried out with Ensis directus to estimate clearance rate and growth rate as a function of the amount of food and presence of silt. Two food levels were tested: low food availability (6.5μg chla/l) and high food availability (16.5μg chla/l) at four silt concentrations (0, 50, 150 and 300mg/l). Clearance rates of E. directus varied between 0.7 and 5.9l/h/g DW. At a silt concentration of 300mg/l clearance rates were significantly lower (16–56%) than rates at 150mg/l, 50mg/l and 0mg/l silt. This indicates that only the highest silt concentration induced a reduction in clearance rate. The tested food levels did not influence the clearance rate of E. directus. Maximum growth rate of E. directus was 0.24mm increase in shell length and 2% increase in wet weight per day. Long-term (10weeks) exposure to silt concentrations of 300mg/l showed significantly higher growth than the 150mg/l treatment. This indicates that exposure to a high silt concentration did not induce a reduction in growth, but stimulated growth. Long-term (10weeks) exposure to a food level of 6.5μg chla per litre reduced the shell growth of E. directus with 40% compared to growth at 16.5μg chla per litre. The laboratory experiments suggest that E. directus is more sensitive to a reduction in algal concentration than to an increase in silt concentration.

Removal of dissolved organic carbon and nitrogen during simulated soil aquifer treatment

Soil aquifer treatment was simulated in 1 m laboratory soil columns containing silica sand under saturated and unsaturated soil conditions to examine the effect of travel length through the unsaturated zone on the removal of wastewater organic matter, the effect of soil type on dissolved organic carbon removal and also the type of microorganisms involved in the removal process. Dissolved organic carbon removal and nitrification did enhance when the wastewater travelled a longer length through the unsaturated zone. A similar consortium of microorganisms was found to exist in both saturated and unsaturated columns. Microbial concentrations however were lowest in the soil column containing silt and clay in addition to silica sand. The presence of silt and clay was detrimental to DOC removal efficiency under saturated soil conditions due to their negative effect on the hydraulic performance of the soil column and microbial growth.

Removal of Estrone (E1), 17β-Estradiol (E2) and 17α-Ethinylestradiol (EE2) During Soil Aquifer Treatment of a Model Wastewater

There is growing concern over the health and environmental effects posed by endocrine disrupting chemicals (EDCs) in the aquatic environment. The removal of three potent EDCs including estrone (E1), 17β-estradiol (E2), and 17α -ethinylestradiol (EE2) in a wastewater using soil columns was investigated. E2 was the most easily removed estrogen, while EE2 was the least removed. Removal efficiencies were improved as the thickness of the unsaturated zone increased whereas increased DOC improved the removal in the saturated columns. Enhanced removal efficiencies were also obtained at lower water flow rates and in the presence of silt and clay.