Dynamics of phosphorus, nitrogen and carbon removal in a horizontal subsurface flow constructed wetland

The dynamics of nitrogen (N), phosphorus (P) and carbon (C) accumulation in the filter material of a horizontal subsurface constructed wetland (HSSF CW; established in 1997) and in a specially designed oil-shale ash filter (2002) for P retention have been studied. Concentrations of N, P and C in filter media (coarse sand) in the HSSF beds show an increasing trend. Both the annual accumulation of P and increasing outflow concentrations of P in the HSSF CW reflect the possible saturation of filter media with P after 8 years working. Tested ash material derived from oil-shale combustion demonstrated very high P removal efficiency in laboratory batch experiments. However, during the first 4 months of the in situ ash filter experiment, the efficiency of P removal was about 71% (an average outflow concentration of 1.9 mg L(-1) was achieved). Subsequently, the efficiency decreased to 10-20%, which might be a sign of saturation or clogging due to quick biofilm development on the ash particles. The increasing of hydraulic retention time and the improvement of design for maximal contact between material and wastewater are considered to be key factors that can provide optimal pH for the removal processes.     

The efficacy and use of small centrifuge for evaluating geotextile tube dewatering performance

Geotextile tube dewatering technology has been widely used over the past two decades for dewatering high water content slurries. The dewatering process in geotextile tubes aims to decrease the volume of the dewatered slurry, which helps in the transportation, disposal, and reuse of the dewatered material. Several researchers have emphasized the effect of the retained sediment (filter cake) properties, in particular final solids content and volume (height) change, on the feasibility of geotextile tube dewatering projects. Retained sediment properties are often evaluated using small scale tests such as rapid dewatering test, falling head test, pressure filtration test (PFT), and field scale tests such as hanging bag test (HBT) and geotextile tube demonstrations test (GDT). In this study, centrifuge test is introduced as an alternative for the widely used pressure filtration and falling head tests to evaluate retained sediments properties. Centrifuge test provides a mechanism for understanding the response of slurries to externally applied pressure in geotextile tube environment. Centrifuge test was used to evaluate maximal solids content of the retained sediments and change in slurry volume of four soils that represent typical dredged soils. Tully sand, Tully fines, Elliott silt loam, and kaolin slurries were used at varying solids concentrations. Slurries were subjected to external stresses between 0.1 and 40 kPa by applying centrifugal speeds between 300 rotation per minute (rpm) and 1800 rpm. Both centrifuge test and PFT were conducted with unconditioned and cationic polyacrylamide conditioned slurries. Centrifuge tests results were compared with PFT results with respect to retained sediments final solids content and volume change. Tests results indicated that the maximal solids concentration of the retained sediments in saturated conditions is unique for each soil and is independent of the initial slurry solids concentration. Tests results also indicated that there is linear relationship between the initial concentration of the slurry and the final volume change at any externally applied stress. Finally, a relationship between the total pumped slurry volume and the final height of the dewatered sediments in a geotextile tube is presented.     

Clogging of stormwater gravel infiltration systems and filters: insights from a laboratory study

Stormwater infiltration systems are widely used in the control of polluted urban runoff. They are very effective in reducing the volume of stormwater runoff and improving its quality, but they are known to be prone to clogging. Whilst it is evident that clogging determines the design lifespan of infiltration systems, quantitative understanding of the clogging process is currently very limited. A laboratory study was therefore undertaken to better understand physical clogging processes, with the ultimate aim of developing a clogging model for stormwater infiltration systems. This paper presents findings from one-dimensional (1-D) experiments conducted on a gravel filter column. Physical clogging was studied under both constant and variable water levels, and for different sediment inflow concentrations. It was found that a clogging layer forms at the interface between the filter and underlying soil, irrespective of the inflow regime of both water and sediment. It was also found that clogging is much slower if the water level is kept at a constant level than if it varies within the column, due to formation of a sediment plug that 'shelters' the filter/soil interface. Most importantly it was shown that physical clogging is mainly caused by migration of sediment particles less than 6 microm in diameter. A simple regression model was proposed and tested for the prediction of clogging due to stormwater sediment.     

Untersuchung der Verockerungsneigung von Vertikalfilterbrunnen im Modellversuch

Operating wells are often influenced by performance losses which increase over time. These losses can be caused by clogging of system elements due to oxidation and precipitation of diluted Fe(II)- and Mn(II)-ions to Fe(III)- and Mn(IV)-hydroxides. The influence of iron clogging on the conductivity of the gravel pack??in particular on the hydraulic gradient in the gravel pack??is analyzed with a combined hydraulic and hydrogeochemical model of a vertical well in which the clogging process is accelerated by hydrochemical modifications. Over 295 h, the iron concentration in the filter gravel increased up to 15 g Fe per kg gravel. According to the preliminary findings, these incrustations induce an increase of the pressure loss in the filter gravel pack of nearly 30?%. After defining a test termination criterion, the model will be used for tests concerning different well material (screen and gravel pack) and methods for reduction of the incrustation (operation and regeneration) as well as for parametric studies.     

On the measurement of particulate association of americium in freshwater

A laboratory investigation tested various filtration methods to study the particulate-water fractionation of ²⁴¹Am added to filtered freshwater (Monaco tap water) adjusted to different pH's. By using a system of washed Nuclepore polycarbonate filters, the particulate association (>0.2 or >1 μm) was found to increase hyperbolically with pH and with time, so that less than 1% of the Am was filterable (i.e. retained by a filter) at pH 4.2 and about 5% was filterable at pH 8.2 after 1 day; light had no apparent effect on the filterability of the Am. These values are somewhat greater than those for particle association of Am in seawater but substantially lower than previous estimates of Am particulate association in filtered freshwater. Filter adsorption problems are identified for other filtration systems commonly employed to assess metal particulate association. The results suggest that Am in freshwater is unlikely to form particles to an appreciable extent at pH's ?8.     

Metal sorption to natural filter substrates for storm water treatment--column studies

Storm water generated from road runoff contains pollutants such as metals that are either dissolved in storm water or bound to particulates. Using detention ponds for the treatment of storm water from road runoff, where particles can settle, can reduce the level of particulate-bound metals in the water, while small particles and dissolved matter pass through the detention pond. Some of these metals can be removed by filtrating water through specially constructed filter systems. This investigation is a laboratory study where different filter substrates were tested in order to evaluate their efficiency in reducing heavy metals from water. Metal solutions were filtered through columns filled with various substrates consisting of combinations of calcium silicate rock (opoka), zeolite and peat. The metal-removal efficiency was correlated to hydraulic load, and for the metal species the reduction efficiency decreased with increased hydraulic load. Mixtures of opoka and zeolite were found to be superior to the other filter-substrate combinations tested with regard to both hydraulic aspects and removal efficiency. Peat mixed with the calcium silicate rock was not successful due to clogging which stopped the experiment. A manufactured product made from the calcium silicate rock (burned opoka) was found to be less useful because of its calcium oxide (CaO) content. Among the tested filter substrates, mixtures of opoka and zeolite seemed to be the most useful compositions with respect to reduction-efficiency and clogging aspects. The removal capacity of metals varied from 0.6 to 1.8 kg m(-3) depending on the metal and the filter substrate.     

Dissolved and particulate metals (Fe, Zn, Cu, Cd, Pb) in two habitats from an active hydrothermal field on the EPR at 13 degrees N

The distribution of Fe, Cu, Zn, Pb, Cd between the dissolved (<2 microm) and the particulate (>2 microm) fractions was measured after in-situ filtration in two hydrothermal habitats. The total metal concentration ranges exhibit a clear enrichment compared with the seawater concentration, accounting for the hydrothermal input for all the metals considered. Iron is the predominant metal (5-50 microM) followed by Zn and Cu. Cd and Pb are present at the nM level. At the scale studied, the behavior of temperature, pH and dissolved iron is semi-conservative whereas the other dissolved and particulate metals are characterized by non-conservative patterns. The metal enrichment of the >2 microm fraction results from the settlement and accumulation of particulate matter close to the organisms, acting as a secondary metal source. The enrichment observed in the dissolved fraction can be related to the dissolution or oxidation of particles (mainly polymetallic sulfide) or to the presence of small particles and large colloids not retained on the 2 microm frit. SEM observations indicate that the bulk particulate observed is characteristic of crystalline particles settling rapidly from the high temperature smoker (sphalerite, wurtzite and pyrite), amorphous structures and eroded particles formed in the external zone of the chimney. Precipitation of Zn, Cu, Cd and Pb with Fe as wurtzite, sphalerite and pyrite is the main process taking place within the area studied and is semi-quantitative. The distribution of the dominant observed fauna has been related to the gradient resulting from the dilution process, with the alvinellids worms colonizing the hotter and more variable part of the mixing zone, but also to the metallic load of the mixing zone. Dissolved and particulate metal concentrations are therefore necessary abiotic factors to be studied in a multiparametric approach to understand the faunal distribution in hydrothermal ecosystems.     

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.     

Influence of clogging substances on pore characteristics and permeability of geotextile envelopes of subsurface drainage pipes in arid areas

This study investigates the influence of clogging substances on pore characteristics and permeability of geotextile envelopes that were used for 3, 7 and 15 years in irrigated farmlands in Xinjiang region, which is arid and suffers from the soil salinity problem. Results show that the macropores (above 125 μm) of envelopes are evidently clogged, whereas the smaller pores less than 100 μm are still unblocked after operation. The permeability coefficients of geotextile envelopes after serving for 3 and 15 years are smaller than the minimum required permeability coefficients after clogging. The main chemical components of clogging substances in the geotextile envelope are silicon dioxide and calcium carbonate. Calcium carbonate content of the geotextile envelope is consistent with calcium carbonate content of soil. Chemical clogging susceptibility increases with the operation time of the subsurface drainage pipes. The ratio of O₉₀ size of envelope material over d₉₀ of soils (O₉₀/d₉₀) and saturation index (SI) can be used to assess the susceptibility of physical and chemical clogging respectively. This study provides a preliminary reference for estimating the clogging susceptibility of geotextile envelopes in arid areas.     

Isoconcentration mapping of particulate matter in Hamedan intercity bus stations

To accomplish this study, the total concentration of suspended particles, PM₁₀ and PM_2.5, was mapped at intercity bus stations in the central square of Hamedan. To measure the particulate matter (PM), portable air sampling systems that collect integrated filter samples were used. The PM concentration was collected at various time intervals and measured gravimetrically. The results were then analysed using the ArcView GIS 3.3 software to map the particulate dispersion patterns. The mean concentrations of the total suspended particles (TSP), PM₁₀ and PM_2.5 were 1220.94 ± 1418.5, 524.7 ± 217.5 and 386 ± 193.6 μg/m³, which were 16, 7.72 and 4.7 times greater than the World Health Organization (WHO) air quality standard, respectively. The PM concentration was not correlated with wind velocity or air temperature, but was correlated with humidity (P = 0.01). Overall, the results of this pilot study indicate that people at bus stations are exposed to respirable particulate matter (RPM) at levels high enough to pose a serious health risk.     

Experimental results and mathematical modelling of an autotrophic and heterotrophic biofilm in a sand filter treating landfill leachate and municipal wastewater

A better understanding of wastewater treatment with soil filters is important to optimise plant operation and reduce the risk of clogging. The article presents results of a treatment concept which uses a combination of SBR and vertical-flow sand filter technology. The SBR was mainly used for denitrification and sedimentation of substances in particulate form. Efficient nitrification was achieved by the planted sand filter. Degradation rates of 10gNH(4)-N/(m(2)xd) were measured for periods with peak loadings. The two-dimensional dynamic model reproduces the biofilm growth and decay of heterotrophic and autotrophic biomass. It is capable of describing the clogging of the sand filter by combining a biochemical and a geometric model. After calibration, the model was used for the calculation of maximum nitrogen degradation performances. Maximum degradation rates of 12gNH(4)-N/(m(2)xd) can be achieved if the COD/TKN ratio is reduced before to a level lower than that of municipal wastewater. The COD was further degraded in the filter than we expected comparing it with activated sludge plants. Within the soil filter a biofilm thickness of up to 110mum is simulated depending on the embankment of gravel and grains of sand. Sensitivity analysis of model parameters showed the high impact of the maximum autotrophic growth rate, the autotrophic yield, the diffusion coefficient for oxygen and the number of contact points of the single grains of sand.     

武山尾矿坝无纺土工织物滤层化学淤堵问题初探

土工织物作为滤层在尾矿坝排渗设施中已得到广泛应用,但有些尾矿坝遇到了土工织物淤堵问题。本文针对武山铜矿尾矿坝排渗系统中发生的土工织物淤堵问题,通过一系列试验研究对无纺土工织物化学淤堵问题进行了初步探讨。研究结果表明氢氧化铁凝胶在织物纤维上的附着是化学淤堵的主要机理,尾矿中含有充分多的细粒黄铁矿且滤层处于非饱和渗流带或饱和- 非饱和交替变化渗流带是土工织物发生严重化学淤堵的必要条件     

Export of mirex from Lake Ontario to the St. Lawrence Estuary

The relative importance of migrating eels and suspended particulate material (biotic and abiotic) as transporters of mirex from Lake Ontario to the St. Lawrence River Estuary is evaluated in the context of a possible adverse impact on the St. Lawrence beluga population. Our estimates suggest that transport of mirex out of Lake Ontario by eels (2270 g annually) is almost twice that due to suspended particulate flux (1370 g annually). Mass balance calculations for mirex in Lake Ontario indicate that transport by migrating eels and particulate matter, combined with coverage of surficial sediments by continuing deposition of new material, could effectively "cleanse" Lake Ontario of mirex inputs in 100 years or less. Using mirex as a prototype to simulate the fate of hydrophobic organic chemicals in Lake Ontario led to a revised sediment budget for this final lake in the Great Lakes-St. Lawrence system. According to this budget, 94% of the suspended particulate material entering Lake Ontario is retained in the depositional basins and, by inference, most hydrophobic organic contaminants and metal forms having a dominant association with the particulate phase, would be expected to behave in a similar fashion.     

The Wind Effect on the Transport and Burning of Firebrands

Firebrands, controlling spot fires, are often responsible for fast damages in wildland and urban fires. However, the behaviours of firebrands are difficult to predict. In this study, we conduct experiments in a wind tunnel to investigate the effect of wind on the smouldering burning and transport of firebrands. Three different sizes of disc wood particles (weighing about 1 g) are heated to generate smouldering firebrands, and then blown out by a horizontal wind of 5 or 7 m/s. In each experiment the transport distance (in the order of 1 m) and mass loss of firebrands are measured to examine their burning behaviours. For the first time, a bimodal distribution (burning and extinction modals) is observed for small firebrands under certain wind speeds (firebrands of 12-mm diameter and 5-mm thickness under a wind speed of 7 m/s in this work). Both the firebrand transport distance and mass loss in the extinction modal are smaller than those in the burning modal. The heat transfer analysis shows that there is a critical wind speed to quench the firebrand and produce a bimodal distribution, and its value increases with both the particle size and the heating duration. The predicted critical wind speed agrees well with experimental measurements.     

Levoglucosan as a Tracer for Smouldering Fire

Detecting fires at an early stage is crucial for mitigating and extinguishing fires. The increased use of biofuels in Northern Europe has led to an increased number of fires in storage facilities. These fires are often caused by self-heating in the interior of the stored materials and slowly develop to smouldering fires. Consequently, these smouldering fires are usually detected several days or weeks after the initial smouldering fire had started. At this point, measures to extinguish the smouldering fire inside the material are difficult as the fire has grown for a long time and is located inside the material. This makes it difficult to gain a successful effect of any extinguishing agents. This paper presents a pilot study in lab scale suggesting levoglucosan as an early tracer for smouldering fires using 600 g cotton as the biomass source. The advantage of detecting levoglucosan as a fire signature is that it serves as a tracer compound for biomass burning and is produced at temperatures of 200–400°C reducing the risk of false alarms from emissions produced at lower temperatures. In this paper, levoglucosan was detected in aerosols emitted in an early stage from smouldering fires and was analyzed by ultrasonic assisted extraction followed by gas chromatographic separation and mass spectrometric detection. First detection of levoglucosan was made in the first sample, collected after 30 min when the smouldering fire was only a few cubic centimeters of the cotton package. In addition, levoglucosan was found in the solid residues of carbonized cotton after the initial smouldering process had moved through the material. The findings should be regarded as screening results to be used for the development of sensors and technology for smouldering fire detection.     

Urban development and particulate air pollution in Coimbatore city,India

Haphazard urbanization and unprecedented vehicular growth that exacerbate air quality are prevalent features in India. Coimbatore, an important industrial city ranking 15th in terms of principal urban agglomerations of India, was classified as a moderately polluted area in National Ambient Air Quality Monitoring survey in 1997. The current study (March 1999–February 2001) was undertaken to assess suspended particulate matter (SPM) in urban and suburban Coimbatore. It was found that in the Coimbatore atmosphere SPM with a diameter of less than 10 µm (respirable fraction, RSPM or PM₁₀) and those with a diameter above 10 µm, the non‐respirable (NRSPM) fraction, ranged between 30–149 µg/m³ and 24.4–460 µg/m³ respectively. The study infers that urban areas, especially those with frequent vehicular traffic and traffic congestion, had comparatively high RSPM exceeding the Indian prescribed standards (60 µg/m³). Emission inventory estimated for current vehicle strength showed that about 840 000 kg of particulate matter was emitted during 2001. Wind speed negatively correlated with RSPM, while it was positively correlated with NRSPM. Temperature had a negative correlation with RSPM values.     

Migration and speciation of lead in a river system heavily polluted from a smelter

Anodic stripping voltammetry was used for the study of the migration and speciation of lead in surface waters affected by atmospheric deposits around a smelter, by ore mining and urban runoff. Three physiocochemical forms of lead were distinguished: dissolved-labile (Pb²⁺, PbOH⁺ and PbCO₃), dissolved-bound (colloids or strong complexes) and particulate (retained by 0.40 μm membrane filter). Labile forms represented a very significant part of lead input from the washout of the atmospheric deposits, whereas most of lead from urban runoff and ore mining was in particulate or bound forms. Rather large stability of high concentrations of the labile forms of lead in the waters was found. It has been concluded that the precipitation of sparingly soluble lead compounds is not a primary factor controlling the concentration of dissolved lead in stream waters. The migration and speciation of lead was strongly affected by water flow rate. With increasing water flow rate, the concentration of particulate and labile lead increased whereas the concentration of bound forms decreased. Most of the lead was carried downstream in a small river during high water flow rate, but sedimented in a larger river. Rapid removal of lead by sedimentation occurred during low streamflow conditions.     

Particle removal efficiency of the portable HEPA air cleaner in a simulated hospital ward

Use of a HEPA (high efficiency particulate air) filter in a room is believed to assist in reducing the risk of transmission of infectious diseases through removing the particles or large droplets to which pathogens may be attached. Use of a portable HEPA filter(s) in hospital wards is hypothesized to increase the effective ventilation rate (for particles only). Use of a portable HEPA filter is also hypothesized to increase the effective airflow rate of the general ward to the standard of an isolation ward for emerging infection diseases. This may be a good solution for housing patients when the number of beds in an isolation ward is insufficient. An experiment was conducted in a full scale experimental ward with a dimension of 6.7 m × 6 m × 2.7 m and 6 beds to test these hypotheses for a portable HEPA filter. The removal efficiency for different size particles was measured at different locations. The influence of the portable HEPA air cleaner on the airflow pattern was also studied through smoke visualization and computational fluid dynamics (CFD) simulations. Results show that the HEPA filter can effectively decrease the particle concentration level. The effective air change rate achieved by the HEPA filter (for particle removal only) is from 2.7 to 5.6 ACH in the ward. The strong supply air jet from the portable HEPA filter interacted with the room airflow pattern and became dominate, introducing global airflow mixing in the room. Background noise levels were also measured and noise level in the room increased when the maximum airflow of the filter was used.     

Clogging in intermittently dosed sand filters used for wastewater treatment

Clogging in intermittent sand filter (ISF) systems was analyzed using an unsaturated flow model coupled with a reactive transport model. Based on the results of a model sensitivity analysis, several variables were determined to be important in the clogging phenomena observed in ISFs, including hydraulic loading rate, influent chemical oxygen demand (COD) concentration, filter dosing frequency, and time of operation. Several modes of operation were identified that minimize the growth of bacteria at the filter surface. Following the sensitivity analysis, several case studies where ISF clogging was documented were simulated using the model. The results from the case study model simulations were found to be correlated with the total suspended solids loading rate (TSSLR) at the point of clogging. A model was developed that relates biomass development at the surface of ISFs with the TSSLR that can be sustained without clogging. The engineering significance of the model is presented in terms of operational and design considerations.     

Detection of Pb-LIII edge XANES spectra of urban atmospheric particles combined with simple acid extraction

Pb-LIII edge XANES spectra of atmospheric particles are directly obtained by fluorescent XAFS spectroscopy using a 19-element solid state detector (SSD). Particulate sample was collected on a quartz fiber filter using a high-volume air sampler, and the filter was cut into small pieces (25x25 mm). Then, surface layer of the filter piece was scaled and accumulated in order to enhance the particle density per filter unit. Use of 10 pieces of the surface layer enables the measurement of Pb-LIII edge XANES spectra on beamline BL01B1 at SPring-8, Hyogo, Japan. The shape of the Pb-LIII edge XANES spectra of the particulate sample is similar to the shapes of the spectra for PbS, PbCO(3), PbSO(4) and/or PbCl(2). Additionally, the filter sample is also divided into water-soluble, 0.1 M HCl-extractable, and residual fractions of Pb compounds by a simple acid extraction procedure. We discuss the possibility of Pb speciation in the particulate samples with combination of highly sensitive XANES spectroscopy and simple acid extraction.