A contribution to environmental risk assessment for transport of cadmium through groundwater layers. Case study of the Sava river (near Zagreb, Croatia) region

Adsorption capacities of cadmium on aquifer material of the Sava River alluvial sediment were determined as a function of flow rate, pH and presence of organic coating using laboratory column technique. In a permeameter with constant hydrostatic pressure, a laboratory coefficient of permeability, K_l, and a specific coefficient of permeability, K_s, have been determined. The value of 28.6 Darcy for specific permeability shows that the sediment belongs to a good aquifer (permeability >1 Darcy). The adsorption capacity of cadmium at the bottom of the breakthrough curve, C_sb, of a fresh sediment at pH 5.8 varied from 0.40 to 0.45 mg g⁻¹ at axial flow rate between 98 and 501 cm h⁻¹. Capacity values of maximum adsorption, C_s, were in the range from 0.67 to 0.72 mg g⁻¹. This implies a significance of C_sb values in risk assessment studies concerning a discharge of cadmium into rivers and lakes and its input to groundwater layers. Distribution coefficients, K_d, were between 26.3 and 28.2 ml g⁻¹. In order to create a more reproducible column, a fraction between 125 and 250 μm was used. In that case C_s values varied from 0.25 mg g⁻¹ at pH 2.5 (organic coating present) to 1.12 mg g⁻¹ at pH 5.8 (organic coating removed).     

Fe(III) homogeneous photocatalysis for the removal of 1,2-dichlorobenzene in aqueous solution by means UV lamp and solar light

Chlorinated hydrocarbons are widely used in chemical industries as solvents and intermediates for pesticides and dyes manufacture. Their presence was documented in rivers, groundwaters and seawaters.

In this work, the oxidation of 1,2-dichlorobenzene in aqueous solutions by means of Fe(III) homogeneous photocatalysis under UV lamp and sunlight irradiations is studied. The results show that the best working conditions are found for pH=3.0 and initial [Fe(III)] concentration equal to 1.0×10⁻⁴ mol L⁻¹ although the investigated system can be utilized even at pH close to 4.0 but with slower abatement kinetics.

Some dicholoroderivatives, such as 2,3-dichlorophenol, 3,4-dichlorophenol and 2-chlorophenol, are identified as oxidation intermediates. The values of the kinetic constant for the photochemical reoxidation of Fe(II) to Fe(III) are evaluated by a mathematical model in the range 1.58–3.78 L mol⁻¹ s⁻¹ and 0.69–0.78 L mol⁻¹ s⁻¹ for the systems irradiated by UV lamp and sunlight, respectively.     

Alteration to lake trophic status as a means to control arsenic mobility in a mine-impacted lake

The relationship between lake trophic status, sedimentary redox conditions and As mobility was examined in mine-impacted Balmer Lake, Canada. Under the current redox regime, the reductive dissolution of As-bearing Fe(III) oxyhydroxides occurs in close proximity to the sediment–water interface, resulting in the remobilization of dissolved As in the shallow porewaters to values as high as 8.5 mg L⁻¹. The shallow depth of the oxic zone limits the extent to which As can be re-sorbed in the interfacial horizons, and as a result, a proportion of the remobilized As escapes into the water column where it poses a water quality concern. Examination of the relationship between summer average chlorophyll a and total P at spring overturn in the lake water column demonstrates that Balmer Lake is currently eutrophic as a result of mining-derived inputs of P (domestic waters) and N (blasting residues and cyanide breakdown products). The results suggest that actively pushing the system towards oligotrophy by reducing non-natural P loadings to the system will decrease rates of in situ production and associated sediment oxygen demand, which will in turn result in increased thickness of the aerobic zone and enhanced As scavenging. Such conclusions are supported by porewater data which indicate that the flux of As to the water column is significantly reduced when the Fe(III) redox cline is situated at deeper sediment depths. In the absence of detailed P-loading data, it is recommended that P inputs be reduced to 10% of the estimated pre-mining P loading of 200 kg yr⁻¹. This implies reducing the collective P-loadings from the two mine sites adjacent to the lake from the approximate current value (150 kg yr⁻¹) to 20 kg yr⁻¹. It is proposed that establishment of oligotrophy in the lake should significantly mitigate the current level of dissolved As in lake waters.     

Relating seismic velocities, thermal cracking and permeability in Mt. Etna and Iceland basalts

We report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from Etna (Italy) and columnar basalt from Seljadur (Iceland). Measurements were made in a servo-controlled steady-state-flow permeameter at effective pressures from 5–80 MPa, during both increasing and decreasing pressure cycles. Selected samples were thermally stressed at temperatures up to 900 °C to induce thermal crack damage. Acoustic emission output was recorded throughout each thermal stressing experiment.

At low pressure (0–10 MPa), the P-wave velocity of the columnar Seljadur basalt was 5.4 km/s, while for the Etnean lava flow basalt it was only 3.0–3.5 km/s. On increasing the pressure to 80 MPa, the velocity of Etnean basalt increased by 45%–60%, whereas that of Seljadur basalt increased by less than 2%. Furthermore, the velocity of Seljadur basalt thermally stressed to 900 °C fell by about 2.0 km/s, whereas the decrease for Etnean basalt was negligible. A similar pattern was observed in the permeability data. Permeability of Etnean basalt fell from about 7.5×10⁻¹⁶ m² to about 1.5×10⁻¹⁶ m² over the pressure range 5–80 MPa, while that for Seljadur basalt varied little from its initial low value of 9×10⁻²¹ m². Again, thermal stressing significantly increased the permeability of Seljadur basalt, whilst having a negligible effect on the Etnean basalt. These results clearly indicate that the Etnean basalt contains a much higher level of crack damage than the Seljadur basalt, and hence can explain the low velocities (3–4 km/s) generally inferred from seismic tomography for the Mt. Etna volcanic edifice.     

Effects of microstructures on dynamic compression of Barre granite

The distribution and characteristics of microstructures (microcrack and grain) of Barre granite (BG) were investigated, and three orthogonal weak planes associated with the preferred orientations of microcracks were identified. It has been demonstrated that both the fracture toughness and the longitudinal wave speed depend on the direction of these weak planes. In this study, disk samples cut from one BG block are prepared for split Hopkinson pressure bar (SHPB) test. The axial directions of the samples are chosen to be parallel to the preferred direction of microcracks and the samples are grouped and denoted by Y (lowest P-wave velocity), Z (highest P-wave velocity), and X (intermediate P-wave velocity). Pulse-shaper technique is adopted to achieve equilibrium of dynamic stresses on both ends of the sample and constant strain rate during the dynamic loading. For samples within the same orientation group, the maximum stress achieved shows clear strain-rate sensitivity. The effect of microcracks on the dynamic compressive response of BG depends on the strain rate for a fixed loading duration (230 μs). For low strain-rate loading (70 s⁻¹) and high strain-rate loading (130 s⁻¹), the maximum dynamic stress achieved is not sensitive to the microcrack orientation; for intermediate strain rate (100 s⁻¹) loading, the maximum achieved stress for Y-samples is the largest. In addition, three dynamic compressive rock failure modes are identified: quasi-elastic, cracked, and fragmented. The correlation between the failure modes and the shape of the stress–strain curves is discussed.     

A comparison of fenuron degradation by hydroxyl and carbonate radicals in aqueous solution

A comparative study of the transformation of the herbicide fenuron (1,1-dimethyl-3-phenylurea) by hydroxyl radicals and carbonate radicals in aqueous solution (pH 7.2-phosphate buffer) has been undertaken. Hydroxyl radical was generated by the well-known photolysis of hydrogen peroxide at 254 nm and carbonate radical was formed by photolysis of Co(NH₃)₅CO₃⁺ at 254 nm. Competitive kinetic experiments were performed with atrazine used as the main competitor for both processes. Accordingly, the second-order rate constant of reaction between fenuron and carbonate radical was found to be (7−12±3)×10⁶ M⁻¹ s⁻¹ [(7±1)×10⁹ M⁻¹ s⁻¹ for hydroxyl radical]. The formation of degradation products was studied by LC-MS in the two cases and a comparison has been performed. The reaction with carbonate radical leads to the formation of a quinone-imine derivative which appears as the major primary product together with ortho and para hydroxylated compounds. These two compounds represent the major products in the reaction with hydroxyl radicals. The reaction of both radicals also leads to the transformation of the dimethylurea moiety.     

On the reoxygenation efficiency of diffused air aeration

One technique used to increase the dissolved oxygen concentration of polluted waters is the bubbling of air through a diffuser pipe located at depth, thereby producing a bubble curtain from which oxygen transfer to the water occurs.

The results of laboratory studies on the aeration efficiency of a diffuser placed along the entire width of a flume, perpendicular to a cross flow are presented (two dimensional aeration). Parameters investigated include (1) diffuser type-porous materials with mean pore sizes of 40, 90 and 180 μm and perforated pipes with 0.4, 0.6 and 1.0 mm diameter ports (2) air flow rate per unit width 3–53 m³ (m h)⁻¹ and (3) cross flow velocity (2.5–15 cm s⁻¹. The effect of variation from the two dimensional situation is also discussed as well as the consequence of using oxygen instead of air, and the sensitivity to discharge angle, port spacing and the free surface. The measured efficiencies are compared with theory as well as available laboratory and field data.

The major conclusions are (1) aeration efficiencies using diffused air aeration are on the order of 2–13%m⁻¹ (2) the aeration efficiency increases with increasing cross flow velocity and decreasing air flow rate per unit width (3) aeration efficiencies using porous filters, for air flow rates less than 40 m³ (m h)⁻¹, are significantly higher (a factor of 2–3) than those achieved using perforated pipes (4) changing the pore size from 40 to 180 μm, the port size from 0.4 to 1.0 mm or the port spacing does not significantly effect the aeration efficiency (5) aeration using oxygen is somewhat less efficient than that using air. However, since equivalent oxygen bubbles contain approximately five times more oxygen than air bubbles, more oxygen is transferred on an absolute basis at the same gas flow rate using compressed oxygen as opposed to air (6) aeration efficiency resulting from aeration over a portion of the entire width can be reasonably predicted using the results of the two dimensional studies and (7) the available laboratory and field data compare well with the results of these laboratory studies.     

The long-term nutrient accumulation with respect to anthropogenic impacts in the sediments from two freshwater marshes (Xianghai Wetlands, Northeast China)

Sediment cores, representing a range of watershed characteristics and anthropogenic impacts, were collected from two freshwater marshes at the Xianghai wetlands (Ramsar site no. 548) in order to trace the historical variation of nutrient accumulation. Cores were ²¹⁰Pb- and ¹³⁷Cs-dated, and these data were used to calculate sedimentation rates and sediment accumulation rates. Ranges of dry mass accumulation rates and sedimentation rates were 0.27–0.96 g m⁻² yr⁻¹ and 0.27–0.90 cm yr⁻¹, respectively. The effect of human activities on increased sediment accumulation rates was observed. Nutrients (TOC, N, P, and S) in sediment were analyzed and nutrient concentration and accumulation were compared in two marshes with different hydrologic regime: an “open” marsh (E-0) and a partly “closed” marsh (F-0). Differences in physical and chemical characteristics between sediments of “open” and partly “closed” marsh were also observed. The “open” marsh sequestered much higher amounts of TOC (1.82%), N (981.1 mg kg⁻¹), P (212.17 mg kg⁻¹), and S (759.32 mg kg⁻¹) than partly “closed” marsh (TOC: 0.32%, N: 415.35 mg kg⁻¹, P: 139.64 mg kg⁻¹, and S: 624.45 mg kg⁻¹), and the “open” marsh indicated a rather large historical variability of TOC, N, P, and S inputs from alluvial deposits. Nutrient inputs (2.16–251.80 g TOC m⁻² yr⁻¹, 0.43–20.12 g N m⁻² yr⁻¹, 0.39–3.03 g P m⁻² yr⁻¹, 1.60–15.13 g S m⁻² yr⁻¹) into the Xianghai wetlands of China are in the high range compared with reported nutrient accumulation rates for freshwater marshes in USA. The vertical variation, particularly for N, P, and S indicated the input history of the nutrients of the Xianghai wetlands developed in three periods—before 1950s, 1950–1980s, and after 1980s. The ratios between anthropogenic and natural inputs showed that the relative anthropogenic inputs of TOC, N, P, and S have been severalfold (TOC: 1.68–11.21, N: 0.47–3.67, P: 0.24–1.36, and S: 1.46–2.96) greater than values of their natural inputs after 1980s. The result is probably attributable, in part, to two decades of surface coal mining activities, urban sewage, and agriculture runoff within the upstream region of the Huolin River. Our findings suggest that the degree of anthropogenic disturbance within the surrounding watershed regulates wetland sediment, TOC, N, P, and S accumulation.     

Anaerobic digestion of wine distillery wastewater in down-flow fluidized bed

In down-flow fluidization, particles with a specific density smaller than the liquid are fluidized downward by a concurrent flow of liquid. This paper describes the application of the down-flow (or inverse) fluidization technology for the anaerobic digestion of red wine distillery wastewater. The carrier employed was ground perlite, an expanded volcanic rock. Before starting-up the reactor, physical and fluidization properties of the carrier material were determined. 0.968 mm perlite particles were found to have a specific density of 280 kg m⁻³ and a minimum fluidization velocity of 2.3 m h⁻¹. Once the down-flow anaerobic fluidized bed system reached the steady-state, organic load was increased stepwise by reducing HRT, from 3.3–1.3 days, while maintaining constant the feed TOC concentration. The system achieved 85% TOC removal, at an organic loading rate of 4.5 kg TOC m³ d⁻¹. It was found that the main advantages of this system are: low energy requirement, because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor so they can be easily drawn out, and particles with high-biomass content, whose specific density have become larger than 1000 kg m⁻³ can be easily recovered.     

Sorption kinetics of heavy oil into porous carbons

Sorption kinetics of heavy oil into porous carbons was evaluated by a concept of liquid sorption coefficient obtained from the weight increase of heavy oil with sorption time, which was measured by a wicking test. Exfoliated graphite, carbonized fir fibers and carbon fiber felts were used as porous materials. It was found that the liquid sorption coefficient of fibrous carbons was twice larger than that of exfoliated graphite. Such a difference in the liquid sorption coefficient between the exfoliated graphite and two fibrous carbons was caused by a difference in effective sorption porosity and tortuosity between them. For the exfoliated graphite and carbonized fir fibers, the liquid sorption coefficient and the effective sorption porosity were strongly dependent on their density. The maximum values of both liquid sorption coefficient and effective sorption porosity of the exfoliated graphite were shown at the bulk density around 16 kg/m³. The liquid sorption coefficient of the carbonized fir fibers increased with increasing the density in the range from 6 to 30 kg/m³. When the carbonized fir fibers were densified above 30 kg/m³, the sorption rate was saturated. On the other hand, the sorption kinetics into the carbon fiber felt was almost independent of the bulk density, because the density of the carbon fiber felt is not effective for the pore structure. The effect of bulk density on the sorption kinetics could be supported from an analysis of pore structure of the porous carbons with different densities, which was measured by mercury porosimeter.     

Evaluation of kinetic parameters of a sulfur-limestone autotrophic denitrification biofilm process

In this study, four kinetic parameters of autotrophic denitrifiers in fixed-bed sulfur–limestone autotrophic denitrification (SLAD) columns were evaluated. The curve-matching method was used by conducting 22 non-steady-state tests for estimation of half-velocity constant, K_s and maximum specific substrate utilization rate, k. To estimate the bacteria yield coefficient, Y and the decay coefficient, k_d, two short term batch tests (before and after the starvation of the autotrophic denitrifiers) were conducted using a fixed-bed SLAD column where the biofilm was fully penetrated by nitrate-N. It was found that K_s=0.398 mg NO₃⁻–N/l, k=0.15 d⁻¹, k_d=0.09–0.12 d⁻¹, and Y=0.85–1.11 g VSS/g NO₃⁻–N. Our results are consistent with those obtained from SLAD biofilm processes, but different from those obtained from suspended-growth systems with thiosulfate or sulfur powders as the S source. The method developed in this study might be useful for estimation of four Monod-type kinetic parameters in other biofilm processes. However, cautions must be given when the estimated parameters are used because the measurements of the biomass and the biofilm thickness could be further improved, and the assumption of sulfur being a non-limiting substrate needs to be proved.     

Manufacturing effects on the hydraulic properties of needlepunched nonwoven geotextiles

Needlepunched nonwoven geotextiles are entangled to form a complex three-dimensional structure by random fibers, accounting for its bulky nature, wide range of pore size distribution, and good drainage. With needlepunched nonwoven geotextiles, water can move in both the vertical and horizontal directions. This paper examines two types of needlepunched nonwovens: one produced from polyester staple fiber and the other made from polyester spunbond continuous filaments. Experimental results indicate that the permittivity of staple needlepunched nonwoven geotextiles varies from 1.77-4.51 s⁻¹; the permeability coefficient varies from 0.63-2.87 × 10⁻² m/s. The permittivity of spunbond needlepunched nonwoven geotextiles varies from 1.13-1.97 s⁻¹; the permeability coefficient varies from 0.48-1.09 × 10⁻² m/s. In addition, the transmissivity of needlepunched nonwoven geotextiles decrease to an essentially constant value as the normal stress is increases. The transmissivity of needlepunched nonwoven geotextiles examined varies from 155-2.75 × 10⁻⁶ m²/s over the normal stress range examined (5-200 kN/m²). The AOS value of 3 denier staple fiber needlepunched nonwovens is less than 0.074 mm, the AOS value of spunbonded 7 denier and, 15 d and 20 d needlepunched nonwovens are 0.21 mm, 0.25 mm and 0.30 mm, respectively.     

Anaerobic biological treatment of phenol at 9.5-15 degrees C in an expanded granular sludge bed (EGSB)-based bioreactor

The aims of this study were to demonstrate the (1) feasibility of psychrophilic, or low-temperature, anaerobic digestion (PAD) of phenolic wastewaters at 10–15 °C; (2) economic attractiveness of PAD for the treatment of phenol as measured by daily biogas yields and (3) impact on bioreactor performance of phenol loading rates (PLRs) in excess of those previously documented (1.2 kg phenol m⁻³ d⁻¹). Two expanded granular sludge bed (EGSB)-based bioreactors, R1 and R2, were employed to mineralise a volatile fatty acid-based wastewater. R2 influent wastewater was supplemented with phenol at an initial concentration of 500 mg l⁻¹ (PLR, 1 kg m⁻³ d⁻¹). Reactor performance was measured by chemical oxygen demand (COD) removal efficiency, CH₄ composition of biogas and phenol removal (R2 only). Specific methanogenic activity, biodegradability and toxicity assays were employed to monitor the physiological capacity of reactor biomass samples. The applied PLR was increased to 2 kg m⁻³ d⁻¹ on day 147 and phenol removal by day 415 was 99% efficient, with 4 mg l⁻¹ present in R2 effluent. The operational temperature of R1 (control) and R2 was reduced by stepwise decrements from 15 °C through to a final operating temperature of 9.5 °C. COD removal efficiencies of c. 90% were recorded in both bioreactors at the conclusion of the trial (day 673), when the phenol concentration in R2 effluent was below 30 mg l⁻¹. Daily biogas yields were determined during the final (9.5 °C) operating period, when typical daily R2 CH₄ yields of c. 3.3 l CH₄ g⁻¹ COD_removed d⁻¹ were recorded. The rate of phenol depletion and methanation by R2 biomass by day 673 were 68 mg phenol g VSS⁻¹ d⁻¹ and 12–20 ml CH₄ g VSS⁻¹ d⁻¹, respectively.     

Pore fabric shape anisotropy in porous sandstones and its relation to elastic wave velocity and permeability anisotropy under hydrostatic pressure

To understand the relationship between pore space anisotropy and petrophysical properties, we developed a novel apparatus capable of simultaneously measuring permeability, porosity and ultrasonic velocities at hydrostatic pressures up to 100 MPa. First, we use magnetic susceptibilities and acoustic wave velocities to identify the principal anisotropy axes under ambient laboratory conditions. This directional anisotropy data is then used to guide experiments on two sandstones (Bentheim and Crab Orchard) under hydrostatic pressure from 5 to 90 MPa. We find the structural anisotropy formed by the void space is well described by velocity anisotropy in both cases. Under hydrostatic pressure, the acoustic anisotropy of Crab Orchard sandstone (COS) decreases from 3% and 7% at 5 MPa (P-wave and S-wave) to 1.5% and 1%, respectively, at effective pressures over 40 MPa; for Bentheim sandstone the decrease is considerably less. Permeability of COS is 125×10⁻¹⁸ m², decreasing rapidly as effective pressure increases, with permeability parallel to bedding approximately twice that normal to bedding. In contrast, permeability of Bentheim sandstone is 0.86×10⁻¹² m², and varies little with effective pressure or coring direction. We relate many of our measurements made under hydrostatic pressure to the contrasting pore fabric between the two rock types, and infer that a critical pressure is required for the initiation of crack closure.     

Laboratory studies of electrical potential during rock failure

We have investigated electrical potential and acoustic emissions signals associated with rock deformation. Five rock types were studied; Clashach, Bentheim and Darley Dale sandstones (all quartz-rich) and a Seljadur basalt and Portland limestone (both quartz-free), both air dry and the rocks were tested in distilled water. Shallow crustal conditions were simulated in a triaxial rock deformation cell with a confining pressure simulating depth of 40 MPa, pore pressures ranging 5–35 MPa, and strain rates 10⁻⁷–10⁻⁴ s⁻¹. Precursory electric potential signals prior to failure were observed in both saturated and dry samples of the quartz-rich sandstones, but only observed in the water saturated quartz-free rocks. Co-seismic electrical signals were obtained in all tests, providing strong evidence that two of the main sources for precursory and co-seismic signals are the piezoelectric and electrokinetic phenomena. Lowering the strain rate resulted in an increase in the number of acoustic emissions. The pore volume changes during compaction and dilatancy remained approximately constant for all strain rates. Streaming potential generated by fluid flow across the sample was also measured at different stages of deformation. The potential signals increased with the pore pressure gradient.     

Wheat straw as substrate for water denitrification

Biological denitrification of drinking water was studied in up-flow laboratory reactors packed with wheat straw which served as the sole carbon source as well as the only physical support for the microorganisms. The highest rates of denitrification (0.053 g N removed l⁻¹ d⁻¹) were observed in fresh reactors during their first week of operation and the efficiency of the process declined thereafter. The addition of fresh wheat straw brought about a temporary improvement of the denitrification performance and a regime of one weekly addition prevented the deterioration of a reactor which was operated for 5 months. The rate of denitrification was affected by the water velocity and decreased at velocities above 0.054 m d⁻¹. Colour and soluble organic carbon associated with fresh straw were removed by adsorption on powdered activated carbon.     

Factors affecting the export of nitrate-nitrogen from drainage basins in southern Ontario

The export of nitrate-N from 21 watersheds near Toronto, Ontario was measured over a 25-month period. The annual average loss ranges from 1.41 to 7.31 kg ha⁻¹. Analysis of these data indicated a very significant correlation between nitrate exports and percentage of each watershed in crops and abandoned agricultural land. A number of soil and topographic variables also had significant correlations with stream nitrate levels. The causal relationships underlying these simple correlations are difficult to evaluate because of considerable multicollinearity between land use and watershed physiography. The separate analysis of stream discharge indicated that agricultural watersheds have lower mean annual discharges (1 s⁻¹ km⁻²) than those watersheds containing extensive areas of forest and abandoned agricultural land. Variations in annual discharge therefore tended to reduce the contrast in nitrate exports between agricultural and non-agricultural watersheds. The influence of watershed characteristics on nitrate levels exhibited considerable seasonal contrasts. During summer low flow conditions nitrate concentration and loss were not correlated with watershed land use, and instead were affected primarily by localised pollution sources and by biological processes within the streams.     

Development of an advanced biological treatment system applied to the removal of nitrogen and phosphorus using the sludge ceramics

To develop a method of forming lake sediment into sludge ceramics with porosity and good biological adhesion for use as a medium for microorganisms in wastewater treatment, a study of the effects of forming conditions was conducted by adjusting the water content of sludge and compounding some additives. By adjusting the water content of the raw material at the kneading/pelletizing step to 40–42% and adding 3% waste glass to the raw materials to make up for the lack of flux, a sludge ceramic with a density in terms of specific gravity of saturated surface dry aggregate of about 1400 kg m⁻³ was formed. In addition, to develop a small-scale wastewater treatment system capable of removing nitrogen and phosphorus, a sludge ceramic was applied as a medium for biological filtration. The results indicated that the BOD removal nitrification rate were superior to those of conventional ceramic media, reached at 95.3% and 87.4%, respectively. The introduction of iron electrolysis resulted in high treatment performance achieving BOD levels of 10 mg L⁻¹ or less, T-N of 10 mg L⁻¹ or less and T-P of 1 mg L⁻¹ or less.     

Interstitial inorganic phosphorus concentrations in lakes Mendota and Wingra

Interstitial P levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth. Interstitial water was obtained by the centrifugation-filtration method. Temporal variations were observed over the entire 15 cm sediment depth interval examined in all four locations evaluated. Interstitial reactive P (IRP) levels in Lake Mendota ranged from 0.014–1.67 mg l⁻¹ at the 5–6 m water column depth and from 1.20–5.75 mg l⁻¹ at the 18–19.5 m depth. IRP levels in Lake Wingra ranged from 0.029–2.15 mg l⁻¹ at 3.5 m and from 0.191–3.96 mg l⁻¹ at 2 m. Variations in interstitial P were attributed to variations in oxidation state of Fe as influenced by oxygen transport and reduction rates.     

Modelling of hydrogen cyanide formation in room fires

A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293 K) and hot (1000 K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01 s⁻¹ to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships.

Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation.

The chemical kinetics model, incorporated into a Reynolds-Averaging Navier–Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire.

The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements.