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.     

Sorption of cadmium(II) and zinc(II) ions from aqueous solutions by cassava waste biomass (Manihot sculenta Cranz)

The sorption of two divalent metal ions, Cd(II) and Zn(II), onto untreated and differentially acid-treated cassava waste biomass over a wide range of reaction conditions was studied at 30°C. The metal ion removal from the spent biomass was also measured. The batch experiments show that pH 4.5–5.5 was the best range for the sorption of the metal ions for untreated and acid-treated biomass. Time-dependent experiments for the metal ions showed that for the two metals examined, binding to the cassava waste biomass was rapid and occurred within 30 min and completed within 1 h. High sorption capacities were observed for the two metals. The binding capacity experiments revealed the following amounts of metal ions bound per gram of biomass: 86.68 mg/g Cd, 55.82 mg/g Zn and 647.48 mg/g Cd, 559.74 mg/g Zn for untreated and acid-treated biomass, respectively. It was further found that the rate of sorption was particle-diffusion controlled, and the sorption rate coefficients were determined to be 2.30×10⁻¹ min⁻¹ (Cd²⁺), 4.0×10⁻³ min⁻¹ (Zn²⁺) and 1.09×10⁻¹ min⁻¹ (Cd²⁺), 3.67×10⁻² min⁻¹ (Zn²⁺) for 0.5 and 1.00 M differential acid treatment, respectively. Desorption studies showed that acid treatment inhibited effective recovery of metal ions already bound to the biomass as a result of stronger sulfhydryl-metal bonds formed. Less than 25% of both metals were desorbed as concentration of acid treating reagent increases. However, over 60% Cd and 40% Zn were recovered from untreated biomass during the desorption study. The results from these studies indicated that both untreated and acid-treated cassava waste biomass could be employed in the removal of toxic and valuable metals from industrial effluents.     

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.     

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.     

Mechanisms and products of ozonolysis of aniline in aqueous solution containing nitrite ion

The presence of nitrite ions (1 × 10⁻⁴ M) in the reaction medium affected the aqueous reaction of aniline (1 × 10⁻⁴ M) and ozone (2.07–2.15 × 10⁻⁴ M) at pH 6.25–10.65; o-, m- and p-nitroaniline were formed in addition to reaction products reported earlier. The combined yield of o- and p-nitroaniline was as high as 8%. Their yields were significantly higher at pH 6.25 and 7.25 than at pH 10.65 and carbonate species-inhibited their formation. The reaction mechanisms for the formation of the nitroanilines involves pernitrous acid, hydroxyl radical and nitrogen dioxide radical as the important intermediates.     

Mesoscale characterization of coupled hydromechanical behavior of a fractured-porous slope in response to free water-surface movement

To better understand the role of groundwater-level changes on rock-slope deformation and damage, a carbonate rock slope (30 m×30 m×15 m) was extensively instrumented for mesoscale hydraulic and mechanical measurements during water-level changes. The slope is naturally drained by a spring that can be artificially closed or opened by a water gate. In this study, a 2-h slope-dewatering experiment was analyzed. Changes in fluid pressure and deformation were simultaneously monitored, both at discontinuities and in the intact rock, using short-base extensometers and pressure gauges as well as tiltmeters fixed at the slope surface. Field data were analyzed with different coupled hydromechanical (HM) codes (ROCMAS, FLAC^3D, and UDEC).

Field data indicate that, in the faults, a 40 kPa pressure fall occurs in 2 min and induces a 0.5–31×10⁻⁶ m normal closure. Pressure fall is slower in the bedding-planes, lasting 120 min, with no normal deformation. No pressure change or deformation is observed in the intact rock. The slope surface displays a complex tilt towards the interior of the slope, with magnitudes ranging from 0.6 to 15×10⁻⁶ rad.

Close agreement with model for both slope surface and internal measurements is obtained when a high variability in slope-element properties is introduced into the models, with normal stiffnesses of k_{n_faults}=10⁻³×k_{n_bedding-planes} and permeabilities of k_{h_faults}=10³×k_{h_bedding-planes}. A nonlinear correlation between hydraulic and mechanical discontinuity properties is proposed and related to discontinuity damage. A parametric study shows that 90% of slope deformation depends on HM effects in a few highly permeable and highly deformable discontinuities located in the basal, saturated part of the slope while the remaining 10% is related to elasto-plastic deformations in the low-permeability discontinuities induced by complex stress/strain transfers from the high-permeability zones. The periodicity and magnitude of free water-surface movements cause 10–20% variations in those local stress/strain accumulations related to the contrasting HM behavior for high- and low-permeability elements of the slope. Finally, surface-tilt monitoring coupled with internal localized pressure/deformation measurements appears to be a promising method for characterizing the HM properties and behavior of a slope, and for detecting its progressive destabilization.     

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.     

A kinetic study of 3-chlorophenol enhanced hydroxyl radical generation during ozonation

Hydroxyl (OH) radical is proposed as an important factor in the ozonation of water. In the present study, the enhancing effect of 3-chlorophenol on OH radical generation was mathematically evaluated using electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO–OH. The initial velocity of DMPO–OH generation in ozonated water containing 3-chlorophenol was quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus which was controlled by home-made software. The initial velocity of DMPO–OH generation increased as a function of the concentration of ozone and the more effectively of 3-chlorophenol concentration. The relation among ozone concentration, amount of 3-chlorophenol and the initial velocity (ν₀) of DMPO–OH generation was mathematically analyzed and the following equation was obtained, ν₀ (10⁻⁶M/s)={9.7×[3-chlorophenol (10⁻⁹M)]+0.0005} exp(57×[ozone (10⁻⁹M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.99. The equation for the enhancing effect by 3-chlorophenol should provide useful information to optimize the condition in ozone treatment process of water containing phenolic pollutants.     

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.     

Zero net growth in a membrane bioreactor with complete sludge retention

A bench-scale membrane bioreactor was operated with complete sludge retention in order to evaluate biological processes and biomass characteristics over the long term. The investigation was carried out by feeding a bench-scale plant with real sewage under constant volumetric loading rate (VLR=1.2 gCOD L_react⁻¹ h⁻¹). Biological processes were monitored by measuring substrate removal efficiencies and biomass-related parameters. The latter included bacterial activity as determined through respirometric tests specifically aimed at investigating long term heterotrophic and nitrifying activity. After about 180 days under the imposed operating conditions, the system reached equilibrium conditions with constant VSS concentration of 16–18 g L⁻¹, organic loading rate (OLR) below 0.1 gCOD gVSS⁻¹ d⁻¹ and specific respiration rates of 2–3 mgO₂ gVSS⁻¹ h⁻¹. These conditions were maintained for more than 150 days, confirming that an equilibrium had been achieved between biomass growth, endogenous metabolism, and solubilization of inorganic materials.     

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.     

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus

Uptake and release of phosphate by a pure culture of Acinetobacter calcoaceticus were investigated under aerobic and anaerobic conditions. The total phosphorus content of this bacterium varied from 0.3 to 1.7 mmol g⁻¹ dry cells or from 0.93 to 5.3% of dry cell weight under various culture conditions. The log-phase cells accumulated polyphosphates of 0.33−0.64 mmol P g⁻¹ dry cells. ³¹P NMR spectra suggested that a portion of polyphosphates was likely bonded to some sort of structural components of the cell. A. calcoaceticus release phosphate linearly with time when transferred from aerobic to anaerobic conditions. The release rate was in the range of 5.9–14.7 × 10⁻³ mmol P g⁻¹ dry cells h⁻¹ and about 4–8% of cellular phosphorus was released during the initial 6 h. During the process of phosphate release acetate was not taken up by this bacterium.     

Kinetics of alachlor transformation and identification of metabolites under anaerobic conditions

Alachlor is one of the two most commonly used herbicides in the United States. In the environment, little mineralization of this compound has been found to occur, and metabolites of alachlor may be formed and could accumulate. The objectives of this study were to determine the rate of alachlor biotransformation and to identify the transformation intermediates formed under aqueous denitrifying, methanogenic, and sulfate-reducing conditions. Second-order biotrasnformation coefficients for alachlor were determined to be 7.6 × 10⁻⁵ (±4.0 × 10⁻⁵), 2.9 × 10⁻³ (±1.6 × 10⁻³), and 1.5 × 10⁻² (±1.4 × 10⁻²) 1 mg VSS⁻¹ day⁻¹ under denitrifying, methanogenic, and sulfate-reducing conditions, respectively. Acetyl alachlor and diethyl aniline were positively identified as transformation products of alachlor under all conditions. In denitrifying reactors aniline was identified as a product of alachlor. When acetyl alachlor was fed as the parent compound, aniline was also identified as a transformation product under methanogenic conditions. This research showed that although alachlor is degraded under denitrifying, methanogenic, and sulfate-reducing conditions, significant concentrations of several metabolites are formed and are only slowly degraded.     

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.     

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.     

Occurrence of nitrifiers and diversity of ammonia-oxidizing bacteria in developing drinking water biofilms

We studied the population dynamics of nitrifying bacteria during the development of biofilms up to 233 or 280 days on polyvinylchloride pipes connected to two full-scale drinking water distribution networks supplying processed and chloraminated surface water. The numbers of nitrifiers in biofilms were enumerated at intervals of 10–64 days by the most probable number (MPN) method at waterworks and at several study sites in distribution network areas. The numbers of nitrifiers increased towards the distal sites. The highest detected MPN counts of ammonia-oxidizing bacteria (AOB) for study areas 1 and 7 were 500 MPN cm⁻² and 1.0×10⁶ MPN cm⁻², and those of nitrite-oxidizing bacteria (NOB) 96 MPN cm⁻² and 2.2×10³ MPN cm⁻², respectively. The diversity of AOB was determined by PCR amplifying, cloning and sequencing the partial ammonia monooxygenase (amoA) gene of selected biofilm samples presenting different biofilm ages. The PCR primers used, A189 and A682, also amplified a fragment of particulate methane monooxygenase (pmoA) gene of methane-oxidizing bacteria. The majority of biofilm clones (24 out of 30 studied) contained Nitrosomonas amoA-like sequences. There were only two pmoA-like sequences of Type I methanotrophs, and four sequences positioned in amoA/pmoA sequence groups of uncultured bacteria. From both study area very similar or even completely identical Nitrosomonas amoA-like sequences were obtained despite of high difference in AOB numbers. The results show that the conditions in newly formed biofilms in drinking water distribution systems favor the growth of Nitrosomonas-type AOB.     

Histological and toxicological responses of the mummichog, Fundulus Heteroclitus (L.) to combinations of levels of cadmium and dissolved oxygen in a freshwater

Impact of dissolved oxygen concentration (D.O.) on toxicity of cadmium to mummichogs in a freshwater medium and histological changes associated with exposure were determined. Levels of mortality were related to duration of exposure, cadmium concentration, and levels of dissolved oxygen. Median tolerance concentrations, at 96h, ranged upward from 1.3 to about 3.0 mg Cd 1⁻¹ at 2.3 and 8.5 mg DO 1⁻¹, respectively. Statistical analyses of mortality data showed factors examined were interdependent and that Cd × DO and Cd × time interactions were significant (P < 0.01). No histopathology was evident at 3 mg Cd 1⁻¹, although histopathology was evident in gills from fish exposed to 28 mg Cd 1⁻¹ for 6 1/2 h.

Responses of mummichogs to cadmium in freshwater are compared with results of a previous study involving exposure of the species to cadmium in seawater and with responses of freshwater fishes subjected to various heavy metals. Differences and similarities in patterns of response are discussed in terms of water balance.     

The relative importance of Lemna gibba L., bacteria and algae for the nitrogen and phosphorus removal in duckweed-covered domestic wastewater

To arrive at detailed nutrient balances for duckweed-covered wastewater treatment systems, five laboratory-scale experiments were carried out in shallow (3.3 cm), 1 l batch systems to assess separately the contributions of duckweed itself, attached and suspended bacteria as well as algae to N- and P-removal in domestic wastewater. Depending on the initial concentrations, our duckweed-covered systems removed 120–590 mg N m⁻² d⁻¹ (73–97% of the initial Kjeldahl-nitrogen) and 14–74 mg P m⁻² d⁻¹ (63–99% of the initial total phosphorus) in 3 days. Duckweed (Lemna gibba L.) itself was directly responsible for 30–47% of the total N-loss by uptake of ammonium and, probably dependent on the initial P-concentrations, for up to 52% of the total P-loss. The indirect contribution of duckweed to the total nutrient removal was also considerable and included the uptake (and adsorption) of ammonium and ortho-phosphate by algae and bacteria in the attached biofilm and the removal of N through nitrification/denitrification by bacteria attached to the duckweed. Together these accounted for 35–46 and 31–71% of the total N- and P-loss, respectively. Therefore, approximately of the total N- and P-loss could be attributed to the duckweed mat. The remaining quarter is due to non-duckweed related components: uptake and nitrification/denitrification by algae and bacteria attached to the walls and the sediment of the system (including sedimentation). Other processes, like NH₃-volatilisation, N-fixation and nutrient uptake as well as nitrification/denitrification by suspended microorganisms did not influence the N- and P-balance of our systems, but could become important with increasing water depths and retention times.     

Combined γ-ray irradiation-activated sludge treatment of humic acid solution from landfill leachate

Humic acid, which is a typical microbially refractory organic substance, was extracted from a landfill leachate. The humic acid solution (COD = 367 mg 1⁻¹; TOC = 293 mg 1⁻¹; BOD = 27 mg 1⁻¹) was applied to a batch scale activated sludge treatment after the modification of its biodegradability by γ-ray irradiation. The BOD increased to 64 mg 1⁻¹ by irradiation of 15 kGy (1.5 Mrad), while the COD and TOC decreased to 231 and 230 mg 1⁻¹, respectively. When the irradiated sample was treated with an activated sludge, the BOD decreased rapidly in 2–3 h to about 15 mg 1⁻¹ which was a similar value as the unirradiated sample was treated. The elimination efficiency of TOC by the sludge treatment was approximately equal to that obtained by irradiation of 15 kGy. These facts suggest a utility of applying microbial processes after radiation treatment of microbially refractory wastewaters.