Phytoplankton biomass and production in the river meuse (Belgium)

The biomass and production of the phytoplankton in a relatively unpolluted reach of the River Meuse (Belgium) were followed through two years (1983 and 1984). Chlorophyll a varied from 0.2 to about 120 mg m⁻³, and production ranged between 0.05 and 5.78 gC m⁻² d⁻¹. The mean photosynthetic quotient (PQ) was 1.25.

The parameters of the light-photosynthesis relationship (P_opt and l_k) were calculated and related to the variations of temperature and light in the water column. A simple model allowed calculations of the annual production, which was estimated to be 494 gC m⁻² yr⁻¹ in 1983 and 547 gC m⁻² yr⁻¹ in 1984.

Finally, a simple model is developed, which explains the relationship between phytoplankton development and discharge; this model shows how the effect of discharge can be described by a “dilution rate” of the plankton growing in the river water.     

Toxicity of chlorine to juvenile spot, Leiostomus Xanthurus

The sensitivity of juvenile spot, Leiostomus xanthurus, to total residual chlorine (TRC) in flowing sea-water was investigated. Incipient LC₅₀ bioassays, histopathology, avoidance tests and the combined effect of thermal stress and TRC were used to assess sensitivity.

Estimated incipient LC₅₀ values were 0.12 mg 1⁻¹ TRC at 10°C and 0.06 mg 1⁻¹ TRC at 15°C. Histological examination of spot used in the incipient LC₅₀ bioassay at 15°C and sacrificed while alive indicated pseudobranch and gill damage occurred in individuals exposed to a measured TRC concentration of 1.57 mg 1⁻¹. Spot exposed to lower concentrations of TRC, 0.02 0.06 mg 1⁻¹ at 15°C and sacrificed alive showed no consistent tissue damage.

Spot demonstrated temperature dependent avoidance responses to TRC. At 10°C, a concentration of 0.18 mg 1⁻¹ was required for significant (X²; P < 0.05) avoidance; at 15 and 20°C, spot showed significant avoidance of TRC concentrations as low as 0.05 mg 1⁻¹.

Simultaneous exposure of spot to thermal stress (5, 10 or 13°C above the acclimation temperature of 15°C) at measured TRC concentrations of 0.05 0.07 and 0.34–0.52 mg 1⁻¹ demonstrated a significant, (Z²) with Yates correction, P < 0.05) increase in sensitivity to TRC with increased temperature and exposure times for some of the groups tested.     

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.     

Effect of different catalysts in SO2 oxidation over polymeric concrete

Polymeric concrete performance in polluted environment has been studied in order to determine outdoor pollutant transfer process. SO₂ oxidation process over different building materials in laboratory-based atmospheric flow chambers is well known; however, the effect of NO_x is not very clear. In order to clarify this process, the effect of NO_x in SO₂ oxidation over the surface of a porcelain material was studied under wetted and unwetted conditions. In the chamber, NO_x can either catalyse SO₂ reaction or undergo oxidation to NO₃⁻. The main conclusion in this work is that for the porcelain samples under wetted conditions NO and NO₂ catalysed the reaction. But in unwetted conditions NO reacts with the sample instead of SO₂.     

Empirical rate equation for trihalomethane formation with chlorination of humic substances in water

Trihalomethane (THM) in drinking water is formed by chlorination of humic substances. In this study, the rates of THM formation in aqueous solution of humic acid were examined under various conditions. The following rate equation was obtained empirically. [THM] = k (pH − a)[TOC][Cl₂]₀^mtⁿ.

Here, [THM] is the concentration of total THM after t h, [TOC] and [Cl₂]₀ are the concentrations of total organic carbon and chlorine dose, k is the rate constant and a, m and n are parameters. The values of k, a, m and n for humic acid as reagent were obtained as 8.2 × 10⁻⁴ (l^mmg^−mh⁻ⁿ), 2.8, 0.25 and 0.36, respectively. The activation energy was obtained as 37 kJ mol⁻¹. Further, it was proved that the above equation could be applied to the rates of THM formation from precursors in actual river and lake waters.     

Studies on marine biological filters: Model filters

Model systems of 401. capacity were used to study chemical changes which affected buffering in continuously recycled sea water and which restricted nitrification in percolating biological filters at 28°C.

Sustained hydrogen ion production during the microbial oxidation of ammonia to nitrite caused continuous carbon dioxide formation from carbonate and bicarbonate. The carbon dioxide was steadily lost to the air through vigorous aeration, leaving < 2 mg inorganic carbon 1⁻¹ in the sea water. Oxidation of nitrate to nitrate did not significantly reduce pH nor deplete buffer capacity.

Ammonia oxidation was severely inhibited by the combination of low pH and dissolved inorganic carbon levels, but similar low levels of pH produced when carbon dioxide was bubbled through the water had only a moderate effect. Inhibition could be rapidly overcome or prevented by additions of inorganic carbon, sodium hydroxide or sodium dihydrogen phosphate.

Values recorded for the maximum specific growth rate of Nitrosomonas and Nitrobacter were 0.53 and 0.81 d⁻¹ respectively. The corresponding generation or doubling times were calculated to be 31.4 and 20.5 h.

Some evidence was found for the uptake of phosphate and the formation of hydroxylamine during nitrification.     

Aerobic treatment of piggery waste

The operating characteristics of laboratory waste treatment systems were studied during the aerobic degradation of pig excrement at different loading rates and temperatures. The treatment systems were of two types: one was operated with floc formation and gravity separation of liquid and suspended solid effluents; and a second was operated without floc formation or separation of the effluent into liquid and solid fractions.

With an operating temperature of 15°C the parameters most affected by loading rate were (1) the concentrations of suspended solids and chemical oxygen demand in the liquid effluent; (2) the pH value of the mixed liquor; (3) nitrification; (4) the BOD of the supernatant from the mixed liquor; and (5) output of suspended solids as a percentage of input.

The concentrations of suspended solids and chemical oxygen demand in the liquid effluents were little affected by loading rates in the range 0·05-0·15 g SS g MLSS⁻¹ d⁻¹ (0·02-0·06 g BOD g MLSS⁻¹ d⁻¹) but increased with increasing loading rate in the range 0·15-0·30 (0·06-0·12 BOD). At loading rates below about 0·17 g SS g MLSS⁻¹ d⁻¹ (0·07 g BOD g MLSS⁻¹ d⁻¹) the mixed liquors were acidic, with pH values down to 5·2, whereas at loading rates above about 0·80 (0·32 BOD) they were alkaline, with pH values up to 8·9. At intermediate loading rates the mixed liquor pH value was more variable though in general the higher the loading rate the higher also the pH value of the mixed liquor. Acidic conditions in the mixed liquors were attributed to the occurrence of nitrification, while in the absence of nitrification the mixed liquors remained alkaline. The concentration of BOD₅ in the supernatant from the mixed liquors increased with increasing loading rate from about 35 mg 1⁻¹ at a loading rate of 0·17 g SS g MLSS⁻¹ d⁻¹ (0·07 g BOD g MLSS⁻¹ d⁻¹) to about 250 mg 1⁻¹ at a loading rate of 1·30 (0·52 BOD). The output of suspended solids from the treatment systems represented about 70 per cent of input suspended solids at loading rates of about 0·15 g SS g MLSS⁻¹ d⁻¹ (0·06 g BOD g MLSS⁻¹ d⁻¹) and increased to about 100 per cent at loading rates of 0·80 (0·32 BOD). Output of chemical oxygen demand was about 60 per cent of input at the lower loading rates and 80–90 per cent at the higher ones.

Operation of treatment units at temperatures of 5 and 10°C instead of 15°C had little effect on the efficiency of degradation at loading rates in the range 0·085-0·20 g SS g MLSS⁻¹ d⁻¹ (0·034-0·08 g BOD g MLSS⁻¹ d⁻¹), but nitrification was prevented at 5°C. At loading rates of 0·77 (0·31 BOD) and 1·46 (0·58 BOD) operation at 25°C appeared to increase the amount of degradation as compared with that achieved at 15°C.

The practical implications of the results and possible future approaches to the aerobic treatment of farm wastes are discussed.     

Denitrification with methanol in tertiary filtration

The large wastewater treatment plants in Switzerland have to be extended by enhanced nitrogen removal to comply with the relevant EU directives. Denitrification in tertiary filtration is a cost-effective alternative to extended denitrification in an activated sludge system which needs additional reactor volume. Full-scale experiments in denitrification with methanol in tertiary filtration were performed at the wastewater treatment plant in Zurich-Werdhölzli during a summer and a winter campaign, each lasting 4 months. One of the original 22-filter cells was equipped with a methanol dosage unit for this purpose. Denitrification rates of about 1.0 kg-N m⁻³ d⁻¹ are attained at temperatures of 12–15°C. The denitrification is reduced significantly after main back-washing. Frequent back-washings (several times per day) lead to methanol breakthroughs due to biofilm loss. The yield coefficient Y_COD was 0.4 kg-COD_xkg-COD⁻¹_me. In spite of the methanol dosage, the quality of the filter effluent is very good during normal operation in the winter campaign. Accumulation of the nitrite intermediate product was observed in summer at temperatures of 20–22°C.     

Variation of fracture toughness of asphalt concrete under low temperatures

This study presents the results of experimental evaluation on fracture toughness of asphalt concrete at various low temperatures (from −5°C to −30°C in 5°C steps). An asphalt cement, penetration grade of 85/100 and two aggregates, a granite and a limestone, were used to prepare asphalt concrete beam specimens which were conditioned using two different procedures and tested under three-point bending setup. The first procedure dealt with evaluation of fracture toughness of the asphalt concrete at a control temperature, −5°C, following conditioning at the specified temperatures. The second procedure dealt with evaluation of fracture toughness at the temperatures at which the samples were conditioned. The results showed that fracture toughness (K_IC) for both aggregate mixtures in both procedures changed in a manner that it increased by lowering temperature from −5°C to −15°C, and then decreased thereunder. An improved mechanical adhesion due to the strengthened grip of asphalt matrix resulted from differential thermal contraction (DTC) is responsible for increased resistance to the applied loads. The reduction of fracture toughness below −15°C is explained as the effect of internal damage due to DTC that is a consequence of the large difference in coefficients of thermal contraction between aggregate and asphalt cement. Granite aggregate mixture showed a slightly better resistance to fracture throughout the temperatures. Relatively good linear relations between average values of σ_f and K_IC were found from the regression analysis. Increasing flexural strength resulted in an increased fracture toughness for all mixtures. K_IC of granite mix showed more critical to the change of σ_f.     

Influence of method and duration of curing and of mix proportions on strength of concrete containing laterite fine aggregate

In this paper, the influence of six curing methods (water, air, moist soil, jute bag, air/water and water/air) on the compressive strength of concrete cube specimens that contain laterite fine aggregate is investigated. Three different mixes of cement, laterite and gravel were used: ; 1:2:4 and 1:3:6 with water/cement ratios of 0.62, 0.75 and 1.02 by weight respectively. Four curing ages of 7, 14, 21 and 28 days were adopted. The results showed that the strength that a particular mix can attain is affected by the curing method used. The water/air curing technique gave the highest strength values of 28.2 Nmm⁻² for Nmm⁻² and 17.4 Nmm⁻² for 1:2:4 and 1:3:6 mixes respectively, while the air-cured specimens gave the lowest strength values of 17.2 Nmm⁻² for Nmm⁻² and 8.0 Nmm⁻² for 1:2:4 and 1:3:6 mixes. The higher the cement/aggregate ratio the higher the strength. Generally, there was increase in strength with age irrespective of the mix and the curing technique.     

A bench study on lead removal from battery manufacturing wastewater by carbonate precipitation

A residual soluble Pb ≤ 0.2 mg/l has been measured after hydrocerussite precipitation in the range of pH 9–10 and filtration with 0.45 μm filter, at a total carbonate concentration (C_T) of about 1.5 × 10⁻⁴ M. Filterability and sedimentation were optimized by minimizing the “relative supersaturation” coefficient during precipitation. Pb abatement was implemented in the pH range 9–9.5, following a preliminary precipitation step consisting of a slow, gradual change of pH from 6.8 to 7.8 with 0.1 M NaOH solution. The crystals formed may settle within 24 h, allowing Pb to be recovered as Pb₃(CO₃)₂(OH)₂.     

Catalytic wet oxidation of phenol over a Pt/TiO catalyst

Wet oxidation of phenol by air or oxygen over a Pt/TiO₂ catalyst is studied in a batch reactor in the temperature range 150–200°C, pressure range 34–82 atm, and a catalyst loading range of 0–4 g catalyst L⁻¹. The catalyst was powdered 4.45% Pt/TiO₂ with a maximum particle size of 105 μm. Results show complete oxidation of phenol and almost complete total organic carbon (TOC) removal. Small amounts of stable organic acids are formed in side reactions of the phenol degradation pathway and are not readily degraded. Experimental results show that the reaction rate decreases by increased oxygen concentration. Theoretical rate expressions are derived, based on postulated oxidation and TOC reduction mechanisms.     

Recovery of ammonia from industrial waste water

Some types of industrial waste water contain high concentration of ammonia, which makes nitrification too costly. It has been found, that ion exchange is an attractive alternative, even the waste water contains such high concentration of competitive ions at 1 g 1⁻¹ Ca²⁺ and 5 g 1⁻¹ Na⁺. However it was found, that the pH increased during the treatment due to the release of OH^- ions left in the interstitial water. Since it is essential for the efficiency that pH is 7·0 or lower, it was necessary to rinse the ion exchangers with acid. The observed data by column experiments agree with the equilibrium data found.     

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.     

Measuring maximum specific growth rate and half saturation coefficient for activated sludge systems using a freeze concentration technique

To measure the maximum specific growth rate (μ_max) and the half saturation coefficient (K_s), a simple respirometric technique was used, where differing volumes of concentrated wastewater were contacted with biomass in a respirometer and the response measured as a change in oxygen uptake rate (ΔOUR). The ΔOUR was then related to the growth rate, and a series of substrate concentration/growth rate relationships determined from which μ_max and K_s were calculated. A freeze concentration technique was developed to concentrate the wastewater. The concentration technique did not alter the response of the microorganisms to the wastewater. Maximum specific growth rates (μ_max) and half saturation coefficients (K_s) were found to vary between 1.3 and 1.9 d⁻¹ and 1.5 and 3.2 mg l⁻¹, respectively.     

Removal of cadmium and manganese by a non-toxic strain of the freshwater cyanobacterium Gloeothece magna.

The ability of both living and dry cells of Gloeothece magna, a non-toxic freshwater cyanobacterium, to adsorb cadmium and manganese is demonstrated in this study. Chlorophyll a content of living cells was not influenced by either cadmium or manganese concentrations, indicating that adsorption of both Cd²⁺ and Mn²⁺ by living cells of G. magna, was independent of the metabolic state of the organism. Moreover, the adsorption of both Cd²⁺ and Mn²⁺ to living cells and dry cells, was dependent on the metal concentrations, and fitted the Freundlich adsorption isotherm. However, dry cells had larger binding capacity for both Cd²⁺ (K_f=912.6) and Mn²⁺ (K_f=2398) than living cells (K_f=151.4 & 63, respectively). The role of the capsular polysaccharides, the main constituents of the cyanobacterial envelope, in binding these two metals was also studied. Polysaccharide extracts of this organism adsorbed high amounts of both Cd²⁺ (115–425 μg mg⁻¹) and Mn²⁺ (473–906 μg mg⁻¹). This study suggests that G. magna would probably be cultured in water bodies contaminated by heavy metals to ameliorate their toxicity. Also dry material of this cyanobacterium being a non-toxic species, could be used as a safe biofilter to remove toxic metals from drinking water.     

Formation equation of halogenated organic compounds when water is chlorinated

Various halogenated organic compounds are formed by chlorination of water. In this study, formation of organic compounds halogenated from a reagent humic acid and extract of a leaf mold were examined under various conditions. The following overall formation equation was obtained from empirical data under the practical wide range when free chlorine remained.

[TOX]=k_TOX[TOC][Cl₂]_ot^β.

Here, [TOX] is the concentration of total organic halogen after t h in units of mg chlorine per liter; [TOC] and [Cl₂]_o are concentrations of total organic carbon and dosed chlorine in units of mg per liter; k_TOX is the rate constant and and β are parameters. From the values of k_TOX, and β, the character of organic substances i.e. precursor of halogenated organic compounds, in water can be evaluated. The values k_TOX, and β for humic acid are 0.053, 0.28 and 0.13, and the values for extract of the leaf mold are 0.032, 0.36 and 0.15, respectively. The activation energies are 10 kJ mol⁻¹ and 11 kJ mol⁻¹ for the reactions of humic acid and leaf mold extract, respectively.     

Mixing effect and combustion efficiency in compartment fires

A new model for compartment fires is proposed in which the new concept of combustion efficiency based on the mixing process of the fuel gas and air has been considered. This new concept was formulated by the mixing parameter, μ. It was defined as μ1 − exp(−τ^*) and τ^* was related to the residence time t_R and mixing time t_M, that is, τ^* = t_R/t_M.

A simple one zone model was used in order to demonstrate the effect of the mixing process. Theoretical results were in good agreement with the experimental results of methanol and PMMA compartment fires, and especially the scale effect of the compartment was predicted successfully. Further, the similarity law for this scale effect was investigated, and the upper and lower limits of flashover were defined using a new number F. This F number was found to be the key parameter for the prediction of the compartment fire behavior.     

On the love strain form of naturally curved and twisted rods

Love proposed in 1944 [A.E.H. Love, A Treatise on the Mathematical Theory of Elasticity. Dover Publications, New York, 1944] that the nonvanishing (linear) strain components of a naturally curved and twist spatial rod, whose centroidal axis is along x and cross-section is in yz plane, can be represented nicely in the form ε_xx = e₁ + zk₂ − yk₃ε_xy = e₂ − zk₁ε = e₃ + yk₁ where e₁, e₂, e₃ are the strain components at y = z = 0 and k₁, k₂, k₃ are the curvatures. Functions e₁, e₂, e₃, k₁, k₂, k₃ depend on x alone. Mottershead [J. E. Mottershead, “Finite elements for dynamical analysis for helical rods”, International Journal of Mechanical Sciences, 22, (1980), pp 252–283], Pearson and Wittrick [D. Pearson and W.H. Witrick “An exact solution for the vibration of helical springs using a Bernoulli-Euler Model”, International Journal for Mechanical Sciences, 28, (1986), pp 83–96], Leung [A.Y.T. Leung “Exact shape functions for helix- elements”, Finite Elements in Analysis and Design, 9, (1991), pp 23–32], and Tabarrok and Xiong [B. Tabarrok and Y. Xiong, “On the buckling equations for spatial rods”, International Journal for Mechanical Sciences, 31, (1980), pp 179–192] have made use of the Love form. We shall show that the Love form is not even valid for two-dimensionally curved beams when shear deformation is considered. The fact that the differential length ds at point P, on the cross-section with distance y, z away from the centroidal axis is different from the differential length dx at point S on the centroidal axis has been neglected. In fact DS = (1 − k₃y + k₂z)dx, where k; are initial curvatures, which contribute to the strain components of the first order of curvatures.     

Modified amperometric membrane probes for determining free and total residual chlorine in saline cooling waters

Modifications have been made to a Delta Scientific model 82124 free available chlorine probe so that it can be used to determine either the free or the total residual chlorine in cooling waters at coastal and estuarine power stations. For measurements of free residual chlorine, the internal filling solution of the probe was changed for one containing potassium bromide at pH 4. When the sample solution was dosed with potassium bromide and pH 4 buffer, the probe had a linear response over the range 0.04–1.0 μg ml⁻¹ Cl₂ and errors caused by changes in salinity were negligible. Total standard deviations for the analysis of 1.0 and 0.1 μg ml⁻¹ Cl₂ solutions were 0.055 and 0.01 μg ml⁻¹ Cl₂ respectively. For measurements of total residual chlorine a potassium iodide solution at pH 4 was used as the probe's internal filling solution and the sample solution was dosed with potassium iodide and pH 4 buffer. The probe had a linear response over the range 0.02-0.5 μg ml⁻¹ Cl₂, with total standard deviations of 0.05 and 0.01 μg ml⁻¹ Cl₂ at concentrations of 0.5 and 0.1 μg ml⁻¹ Cl₂ respectively.