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.     

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.     

The maturity method: Modifications to improve estimation of concrete strength at later ages

Two modifications have been proposed for the Nurse–Saul maturity function to get better estimates of compressive strength of concrete cured at different temperatures. The modifications account for the effect of w/c ratio on the temperature dependence of strength development and the effect of curing temperature on the long-term strength. The effect of the proposed modifications on the estimation of concrete strength using the Nurse–Saul maturity function have been compared with the estimation using unmodified Nurse–Saul equation with two different datum temperatures (i.e., T₀ = −10 °C and T₀ = 0 °C). The results show that applying the proposed modifications improves the accuracy of estimated concrete strength at different curing temperatures, especially at later ages.     

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.     

Micro-organisms and manganese cycling in a seasonally stratified freshwater dam

This work describes investigations into the role that biotic and abiotic mechanisms play in the manganese redox cycle in a freshwater dam over a twelve month period. Enzymatic control of manganese oxidation was taking place with a temperature optimum of approx. 30°C. Manganese oxidation was only significant above about 19°C. The temperature and season play vital roles in determining the extent to which abiotic and microbial mechanisms contribute to manganese oxidation. Results showed that microbial catalysis is overwhelmingly responsible for manganese oxidation in the lower epilimnion from November to May. Significant abiotic catalysis (up to 25%) can occur in late summer/autumn when the water temperature is greatest. Mn(II) oxidation, pseudo-first order rate constants to 1.12 × 10²² M⁻⁴ · d⁻¹ were measured while poisoned sample experiments confirmed the role of biological mediation. In winter, biological control could not occur because of the lower temperature of the water column. The measurement of “x” in MnO_x showed that higher manganese oxidation states were expected when the manganese oxidation rate was at a maximum and therefore when microbial activity was greatest. Direct microbial reduction of MnO_x in the water column was of much less significance. However, indirect reduction may have taken place through the reaction of MnO_x with sulfide. The results of this work have important implications for the design and operation of artificial destratification units for the control of manganese speciation.     

Laboratory evaluation of fatigue characteristics of recycled asphalt mixture

This paper presents the results of a laboratory study of evaluating the fatigue characteristics of hot-mix asphalt (HMA) mixtures using different testing methods. In this study, the fatigue performance of HMA mixtures was evaluated with the Superpave indirect tension (IDT) tests and beam fatigue test. The HMA mixtures containing 0%, 10%, 20%, and 30% of recycled asphalt pavement (RAP) were plant prepared with one source of aggregate, limestone, and one type of binder, PG 64–22. The fatigue properties tested included indirect tensile strength (ITS), failure strain, toughness index (TI), resilient modulus, DCSE_f, energy ratio, plateau value, and load cycles to failure. The results from this study indicated that both Superpave IDT and beam fatigue tests agreed with each other in ranking the fatigue resistance of mixtures when proper procedures were followed.     

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.     

Factors influencing oxygen transfer in fine pore diffused aeration

A bench-scale experiment was conducted in a 701. tank of tap water to examine the effect of four design variables on oxygen transfer in a fine pore diffused aeration system. The experiment used non-steady state gas transfer methodology to examine the effect of air flow rate, air flow rate per diffuser, orifice diameter and reduced tank surface area on the overall oxygen transfer coefficient (K_La₂₀, h⁻¹); standard oxygen transfer rate (OT₂, g O₂ h⁻¹); energy efficiency (E_p, g O₂ kWh⁻¹) and oxygen transfer efficiency (E_o, %). The experiments demonstrated that K_La₂₀ and OT_s increased with air flow rate (9.4–18.8 1 min⁻¹) in the 40 and 140 μ diameter orifice range; however, E_p and E₀ were not affected. Reducing the air flow rate per fine pore diffuser (40 and 140 μ diameter pore size) significantly increased K_La₂₀, OT_s, E_p and E₀. A decrease in orifice diameter from 140 to 40 μ had no effect on K_La₂₀, OT_s, E_p and E₀. A reduction in tank surface area had a marginally significant inverse effect on K_La₂₀ and OT_s, and no effect on E_p and E_o. The mean bubble size produced by the 40 and 140 μ diffusers was 4.0 and 4.2 mm, respectively. There was no consistent effect of air flow rate on bubble size within the range of air flow rates used in this experiment. In clean water aeration applications, the optimum system efficiency will be obtained using the largest number of fine pore diffusers operated at low air flow rates per diffuser. In wastewater treatment plants, higher air flow rates per diffuser should be used to prevent diffuser biofouling and keep biological solids in suspension. Wastewater systems are purposely operated at less than optimum transfer efficiencies in exchange for reduced diffuser maintenance and improved mixing. In either situation, changes in tank surface area and diffuser pore size (provided that pore diameter remains between 40 and 140 μ) are unlikely to have any significant effect on aeration system efficiency.     

Solubility of organic chemicals in octanol, triolein and cod liver oil and relationships between solubility and partition coefficients

The solubilities of 54 chemicals were measured in octanol, triolein and cod liver oil. Solubility of most chemicals increased with temperature between 4 and 20°C. Values of solubility in water and octanol/water partition coefficient (K_ow) for these chemicals were compiled from the literature to examine their relationships with solubility in the three solvents. Regression analyses indicated highly significant relationships between (1) the chemicals' solubility in water and the three solvents, (2) solubility in water and K_ow, (3) solubility in other solvents and K_ow and (4) solubility ratio of solvent/water and K_ow. Relationships 2–4 tend to be less well defined with increasing K_ow, this responses may be attributed to K_ow values that were derived by extrapolation or calculation. Further analyses between log solubility ratios and log K_ow values up to 5.0, indicate a linear relationship where the regression coefficient was not significantly different from 1.0, and a regression intercept that included zero. This response would suggest K_ow could be calculated from the solubility ratios of chemicals that are not miscible in solvents.     

Biocenosis diversity and denitrification efficiency

During denitrification carried out in the presence of methanol, glycerol, acetic and lactic acids as a C-source, the microbial growth parameters such as: maximum attainable biomass production (P_{x max}), “optimal” biomass residence time (Θ_x), biomass yield coefficients (Y_N and Y_C) and specific biomass loss rate constants (b_N and b_C) were estimated. Also, the following process parameters: maximum attainable biomass N and C removal rates (ΔB_{x, Nmax} and ΔB_{x, Cmax}) and corresponding rate constants (K_{Bx, N} and K_{Bx, C}) were calculated. The values of these parameters were interpreted in relation to the chemical structure of the C-sources for denitrification and degree of their assimilability by the bacteria and fungi which dominated in biocenoses.     

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.     

Effects of elevated temperatures on properties of concrete

Concrete material in structures is likely exposed to high temperatures during fire. The relative properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. This paper presents the effects of elevated temperatures on the physical and mechanical properties of various concrete mixtures prepared by ordinary Portland cement, crushed limestone, and river gravel. Test samples were subjected to elevated temperatures ranging from 200 to 1200 °C. After exposure, weight losses were determined and then compressive strength test was conducted. Test results indicated that weight of the specimen significantly reduced with an increase in temperature. This reduction was very sharp beyond 800 °C. The effects of water/cement (w/c) ratio and type of aggregate on losses in weight were not found to be significant. The results also revealed that the relative strength of concrete decreased as the exposure temperature increased. The effect of high temperatures on the strength of concrete was more pronounced for concrete mixtures produced by river gravel aggregate. The results of the physical and mechanical tests were also combined with those obtained from differential thermal analysis, and colour image analysis.     

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).     

Effects of elevated operating temperatures on methanol removal kinetics from synthetic kraft pulp mill condensate using a membrane bioreactor

The feasibility of biologically removing methanol from kraft pulp mill evaporator condensate was investigated, using a high temperature membrane bioreactor (MBR). Over the range of temperatures investigated (55–70°C), a mixed culture of methanol-utilizing microorganisms could be successfully developed, using synthetic condensate as a feedstock. A maximum specific methanol utilization coefficient of approximately 0.81 day⁻¹ occurred at an operating temperature of 60°C. Over 99% of the methanol was removed from the condensate at operating temperatures of 55 and 60°C. Above 60°C, the specific methanol utilization coefficient declined sharply, indicating that at high operating temperatures, the inactivating effect of temperature on the mixed culture of microorganisms must be considered. A relatively simple model was proposed and used to estimate the effect of high temperatures on methanol removal kinetics in an MBR over the range of temperatures investigated. The operating temperature also had a significant effect on the observed growth yield. At increasing operating temperatures, a larger fraction of the methanol consumed was converted to energy, reducing the observed growth yield.     

Algal growth in warm temperate reservoirs: kinetic examination of nitrogen, temperature, light, and other nutrients

Nutrient limited growth of the phytoplankton assemblage in two Texas reservoirs was studied by a combination of nutrient addition experiments and statistical modeling. Dilution bioassays were run to ascertain the qualitative and quantitative patterns in nutrient limitation. Algal growth was frequently and strongly nutrient limited, particularly when temperature was >22°C. By itself, N was more often stimulatory than P, though strong additional enhancement of growth by P and trace nutrients was often detected. Monod growth kinetics indicated that half-saturation constants for N limited growth for the entire algal assemblage were in the range 20–200 μg N/L, relatively high compared to literature values, and increased with increasing temperature. Maximal growth was also an increasing function of temperature. A single temperature-dependent model was fit to the growth dynamics for all experiments showing N-limitation. The model μ=0.0256·T([DIN]/66.0+[DIN]) where μ is specific growth rate (d⁻¹), T is temperature (°C) and [DIN] is dissolved inorganic N (μmol/L) fit the experimental results reasonably well (r²=0.82). However, only a modest predictive power for growth in the controls (our best estimate of growth in situ) was achieved (r²=0.26). Thus, even with unusually detailed, site-specific fitting of model parameters, accurately modeling algal growth in natural ecosystems can remain a challenge.     

高温后页岩轻骨料混凝土断裂特性

为研究页岩轻骨料混凝土Ⅰ型断裂性能随温度的变化规律,对页岩轻骨料混凝土试件进行100,200,300,400 ℃加热处理,自然冷却至常温。采用三点弯曲梁法对15个缝高比为0.4的轻骨料混凝土小梁进行断裂试验,依据荷载-跨中挠度曲线计算断裂能及断裂韧度。结果表明:起裂韧度与失稳韧度均随温度升高先上升后下降,起裂韧度的转折点在200 ℃左右,失稳韧度的转折点在300 ℃左右; 黏聚韧度呈现下降—上升—下降的趋势,其随温度变化规律与起裂韧度、失稳韧度存在较大的关联性,当温度为300 ℃时裂尖端的黏聚力阻止裂缝扩展的能力最为显著; 断裂能呈现出基本不变—增大—减小的3个变化阶段,当温度为200 ℃左右时断裂能达到最大值,断裂能随温度变化规律的拟合曲线上升段为二次抛物线,下降段为直线; 在所研究的温度范围内,页岩轻骨料混凝土的断裂性能受高温影响较为显著; 所得结论为高温状态下轻骨料混凝土结构裂缝扩展研究和结构设计提供了试验依据。     

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.     

Preservation du contenu en o-phosphate d''echantillons d''eau du fleuve saint-laurent

On a étudié l'efficacité d'un certain nombre de produits comme préservatifs du contenu en o-phosphate d'échaotillons d'eau du fleuve St-Laurent à des températures d'entreposage de −10°, 4° et 20°C. Parmi les produits testés soit le thymol (0.01%), le fluorure de potassium (0.01%), ;lácide sulfurique (0.0 N), le chlorure de tributylétain (0.001%) et le chloroforme (5 ml/l), seuls les deux derniers se sont revélés potentiellement intéressants. Une série d'expériences a confirmé que le contenu en o-phosphate pouvait ètre préseré de façon süre pendant au moins deux sernaines par un entreposage à 4°C en présence de chloroforme (5 ml/l).

Abstract

The effectiveness of some materials in preserving the o-phosphate content of water samples from the St-Lawrence River at storage temperatures of −10°, 4° and 20°C was studied.

Tests were done with thymol (0.01%), potassium fluoride (0.01%), sulfuric acid (0.1 N), tributylin chloride (0.001%) and chloroform (5 ml/l), the last two products showing some activity. From further testing it can be concluded that the o-phosphate content is stable for at least two weeks of storage at 4°C with chloroform added as preservative.     

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.     

Thermal sensation and comfort with different task conditioning systems

Subjective experiments with task conditioning systems, 3DU⁺, PEM, TU, and RCU were conducted to investigate the effect of three different types of Task air-conditioning systems on thermal comfort in a climate chamber. The chamber was conditioned at 28 °C/50%RH with task systems and 26 °C/50%RH without them. Under the condition with the task conditioning systems, the average rating of comfort sensation was between comfortable (0) and slightly uncomfortable (−1). For males it was between −0.5 and −0.7 and for females between −0.3 and −0.4. This was equal to or even better than that in condition without task system. It was found that these systems were effective in providing thermal comfort. The parts to which subjects wanted to diffuse air were different for each system. However, the individual control of task conditioning system contributed to create the preferred environment.