Enrichment of a K-strategist microbial population able to biodegrade p-nitrophenol in a sequencing batch reactor

The biological treatment of a high-strength p-nitrophenol (PNP) wastewater in an aerobic Sequencing Batch Reactor (SBR) has been studied. A specific operational strategy was applied with the main aim of developing a K-strategist PNP-degrading activated sludge. The enrichment of a K-strategist microbial population was performed using a non-acclimated biomass coming from a municipal WWTP as inoculum, and following a feeding strategy in which the PNP-degrading biomass was under endogenous conditions during more than 50% of the aerobic reaction phase. Hundred per cent of PNP removal was achieved in the whole operating period with a maximum specific PNP loading rate of 0.26 g PNP g⁻¹ VSS d⁻¹. A kinetic characterization of the obtained PNP-degrading population was carried out using respirometry assays in specifically designed batch tests. With the experimental data obtained a kinetic model including substrate inhibition has been used to describe the time-course of the PNP concentration and specific oxygen uptake rate (SOUR), simultaneously. The kinetic parameters obtained through optimization, validated with an additional respirometric test, were k_max = 1.02 mg PNP mg⁻¹ COD d⁻¹, K_s = 1.6 mg PNP L⁻¹ and K_i = 54 mg PNP L⁻¹. The values obtained for the K_s and k_max are lower than those reported in the literature for mixed populations, meaning that the biomass is a K-strategist type, and therefore demonstrating the success of the operational strategy imposed to obtain such a K-strategist population. Moreover, our measured K_i value is higher than those reported by most of the bibliographic references; therefore the acclimated activated sludge used in this work was evidently more adapted to PNP inhibition than the other reported cultures.     

A comprehensive study on the biological treatabilities of phenol and methanol—III Treatment system design

The effects of temperature, pH, salinity, and nutrients on bacterial activities were investigated and evaluated using a statistical method. The substrate utilization rate coefficient (k) decreased as pH deviated from neutral and as salinity increased, and the unfavorable pH and salinity alleviated the temperature effect on k. The modified Arrhenius equation, k_T2 = k_T1 θ(^T2−T1), was not effective in describing the temperature effect on k: the temperature coefficient (θ) ranged between 1.0–1.4 depending on the temperature range, pH, salinity, and substance (phenol or methanol). The endogeneous respiration activity was affected by various environmental factors such as pH, temperature, and salinity; however, the cell decay coefficient (k_d) turned out to be correlated to a single parameter, k. Thus, k_d = 0.066 k^0.87 and k_d = 0.0115 k^0.634, where k and k_d are based on the unit of h⁻¹, were proposed for the prediction of cell decay coefficient for phenol and methanol acclimated activated sludge, respectively. In batch treatment of 770 mg l⁻¹ of phenol and 1000 mg l⁻¹ of methanol as TOC, nitrogen and phosphorus did not have any recognizable effect on k, while trace elements such as Fe²⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Zn²⁺, etc. showed a slightly perceptible effect on it. The absence of extra-cellular nitrogen and phosphorus resulted in a greater cell yield; however, the cells in this condition decayed more rapidly than normal cells. The primary factor affecting the substrate decomposition rate in natural systems was pH: phenol decomposition resulted in a considerable decrease in pH so that the buffering capacity of the water was the most important factor, and methanol decomposition did not affect pH significantly so that the initial pH of the water was the most important factor. An initial lag phase was observed in 8 out of 115 phenol batch tests and 31 out of 66 methanol batch tests.     

Effects of mixing velocity on anaerobic fixed film reactors

Four laboratory-model upflow anaerobic fixed film reactors (AFFR 1, 2, 3 and 4) treating landfill leachate were subject to identical volumetric organic load (7 kg COD m⁻³ d⁻¹) and hydraulic retention time (3d), but the contents in each unit were continuously recirculated for 10 months at four different velocities, respectively, of 21, 66, 680 and 3063 cm h⁻¹. The objective was to assess the effects of such mixing velocities (ν) on COD removal efficiencies (E), mean cell residence time (MCRT) and substrate utilization rate (U expressed as g COD removed d⁻¹ g⁻¹ VSS). The results showed that the relationships between E and ν and MCRT and ν were inverted U-shaped curves. The two middle reactors (AFFR 2 and 3) had near-optimum velocities (ν₂ and ν₃) with maximum E values of 88–89%. AFFR 4 had a high value of ν scouring biofilm on the biorings, resulting in higher concentrations of SS, VSS and COD in the effluent. All four reactors had nearly similar values of U (1.85–2.14 g COD d⁻¹ g⁻¹ VSS). The value of ν₁ (AFFR 1) was too low to enhance performance and ν₄ was too high to retain the biomass. The optimum recycle velocity, under the test conditions, was in the range of 66–680 cm h⁻¹.     

Palm oil refinery wastes treatment

Effluent from the refining of crude palm oil was subjected to physical-chemical and biological treatment. An inclined corrugated parallel plates oil separator spaced at 25 mm was used with hydraulic loading rates of 0.2, 0.5 and 1 m³ m⁻²-h. 91% oil and grease removal could be achieved at 0.2 m³ m⁻²-h. Coagulation and flocculation carried out on batch samples after oil and grease separation revealed that with 100 mg l⁻¹ alum addition BOD was reduced from 3500 to 450 mg l⁻¹ and COD from 8600 to 750 mg l⁻¹ after 30 min settling. Higher doses of alum and doses of polyelectrolyte, activated carbon and sodium hypochloride did not yield significant additional reductions in BOD and COD. Batch dissolved air flotation (DAF) removed 90% of the suspended solids with 2.7% solids in the thickened sludge at an A/S ratio of 0.014. This method yielded the similar effluent quality as the inclined corrugated plates oil and grease separator. Field data from a DAF plant compare closely with data achieved in this study. Activated sludge treatment on the effluent from the oil separator yielded a BOD of 46 mg l⁻¹ with a loading rate of 0.3 g BOD (g MLVSS)⁻¹-day. Total dissolved solids (TDS) remained high and removal through coagulation and chemical oxidation brought the COD level down to around 180 mg l⁻¹. Biokinetic coefficients Y, k_dK and K₃ were found to be 0.85 g VSS (g BOD)⁻¹, 0.016 day⁻¹, 0.12 g BOD (g VSS)⁻¹-day and 510 mg l⁻¹ BOD respectively.     

The extent of reversibility of polychlorinated biphenyl adsorption

The extent of reversibility of PCB bonding to sediments has been characterized in studies on the partitioning behavior of a hexachlorobiphenyl isomer. Linear non-singular isotherms have been observed for the adsorption and desorption of 2.4.5.2′,4′,5′ hexachlorobiphenyl (HCBP) to 1100 ppm sediment suspensions. Partition coefficients, π(1 kg−1), for desorption from lake sediments (Saginaw Bay. Lake Huron. Michigan) are substantially greater (π_d 20.000–35.000) than those obtained for adsorption (π₄ 9000–14,000). HCBP was found to be more weakly adsorbed to montmorillonite (π_a − 3000, π_d 9000) and kaolinite (π_a 1000, π_d 3000) clay samples than to the natural sediment samples. Desorption results (π_d) for Saginaw Bay sediments were quite similar to π values (15,000–35.000) calculated from field measurements of aqueous and particulate PCB concentrations. For Saginaw Bay sediments and clay minerals partitioning appeared to be correlated both to sediment surface area and to sediment organic content. A regression analysis using both of these variables explained 90% of the observed variations. HCBP adsorption at 40 C (π_a 14,000) was significantly greater than at 1° C (π_a 6500) resulting in a calculated enthalpy of adsorption of +3.3 kcal mol⁻¹. Non-singular isotherm behavior was not found to be readily attributable to microbiological, kinetic or experimental effects. Evidence from consecutive desorption studies suggests that while HCBP adsorption may ultimately be reversible. release from sediments appeared to involve desorption along two distinct isotherms. These results have been interpreted in terms of possible similarities between the sorption properties observed in the distilled water systems of the present study and PCB bonding processes in natural water systems.     

Hypolimnetic aeration: field test of the empirical sizing method

A hypolimnetic aeration system was recently installed in a small (16 ha S_α) eutrophic lake and a comparison made between measured performance and predicted performance from an empirical sizing method. The design variables used to size the system were: hypolimnetic volume 451,600 m³; maximum hypolimnetic oxygen consumption 0.2 mg l⁻¹ d⁻¹; aerator input rate 2 mg l⁻¹; water velocity 0.76 m s⁻¹ and depth of air release 12.2 m. A 3.7 kW compressor (0.57 m³ min⁻¹) generated a water velocity of 0.46 m s⁻¹, a water flow of 17.7 m³ min⁻¹ and a theoretical hypolimnetic circulation period of 18 days. Dissolved oxygen increased by an average of 1.6 mg l⁻¹ on each cycle through the aerator, and aerator input rates ranged from 0.6 to 2.6 mg l⁻¹. Hypolimnetic oxygen consumption averaged 0.12 mg l⁻¹ d⁻¹ and ranged between 0.02 and 0.21 mg l⁻¹ d⁻¹. The aeration system was unable to meet the daily oxygen demand (90 kg) as the water velocity was slower than expected (0.46 m s⁻¹). To avoid undersizing future aeration installations the following recommendations should be considered when using the empirical sizing formula: (1) estimates of oxygen consumption should be annual maximums from aerobic hypolimnia; (2) aerator input rates should be conservative (e.g. 1–4 mg l⁻¹) and increase with depth; (3) water velocity of 0.45–0.50 m s⁻¹ should initially be used when no information on actual bubble size or velocity is available; (4) aeration start-up should be timed to avoid periods of accumulated oxygen demands.     

Oxygen depletion of Hamilton Harbour

Processes involved in the oxygen cycles of the highly eutrophic Hamilton Harbour were studied. Sediment oxygen demand k_s(O₂ m⁻² day⁻¹) was measured by an in situ method and was determined to be dependent on oxygen concentrations c (m l⁻¹) in the water phase. This dependence was expressed by the equation k_s = 0.72 + 0.26 c. The water column oxygen demand of the harbour was determined experimentally and revealed a significant dependence on oxygen concentration. It was estimated that over 80% of the oxygen supplied to the harbour was used within the water column. The sediment oxygen consumed about 18% of the oxygen entering the harbour and was relatively most important in the early stages of stratification when the hypolimnetic dissolved oxygen concentrations were high. The main sources of oxygen were atmospheric reaeration (80%), lake-harbour exchange (10%) and photosynthesis (10%).     

Growth kinetics of the filamentous microorganism Sphaerotilus natans in a model system of a food industry wastewater

Bulking by Sphaerotilus natans has been attributed to several factors such as low dissolved oxygen in the aeration basin, wastes with high C:N ratios and phosphorus limitation; however, the occurrence of bulking has been reported in fruit, vegetable, meat and poultry wastewaters in which the ratio C:N is variable.Growth of S. natans was analyzed in a model system of a food industry wastewater (potato processing waste) that was characterized by HPLC determining that citric acid was the most important identified component. The effect of several carbon sources on S. natans growth was also studied; different C:N ratios were tested in a continuous culture system (chemostat). This strain grew in a mineral medium with citric acid as a sole carbon source, in spite of the contradictory results found in literature. Chemostat studies showed that the medium was carbon-limited when C:N ratios <19 mgCOD (mgN-NH₃)⁻¹. Monod kinetic growth coefficients, determined for this strain in chemostat were: maximum specific growth rate, μ_max=0.301 h⁻¹; Monod constant, K_S=4.6 mgCOD l⁻¹; true biomass growth yield, Y^T_X/S=0.490 mgVSS (mgCOD)⁻¹; endogenous decay rate, k_d=0.011 h⁻¹ and maintenance coefficient, m_S=0.022 mgCOD (mgVSS)⁻¹ h⁻¹. The obtained parameters were compared with literature data and the effect of glucose and citric acid as carbon sources was discussed; these parameters are useful in modeling the growth of S. natans in potato processing wastewaters (or in other effluents under carbon-limiting conditions) especially when citrate is the main component and can be used to control filamentous bulking by metabolic or kinetic selection.     

Oxygen uptake of bottom sediments studied in situ and in the laboratory

Oxygen uptake by soft bottom sediments was measured in situ with an oxygen electrode in a bell jar. Values in the range 0·3-3·0 g O₂ m⁻² d⁻¹ were obtained at 19 localities in fresh and brackish water. Comparative measurements were made in the laboratory on sediment cores. These gave consistently lower values than the in situ measurements. Laboratory experiments showed that the oxygen uptake depended on the oxygen concentration and that the temperature coefficient decreased with increasing temperature. There was no simple correlation between oxygen uptake and content organic matter in sediments.     

Effects of salinity on synthesis of DNA, acidic polysaccharide, and growth in the blue-green alga, Gomphosphaeria aponina

A blue-green alga, Gomphosphaeria aponina, was grown in artificial sea water at salinities 20–36%. Fair to good growth was obtained at all salinities, and growth constants (K_e) were obtained. A parabolic relationship was obtained for the growth salinity relationship, e.g. (S−S_max)² = −2p(K_e−K′_e), where S and S_max is the given salinity and the maximum salinity, respectively, for which growth constants K_e and K_e^′ were obtained; p is a constant. The rate of DNA synthesis increased linearly with growth constant above K_e = 0.95 day⁻¹. Linear correlation coefficients were obtained for rate of polysaccharide synthesis and the rate of DNA synthesis, as well as for the rate of DNA synthesis and the rate of synthesis of aponin. The latter is material isolated from G. aponina and has cytolytic activity toward the Florida red tide organism, Gymnodinium breve, an unarmoured dinoflagellate.     

Ageing of aluminium hydroxide flocs

The ageing processes of kaolinite suspensions flocculated with Al₂(SO₄)₃ under a variety of different but well-controlled flocculation conditions were studied by measuring their average diameter, diameter distribution, strength and electrophoretic mobility.Three periods could be distinguished in the ageing process. Initially shrinkage of the flocs is mainly due to cementation-aggregation. In the first 6–8 h, dependent on the flocculation conditions, the average diameter reduces from 500 to 220 μm. During the following 4 days a shrinkage to 180 μm occurs, mainly due to condensation-polymerization and crystallization. In the third period, the average diameter increases because of Oswald ripening of the crystals.During each period the change of the diameter as a function of age can mathematically be described by: d_f,i = d∞ + d′· t_i^+i−ω. With d_∞, d′ and ω constants dependent on the flocculation conditions.During ageing, the floc diameter distribution narrows. The shrinkage of the flocs during ageing is definitely not due to erosion of particles from the floc surface.The change of the electrophoretic mobility during ageing provides information on the thickness and homogeneity of the layer of insoluble hydroxides around the destabilized clay particles.The influence of a wide range of different flocculation process parameters on the floc ageing process is summarized, as is the influence of the ageing process on floc strength and floc density. The evolution of the effective floc density can be described by: .The constants K_p and a are functions of the ratio quantity of suspended solids vs coagulant dose.     

Effects of loading rate on rock fracture

By means of a wedge loading applied to a short-rod rock fracture specimen tested with the MTS 810 or SHPB (split Hopkinson pressure bar), the fracture toughness of Fangshan gabbro and Fangshan marble was measured over a wide range of loading rates, =10⁻²–10⁶ MPa m^1/2 s⁻¹. In order to determine the dynamic fracture toughness of the rock as exactly as possible, the dynamic Moiré method and strain–gauge method were used in determining the critical time of dynamic fracture. The testing results indicated that the critical time was generally shorter than the transmitted wave peak time, and the differences between the two times had a weak increasing tendency with loading rates. The experimental results for rock fracture showed that the static fracture toughness K_Ic of the rock was nearly a constant, but the dynamic fracture toughness K_Id of the rock ( ≥10⁴ MPa m^1/2 s⁻¹) increased with the loading rate, i.e. log(K_Id)=a log +b. Macroobservations for fractured rock specimens indicated that, in the section (which was perpendicular to the fracture surface) of a specimen loaded by a dynamic load, there was clear crack branching or bifurcation, and the higher the loading rate was, the more branching cracks occurred. Furthermore, at very high loading rates ( ≥10⁶ MPa m^1/2 s⁻¹) the rock specimen was broken into several fragments rather than only two halves. However, for a statically fractured specimen there was hardly any crack branching. Finally, some applications of this investigation in engineering practice are discussed.     

Towards a better understanding of high rate biological film flow reactor theory

On the assumption that performance of biological film flow reactors is independent of oxygen transfer, a theoretical extension of a mathematical model (after Ames) is described. This predictive and interpretive model incorporates both mass transfer-limitations between biomass and liquid film, and kinetic biological reaction rate of organic “food” utilization.Given general boundary conditions for the differential equations describing the mass transfer process, it is shown that: C_e = C_r + (C_l − C_r.exp(−K_m D/Q) where by definition: C_t = α C_s + C_r1/K_m = 1/K_LA_γ + α/Kx.For an influent concentration biochemical oxygen demand (C_i) and resultant effluent concentration (C_e) obtained during film flow through a packed media depth (D), the Model proposes that the residual concentration (C_r) is a function of surface irrigation rate (Q) and biomass activity. If this term is negative, adsorption occurs; while if positive, desorption from the biomass film at concentration (C_s) takes place.An overall mass transfer coefficient (K_m) is defined by a series equation where the usual mass transfer coefficient (K_L) is primarily a function of Reynolds Number [surface irrigation rate (Q) and specific surface area (A_V)], Schmidt Number (diffusivity of organic “Food”) and concentration. “Food” utilization at active sites on the biological film is governed by a specific adsorption coefficient (α) and explained by a Langmuir analogy. Biological conversion of “food” is described by a kinetic rate constant (K), while the necessary oxygen is defined by (X).This predictive model was developed from a wide range of pilot plant data, successfully tested further on a variety of published results and on actual full scale operating plants.Parameters derived from this Model, in terms of Height of Transfer Unit and Kinetic Reaction coefficient, characterize organic “treatability” for a variety of wastes.     

Pentachlorophenol biodegradation—I: Aerobic

The biodegradation of pentachlorophenol (PCP) was tested in a three phase protocol. Phase I involved acclimation; phase II allowed determintion of biodegradation kinetics through use of continuous stirred tank reactors (CSTR) operated at solids retention times of 3.2, 7.8, 12.8 and 18.3 days; phase III assessed the importance of volatilization and sorption in PCP removal and evaluated the extent of biodegradation. Over the range of SRT's studied, PCP was found to be biodegradable with first order kinetics; the rate constant (μ_m/K_s) had a value of 0.0017 l μg⁻¹d⁻¹. The minimum concentration of PCP attainable in a CSTR was found to be 27 μg l⁻¹. Additional studies suggested that the full relationship between the PCP degradation rate and the PCP concentration followed an inhibition-type function, with the maximum rate occurring at a PCP concentration of around 350 μg l⁻¹. Radioisotopic studies revealed that PCP was mineralized by the culture, with the liberation of CO₂ and the incorporation of carbon into cell material. Neither volatilization nor sorption removed significant amounts of PCP from the reactors.     

Sorption and accumulation of cadmium in the sediment of the Tama River

Cadmium contents in the water and the sediment samples collected from the Tama River and several branches were measured. Cadmium (above 0.005mgl⁻¹) was detected in only four of the water samples, while the sediment samples showed cadmium content of 1.0–9.8 μg g⁻¹ dry sediment. Cadmium concentration in the sediments of the main stream was correlated against ignition loss of the samples and it was found that 1 g of ignition loss (organic matter) corresponded to 35 μg of cadmium.The batch adsorption experiment in the laboratory using an aqueous solution of cadmium for 14 sediment samples with a higher concentration of cadmium indicated that the amount adsorbed by the sediment is highly dependent on the ignition loss. The amount adsorbed on unit mass of ignition loss q_IL could be correlated by a Freundlich-type equilibrium relation as where C is the equilibrium concentration in the aqueous phase ranging between 7 × 10⁻³ and 10 mg l⁻¹, while k_IL and n are equilibrium constants.The adsorption rate measurement showed that the intraparticle diffusion coefficient of cadmium in the sediment was about 1.1 × 10⁻⁶ cm²s⁻¹, which is of a reasonable order of magnitude assuming the pore diffusion mechanism inside the particle.The results suggest that suspended solid particles of high organic content in flowing water contribute significantly to the transport of cadmium along the river.     

Effects of inhibitors on nitrification in a packed-bed biological flow reactor

The individual effect of trivalent arsenic, hexavalent chromium and fluoride on nitrification is studied under continuous load in a packed bed biological flow reactor. The results show that Michaelis-Menten rate expression gives the best representation of nitrification data in the absence of inhibitors. However, in the presence of inhibitors, the system follows a non-competitive mode of inhibition with the following rate expression: The values of V_max and K_s are estimated as 1.466 mg l⁻¹ min⁻¹ and 2.349 mg l⁻¹ respectively. The inhibitor constant K_i is evaluated as 273 mg l⁻¹ for trivalent arsenic, 56 mg l⁻¹ for hexavalent chromium and 1185 mg l⁻¹ for fluoride.     

Ozone oxidation of pharmaceuticals, endocrine disruptors and pesticides during drinking water treatment

This study investigates the oxidation of pharmaceuticals, endocrine disrupting compounds and pesticides during ozonation applied in drinking water treatment. In the first step, second-order rate constants for the reactions of selected compounds with molecular ozone (k_O3) were determined in bench-scale experiments at pH 8.10: caffeine (650 ± 22 M⁻¹ s⁻¹), progesterone (601 ± 9 M⁻¹ s⁻¹), medroxyprogesterone (558 ± 9 M⁻¹ s⁻¹), norethindrone (2215 ± 76 M⁻¹ s⁻¹) and levonorgestrel (1427 ± 62 M⁻¹ s⁻¹). Compared to phenolic estrogens (estrone, 17β-estradiol, estriol and 17α-ethinylestradiol), the selected progestogen endocrine disruptors reacted far slower with ozone. In the second part of the study, bench-scale experiments were conducted with surface waters spiked with 16 target compounds to assess their oxidative removal using ozone and determine if bench-scale results would accurately predict full-scale removal data. Overall, the data provided evidence that ozone is effective for removing trace organic contaminants from water with ozone doses typically applied in drinking water treatment. Ozonation removed over 80% of caffeine, pharmaceuticals and endocrine disruptors within the CT value of about 2 mg min L⁻¹. As expected, pesticides were found to be the most recalcitrant compounds to oxidize. Caffeine can be used as an indicator compound to gauge the efficacy of ozone treatment.     

Modified curcumin and dianthrimide methods for the determination of boron in the presence of high levels of nitrate and organics

Modifications have been made to the curcumin and 1,1′-dianthrimide methods for boron analysis so that they may be used in the presence of up to 700 mg l⁻¹NO⁻₃ and 500 mg l⁻¹ organic carbon. In the curcumin method, nitrate is removed by alkaline reduction using a slurry of aluminum powder. In the dianthrimide method, nitrate up to 1000 mg l⁻¹NO⁻₃ is removed in the dehydration-with-sulfuric-acid step; organics are most conveniently removed by treatment of the dehydrated sample with solid potassium persulfate. With dianthrimide, an automated procedure is used for the colour formation and measurement steps.     

Nickel stimulation of anaerobic digestion

An acetate-enriched methanogenic culture was assayed for nutritional stimulation by nickel in combination with other inorganic and organic nutrients, i.e. iron, cobalt, yeast extract, riboflavin and vitamin B₁₂. Acetate was automatically maintained at 2–3 g l⁻¹ by a pH Stat system so that substrate was not limiting. In the absence of nickel, the specific acetate utilization rates were in the range of 2–4.6 g acetate g⁻¹ VSS day⁻¹. In the presence of nickel, this rate was as high as 10 and when both nickel and yeast extract were supplemented this rate temporarily increased to 12–15 g acetate g⁻¹ VSS day⁻¹ . The maximum acetate utilization rate was observed to be 51 g l⁻¹ day⁻¹ as compared to 3.3 g l⁻¹ day⁻¹ for conventional high-rate digestion. Daily phosphate additions were required to sustain these high acetate utilization rates. An acetate utilization rate of 20–30 g l⁻¹ day⁻¹ was maintained for over 25 days. Microscopic examination of the culture revealed a predominance of a sarcina whenever stimulation was noted.