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.     

Nitrate reduction by denitrifying bacteria in single and two stage continuous flow reactors

Denitrification by a mixed bacterial population of medium containing 1000 mg NO₃⁻-N1⁻¹ and acetate as carbon source was studied in batch, a single stage continuous flow stirred reactor (CFSTR) and a two stage CFSTR at 30°C. The optimum pH for denitrification, nitratase, nitrite reductase activities and growth was found to be 7.5 in batch culture. A single stage CFSTR growth limited by nitrate had an optimum denitrification rate of 0.13 mg NO₃⁻-N mg⁻¹ cells h at a residence time of 8 h. The experimentally observed carbon to nitrate ratio (mg CH₃ COO⁻-C mg⁻¹ NO₃⁻-N)was 1.7 for the dilution rates of 0.02–0.18 h⁻¹. For the second stage CFSTR, bacteria growing at the maximum rate of 0.25 h⁻¹ and not limited by nitrate had a denitrification rate of 0.24 mg NO₃⁻-N mg⁻¹ h. Dissolved oxygen (up to 9.5 mg 1⁻¹) did not effect denitrification rates in the second stage CFSTR. As the second stage CFSTR runs progressed extensive wall growth occurred and concurrently the output gas contained increasing quantities of nitrous oxide. A development from this study would be a two stage CFSTR with wall growth in the second stage which would make an efficient nitrate removal process.     

Responses of Cyperus involucratus Rottb. to nitrogen and phosphorus, with reference to wastewater reclamation

There is increasing use of aquatic plants in biosystems to ameliorate wastewaters. Cyperus involucratus Rottb. is a large emergent aquatic plant which may be useful in treating wastewater because it grows quickly, does not die back in winter, has little weed potential and grows in dryland situations. Many wastewaters contain high levels of N and P, and the capacity of C. involucratus to take up these nutrients was studied under glasshouse conditions. Maximum growth was attained between 84 and 168 mg NO₃-Nl⁻¹ and 1–5 mg PO₄-Pl⁻¹. At a low level of supplied NO₃-N, most of the N in plant organs was reduced-N; at levels of supplied NO₃-N above 84 mg l⁻¹, there was considerable accumulation of NO₃-N in plant organs. The accumulation of NO₃-N was greatest in culms where it made up over 50% of their N content when plants were grown on 350 mg NO₃-Nl⁻¹. Linear regression equations best described the relationships between dry matter and reduced-N contents in roots, culms and leaves. Over 60% of the total plant N and P accumulated in above ground organs, and concentrations of up to 0.53% P and 3.4% N (dry wt basis) were recorded in leaves. C. involucratus would be a suitable plant for wastewater reclamation on account of its high dry matter production, its ability to tolerate hyper-eutrophic levels of N and P, and the accumulation of most of the N and P in the harvestable portions of the plant.     

Denitrification en continu a l'aide de microorganismes immobilises sur des supports solides

In this paper, we describe a study of biological denitrification by immobilized cells. Nitrates are reduced in sterile solutions by Pseudomonas aeruginosa immobilized in a fixed bed reactor, and in synthetic waste water by mixed cultures immobilized into a fluidized bed reactor.The fixed bed reactor is a Plexiglas column filled with corn stovers (Table 1). It is 0.05 m in diameter and 0.55 in height, its volume being approx. 11. The fresh medium is injected at the base of the column and the liquid level is regulated by an overflow weir. Reactor and carrier are sterilized with ethylene-oxide. After sterilization 1 l. of a growing batch culture of Pseudomonas aeruginosa is introduced aseptically and the reactor is then fed continuously (45 ml h⁻¹) with fresh medium (N---NO₃ = 40 mg l⁻¹) until the first steady state is reached.Nitrates and nitrites are determinated by means of a colorimetric method.Reactor efficiency remains constant for over 40 days. Nitrates and nitrites concentrations are measured inside the reactor for flow varying from 2 to 16 ml min⁻¹ (Fig. 2). Reductions of nitrates and nitrites seem to be two first-order reactions (Fig. 3 and Table 2) and constant rate increases with flow rate (Fig. 4). Until nitrate concentration reaches 960 mg/l⁻¹ (N---NO₃) degradation is correct (Figs 5 and 6), beyond nitrites, which have been formed, seem to be inhibitor.Using this reactor, 50 mg N---NO₃ have been reduced per hour and per liter of empty reactor, but it may be possible to reduce 140 mg N---NO₃ l⁻¹ h⁻¹ if fresh medium contains 200 mg N---NO₃ l⁻¹.The fluidized bed reactor is a Plexiglas column filled with earthenware. It is 0.05 m in diameter and 3.15 m in height, its volume being approx. 6.201. Fresh medium is injected at the base of the column and the liquid level is regulated by an overflow weir. Figure 7 shows the retention time of the liquid in the reactor in relation to flow. The first steady state has been reached after 2 weeks, and it has not been possible to know half life time of the column.Four experiments were conducted (Table 3) and, for each nitrate, nitrite and methanol concentrations in the reactor were measured (Fig. 8). So, it appears that reduction of nitrates and nitrites are two first-order reactions (Table 4) and that constant rate values, which are higher than in fixed bed reactor, increase with flow.The reactor is more affected by a flow shift than by a nitrate concentration shift in fresh medium, and biomass linked onto carrier is about 76 mg of dry matter g⁻¹ of earthenware.So, our fluidized bed column is able to reduce 560 mg N---NO₃ h⁻¹ l⁻¹ of empty reactor, then retention time of liquid is less than 3 min.     

The use of an upflow fixed bed reactor for treatment of a primary settled domestic sewage

This study presents and demonstrates results obtained from an half full-scale upflow fixed bed reactor (UFBR) treating a primary settled domestic sewage. This study used expanded clay with an effective size of 2.7 mm containing hematite and magnetite as a granular medium.The content of TSS in the effluent treated was always between 10 and 20 mg l⁻¹ for bed depths ranging from 2 to 3 m and filtration rates of 3–6 m³m⁻²h⁻¹.The profiles taken all along the reactor show that the activity of the biomass is constant over the whole height of the reactor. Moreover, an air/water volume ratio of 2:1 is amply sufficient to satisfy the oxygen demand of the biomass. The average removal efficiency based on the soluble COD remains virtually unchanged as a function of the filtration rate at about 70% of the influent. For a final BOD₅ of 30 mg l⁻¹, loadings of 4.5–8 kg BOD₅m⁻³ can be applied. This corresponds to filtration rates of 3–6 m³m⁻²h⁻¹. The removal efficiencies for BOD₅ are then about 80%.After optimization of the backwashing conditions, the consumption of backwash water is about 5% of the volume of filtered water.Sludge measurements carried out during our experiments indicate an excess sludge production of 1 kg kg⁻¹ BOD₅ eliminated. The nature of these sludges is very similar to the biological sludges produced in the high rate activated sludge process.This study has made it possible to establish design parameters of an UFBR and to develop technology for applications. These results are applied to two wastewater treatment plants which began to operate in 1984: these plants serve population equivalents of 40,000 and 11,000.     

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.     

Denitrification with a bacterial disc unit

An enclosed rotating disc unit was operated anaerobically as a denitrifying system, with methanol as the hydrogen donor. As the bacterial population became established, denitrification rate increased by 1·5 mg NO₃⁻—N reduced m⁻² h⁻², to a maximum rate of 260 mg NO₃⁻—N reduced m⁻²h⁻¹. The C:N ratio necessary for complete denitrification was found to be 2·6:1. Optimum pH for denitrification lay in the range between pH 7·0 and 8·5. Q₁₀ values were 1·38 between 10 and 30°C, −2·66 above 30°C and 13·06 below 10°C.     

Uptake and release of zinc by aquatic bryophytes (Fontinalis antipyretica L. ex. Hedw.)

The zinc uptake and posterior release by an aquatic bryophyte—Fontinalis antipyretica L. Ex Hedw.—was experimentally studied in laboratory exposing the plants to different zinc concentrations in the range, 1.0–5.0 mg l⁻¹, for a 144 h contamination period, and then exposed to metal-free water for a 120 h decontamination period. The experiments were carried out in perfectly mixed contactors at controlled illumination, using mosses picked out in February 1997, with a background initial zinc concentration of 263 mg g⁻¹ (dry wt.). A first-order mass transfer kinetic model was fitted to the experimental data to determine the uptake and release constants, k₁ and k₂, the zinc concentration in mosses at the end of the uptake period, C_mu, and at the equilibrium, for the contamination and decontamination stages, C_me and C_mr, respectively. A bioconcentration factor, BCF=k₁/k₂ (zinc concentration in the plant, dry wt./zinc concentration in the water) was determined. A biological elimination factor defined as BEF=1−C_mr/C_mu was also calculated. BCF decreases from about 4500 to 2950 as Zn concentration in water increases from 1.05 to 3.80 mg l⁻¹. BEF is approximately constant and equal to 0.80. Comparing Zn and Cu accumulation by Fontinalis antipyretica, it was concluded that the uptake rate for Zn (145 h⁻¹) is much lower than for Cu (628 h⁻¹) and the amount retained by the plant decreased by a factor of about seven.     

An improved hydrazine reduction method for the automated determination of low nitrate levels in freshwater

An automated nitrate determination is described in which nitrate is reduced to nitrite with hydrazine sulphate under alkaline conditions in the presence of Cu²⁺ and Zn²⁺. Interferances encountered in natural water samples were eliminated by the addition of Zn²⁺ to the Cu²⁺ catalyst solution.The method is suitable for the determination of low NO₃−N concentrations and compares favourably with the manual copperised cadmium technique for freshwater samples containing 10–800 mg m⁻³ NO₃−N. The method is also linear at nitrate concentrations below 10 mg N m⁻³. The standard deviations (S.D.) of blanks and of samples containing 2 mg NO₃−N m⁻³ were 0.013 and 0.06 mg N m⁻³ respectively at an analysis rate of 30 samples h⁻¹.     

Comparison of chlorine and chlorine dioxide toxicity to fathead minnows and bluegill

The comparative toxicity of total residual chlorine (TRC) and chlorine dioxide (ClO₂) was evaluated by conducting 96 h flow-through bioassays with three types of fish. The fish were subjected to an intermittent exposure regime in which biocide residuals were present for approx. 2-h periods beginning at 0, 24, 48 and 72 h into the tests. These conditions simulated the antifouling procedure (1 h day⁻¹ biocide addition) used to control biofouling of nuclear reactor heat exchangers at the Savannah River Plant near Aiken, South Carolina. LC₅₀ values showed that ClO₂ was approx. 2–4 times more toxic than TRC to: (1) juvenile and 1-year-old fathead minnows (Pimphales promelas); and (2) young-of-the-year bluegill (Lepomis macrochirus).The TRC mean 96-h LC₅₀ values were: 0.08 mg l⁻¹ for juvenile fathead minnows, 0.35 mg l⁻¹ for adult fathead minnows and 0.44 mg l⁻¹ for young-of-the-year bluegills. The ClO₂ mean LC₅₀ values were: 0.02 mg l⁻¹ for juvenile fathead minnows, 0.17 mg l⁻¹ for adult fathead minnows and 0.15 mg l⁻¹ for young-of-the-year bluegills.     

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.     

Kinetics of attached microbial growth in a continuous stirred tank reactor

Kinetics of attached heterotrophic microbial growth was investigated experimentally using a continuous stirred tank reactor (121) for stream self-purification studies. Glucose was fed as the only source of carbon to the reactor in low concentration (4.5 27. mg-glucose l⁻¹).Substrate consumption rate was dependent not on substrate concentration but on substrate loading. Oxygen consumption rate had a linear relationship with substrate consumption rate. The respiration rate of attached microbial population was 9 mgO₂g⁻¹ cell per hour.At steady state, attached growth rate was independent of substrate consumption rate because the attached growth was presumably suppressed by the limitation on attached surface area. Growth yield for substrate decreased with increasing substrate loading.     

Detoxification of seawater used for gas scrubbing in the steel industry

Cyanide ion present in seawater after scrubbing blast furnace and coke ovens gases can be removed by sedimentation of hexacyanoferrate complexes followed by oxidation of residual cyanide with Caro's acid. Zinc ion is removed at the same time by adsorption on the hexacyanoferrate/hydrous ferric oxide precipitate.Sulphide is precipitated as ferrous sulphide, then oxidised by atmospheric oxygen. At 25°C and using an Fe/CN ratio of 1·00, initial concentrations of 50 mg l⁻¹ of CN⁻ and 10 mg l⁻¹ of Zn²⁺ in seawater are reduced to 5–7 mg l⁻¹ and 0·1 mg l⁻¹. Subsequent treatment with H₂SO₅/CN = 1·2 reduces the [CN⁻] to 0·1 mg l⁻¹.Treatment of a combined blast furnace/coke ovens effluent ([CN⁻] = 24 mgl⁻¹, [Zn²⁺] = 4·0 mgl⁻¹) with Fe/CN = 1·5 reduced [CN⁻] to 0·2 mg l⁻¹ and [Zn²⁺] to <0·1 mgl⁻¹. Subsequent treatment with H₂SO₅/CN = 2·0 reduced [CN⁻] to 0·2 mg l⁻¹. The process operates best in the pH range 7–9 and so is not affected by the buffer characteristics of seawater.     

The effects of phenol and some alkyl phenolics on batch anaerobic methanogenesis

Phenol and seven alkylphenols (o-, m- and p-cresol, 2.5-, 2.6-, 3.4- and 3,5-dimethylphenol) were added at various concentrations to aliquots of domestic anaerobic sludge in Hungate serum bottles and these were incubated at 37°C. The concentration of methane in the headspace gas was monitored to determine if the phenolics were fermented to methane or if they inhibited the anaerobic process. Only phenol and p-cresol were fermented to methane. At 500 mg l⁻¹ (but not at 300 mg l⁻¹) 2,5-, 3,4- and 3,5-dimethylphenol reduced the rate and the amount of methane produced. The cresols were inhibitory at 1000 mg l⁻¹ but not at 400 mg l⁻¹.In cultures supplemented with acetate and propionate (VOA), and in unsupplemented cultures, phenol at concentrations up to 500 mg l⁻¹ was fermented to methane. Between 800 and 1200 mg l⁻¹ phenol, methane production was neither enhanced nor inhibited relative to control cultures containing no phenol. Inhibition of methane production was evident when phenol was present at 2000 mg l⁻¹. Thus the methanogens are less susceptible to phenol inhibition than are the phenol-degrading acid formers. In similar experiments with p-cresol: enhanced methane production was observed at concentrations of 400 mg l⁻¹; no enhancement or inhibition was observed at 600 mg l⁻¹; and inhibition was noted when p-cresol was present at 1000 mg l⁻¹.     

Studies on the toxicity of copper sulphate to stone loach Noemacheilus barbatulus (L.) in hard water

The toxicity of copper sulphate to Noemacheilus barbatulus was studied for 64 days in a water of total hardness 249 mg l⁻¹ as CaCO₃. The 63-day lc₅₀ was approximately 0.25 mg Cu l⁻¹. Larger fish survived longer, and at concentrations greater than 0.29 mg l⁻¹ fish hid less during daylight. Noemacheilus surviving 0.12 mg Cu l⁻¹ for 64 days shed copper when placed in clean water for 7 days: gill, muscle, eye and vertebrae lost significant amounts of copper during this period. The opportunity to shed copper during a short period when the poison supply to their tank failed, may have allowed fish exposed to 0.49 mg l⁻¹ to live 12 days longer than expected. The sensitivity of Noemacheilus to copper, cadmium and zinc was compared with that of rainbow trout. Salmo gairdneri.     

The toxic effects of trinitrotoluene (TNT) and its primary degradation products on two species of algae and the fathead minnow

The effects of alpha trinitrotoluene (alpha TNT) and its primary degradation product (TNTcc), commonly referred to as “pink water”, were determined on members of two trophic levels. The growth responses of the algae Selenastrum capricornutum and Microcystis aeruginosa were examined through static bioassays. Death and behavioral responses of the fathead minnow (Pimephales promelas) were determined using a proportional diluter. Alpha TNT and TNTcc were both more toxic to the fathead minnow than to either species of alga. Five and 15 mg l⁻¹ alpha TNT inhibited S. capricornutum and M. aeruginosa growth, respectively. TNTcc inhibited S. capricornutum growth at concentrations above 9 mg l⁻¹; it was lethal to M. aeruginosa at 50 mg l⁻¹, but stimulated growth at lower concentrations. The 96-h lc₅₀ values based on the death response of the fathead minnow to alpha TNT and TNTcc were 2.58 and 1.60 mg l⁻¹, respectively. The 96-h ec₅₀ values based on the behavioral responses were 0.46 and 0.64 mg l⁻¹, respectively. There was no response to concentrations of 0.05 mg l⁻¹ alpha TNT and 0.07 mg l⁻¹ TNTcc.     

An improved determination of chemical oxygen demand in water and wastes by a simplified acid dichromate digestion

A simplified and improved chemical oxygen demand (COD) procedure is suitable for water and waste water samples containing up to 1500 mg Cl l⁻¹. Samples are digested with sulfuric acid, potassium dichromate, silver sulfate, mercury(II) sulfate and sulfamic acid in open glass tubes for 2 h at 140 ± 2°C without boiling, and excess dichromate is determined colorimetrically at 440 nm. The use of 49-position digestion racks, a large oven and a spectrophotometer fitted with a 1-cm flow cell allow analysis of ca. 12 samples h⁻¹. A correction for chloride interference is not required in the 0–500 mg Cl l⁻¹ range. The detection limit is 3 mg l⁻¹, and the relative standard deviation at the 112 mg COD l⁻¹ level is 4.3%. Thirty-five waste water samples were analyzed by the standard dichromate reflux method and by the proposed procedure. There was no significant difference between the two sets of data (P > 0.25). Recovery data for 15 major water pollutants including benzene, toluene and pyridine are presented.     

Restoration of heavily polluted branches of the Shatt Al-Arab river, Iraq

In view of the desire to improve the water quality of the heavily polluted branches of the Shatt al-Arab River at the City of Basrah, it was proposed to maintain effective flushing as well as contracting sewerage system. The present study was conducted in order to examine the water quality of these branches in an attempt to evaluate the effectiveness of the proposed flushing system. It has been found that their waters contained very low levels of dissolved oxygen and relatively high amounts of both COD and BOD₅. The annual average water quality parameters for Basrah Branches were: dissolved oxygen 3.4 ppm; pH 7.67; hydrogen sulphide 1.4 ppm; ammonia 97 μg-at. N l⁻¹; COD 15.9 mg l⁻¹; BOD₅ 12.7 mg l⁻¹; dissolved silicates 202 μg-at. Si l⁻¹; dissolved reactive phosphate 13.4 μg-at. P-PO₄³⁻ l⁻¹; nitrate 10.4 μg-at. N-NO₃⁻ l⁻¹; nitrite 2.1 μg-at. N-NO₂⁻ l⁻¹ and chlorophyll-α 14.3 mg m⁻³. Based on our calculations, it has been concluded that the proposed system is effective, thus within a flushing cycle all of the above mentioned parameters will become within the acceptable values of the Shatt al-Arab water quality. Moreover, this system has no appreciable effect upon the water quality characteristics of the Shatt al-Arab River due to the fact that it discharges a high volume of water annually. However, It has been recommended to dredge the deposited sludge to a minimum depth of 50 cm.     

The growth inhibition of planktonic algae due to surfactants used in washing agents

A survey of inhibitory effects of nonionic and anionic surfactants, including a soap, used in washing agents, on the growth on three species of freshwater phytoplankton, Selenastrum capricornutum, Nitzschia fonticola and Microcystis aeruginosa was conducted. Based on the specific growth rate, μu estimated from a short period (2 or 3 days) cultivation of test algae, the growth inhibition was determined using EC₅₀ values where μu in the culture medium with surfactant decreased 50% of that without surfactant.The EC₅₀ values of nonionic and anionic surfactants tested here for S. capricornutum ranged from 2 to 50 mg l⁻¹ and from 10 to 100 mg l⁻¹, respectively. The tolerances of three species of algae tested with three surfactants, LAS, AE (EO:9) and soap, were different and the inhibitory effects were species specific. EC₅₀ values of LAS, AE (EO:9) and soap for S. capricornutum were 50–100, 4–8 and 10–50 mg l⁻¹, respectively. Those for N. fonticola were 20–50, 5–10 and 20–50 mg l⁻¹, and those for M. aeruginosa were 10–20, 10–50 and 10–20 mg l⁻¹, respectively.     

Hyperconcentrated cultures of Scenedesmus obliquus: A new approach for wastewater biological tertiary treatment?

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l⁻¹) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l⁻¹) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l⁻¹) and decanted; the sedimented culture (5 g dry wt l⁻¹) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l⁻¹). The rate of exhaustion of nitrogen (N-NH₄⁺) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l⁻¹); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH₄⁺) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO₄³⁻) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.