The electrolytic respirometer—I factors affecting oxygen uptake measurements

The electrolytic respirometer provides a more accurate and more complete measurement of biochemical oxygen demand (BOD) of wastewaters samples than normally is obtained by the standard dilution BOD method. Laboratory and field studies have shown that the electrolytic respirometer is a dependable instrument for making BOD measurements, is simple to operate, and provides a continuous readout of the oxygen uptake reaction.The major factors affecting oxygen uptake measurements with the electrolytic respirometer are the mixing rate and the concentration of oxygen demanding material in the sample. These system limitations can be overcome by using simple procedures such as increased mixing rate or enrichment of the oxygen in the air in contact with the sample.The precision of BOD measurement with the electrolytic respirometer was considerably greater than with the dilution method.     

A respirometric study of the influence of aliphatic alcohols on activated sludges

The influences of primary aliphatic alcohols on oxygen consumption of activated sludges in endogenous states were measured using a laboratory respirometer. The alcohols studied were n-propanol to n-octanol. Using beef extract as a reference substrate, results demonstrated a two-stage action for all the primary alcohols studied. It was found that these alcohols enhanced the dissolved oxygen uptake rate by the biomass when they were below critical concentrations, but had inhibiting effects above these concentrations. The critical concentration has been observed to decrease with increasing size of the alcohol molecule. The results obtained are explained in terms of modifications to lipid membranes observed by other workers.     

A simple respirometer for measuring oxygen and nitrate consumption in bacterial cultures

A simple respirometer is described to measure simultaneously oxygen and nitrate concentrations. It proved to be an easy tool in denitrification studies. This was tested with Pseudomonas aeruginosa.     

The role of benthic films in the oxygen balance in an East Devon river

A portable respirometer has been used to measure oxygen uptake and production rates, by fixed and suspended organisms in an East Devon river which receives papermill effluent. Benthic respiration dominates the oxygen balance in the stretch most affected by the effluent and increases the effective BOD decomposition rate by a factor of up to 12: Values of decomposition rate of 3.5–4.5 (day⁻¹) have been measured in the stream.     

Experiments with haliscomenobacter hydrossis in continuous culture without and with zoogloea ramigera

A study has been made of the sheath-forming bacterium Haliscomenobacter hydrossis, by growing the organism in continuous culture. Glucose together with components from trypticase soy broth/yeast extract were used as the energy source. At low dilution rates glucose was a more important energy source than components from trypticase soy broth/yeast extract. H. hydrossis was unable to produce large amounts of reserve material even in the presence of an excess of glucose. The minimum doubling time was approximately 13 h in the complex medium. The uptake sequence of amino acids derived from the trypticase soy broth yeast extract was found to be as follows: glutamic acid, glycine, methionine, tryptophan, lysine and arginine were easily consumed by the micro-organism, whereas the other amino acids were taken up mainly at low dilution rates.Competition experiments were carried out with H. hydrossis and Z. ramigera at two different dilution rates (0.016 and 0.005 h^-t). At both dilution rates Z. ramigera was dominantly present in the cultures.Finally the glucose respiration and glucose uptake of a washed cell suspension of H. hydrossis was studied. The oxygen uptake rate increased only very slightly upon addition of glucose. The difference between endogenous respiration and oxygen uptake rate in the presence of glucose was increased when the washed cells had been aerated a period of time.     

Benthic oxygen demand in Lake Apopka, Florida

The benthic oxygen demand of Lake Apopka, Florida was determined using laboratory core uptake and flow through system techniques. The core-uptake for 5 stations in Lake Apopka averaged 67 mg O₂ m⁻²-h and partitioning experiments indicated that the oxygen uptake was primarily biological, with bacterial respiration dominating. No significant statistical correlations were found between core oxygen uptake rates and TKN levels (r = 0.33), percent volatile solids (r = 0.49), or macroinvertebrate densities (r = 0.59). Sediment oxygen uptake rates (D_B) were logarithmically related to flow rate in the following form D_B = − A + B In flow. Flow-through system sediment oxygen uptake at each station approached similar maximum uptake rates of 130 mg O₂ m⁻²-h at high (> 200 l h⁻¹) flow rates. Lake Apopka is an extremely shallow, wind mixed system and sediment uptake rates are expected to approximate this value during periods of intense wind mixing. The relatively low sediment uptake rates obtained for Lake Apopka, a hypereutrophic lake, supports the view that during eutrophication sediment respiration is progressively replaced by respiration in the water column.     

In-Situ sediment oxygen demand in five Southwestern U.S. lakes

In-situ sediment oxygen demand (SOD) was measured for five southwestern lakes from 1985 to 1988. Age, morphometry and trophic states varied among the lakes but all were thermally stratified and had anoxic hypolimnia during summer months. SOD measurements were obtained with a hemispherical, sealed chamber-type benthic respirometer fitted with a submersible recirculation pump and a sensor package for recording dissolved oxygen, temperature, conductivity and pH. SOD measurements were obtained at between two and four sites on most lakes. Temperature corrected values ranged from 0.34 to 9.02 g O₂/m²·day. These data significantly expand the currently limited accessible SOD data base for Southwestern lakes.     

Kinetics of sediment oxygen demand

Sediment oxygen demand (SOD) is expressed in terms of oxygen uptake when using a batch method. For small quantities of sediment, the oxygen uptake is independent of initial oxygen present. The kinetics of the SOD reaction in a batch method can best be explained by the relationship SOD = k log t + c. This empirical relationship is perceived to be the result of an inhibition effect that comes into play through the oxidation of iron (Fe²⁺) on the surface of the sediment. The formation of an insoluble coating (Fe³⁺) presumably reduces the rate of oxidation and consequently the rate of oxygen uptake at the surface of the sediment. A derivation of this relationship is offered in support of this view.     

A simple continuous-flow respirometer for comparative respiratory changes in medium-sized aquatic organisms

A continuous-flow respirometer was designed to accommodate medium-sized aquatic organisms for comparative respiratory studies. The apparatus is simple in design, easily constructed and can be adapted to various flow rates, aquatic organisms and experimental designs. The system was tested with golden shiners. Notemigonous crysoleucas Mitchill, and with the blue crab. Callinectes sapidus Rathbun, and found to be a useful tool in physiological studies.     

The electrolytic respirometer—II Use in water pollution control plant laboratories

The electrolytic respirometer provides a direct and continuous measure of oxygen uptake in a wastewater sample. The principal advantages of this method are that (1) little or no dilution of the sample is required, (2) larger and more representative samples can be analyzed, (3) tests can be run for days or weeks without interruption, (4) the equipment is simple to operate, (5) no titrations are required, and (6) BOD can be measured with significantly greater precision than with other methods.

The use of electrolytic respirometers in research laboratories and water pollution control plant and industrial laboratories demonstrated that the method is technically and economically justified for plant control and evaluation purposes. This method was well received by treatment plant operators and laboratory analysts when used for purposes ranging from routine measurement of BOD to investigating the treatability of industrial wastes.     

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.     

Oxygen consumption and activity of the white sucker (Catostomus commersoni), in lethal and nonlethal levels of the organochlorine insecticide, methoxychlor

The survival, oxygen consumption and spontaneous activity of suckers were determined at 15°C in water containing different concentrations of methoxychlor in ethanol, ethanol, and no added substances. A dynamic bioassay was used to estimate the 96 h LC50, which was found to be 0·0345 ppm. Routine oxygen consumption was determined in a continuous-flow respirometer, and the activity was recorded in separate experiments by measuring the water disturbance using silver wire electrodes.After 24 h fish exposed to untreated, ethanol-treated and 0.01 ppm methoxychlor-treated water had oxygen uptake rates which were relatively constant and near standard levels. At 0.10 ppm methoxychlor (lethal to all fish within 85 h), oxygen consumption rates were 2–3.5 × as high as those of control fish. Activity also greatly increased. The fish lost their balance along with the coordination between opercular and locomotor movements. Suckers that died in 0.04 ppm methoxychlor showed oxygen uptake rates and poisoning symptoms similar to 0.10 ppm treated fish, while those that survived this treatment had rates similar to control fish. The increase in ventilation which accompanies this hyperactivity may result in increased uptake of insecticide and thereby explain the irreversible nature of the response.     

Diurnal changes in radionuclides uptake by phytoplankton in small scale ecosystems

A continuous release of cesium-134 and strontium-85 into a simulated river system was maintained for more than 3 weeks for the purpose of evaluating the influence of photosynthetic oxygen production on cesium and strontium uptake. The flow rates and radioisotope concentration were maintained at a constant input throughout the experiment.The flow through time in the model river system was 6 h. Samples were taken from various stations every 4 h over a 36 h time interval. Temperature, dissolved oxygen, as well as other routine measurements were made. Samples were processed for plankton count and radioactivity in both the suspended phytoplankton and the water.The uptake of ¹³⁴Cs by phytoplankton was related to diurnal photosynthetic production of oxygen and a linear relationship exists between rate of change in ¹³⁴Cs concentration and the rate of net photosynthetic oxygen production.     

Fine and ultrafine particle exposures on 73 trips by car to 65 non‐smoking restaurants in the San Francisco Bay Area

A number of studies indicate cooking is a major source of exposure to particulate matter, but few studies have measured indoor air pollution in restaurants, where cooking predominates. We made 73 visits by car to 65 different non‐smoking restaurants in 10 Northern California towns while carrying portable continuous monitors that unobtrusively measured ultrafine (down to 10 nm) and fine (PM_2.5) particles to characterize indoor restaurant exposures, comparing them with exposures in the car. The mean ultrafine number concentrations in the restaurants on dinner visits averaging 1.4 h was 71 600 particles/cm³, or 4.3 times the mean concentration on car trips, and 12.3 times the mean background concentration in the residence. Restaurants that cooked dinner in the same room as the patrons had higher ultrafine concentrations than restaurants with separate kitchens. Restaurant PM_2.5 mass concentrations averaged 36.3 μg/m³, ranging from 1.5 to 454 μg/m³, but were relatively low on most visits: 43% of the indoor means were below 10 μg/m³ and 66% were below 20 μg/m³, with 5.5% above 100 μg/m³. Exposure to fine and ultrafine particles when visiting a restaurant exceeded the exposure a person received while traveling by car to and from the restaurant.     

Some factors affecting floc formation by Zoogloea ramigera, strain I-16-M

A comparison was made between cells of Zoogloea ramigera occurring in flocs and in suspension. Suspended cells were obtained by adding cellulose to the growth medium, which prevented floc formation without damaging the cells. Differences in protein synthesis and poly-β-hydroxybutyrate production of cells in suspension and cells in flocs were only found between slowly shaken cultures. Increasing the oxygen content of such cultures did not raise the growth limitation of the cells in flocs. The oxygen uptake of the suspended cells was found to represent a zero order reaction at an oxygen concentration of the culture above 0.1 mg/l. and that of cells in flocs above 1.5 mg/l. Below 20 mg/ml glucose the glucose respiration rate of cells in flocs was lower than that of suspended cells. Above approx 20 mg/l. glucose, the glucose respiration of both types of cells was almost a zero order reaction.     

Activated sludge monitoring with combined respirometric-titrimetric measurements

A short review of different respirometric methods is presented, and advantages and disadvantages of different principles are discussed. In this study a combined respirometric-titrimetric set-up was applied to monitor the degradation processes during batch experiments with activated sludge. The respirometer consists of an open aerated vessel and a closed non-aerated respiration chamber. It is operated with two oxygen probes resulting in two sources of information on the oxygen uptake rate; both collected at a high frequency. The respirometer is combined with a titrimetric unit that keeps the pH of the activated sludge sample at a constant value through the addition of acid and/or base. The cumulative amount of added acid and base serves as a complementary information source on the degradation processes. Interpretation of respirometric data resulting from validation experiments (additions of acetate and urea as ammonium source) showed that the set-up provided reliable data. Data interpretation was approached in two ways: (1) via a basic calculation procedure, in which the oxygen uptake rates were obtained by an oxygen mass balance over the respiration chamber, and (2) via a model-based procedure in which substrate transport was included for a more accurate data interpretation. Simulation examples showed that the presence of substrate transport in the model may be crucial for a correct data interpretation, since experimental conditions (e.g. low flow rate) and/or the biodegradation kinetic parameters (e.g. high Ks) may otherwise lead to data interpretation errors. Earlier studies already pointed out that titrimetric data can be related to nitrification, and this was also confirmed in this study. However, in addition, it was shown here for experiments with acetate that the amount of acid dosed was clearly related to the amount of acetate degraded. This indicates that the titrimetric data can be used to study the carbon source degradation. For the titrimetric data in this study, a model-based analysis was however only applied for the nitrification process. For an experiment with ammonium, it was illustrated that the estimation of biodegradation kinetics on a combined respirometric-titrimetric data set significantly improves confidence intervals of the parameters compared to the parameter estimation based on respirometric or titrimetric data separately.     

Effect of phenol on oxygen uptake rate of a laboratory population of Chironomus attenuatus (walk.)

A laboratory population of fourth-instar larval forms of Chironomus attenuatus Walker received a continuous life-long exposure of 0, 2.8, 8.2, 11.2, 16.3, and 22.4 ppm phenol. Measurements were taken of water temperature, pH, and dissolved oxygen concentration. Larvae exposed to the different phenol concentrations were analyzed for oven-dry weight and ash-free weight. The oxygen uptake was determined. The regression of oxygen uptake (Y), adjusted for phenol level, pH, and oxygen concentration, on ash-free weight (X) was log Y = 0.173–0.478 log X. The regression of adjusted oxygen uptake (Y) on phenol concentration (X) was Y = 1.632 + 0.299 log X. Calories lost through respiration (Y) were related to phenol level (X) by the equation, Y = (2.10 × 10^?3) + (3.86 × 10^?4) log X. The ash-free weight per individual (Y) decreased with increasing phenol concentration (X) as explained by the equation, Y = 0.753 ? 0.114 log X.     

The effect of intermittent chlorination on freshwater phytoplankton

Lake Michigan phytoplankton showed a significant loss of chlorophyll a and permanent reduction of carbon uptake rates after exposure for 30 min to concentrations of total residual chlorine at or above 1 mg l⁻¹. At this level the photosynthetic system of the algae was irreversibly destroyed. Below 0.1 mgl⁻¹ total residual chlorine only slight changes in chlorophyll a were noted, and, following an initial decrease, carbon uptake rates exhibited nearly complete recovery after 24 h.     

From air to clothing: characterizing the accumulation of semi‐volatile organic compounds to fabrics in indoor environments

Uptake kinetics of semi‐volatile organic compounds (SVOCs) present indoors, namely phthalates and halogenated flame retardants (HFRs), were characterized for cellulose‐based cotton and rayon fabrics. Cotton and rayon showed similar accumulation of gas‐ and particle‐phase SVOCs, when normalized to planar surface area. Accumulation was 3–10 times greater by rayon than cotton, when normalized to Brunauer–Emmett–Teller (BET) specific surface area which suggests that cotton could have a longer linear uptake phase than rayon. Linear uptake rates of eight consistently detected HFRs over 56 days of 0.35–0.92 m³/day.dm² planar surface area and mass transfer coefficients of 1.5–3.8 m/h were statistically similar for cotton and rayon and similar to those for uptake to passive air sampling media. These results suggest air‐side controlled uptake and that, on average, 2 m² of clothing typically worn by a person would sequester the equivalent of the chemical content in 100 m³ of air per day. Distribution coefficients between fabric and air (K′) ranged from 6.5 to 7.7 (log K′) and were within the range of partition coefficients measured for selected phthalates as reported in the literature. The distribution coefficients were similar for low molecular weight HFRs, and up to two orders of magnitude lower than the equilibrium partition coefficients estimated using the COSMO‐RS model. Based on the COSMO‐RS model, time to reach 95% of equilibrium for PBDEs between fabric and gas‐phase compounds ranged from 0.1 to >10 years for low to high molecular weight HFRs.     

Modelling of the activated sludge process for microprocessor-based state estimation and control

A simple dynamic model of the activated sludge process including the volatile suspended solids (VSS) concentration in the aeration basin, the VSS or suspended solids (SS) concentration in the recycle flow and the SS concentration in the effluent was obtained by simplifying a comprehensive model using empirically verified assumptions. The model can be used for on-line estimation of the influent BOD-load and the effluent BOD, in combination with a recursive algorithm for oxygen uptake rate (OUR) and k_La estimation requiring only dissolved oxygen and air flow rate measurements. The estimation procedure has been implemented and tested at a real plant using a microprocessor. Control of the activated sludge process is discussed and concluded to be a hierarchical two-level problem. The upper level control actions are aimed at bringing the process to an optimal state of operation. For this purpose verbally formulated control laws are used. On the lower level the control task is to maintain the process in the optimal state.