Ultimate Biochemical Oxygen Demand Research Articles

Determination of the amount of oxygen required for each function in the bacterial cell during phenol biodegradation in wastewater: a unique concept

The goal of this study is to provide more in-depth study into the biodegradation of phenol and to determine the amount of oxygen required for each function in the bacterial cell which is fundamental in understanding of cell metabolism and biology. The total amount of oxygen consumed by bacteria is determined using manometric technique. In the biodegradation of phenol (less than 150 mg/L) the oxygen consumed up to the plateau (the stage associated with the termination of carbon) is found to be composed of three portions, one is used to directly oxidize portion of the substrate to produce energy to allow normal cell functions to sustain life which is estimated to be 50% of the plateau BOD (biochemical oxygen demand), the second portion is to oxidize energy storage intermediate (most probably carbon mono oxide, CO, is oxidized to CO2) to release energy which is then used to power reproduction which is estimated to be 41.75% of the plateau BOD, third portion is incorporated into the produced new cells which is estimated to be 8.25% of the plateau BOD. The correlation coefficient between the initial phenol concentration and the ultimate BOD values is found to be r = 0.9999. This value of correlation coefficient, r, may indicate that microbes are, in a way, estimating the amount of food available and they grow and reproduce accordingly. This article provides a better understanding of cell metabolism and biology. This understanding of cell metabolism may offer better understanding of human cells. The results of this research paves the way for a similar research on human cells where abnormal oxygen uptake may assist in early prediction of cells dysfunction and diseases and may help in early taking the necessary precautions to avoid illness.

Regression-based analytical models for dissolved oxygen in wastewater.

The limited freshwater resources and increasing demand for clean water require minimizing organic contamination in wastewater. High levels of biochemical oxygen demand (BOD) in water reduce available oxygen, harm ecosystem biodiversity, and degrade water quality. Here, regression-based analytical models are suggested to minimize organic contamination by estimating desired dissolved oxygen (DO) and dilution factors (df) correlated to the organic decomposition. Training datasets of defined independent inputs (i) ultimate biochemical oxygen demand (UBOD), (ii) minimum BODT (BODM), (iii) average BODT (BODA), (iv) COD, (v) O2 consumption (X), and (vi) time (T) were collected and/or calculated based on literature. Results showed that there should be specified oxygen dosing amounts dependent upon BOD5 levels, noting that BOD5 and DO5 are inversely proportional (proportionality might differ based on the microbial concentration). An increase in df is predominated by BOD5, with df≈9.2 for storm (STM), df≈12 × 103 for industrial (IND), and df≈18.5-28.5 for domestic (DOM) wastewaters. Mixing/matching between the input features used in training regressors including medium trees (MT) and ensembles boosted trees (EBT) showed high accuracy > 94% for predictor combinations: (i) MT-[UBOD-X], MT-[UBOD-X-T-COD], and EBT-[UBOD-X-T-COD] for DO5 predictions, and (ii) EBT-[BODM-BODA] and EBT-[BODM-BODA-UBOD-X-T-COD] for df predictions, knowing the general term XX-[a-b-c-d-e-f] has XX = regressor and a,b,c,d,e,f = predictors for the training parameters used as inputs. The models are capable of predicting changes in DO5 against BOD with deviations 5-10%, whereas a suggested correction factor [Formula: see text] further reduced this deviation to < 5%, where i = 0, 1, 2…6 refers to the BODM datapoint and its corresponding UBOD with the constant α = f(i). The optimized collective models (cubic equations derived for df and DO5 from BODM that is an exponent function in UBOD) would enable effluent quality evaluation to manage organic contamination, bridging the gap between science and industry best practices.

Predicting the fate and the biological treatment parameters of phenol in a wastewater from its initial concentration

Microbial degradation is an important process for removing many organic chemicals from natural waters. The estimation of biodegradability of chemicals which reach the aquatic environment is necessary in assessing the hazard associated with their use. Phenol has many industrial applications and it finds its way into wastewater streams. It is toxic to several biochemical reactions. However, biological transformation of phenol to non-toxic entities is possible. In this article, the data of biodegradation of phenol at different concentrations were studied. For phenol concentrations equal to or less than 147 mg/L, the plateau (the stage associated with the termination of carbon) BOD (biochemical oxygen demand) was calculated to be 169.47% of the corresponding initial phenol concentration, the BOD of the biomass produced up to the plateau was calculated to be 70% of the corresponding initial phenol concentration. This study shows that the biomass produced up to the plateau, the plateau BOD, and the ultimate BOD can all be estimated for phenol concentrations less than 147 mg/L just if the initial phenol concentration is known and without having to repeat the time-consuming BOD experiments.

Predicting Optimum Dilution Factors for BOD Sampling and Desired Dissolved Oxygen for Controlling Organic Contamination in Various Wastewaters

High biochemical oxygen demand (BOD) concentrations in water minimize oxygen availability, damage ecosystem biodiversity, impair water quality, and spoil freshwater. The increased level of BOD is an indication of severe organic pollution of freshwater. Thus, this study aims to establish empirical correlations between the 5-day biochemical oxygen demand (BOD5) and organic decomposition time to control organic pollution in various wastewater effluents. Ultimate biochemical oxygen demand (UBOD) and minimum and average BODt data sets along with their reaction rates were collected from earlier sampling analyses in the plants used for industrial, domestic (sanitary), and storm (surface) wastewater treatment. Average BOD5/COD ratios were then utilized to calculate existing 5-day dissolved oxygen (DO5) concentration for the estimation of experimental dilution factors (dfs) as a good start in sampling analysis to reach an optimum DO5 concentration. Moreover, the relationships between average BOD5 vs. COD, and BOD5 vs. DO5, were obtained based on the literature with 60–70% oxygen consumption rates required for organic decomposition. Results showed that such BOD5 relationships with time (power equations) or with COD (linear correlations) are helpful for wastewater engineers to generate valuable and accurate results for quality control, without the need to conduct laboratory experiments. The proposed regression equations would facilitate effluent quality assessment, allowing selection of optimal processes to control microbiological contamination or organic constituents in wastewaters.

Fuzzy Optimization Model for Waste Load Allocation in a River with Total Maximum Daily Load (TMDL) Planning

In traditional waste load allocation (WLA) decision making, water quality-related constraints must be satisfied. Fuzzy models, however, can be useful for policy makers to make the most reasonable decisions in an ambiguous environment, considering various surrounding environments. We developed a fuzzy WLA model that optimizes the satisfaction level by using fuzzy membership functions and minimizes the water quality management cost for policy decision makers considering given environmental and socioeconomic conditions. The fuzzy optimization problem was formulated using a max–min operator. The fuzzy WLA model was applied to the Yeongsan River basin, which is located in the southwestern part of the Korean Peninsula and Korean TMDLs were applied. The results of the fuzzy model show that the pollutant load reduction should be increased in the Gwangju 1 and Gwangju 2 wastewater treatment plants (WWTPs) and in subcatchments with high pollutant load. In particular, it is necessary to perform advanced wastewater treatment to decrease the load of 932 kg ultimate biochemical oxygen demand (BODu)/day in the large-capacity Gwangju 1 WWTP and reduce the BODu emission concentration from 4.3 to 2.7 mg/L during the low-flow season. The satisfaction level of the fuzzy model is a relatively high at 0.81.

Proposal of upgrading Isfahan north wastewater treatment plant: An adsorption/bio-oxidation process with emphasis on excess sludge reduction and nutrient removal

There is a rising challenge in managing the activated sludge process due to excess sludge disposal from the wastewater treatment plant and inadequate effluent quality due to the stricter standard of effluent quality. Hence, the incorporation of oxic-settling-anoxic process and ultrasonic waves in the return sludge line was proposed to assess the excess sludge reduction and nutrient removal in the adsorption/bio-oxidation activated sludge process as a proposal upgrading. The results indicated that sludge production from adsorption/bio-oxidation process could be reduced using oxic-settling-anoxic and ultrasonic by 50% at each studied mixed liquor suspended solids level. Compared to the adsorption/bio-oxidation process, the total and soluble chemical oxygen demand removal efficiencies in adsorption/bio-oxidation process with oxic-settling-anoxic and ultrasonic slightly decreased suggesting a lysis phenomenon. During the operation of adsorption/bio-oxidation process with oxic-settling-anoxic and ultrasonic, the total Kjeldahl nitrogen removal efficiency improved in A and B stages, with 38.3 ± 8.1% and 83.1 ± 6.5% versus 36.8 ± 14.5% and 75.1 ± 7.3%, respectively. According to the stoichiometric calculations, in B stage of adsorption/bio-oxidation process with oxic-settling-anoxic and ultrasonic, the soluble available ultimate biochemical oxygen demand and net NO3 produced for denitrification were 69.5 and 43.8 mg/L, respectively. Overall, the experimental data revealed that the adsorption/bio-oxidation process with oxic-settling-anoxic and ultrasonic produced lower excess biological sludge and better total Kjeldahl nitrogen removal efficiency compared to the adsorption/bio-oxidation system alone.

An evaluation of solutions to moment method of biochemical oxygen demand kinetics

This paper evaluated selected solutions of moment method in respect to Biochemical Oxygen Demand (BOD) kinetics with the aim of ascertain error free solution. Domestic-institutional wastewaters were collected two-weekly for three months from waste-stabilization ponds in Obafemi Awolowo University, Ile-Ife. BOD concentrations (BOD c ) were determined daily for 8 days using standard method. The BOD c were used to determine parameters in BOD kinetics (ultimate BOD concentration and BOD removal rate) using Microsoft Excel Solver, non-linear regression (exponential) and least squares methods (three graphs). Accuracies of these solutions were evaluated using relative error, Akaike Information Criterion (AIC), and model of selection criterion (MSC). The study revealed that ultimate BOD c was in the range of 1368.7 to 860.6 mg/L and BOD c removal rate was between -0.139 and -0.470 /d. The averages of MSC were 4.18; 0.01; 1.49, 1.28 and 1.61 for Microsoft Excel Solver, non-linear and three least square methods (graphs 1, 2 and 3) respectively. The result revealed that Microsoft Excel Solver provided an improved solution of moment method, and a good description of BOD c removal trend based on MSC and AIC than the other solutions. The study concluded that Microsoft Excel Solver solution to the method is a valuable solution at higher confidence level based on lower values of AIC and high values of MSC. http://dx.doi.org/10.4314/njt.v37i1.1

The comparison of different mathematical methods to determine the BOD parameters, a new developed method and impacts of these parameters variations on the design of WWTPs

One of the most common tests for the determination of strength and organic content of wastewater is the biochemical oxygen demand (BOD). This test is widely applied to define organic water pollution and to control the performance of wastewater treatment plants. Generally, BOD is standardized by the measurement of oxygen consumption in 5days (BOD5). But, determination of the ultimate biochemical oxygen demand (BODu), which is taken 28days and the reaction rate constant (k) are necessary to understand the organic strength of the wastewater. In this study, the different mathematical methods in order to determine the BOD parameters (BODu, k) and two different BOD test method (respirometer and dilution method) are investigated comparatively. Also, a new method based on cubic spline method to estimate ultimate BOD values is developed. Moreover, the impacts of BOD parameters on the design of an activated sludge and aerated lagoon systems are analyzed by using a written user-friend program, which is developed for designing WWTPs by the mean of C++ programming language.Analytical results show that there is a satisfactory linear relationship between respirometric and dilution BOD values. Also, the mathematical methods, including new developed method generally provide consistent results with high correlation coefficients. On the other hand, it is found that LOG differences method for respirometric test and the new developed method for dilution test do not give good correlation coefficients. Moreover, activated sludge and aerated lagoons systems’ sizes show significant changing depending on the variations of the BOD parameters. Consequently, BOD parameters show significant changes depending on the different test and mathematical methods. Therefore, the changing of these parameters impact a lot of situation such as ultimate BOD estimation, the wastewater treatment plants design, the dimensions of the plants and cost of the plants.

Demanda Bioquímica de Oxigênio em Diferentes Tempos de Incubação das Amostras

BIOCHEMICAL OXYGEN DEMAND OF SAMPLES UNDER DIFFERENT INCUBATION TIMES The biochemical oxygen demand (BOD) is an factor of great importance for monitoring and design of biological treatment systems, as well as a reference for legislation and verifi cation of environmental impacts. The standard measure for quantifying the organic material concentration is performed by reading after 5 days of incubation at 20 o C ( ) of the water sample, allowing comparisons between different authors and different climatic conditions. However, the long period needed for analysis hinders decision-making in wastewater treatment stations. Moreover, the lack of fl exibility regarding the day of determining the BOD values indicates operational problems. Few studies have attempted to relate the values of BOD obtained at different times with those measured after fi ve days. In literature there is only information between the values of and the ultimate biochemical oxygen demand (UBOD), and between the and chemical oxygen demand (COD). Thus, this study aimed to obtain the BOD values at different times of sample incubation, which were compared with the values of , assessing the possibility of relating them by correction factors in samples of sewage, swine and dairy wastewaters. The results showed that the correction factors vary with the type of wastewater, with the organic matter concentration that it presents, and with the relationship between biochemical and chemical oxygen demand (biodegradability of organic material), requiring that it be determined on a case by case basis for each situation, which is hardly feasible.

NOTA TÉCNICA: DEMANDA BIOQUÍMICA DE OXIGÊNIO EM DIFERENTES TEMPOS DE INCUBAÇÃO DAS AMOSTRAS

A demanda bioquímica de oxigênio (DBO) é uma análise de grande importância para monitoramento e dimensionamento de sistemas de tratamento biológico, além de ser referencial para legislação e verificação de impactos ambientais. A medida padrão de quantificação da concentração de material orgânico é feita com leitura após 5 dias de incubação à 20 ºC (〖"DBO" 〗_5^20) da amostra de água, propiciando comparações entre os diversos autores e em diferentes condições climáticas. Porém, em razão do longo tempo demandado para análise, há prejuízo nas tomadas de decisão em estações de tratamento de águas residuárias. Além disso, a falta de flexibilidade, no que se refere ao dia de determinação dos valores de DBO, traz transtornos do ponto de vista operacional. Poucos são os estudos que tentaram relacionar os valores de DBO obtidos em tempos diferentes com os lidos após cinco dias. Na literatura existem apenas informações entre os valores de〖"DBO" 〗_5 e a demanda bioquímica de oxigênio última (〖"DBO" 〗_u), e entre a 〖"DBO" 〗_5 e a demanda química de oxigênio (DQO). Assim, neste estudo, teve-se como objetivo a obtenção dos valores de DBO em diferentes tempos de incubação da amostra, os quais foram comparados com os valores de 〖"DBO" 〗_5, verificando-se a possibilidade de relacioná-los por meio de fatores de correção em amostras de esgoto sanitário e águas residuárias da suinocultura e de laticínios. Os resultados indicaram os fatores de correção variam com o tipo de água residuária, com a concentração de matéria orgânica que ela apresenta e com a relação entre as demandas bioquímica e química de oxigênio (biodegrabilidade do material orgânico), tendo que se ser determinado caso a caso, para cada situação, o que é pouco exequível.

Measurement of biochemical oxygen demand of the leachates

Biochemical oxygen demand (BOD) of the leachates originally from the different types of landfill sites was studied based on the data measured using the two manometric methods. The measurements of BOD using the dilution method were carried out to assess the typical physicochemical and biological characteristics of the leachates together with some other parameters. The linear regression analysis was used to predict rate constants for biochemical reactions and ultimate BOD values of the different leachates. The rate of a biochemical reaction implicated in microbial biodegradation of pollutants depends on the leachate characteristics, mass of contaminant in the leachate, and nature of the leachate. Character of leachate samples for BOD analysis of using the different methods may differ significantly during the experimental period, resulting in different BOD values. This work intends to verify effect of the different dilutions for the manometric method tests on the BOD concentrations of the leachate samples to contribute to the assessment of reaction rate and microbial consumption of oxygen.

Restructuring BOD : COD Ratio of Dairy Milk Industrial Wastewaters in BOD Analysis by Formulating a Specific Microbial Seed

BOD (Biochemical oxygen demand) is the pollution index of any water sample. One of the main factors influencing the estimation of BOD is the nature of microorganisms used as seeding material. In order to meet the variation in wastewater characteristics, one has to be specific in choosing the biological component that is the seeding material. The present study deals with the estimation of BOD of dairy wastewater using a specific microbial consortium and compares of the results with seeding material (BODSEED). Bacterial strains were isolated from 5 different sources and were screened by the conventional BOD method. The selected microbial seed comprises of Enterobacter sp., Pseudomonas sp. BOD : COD (Chemical oxygen demand) ratio using the formulated seed comes in the range of 0.7-0.8 whereas that using BODSEED comes in the ratio of 0.5-0.6. The ultimate BOD (UBOD) was also performed by exceeding the 3-day dilution BOD test. After 90 days, it has been observed that the ratio of BOD : COD increased in case of selected consortium 7 up to 0.91 in comparison to 0.74 by BODSEED. The results were analyzed statistically by t-test and it was observed that selected consortium was more significant than the BODSEED.

Ultimate biochemical oxygen demand in semi-intensively managed shrimp pond waters

Three independent studies were conducted to quantify ultimate biochemical oxygen demand (UBOD) and the corresponding decomposition rate constant for production pond (average 21.5 ha each) waters and effluents on six semi-intensively managed marine shrimp ( Litopenaeus vannamei) farms in Honduras. Samples were collected during the rainy season in studies 1–3 and during the dry season only in Study 1. Pond water samples were collected during the culture period and/or at harvest. The dry season 30-d biochemical oxygen demand (BOD 30) of pond waters across all farms was 26% lower and UBOD was 54% lower, but the decomposition rate constant was more than twice as great as during the rainy season. During the dry season, biochemical oxygen demand was nearly completely expressed after 30 d of incubation whereas during the rainy season BOD was about 65% expressed after 31 d of incubation and the correlation between BOD 31 and UBOD was less strong compared to the dry season. Water quality variables were correlated with measures of BOD during rainy and dry seasons, but only the correlation between chlorophyll a and BOD measures was predictive. In studies 2 and 3, BOD after 88–94 d of incubation was expressed almost completely and corresponded closely with computed UBOD. No significant differences in UBOD were detected in pond samples taken after 30, 61, or 71 (harvest) d of grow out in study 3. Mean decomposition rate constant ranged from 0.054 to 0.071 d −1 in studies 1–3 (rainy season), compared to 0.123 d −1 in Study 1 (dry season).

Improvement of the analysis of the biochemical oxygen demand (BOD) of Mediterranean seawater by seeding control

Biochemical oxygen demand (BOD) is a useful parameter for assessing the biodegradability of dissolved organic matter in water. At the same time, this parameter is used to evaluate the efficiency with which certain processes remove biodegradable natural organic matter (NOM). However, the values of BOD in seawater are very low (around 2mgO2L−1) and the methods used for its analysis are poorly developed. The increasing attention given to seawater desalination in the Mediterranean environment, and related phenomena such as reverse osmosis membrane biofouling, have stimulated interest in seawater BOD close to the Spanish coast. In this study the BOD analysis protocol was refined by introduction of a new step in which a critical quantity of autochthonous microorganisms, measured as adenosine triphosphate, is added. For the samples analyzed, this improvement allowed us to obtain reliable and replicable BOD measurements, standardized with solutions of glucose–glutamic acid and acetate. After 7 days of analysis duration, more than 80% of ultimate BOD is achieved, which in the case of easily biodegradable compounds represents nearly a 60% of the theoretical oxygen demand. BOD7 obtained from the Mediterranean Sea found to be 2.0±0.3mgO2L−1 but this value decreased with seawater storage time due to the rapid consumption of labile compounds. No significant differences were found between two samples points located on the Spanish coast, since their organic matter content was similar. Finally, the determination of seawater BOD without the use of inoculum may lead to an underestimation of BOD.

Biochemical Oxygen Demand Relationships in Typical Agricultural Effluents

Understanding the variables controlling biochemical oxygen demand (BOD) of effluents from agricultural systems is essential for predicting and managing the water quality risks associated with agricultural production. In this study, short- and long-term oxygen demand behaviors of waters from primarily agricultural sources and their relationships with other parameters were evaluated. A total of 46 water samples were generated from diverse organic sources commonly associated with agricultural activities and analyzed for BOD and other various water quality parameters. Short-term BOD (BOD2 and BOD5) were significantly correlated with total organic carbon (TOC), particulate organic carbon (POC), and dissolved organic carbon (DOC) (R 2 = 0.62–0.77, p < 0.001), likewise to total nitrogen, total Kjeldahl nitrogen, and nitrite–nitrogen (NO2–N) (R 2 = 0.40–0.55, p < 0.001). Long-term BOD (BOD60) was generally poorly correlated with these C and N fractions. Phosphate (PO4–P) exhibited a positive and linear relationship with both short- and long-term BOD, whereas chloride (Cl) tended to inhibit oxygen demand. Multivariate combinations of each of TOC, POC, and DOC with NO2–N, and Cl or PO4–P improved the predictions of both short- and long-term BOD. The ultimate BOD (BODu) derived from the first-order kinetics was highly correlated with BOD60 (R 2 = 0.81, p < 0.001) whereas BOD60 was correlated with BOD5 (R 2 = 0.60, p < 0.001). Overall the results indicated that C and N forms along with PO4–P and Cl were the dominant factors controlling the oxygen demand behaviors of agricultural effluents.

Utilization of Weibull Techniques for Short-Term Data Analysis in Environmental Engineering

Failures and disadvantages of biological treatment plants reported in the literature indicates that there is a need to apply extreme value distributions in the establishment of design parameters including ultimate biochemical oxygen demand (BOD) and the BOD removal rate constant. This paper presents the application of extreme value distributions in environmental engineering. Wastewater samples were collected from a domestic-institutional wastewater treatment plant weekly for 15 months. BOD concentrations were determined for the first 6 days using respirometric method. Ultimate BOD (Lo ) and BOD removal rate constant (k) were determined using nonlinear regression method. Lo and k were used in the application of extreme value distribution and environ–economics analysis. The study revealed that extreme value distributions can be used in environmental pollution control to select design parameters. The values of a and b in a reliability function were 0.192 and 9.638, 0.333 and −6.867 for k and Lo, respectively. Prediction of reliability agreed with the practical values using a Weibull plot, F(1,59) = 1.75 and 0.273 for k and L0 , respectively. The design parameters at 90, 95, 99, and 99.5% reliability for k and Lo were 0.275, 0.288, 0.226, and 0.208/day and 2106.10, 2130.46, 2155.97, and 2158.62 mg/L, respectively. Kk values were 102,030 and 0.000005 for k and Lo , respectively. In environ–economics analysis reliability of 0.986 (98.6%) was found to be economical for the design of a domestic–institutional wastewater treatment plant studied with a risk cost of 706.2 Euro (12.36 × 104 Naira) per annual per 1,000 mg of BOD. It was concluded that utilization of extreme value distributions in the selection of design parameters such as Lo and k will help in simulation and improve design of biological treatment plants.

Virtues of acclimated microbial cultures in wastewater characterization and treatment

Biochemical Oxygen Demand (BOD) is one of the parameters used to characterise wastewater. It is used to gauge the pollution strength of wastewater and it is an imperative test in stream pollution control activities. However, BOD measure alone can be misleading. This paper evaluates how acclimation of BOD seed microbial cultures influences the characterisation of wastewater, mainly based on BOD results. BOD tests on refinery wastewater confirmed that the use of acclimated cultures results in higher BOD levels than the ones from tests done using standard laboratory seed cultures. For example, for the same sample of wastewater, tests done with standard seed cultures gave an ultimate BOD (BODu) value of 122 mg/L whereas a test carried out using acclimated seed cultures gave a BODu value of 533 mg/L. Generally, tests mediated with acclimated seed cultures had higher reaction rates and larger BODu values. The recalcitrance of refinery wastewater was indicated by its COD/BOD ratio of up to 16:1 as opposed to a ratio of 1:5.1 - 3.0:1 for easily biodegradable wastes. The main take-home message from this paper is two-pronged: 1) BOD tests on recalcitrant wastewater must be done using acclimated seed cultures, and 2) the assessment of the strength of recalcitrant or toxic wastewater must be based on both BOD and COD tests.Journal of Building and Land Development Vol. 13 (1) 2006: pp. 32-38

Maximum Nitrogen Removal in the Step‐Feed Activated Sludge Process

This paper presents a mathematical framework that can be used to determine the flow distributions for a step-feed activated sludge process that result in maximum nitrogen removal. The model indicates that nitrogen removal efficiency in a step-feed activated sludge process is highly dependent on the ultimate biochemical oxygen demand (BOD(L))-to-total Kjeldahl nitrogen (TKN) ratio of the wastewater. For typical domestic wastewater, which has a relatively high BOD(L)-to-TKN ratio, the step-feed process will outperform the Modified Ludzack-Ettinger process for nitrogen removal, when the flow to each step is optimally distributed. Using plant-specific water quality data and operating conditions from a 1-year period, nitrogen removal performance for four step-feed activated sludge plants operated by the Sanitation Districts of Los Angeles County (California) was calculated using the developed model. The calculated nitrogen removal efficiencies match well with the actual plant performance data. These results validate the model as a useful tool for predicting nitrogen removal in a step-feed activated sludge process. Other analyses revealed that improvements in nitrogen removal at existing facilities are achievable by adjusting the split of primary effluent flow to each anoxic zone several times during the day. The timing of the adjustments and the optimal flow splits can be determined from data on diurnal fluctuations in BOD(L) and TKN concentrations. An example is provided to illustrate the application of such an operating strategy and the potential enhancement of nitrogen removal.

A double exponential model for biochemical oxygen demand

Biochemical oxygen demand (BOD) exertion patterns in anaerobically treated farm dairy wastewater were investigated on a laboratory scale. Oxygen uptake was typically characterised by a period of rapid oxygen exertion, a transitional “shoulder” phase and a period of slower activity. A multi-species model, involving rapidly degradable and slowly degradable material, was developed, leading to a double exponential model of BOD exertion as follows: BOD t = BOD u 1 ′ ( 1 - e - k 1 t ) + BOD u 2 ′ ( 1 - e - k 2 t ) where t is time, BOD u 1 ′ and BOD u 2 ′ are apparent ultimate BOD (BOD u ) values, and k 1 and k 2 are rate constants. The model provided an improved description of BOD exertion patterns in anaerobically treated farm dairy wastewater in comparison to a conventional single exponential model, with rapidly degradable rate constant values ( k 1) ranging from 2.74 to 17.36 d −1, whilst slowly degradable rate constant values ( k 2) averaged 0.25 d −1 (range 0.20–0.29). Rapidly and slowly degradable apparent BOD u estimates ranged from 20 to 140 g/m 3 and 225 to 500 g/m 3, respectively, giving total BOD u levels of 265–620 g/m 3. The mean square error in the curve fitting procedure ranged between 20 and 60 g 2/m 6, with values on average 70% lower (range 31–91%) than those obtained for the single exponential model. When applied to existing data for a range of other wastewaters, the double exponential model demonstrated a superior fit to the conventional single exponential model and provided a marginally better fit than a mixed order model. It is proposed that the presence of rapidly degradable material may be indicated from the value of the first rate constant ( k 1) and the time to 95% saturation of the first exponential function. Further model development is required to describe observed transitional and lag phases.

Biochemical Oxygen Demand in Channel Catfish Ictalurus punctatus Pond Waters

AbstractA study of the biochemical oxygen demand (BOD) of waters from ten channel catfish ponds at Auburn, Alabama, revealed that the 5‐d BOD (BOD5) seldom exceeded 8 mg/L and that the ultimate BOD (BODu) was usually less than 30 mg/L. Water samples from catfish ponds usually needed to be diluted only 2 or 3 times to permit BOD5 measurements, and nitrification occurred even during a 5‐d incubation period. Catfish pond waters were not extremely high in ammonia nitrogen concentration, and ammonia nitrogen introduced in the ammonium chloride‐enriched dilution water caused an appreciable increase in BOD of some samples. Plankton respiration is a major component of carbonaceous BOD (CBOD) in catfish pond waters. Thus, the BOD is not expressed as rapidly during 5‐d incubations as in typical waste‐water. The ultimate BOD (BODu) would be a good measurement of oxygen demand for catfish pond effluents, but it is difficult to measure. Data from this study suggest that BODu can be estimated from BOD5, but the correlation is not strong (R2= 0.62). An alternative is to develop a short‐term BOD measurement specifically for effluents from channel catfish and other aquaculture ponds. This study suggests that a 10‐d BOD conducted without nitrification inhibition or addition of ammonia nitrogen in dilution water might be a better alternative to standard BOD5 or BODu measurements normally used in wastewater evaluation.