Estimation and comparison of methods for nitrification ...

Environmental Technology

ISSN: 0959-3330 (Print) 1479-487X (Online) Journal homepage: http://www.tandfonline.com/loi/tent20

Estimation and comparison of methods for nitrification rate constant in river systems Yongming Xie & N. Biswas To cite this article: Yongming Xie & N. Biswas (1991) Estimation and comparison of methods for nitrification rate constant in river systems, Environmental Technology, 12:3, 249-256, DOI: 10.1080/09593339109385002 To link to this article: http://dx.doi.org/10.1080/09593339109385002

Published online: 17 Dec 2008.

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Date: 05 July 2016, At: 06:21

Environmental Technology, Vol 12. pp 249-256

© PubUcaüorw Division Selper l i d , 1991

ESTIMATION AND COMPARISON OF METHODS FOR NITRIFICATION RATE CONSTANT IN RIVER SYSTEMS YONGMING XIE 1 * and N. BISWAS2 1

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Research Center for Eco-environmental Sciences, Academia Sinica, P.O. Box 934, Beijing (China) *Present Address: Department of Civil and Environmental Engineering, University of Windsor, 401 Sunset Avenue.Windsor, Ontario N9B 3P4 Canada 2

Department of Civil and Environmental Engineering, University of Windsor, 401 Sunset Avenue, Ontario, N9B 3P4, Canada

ABSTRACT

Methods to estimate nitrification rate, Kn, for river systems are proposed in this paper. Taking the Toujiang River in China as an example, a detailed comparison of the methods proposed in this study is presented. There is a good fit by using First-Order, Two-Station and the Least-Squares method. A relationship between the measured and the theoretical nitrogenous oxygen demand (NOD) is developed and has been applied to estimate the influence of nitrification on oxygen balance for a river system without determining the NOD.

INTRODUCTION A number of research papers dealing with the study of nitrification have been published in the past few decades(l-S). The results of these studies have demonstrated the influence of nitrification on stream oxygen balance and clearly indicated the necessity of considering inorganic nitrogen oxidation in the study of water quality models for river systems. However, parameter estimation is one of the most important components for establishing water quality models. For a biochemical process, such as nitrification of rivers, this is a significant step for the study of models and the prediction of behavior of pollutants in water. It can influence the accuracy of established models in predicting the concentrations of pollutants in water bodies. In river systems, nitrification is one of the complicated biochemical processes. Researchers have developed various models to describe nitrification in rivers under different

conditions. Huang et al. (3) studied nitrification and reported that the rate of oxidization of ammonia nitrogen is linear with time, that is, the reaction of oxidation for ammonia nitrogen obeys a zero-order kinetics. In this case, it is not difficult to estimate the rate of oxidation for ammonia nitrogen. Other researchers (4,5) found that nitrification of surface water under natural environmental conditions can be expressed by firstorder kinetics. Haug et al.(G) studied nitrification and found the rate of ammonia-N oxidation to be a function of ammonia nitrogen concentration which can be described by the following equation: dN/dt=-Kn(N)b

(1)

in which, N is the concentration of ammonia (mgl/ 1 ); K,, is the rate constant.from 0.38 to 2.59 (d"1); b is an exponent ranging from 0.93 to 1.48. Knowles et a/.(7) suggested that the nitri-

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fication rate constant K,, was related to the temperature daring reaction, and they determined the nitrification constants by numerically integrating the differential equations describing the bacteria growth and proposed an empirical formula based on the experimental results. Garland (8), in studying nitrification in the Trent River, proposed that the decay rate of ammonia nitrogen shows that the seasonal effect manifests itself as a dependant on both the velocity and temperature of the river water. Wezernak and Gannon (9) proposed a relationship between substrate and nitrification reaction, and took into account the influence of bacteria on the process. Courchaine (10) plotted nitrogenous biochemical oxygen demand on a logarithmic scale to calculate the rate of nitrification. Thomann et al. (11) estimated Kn by using the BOD data measured during the second stage of deoxygenation. Neider and Mead (12) evaluated K„ from the measured date at two or more locations along a stream by using simplex method. Wezernak and Gannon (1967) applied the integrated solution of the first-order kinetic equation to estimate, nitrogenous oxidation constants. Bansal (13) suggested that the rate of nitrification was related to hydraulic conditions, such as depth, velocity etc., under constant temperature and described in Equation (2): C(H) d

(2)

in which, H is average depth of water (m), C and d are constants related to the characters of the studied river. All the methods described above have been proposed under different experimental conditions. In this paper, several methods have been used to evaluate parameters related to nitrification in the Toujiang River. The purpose of this paper is to evaluate and compare several methods in estimating the rate constant of nitrification in a river system and to use these methods in practice. EXPERIMENTAL DATA Five experiments simulating the nitrification of the Toujiang River were carried out in the laboratory under environmental conditions similar to those in the river system. The aparatus and the experimental methods have been described by Xie (4). All data used in this study are listed in Table 1.

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RESULTS AND DISCUSSION Empirical Formulae Knowles et aZ.(7) suggested that the nitrification rate constant Kn can be calculated by a linear log-equation which is only related to the reaction temperature T (8-23 °C): Log (!£„) = 0.026T- 0.492

(3)

Garland (8) found that the rate coefficient for ammonia nitrogen oxidation, Kn was proportional to temperature T, bacteria concentration B and was inversely proportional to velocity, u, over a limited range of conditions. And the relationship is given as follow: K„ = 0.0833T + 0.0646B + 2.1234/u

(4)

When the bacteria concentration is constant, Equation (4) becomes the following form: (5)

K„ = -£.6272 + 0.0789T + 2.5773/u

This finding was specific for the River Trent, and it was successfully used to estimate the rate of nitrification for the Lijiang River in China by the multi-regression method (2). Because the bacteria concentration was not determined for the Toujiang River, Equation 4 was not used in this paper and as a result was not compared to other methods. The results calculated by empirical equations 3 and 5 for the Toujiang River are listed in Table 2. The results indicate that K„, calculated by different empirical equations, shows a good agreement. First-order Equation According to the experimental results obtained in the laboratory by simulation experiments, the nitrification process of the Toujiang River follows the first-order kinetics. A first-order equation can be used to describe the nitrification of the Toujiang River: dN/dt = - K„t

(6)

The solution of this equation is obtained by integrating. (7)

where, N t and No are the concentrations of 1 ammonia nitrogen (mgL" ) at time t and 0, respectively. The K„ values calculated using Eq.7 with the data given in Table 1 are tabulated in Table 2 and the correlation coefficients, r, are found to be over 0.95. From the Table 2, it is obvious that the values of Kn are different from those calculated

Table 1.

Laboratory data measured during nitrification process.

Test No.

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by empirical equations. Since the relationship between the rate of nitrification and temperature, as well as velocity, are empirical, it is subject to limitations in its applicability to other streams and rivers, and for other ambient conditions. They must be calibrated using the data from the river/stream under study.

1 (27.5°C)

2 (17.0°C)

3

(18.9°C)

4

(27.8°C)

5 (20°C)

Time (d)

Ammonia-N (mgL-1)

Nitrite-N (mgL-1)

Nitrate-N (mgL"1)

0 1.0 1.5 2.0 3.0 4.0 4.5

5.62 4.40 3.47 2.54 0.12 0.01 0.01

0.28 0.50 0.77 1.16 1.08 0.06 0.04

3.30 3.05 3.33 3.71 5.50 6.69 6.19

0 1.0 1.5 2.0 4.0 4.5 5.0

5.54 4.82 4.72 4.45 3.96 3.08 2.73

0.30 0.46 0.63 1.10 1.01 0.65 0.35

2.02 2.52 2.76 3.08 3.54 3.79 4.53

0 1.0 2.0 3.0 4.0 5.0

5.04 3.83 2.60 1.23 0.17 0.15

0.25 0.40 0.59 0.95 1.08 0.47

2.13 2.34 2.78 3.09 4.57 5.78

0 1.0 2.0 3.0 4.0 5.0

5.48 3.78 1.47 0.06 0.04 0.04

0.21 0.51 0.82 1.20 0.74 0.25

2.13 3.01 4.07 5.84 6.07 6.32

0 2.0 3.0 5.0 6.0 7.0

4.44 3.42

0.18 0.35 0.51 1.09 0.87 0.23

2.31 2.74 3.43 4.57 5.07 5.69

2.11

0.04 0.04 0.04

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The calibration of Kn for temperature variation is already included in the empirical formulae 3 and 5, therefore, no modification is necessary. However, for other methods K„ value must be calibrated for different temperatures. In this study, all simulation tests were performed at a constant temperature. The conversion of Kn values to the reference temperature is based on an approximate form of the Arrhenius equation:

took @ as an empirical coefficient and proposed coefficients of temperature calibration in different experimental conditions (see Table 3 for reference). Two-Station Method Wezernak et al.(5) proposed a nitrification model to predict the fate of ammonia nitrogen in river systems. They suggested that the rate of formation of oxidized substrate is proportional to the product of substrate (ammonia nitrogen) and bacteria concentration. The relationship is given by:

(8)

K n (T)

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where, KnCD, K„(20) are the rate constants (d"i ) of nitrification at temperature T and 20 °C, respectively, @ is temperature calibration coefficient which can be obtained by NOD test or from empirical equations. Most researchers Table 2.

dN/dt

(9)

The results estimated by different methods

Test

Temp.T

Velocity.u

No.

t)(l.ht))=Nu(l.EXPCK1t))+NuhtEXP(-K't) (17) oxidation process, the CBOD (carbonaceous BOD) is oxidized first followed by the oxidation of Now, Substituting nitrogenous compounds, which is represented by NBOD (Figure l).If the main coordinate a = N u ; b = N u h; Fj = l-EXP(-K't); F 2 = tEXR-lCt), axis(BOD vs t) in Figure 1 is moved up to the point O', we obtain a coordinate system which can be we obtain, represented by X'-Y'. Now, we can only consider the nitrogenous BOD, and an equation describing (18) this process, which is similar to carbonaceous

Figure l.Typical BOD process of surface water

BOD

CBOD

Time, d a y

of K„ is calculated to be 0.115 (d' 1 ). This method has also been successfully used to estimate the rate constant of CBOD (2). In order to compare with the values calculated by other methods, K„ value has been calibrated by the Eq.8 with 1.099 for @ and are listed in Table 2 under heading, LSM(a).

The constants a and b can be calculated by the Least Squares method. When the difference of the measured and calculated values reaches a minimum, the value of K' is approximately equal the rate constant K^ Using the data given in Table 4 the values of Kn were calculated by this method for the Toujiang River and are found to be 0.122 and 0.108 (d' 1 ), respectively. The averaged value

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Table 4.

Nitrogenous BOD Data.

Time (d) 1.0 1.5 2.0 4.0 5.0 6.0

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10.0

•

Test 1 Nitrogenous BODdngL"1) 0.89 1.25 2.02 3.80 4.36 5.05 6.77

Time (d) 1.0 1.5 2.0 4.0 5.0 6.0 8.0

B. The second method is based on the expansion of the exponential term in equation 15, thus the exponential term can be expanded as follows; (Knt)3/4I +...)

Relationship between Measured and Theoretical NOD

(19)

The detailed study of the determination of nitrogenous oxygen demand has been proposed by Xie (4) and Wezernak (9). According to the stoichiometry, the relationship between nitrogenous BOD ,and the total amount of oxdizable nitrogen can be expressed approximately,

and = (l-K^t + ( K ^ ß l - (K„t)?/41 + ...)

(20)

Then we have l-EXP(-Knt) = KntU+Knt/3!)-3

4x16 Nitrogenous BOD Amount of oxidizable nitrogen" 14

(21)

(22)

(t/N) L

(23)

or

Substituting Y=(t/N)1/3, a=(KnLnOr1/3, bsKn^oL^173), we can get a linear equation Y=a+bt. This equation can easily be solved by using the technique of Least Squares. Prom Eq. 22 and 23 the K„ value can be calculated by the following equation, K,, =eb/a.

4.57 (Om

(24)

(NOD)m = 0.2560 + 0.4746(NOD)th; r=0.9O75

The calculated results of K^ by using method (a) are, 0.065 and O.OSSid'1), respectively and the average K„ is found to be 0.077(d'1). The results calibrated under different temperatures by using Eq.8 with 1.099 as @ value, are given in Table 2 and they indicate that method (a) is in good agreement with method (b).

(25)

Wezernak et al.(9) found the nitrogenous oxygen demand coefficient, fn, to be 4.33, and Xie (4) determined the coefficient to be 2.169 for the Toujiang River. The experimental results indicate that the coefficient, fn, obtained for nitrification is lower than the theoretical one. This can be attributed partly to the respiration of nitrogenous bacteria and partly to the complexity of the nitrogenous substrate composition. In order to predict the effect of nitrification on oxygen balance, the relationship between the measured and the theoretical NOD has been developed using the data for the Toujiang River (Table 5). The relationship can be expressed using the following equation:

Substituting Eq.21 into Eq.15, then: N=L n0 K n t(l + K n t/6)- 3

Test 2 Nitrogenous (mgL"1) 0.79 1.36 2.23 3.60 3.96 4.16 5.67

(NOD) th = 4.57NOX

26) (27)

where, (NOD)m and (NOD)th are the values of the measured and theoretical NOD (mgL"1), respectively. Nox is the concentration of oxidized ammonia nitrogen (mgL'1).

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Table 5.

Measured and calculated NOD values

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Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Measured (mgL" 1 ) 1.25 0.89 3.80 6.77 0.79 0.78 4.16 3.96 5.67 3.94 1.70 5.05 4.36 1.36 2.23 3.60 4.23

Oxidized N (mgL'1)

Theoretical* (mgL"1)

0.41 0.48 1.48 2.04 0.28 0.28 1.76 2.43 2.02 1.83 0.48 2.14 2.15 0.54 1.20 1.85 1.77

1.87 2.19 6.79 9.32 1.28 1.28 8.04 11.11 9.23 8.36 2.19 9.78 9.82 2.47 5.48 8.45 8.09

Theoretical value is 4.57 times the amount of oxidized ammonia.

The equation can be utilized to evaluate the effects of nitrification on water quality. This study shows that when the NOD values are not available, we can use this method to predict the influence of the nitrification process on the overall oxygen balance in a river. CONCLUSION The following conclusions can be reached through this study: The results indicated that although there are some differences in the calculated 1^ values by using the methods discussed in this paper, the methods can be used to estimate the rate constant of nitrification for a river system. The value of Kn indicated that there was a good agreement with

those calculated by the Eirst-Order Equation, Two-Station Method and the Method of LeastSquares. The empirical equations can be utilized to estimate nitrification rate after modifying the data obtained under the studied conditions. Since the relationships are empirical, they have some limitations and case should be taken before applying these equations to other streams and/or surface waters. The analysis of the measured and the theoretical NOD indicated that the actual NOD in the field is different to that from the values obtained using the stoichiometry. The relationship developed in this study can be used to evaluate the influence of nitrification on the oxygen balance for river systems without NOD data.

REFERENCES 1. 2. 3. 4. 5. 6.

S. McCutcheon, J. Environ. Eng. ASCE, 113, 628-646(1987). Y.Xie, Collection for Environmental Science, 8, 15-43(1987), Beijing. C.S.Huang et al., J. Environ. Eng. Div., ASCE, 100, 409-422(1974). Y. Xie, Intern. J. Environ. Studies, 31, 297-303(1988), England. C.T. Wezernak et al., J. San. Eng. Div. ASCE, 84, 883-895(1968). R.T. Haug and P.L. McCarty, "Nitrification with the submerged Filter", Presented at the 44th Annual conference of water Pollution Control Federartion, San Francisco, Oct., 1971.

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7. 8. 9. 10. 11. 12. 13. 14. 15.

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16.

C. Knowles et al., J. of Gen. Microbiol., 38, 263-278(1965). J.H.N. Garland, in Mathematical Models in Water Pollution Control, A. James. ed., Wiley, Chichester, 1978, pp.167-205. C.T. Wezernak and J.J. Gannon, Appl. Microbiol., 15, 1211-1215(1967). R.J. Courchaine, J. Water Pollut. Control Fed., 40, 835-847(1968). R.V. Thomann et al., in Environ. Eng. Sci. Program, Manhattan College, Bronx, N. Y. (1971). J.A. Nelder and R. Mead, Comput. J., 7, 308-313(1965). M.K. Bansal, J. Water Pollut. Control Fed., 48, 2380-2393(1976). J.R. Richard et al., J. Water Poll. Control Fed., 50, 2016-2028(1978). F. Stratton, "Nitrification Effects on Oxygen Resources in Streams" Ph.D. Thesis, Stanfard University (1966). A.M. Buswell. et al., Appl. Microbiol., 2, 21-25(1954).

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