Multi-scene Optimization Method of Water COD Measurement Based on Direct Spectroscopy

Enhua Liu; Decao Wu; Jie Wang; Wanyao Tan; Junhao Pu; Binbin Luo; Bin Tang; Zourong Long; Mingfu Zhao

doi:10.3788/AOS202141.2230001

Acta Optica Sinica, Volume. 41, Issue 22, 2230001(2021)

Multi-scene Optimization Method of Water COD Measurement Based on Direct Spectroscopy

Enhua Liu, Decao Wu^*, Jie Wang, Wanyao Tan, Junhao Pu, Binbin Luo^**, Bin Tang, Zourong Long, and Mingfu Zhao

Chongqing Key Laboratory of Optical Fiber Sensor and Photoelectric Detection, Chongqing University of Technology, Chongqing 400054, China

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Figures & Tables(10)

Fig. 1. Turbidity direct fitting correction results based on modified power function. (a) Fitting results of the particles’ simulation spectra by modified power function with particle size of 0.1－100 μm; (b) turbidity direct fitting correction results of diatomite sample spectra

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Fig. 2. Spectra of samples with different COD concentrations in two scenes. (a) Original spectra；(b) absorbance normalized spectra

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Fig. 3. Flow chart of multi－scene optimized COD measurement method

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Fig. 4. Schematic of water sample spectrum measurement system

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Fig. 5. Scene matching results of the sample spectra in the test set. (a) Scene matching rate of the sample spectra；(b) C_max of the sample spectra

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Fig. 6. Scenes matching results of test set based on three typical classification methods. (a) SVM; (b) BP－ANN; (c) K－NN

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Fig. 7. Influence of three turbidity characteristic fitting functions on SLCSM－PLS COD calculation

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Table 1. Accuracy statistics of four scene－matching methods
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Table 1. Accuracy statistics of four scene－matching methods
Method Accuracy /%
BP－ANN 55.56
K－NN 62.22
SLCSM 100.00
SVM 91.11

Table 2. Experimental results of multi－scene COD calculation

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Table 2. Experimental results of multi－scene COD calculation

Scene label	Actual value /(mg·L^－1)	Holistic PLS modeling		SVM－PLS modeling		SLCSM－PLS modeling
Scene label	Actual value /(mg·L^－1)	Calculation value /(mg·L^－1)	Error rate /%	Calculation value /(mg·L^－1)	Error rate /%	Calculation value /(mg·L^－1)	Error rate /%
1	80.44	1175.93	1361.87	79.08	1.69	79.08	1.69
2	141.18	130.46	7.59	140.75	0.30	140.75	0.30
3	37.78	545.59	1344.12	264.43	599.92	36.59	3.15
4	160.88	1573.13	877.83	160.81	0.04	160.81	0.04
5	109.93	862.32	684.43	111.14	1.10	111.14	1.10
6	3.63	220.67	5979.06	40.72	1021.76	3.64	0.28
7	20.01	285.89	1329.45	19.69	1.60	19.69	1.60
8	6.03	156.08	2488.39	5.91	1.99	5.91	1.99
9	6.12	75.15	1127.94	23.82	289.22	6.02	1.63
10	10.31	100.77	877.40	19.24	86.61	10.10	2.04
Average execution time /s		0.363		0.553		0.762

Table 3. Statistics of the influence of three turbidity characteristic fitting functions on the error rate of COD calculation in SLCSM－PLS method

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Table 3. Statistics of the influence of three turbidity characteristic fitting functions on the error rate of COD calculation in SLCSM－PLS method

Scene label	Error rate /%
Scene label	Power function	Exponential function	Quadratic polynomial
1	1.69	11.43	14.06
2	0.30	10.49	40.57
3	3.15	13.24	12.25
4	0.04	8.45	9.61
5	1.10	54.73	65.76
6	0.28	2.93	2.09
7	1.60	10.27	9.53
8	1.99	9.62	8.98
9	1.63	2.34	2.29
10	2.04	2.95	3.17
Average error rate	1.36	12.65	16.83

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Enhua Liu, Decao Wu, Jie Wang, Wanyao Tan, Junhao Pu, Binbin Luo, Bin Tang, Zourong Long, Mingfu Zhao. Multi-scene Optimization Method of Water COD Measurement Based on Direct Spectroscopy[J]. Acta Optica Sinica, 2021, 41(22): 2230001

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