DEVELOPMENT OF A WATER QUALITY INDEX WITH A REDUCED NUMBER OF PARAMETERS

de Oliveira, Amanda R. M; Borges, Alisson C.; da Silva, Greicelene J; Nascimento, Moysés

doi:10.1590/1809-4430-Eng.Agric.v42n3e20220006/2022

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Scientific Paper • Eng. agríc. (Online) 42 (3) • 2022 • https://doi.org/10.1590/1809-4430-Eng.Agric.v42n3e20220006/2022 copy

DEVELOPMENT OF A WATER QUALITY INDEX WITH A REDUCED NUMBER OF PARAMETERS

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

The development of water quality indices (WQIs), duly modified and using a small number of parameters, may be of great economic use. The purpose of this work was to develop a WQI with a reduced number of parameters (WQI_red), in relation to what is used in the Brazilian state of Minas Gerais (WQI_IGAM), in the basin of the Doce River. Four different scenarios were analysed, with the absence of the following parameters for the calculation of the WQI_red: BOD, E. coli and phosphate; BOD and E. coli; BOD, E. coli and total solids (TS); BOD, E. coli, phosphate and TS. The redistribution of the weight attributed to the eliminated parameters was done according to the following methods: (i) in weighted form, through optimisation of the correlation between the WQI_red and the WQI_IGAM; (ii) based on the cluster analysis. The best scenario found was that of the WQI_red considering only DO, pH, temperature variation, nitrates and turbidity, with the weights being redistributed based on cluster analysis. This scenario maintained satisfactory performance, with a minimum difference being observed between WQI_IGAM and WQI_red, in terms of management purpose. The WQI_red as proposed makes it possible to establish a monitoring control system operating in real time in the Doce river basin, as all the parameters considered can be obtained with the use of multiparameter probes.

Cluster analysis; analytic cost; monitoring in real time

Missing Parameters	r	Classes that were maintained (%)	Over- estimated (%)
BOD, E. coli and phosphates	0.73*	22	78
BOD, E. coli, phosphates and ΔT	0.73*	27	73
BOD and E. coli	0.75*	21	79
BOD, E. coli and ΔT	0.75*	23	77
BOD, E. coli and total solids	0.75*	20	80
BOD, E. coli, total solids and ΔT	0.75*	22	78
BOD, E. coli, phosphates and total solids	0.73*	21	79
BOD, E. coli, phosphates, total solids and ΔT	0.73*	24	76

Quality Parameters	DO	E. coli	pH	BOD	Nitrates	Phosphates	ΔT	Turbidity
E. coli	0.10*
pH	0.10*	0.03
BOD	0.08*	0.10*	-0,.01
Nitrates	-0.02	-0.01	-0.26*	0.08
Phosphates	-0.04	0.25*	-0.07	0.17*	0.19*
ΔT	0.00	0.00	0.00	0.00	0.00	0.00
Turbidity	-0.09*	0.34*	0.11*	0.10*	-0.15*	0.52*	0.00
TS	-0.03	0.28*	0.05	0.15*	-0.03	0.48*	0.00	0.65*

Missing Parameters	r	Classes that were maintained (%)	Over- estimated (%)	Under- estimated (%)
BOD, E. coli and phosphates	0.71*	54	37	9
BOD, E. coli, phosphates and ΔT	0.71*	50	37	13
BOD and E. coli	0.73*	52	43	5
BOD, E. coli and ΔT	0.72*	55	39	6
BOD, E. coli and total solids	0.72*	55	38	7
BOD, E. coli, total solids and ΔT	0.72*	48	39	13
BOD, E. coli, phosphates and total solids	0.70*	50	36	14
BOD, E. coli, phosphates, total solids and ΔT	0.70*	48	34	18

WQI_red = f(DO, pH, ΔT, phosphates, nitrates, turbidity)			WQI_red = f(DO, pH, ΔT, nitrates, turbidity).
Level	BAND I	BAND II	BAND I	BAND II
Excellent	95* < WQI ≤ 100*	95 < WQI ≤ 100	97* < WQI ≤ 100*	97 < WQI ≤ 100
Good	77 < WQI ≤ 95*	83 < WQI ≤ 95	75 < WQI ≤ 97*	82 < WQI ≤ 97
Fair	50 < WQI ≤ 77	27 < WQI ≤ 83	46 < WQI ≤ 75	25 < WQI ≤ 82
Poor	17 < WQI ≤ 50	20 < WQI ≤ 27	10 < WQI ≤ 46	15 < WQI ≤ 25
Very Poor	WQI ≤ 17	WQI ≤ 20	WQI ≤ 10	WQI ≤ 15

	WQI_red = f(DO, pH, ΔT, phosphates, nitrates, turbidity)		WQI_red = f(DO, pH, ΔT, nitrates, turbidity)
	BAND I	BAND II	BAND I	BAND II
CClass that was maintained	65	67	65	68
Overestimated	27	18	26	15
Underestimated	8	15	9	17

Associação Brasileira de Engenharia Agrícola SBEA - Associação Brasileira de Engenharia Agrícola, Departamento de Engenharia e Ciências Exatas FCAV/UNESP, Prof. Paulo Donato Castellane, km 5, 14884.900 | Jaboticabal - SP, Tel./Fax: +55 16 3209 7619 - Jaboticabal - SP - Brazil
E-mail: revistasbea@sbea.org.br

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[1] *Corresponding author. Federal University of Viçosa/Viçosa - MG, Brazil. E-mail: borges@ufv.br | ORCID ID: https://orcid.org/0000-0002-9729-6439