Overall Index of Pollution
A major objective of water quality control work is to reduce the incidence of water-related diseases thereby developing water resources of wholesome quality, i.e. water free from visible suspended matter, excessive color, taste and odour, objectionable dissolved matter, aggressive constituents, and bacteria indicative of fecal pollution. The quality of water is defined in terms of its physical, chemical, biological, and bacteriological parameters. Water Quality Criteria are defined as the acceptable levels of concentrations of specific water quality parameters and may vary with the type of use such as drinking, bathing and domestic use, irrigation, recreation and industrial use. The standards/criteria indicate the suitability of water for a specific use e.g. as per the classification scheme of Inland Surface Water by Central Pollution Control Board (CPCB) in India, the criteria for total dissolved solids is 500 mg L−1 for drinking and 2100 mg L−1 for irrigation and industrial cooling. Thus, the criteria are developed for specific individual parameters. However, if this information on water quality parameters measured individually is
transformed into a single number (Index) representing the overall quality of water, it will be very useful to the public.
In the present article, the development of Overall Index of Pollution (OIP) considers the important surface water quality indicator parameters viz. pH, turbidity, dissolved oxygen (DO), biochemical oxygen demand (BOD), hardness, total dissolved solids (TDS), total coliform and some of the toxicity indicator parameters viz. Arsenic (As) and Fluoride (F). The classification of water quality is made very general such as Excellent, Acceptable, Slightly Polluted, Polluted and Heavily Polluted. The concentration levels/ranges of the indicator parameters are defined with due consideration to the Indian standards in the proposed classes. Wherever, such criteria were not defined reference was made to European Community Standards, WHO Guidelines etc.
Uses and Limitation:
It will be of immense use for determining the surface water quality status with reference to specific individual parameter, and for assessing the overall water quality status in Indian context.
However, comparative assessments of water quality at different places or at different times can be made only when the parameters included in the OIP are the same, and accordingly recommendations may be made regarding the specific use of water.
Categorization Table
The numerical estimate of OIP corresponds to following classes:
Standards Required
The concentration levels/ranges of the indicator parameters are defined with due consideration to the Indian standards in the proposed classes. Wherever, such criteria were not defined reference was made to European Community Standards, WHO Guidelines etc.
Variables Selection
The water quality parameters viz. Turbidity, pH, Color, DO, BOD, TDS, Hardness, Cl, SO4, NO3, Total Coliform, As and F are considered as the significant indicator parameters of surface water quality in the present study.
Calculation of Overall Index of Pollution:
Overall Index of Pollution (OIP) is estimated as the average of all the pollution indices (Pi) for individual water quality parameter considered in this study and is given by the mathematical expression:
where Pi = pollution index for ith parameter. i = 1, 2, . . ., n and n = number of parameters.
Different water quality parameters are measured in different units of measurement. Hence, it is necessary to bring them into the commensurate unit so that the integrated index can be obtained and used for decision making. For this purpose, an integer value is assigned to each of the classes C1, C2, C3, C4 and C5, in geometric progression i.e. 1, 2, 4, 8 and 16 respectively, where, the number termed as class index indicates the level of pollution in numeric terms. This forms the basis for comparison of water quality from Excellent to Heavily Polluted (Table I). Mathematical expressions are fitted for each of the parameter concentration levels to obtain this numerical value called an index (Pi) indicating the level of pollution for that parameter. These mathematical equations are given in Table II. The value function curves, wherein, the concentration of the parameter is taken on Y-axis and index value on X-axis are plotted for each of the parameter. These curves give the pollution index (Pi) for individual pollutants. For any particular concentration, the corresponding index can be read directly from these curves.
Table 1. Mathematical expression for value function curves
Case Studies based on Overall Index of Pollution
Case study 1
OIP was applied to assess the water quality status at a few sampling stations on the Yamuna River. The various sampling stations from Sonipat to Allahabad on the Yamuna River were selected. The observed water quality data in the month of June for three consecutive years 1995–1997 at six stations viz. Hathnikund (HK), Kalanaur (KN), Palla (Pl), Nazimuddin Bridge (NB), Mazawali (MZ) and Etawah (ET) were considered for estimation of OIP. Pollution indices for each of the water quality parameter measured at these stations were estimated using value function curves for each parameter or using the mathematical expression for that curve. The OIP was calculated by taking the average of all the pollution indices for individual water quality parameters.
At Hatnikund, the overall water quality was in the range Excellent to Acceptable for all the three years. At Kalanaur, it was slightly polluted in 1996, but Excellent in 1995 and 1997. At Palla, water quality was always Excellent. At Nizamuddin Bridge (at the center of river), water quality status was indicated as Polluted and Heavily polluted. This is obvious because number of drains meet river Yamuna upstream of this point in the stretch under consideration. At sampling point Mazawali, water quality status was always slightly polluted and at station Etawah there was improvement in water quality from Slightly Polluted to Acceptable from the year 1995 to 1997. Thus, based on the estimated values of OIPs, the sampling stations where pollution control measures are required can be identified. The detailed about the specific parameters responsible for pollution can be obtained by referring to the concentration ranges and the level of treatment required to make the water suitable for designed use at that location can be decided.
Case study 2
Drinking water quality is determined by the water’s biological, chemical, and physical features. Water sampling was carried out in 20 villages in the Pune and Satara districts of Maharashtra, with 15 falling in a low rainfall zone. Samples were collected from rivers, open wells, and bore wells, four times in a period of a year covering all seasons. A total of 206 water samples were analyzed for their physical, chemical, and bacteriological properties. Physical and chemical properties were expressed in the form of a modified Water Quality Index (WQI). Additionally, the modified WQI was compared to an Overall Pollution Index (OIP) for rivers. The present investigation is an attempt to analyze the impact of seasonal changes on water quality of different water bodies using two different WQIs. To understand the degree to which water quality is affected by faecal bacteria, modified WQI with exclusion of faecal coliforms (FC) and OIP with inclusion of FC were compared with each other in river water bodies. Modified WQI values and bacterial counts were at a maximum during the onset of the monsoon. In terms of bacteriological contamination, the number of FC and intestinal enterococci (IE) in the water bodies was of major concern since it would impact human health.
References
Rutuja Dhawde, Nuzhat Surve, Ragini Macaden, Aina Charlotte Wennberg, Isabel Seifert-Dähnn, Appasaheb Ghadge and Tannaz Birdi Physicochemical and Bacteriological Analysis of Water Quality in Drought Prone Areas of Pune and Satara Districts of Maharashtra, India. Environments 2018, 5, 61; doi:10.3390/environments5050061
Shukla A.K., Ojha C.S.P., Garg R.D. (2017) Application of Overall Index of Pollution (OIP) for the Assessment of the Surface Water Quality in the Upper Ganga River Basin, India. In: Garg V., Singh V., Raj V. (eds) Development of Water Resources in India. Water Science and Technology Library, vol 75. Springer, Cham