Water Quality Indices


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Water Quality Assessment in Terms of Water Quality Index

Acidity: Acidity refers to all substances in the water neutralizing alkali, i. In the surface water, the integration of CO2 or discharge of acid-containing wastewater by machinery, mineral processing, electroplating, pesticides, printing and dyeing, chemical and other industries shall result in lower pH in the water body.

Due to acid corrosion, the normal living conditions for fish and other aquatic organisms and crops are destroyed. Acid-containing wastewater can also corrode pipelines and ships and destroy buildings. Therefore, the acidity is an important indicator in the measurement of the changes in water bodies. Alkalinity: Contrary to acidity, alkalinity refers to all substances in the water neutralizing acid, i.

There are various sources of alkalinity in water. The alkalinity of surface water is basically the function of content of carbonate, bicarbonate and hydroxide, so the total alkalinity is also regarded as the sum of the concentrations of these components. Alkalinity indicators are commonly used in the evaluation of the buffering capacity of water and the solubility and toxicity of metals in water and it is also an indicator in evaluating the process of water and wastewater treatment. If the alkalinity is mainly caused by an excessive amount of alkali metal salts, then it also is a major reference in determining whether the water is suitable for irrigation.

Carbon dioxide: Carbon dioxide exists in water mainly in the form of dissolved gas molecules, but a small amount of it also combines with water and generates carbonic acid which would have reaction with alkaline substances in rocks the sediments of which can be removed from water via precipitation. Carbon dioxide plays a unique part in the biochemical reactions between water and organisms.


  • Inside Out Pre-Intermediate.
  • Evaluation of various water quality indices for indexing river water;
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Carbonate compounded state it has dissolved could have homogeneous and heterogeneous carbonate reactions with the lithosphere and atmosphere which is beneficial to the regulation of pH and composition of natural water. The main source of carbon dioxide in surface water is the decomposition of organic matters in the water and sediment as well as aquatic respiration.

It can also be absorbed from the air. Therefore, its content can be an indirect indicator of the water body subjected to organic pollution. Composite indicator of organic pollution and nutrients includes: Dissolved oxygen: The dissolved oxygen content in natural water depends on the balance between water and atmospheric oxygen. Saturation of dissolved oxygen is closely related to the partial pressure of oxygen in the air, atmospheric pressure, water temperature. Dissolved oxygen in clean surface water is generally close to saturation.

But because of the growth of algae, dissolved oxygen may be too saturated. The dissolved oxygen in the water bodies affected by organic and inorganic reduction substances would be lower. When the atmospheric oxygen is late in supplement, the dissolved oxygen in water would decrease gradually, even closer to zero.

Water quality index

Thus, anaerobic bacteria would breed and water quality deteriorates, leading to fish mortality. The content of dissolved oxygen in wastewater depends on the treatment processes before waste water discharging. It is normally at low levels and varies widely.

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The discharge of large amount of wastewater, which causes an increase of ozone-depleting substances in the water and decrease of dissolved oxygen, accounts for the major reason for the death of fish. Therefore, dissolved oxygen is an important indicator of water quality evaluation. Chemical oxygen demand COD refers to the amount of oxidant consumed in the oxidation of water samples in specified condition.

Chemical oxygen demand reflects the contamination degree of the restored the materials in water which include organic matter, nitrite, ferrous salt, sulfide and so on. It is common for water to be contaminated; therefore, COD can also be used as an indicator of relative content of organic matters, was organic pollution is very common, so the chemical oxygen demand but also as one of the indicators relative content of organic matter, but it only reflects the oxidation of organic pollution not polycyclic aromatic hydrocarbons, PCB, dioxin-like pollution, etc.

The chemical oxygen demand of water samples may vary with the types and the concentration of oxidant that has been added, the acidity of reaction solution, reaction temperature and time, as well as the presence or absence of catalysts. Therefore, the chemical oxygen demand is also a condition indicator. China uses potassium dichromate method in testing wastewater, the measured value of which is called chemical oxygen demand.

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Permanganate index refers to the amount of potassium permanganate consumed as oxidant to deal with water samples in acid or alkaline medium. Both permanganate index and CODcr are referred to as chemical oxygen demands, only that they are values measured under different conditions. Thus, permanganate index is often considered as a comprehensive index of the degree of pollution of the surface water by organic pollutants and reduction inorganic substances. Biochemical oxygen demand BOD : Domestic sewage and industrial wastewater contains large amount of organic matters in various forms.

When the waters are polluted, the decomposition of organic matters in the water would consume a lot of dissolved oxygen, and thereby undermining the balance of oxygen in water, deteriorating water quality and causing death to fish and other aquatic organisms because of hypoxia. Organic matters contained in water are complicated which makes it difficult to determine their ingredients one by one.

People often use the oxygen consumed by organic compounds in water under certain conditions to indirectly test the content of organic matters in water, and biochemical oxygen demand is one of the important indicators fall into this category.

Development of river water quality indices-a review.

Total organic carbon TOC is a composite indicator of the total organic matters contained in water by testing the content of carbon. As the TOC was determined by combustion method, all the organic matters in water can be oxidized, making it a more direct method than BOD5 or COD in determining the total amount of organic matters.

Therefore, it is often used to evaluate the degree of organic pollution in water. Phosphorus: The percentage content of the weight of phosphorus in the earth's crust is about 0. Phosphorus exists in nature in the forms of all kinds of phosphates. Phosphorus exists in the cells, bones and teeth, and is essential for plants and animals and the human body. Daily need of phosphorus of 1. Phosphorus that exists in the form a single mass phosphorus will be harmful to the environment.

Yellow phosphorus is an important chemical raw material. Having been cooled by the exhaust gas of the water spray washing melting furnace, it turns into "phosphorus poisonous water" which contains a great deal of soluble phosphorus and suspended-state phosphorus elements, causing great harm to the environment.

Phosphorus is a highly toxic substance which once enters the living body can cause acute poisoning. Therefore, the element phosphorus is a pollutant that can not be ignored. TP: In the natural water and waste water, almost all phosphorus in various phosphate forms exist, they are divided into orthophosphate, condensed phosphates pyrophosphate, metaphosphate and multi-phosphate and organic phosphorus combined e. They exist in the solution, humus particles or aquatic organisms.

The content of phosphate in natural water in general is not high, but is relatively high in industrial wastewater and domestic sewage like fertilizer, smelting and synthetic detergent industries. Phosphorus is one of the elements necessary for biological growth, but the high content of phosphorus in water in excess of 0. Therefore, Phosphorus is an important indicator of water quality evaluation.

Kjeldahl Nitrogen: Kjeldahl method refers to the content of nitrogen tested via the measure of Kjeldahl. It includes ammonia nitrogen and organic nitrogen compounds tested to be able to translate into ammonium compounds under this condition. Such organic nitrogen compounds mainly refer to the proteins, amino acids, nucleic acid, urea, and a large number of synthetic organic nitrogen compounds whose nitrogen are negative trivalent.

It does not include nitrogen compounds like azide compounds, in conjunction nitrogen, azo, hydrazone, nitrate, nitrite, nitro, nitroso, nitrile, oxime and semi-Kabbah hydrazone. As in most cases, it is the former ammonium that exists in water; therefore, the difference between Kjeldahl nitrogen and ammonia nitrogen shall be the organic nitrogen. The determination of organic nitrogen or Kjeldahl nitrogen mainly aims to know the situation of water pollution. Environmental Monitoring and Assessment.

Product description

January , Cite as. The use of water quality indices WQIs as a tool to evaluate the status of water quality in rivers has been introduced since the s. The WQI transforms selected water quality parameters into a dimensionless number so that changes in river water quality at any particular location and time could be presented in a simple and easily understandable manner. Although many WQIs have been developed, there is no worldwide accepted method for implementing the steps used for developing a WQI. Thus, there is a continuing interest to develop accurate WQIs that suit a local or regional area.

This paper aimed to provide significant contribution to the development of future river WQIs through a review of 30 existing WQIs based on the four steps needed to develop a WQI. These steps are the selection of parameters, the generation of sub-indices, the generation of parameter weights and the aggregation process to compute the final index value. From the 30 reviewed WQIs, 7 were identified as most important based on their wider use and they were discussed in detail. It was observed that a major factor that influences wider use of a WQI is the support provided by the government and authorities to implement a WQI as the main tool to evaluate the status of rivers.

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