What are the water pollution indices?

    Answer: Evaluation of water pollution status and pollution levels can be indicated by several indicators, which can be divided into two specific categories: one is physical and chemical indicator, the other is a composite indicator of organic pollution and nutrients.

    1. Physical and chemical indicator includes:

    Water temperature: physical and chemical properties of water and water temperature are closely linked. The solubility of water soluble gases (such as oxygen, carbon dioxide, etc.), biological and microbial activity in water, non-ionic ammonia, salinity and pH, and other solutes are subject to water temperature changes.

    Color: pure water is colorless and transparent. Clean water, when shallow, should be colorless, and light green or blue when deep. The existence of humus, soil, plankton, iron and manganese and other metal ions in natural water can tinge water with colors. Waste water generated from textile, printing and dyeing, paper making, food, organic synthesis industries often contains a lot of dye, biological pigments and colored suspended particles, constituting the major way of water pollution by coloring the water body. Colored water often gives a sense of unhappiness, and when it is released into water, the natural water will be consequently colored, reducing the light transmittance of water and affecting the growth of aquatic organisms. Water color is calculated in ??degree??, that is, when each liter of solution contains 2mg cobalt chloride 6 hydrate (??) (equivalent to 0.5mg of cobalt) and 1mg platinum (as hexavalent chloride platinum (??) in the form of acid) , water color will be 1 degree.

    Odor: odorless and tasteless water, though contaminants absence cannot be ensured, can help build up trust of users to the water quality. Some organic and inorganic materials generated by foul water come mainly from domestic and industrial sewage, decomposition of natural materials, or the activities of micro-organisms and biological organisms. Some substances, as long as ??g/10 of them exists in the water, can easily be detected. However, it is difficult to determine the composition of the material producing foul.

    Turbidity is to describe water containing silt, clay, organic, inorganic, and suspended materials such as plankton and micro-organisms, the sediment of which is not only slow but difficult. As the turbidity caused by iron and manganese hydroxide is very harmful to human life, we must use special methods to remove them. Natural water, after going through the process of coagulation, sedimentation and filtration treatments, can become clear water.

    Transparency refers to the clarity of sample water. Clean water is transparent, but when there are suspended matters and colloids in water, its transparency will be reduced. The transparency degree of groundwater is usually high which also changes constantly as its water supply conditions and environmental conditions are changing. Transparency is contrary to turbidity. The more suspended solids in water, the lower its transparency will be.

    pH refers to the negative logarithm of hydrogen ion activity in water. PH =- lg??H . The pH value of natural water is usually between 6 and 9, which is also a controlled scope of the PH value for our wastewater discharge. Not only is PH closely related to water solubility, chemical form, attribute, activities and effects, but it also has a significant impact on the activities of aquatic life.

    Residue: The total residue refers to the material left in the containers after the evaporation or drying of water or sewage in a certain temperature, including the "unfilterable residue" (all the residues that is trapped in the filter, also known as suspended solids) and "filterable residue" (all residues that can go through the filter, also known as soluble solids). Suspended solids can affect the transparency of water, reduce photosynthesis of algae in the water, restrict the normal movement of aquatic organisms, slow underwater activity, result in hypoxic at the bottom of the water, and reduce the assimilation ability of water body..

    Salinity: Salinity refers to the total amount of inorganic mineral compositions contained in water. Regular consumption of low-mineral water will destroy the balance of alkali metals and alkaline earth metal ions in human body, resulting in disease. Regular consumption of high-mineral water will lead to stone disease. Salinity is an important indicator to determine the chemical compositions of water and is used in the evaluation of irrigation water applicability as a major indicator by evaluating the total water salinity. It is commonly used in the analysis of natural water quality and is mainly expresses by the sum of the mass of major ions tested.

    Conductivity: Conductivity is a numerical solution of conduction current capabilities. The conductivity of pure water is very low, but when the water contains inorganic acid, alkali or salt, the conductivity can increase. Conductivity is often used in the indirect speculation of the total concentration of ions in water. The conductivity of aqueous solution depends on the nature and concentration of ions and the temperature and viscosity of the solution. Conductivity varies with temperature. Every increase of 1 ?? in the temperature shall cause an increase of the conductivity by 2% or so. The standard temperature for determination of the conductivity is set at 25 ??.

    Oxidation-reduction potential: A water body is a quite complex system that contains several oxidation-reduction couples whose oxidation-reduction potentials are a combined result of oxidation and reduction of a number of oxidation substances and reduction substances. Oxidation-reduction potential is significant in the migration and transformation of pollutants of the water environment. The natures of the main solutes in the water depend to a large extent on the type, speed and balance of water oxidation.

    Acidity: Acidity refers to all substances in the water neutralizing alkali, i.e. total amount of materials which release H or generate H through the hydrolysis. 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.e. total amount of materials which can accept proton H . 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. 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.

    2. 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. 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. 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.

    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.

    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 0.118%. 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 1.4g for a normal person can be supplemented through water and food, but in the forms of inorganic phosphate or organic phosphorus compounds. 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. Lethal dose for human intake is 1mg/kg. 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.g., phospholipids, etc.). 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 0.2mg / L) can cause algae overgrowth until the number reached hazardous levels (known as eutrophication), resulting in reduction of transparency of lakes and rivers and the deterioration of water quality. 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. It is an important indicator especially in the assessment of eutrophication in lakes and reservoirs.

    TN: The discharge of great deal of domestic sewage, agricultural drainage, or nitrogen-containing industrial waste water into water bodies would cause the organic nitrogen and various inorganic nitrogen compounds to increase and a large number of organisms and micro-organisms to breed, consuming a great deal of dissolved oxygen in water and leading to water quality deterioration. When there are excessive nitrogen and phosphorus substances in lakes and reservoirs, there will be serious phytoplankton reproduction and eutrophication of water body. Therefore, the total nitrogen is an important indicator in the assessment of water quality.

    Nitrate Nitrogen: nitrate nitrogen in water is the most stable of the nitrogen compounds in the forms of nitrosyl and ammonia nitrogens in the aerobic environment, as well as the final product of decomposition of nitrogen-containing compounds after inorganic reaction. Nitrite can be generated by the oxidation into nitrate which, in the anaerobic environment, would also be reduced to nitrite under the reaction of micro-organisms. In the water are significant differences between nitrate nitrogen contents, ranging from the tens of micrograms per liter to tens of milligrams per liter. The content of nitrate nitrogen in clean water is very low, but it is relatively high in polluted waters and some deep underground waters. Intake of nitrate or the nitrite generated by the role of gut microbes can be poisoning. Nitrate nitrogen content in water up to tens of mg/l can cause poisoning to the baby.

    Nitrite Nitrogen refers to the intermediates of nitrogen cycle and is unstable. It can be oxidized to nitrate or reduced to ammonia according to environmental conditions. Nitrite allows the body's normal hemoglobin (low iron hemoglobin) to be oxidized into methemoglobin which leads to methemoglobinemia and loss of ability to transport oxygen by hemoglobin in the body, hence hypoxia symptoms. Nitrite reacts with sec-amines to produce carcinogenic nitrosamines substances in low pH conditions.

    Ammonia refers to the chemical combination of ammonia in the form of ammonia or ammonium ions. The composition ratio between the two depends on the pH value and temperature of water. When the pH value is high, the proportion of free ammonia is higher. On the contrary, when the pH value is low, the proportion of ammonia is lower. But water temperature is an opposite case. The main source of ammonia in water is the decomposition products of nitrogen-containing organic compounds under reaction of micro-organisms in some industrial wastewater like coking wastewater and drainage from the ammonia fertilizer plants. In addition, in oxygen-free environment, the nitrite existing in water can also be affected by micro-organisms and reduced to ammonia. In an aerobic environment, ammonia in water can also turn into nitrite and may even further turn into nitrate. The determination of various forms of nitrogen compounds in water contributes to the evaluation of water pollution and its "self-purification" state. Fish can be very sensitive to the ammonia in water. High levels of ammonia nitrogen will lead to fish death.