{"id":6071,"date":"2020-10-13T14:47:57","date_gmt":"2020-10-13T09:17:57","guid":{"rendered":"http:\/\/astan.lk\/al_virtualclassroom\/?p=6071"},"modified":"2020-10-13T14:47:35","modified_gmt":"2020-10-13T09:17:35","slug":"hydrosphere","status":"publish","type":"post","link":"https:\/\/astan.lk\/al_virtualclassroom\/hydrosphere\/","title":{"rendered":"Hydrosphere"},"content":{"rendered":"

Water quality<\/strong>
\nPhysical Parameters<\/u>
\n(i) Temperature
\nTemperature should less than 40 0C. Hot water accelerates the biological processes. It reduces the dissolved O2 and affects the aquatic organisms.<\/p>\n

(ii) pH Value
\n\u2022 A pH range of 6.0 – 9.0 appears to provide protection for the life of fresh water fish and bottom dwelling invertebrates.
\n\u2022 pH of water may also be changed due to dissolved gas from air such as CO2, SO2 and the mixing with industrial effluents.
\n\u2022 Normal pH range of ground water which is useful is 6.0 – 8.5.
\nIf pH < 6.5 it is acidic water which is corrosive. Usually soda ash is used to neutralise the acidity.
\n\u2022 Dolomite can also be used in agriculture. Dolomite slowly neutralises acidity of water.
\n2H+<\/sup>(aq) + CaCO3<\/sub>.MgCO3<\/sub>(s) \u2192\u00a0Ca2+<\/sup>(aq) + Mg2+<\/sup>(aq) + 2 HCO3<\/sub>–<\/sup>(aq)<\/p>\n

(iii) Conductivity
\n\u2022 Conductivity is a measure of the ability of an aqueous solution to conduct an electric current.
\n\u2022 Conductivity depends on the following factors.
\n\u2022 Concentration of ions \u2022 Mobility of ions
\n\u2022 Oxidation state \u2022 Temperature of water<\/p>\n

\u2022 The unit used to measure the conductance is ohm-1<\/sup> = \u03a9-1<\/sup> or Siemens (S). Conductance = 1\/Resistance
\nThis measures the ionic strength but does not identify the ions present.<\/p>\n

(iv) Turbidity
\nSediments in the water prevents the penetration of light to the bottom of water bodies. This will reduce the photosynthesis activity and also creates anaerobic environment introducing a bad smell to the water.<\/p>\n

(v) Dissolved amount of oxygen and water quality
\n\u2022 O2 is required for the metabolism of aerobic organisms and also influences some chemical reactions.
\n\u2022 O2 in air dissolves in water. Photosynthesis is the process of producing O2.
\n\u2022 Concentration of dissolved O2 decreases as temperature increases.
\n\u2022 Submerged green plants and algae increase the dissolved O2 content in a water body in the day time.
\n\u2022 Decaying organic matter consumes dissolved O2 in a water body.<\/p>\n

Chemical oxygen demand (COD)
\n(CHO)n<\/sub>(aq) + O2<\/sub>(g) \u2192\u00a0x CO2<\/sub>(g) + y H2<\/sub>O(l)
\n\u2022 Amount of oxygen required in mg dm-3 for this oxidation of organic matter wastes to be carried out chemically is called chemical oxygen demand (COD).<\/p>\n

\u2022 Since the amount of O2<\/sub> consumed cannot be easily quantified, dichromate is used for laboratory determination. In this determination the sample is heated with an acid solution of potassium dichromate. All oxidizable organic matter will react with dichromate at this stage.Silver sulphate is generally added as a catalyst.
\n\u2022 Chloride present in water can be oxidized to chlorine under these conditions by dichromate.This is prevented by converting chloride to undissociated mercuric chloride. The excess of unreacted dichromate is determined by titrating with iron(II) ammonium sulphate.
\nCr2<\/sub>O7<\/sub>2-<\/sup>(aq) + 14H+<\/sup>(aq) + 6e \u2192\u00a02Cr3+<\/sup>(aq) + 7H2<\/sub>O(l)<\/p>\n

\u2022 \u0399n acidic medium;
\nO2<\/sub> (g) + 4H+<\/sup>(aq) + 4e \u2192 2H2<\/sub>O(l) \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (CHO)n<\/sub>(aq) + O2<\/sub>(g) \u2192\u00a0x CO2<\/sub>(g) + y H2<\/sub>O(l)<\/p>\n

\u2022 If the organic matter is oxidized by acid dichromate, then
\nCr2<\/sub>O7<\/sub>2-<\/sup>(aq) + 14H+<\/sup>(aq) + 6e \u2192\u00a02Cr3+<\/sup>(aq) + 7H2<\/sub>O(l)
\n1 mol O2<\/sub>(aq) \u2261\u00a02\/3 mol of Cr2<\/sub>O7<\/sub>2-<\/sup>(aq)
\nBiochemical oxygen demand \/ Biological oxygen demand (BOD)<\/strong>
\n(CHO)n<\/sub>(aq) + O2<\/sub>(g) \u2192\u00a0x CO2<\/sub>(g) + y H2<\/sub>O(l)
\n\u2022 Amount of O2 required to be carried out for the above oxidation by microorganisms is called biochemical oxygen demand.
\n\u2022 The consumed dissolved oxygen can be used to determine the BOD value.
\n\u2022 Substances which use up dissolved oxygen will contribute to the value of BOD. Pollutants such as human and animal wastes, food canneries, meat etc. controls the BOD.<\/p>\n

\u2022 When a water sample is saturated with oxygen, the initial concentration of dissolved oxygen can be determined. If it is incubated at 20 0C for a known period, usually 5 days, the microorganisms in the water oxidize the organic matter. The oxygen that remains in the water can be measured. The oxygen used up or the BOD value can be calculated , for the particular water body.<\/p>\n

Dissolved ionic compounds<\/h4>\n

Hardness<\/strong>
\n\u2022 Hardness isdue to dissolved metal ions, namely Ca2+ and Mg2+. Here the contribution of Ca and Mg are the most considered and other metals are negligible because they are less soluble in water. Therefore, we discuss Ca and Mg only here. Hard water has no adverse health effects. Hard water is less desirable because it requires more soap for cleaning. It forms scum and curd and it toughens vegetables during cooking and forms scales in boilers, hot water heaters and pipes. The composition of ground water naturally reflects the underlying geology, the residence time in the rock, the previous composition of the ground water and in some instances, the flow path. Due to the slower movement of ground water in the aquifers as compared to that of surface water, the composition of the former shows a negligible variation with time for a given aquifer<\/p>\n

.
\nCa2+<\/sup>(aq) \/ Mg2+<\/sup>(aq) + 2HCO3<\/sub>–<\/sup>(aq) \u2192 CaCO3<\/sub>(s) + MgCO3<\/sub>(s) + CO2<\/sub>(g) + H2<\/sub>O(l)<\/p>\n

\u2022 Aquifer – A porous permeable rock layer containing water (Groundwater).<\/p>\n

Iron (Fe)<\/strong>
\n\u2022 The primary source of iron in water is rock layers containing iron ore. Iron is typically dissolved in water and when brought to the surface, can form \u2018rust\u2019 which may settle out. Another source of iron is iron-reducing bacteria, which depends upon iron to live. The commonest iron containing water is red , laundry spotting, metallic in taste and staining of plumbing fixtures. These are usually due to the presence of iron above 0.3mg dm-3<\/sup>. Iron affects the taste of drinking water.<\/p>\n

Fluoride (F–<\/sup>)
\n\u2022 Varying amounts of fluoride are found in groundwater of different areas of Sri Lanka. For example, due to the apatite ore in Eppawala fluoride, concentration of ground water in the surrounding areas is high. Fluoride can affect teeth during the period when permanent teeth are being formed. For tropical countries the fluoride content should not exeed 0.6 mg\u00a0dm-3<\/sup>
\nNitrates
\n\u2022 Nitrate is a common contaminant found mainly in ground water. High nitrate concentrations can be particularly dangerous to babies under six months, since nitrates interfere with the ability of blood to carry oxygen. Nitrate also causes cancer. Fertilizers, human and animal sewage are usually enriched with of nitrogenous compounds which may enter into a ground water body as a result of leaching. The conversion of ammonia to nitrate is brought about by highly specialized soil bacteria.<\/p>\n

Phosphates
\n\u2022 Phosphate ions are added to water by chemical fertilizers and artificial detergents. Due to nitrates ions and phosphate ions, an eutrophication condition arises in water and enhances the growth of algae. As a result, amount of dissolved oxygen in water decreases.<\/p>\n

Methods of water purifications<\/h4>\n

Sedimentation<\/strong>
\n\u2022 The separation of a suspension of solid particles into a concentrated slurry. The supernatant liquid, after sedimentation is clear.
\n\u2022 If the effluent is suitable it will be discharged into waterways. Otherwise it is passed to a secondary treatment.<\/p>\n

Coagulation<\/strong>
\n\u2022 Muddy river water in large water supply schemes can be coagulated using aluminium salt(alum).
\n\u2022 Water is stored in large tanks and can be coagulated with A1(III) or Fe(III).
\n\u2022 A gelatinous precipitate of aluminum hydroxide or iron(III) hydroxide is formed. As it settles and sinks to the bottom, the precipitate carries suspended material with it as sludge.
\nFlocculation and Filtration<\/strong>
\n\u2022 During the flocculation smaller particles are agglomerated to form bigger particles and these particles are filtered.
\n\u2022 After that water is passed slowly through sand filters. Different types of sand filters are used for water flow.
\n\u2022 Fine sand
\n\u2022 Course sand
\n\u2022 Gravel
\n\u2022 Stones<\/p>\n

\u2022 Filtration removes microbes and other suspended particles from water. Many filters will also remove some harmful chemicals found in water.<\/p>\n

Disinfection process<\/strong>
\n\u2022 Use of chlorine
\nCl2<\/sub>, ClO2<\/sub> ,chloroamines are used as disinfectants. They kill bacteria by oxidising. The residual Cl2<\/sub> prevents the formation of further bacteria. But excess Cl2<\/sub> reacts with organic substances and forms harmful substances including trihalomethanes and chlorinated phenols.
\n\u2022 Use of ozone
\nOzone also destroys bacteria by oxidation. But it dissociates quickly. Ozone does not give further protection from bacteria. Therefore the water disinfected by ozone has to be used quickly. Since ozone doesn\u2019t give any side effects it is preferably used by human. Unlike Cl2<\/sub>, ozone needs no storage and it can be generated easily.<\/p>\n

\u2022 Use of UV radiation
\nIt kills both the bacteria and viruses. As ozone it cannot have a further protection from bacteria.<\/p>\n","protected":false},"excerpt":{"rendered":"

Water quality Physical Parameters (i) Temperature Temperature should less than 40 0C. Hot water accelerates the biological processes. It reduces the dissolved O2 and affects the aquatic organisms. (ii) pH Value \u2022 A pH range of 6.0 – 9.0 appears to provide protection for the life of fresh water fish and bottom dwelling invertebrates. \u2022 […]<\/p>\n","protected":false},"author":842,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[14,1682],"tags":[],"class_list":["post-6071","post","type-post","status-publish","format-standard","hentry","category-chemistry","category-unit-16"],"acf":[],"yoast_head":"\nHydrosphere - Learning & Education Portal<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/astan.lk\/al_virtualclassroom\/hydrosphere\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Hydrosphere - Learning & Education Portal\" \/>\n<meta property=\"og:description\" content=\"Water quality Physical Parameters (i) Temperature Temperature should less than 40 0C. 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