<div class="MsoNormal" style="text-align: center;"> <b><span style="font-size: 28pt; line-height: 115%;">Sulfur Cycle and its Environmental Impacts<u><o:p></o:p></u></span></b></div> <div class="MsoNormal"> <b><u><span style="font-size: 28.0pt; line-height: 115%;"><br /></span></u></b></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">Sulfur is one of primary nutrients for both animal and plant life. It is component element that makes up some proteins, enzymes and vitamins. Sulfur accounts for 5 of dry weight of organisms. Plants take sulfur in the soluble form while animals depend on the sulfur containing plant and other animal materials.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">After uptake of inorganic sulfur, it becomes organic sulfur in the plants and microorganisms. After decomposition of organic matter, sulfur compounds are converted again into inorganic sulfur or sulfur in cells of microorganisms. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">Sulfur is entered into the atmosphere as a result of both natural and anthropogenic process.  Volcanic eruptions, organic matter decomposition, forest fire and microbial activities are the natural process that helps to cycle sulfur. Fossil fuel burning and industrial activities release sulfur dioxide and hydrogen sulfide in large scale into the environment. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">The major reservoir pool of sulfur is ocean. Sulfur can be found in large concentration in as dissolved from or sediments forms. Gypsum and pyrite are the examples for sulfur bearing minerals. Leaching and rock sediments are the major sources that release sulfur into ocean. Oxidation number of sulfur varies from -2 to +6. But sulfate with oxidation number of +2 is most stable form of sulfur.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Main steps of sulfur cycle:<o:p></o:p></span></b></div> <div class="MsoListParagraphCxSpFirst" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">1)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">    </span></span><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Conversion of organic sulfur into inorganic sulfur</span></b><span style="font-size: 14.0pt; line-height: 115%;"> (H</span><span style="font-size: 9.0pt; line-height: 115%;">2</span><span style="font-size: 14.0pt; line-height: 115%;">S)<o:p></o:p></span></div> <div class="MsoListParagraphCxSpMiddle" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><b><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">2)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;">    </span></span></b><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Oxidation of element sulfur, thiosulfate and hydrogen sulfide into sulfate<o:p></o:p></span></b></div> <div class="MsoListParagraphCxSpMiddle" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">3)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">    </span></span><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Reduction of sulfate into hydrogen sulfide</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Chemoorganotrophic anaerobic respiratory bacteria use non oxygen terminal electron acceptor at the end of their electron transport chain. They use sulfate as their terminal electron acceptor and reduce it into hydrogen sulfide. <o:p></o:p></span></div> <div class="MsoListParagraphCxSpMiddle" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">4)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">    </span></span><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Sulfur assimilation</span></b><span style="font-size: 14.0pt; line-height: 115%;">: It is the reduction of sulfate into organic sulfhydryl groups. The oxidation number of sulfur changes from +6 to -2.<o:p></o:p></span></div> <div class="MsoListParagraphCxSpMiddle" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">5)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">    </span></span><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Sulfur dissimilation</span></b><span style="font-size: 14.0pt; line-height: 115%;">: it is the reduction of organic sulfur containing substance into inorganic hydrogen sulfide. <o:p></o:p></span></div> <div class="MsoListParagraphCxSpLast" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <!--[if !supportLists]--><span style="font-size: 14.0pt; line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;">6)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">    </span></span><!--[endif]--><b><span style="font-size: 14.0pt; line-height: 115%;">Oxidation of hydrogen sulfide into element sulfur</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Green sulfur bacteria and purple sulfur bacteria perform photosynthesis to ATP synthesis. They use hydrogen sulfide as their electron donor. They reduce it into element sulfur.  <o:p></o:p></span></div> <div class="MsoListParagraphCxSpLast" style="margin-left: .75in; mso-add-space: auto; mso-list: l0 level1 lfo1; text-indent: -.25in;"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Sulfur compounds acts as the electron donors and electron acceptors for microorganisms</span></b><span style="font-size: 14.0pt; line-height: 115%;">. Anaerobic respiratory bacteria including <b><i>Thiobacuillus thioxidans</i></b> use element sulfur, thiosulfate or hydrogen sulfide as their substrate. They oxidize these sulfur compounds to run electron transport chains. They oxidize them into sulfate.  Theses sulfate dissolve and spread though the aquatic body. When sulfate reach into bottom where the anaerobic environmental condition exists anaerobic respiratory microorganisms use it as their terminal electron acceptor at their electron transport chain. They reduce sulfate into hydrogen sulfide. These hydrogen sulfide moves upward. Both green sulfur and purple sulfur bacteria which inhabit in the above layers of aquatic water body us use hydrogen sulfide as their electron donor in their photosynthesis. They oxidize hydrogen sulfide into element sulfur. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Effects of acidification of aquatic bodies</span></b><span style="font-size: 14.0pt; line-height: 115%;">: These sulfates make the environments extremely acidic. They dissolve minerals in the bottom of the aquatic bodies. Toxic metal ions including Al3+ release into the water. These toxic metal ions cause detrimental effects to some aquatic plants and animals. Acid dissolves the shells of aquatic animals including coelenterates, gastropods. Shell of eggs including fishes is dissolved by acids. pH below 5 does not allow fish eggs to hatch. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Oxidation of hydrogen sulfide is more beneficial</span></b><span style="font-size: 14.0pt; line-height: 115%;"> than oxidation of element sulfur into sulfate because oxidation of hydrogen sulfide from -2 to +6 release eight electrons while oxidation of element sulfur from 0 to +6 releases six electrons. So hydrogen sulfide can take more electrons for their electron transport chin and produce more ATP.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="separator" style="clear: both; text-align: center;"> <a href="https://2.bp.blogspot.com/-AuaemAQDG8w/WMgql6d6_mI/AAAAAAAAA6A/JMdAjkh0HWQYD5upJW0981kMMUG5F_8sgCLcB/s1600/image.PNG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="304" src="https://2.bp.blogspot.com/-AuaemAQDG8w/WMgql6d6_mI/AAAAAAAAA6A/JMdAjkh0HWQYD5upJW0981kMMUG5F_8sgCLcB/s640/image.PNG" width="640" /></a></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <br />

Sulfur Cycle and its Environmental Impacts Sulfur is one of primary nutrients for both animal and plant life. It is component element t...

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Sewage Water Treatment Plant

<div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Sewage is the combination of both black water and grey water</span></b><span style="font-size: 14.0pt; line-height: 115%;">. Black water carries wastewater that is released through the toilets including urine and excreta, kitchen and bathroom. Grey water carries wastewater from bathrooms and kitchen. Release of sewage into public sewer system is compulsory in the highly urbanize area. Release of sewage without proper treatment into surface water sources and ground water sources cause serve health, economic and environmental problems. <o:p></o:p></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Sources of sewage</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Toilets, bathrooms and kitchen are the sources of releasing sewage. <o:p></o:p></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Composition of sewage</span></b><span style="font-size: 14.0pt; line-height: 115%;">: wastewater from toilets contains pathogens in large quantities.  Biodegradable organics (BOD) releases from both toilets and kitchens. It causes the depletion of oxygen in the water sources and affects the aquatic plant and animal life. Excessive amount of nutrients (N, P, K) also release through both toilets and kitchen. They are able to accelerate the growth of algae. The sudden increase of algal<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"> growth is referred to as the eutrophication. Hot and cold water release through the kitchens and bathrooms. It affects the temperature stability of the aquatic bodies. Detergents releases through the cleaning of bathrooms and toilets.</span> <span style="font-size: 14.0pt; line-height: 115%;">Sediments are another pollutant that reduces the light penetration through aquatic bodies.<o:p></o:p></span></div> <div class="MsoNormal"> <br /></div> <br /> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Collection of the sewage</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Later sewers collect sewage from individual houses into primary gully. Then sewage from primary gullies is flowed into secondary gullies by using branched sewers. Then according to the slope, sewage from all secondary gullies is drained along the road into the main gully.</span> <span style="font-size: 14.0pt; line-height: 115%;">The main gullies are connected to the treatment plant via large sewer.  Here collection of the sewage is done by using gravity instead of pumping. Therefore sewers are constructed with slope. Thereby it reduces the cost of treatment of sewage.</span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="separator" style="clear: both; text-align: center;"> <a href="https://2.bp.blogspot.com/-GZoTIiipDWY/WMgpSlQ9QII/AAAAAAAAA5w/nfRiEWkyGcAwjW8ErjlvX0_Vl9-MZr4FwCLcB/s1600/sawege_plan.PNG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="392" src="https://2.bp.blogspot.com/-GZoTIiipDWY/WMgpSlQ9QII/AAAAAAAAA5w/nfRiEWkyGcAwjW8ErjlvX0_Vl9-MZr4FwCLcB/s640/sawege_plan.PNG" width="640" /></a></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><span style="font-size: 14pt;">The treatment process is operated as flowing diagram.</span></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><span style="font-size: 14pt;"><br /></span></span></div> <div class="separator" style="clear: both; text-align: center;"> <a href="https://3.bp.blogspot.com/-km4XaxRwZNk/WMgpfSQIFRI/AAAAAAAAA50/283bPw4j-2483u4kXCyQ-M3SG1_ZWVcPQCLcB/s1600/sawege_plan_02.PNG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="398" src="https://3.bp.blogspot.com/-km4XaxRwZNk/WMgpfSQIFRI/AAAAAAAAA50/283bPw4j-2483u4kXCyQ-M3SG1_ZWVcPQCLcB/s640/sawege_plan_02.PNG" width="640" /></a></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><span style="font-size: 14pt;"><br /></span></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><span style="font-size: 14pt;"><br /></span></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><span style="font-size: 14pt;"><br /></span></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">Incoming sewage is passed through a metallic bar screen. It removes the large materials including sanitary napkins, grits, glass pieces and straws. Those are sent and disposed in the sanitary land fill.  Thereby it helps to protects the pumps and other equipment from wrapping or damage them.  <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Sedimentation tank</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Then water is transferred into a sedimentation tank by using pump system. Here it is allowed water to settle down under gravity. Large floatable materials are collected at the bottom of the sedimentation tank. They are removed and directed to the central sludge treatment facility. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Aeration tank</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Water is transferred into a tank with continuous aeration. Here biodegradable organics are removed by using digestion of aerobic respiratory bacteria. They oxidize organic matter completely into carbon dioxide and water without leaving any residues. . Retention time of wastewater is 4-8 hours in the aeration tank. The amount of sediments can be reduced by extending the retention time from 1-2 days. Mechanical aerators are employed for aeration. <o:p></o:p></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Secondary clarifier</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Then wastewater is transferred into another settling tank. Here as microorganisms are higher than the available food, they tend to form flocs via attaching to each other. They settle down under gravity at the bottom of the settling tank. They are removed as the sludge. Part of the sludge is removed as the activated sludge. Rest is transferred into the central sludge treatment facilities to dispose in a proper manner. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Disinfection</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Chlorine, ozone and UV are the common method of disinfection. But chlorine is the economical viable method. Chorine solution is added drop wisely by using specialized machine. Excess chorine generates disinfection byproducts (dbp) including chloroform. They may cause serve health problems therefore excess chlorine have to be removed before discharge water into natural water bodies. Sodium metabisulfate is added to remove excess chorine. . But both ozone and UV do not leave resides that need to be removed before discharges. But use of ozone as a disinfection method is costly because ozone has to be produced in-site due to the instability. It requires highly specialized expensive equipment to generate ozone. Therefore use of UV is environmental friendly and cost effective. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Wetland system</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Even after primary and secondary treatment, wastewater still contains excess nutrients including phosphate and nitrate, sediments and non-degraded organic matter. If wastewater is released at this level of treatment, it may pollute the both groundwater table and surface water sources. So construction of artificial wetland is the economical viable method as a tertiary treatment. It removes pollutant from water via biological, physical and chemical methods. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Reuse and disposal of treated wastewater: </span></b><span style="font-size: 14.0pt; line-height: 115%;">After treatment, water can be reused within the plant. Flushing toilets and watering plants are done by using treated water. If water is not reused, it can be discharged into natural water bodies, after tastings for the national and international standards. COD, BOD and suspended solid are checked once every week. Parameters in the natural water bodies also tested recently. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <b><span style="font-size: 14.0pt; line-height: 115%;">Sludge treatment</span></b><span style="font-size: 14.0pt; line-height: 115%;">: Sludge collected from primary and secondary clarifier is transferred to a tank. It is similar to typical sedimentation tank in the design. Here sludge is settled down under gravity. So it increases the thickness of gravity. Then sludge is collected and directed into either anaerobic digester or drying bed. Sludge is degraded into carbon dioxide by using anaerobic respiratory bacteria. Then this carbon dioxide is reduced into methane which is combustible gas. Methane can be used for electricity generation or directly use in cookers.  In drying beds, sludge is filtered through a sand and gravel filter. Remaining liquid fraction is accumulated as the leachate at the bottom. The leachate is collected via pipe systems into central treatment facilities and treats. The liquid fraction of sludge is further reduced by using filtration, drying via sunlight and wind. The sludge is collected from the surface f the drying beds. It can be reused or disposed in sanitary land fill. <b><o:p></o:p></b></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><br /></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;"><b><span style="font-size: 14.0pt; line-height: 115%;">Reuse and disposal of sludge</span></b><span style="font-size: 14pt; line-height: 115%;">: Sludge can be used as a resource. Sludge is used for compost production. Plant materials are added to adjust the proper carbon to nitrogen ratio for microbial decomposition.  It can be applied as a soil conditioner and fertilizer. It as a fertilizer, it adds primary nutrients such as nitrogen, phosphorous and potassium. Thereby it increases the growth of plants. It as a soil conditioner, it improves the biological, chemical and physical properties. If sludge is not reused, it is needed to be disposed in a sanitary landfill because sludge contains the most of the worst materials of wastewater.</span> <o:p></o:p></span></div>

Sewage Water Treatment Plant

Sewage is the combination of both black water and grey water . Black water carries wastewater that is released through the toilets includin...

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