INTRODUCTION• Physical, chemical or biological change in the water quality thatadversely affects the living organisms or makes water unsuitable fordesired uses is water pollution.• Water pollution abatement technologies are used to reduce theharmful effects of polluted water.• It mainly includes wastewater treatment that uses physical, chemicaland biological methods to remove contaminants.• The treatment of wastewater is mainly carried out in 3 stages– Primary treatment– Secondary treatment– Tertiary treatment
PRIMARY TREATMENT• Removes solids that are suspended in the waste water via physicalsettling or filtration.• The major steps are:1. Wastewater is screened to remove larger objects2. Then grit is removed3. Rest of the solids are finally extracted using gravity in largesedimentation tanks.
BAR SCREEN• Wastewater first pass through bar screens (or bar racks).• It removes coarse solids like sticks, stones and other largeobjects.• Screens of various size & shape are used depending on thenature of solids to be removed.• Bar screens consist of parallel metal bars, which have 20 –60mm bars for coarse screens & 10 – 20mm bars for fine &medium screens.• It should be manually cleaned continuously to avoid cloggingproblems.
GRIT CHAMBER• Grit – small & dense materials like sand, dirt or broken glass.• It is usually removed in grit chamber.• It is a chamber in which the velocity of waste water flow isreduced to a point where the denser grit will settle out, but theorganic solids will remain in suspension.• Usually the velocity of flow will be b/w 0.15 – 0.3m/s
SEDIMENTATION TANK• From grit chamber the effluent is passed into a primary settling tank(Sedimentation tank).• Here the suspended solids are removed by gravitational settlingunder motionless conditions.• Flocculants ( chemicals used to precipitate insoluble substances) areadded to water to promote sedimentation.• The purpose of flocculation is to cause small pollutant particles toaggregate and form large enough floc so that they settle down fast.• Wastewater is let to stand for 2 – 3 hrs and it results in the removalof 50% - 65% of suspended solids• The settled solids is called primary sludge or raw sludge.
SEDIMENTATION TANK• It usually have– Inlet zone– Settling zone– Sludge zone– Outlet zone
SECONDARY TREATMENT• After primary treatment the effluent undergoes a secondarytreatment which degrades the biological content of the sewage.• This usually uses biological processes.• Microorganisms are introduced to the wastewater and consume theorganic matter, oxygen is delivered to the system ensuringmicroorganism survival.• This biological process occurs naturally in nature, but is acceleratedin secondary treatment systems.• This is mainly done by activated sludge process, trickling filters,aerated lagoons and oxidation ponds.
ACTIVATED SLUDGE PROCESS• Activated Sludge Process uses micro organisms to feed on organiccontaminants in waste water.• Basic principle– When micro organisms grow, they form particles that clumptogether– These particles ( floc) are allowed to settle to the bottom of thetank, leaving a relatively clear liquid free of organic material andsuspended solids.• Thus, the settled organic matter that consist of several activated microorganisms are called activated sludge.
ACTIVATED SLUDGE PROCESSProcess• Waste water is aerated - forms floc with micro organism.• These micro organism breaks down the suspended organic matter andproduce stable solids and multiplies to form more micro organisms.• The wastewater from aeration tank is passed into the settling tank (clarifier)and solids settle down – activated sludge.• A part of the settled sludge is returned to the influent of theaeration tank – returned activated sludge.• Periodically, the excess solids and organismsare removed from the system –waste activated sludge – fed into the sludge digestor.
SLUDGE DIGESTION• The sludge which settles in the sedimentation basin is pumpedto the sludge digestors where a temperature of 30–35ºC ismaintained.• It is designed to encourage the growth of anaerobic bacteriathat decreases organic solids by reducing them to solublesubstances & gases (CO2 & CH4).Complex organiccompoundsAcid formingbacteriaorganic acidsMethane formingbacteriaCH4, CO2, H2S &othercompounds1st stage conversion 2nd stage conversion
OXIDATION POND• Oxidation ponds are large, shallow ponds designed to treat waste waterthrough the interaction of sunlight, bacteria and algae.• Algae grow within the pond and utilize sunlight to produce oxygen duringphotosynthesis.• This O2 is used by the aerobic bacteria in the oxidation pond tobreakdown the organic waste in the wastewater.• The broken down solidssettle down in theponds, resulting ineffluent that is relativelywell treated.
AERATED LAGOON• It is a treatment pond with artificial aeration to promote thebiological oxidation of waste water.• Natural lagoons are made up of three layers an aerobic (layer withoxygen), an anaerobic (layer with no oxygen) and a facultative(mixed layer).• In a constructed aerated lagoon air is pumped into the lagoon to turnthe whole pond into an aerobic zone.• Adding air to the water speeds up the natural processes that breakdown organic waste.• Mechanical aeration device is present which supply the oxygenneeded by bacteria for stabilization
TRICKLING FILTERS• Trickling Filter is an aerobic treatment system that utilizesmicroorganisms attached to a medium to remove organic matter fromwastewater.• It consist of a bed of packing material to which microbes are attached.• This microbial growth on the filtering medium consists of bacteria, fungi,algae etc and is called biological slime.
PROCESS• Wastewater is sprayed into the air, then allowed to trickle through themedia.• Microorganisms, attached to the media, break down organic material inthe wastewater.• When more & more wastewater is passed, the slime layer thickens andeventually gets detatched from the surface. This is called sloughing.• A settling tank after the trickling filter, removes the detatched bacterialfilm and some suspended matters.
TERTIARY TREATMENT• It is the final treatment the waste water undergoes before it isdischarged into the environment.• Also referred to as effluent polishing.• The purpose of 30 treatment is to improve the 20 treated wasteby removing the nutrients and dissolved solids.• The major processes done are:– Filteration– Nutrient removal– Disinfection
• FILTERATION• Either sand or activated charcoal is used to filter treatedeffluent.• NUTRIENT REMOVAL• High levels of nutrients such as N2 & P must be removed –otherwise eutrophication.• Phosphorous removal• Phosphorous can be removed by Polyphosphate accumulatingorganisms (PAOs).• It can also be removed by chemical precipitation, usually withsalts of Fe, Al or lime.
• Nitrogen removal• In wastewaters, much of the nitrogen is found in the form ofammonia.• When secondary treatment is used, a great deal of this ammonia isdischarged in the effluent.• Bacteria can utilize this ammonia as an energy source and convertammonia to nitrite and nitrate.NH3 NO2 NO3• DISINFECTION• To kill micro – organisms present in water• Chlorination is the most common method.• UV light & ozone can also be used for disinfection.Nitrosomonas Nitrobacter
RECENT DEVELOPMENTS• New Wastewater Treatment System Removes HeavyMetals• Resulting from the combination of watertreatment investigations with the latest inmaterial science, a new type of nano materialcalled nano structured silica was foundto detect and eliminate heavy metals from wastewaters inefficient and economically viable ways.• This investigation has been published on the 2011 June releaseof Journal of Separation Science and Journal of ColloidInterface Science
CONCLUSION• Waste water treatment is done to remove contaminants fromwater.• It is broadly classified into primary, secondary and tertiarytreatments.• After going through all these processes, the water obtainedwill be hygenic & safe for discharging into the environment.
BIBLIOGRAPHY• Aloka Debi, Environmental Sience and Engineering (2008),University Press, Hyderabad• Chaudary D.S and Sundaravadivel M, Environmental management(2004), Scitech Publications, Chennai.• Madhab Chandra Dash and Satya Prakash Dash, Fundamentals ofEcology, 3rd edition, McGraw Hill Companies, New Delhi.• http://water.me.vccs.edu/courses/ENV108/lesson1_2.htm• http://www.fao.org/docrep/t0551e/t0551e05.htm