10. Ironically, only 2.5 % of the world’s water is fresh, with a mere 0.3 % available from rivers, lakes and reservoirs
11. Unfortunately, the number of people with access to clean water for drinking and sanitation is decreasing rapidly due to a number of factors
12. Each year, roughly 450 cubic kilometres of waste water is discharged into rivers, streams and lakes
13. According to a development report by the United Nations, every human being needs to consume 20-50 litres of freshwater, free of contaminants, each day.
14.
15. Many hydrological systems in developing regions are, or are getting close to, being stressed beyond repair.
16. Industrial pollution, uncontrolled domestic discharges from urban areas, diffuse pollution from agriculture and livestock rearing, and various alterations in land use or hydro infrastructure may all contribute to non-sustainable use of water resources, eventually leading to negative impacts on the economic development of many countries or even continents.
51. Additional microorganismsIn any biological treatment system there will be an accumulation of microbial and non-biodegradable solids that need to be managed and disposed properly
90. OR, ALTERNATIVELY, the tank capacity may be designed from the F/M & MLSS Conc. F/M = Q S0 / XV
91.
92. TYPICAL SUSPNDED SOLIDS MASS BALANCE FOR RETURN SLUDGE CONTROL S AERATION TANK SECONDARY CLARIFIER Q S0 X0 V Q+Qr X ____________________________________________________________________________ QeXe Qr, Xr Q*w,Xr Schematic Diagram of Activated-Sludge Process the Mass balance around the settling tank is as follows :-- Accumulation = Inflow -- Out flow = X ( Q + Qr) - Qr.Xr- Xr Q*w , Qr = XQ –XrQ*w Xr - X
94. Membrane Bioreactors •Suspended growth – similar to activated sludge •Two parts – biological unit and membrane filter •High effluent quality BOD<5 mg/L, TSS<5 mg/L •Greater potential for removal of endocrine disruptingchemicals, pharmaceuticals,
101. Sequencing Batch Reactor (SBR) Cyclic processes of fill, react, settle, effluent removal, and idle are controlled by time to achieve objectives. Short aerating/non-aerating periods at a HRT = 10 days resulted in removals of COD (93%), SS (98%), and all NH3 converted to NO3.
102. Sequencing Batch Reactor (SBR) • Type of activated sludge process • Five steps • Fill • React (aeration) • Settle • Draw (decant) • Idle •Example – Duke
103.
104. Rotating Biological Contactors •Aerobic system •Series of closely spaced circular disks rotate -submerged in wastewater •Reliable - withstand hydraulic and organic surges •Low energy costs •Potential mechanical failure
116. Amount of oxygen Removal of odor Oxygen demand = 1/2 to 1/3 BOD Removal of organic matter Oxygen demand = BOD Removal of nutrients Oxygen demand = BOD + NH3-N
117.
118. Floating aerators provide continuous aeration.
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