From a satellite image, the planet earth looks like a blue pearl --- more than 70 percent of the planet is composed of water.
Ironically, only 2.5 % of the world’s water is fresh, with a mere 0.3 % available from rivers, lakes and reservoirs
Unfortunately, the number of people with access to clean water for drinking and sanitation is decreasing rapidly due to a number of factors
Each year, roughly 450 cubic kilometres of waste water is discharged into rivers, streams and lakes
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.
By 2025, there will be 48 countries and by 2050 there will be at least 54 countries facing this phenomenon Water Stress.
Economic growth in most of the world has been so vigorous that nearly all new development activity creates stress on the “Pollution carrying capacity" of the environment.
Many hydrological systems in developing regions are, or are getting close to, being stressed beyond repair.
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.
Lowering of groundwater tables , irreversible pollution of surface water and associated changes in public and environmental health are typical manifestations of this kind of development.
Technology, particularly in terms of performance and available waste-water treatment options, has developed in parallel with economic growth.
However, technology cannot be expected to solve each pollution problem.
Typically, a Wastewater treatment plant transfers 1 m3 of wastewater into 1-2 litres of concentrated sludge.
Wastewater treatment systems are generally capital-intensive and require expensive, specialised operators
Other benefits No odor regeneration was discerned over the first 28 days after storage of aerobically treated manure (2.4 days). Aerobic treatment can reduce odor emissions from land spreading operations up to 90%.
HYDRAULIC RETENTION TIME (HRT) HRT = VOLUME/ FLOW RATE (V/Q) THE RESIDENCE TIME FOR THE LIQUID FRACTION IN THE BIO – REACTOR SOLID RETENTION TIME (SRT) SRT= THE RATIO OF AMOUNT OF BIOMASS WITHIN THE SYSTEM TO THE GROWTH RATE OF NEW MICROORGANISM
Biological Kinetics Equations, 0C.QY(S0—S) V = _______________ , X(1+kd.0c) where V = Volume of the reactor, S0 = Influent Soluble BOD5, S = Effluent Soluble BOD5, Q = Influent wastewater flow rate,m3/D0c 0c = Mean Cell residence time based on solids,(d),adopted for design controls quality, Settleability & drainability of Biomass, O2 requirement & quantity of waste activated sludge. kd = ENDOGENOUS DECAY COEFFICENT,d-1 (0.06/d) for Municipal waste wter Y =Yield Coefficent over finite period of log growth, g/g (0.5) X = MLSS, Conc., mg/l The volume of the aeration tank is calculated for the selected value of 0c by assuming a suitable value of MLSS Conc
OR, ALTERNATIVELY, the tank capacity may be designed from the F/M & MLSS Conc. F/M = Q S0 / XV
BY THE SLUDGE RECIRCULATION RATE & THE SLUDGE SETTLEABILITY AND THE THICKENING IN THE SECONDARY SEDIMENTATION TANK.
THE SLUDGE SETTLEABILITY IS DETERMINED BY THE SLUDGEVOLUME INDEX (SVI)
IS DEFINED AS THE VOL. in mm OCCUPIED BY 1 gm OF A ACTIVATED SLUDGE MIXD LIQUER SOLIDS ( dry wt.) AFTER SETTLING FOR 30m IN 1000 ml GRADUATED CYLINDER.
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
LATEST BIOLOGICAL TREATMENTS Fixed media attached growth Process
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,
Attached growth aeration process with some suspended growth as well
ADVANTAGECompactness, Process Simplicity Biomass stability Best for Retrofit/ upgradtation of Existing plant Roughing or Polishing Trratment for Strong Industrial Plant
Suspended Growth Process - The Sequential Batch Reactor (SBR)
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.
Sequencing Batch Reactor (SBR) • Type of activated sludge process • Five steps • Fill • React (aeration) • Settle • Draw (decant) • Idle •Example – Duke