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- NITRIFICATION
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- Nitrification is the process by which we consider ammonia and
- organic nitrogen specifically, being broken down to nitrate
- nitrogen. The form of nitrogen that is in raw sewage may be
- biologically oxidized to nitrate after the carbonaceous oxygen
- demand is met. Nitrification can be accomplished in a seperate
- second stage of treatment (after carbonaceous treatment) or
- accomplished along with carbonaceous treatment.
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- The degree of nitrification is wholly dependent upon solids
- retention time under aeration. Temperature and pH are other
- important factors. Temperature will affect carbonaceous treatment
- by speeding up metabloism and rate of synthesis thereby
- accomplishing carbonaceous stabalization quicker and decreasing the
- overall time needed for nitrification. In hot climates, processes
- have been documented as going into nitrification in as little as
- three days solids retention time...but on the average, a retention
- time of 10 days at 18°C is considered a mean retention time to
- accomplish nitrification. A minimum loading rate of .25 lbs of BOD
- per day per lb of MLVss (F/m) is considered necessary to accomplish
- nitrification. A pH of 8.5 is considered optimum for nitrification
- while at lower pH's the decrease in efficiency of Nitrogen
- conversion is significantly reduced. At pH 7.0, nitrogen
- conversion can be less than 50% of what it would be at pH 8.5 for
- instance. A similar relationship exists with temperature where at
- 10°C, the rate of nitrogen conversion is about half as it is at
- 20°C. Oxygen demand is greatly increased to accomplish
- nitrification.
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- TROUBLE GUIDE
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- ┌───────────────────────────────────────────────────────────────────┐
- │ indicators/observations│ cause │ check │ solution │
- ├────────────────────────┼─────────────┼───────────┼────────────────┤
- │1.decrese in nitrifi- │1a.need more │1a.akalin- │1a.if alkalinity│
- │ cation pH with loss │alkalinity; │ity in eff.│is less than │
- │ of nitrification │acidic levels│of aerator │30 mg/l start │
- │ │1b.addition │1b.raw │addition of lime│
- │ │of acidic │pH and alk.│or NaOH. │
- │ │wastes to │ │1b.control │
- │ │sewer │ │source of dump. │
- ├────────────────────────┼─────────────┼───────────┼────────────────┤
- │2.inability to complete-│2a.low oxygen│2a.D.O. min│2a.increase │
- │ ly nitrify │2b.low temp. │ should be │ oxygen supply │
- │ │2c.increase │ >1.0 ppm │ or decrease │
- │ │ in infl. BOD│2b.therm. │ MLss. │
- │ │ loading. │2c.infl. │2c.decrease │
- │ │2d.activated │ levels of │ raw flow into │
- │ │sludge too │ BOD │ aeration tank │
- │ │low(MLVss) │2d.SRT │ or increase │
- │ │2E.Peak NH4 │should be │ MLss │
- │ │ concentra- │>10 days in│2d.add tankage │
- │ │ tions exceed│temperature│for aeration; │
- │ │ available │less than │increase SRT; │
- │ │ oxygen. │18°C. │ pretreat raw │
- │ │ │ │(air stripping │
- │ │ │ │or chlorination)│
- ├────────────────────────┼─────────────┼───────────┼────────────────┤
- │3.Loss of solids from │3.if not │3.hydraulic│3.increase │
- │ final clarifier │hydraulic │flows and │return rates; │
- │ │or mechanic- │clarifier │decrease SRT; │
- │ │al then due │design load│increase raw │
- │ │to denitrifi-│check set- │flow; create │
- │ │cation │tleometer │anoxic zone in │
- │ │ │testing for│aeration. │
- │ │ │gas pockets│ │
- │ │ │clumps, or │ │
- │ │ │inverting │ │
- │ │ │sludge in a│ │
- │ │ │short time │ │
- ├────────────────────────┼─────────────│───────────│────────────────┤
- │4.in a two stage system │4.Nitrifica- │4.Nitrates │4.Transfer │
- │SVI of nitrified sludge │tion is occu-│in first │sludge from │
- │is very high │ing in first │stage │first stage reac│
- │ │stage reactor│ │tor to second │
- │ │ │ │stage reactor │
- │ │ │ │and lower SRT │
- │ │ │ │in first reactor│
- └────────────────────────┴─────────────┴───────────┴────────────────┘
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- Denitrification
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- Denitrification is accomplished by allowing oxygen levels to
- fall into faculative conditions whereupon anaerobes and
- faculative bacteria will be forced to obtain oxygen from the
- converted nitrates(NO3) and nitrites(NO2) that are the products of
- nitrification. This releases the nitrogen from the nitrite form
- as nitrogen gas. This can cause problems if this happens while in
- a clarifier as the nitrogen gas will cause the sludge blanket to
- rise to the surface and cascade over the clarifier weirs. Anoxic
- zones can be created in aeration bays or holding tanks where the
- oxygen is held to very low levels creating the faculative
- conditions that will allow the sludge to denitrify before
- entering the clarifier. Care needs to be taken in such anoxic
- zones that detention times do not carry the activated sludge into
- septic conditions.
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