Grade 3 wastewater Guide Rated A+

Grade 3 wastewater Guide Rated A+ Svl Ans- How well activated sludge mls compact. Volume in milliliters occupied by 1 gram of activated sludge mixed liquor after 30 min of settling. Conventional activated sludge Ans- Mcrt 15 days, f-m .2-.4, org. Loading 20-40, mlss , aerator det. Time 4-8 hrs, return rate 25-50% Complete mix activated sludge Ans- Mcrt 5-15, f-m .2-.6, org. Loading 50-120, mlss , aerator det. Time 3-5, return rate 25-100% Step feed aeration activated sludge Ans- Mcrt 5-15, f-m .2-.4, org loading 40-60, mlss , aerator det time 3-5, return rate 25-75% Extended aeration activated sludge Ans- Mcrt 20-30, f-m .05-.15, org loading 10-25, mlss , aerator det time 18-36, return rate 75-150% Contact stabilization activated sludge Ans- Mcrt 5-15, f-m .2-.6, org loading 60-75, mlss - 10000, aerator det time .5-1 3-6, return rate 25-100% Disadvantages of conventional activated sludge Ans- 1) Aeration could not supply enough oxygen to biomass at beginning of tank. Caused filamentous growth and liquid solids separation in secondary clarifier. 2) biomass was vulnerable to toxins due to lack of dilution prior to the passing of the pre treatment act. Mcrt Ans- Most important aspect of activated sludge process in the operators control is the mean cell residence time. Mcrt fixes the growth rate of the microorganism in the mixed liquor. Which controls sludge quality. Also whether or not nitrification will occur. Nh3 Ans- Unionized form of ammonia . Highly toxic to fish and wild life. Nh4+ Ans- Ammonium Nh4+H+nh3 Ans- Ammonia and ammonium are in chemical equilibrium. Ammonia and ammonium in equilibrium Ans- The ph and temperature of the water will determine if there will be more nh3 or nh4+ Nitrification Ans- Biological oxidation of ammonia first to nitrite NO2 then to nitrate NO3. Uses AOB and NOB bacteria. AOB Ans- Ammonia oxidizing bacteria. Oxidize ammonia to nitrite. Ex. Nitrosomonas. AOB oxidize ammonia not ammonium. NOB Ans- Nitrite oxidizing bacteria. Oxidize nitrite to nitrate Ex Nitrobacter Nitrifiers Ans- AOB and NOB. Nitrifiers are slow growers. Longer mcrt is needed to allow nitrifiers to grow in activated sludge system. Growth rate of nitrifiers is temperature dependent. A longer mcrt is needed to support nitrification as the wastewater temperature decreases. They are strict aerobes. Very sensitive to DO concentration maintained in aeration basin. Nitrifiers start being inhibited below 1.5mg DO/L. Substantially inhibited below 1 mg DO/L and completely inhibited below .5mg DO/L Nitrification all or none Ans- Either mcrt is long enough to allow nitrifiers to populate the mixed liquor or it's not. When mcrt is long enough complete nitrification will occur if enough DO is provided. 1 lb ammonia-nitrogen oxidized during nitrification requires Ans- 4.6lbs oxygen Nitrification is required because Ans- Reduce toxicity from release of unionized ammonia. Reduce oxygen demand in receiving waters caused by nitrification. It's is the first step in nitrogen removal. Nitrification produces Ans- Makes acid which consumes alkalinity. This can cause drop in ph which can interfere with treatment process. Denitrification Ans- Reduction of nitrate to nitrogen gas. Facultative bacteria use nitrate ion as a source of oxygen. Operational problem of denitrification Ans- In secondary clarifier entrapped nitrogen gas causes sludge to float to the surface, potentially allowing solids to escape in effluent. This can happen when the activated sludge is not returned to the aeration basin quickly enough or if inadequate DO is present in the mixed liquor when it is discharged to the secondary clarifier. Second step in nitrogen removal Ans- Denitrification. Allows nitrogen gas to escape into the atmosphere. 3 conditions required for denitrification to occur Ans- Nitrate present (nitrification must occur first), no oxygen present, readily degradable BOD present. Nitrogen removal plants Ans- Denitrification typically carried out in anoxic zones before the aerobic zones in the aeration basins where the BOD is available. Nitrate is delivered to the anoxic zone in the RAS flow and when used the mixed liquor recycle flow abbreviated MLR. Polymers Ans- Long chain organic molecules called polyelectrolytes. Used in dafts, centrifuges, and belt presses to lower concentration of suspended solids. Cationic Ans- Positive electric charge Anionic Ans- Negative electrical charge Nonionic Ans- No electrical charge Coagulation Ans- Neutralization of electrical charges on sludge particles Flocculation Ans- Agglomeration of coagulated particles to form a heavier flocc Colloidal sludge particles Ans- Have negative electrical charge so a cationic polymer is used sludge thickening and dewatering Cept Ans- Anionic polymers used to enhance floccilulation of positively charged metal hydroxide precipitates Dry polymers Ans- Powders, granules, beads, or flakes, 90to95% active polymer; spills are a safety hazard due to the hydroscopic nature, after dissolving in water must be consitioned Emulsion polymers Ans- Clear to white, milky liquids, a dispersion of polymer particles in a hydrocarbon oil; 25 to 50 % active polymer; initial breaking of the emulsion and aging are critical for emulsion polymers. Mannich polymers Ans- Clear to milky liquids with high molecular weights; very high viscosity make them difficult to pump; active polymer content 2 to 10%; may have ph up to 12 which may lead to scale formation, relatively short shelf life; don't require pre wetti