Activated Sludge Operation in the Extreme Conditions of MLSS, TDS, and Temperature

Three case studies of activated sludge operating at extreme conditions are presented. In case study #1, MBR treats pharmaceutical manufacturing wastewater with COD of 25 000 mg/L, TDS of 23 000 mg/L and high temperatures. Complete nitrification is achieved as long as TDS is kept under 20 000 (preferably 15 000) mg/L. The most striking feature of this installation is that it operates at very high MLSS concentrations, reaching up to 40 000 mg/L. Case study #2 discusses an MBR which is treating leachate from a municipal landfill with complete nitrification and partial denitrification. It operates at MLSS levels of 15 000 to 20 000 mg/L, influent COD/NH3-N of 4 000/1 000 mg/L and TDS of 15 000 to 20 000 mg/L. Elevated process temperatures (up to 108 deg F/42°C) are observed due to high energy mechanical equipment and heat of the biological reactions. Despite very high substrate concentrations, salinity and operating temperatures, essentially full nitrification and significant denitrification is being achieved. Case study #3 involves a conventional activated sludge plant with a secondary clarifier, treating ammonia, phenol and thiocyanate-rich wastewater from a coke manufacturing facility. Full nitrification, complete removal of phenol and 75% COD removal efficiency were typically achieved. The plant maintains as low an F/M ratio (high MLSS) as practical by operating with the sludge blanket close to the clarifier weir and with the resulting MLSS reaching 10 000 mg/L.