METHODS FOR MEASURING NITRIFIER MAXIMUM SPECIFIC GROWTH RATE: CRUCIAL FOR PLANT CAPACITY RATING

摘要

Nitrification kinetics is one of the most important parameters in activated sludge process designrnand determines the necessary solids retention time (SRT) and aeration tank volume to meet anrneffluent ammonia-nitrogen (NH4-N) concentration goal. The necessary SRT is directly related tornthe maximum specific growth rate of the nitrifying bacteria (μmax), a key term in the Monodrngrowth kinetics equation. Reported values for μmax vary by a factor of five. In view of thernuncertainty about nitrification kinetics, methods are needed to provide site-specific assessmentsrnof nitrification kinetics for use in plant capacity evaluation and optimization. The purpose of thernwork reported here was to evaluate three different bench-scale methods for μmax determinations.rnThe three test methods are the Low F/M SBR, High F/M, and Washout test methods. The LowrnF/M method requires operating a sequencing batch reactor (SBR) for a time period equal to atrnleast three SRTs, followed by a series of batch nitrification rate tests using the SBR mixed liquor.rnIn the High F/M test, a small seed is placed in a reactor with a wastewater sample spiked withrnNH4-N and alkalinity, and exponential increase in nitrate and nitrite (NOx-N) concentrations isrnfollowed over about a 5-7 day period. For the Washout test, a nitrifying mixed liquor is placed inrna reactor fed with wastewater spiked with NH4-N and alkalinity and the reactor NH4-N andrnNOx-N concentrations are monitored with time over about a 5-7 day period. The feed rate to thernreactor is selected so that a low enough SRT exist and the nitrifying bacteria are washout out ofrnthe reactor over time. Tests were done with all these methods using wastewater from the Renton,rnWA. and Puyallup, WA. wastewater treatment plants. The model fitting methods to obtain maxrnfrom the data obtained for each method are presented, and the results of experiments to assessrnsome key operating variables for the Low F/M and High F/M methods are presented.rnAll three methods provide reliable μmax values from test data, and advantages and disadvantagesrnof using a particular method is presented. To obtain μmax values a value for the endogenousrndecay coefficient for nitrifying bacteria is critical. Tests at temperatures ranging from 12 to 220Crnfound a 200C specific endogenous decay coefficient of 0.17 g/g-d, with a temperature correctionrnfactor of 1.03. A temperature correction factor of 1.072 was obtained for μmax. Reports onrnnitrification kinetics must include both μmax and decay coefficient values.