The Exploration Of Single-stage Autotrophic Nitrogen Removal In A SBBR System By Microcalorimetry

Single-stage autotrophic denitrification process in a steady SBBR reactor was investigated by microcalorimetry with RD496-2000 microcalorimeter (Mianyang CP Thermal Analysis Instrument Co.LTD of China academy of engineering physics). Under the given conditions, the activated sludge, originally withdrawn from the SBBR reactor and put in the reacting container of the microcalorimeter, underwent a series of biochemical reactions. The concomitant heat effect was recorded as thermograms by which the mechanism of single-stage autotrophic denitrification process was interpreted in thermal sense through the construction of thermodynamic models.The flow rate and pressure of the gas from the gas supply system was fixed at 6ml/min and 0.06MPa respectively. Under the controlled condition, the activated sludge in the reacting container was well mixed with nutrient solution. The sensitivity, S of the microcalorimeter fluctuates slightly with the varying environment. Under the operational condition, the value of S was test to be 63uv/mW. The nutrient solution was added into the reacting container with a syringe. Within a confidence interval of 95%, the error of the results was <10%.The results showed not all the NH4+-N introduced into the activated sludge in the reacting container participated the autotrohic nitrogen removal process; some still existed in the system in other nitrogen form. The enthalpy variance between the tested value and that calculated according to SHARON-ANMMOX process was not significant. Meanwhile, the nitrogen removal rate determined by thermogram was close to the measured value. It was noticed from the thermograms that NO2--N and NH2OH-N did appeared as inevitable intermediates in the course of nitrogen removal. In the autotrophic nitrogen removal system, N is recycled among NH4+-N, NO2--N and NH2OH-N.The thermogram obtained with NH4+-N addition was researched with restrictive microbial metabolic exponential model and generalized logistic growth thermal dynamic model. The thermogram was divided into heat accumulation stage and heat dissipation stage indicating with different ks of the restrictive microbial metabolic exponential models. The amplitude of heat variation k was 0.0095 (>0) in heat accumulation stage; wheras k was -0.0017 (<0) in the heat dissipation stage. The absolute value of k reflected the rate of heat change, corresponding with the slope of thermogram curve. In generalized logistic growth thermal dynamic model, heat accumulation and dissipation stages were incorporated in one expression. The bacteria metabolic rate constant K indicates the activity of the micro-organisms in the system. In this study, K was 0.0032, exhibiting a relatively active system and a heat increasing trend. Fortunately, the indicator of substrate degradation degree, v of -0.8375 was very close to its upper limit, -1. In the form of percentage, v was 83.75%, in good agreement with the tested NH4+-N removal rate, around 90%.According to the results, it is feasible to realize effective and convenient manipulation of single-stage autotrophic nitrogen removal in a SBBR system without the conventional approach of trival and time-consuming materials detection by microcalorimetry. On-line thermogram is promising in waste water field. How to analyze a thermogram of coupled miscellaneous biochemical reactions is still to be further investigated.