Study on the aerobic biodegradability and degradation kinetics of 3-NP; 2,4-DNP and 2,6-DNP.

Four biodegradability tests (BOD(5)/COD ratio, production of carbon dioxide, relative oxygen uptake rate and relative enzymatic activity) were used to determine the aerobic biodegradability of 3-nitrophenol (3-NP), 2,4-dinitrophenol (2,4-DNP) and 2,6-dinitrophenol (2,6-DNP). Furthermore, biodegradation kinetics of the compounds was investigated in sequencing batch reactors both in the presence of glucose (co-substrate) and with nitrophenol as the sole carbon source. Among the three tested compounds, 3-NP showed the best biodegradability while 2,6-DNP was the most difficult to be biodegraded. The Haldane equation was applied to the kinetic test data of the nitrophenols. The kinetic constants are as follows: the maximum specific degradation rate (K(max)), the saturation constants (K(S)) and the inhibition constants (K(I)) were in the range of 0.005-2.98 mg(mgSS d)(-1), 1.5-51.9 mg L(-1) and 1.8-95.8 mg L(-1), respectively. The presence of glucose enhanced the degradation of the nitrophenols at low glucose concentrations. The degradation of 3-NP was found to be accelerated with the increasing of glucose concentrations from 0 to 660 mg L(-1). At high (1320-2000 mg L(-1)) glucose concentrations, the degradation rate of 3-NP was reduced and the K(max) of 3-NP was even lower than the value obtained in the absence of glucose, suggesting that high concentrations of co-substrate could inhibit 3-NP biodegradation. At 2,4-DNP concentration of 30 mg L(-1), the K(max) of 2,4-DNP with glucose as co-substrate was about 30 times the value with 2,4-DNP as sole substrate. 2,6-DNP preformed high toxicity in the case of sole carbon source degradation and the kinetic data was hardly obtained.

[Anaerobic degradation kinetics of 2,4-dinitrophenol].

With glucose as co-substrate, anaerobic degradation kinetics of 2,4-dinitrophenol (2,4-DNP) were investigated in batch culture. The results show that 2,4-DNP and glucose can be degraded by the bacteria simultaneously. Although the effect of COD on 2,4-DNP degradation was minimal, addition of 2,4-DNP effected COD degradation obviously. The rate of 2,4-DNP degradation increased with increasing initial 2,4-DNP concentrations up to 225 mg/L. Further increase in initial 2,4-DNP concentrations caused decrease in the rate of degradation because of substrate inhibition. Uncompetitive inhibition equation is proposed to describe the degradation of 2,4-DNP. With non-linear regression technology, the kinetic model parameter q(max), K(s) and K(i) are found to be 3.24 mg/(h x g), 196.23 mg/L and 165.91 mg/L respectively. The experimental data verification for the model equation is satisfactory.