[Effects of different co-substrates on degradation of nitrophenols using upflow anaerobic sludge bed (UASB) reactors].

The removal efficiencies of 3-nitrophenol (3-NP) and 2, 6-dinitrophnol (2, 6-DNP) were investigated in two lab-scale upflow anaerobic sludge bed (UASB) reactors using two different co-substrates. Initially, glucose was used as co-substrate and followed by sodium acetate. The results showed that glucose was found to be a better co-substrate for 3-NP degradation compared to sodium acetate. While for the degradation of 2,6-dinitrophenol, sodium acetate was better. For the study of 3-NP degradation, input COD concentration was kept as 2,500 mg/L and hydraulic retention time (HRT) was kept as 26 h with glucose as co-substrate. Maximum 3-NP concentration was 254.6 mg/L and 3-NP removal efficiencies were always more than 99.0%. While HRT was 30 h with sodium acetate as co-substrate, maximum 3-NP concentration was 71.6 mg/L and over 90.0% 3-NP removal efficiencies could be obtained. For the study of 2,6-DNP degradation, HRT was 35 h using the same input COD concentration as 3-NP degradation. The maximum 2,6-DNP concentration was 170.0 mg/L and 2,6-DNP removal efficiencies were always more than 98.0% using glucose as co-substrate. While HRT was 30 h with sodium acetate as co-substrate, maximum 2,6-DNP concentration was 189.5 mg/L and over 99.2% 2,6-DNP removal efficiencies could be 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.

[Study on 3-nitrophenol wastewater treatment in UASB].

Characteristics of anaerobic granules before and after acclimation, removal efficiencies of 3-nitrophenol (3-NP) and performance of 3-NP wastewater treatment were investigated in a lab-scale upflow anaerobic sludge bed (UASB). The results showed that granular sludge acclimatized to 3-NP rapidly during acclimation. Using SEM, the filamentous bacteria was the predominant bacteria on the surface of granules. Throughout the study of 3-NP wastewater anaerobic degradation, hydraulic retention time (HRT) and input COD concentration were kept constant as 26 h and 2 500 mg/L, respectively. While 3-NP concentrations increasing from 20 mg/L to 250 mg/L gradually, COD removal decreased from 95.2% to 85.1% and 3-NP removal efficiencies were always more than 99%. 3-AP was found to be the major intermediate during the degradation of 3-NP. Out of the total input of 3-NP concentration, on molar basis, about 58.7% - 111.9% of 3-NP was recovered in the form of 3-AP. With increasing 3-NP concentration, the variations of gas production were minimal. The minimum methane percentage was 65% and the maximum was 74%.

[Anaerobic biodegradation of nitrophenols with glucose as co-substrate].

A batch anaerobic test was conducted to examine the biodegradation of 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,6-dinitrophenol through measuring accumulative methane production. The Relative activity values were used to judge the inhibition level of nitrophenols on methanogenic bacteria. The test conditions was as follow: glucose was used as co-substrate and the temperature is 35 degrees C. It didn't cause inhibition when concentrations of 2-nitrophenol, 4-nitrophenol, 2,6-dinitrophenol and 2,4-dinitrophenol were below 24mg/L, 20mg/L, 12mg/L and 4mg/L respectively. Slight inhibition was caused when concentrations of 4-nitrophenol and 2,6-dinitrophenol were 24mg/L and 16mg/L-24mg/L respectively. Middle inhibition when concentrations of 2,4-dinitrophenol were 8mg/L-24mg/L was observed. The inhibition level was 2,4-dinitrophenol > 2,6-dinitrophenol > 4-nitrophenol > 2-nitrophenol.