Anoxic-oxic Activated Sludge Process Research Articles

Degradation of Nonylphenol Polyethoxylates and its Microflora Structure in an Anoxic-Oxic Activated Sludge Process

An anoxic-oxic activated sludge process (AOASP) was carried out to degrade nonylphenol polyethoxylates (NPEOs). The carbon source in influent was replaced stepwise by a mixture of nonylphenol decaethoxylate (M-NP10EO). The 2nd-derivative UV-spectrometry was applied to determine the total amount of M-NP10EO in water samples. Chemical oxygen demand (COD) removal efficiency achieves about 85% under the highest M-NP10EO loading rate, and M-NP10EO removal efficiency is about 80%. Denaturing gradient gel electrophoresis (DGGE) results of activated sludges show that the microbe species decrease but gradually stabilize with the increase of M-NP10EO concentration in influent. Fluorescence in situ hybridization (FISH) results of activated sludges showe that the dominant microflora under the highest M-NP10EO loading rate is β-Proteobacteria (35%), followed by α-Proteobacteria (15%), γ-Proteobacteria (5%) and Actinobateria (4%).

Experiments and theoretical analysis on optimal step ratio and volume allocation for the step-feed anoxic-oxic activated sludge process.

Experiments and theoretical analysis on optimal step ratio and volume allocation for the step-feed anoxic-oxic activated sludge process.

Effect of salinity on nitrous oxide emission in the biological nitrogen removal process for industrial wastewater

The effects of wastewater salinity on both nitrogen removal efficiency and N 2O emission rate were investigated in a single nitrification process, a single denitrification process and an anoxic–oxic activated sludge process. In the single nitrification process, by increasing the salt concentration from 1.0 to 2.0 wt%, the N 2O conversion ratio in the steady state increased by 2.2 times, from 0.22 to 0.48%. In the single denitrification process, a minimal change in the N 2O conversion ratio was observed in the steady state even when the salt concentration was increased from 3.0 to 5.0 wt%. From the results of the anoxic–oxic activated sludge process, it was found that a salt concentration increase from 1.6 to 3.0 wt% significantly increases the N 2O conversion ratio from 0.7 to 13%. It is suggested that an increase in salt concentration markedly influences N 2O emission both directly and indirectly via the inhibition of N 2O reductase activity. The indirect inhibition is due to the high concentration of dissolved oxygen which is transported from the oxic tank to the anoxic tank through the circulated liquid. Thus, the salt concentration should be maintained below 3.0% to suppress N 2O emission in an anoxic–oxic activated sludge process.

Effect of Step Feed Ratio and Temperature on Nitrogen Removal in an Anoxic-Oxic Activated Sludge Process.

『大阪大学大学院工学研究科環境工学専攻生物圏・水環境工学研究室 研究活動報告』, Vol.12(2000.4.1～2001.3.31), pp.105-113, 大阪大学大学院工学研究科環境工学専攻生物圏・水環境工学研究室, 2001.5 に掲載

生物学的嫌気好気活性汚泥法におけるＮ２Ｏ発生に及ぼすＳＲＴ，ＤＯの影響

Biological anoxic-oxic activated sludge process, which treated domestic wastewater, was investigated to examine the effects of SRT and DO on nitrogen removal and emission of N20, which is causing global warming. The results obtained were as follows: The greater part of N20 emission was observed through nitrification, that amounted to about 4.5 times as that through denitrification. Alternation of SRT or MLSS, to some extent, had no influence on N20 emission through denitrification in anoxic tanks, as far as the nitrogen removal was made effectively under appropriate nitrogen loading. The amount of N20 emitted through nitrification at the run of 10-days SRT reaced about twice as that at the run of 20-days SRT, which led to that enough SRT could suppress N20 emission through nitrification. Besides, keeping high nitrification efficiency was important for suppression of N20 emission. It was clarified that control of carrying DO into the anoxic tank by nitrified water could reduce N20 emission through denitrification in anoxic tanks.

Specific oxygen uptake, nitrification and denitrification rates of a zinc-added anoxic/oxic activated sludge process

The specific oxygen uptake rate (SOUR), specific nitrification rate (SNR) and specific denitrification rate (SDNR) of an anoxic-oxic activated sludge process fed with zinc-added synthetic wastewaters were investigated. Two different characteristics of synthetic wastewaters were used, i.e., 500 mg/l COD, 40 mg/l TKN and 10 mg/l P (representing normal COD load) for Model A while 3500 mg/l COD, 175 mg/l TKN and 25 mg/l P (representing high COD load) for Model B. The zinc doses varied from 0 (control) to 10, 25, 35 and 50 mg/l. When the two systems reached steady states, they were further shocked with 300 mg/l zinc for 4 consecutive days before returning to their initial conditions. The SRT and F/M ratio of both models were 10 days and 0.26-0.47 day−1, respectively. The endogenous SOURs of both models were not much affected by the increase of zinc concentration. They were about 7.5 to 10 and 9.4 to 11.5 mg O2/g MLSS-hr, for Models A and B, respectively. In Model A, as the zinc increased from 0 to 50 mg/l, the SNRs dropped from 4.0 to 1.4 mg NH4+-N /g MLSS-hr whereas the initial SDNRs fell from 19.6 to 5.3 mg NO3− /g MLSS-hr. Meanwhile, the SNRs of Model B were relatively constant (1.5-1.8 mg NH4+-N /g MLSS-hr) while the initial SDNRs dropped from 16.2 to 8.3 mg NO3− /g MLSS-hr. That is, under high COD load conditions, the zinc dose applied here did not significantly affect the carbon removing heterotrophs and nitrifiers while a slight effect was seen on the denitrifiers and significant retardation was observed for both nitrifiers and denitrifiers in case of normal COD load. During the shock period, the SNRs of Model A dropped to 0.67 to 1.26 mg NH4+-N /g MLSS-hr whereas the initial SDNRs decreased drastically to 1.5 to 3.0 mg NO3− /g MLSS-hr. The impact from the zinc shock in such circumstances was obviously higher on the denitrifiers than on the nitrifiers. In Model B, the SNRs were 0.77 to 1.5 mg NH4+-N /g MLSS-hr and the initial SDNRs were 2.9 to 6.18 mg NO3− /g MLSS-hr. Not much effect on nitrifiers was evident in this case. For Model A, the recoverability of the heterotrophs and the nitrifiers was not so good, while that of the denitrifiers was quite satisfactory. However for Model B, those recuperation abilities were comparable for all three organisms. The data therefore suggested that there may be some differences in the species domain between the carbon removing microorganisms and the denitrifiers, however, further investigations for confirmation are required.

Specific oxygen uptake, nitrification and denitrification rates of a zinc-added anoxic/oxic activated sludge process

The specific oxygen uptake rate (SOUR), specific nitrification rate (SNR) and specific denitrification rate (SDNR) of an anoxic-oxic activated sludge process fed with zinc-added synthetic wastewaters were investigated. Two different characteristics of synthetic wastewaters were used, i.e., 500 mg/l COD, 40 mg/l TKN and 10 mg/l P (representing normal COD load) for Model A while 3500 mg/l COD, 175 mg/l TKN and 25 mg/l P (representing high COD load) for Model B. The zinc doses varied from 0 (control) to 10, 25, 35 and 50 mg/l. When the two systems reached steady states, they were further shocked with 300 mg/l zinc for 4 consecutive days before returning to their initial conditions. The SRT and F/M ratio of both models were 10 days and 0.26–0.47 day−1, respectively. The endogenous SOURs of both models were not much affected by the increase of zinc concentration. They were about 7.5 to 10 and 9.4 to 11.5 mg O2/g MLSS-hr, for Models A and B, respectively. In Model A, as the zinc increased from 0 to 50 mg/l, the SNRs dropped from 4.0 to 1.4 mg NH4+-N /g MLSS-hr whereas the initial SDNRs fell from 19.6 to 5.3 mg N03− /g MLSS-hr. Meanwhile, the SNRs of Model B were relatively constant (1.5–1.8 mg NH4+-N /g MLSS-hr) while the initial SDNRs dropped from 16.2 to 8.3 mg NO3− /g MLSS-hr. That is, under high COD load conditions, the zinc dose applied here did not significantly affect the carbon removing heterotrophs and nitrifiers while a slight effect was seen on the denitrifiers and significant retardation was observed for both nitrifiers and denitrifiers in case of normal COD load. During the shock period, the SNRs of Model A dropped to 0.67 to 1.26 mg NH4+-N /g MLSS-hr whereas the initial SDNRs decreased drastically to 1.5 to 3.0 mg NO3− /g MLSS-hr. The impact from the zinc shock in such circumstances was obviously higher on the denitrifiers than on the nitrifiers. In Model B, the SNRs were 0.77 to 1.5 mg NH4+-N /g MLSS-hr and the initial SDNRs were 2.9 to 6.18 mg NO3− /g MLSS-hr. Not much effect on nitrifiers was evident in this case. For Model A, the recoverability of the heterotrophs and the nitrifiers was not so good, while that of the denitrifiers was quite satisfactory. However for Model B, those recuperation abilities were comparable for all three organisms. The data therefore suggested that there may be some differences in the species domain between the carbon removing microorganisms and the denitrfiers, however, further investigations for confirmation are required.

Theoretical analysis on nitrogen removal of the step-feed anoxic-oxic activated sludge process and its application for the optimal operation

The nitrogen removal efficiency of the step-feed anoxic-oxic activated sludge process, which has two anoxic tanks and two oxic tanks, was theoretically discussed on the basis of the stoichiometry of denitrification and nitrification reactions. As the first step, effluent NH4-N and NO3-N concentrations were formulated with four parameters; 1) a, equivalent ratio of alkalinity to ammonia in influent, 2) b, that of substrate to ammonia, 3) r, step ratio of influent to the second anoxic tank and 4) R, return (+ recycle) sludge ratio. This calculus was done for the possible sixteen (=24) cases which show different reaction patterns in four tanks, and 12 cases out of 16 were found to be available. The effects of step ratio, r were examined in its range of 0 - 1 at a fixed R value, and it was found that the increase of r alters the outcome in a different way depending on the ranges of a and b. Consequently, zoning of a-b coordinates was successfully made, and the optimal r value for maximum total nitrogen removal was obtained in each zone. In addition, the optimal volume allocation of the four tanks was discussed and the ratios were formulated for each zone.

Theoretical analysis on nitrogen removal of the step-feed anoxic-oxic activated sludge process and its application for the optimal operation

The nitrogen removal efficiency of the step-feed anoxic-oxic activated sludge process, which has two anoxic tanks and two oxic tanks, was theoretically discussed on the basis of the stoichiometry of denitrification and nitrification reactions. As the first step, effluent NH4-N and NO3-N concentrations were formulated with four parameters; 1) a, equivalent ratio of alkalinity to ammonia in influent, 2) b, that of substrate to ammonia, 3) r, step ratio of influent to the second anoxic tank and 4) R, return (+ recycle) sludge ratio. This calculus was done for the possible sixteen (=24) cases which show different reaction patterns in four tanks, and 12 cases out of 16 were found to be available. The effects of step ratio, r were examined in its range of0 – 1 at a fixed R value, and it was found that the increase of r alters the outcome in a different waydepending on the ranges of a and b. Consequently, zoning of a-b coordinates was successfully made, andthe optimal r value for maximum total nitrogen removal was obtained in each zone. In addition, the optimal volume allocation of the four tanks was discussed and the ratios were formulated for each zone.

Anoxic–oxic activated‐sludge of cyanides and phenols

The anoxic-oxic activated-sludge process has been evaluated in a laboratory investigation as a means for effective treatment of cyanide-laden wastewaters, with phenols used as the organic carbon sources for denitrification reactions. The performance of the process was evaluated at different levels of feed cyanide concentration and mean cell residence time (MCRT). The results obtained indicate that the phenolic compounds used can be effectively used as the organic carbon sources to promote denitrification reactions. The effects of cyanide inhibition on overall TOC removal can be alleviated at longer MCRTs. Between 1.2 and 2.2 g TOC can be utilized per gram NO(2) + NO(3) (-) -N removed in the anoxic chamber depending on the prevailing MCRT. Microbial oxidation of cyanide and thiocyanate which yields ammonia is the main mechanism responsible for the removal of cyanide and thiocyanate observed in the anoxic-oxic activated-sludge process. Excellent removal efficiencies have been observed with feed concentrations up to 60 mg CN(-)/L and 100 mg SCN(-)/L Frequent exposure of autotrophic and aerobic cyanideutilizing microbes does not impede their activities in the oxic environment. Good nitrification and denitrification efficiencies are attainable in the anoxic-oxic activated-sludge process in the presence of high feed cyanide and thiocyanate concentrations, provided that MCRT is maintained at a desirable level. As a result, the microbial degradation of cyanide and thiocyanate in conjunction with nitrification and denitrification to produce innocuous nitrogen gas is feasible in the anoxic-oxic activated-sludge process.