Toxicity reduction of municipal wastewater by anaerobic-anoxic-oxic process.

OBJECTIVE: This study was conducted to optimize the operational parameters of anaerobic-anoxic-oxic (A²/O) processes to reduce the toxicity of municipal wastewater and evaluate its ability to reduce toxicity. METHODS: A luminescent bacterium toxicity bioassay was employed to assess the toxicity of influent and effluent of each reactor in the A²/O system. RESULTS: The optimum operational parameters for toxicity reduction were as follows: anaerobic hydraulic retention time (HRT) = 2.8 h, anoxic HRT = 2.8 h, aerobic HRT = 6.9 h, sludge retention time (SRT) = 15 days and internal recycle ratio (IRR) = 100%. An important toxicity reduction (%) was observed in the optimized A²/O process, even when the toluene concentration of the influent was 120.7 mg·L⁻¹. CONCLUSIONS: The toxicity of municipal wastewater was reduced significantly during the A²/O process. A²/O process can be used for toxicity reduction of municipal wastewater under toxic-shock loading.

Determination of textile dyeing wastewater COD components by comparison with respirometry and full-scale data.

A Modified Activated Sludge Model No. 1 (M-ASM1), including six COD components (S1, S(S), X1, X(S), X(H), and S(O)) and three biochemical processes (aerobic growth of heterotrophs, aerobic decay of heterotrophs and hydrolysis of entrapped organics) was used to simulate the anaerobic hydrolysis-aeration-sedimentation treatment series in a full-scale textile dyeing wastewater treatment plant (WWTP) with an influent flow rate of 200,000 m3/d. Using a respirometry method, the influent COD components of the WWTP activated sludge system were estimated. Then, calibration equations were set up depending on the full-scale treatment plant running data in order to calibrate the measurement results. This paper indicates that the influent COD components of a low biodegradability wastewater can be estimated using a respirometry method coupled with a calibration procedure based on full-scale plant running data.

Simultaneous nitrogen and phosphor removal in an aerobic submerged membrane bioreactor.

Simultaneous nitrification and denitrification (SND) effect and phosphor removal were investigated in a one-staged aerobic submerged membrane bioreactor on pilot-scale with mixed liquor suspended solids (MLSS) 19-20 g/L. The effects of DO concentration, sludge floc size distribution on SND were studied. Test results suggested that SND was successfully performed in the membrane bioreactor (MBR) and about 70% total nitrogen removal efficiency was achieved when DO concentration was set to 0.2-0.3 mg/L. The main mechanisms governing SND were the suitable sludge floc size and the low DO concentration which was caused by low oxygen transfer rate with such a high MLSS concentration in the MBR. In the meantime, phosphor removal was also studied with polymer ferric sulfate (PFS) addition and 14 mg/L dosage of PFS was proper for the MBR to remove phosphor. PFS addition also benefited the MBR operation owing to its reduction of extracellular polymer substances (EPS) of mixed liquor.

Biodegradation kinetic of organic compounds of acrylic fiber wastewater in biofilm.

A group function relation curve between flux (J) and bulk phase concentration of substrate (S) was set up. The biodegradation kinetic of organic compounds of acrylic fiber wastewater in biofilm is studied (the treatment technology is coagulation/sedimentation-anoxic/aerobic biofilm process), and the results showed that the concentration of non-degradation pollutants in effluent is 77 mg/L. In aerobic zone, the half-rate constant is 72.84 mg/L, the maximum removal rate of organic compounds at unit area filler is very low, 0.089 g/(m2 x d), which corresponds to the fact that there are some biorefractory compounds in the wastewater.

[Mechanisms of the improvement in dewaterability of alkaline fermented sludge by simultaneous ammonium and phosphate recovery].

Simultaneous ammonium and phosphate recovery could notably improve the dewaterability of alkaline fermented sludge, the mechanisms of which, however, remains unclear at present. The influence of zeta potential, divalent ions, extracellular polymeric substances (EPS), dissolved polymers and struvite were studied in batch experiments. Under the optimal ammonium and phosphate recovery condition [i. e. pH =10.0, n(P)/n(N) = 1.3 mol x mol(-1), n(Mg)/n(N) = 1.9 mol x mol(-1)], it was found that magnesium ion could not only decrease the absolute value of zeta potential to 14 mV, but also reduce the monovalent to divalent ions ratio to 9 mol x mol(-1), which promoted the dewaterability of alkaline fermented sludge; also, the dissolved polymers and EPS, especially the dissolved protein and the loosely bound EPS, reduced remarkably. Results showed that all the factors above promoted sludge dewatering. Furthermore, the struvite formed during ammonium and phosphate recovery improved the dewaterability.

[Activated sludge model based COD fractionation in wastewater characterization].

The successful application of activated sludge model (ASM) in wastewater treatment plant mainly depends on the correctness of wastewater fractionation. Based on three batch oxygen uptake rate (OUR) tests, a COD fractionation protocol and the corresponding Matlab program were developed to aid the standardization of COD fractionation in wastewater. COD fractionation results of two wastewater treatment plants (WWTP) in Shanghai show that COD in wastewater of the Quyang WWTP is composed of 8.1% +/- 1.6% readily biodegradable COD (S(s)), 6.3% +/- 2.2% soluble inert COD (S(I)), 45.5% +/- 3.5% slowly biodegradable COD (X(S)), 31.1% +/- 2.1% particulate inert COD (X(I)) and 9.0% +/- 1.1% heterotrophic biomass (X(H)), and those fractions in wastewater of the Bailonggang WWTP are 11.1% +/- 2.2%, 9.9% +/- 2.0%, 38.9% +/- 10.7%, 23.3% +/- 9.8% and 16.9% +/- 1.8%, respectively. Compared to the Quyang WWTP, wastewater of the Bailonggang WWTP showed lower X(S) and X(I) contents in COD, but greatly higher X(H)/COD value, indicating that long pipeline transportation could significantly influence the concentration of COD fractions.

[Relationship between typical organic matters in domestic wastewater and water characteristic parameters in activated sludge models].

The contribution of typical organic matters such as proteins, sugars, lipids and linear alkylbenzene sulfonate (LAS) to COD of the domestic wastewater was investigated. Nitrate utilization rate was used to determine wastewater characteristic parameters. Relationship between these typical organic matters and wastewater characteristic parameters (Ss, Xs, SI, XI) in activated sludge models were investigated. The results showed that YH of activated sludge under denitrifying conditions was 0.683. Proteins, sugars, lipids and LAS accounted for 24%-35%, 17%-35%, 5.78%-10.56% and 3.77%-7.23% of the total COD, respectively. It indicated that these four pollutants were the main COD source in the domestic wastewater. SS and XI were in the ranges of 22%-29% and 29%-38% of the total COD, respectively. Concentrations of the four typical target organic matters (proteins, sugars, lipids and LAS) correlated well with the wastewater characteristic parameters (Ss, Xs, SI, XI) of activated sludge models (ASMs) with the correlative coefficients above 0.9.

[Fractionation of soluble COD in wastewater based on batch respirometric method].

A fractionation protocol of soluble COD (SCOD) was put forward by combining respirometric method with hydrolysis kinetics of soluble slowly biodegradable COD (S(H)). SCOD fractionation results of two wastewater treatment plants (WWTP) in Shanghai show that the SCOD in sand basin effluents (typical domestic wastewater) of WWTP A is composed of 43.5%-58.6% S(H), 21.8%-35.2% readily biodegradable COD (S(S)) and 15.4%-30.9% soluble inert COD (S(I)), and those SCOD fractions in sand basin effluents (combined sewers after long pipeline transportation) of WWTP B are 34.5%-45.2%, 29.3%-37.7% and 25.6%-31.2%, respectively. The linear regression results of respirometric tests data from nine samples demonstrate that the first-order kinetics can reliably describe hydrolysis process of S(H), and the kinetic constants of S(H) from WWTP A and B are respectively 28.00-39.77 d(-1) and 26.48-29.52 d(-1). Experimental results demonstrate that this protocol can achieve theoretical partition for the integration area of S(S), and also eliminate the effect of soluble microbial products on S(I) determination.

[Biological nitrogen and phosphorus removal in the anaerobic-aerobic-anoxic-aerobic-anoxic-aerobic sequencing batch reactors].

The biological nitrogen and phosphorus removal was investigated in two anaerobic-anoxic-aerobic sequencing batch reactors (SBRs), which were fed with synthetic and municipal wastewater, respectively. The operating cycle of (AO)3 SBR was 1.5 h anaerobic --> 1 h aerobic --> 1 h anoxic -->20 min aerobic --> l h anoxic --> 20 min aerobic. The removal efficiency of COD, total nitrogen and total phosphorus for synthetic wastewater was 88%, 89%, 99%, respectively, while it was 85%, 75% , 99.5% for municipal wastewater. Furthermore, it was observed that though there were much differences in polyhydroxyalkanoates (PHAs) accumulation and phosphorous release in the anaerobic stage between two SBRs, the ratio of the anoxic energy production efficiency to the aerobic one was close to each other (49% versus 50%).

[Sorption and degradation of 17beta-estradiol to anoxic activated sludge].

Batch experiments were conducted to investigate the sorption isotherms and degradation kinetics of 17beta-estradiol (E2) at a low levels (microg/L) by anoxic activated sludge. The effects of temperatures and the concentrations of electron acceptor on the sorption and degradation were also investigated. Results showed that, when the initial concentrations of E2 were 5-15 microg/L, E2 was completely degraded after 2 h under anoxic conditions. Anoxic degradation of E2 in the activated sludge can be described by first-order reaction kinetics. During degradation, E2 sorption was well correlated by both Freundlich and linear adsorption isothermal model at different temperatures. The biodegradation behavior was inside the sludge phase. The transfer of the compound between the water phase and the sludge phase followed a linear adsorption isotherm. Temperature exerted significant effects on both the sorption and degradation of E2. The increase of temperature enhanced the E2 biodegradation rate but decreased E2 adsorption capacity on the sludge. The first-order reaction constants for E2 anoxic degradation at the temperatures of 10, 20 and 30 degrees C were 2.411, 3.045, and 3.527 h(-1), respectively. The distribution coefficients (k(d)) were 540.9, 460.4, 396.9 L/kg for 10, 20, 30 degrees C, respectively. To some extent, the first-order rate constant of E2 anoxic degradation was infected by NO3-; -N concentration (10-30 mg/L).

[Characteristics of microbial biomass in subsurface constructed wetland treating eutrophic water].

A subsurface horizontal-flow constructed wetland planted with Phragmites australis was developed and used to treat eutrophic water for nearly two years at fixed hydraulic loading rate. Substrate samples were taken at different depths respectively in the front, middle and back sites of wetland in January, May, August and October in the second year. Microbial biomass (MB) content was measured using the chloroform fumigation incubation method. The results show that the front sites have higher levels of microbial biomass carbon (MB-C), microbial biomass nitrogen (MB-N) and microbial biomass phosphorous (MB-P) than that in middle sites and back sites. The upper layers have higher levels of MB than that in the deeper layers. The MB content of wetland in January and May is higher than that in October and August. The relationship between MB and TN, TP removal efficiency of the constructed wetland was investigated. The wetland shows no apparent correlation of MB and TN removal efficiency. However, strong negative correlation is observed between MB-C and TP removal efficiency (r = -0.98, p < 0.05) and between MB-N, MB-P and TP removal efficiency (r = -0.99, p < 0.01). In constructed wetland, MB is also an active nutrient storage involved in nutrient cycling and can be used by wetland plant. MB content varies among a range level with plant growth and temperature in a growth year. Under experiment conditions, the range of MB-C, MB-N and MB-P was respectively 85.0-160.6, 16.3-34.9 and 3.12-5.77 microg x g(-1) in the second year. Seasonal variation of MB and nutrient removal is resulted from the factors integrated with temperature, microorganisms, plant, substrate and enzyme.

[Transformation of linear alkylbenzene sulphonate in the anaerobic-anoxic-oxic wastewater treatment process].

The removal characteristics of linear alkylbenzene sulphonate (LAS) was studied in anaerobic/anoxic/oxic (AAO) municipal wastewater treatment processes. A removal (biological degradation and sorption) model was formulated, and kinetic parameters were evaluated with batch experiments under anaerobic, anoxic, oxic conditions. The resulting model calculations were then compared with sampling campaigns performed on AAO process. The results show that the removal efficiency of LAS in the AAO activated sludge processes is more than 99%. Effluent concentrations vary between 0 and 20 microg L(-1). The concentration of LAS adsorbed by sludge in anaerobic tank, anoxic tank, aerobic tank is 490 - 710 microg g(-1), 280 - 390 microg g(-1) and 69 - 109 microg g(-1) respectively. From the result of biodegradation kinetic tests, it can be concluded that LAS is well biodegraded under anaerobic/anoxic/oxic conditions, and the removal rate of LAS in anaerobic and anoxic conditions accounts for respectively 67% and 71% of that in oxic condition. The model can well forecast the effluent quality of anaerobic/ anoxic/oxic tank of the AAO process, and the relative error is less than 8%.

[Long-term and short-term effects of propionic/acetic acid ratios on metabolism of glycogen-accumulating organisms].

Three activated sludges enriched with glycogen accumulating organisms (GAO) were acclimatized respectively with different ratios of propionic to acetic acid (i.e. biomass SBR-A, C and E) . The effect of different ratios of propionic/acetic acid on the metabolism of long-term cultivated GAO was investigated. Cultivated with high propionic/acetic acid ratio, GAO consumed less glycogen and synthesized less poly-beta-hydroxyalkanoates (PHA) in the anaerobic phase, and in the aerobic phase accumulated less glycogen and degraded less PHA, and at the same time the microbial growth was lower. When the carbon mole of acetic acid equaled that of propionic acid in the influent, GAO utilized acetic acid faster than propionic acid. Batch tests were carried out with biomass SBR-A and SBR-E to study the transient response of long-term cultivated GAO to short-term change of propionic/acetic acid ratio. The GAO cultivated with a high propionic/acetic acid ratio was able to utilize acetic acid immediately when the concentration of acetic acid in the feed suddenly increased. But when the biomass cultivated with a low propionic/acetic acid ratio was feed with high ratio propionic/acetic acid wastewater, the propionic acid uptake rate was only 41.1% of the rate of the GAO long-term cultivated with high propionic/acetic acid. The sudden increase of propionic/acetic acid ratio could effectively inhibit the metabolism of GAO.

[Adsorption characteristics of 17beta-estradiol to anaerobic and anoxic sludge].

Adsorption tests were performed to measure the adsorption capacity of anaerobic and anoxic inactivated sludge for 17beta-estradiol. The effects of pH and temperature were also investigated. The adsorption equilibrium was established in 30 min; no significant pH effect was observed in the pH range of 6-9 at 20 degrees C; when pH >9, the adsorptive capacities decreased with increasing pH value; the adsorptive capacities decreased with increasing temperature. The experimental data of equilibrium concentrations were well correlated by both Freundlich and linear adsorption isothermal models. Distribution coefficients (Kd) decreased with increasing temperature. The distribution coefficients (Kd) of anaerobic inactivated sludge were 629.2 (10 degrees C) > 534.9 (20 degrees C) > 405.6 (30 degrees C), and those of anoxic inactivated sludge were 601.2 (10 degrees C ) > 491.3 (20 degrees C) > 360.1 (30 degrees C). Comparatively, Freundlich parameters K(F), 1/n and Kd of the anaerobic and anoxic activated sludge were measured at 20 degrees C; Distribution coefficient of anoxic activated sludge was lower than that of anaerobic activated sludge. No significant differences were observed between activated and inactivated sludge. The adsorption abilities of anaerobic activated/inactivated sludge were greater than those of anoxic activated/inactivated sludge.

[Treatment of SBR after wet air oxidation of emulsification wastewater].

This article studied the change of possible biochemistry and toxicity of emulsification wastewater before and after wet air oxidation and also studied the treating effect of wet air oxidation on emulsification wastewater after SBR process. The experimental results indicate that the toxicity of emulsification wastewater is equivalent to that of 0.12 mg/L HgCl2, while initial COD 48,000 mg x L(-1) and BOD5/COD (B/C) 0.072 3 in the inlet wastewater, and that the wastewater is highly concentrated organic wastewater. After WAO treatment, the value of BOD5/COD increases clearly. While the temperature is higher, the rise scope of B/C is bigger, and the biological toxicity reduces more. At 220 degrees C and 240 degrees C, the biological toxicity of wastewater decreases by 18.3% and 50.8% after WAO treatment, respectively. It can be seen that SBR treatment process has a perfect effect on WAO output water at 220 degrees C and has the strong anti-impact load ability. With respect to the initial COD 1500-3000 mg/L in the inlet wastewater, it exhibits the efficiency of 94.6%-96.1% COD removal. While initial COD 2000 mg/L in the inlet wastewater, the average COD in the outlet wastewater is 96.0 mg/L. The WAO-SBR process developed with respect to the emulsification wastewater treatment has a potential application prospect.

[Addition of propionic acid on simultaneous biological phosphorus and nitrogen removal in anaerobic-low dissolved oxygen system].

Two lab-scale sequencing batch reactors (SBRs) were operated under conditions of anaerobic-low dissolved oxygen (DO) (0.15 - 0.45 mg x L(-1)), and the influences of addition of propionic acid on simultaneous biological nitrogen and phosphorus removal system were investigated. The results showed that the simultaneous nitrification, denitrification and phosphorus removal (SNDPR) occurred in both SBR1 (acetic and propionic acid as mixed carbon source with the carbon molar ratio of 1.5/1) and SBR2 (acetic acid as sole carbon source), and ammonia was completely oxidized during the aerobic period without substantive nitrite accumulation. Compared with SBR2, SBR1 showed less anaerobic phosphorus release and more polyhydroxyvalerate (PHV) synthesis, but the aerobic end phosphorus and nitrate concentrations were lower. The total nitrogen and phosphorus removal efficiencies were higher in SBR1 (68% and 95%, respectively) than in SBR2 (51% and 92%, respectively) suggesting that the addition of propionic acid to SNDPR system would be helpful.

[Influence of wastewater initial pH on enhanced biological phosphorus removal in sequencing batch reactor (SBR)].

Two laboratory-scale sequencing batch reactors (SBRs) were operated continuously to investigate the influence of wastewater initial pH on enhanced biological phosphorus removal (SBR1: pH = 6.8; SBR2: pH = 7.6). Results show that SBR2 exhibits greater anaerobic phosphorus release than SBR1. During aerobic stage, SBR2 degrades less polyhydroxyalkanoates (PHA) than SBR1, and the ratio of glycogen synthesis to PHA degradation in SBR2 is much less than that of SBR1, but SBR2 takes up more phosphorus. Further studies show that due to less glycogen synthesis in SBR2 than in SBR1, lower PHA degradation in SBR2 doesn't result in lower phosphorus uptake. The higher phosphorus uptake and PHA utilization efficiency in SBR2 is probably caused by its more phosphorus accumulating organisms (PAO). At the end of aerobic phase, SBR2 has significantly higher phosphorus removal efficiency than SBR1 (93.67% against 65.06%). Thus, the efficiency of enhanced biological phosphorus removal can be significantly improved by controlling the initial pH of wastewater. This method is much more convenient than controlling the entire process pH of wastewater biological treatment.

[Effect of SRT on denitrifying phosphorus removal in A/A/O process].

Based on a laboratory-scale anaerobic-anoxic-oxic process acclimated with municipal wastewater, effect of SRT on denitrifying phosphorus removal occurred in the system was investigated. The results indicate that the contribution of anoxic denitrifying phosphorus removal to total phosphorus removal becomes larger with prolonging the sludge retention time. DNPAOs' denitrification and P uptake capacities per anoxic PHAs utilized are quickly increased, while PAOs' P uptake capacity per aerobic PHAs utilized is rarely influenced by SRT. When SRT is set at 12 days, anoxic phosphorus uptake efficiency and biological nutrient removal efficiency are best. The results also show that the COD amountrequired for removing per nitrogen decreases and for removing per phosphorus increases with prolonging the sludge retention time. For the national typical municipal wastewater, the COD amount required for removing per nitrogen and phosphorus under SRT of 12 and 15 days is less than that of under SRT of 8 days, which indicates that anoxic denitrifying phosphorus removal can really decrease the demand of carbon and energy sources.

[Cometabolic biodegradation of nitrogenous heterocyclic compounds indole and pyridine under anoxic conditions].

Based on the traditional theory of denitrification under anoxic conditions, and with the addition of nitrate, experiments were conducted to investigate the cometabolic biodegradation of nitrogenous heterocyclic compounds-indole and pyridine. Results show that the optimum ratio of COD to nitrate (C/N) is 8.4 to approximately 8.9. Under the conditions with temperature of 28 degrees C and pH of 7.0 to approximately 7.5, the nitrate reductase activity (NRA) is in the best state. Addition of pyridine can promote NRA and the degradation of indole. When the initial concentration of indole is 150 mg/L, the concentration ratio of indole to pyridine is 1 to approximately 10, and under the optimum C/N conditions, the degradation of indole meet with zero-order kinetics. There was no accumulation of nitrite during the reaction. When the concentration ratio of pyridine to indole is less than 0.25, with the increase of pyridine concentration, there is a faster augment rate for NRA and the degradation of indole than the situation when the concentration ratio of pyridine to indole is more than 0.25.

[Research on substrate transformation mechanism in A2/O process].

Based on a laboratory-scale anaerobic-anoxic-oxic process acclimated with real wastewater, substrate transformation mechanism and the effect of nitrate on substrate transformations occurred in the system were investigated. The results indicated that under the anaerobic condition without nitrate, phosphorus-accumulating organisms (PAOs) could take up 51% of COD consumed and store them to PHAs; anoxic and aerobic specific phosphorus uptake rates were 3.87 mg/(g x h) and 6.54 mg/(g x h), and the anoxic and aerobic ratios of phosphorus uptake and PHAs utilized, nu(P/PHA). were 0.38 and 0.78, respectively. While under the anaerobic condition containing nitrate, only 30.8% of COD consumed was taken up by PAOs and 61.5% was used as the denitrifying carbon source; specific phosphorus uptake rates of anoxic and aerobic sludge were 2.24 mg/(g x h) and 4.58 mg/(g x h), and the nu(P/PHA) under the anoxic and aerobic conditions were 0.35 and 0.77, respectively. Furthermore, in both systems, there was a good linear relationship between COD consumption and phosphate release under the anaerobic condition. The nitrate existed in the anaerobic condition could decrease anaerobic phosphorus release rate and efficiency of PAOs, resulting in a decreased amount of PHAs synthesis and consequently affecting anoxic and aerobic phosphorus uptake rates. However, phosphorus uptake capacity was not influenced by nitrate and the amount of PHAs synthesized in the anaerobic stage.