Anoxic Process Research Articles

Diversity of NosZ gene in three municipal wastewater treatment plants located in different geographic regions

Diversity of nitrous oxide reductase genes (NosZ) in activated sludge was compared in the biological treatment process (BTCs, anaerobic, anoxic and aerobic process) of three municipal wastewater treatment plants located in different geographic regions. A total of 18 specific bands generated after polymerase chain reaction- denaturing gradient gel electrophoresis (PCR-DGGE) analysis. The diversity of NosZ in MWTPs of Nanjing is higher than that of Xiamen and Foushan, and the similarity of DGGE bands from BTCs in the same MWTP is obviously higher than that of the same BTC in different MWTPs. 12 of 18 unique bands were selected, sequenced and identified by searching against Genbank using BLASTn, and the highest identity and score values of the isolated sequences were the NosZ gene of uncultured bacterium in non-redundant database of Genbank. However, the most probable affiliations of the bacteria harboring the NosZ gene were the denitrifying bacteria from α- or β-proteobacteria, including Alicycliphilus denitricans, Herbaspirillum sp., Paracoccus denitrificans, and Rhodopseudomonas palustris. Phylogenetic analysis of the twelve sequences indicated that all the sequences could be divided into two main clusters. Each cluster not only contains species from αproteobacteria but also from β-proteobacteria.

Nitrite accumulation under constant temperature in anoxic denitrification process: The effects of carbon sources and COD/NO3-N

Effects of external carbon sources and COD/NO3-N on nitrite accumulation through denitrification were studied at a temperature of 28±2.0°C using mixed activated sludge. Nitrite accumulation was observed for each type of carbon source studied. Glucose resulted in the greatest nitrite accumulation and production rate, which were 14.51±2.41mg/L and 0.121±0.013gN/(gVSSd), respectively. Moreover, a higher COD/NO3-N ratio ranging from 1.0 to 15.0 increased accumulation to the maximum value of 0.34±0.03gN/(gVSSd). It was assumed that the competition for electrons between nitrite reductase and nitrate reductase led to different reduction rates and finally caused the accumulation. In addition, it was reasonable to use the pH and ORP as proxies for monitoring the real endpoint of the denitrification process with the addition of carbon sources.

Startup Research of Integrated Anoxic Aerobic Process in Printing and Dyeing Wastewater Treatment

Based on the treatment situation and the modification of effluent standard of printing and dyeing wastewater, a novel integrated and three-dimensional anoxic-aerobic process (A/O) is put forward. The experiment studies the startup of A/O process with simulated printing and dyeing wastewater. The results show that the removal efficiencies of CODcr, NH4+-N and chroma are 67.6%, 90.9% and 54.5% at the steady stage, respectively. The novel A/O process has perfect and steady performance for treatment of printing and dyeing wastewater.

Occurrence and fate of steroid estrogens in the largest wastewater treatment plant in Beijing, China

Concern over steroid estrogens has increased rapidly in recent years due to their adverse health effects. Effluent discharge from wastewater treatment plants (WWTPs) is the main pollutant source for environmental water. To understand the pollutant level and fate of steroid estrogens in WWTPs, the occurrence of estrone (E1), 17-β-estradiol (E2), estriol (E3), and 17-β-ethinylestradiol (EE2) was investigated in the Gaobeidian WWTP in Beijing, China. Water samples from influent as well as effluent from second sedimentation tanks and advanced treatment processes were taken monthly during 2006 to 2007. In influent, steroid estrogen concentrations varied from 11.6 to 1.1 × 10(2) ng/l, 3.7 to 1.4 × 10(2) ng/l, no detection (nd) to 7.6×10(2) ng/l and nd to 3.3 × 10(2) ng/l for E1, E2, E3, and EE2, respectively. Compared with documented values, the higher steroid estrogen concentrations in the WWTP influent may be due to higher population density, higher birthrate, less dilution, and different sampling time. Results revealed that a municipal WWTP with an activated sludge system incorporating anaerobic, anoxic, and aerobic processes could eliminate natural and synthetic estrogens effectively. The mean elimination efficiencies were 83.2%, 96.4%, 98.8%, and 93.0% for E1, E2, E3, and EE2, respectively. The major removal mechanism for natural estrogens and synthetic estrogen EE2 were biodegradation and sorption on the basis of mass balance in water, suspension particles, and sludge. In the WWTP effluent, however, the highest concentrations of E1, E2, E3, and EE2 attained were 74.2, 3.9, 5.1, and 4.6 ng/l, respectively. This is concerning as residual steroid estrogens in WWTP effluent could lead to pollution of the receiving water. Advanced flocculation treatment was applied in the WWTP and transformed the residual estrogen conjugates to free species, which were reduced further by filtration with removal shifting from 32% to 57% for natural estrogen, although no EE2 was removed.

Occurrence and fate of quinolone and fluoroquinolone antibiotics in a municipal sewage treatment plant

This study developed a method for analysis of nineteen quinolone and fluoroquinolone antibiotics (FQs) in sludge samples, and investigated the occurrence and fate of the FQs in a municipal sewage treatment plant (STP) with anaerobic, anoxic, and aerobic treatment processes. Eleven compounds, including pipemidic acid, fleroxacin, ofloxacin, norfloxacin, ciprofloxacin, enrofloxacin, lomefloxacin, sparfloxacin, gatifloxacin, moxifloxacin, and sarafloxacin (only in sludge), were detected in the STP. The predominance of ofloxacin and norfloxacin, followed by lomefloxacin, ciprofloxacin, gatifloxacin, and moxifloxacin, were found in wastewater, suspended solids, and sludge. The total concentrations of FQs were 2573 ± 241 ng/L, 1013 ± 218 ng/L, and 18.4 ± 0.9 mg/kg in raw sewage, secondary effluent, and sludge, respectively. Extremely low mass change percentages were observed for FQs in anaerobic, anoxic, and aerobic treatment units, suggesting biodegradation to be of minor importance in the removal of FQs in STPs. 50–87% of the initial FQs loadings (except for pipemidic acid (36%)) were ultimately found in the dewatered sludge. Mean removal efficiencies of FQs in the STP were 56–75%, except for new generation drugs such as moxifloxacin (40 ± 5%) and gatifloxacin (43 ± 13%). A significant positive correlation was found between removal efficiencies and K d of FQs. The major factor in the removal of FQs in the STP was sorption to sludge, which was not governed by hydrophobic interactions. The long-term cycling and persistence of FQs in the STP has made activated sludge as a huge reservoir of FQ antibiotics.

Decolorization and partial mineralization of a polyazo dye by Bacillus firmus immobilized within tubular polymeric gel

The degradation of C.I. Direct red 80, a polyazo dye, was investigated using Bacillus firmus immobilized by entrapment in tubular polymeric gel. This bacterial strain was able to completely decolorize 50 mg/L of C.I. Direct red 80 under anoxic conditions within 12 h and also degrade the reaction intermediates (aromatic amines) during the subsequent 12 h under aerobic conditions. The tubular gel harboring the immobilized cells consisted of anoxic and aerobic regions integrated in a single unit which was ideal for azo dye degradation studies. Results obtained show that effective dye decolorization (97.8%), chemical oxygen demand (COD) reduction (91.7%) and total aromatic amines removal were obtained in 15 h with the immobilized bacterial cell system whereas for the free cells, a hydraulic residence time of 24 h was required for an equivalent performance in a sequential anoxic and aerobic process. Repeated-batch experiments indicate the immobilized cells could decolorize C.I. Direct red 80 and reduce medium COD in five successive batch runs with enhanced activity obtained after each consecutive run, thus suggesting its stability and potential for repeated use in wastewater treatment. UV–visible spectrophotometry and HPLC analysis were used to confirm the partial mineralization of the dye. Data from this study could be used as a reference for the development of effective industrial scale biotechnological process for the removal of dyes and their metabolites in textile wastewater.

Influence of aeration intensity on the performance of A/O-type sequencing batch MBR system treating azo dye wastewater

Among the numerous parameters affecting the membrane bioreactor (MBR) performance, the aeration intensity is one of the most important factors. In the present investigation, an anoxic/aerobic-type (A/O-type) sequencing batch MBR system, added anoxic process as a pretreatment to improve the biodegradability of azo dye wastewater, was investigated under different aeration intensities and the impact of the aeration intensity on effluent quantity, sludge properties, extracellular polymeric substances (EPS) amount generated as well as the change of permeation flux were examined. Neither lower nor higher aeration intensities could improve A/O-type sequencing batch MBR performances. The results showed 0.15 m3·h−1 aeration intensity was promising for treatment of azo dye wastewater under the conditions examined. Under this aeration intensity, chemical oxygen demand (COD), ammonium nitrogen and color removal as well as membrane flux amounted to 97.8%, 96.5%, 98.7% and 6.21 L·m−2·h−1, respectively. The effluent quality, with 25.0 mg·L−1COD, 0.84 mg·L−1 ammonium nitrogen and 8 chroma, could directly meet the reuse standard in China. In the meantime, the sludge relative hydrophobicity, the bound EPS, soluble EPS and EPS amounts contained in the membrane fouling layer were 70.3%, 52.0 mg·g−1VSS, 38.8 mg·g−1VSS and 90.8 mg·g−1VSS, respectively, which showed close relationships to both pollutant removals and membrane flux.

Soil aquifer treatment of artificial wastewater under saturated conditions

A 2000 mm long saturated laboratory soil column was used to simulate soil aquifer treatment under saturated conditions to assess the removal of chemical and biochemical oxygen demand (COD and BOD), dissolved organic carbon (DOC), nitrogen and phosphate, using high strength artificial wastewater. The removal rates were determined under a combination of constant hydraulic loading rates (HLR) and variable COD concentrations as well as variable HLR under a constant COD. Within the range of COD concentrations considered (42 mg L −1–135 mg L −1) it was found that at fixed hydraulic loading rate, a decrease in the influent concentrations of dissolved organic carbon (DOC), biochemical oxygen demand (BOD), total nitrogen and phosphate improved their removal efficiencies. At the high COD concentrations applied residence times influenced the redox conditions in the soil column. Long residence times were detrimental to the removal process for COD, BOD and DOC as anoxic processes and sulphate reduction played an important role as electron acceptors. It was found that total COD mass loading within the range of 911 mg d −1–1780 mg d −1 applied as low COD wastewater infiltrated coupled with short residence times would provide better effluent quality than the same mass applied as a COD with higher concentration at long residence times. The opposite was true for organic nitrogen where relatively high concentrations coupled with long residence time gave better removal efficiency.

Analysis on Mass Balance and Optimization of Operating Performance in Anaerobic-Anoxic-Aerobic Oxidation Ditch Process

The equations of COD, nitrogen and phosphate mass balance is established and the results show that the COD, nitrogen and phosphorus balance ratios are 98.3%, 73.1%, 98.4%. COD removal is achieved by the discharge of aerobic oxidation and excess sludge, accounting for 86.3% of the total. The loss of nitrogen balance is due to the existing of SND. Nitrogen removal is mainly achieved by the discharge of denitrification process, including anoxic denitrification process (33.6%) and SND process (23.3%). In order to solve the problem of large energy consumption, some optimized control measures are proposed and the test results indicate that TN removal rate has increased from 89.2% to 93.1%, tons of water at power consumption has dropped from 0.35 to 0.26kW•h/m3.

Long-chain acylhomoserine lactones increase the anoxic ammonium oxidation rate in an OLAND biofilm

The oxygen-limited autotrophic nitrification/denitrification (OLAND) process comprises one-stage partial nitritation and anammox, catalyzed by aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB), respectively. The goal of this study was to investigate whether quorum sensing influences anoxic ammonium oxidation in an OLAND biofilm, with AnAOB colonizing 13% of the biofilm, as determined with fluorescent in situ hybridization (FISH). At high biomass concentrations, the specific anoxic ammonium oxidation rate of the OLAND biofilm significantly increased with a factor of 1.5 ± 0.2 compared to low biomass concentrations. Supernatant obtained from the biofilm showed no ammonium-oxidizing activity on itself, but its addition to low OLAND biomass concentrations resulted in a significant activity increase of the biomass. In the biofilm supernatant, the presence of long-chain acylhomoserine lactones (AHLs) was shown using the reporter strain Chromobacterium violaceum CV026, and one specific AHL, N-dodecanoyl homoserine lactone (C(12)-HSL), was identified via LC-MS/MS. Furthermore, C(12)-HSL was detected in an AnAOB-enriched community, but not in an AerAOB-enriched community. Addition of C(12)-HSL to low OLAND biomass concentrations resulted in a significantly higher ammonium oxidation rate (p < 0.05). To our knowledge, this is the first report demonstrating that AHLs enhance the anoxic ammonium oxidation process. Future work should confirm which species are responsible for the in situ production of C(12)-HSL in AnAOB-based applications.

Occurrence and behavior of non-steroidal anti-inflammatory drugs and lipid regulators in wastewater and urban river water of the Pearl River Delta, South China

Occurrence of five non-steroidal anti-inflammatory drugs (salicylic acid, ibuprofen, naproxen, indomethacin and diclofenac) and three lipid regulators (bezafibrate, clofibric acid and gemfibrozil) was investigated in wastewater, sewage sludge, and river water of the urban section of the Pearl River at Guangzhou in South China. Behavior and fate of the pharmaceuticals during treatment in two sewage treatment plants (STPs) were also studied in depth by determining concentrations in the influents and effluents at major treatment units and the sewage sludge. Concentrations of the pharmaceuticals in the raw wastewater were mostly at ng L(-1) levels except salicylic acid whose concentrations ranged from 9.6 to 23.3 μg L(-1). No significant amount of the pharmaceuticals was detected in the suspended particulate matter of wastewater and sewage sludge. Salicylic acid, indomethacin, and naproxen were almost completely removed (≥ 99%); gemfibrozil, ibuprofen and bezafibrate were significantly removed (>75%), whereas diclofenac and clofibric acid were removed by 60-70% during treatment in the STPs. Generally, biodegradation was the governing process for elimination of the investigated pharmaceuticals. Anaerobic biodegradation was responsible for most of the removal of diclofenac whereas aerobic biodegradation also played an important role in elimination of the other pharmaceuticals except SA, which was nearly completely removed after the anoxic process. In the Pearl River, the pharmaceuticals were widely detected. Both the concentrations and detection frequency were higher in March 2008 than those in the other seasons, which may be ascribed mainly to less dilution caused by lower precipitation. Besides the STPs, urban canals directly connected with the Pearl River may also be important contributors to the pharmaceutical contamination in the river.

철 석출장치가 결합된 무산소.호기공정에 의한 인 제거 특성

In this study, the (phosphorous removal) the characteristics of phosphorous removal due to (the iron compound precipitated) iron compound precipitation by iron electrolysis in (the anoxic. oxic process) anoxic and oxic processes (equipped with the) in an iron precipitation device were analyzed. During the device operation period, the average concentration of BOD, T-N, and T-P were 219.9 mg/l, 54.6 mg/l and 6.71 mg/l, respectively. The BOD/ ratio was 0.74, and the BOD/T-N and BOD/T-P ratios were 4.0 and 32.8, respectively. The removal rate of (the organic matters) organic matter (BOD and ) was very high at 91.6% or higher, and that of nitrogen was 80.5%. The phosphorous concentration (of the final) in the treated water was 0.43 mg/l (0.05-0.74 mg/l) on average, and the removal efficiency was high at 90.8%. The soluble T-P concentrations in (an) the anoxic reactor, oxic reactor (II) and final treated water were 1.99 mg/l, 0.79 mg/l and 0.43 mg/l, respectively, which indicated that the phosphorous concentration in the treated water was very low. Regardless of the changes in the concentrations of (organic matters) organic matter, nitrogen and phosphorous in the influent, the quality of the treated water was relatively stable and high. The removal rate of T-P somewhat increased with the increase in the F/M ratio in the influent, and it also linearly increased in proportion to the T-P loading rate in the influent. In the treatment process used in this study, phosphorous was removed (using) by the precipitated iron oxide. Therefore, the consumption of organic (matters) matter for biological phosphorus removal was minimized and (most of the organic matters were) was mostly used as the organic carbon source for the denitrification in the anoxic reactor. This (can be an economic) treatment process (without the need for the supply of additional organic matters) is economic and does not require the supply of additional organic matter.

Hydro‐biogeochemical coupling beneath a large polythermal Arctic glacier: Implications for subice sheet biogeochemistry

We analyze the interannual chemical and isotopic composition of runoff from a large, high Arctic valley glacier over a 5 year period, during which drainage evolved from a long‐residence‐time drainage system feeding an artesian subglacial upwelling (SGU) at the glacier terminus to a shorter‐residence‐time drainage system feeding an ice‐marginal channel (IMC). Increased icemelt inputs to the SGU are thought to have triggered this evolution. This sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time. The biogeochemistry of the SGU is consistent with prolonged contact between meltwaters and subglacial sediments, in which silicate dissolution is enhanced, anoxic processes (e.g., sulphate reduction) prevail, and microbially generated CO2 and sulphide oxidation drive mineral dissolution. Solute in the IMC was mainly derived from moraine pore waters which are added to the channel via extraglacial streams. These pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate/silicate dissolution. We present the first evidence that microbially mediated processes may contribute a substantial proportion (80% in this case) of the total glacial solute flux, which includes coupling between microbial CO2‐generation and silicate/carbonate dissolution. The latter suggests the presence of biofilms in subglacial/ice‐marginal sediments, where local perturbation of the geochemical environment by release of protons, organic acids, and ligands stimulates mineral dissolution. These data enable inferences to be made regarding biogeochemical processes in longer‐residence‐time glacial systems, with implications for the future exploration of Antarctic subglacial lakes and other wet‐based ice sheet environments.

Monitoring of microbial storage products and the effciency of an activated sludge plant performing anoxic phosphorus removal under different operational conditions

The present work focuses on the operation of a continuous flow laboratory scale plant for enhanced biological phosphorus removal (EBPR) from synthetic wastewater. After the acclimatization period, basic operational conditions, namely the influent COD concentration and the anoxic to anaerobic tank volumes ratio, varied, in order to evaluate their impact to the system performance. The progressive increase of the influent COD concentration from 200 mg COD/l to 300 and 400 with constant influent phosphate concentration of 15 mg PO -3 4 -P/l, led to proportional increase of the intracellular PHAs used during the anoxic phosphorus uptake process and to the respective amount of nitrate denitrified. However, the highest phosphorus uptake rate and the maximum net phosphorus removal were observed for the influent COD/P concentrations ratio of 20 (300 mg COD/l). Interestingly, this was also the ratio where the maximum carbohydrates synthesis and biomass P content during the anoxic phase were observed, indicating this, as the optimum ratio for the system efficiency. In a second operational period and for this particular COD/P ratio, three different anaerobic hydraulic residence times (HRT) were imposed, by increasing the volume of the anaerobic tank, in order to achieve anoxic to anaerobic HRT ratios of 2.33, 1.75 and 1.4. The experimental results indicated that decreased ratio values led to increased PHAs utilization for phosphorus removal. Furthermore, despite the considerable increase of the specific P uptake rate, the specific anaerobic P release rate remained almost constant, irrespective to the anoxic to anaerobic HRT ratio. The maximum net phosphorus removal was observed for the minimum ratio, indicating that increased anaerobic contact time enhances the activity of polyphosphate accumulating organisms (PAOs) in the EBPR plant. The biomass growth yield was not influenced by the anoxic to anaerobic HRT ratio and remained constant at 0.27 gVSS/gCOD. Phosphorus removal under alternative anaerobic/anoxic conditions proved its practical feasibility and satisfactory efficiency in a continuous flow activated sludge system.

The removal of nutrients from non-point source wastewater by a hybrid bioreactor

The aim of this project was to establish an economical and environmentally benign biotechnology for removing nutrients from non-point source wastewater. The proposal involves a hybrid bioreactor comprised of sequential anaerobic, anoxic and aerobic (A(2)/O) processes and an eco-ditch being constructed and applied in a suburban area, Kunming, south-western China, where wastewater was discharged from an industrial park and suburban communities. The results show that the hybrid bioreactor fosters heterotrophic and autotrophic microorganisms. When the hydraulic load is 200 m(3) per day with the running mode in 12h cycles, the removal efficiencies of the nutrients were 81% for TP, 74% for TDP, 82% for TN, 79% for NO(3)-N and 86% for NH(4)-N. The improved bacterial community structure and bacterial habitats further implied enhanced water quality and indicates that the easily-deployed, affordable and environmentally-friendly hybrid bioreactor is a promising bio-measure for removing high loadings of nutrients from non-point source wastewater.

Revisiting Coos Bay, Oregon: A re-examination of funginite–huminite relationships in Eocene subbituminous coals

Coal petrography has advanced significantly since Reinhardt Theissen and James Schopf pioneered the use of thin sections to examine coals from Coos Bay Oregon, and to many coal petrographers the nomenclature used in that study is irrelevant. The Schopf (1947) study was a ground-breaking examination of maceral relationships that need to be part of the working vocabulary of modern petrographers. To support this, a re-examination of the Coos Bay thin section collection was undertaken, using modern nomenclature for low-rank coals under reflected light. This particular collection was chosen in part because of the abundance of fungal material reported by Schopf. Fungal material in coal and its association with huminite/vitrinite macerals provides important information about the decompositional history of the coal and allows coal dominated by oxic processes to be differentiated from coal dominated by anoxic processes. In the Coos Bay samples, predominantly oxic intervals contain well-preserved fungi, including spores, sclerotia, and hyphae, while anoxic intervals contain no fungi. ►Revisitation of Schopf (1947) ground-breaking examination of maceral relationships. ►Use of modern reflected light nomenclature for thin sections. ►Huminite–funginite relationships explored. ►Oxic, attrinite-rich intervals are also rich in funginite. ►Further evidence for multiple pathways of inertinite formation

Fjord water circulation patterns and dysoxic/anoxic conditions in a Mediterranean semi-enclosed embayment in the Amvrakikos Gulf, Greece

Oceanographic research in the Amvrakikos Gulf in Western Greece, a semi-enclosed embayment isolated from the Ionian Sea by a narrow, shallow sill, has shown that it is characterised by a fjord-like oceanographic regime. The Gulf is characterised by a well-stratified two layer structure in the water column made up of a surface layer and a bottom layer that are separated by a strong pycnocline. At the entrance over the sill, there is a brackish water outflow in the surface water and a saline water inflow in the near-bed region. This morphology and water circulation pattern makes the Amvrakikos Gulf the only Mediterranean Sea fjord. The investigations have also shown that the surface layer is well oxygenated, whereas in the pycnocline, the dissolved oxygen (DO) declines sharply and finally attains a value of zero, thus dividing the water column into oxic, dysoxic and anoxic environments. At the dysoxic/anoxic interface, at a depth of approximately 35 m, a sharp redox cline develops with Eh values between 0 and 120 mV occurring above and values between 0 and −250 mV occurring below, where oxic and anoxic biochemical processes prevail, respectively. On the seafloor underneath the anoxic waters, a black silt layer and a white mat cover resembling Beggiatoa-like cells are formed. The dysoxic/anoxic conditions appeared during the last 20 to 30 years and have been caused by the excessive use of fertilisers, the increase in animal stocks, intensive fish farming and domestic effluents. The inflicted dysoxia/anoxia has resulted in habitat loss on the seafloor over an area that makes up just over 50% of the total Gulf area and approximately 28% of the total water volume. Furthermore, anoxia is also considered to have been responsible for the sudden fish mortality which occurred in aquaculture rafts in the Gulf in February 2008. Therefore, anoxic conditions can be considered to be a potential hazard to the ecosystem and to the present thriving fishing and mariculture industry in the Gulf.

Biogeochemical processes of carbon and sulfur cycles in sediments of the outer shelf of the Black Sea (Russian Sector)

Within the mass of recent (unit-I) and ancient Black Sea (unit-II) sediments on the outer shelf of the Russian sector of the Black Sea, the rates of anoxic processes participating in diagenetic transformations of carbon and sulfur compounds were first measured using 35S and 14C radioactive tracers. The main energy source for biogeochemical processes in (unit-I) sediments is the organic matter (OM) supplied to the bottom from the water mass. In (unit-II) sediments, this is methane in a migratory form proved by the excess of its oxidation rate over that of its generation. In recent silt, the primary microbial process is sulfate reduction; in unit-II, this is methane anoxic oxidation by the consortium of archeides and sulfate reductants. The organic matter produced in methane oxidation, in turn, acts as an energy source for the community of anaerobic heterotrophic microorganisms in the bottom sediments, which are remote from the water-sediment interface.

Innovative Biological Process for Treatment of Coking Wastewater

Coking wastewater was treated by an A-O(1)-O(2) biofilm system composed of an anoxic bioreactor and two aerobic ones. To improve removal efficiency of organic pollutants, the anoxic bioreactor was used to investigate organic removal via anoxic process with enhanced denitrification, and the first aerobic bioreactor was used to test the feasibility of nitrogen removal via nitrite in an attached growth system. Concentrations of ammonium nitrogen (NH(4)(+)-N), phenols, and chemical oxygen demand (COD) in the wastewater ranged between 200 and 500, 250 and 350, and 1,700 and 2,200mg L(-1), respectively. Removal of organic pollutants through anoxic process was enhanced by raising NO(3)(-)-N/COD ratio in the influent of anoxic bioreactor. Removal efficiencies for total organic compounds of 17.84%, 41.78%, 82.63%, and 88.73% were obtained at NO(3)(-)-N/COD ratios of 1:10, 1:5, 1:3, and 1:2, respectively. Shortcut nitrification was obtained in the first aerobic bioreactor when dissolved oxygen was 2.0-3.0 mg L(-1) at 35 degrees C +/- 1 degrees C. Both ammonia oxidation ratio and nitrite accumulation ratio were maintained above 85%, with ammonia load ranging from 0.22 to 0.30 g NH(4)(+)-N (L day)(-1) by adjusting the hydraulic retention time and influent NH(4)(+)-N concentration. Gas chromatography/mass spectrometry analysis demonstrated that most of organic compounds were decomposed at the enhanced denitrification stage and the high removal efficiency of total organic compounds was obtained through the A-O(1)-O(2) process. This study was presumed to provide a better option for the treatment of coking wastewater.

Evaluating the structural identifiability of the parameters of the EBPR sub-model in ASM2d by the differential algebra method

The calibration of ASMs is a prerequisite for their application to simulation of a wastewater treatment plant. This work should be made based on the evaluation of structural identifiability of model parameters. An EBPR sub-model including denitrification phosphorus removal has been incorporated in ASM2d. Yet no report is presented on the structural identifiability of the parameters in the EBPR sub-model. In this paper, the differential algebra approach was used to address this issue. The results showed that the structural identifiability of parameters in the EBPR sub-model could be improved by increasing the measured variables. The reduction factor η NO 3 was identifiable when combined data of aerobic process and anoxic process were assumed. For K PP , X PAO and q PHA of the anaerobic process to be uniquely identifiable, one of them is needed to be determined by other ways. Likewise, if prior information on one of the parameters, K PHA , X PAO and q PP of the aerobic process, is known, all the parameters are identifiable. The above results could be of interest to the parameter estimation of the EBPR sub-model. The algorithm proposed in the paper is also suitable for other sub-models of ASMs.