Aerobic Cycles Research Articles

A novel Pseudomonas aeruginosa strain performs simultaneous heterotrophic nitrification-aerobic denitrification and aerobic phosphate removal

Nitrogen and phosphate removal from wastewater relies on different functional bacteria. In this study, a novel strain affiliated with Pseudomonas aeruginosa was isolated from activated sludge by gradient dilution and performed heterotrophic nitrification-aerobic denitrification and aerobic phosphate removal (HNADPR). The strain showed an ammonium removal efficiency of 87% and a phosphate removal efficiency of 97% under optimal conditions, such as C/N ratio of 10, P/N ratio of 0.1, temperature of 30°C, and pH of 7.5–8.5. The modified Gompertz model could fit well the heterotrophic ammonium nitrification, aerobic nitrite/nitrate denitrification, and aerobic phosphate removal processes. Functional gene amplification indicated that ammonium removal followed the complete HN-AD pathway (NH4+ → NH2OH → NO2− → NO3− → NO2− → NO → N2O → N2). Phosphate removal only occurred under aerobic conditions and ceased under anaerobic conditions. In successive aerobic cycles, the strain persistently took up phosphate. In wastewater, phosphate was aerobically converted into cell membrane, intracellular and extracellular polymeric substrates (EPS). Phosphorus in the form of phosphate monoester was pooled in EPS. A hypothetic aerobic phosphate removal model for strain SNDPR-01 is proposed to improve our understanding of the novel bacterial function of HNADPR.

Biodegradation of Bisphenol-A and 17β-Estradiol Under Alternating Aerobic/Anoxic Conditions

Certain methods for reusing treated municipal wastewater, such as soil-aquifer treatment (SAT), are characterized by alternating cycles of aerobic and anoxic conditions. It is not yet known how these alternating redox conditions affect biodegradation of potentially harmful endocrine-disrupting compounds (EDCs) from treated effluents. To address this question, batch mesocosms were constructed and redox conditions in mesocosms were controlled by switching the atmosphere between air (to induce aerobic conditions) and nitrogen (to induce anoxic or anaerobic conditions). The length of anoxic cycles was varied to determine how this affects biodegradation of two target EDCs, bisphenol-A (BPA) and 17β-estradiol (E2). Important findings include: (1) BPA was biodegraded only during aerobic cycles, but E2 was biodegraded during both aerobic and anoxic cycles; (2) when redox conditions were switched from anoxic to aerobic, biodegradation of target EDCs commenced after a lag period during which no biodegradation was observed; and (3) lag time for biodegradation in the aerobic cycle was longer when anoxic cycles were longer in duration. As expected, more rapid biodegradation of both BPA and E2 was observed under aerobic conditions than under anoxic conditions, though the effect was not statistically significant for E2. Results suggested that, in actual SAT systems, length of flooding and drainage cycles may have an important effect on the degree of biodegradation achieved and, hence, on the ability of the system to provide water of acceptable quality.

Performance of aerated submerged biofilm reactor packed with local scoria for carbon and nitrogen removal from municipal wastewater

An up-flow submerged biofilm reactor packed with scoria was evaluated for municipal wastewater treatment. The reactor was operated two cycles (with and without effluent recycle) as single aerobic reactor at hydraulic loading rate (HLR) of 3.5-4.0 L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2 L/L/day). Results indicated better removal efficiency in case of anaerobic/aerobic cycles especially for ammonia and total nitrogen. Effluent recycling in the aerobic reactor enhanced ammonification with significant reduction in ammonia and nitrogen removal, while in case of single anaerobic/aerobic reactor the effluent recycling improved ammonia and nitrogen removal and kept nitrate concentration in the final effluent below 10 mg N/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46-74 ml/g for aerobic cycles and 18-50 ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145 g TSS/g COD removed.

The effect of biological sulfate reduction on anaerobic color removal in anaerobic–aerobic sequencing batch reactors

Combination of anaerobic-aerobic sequencing processes result in both anaerobic color removal and aerobic aromatic amine removal during the treatment of dye-containing wastewaters. The aim of the present study was to gain more insight into the competitive biochemical reactions between sulfate and azo dye in the presence of glucose as electron donor source. For this aim, anaerobic-aerobic sequencing batch reactor fed with a simulated textile effluent including Remazol Brilliant Violet 5R (RBV 5R) azo dye was operated with a total cycle time of 12h including anaerobic (6h) and aerobic cycles (6h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (sulfate). Performance of the anaerobic phase was determined by monitoring color removal efficiency, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), color, specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2-dioxygenase), and formation of aromatic amines. The presence of sulfate was not found to significantly affect dye decolorization. Sulfate and azo dye reductions took place simultaneously in all operational conditions and increase in the sulfate concentration generally stimulated the reduction of RBV 5R. However, sulfate accumulation under anaerobic conditions was observed proportional to increasing sulfate concentration.

Enhanced degradation of 14C-HCB in two tropical clay soils using multiple anaerobic–aerobic cycles

The aim of the study was to induce and enhance the degradation of hexachlorobenzene (HCB), a highly-chlorinated persistent organic pollutant, in two ecologically different tropical soils: a paddy soil (PS) and a non-paddy soil (FS). The degradation of HCB was enhanced using two anaerobic–aerobic cycles in model laboratory experiments. There was greater degradation of HCB in the PS (half-life of 224 days) relative to the FS (half-life of 286 days). It was further shown that soils amended with compost had higher metabolite concentrations relative to the non-amended soils. In the first cycle, there was little degradation of HCB in both soils. However, in the second cycle, there was enhanced mineralization in the PS under aerobic conditions, with the compost-treated samples showing higher mineralization. There was also extensive volatilization in both soils. The metabolite pattern revealed that the increased mineralization and volatilization was due to the formation of lower chlorinated benzenes.

Effect of nitrate on anaerobic azo dye reduction

The aim of the study was to investigate the effect of nitrate on anaerobic color removal efficiencies. For this aim, anaerobic-aerobic sequencing batch reactor (SBR) fed with a simulated textile effluent including Remazol Brilliant Violet 5R azo dye was operated with a total cycle time of 12 h, including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (nitrate) and performance of the system was determined by monitoring color removal efficiency, nitrate removal, nitrite formation and removal, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2 dioxygenase), and formation and removal of aromatic amines. Variations of population dynamics of microorganisms exposed to various amount of nitrate were identified by denaturing gradient gel electrophoresis (DGGE). It was found that nitrate has adverse effect on anaerobic color removal efficiency and color removal was achieved after denitrification process was completed. It was found that nitrate stimulates the COD removal efficiency and accelerates the COD removal in the first hour of anaerobic phase. About 90 % total COD removal efficiencies were achieved in which microorganism exposed to increasing amount of nitrate. Population dynamics of microorganisms exposed to various amount of nitrate were changed and diversity was increased.

Carbon steel corrosion under anaerobic–aerobic cycling conditions in near-neutral pH saline solutions. Part 2: Corrosion mechanism

A corrosion mechanism has been developed to describe tubercle formation along pipeline steels during successive anaerobic–aerobic cycles. Small concentrations of O 2 under nominally anaerobic conditions can lead to the separation of anodes and cathodes. Under subsequent aerobic conditions localized corrosion is then promoted by O 2 reduction on the general magnetite-covered surface. Subsequently, the conversion of magnetite to maghemite passivates the general surface, and focuses corrosion within one major tubercle-covered pit. On switching from aerobic to anaerobic conditions, corrosion is temporarily supported by the galvanic coupling of lepidocrocite (γ-FeOOH) reduction (to γ-Fe-OH·OH) to steel dissolution primarily within the tubercle-covered pit.

APPEARANCE OF NOVEL G‐BACTERIA BELONGING TO ACIDOBACTERIA IN A DAIRY WASTEWATER TREATMENT PLANT

A dairy wastewater treatment plant operates a sequencing batch reactor (SBR) and stimulates enhanced biological phosphorus removal (EBPR) process with alternating anaerobic and aerobic cycles. Occasionally, the plant suffers from a high suspended solids problem in the supernatant. Interestingly, the occurrence of high suspended solids coincided with times when the EBPR process failed to remove phosphorus. To find out if there was a relationship between the EBPR failure and the high suspended solids problem, effluent samples were collected from the site during the period of poor phosphorus removal and examined microscopically. It was found that cocci‐shaped bacteria (3–4 µm in diameter) were abundant in the effluent samples and they were clustered in tetrads. These were believed to be G‐bacteria and results of both Gram and Neisser staining tests were negative, suggesting that they had few intracellular polyphosphate granules. Using polymerase chain reaction (PCR), cloning and deoxyribonucleic acid (DNA) sequence analysis, the phylogenetic information of in situ G‐bacteria was obtained. It was found that all of the recovered clones were clustered in the phylum of Acidobacteria.

Could polyphosphate-accumulating organisms (PAOs) be glycogen-accumulating organisms (GAOs)?

Polyphosphate (poly-P) is known to be a key compound in the metabolism of polyphosphate-accumulating organisms (PAOs). In this study, a sludge highly enriched (80%) in Candidatus Accumulibacter phosphatis (hereafter referred to as Accumulibacter), a widely known PAO, was used to study the ability of these microorganisms to utilize acetate anaerobically under poly-P-limiting conditions. The biomass was subject to several anaerobic and aerobic cycles, during which the poly-P pool of PAOs was gradually emptied by supplying feed deficient in phosphate and washing the biomass at the end of each anaerobic period using media containing no phosphorus. After three cycles, phosphorus was hardly released but PAOs were still able to take up acetate and stored it as polyhydroxyalkanoates (PHA), as demonstrated by post-FISH chemical staining. Glycogen degradation increased substantially, suggesting PAOs were using glycogen as the main energy source. This is a key feature of glycogen-accumulating organisms (GAOs), which are known to compete with PAOs in enhanced biological phosphorus removal (EBPR) systems. The ratios between acetate uptake, polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) production, and glycogen consumption agree well with the anaerobic models previously proposed for GAOs.

Evaluation of Sludge Yield and Phosphorus Removal in a Cannibal Solids Reduction Process

The potential for simultaneous sludge minimization and enhanced biological phosphorus removal (EBPR) in Cannibal solids reduction processes was investigated. To simulate a Cannibal-EBPR system, a sequencing batch reactor (SBR) operated with anaerobic and aerobic cycles was coupled with an anaerobic sidestream bioreactor, which received mixed liquor from the SBR and returned the same amount of treated sludge back to the SBR. The biomass yield in the Cannibal-EBPR system was estimated to be 0.16 mg volatile suspended solids (VSS)/mg chemical oxygen demand, which represented a 16–33% reduction in solids production compared to a Control-EBPR system operated with a 10-day solids retention time, for which conventional digestion of excess sludge was assumed. Regarding EBPR, greater than 98% phosphorus removal was sustainable in the Cannibal-EBPR system, but a mass balance on total phosphorus could not be closed, with nearly 33% of the phosphorus unaccounted. The fate of the missing phosphorus could not be resolved.

Glucose metabolism and kinetics of phosphorus removal by the fermentative bacterium Microlunatus phosphovorus.

Phosphorus and carbon metabolism in Microlunatus phosphovorus was investigated by using a batch reactor to study the kinetics of uptake and release of extracellular compounds, in combination with (31)P and (13)C nuclear magnetic resonance (NMR) to characterize intracellular pools and to trace the fate of carbon substrates through the anaerobic and aerobic cycles. The organism was subjected to repetitive anaerobic and aerobic cycles to induce phosphorus release and uptake in a sequential batch reactor; an ultrafiltration membrane module was required since cell suspensions did not sediment. M. phosphovorus fermented glucose to acetate via an Embden-Meyerhof pathway but was unable to grow under anaerobic conditions. A remarkable time shift was observed between the uptake of glucose and excretion of acetate, resulting in an intracellular accumulation of acetate. The acetate produced was oxidized in the subsequent aerobic stage. Very high phosphorus release and uptake rates were measured, 3.34 mmol g of cell(-1) h(-1) and 1.56 mmol g of cell(-1) h(-1), respectively, values only comparable with those determined in activated sludge. In the aerobic period, growth was strictly dependent on the availability of external phosphate. Natural abundance (13)C NMR showed the presence of reserves of glutamate and trehalose in cell suspensions. Unexpectedly, [1-(13)C]glucose was not significantly channeled to the synthesis of internal reserves in the anaerobic phase, and acetate was not during the aerobic stage, although the glutamate pool became labeled via the exchange with intermediates of the tricarboxylic acid cycle at the level of glutamate dehydrogenase. The intracellular pool of glutamate increased under anaerobic conditions and decreased during the aerobic period. The contribution of M. phosphovorus for phosphorus removal in wastewater treatment plants is discussed on the basis of the metabolic features disclosed by this study.

Products from primary sludge fermentation and their suitability for nutrient removal

Both denitrification and biological phosphorus removal depend on the presence of readily biodegradable carbon. Primary sludge fermentation is one way of producing such substrates. Soluble products of sludge fermentation are mainly short-chain fatty acids with two to five carbon atoms (84% of dissolved COD). In considering molar degradation rates by denitrifying organisms in batch experiments, the acids can be divided into two groups: the preferentially degraded linear forms of C2 to C5 acids and the branched C4 and C5 acids. The non-identified fraction (16% COD) which might contain acids with more than five carbon atoms is also removed by the activated sludge either by degradation or adsorption. In batch experiments with anaerobic and aerobic cycles, the uptake rate for short-chain fatty acids by phosphorus accumulating organisms and the ratio of phosphorus release to substrate uptake are determined. Acetate and propionate are taken up much faster than the C4 and C5 acids, which show very similar rates. For the ratio of phosphorus release to substrate uptake the situation is more complicated. The acids with four carbon atoms show by far the highest values.

Products from primary sludge fermentation and their suitability for nutrient removal

Both denitrification and biological phosphorus removal depend on the presence of readily biodegradable carbon. Primary sludge fermentation is one way of producing such substrates. Soluble products of sludge fermentation are mainly short-chain fatty acids with two to five carbon atoms (84% of dissolved COD). In considering molar degradation rates by denitrifying organisms in batch experiments, the acids can be divided into two groups: the preferentially degraded linear forms of C2 to C5 acids and the branched C4 and C5 acids. The non-identified fraction (16% COD) which might contain acids with more than five carbon atoms is also removed by the activated sludge either by degradation or adsorption. In batch experiments with anaerobic and aerobic cycles, the uptake rate for short-chain fatty acids by phosphorus accumulating organisms and the ratio of phosphorus release to substrate uptake are determined. Acetate and propionate are taken up much faster than the C4 and C5 acids, which show very similar rates. For the ratio of phosphorus release to substrate uptake the situation is more complicated. The acids with four carbon atoms show by far the highest values.

Biodegradation of an inhibitory nongrowth substrate (nitroglycerin) in batch reactors

Biodegradation of nitroglycerin (NG), an inhibitory, nongrowth substrate present in a multicomponent munition wastewater, was investigated in a pilot-scale batch reactor operated with both aerobic and anoxic cycles. A mixed culture was initially acclimated by gradual introduction of NG into influent and subsequently exposed to actual NG-laden production wastewater. System performance revealed that NG was amenable to aerobic biodegradation without adverse impact on removal efficiencies of other pollutants. Temporal NG concentration profiles indicated that an influent concentration of approximately 200 mg/L of NG was reduced to below detection limits in less than 5 h of aeration with no appreciable (<4%) biosorption. Failure of NG-acclimated cultures to utilize NG as a sole carbon source in bench-scale reactors suggested that NG behaved as a non-growth substrate and its degradation possibly occurred by cometabolism. Ethyl acetate present in the waste stream was an adequate growth substrate in terms of both biological and physicochemical properties. High concentrations of NO(3)-N, produced as a result of aerobic degradation of NG and other nitrogenous compounds of the waste, were treated in an anoxic phase. Approximately 95 mg/L of NO(3)-N was denitrified to below detection limits in 5 h of anoxia without the addition of external carbon sources. Two SRB cycle schemes with different static-fill times exhibited significant differences in treatment efficiencies.

Nitrous oxide emission as affected by alternate anaerobic and aerobic conditions from soil suspensions enriched with ammonium sulfate

The effect of several anaerobic and aerobic cycles of varying duration on N 2O emission and labelled N loss was investigated in ( 15NH 4) 2SO 4 amended soil suspensions. No N 2O was evolved from the continuously-anaerobic treatment. The continuously-aerobic treatment produced approximately 0.8 μg N 2O-N g −1 dry soil in 56 days. Alternate anaerobic-aerobic cycles increased the net N 2O evolution with 7.2 μg N 2O-N g −1 dry soil produced in 56 days from the 7-day anaerobic, 7-day aerobic treatment. The net N 2O evolution increased further when the duration of the anaerobic and aerobic periods was increased from 7-7 days to 14-14 days (15.7μg N 2O-N g −1 dry soil in 56 days), although the total 15N loss from the system was approximately the same for the two treatments. The results of this study show that N 2O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.

Age dependent changes of certain peptide hydrolases and dehydrogenases in bovine dental pulp.

The concentrations of certain peptide hydrolases and enzymes of the aerobic and anaerobic catabolic cycles in the fibroblasts of bovine dental pulp have been examined as a function of the developmental stage of the tissue. It was shown that the enzyme content does not change uniformly during the aging process. Anaerobic catabolic pathways remained unchanged or increased with cell maturity whereas the citric acid cycle activity decreased. Peptide hydrolases remained essentially constant.

Radio and tv

An up-flow submerged biofilm reactor packed with scoria was evaluated for municipal wastewater treatment. The reactor was operated two cycles (with and without effluent recycle) as single aerobic reactor at hydraulic loading rate (HLR) of 3.5–4.0 L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2 L/L/day). Results indicated better removal efficiency in case of anaerobic/aerobic cycles especially for ammonia and total nitrogen. Effluent recycling in the aerobic reactor enhanced ammonification with significant reduction in ammonia and nitrogen removal, while in case of single anaerobic/aerobic reactor the effluent recycling improved ammonia and nitrogen removal and kept nitrate concentration in the final effluent below 10 mg N/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46–74 ml/g for aerobic cycles and 18–50 ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145 g TSS/g COD removed.