High Dissolved Oxygen Concentration Research Articles

Simultaneous nitrogen and organic carbon removal in aerobic granular sludge reactors operated with high dissolved oxygen concentration

Simultaneous nitrification and denitrification (SND) together with organic removal in granules is usually carried out without Dissolved Oxygen (DO) concentration control, at "low DO" (with a DO<30-50% of the saturation value, about 3-4 mg/L) to promote anoxic conditions within the aggregates. These conditions can sometimes be in detrimental of the stability of the granules itself due to a lack of shear force. In this work, the authors achieved SND without oxygen control with big sized granules. More specifically, the paper presents a experimentation focused on the analysis of two Sequencing Batch Reactors (SBRs), in bench scale, working with different aerobic sludge granules, in terms of granule size, and high DO concentration, (with concentration varying from anoxic conditions, about DO ∼0 mg/L, to values close to those of saturation, >7-8 mg/L, during feast and famine conditions respectively). In particular, different strategies of cultivation and several organic and nitrogen loading rate have been applied, in order to evaluate the efficiencies in SND process without dissolved oxygen control. The results show that, even under conditions of high DO concentration, nitrogen and organic matter can be simultaneously removed, with efficiency >90%. Nevertheless, the biological conditions in the inner layer of the granule may change significantly between small and big granules, during the feast and famine periods. From point of view of granule stability, it is also interesting that with a particle size greater than 1.5mm, after the cultivation start-up, the granules are presented stable for a long period (about 100 days) and, despite the variations of operational conditions, the granules breaking was always negligible.

Effects of Solid Waste and Industrial Effluents on Water Quality of Turag River at Konabari Industrial Area, Gazipur, Bangladesh

The study was conducted to investigate the effects of solid waste and industrial effluents on the water quality of Turag River. Both the upstream and downstream sampled water from the selected points were analyzed for color, odor, pH, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), biological oxygen demand (BOD), copper (Cu), cadmium (Cd), iron (Fe), lead (Pb) and zinc (Zn) concentrations. Results of the study showed that the color of water was light to dark black and emitted noxious smell due to the industrial effluents. The upstream water was slightly alkaline with comparatively high DO content while low concentration of other parameters. The water after the solid waste and effluents received points as well as middle and downstream points was slightly alkaline with higher levels of other parameters when compared with upstream point. The minimum and maximum values of pH, EC, TDS, DO and BOD were 7.24-7.61, 425-2277 ?S/cm, 239-1349 ppm, 1.22-3.66 ppm and -2.44-0.86 ppm, respectively. The continuous dumping of waste materials resulted in a marked increase in the concentration of metals in the river water varied in the order of Fe &gt; Zn &gt; Pb &gt; Cu &gt; Cd. The study concluded that the downstream water in the river was almost polluted and unsuitable for human consumption and aquaculture purposes.DOI: http://dx.doi.org/10.3329/jesnr.v5i2.14817 J. Environ. Sci. &amp; Natural Resources, 5(2): 213-218 2012

Differential response to abiotic conditions, predation risk, and competition determine breeding site selection by two anuran species

Sympatry of species has been a central debate in ecology for decades but the mechanisms that allow coexistence are still heatedly disputed. The main paradigms include the importance of abiotic conditions, predation risk, and competition as determinants of community structure. In this study, we investigated oviposition-site selection of two anuran species, Asiatic toads (Bufo gargarizans) and dark-spotted frogs (Pelophylax nigromaculata), which coexist in southwestern China. We sampled the abiotic and biotic attributes of 36 B. gargarizans breeding sites and 34 adjacent unused sites, and 30 P. Nigromaculata spawning sites and 36 nearby unused sites. Our results showed that these two anuran species differed in the use of the main habitat types. B. gargarizans selected larger spawning sites with low levels of disturbance, high dissolved oxygen content, and the presence of fish. Conversely, P. nigromaculata preferred smaller waterbodies that were shallow, clear, and free of fish and B. gargarizans tadpoles. We conclude that differential habitat use and differences in response to abiotic conditions, predation risk, and competition, contributes to facilitating local coexistence and high species diversity in pond communities.

α-Ketoglutaric acid production from rapeseed oil by Yarrowia lipolytica yeast

The possibility of using rapeseed oil as a carbon source for microbiological production of α-ketoglutaric acid (KGA) has been studied. Acid formation on the selective media has been tested in 26 strains of Yarrowia lipolytica yeast, and the strain Y. lipolytica VKM Y-2412 was selected as a prospective producer of KGA from rapeseed oil. KGA production by the selected strain was studied in dependence on thiamine concentration, medium pH, temperature, aeration, and concentration of oil. Under optimal conditions (thiamine concentration of 0.063 μg g cells(-1), pH 3.5, 30 °C, high dissolved oxygen concentration (pO2) of 50 % (of air saturation), and oil concentration in a range from 20 to 60 g l(-1)), Y. lipolytica VKM Y-2412 produced up to 102.5 g l(-1) of KGA with the mass yield coefficient of 0.95 g g(-1) and the volumetric KGA productivity (QKGA) of 0.8 g l(-1) h(-1).

Enhanced heme protein expression by ammonia-oxidizing communities acclimated to low dissolved oxygen conditions

This study has investigated the acclimation of ammonia-oxidizing communities (AOC) to low dissolved oxygen (DO) concentrations. Under controlled laboratory conditions, two sequencing batch reactors seeded with activated sludge from the same source were operated at high DO (near saturation) and low DO (0.1 mg O₂/L) concentrations for a period of 220 days. The results demonstrated stable and complete nitrification at low DO conditions after an acclimation period of approximately 140 days. Acclimation brought about increased specific oxygen uptake rates and enhanced expression of a particular heme protein in the soluble fraction of the cells in the low DO reactor as compared to the high DO reactor. The induced protein was determined not to be any of the enzymes or electron carriers present in the conventional account of ammonia oxidation in ammonia-oxidizing bacteria (AOB). Further research is required to determine the specific nature of the heme protein detected; a preliminary assessment suggests either a type of hemoglobin protein or a lesser-known component of the energy-transducing pathways of AOB. The effect of DO on AOC dynamics was evaluated using the 16S rRNA gene as the basis for phylogenetic comparisons and organism quantification. Ammonium consumption by ammonia-oxidizing archaea and anaerobic ammonia-oxidizing bacteria was ruled out by fluorescent in situ hybridization in both reactors. Even though Nitrosomonas europaea was the dominant AOB lineage in both high and low DO sequencing batch reactors at the end of operation, this enrichment could not be linked in the low DO reactor to acclimation to oxygen-limited conditions.

Genetic Diversity and Environmental Preferences of Monothalamous Foraminifers Revealed through Clone Analysis of Environmental Small-Subunit Ribosomal DNA Sequences

Foraminifers form an important link between bacteria and macrobenthos in natural food webs and thereby play a major role in biogeochemical cycling. There have been few studies conducted to clarify these relationships, although the biomass of foraminifera, particularly the soft-shelled monothalamous taxa, is high in the deep seas. Molecular tools are now being used to study evolution and genetic diversity in widely separated oceanic environments. However, the relationship between genetic diversity and the ambient environment is not well understood. To test the idea that environmental conditions can affect genetic diversity, we conducted molecular phylogenetic analyses based on clone analysis of environmental DNA for benthic foraminifers and environmental measurements in sediments from various oceanic environments. Monothalamous foraminifers were found in dysoxic ( 120 ?M) environments. The number of phylotypes was higher in the oxic environments of central Sagami Bay, Japan, and the east equatorial Pacific Ocean, than in the lower-oxygen areas of Sagami Bay. Phylotypes closely related to the genus Ovammina and some other saccamminids, as well as the calcareous genus Stainforthia, were preferentially found in lower dissolved-oxygen (DO) environments, while phylotypes of other saccamminids, Hippocrepinella, and an unidentified foraminiferal species, occurred at higher DO concentrations. Our analysis suggests that novel monothalamous phylotypes exist in habitats ranging from the sulfide-enriched environments of chemosynthetic ecosystems to those with high concentrations of DO as at the abyssal depths and in well-mixed bioturbated sediments.

The impact of anthropogenic pollution on limnological characteristics of a subtropical highland reservoir “Lago de Guadalupe”, Mexico

“Lago de Guadalupe ” is an important freshwater ecosystem located in the northern part of the metropolitan area surrounding Mexico City, under high demographic pressure. It receives approximately 15 hm3 ·y-1 of untreated municipal wastewater from the surrounding municipalities. In order to develop a comparative assessment of the pollution effect over the limnological characteristics of Lago de Guadalupe , this lake was characterised from February 2006 to July 2009, and the results were compared with those obtained from a non-polluted lake “Lago el Llano ” located in the same drainage area. Lago de Guadalupe was hypereutrophic with anoxic conditions throughout most of the water column. In contrast, Lago el Llano was mesotrophic with high dissolved oxygen concentrations throughout the entire water column with a clinograde profile. Both reservoirs had a monomictic mixing regime. The longitudinal zonation of physicochemical and biological variables were investigated in order to better understand the processes controlling the water quality across the reservoir during its residence time. This study shows the impact of anthropogenic pollution on the limnological characteristics of a subtropical reservoir and confirms that under adequate management schemes, namely avoiding pollution and wastewater discharges, subtropical reservoirs can be prevented from developing eutrophic conditions.

The optimal dissolved oxygen profile in a nitrifying activated sludge process – comparisons with ammonium feedback control

Ammonium feedback control is increasingly used to determine the dissolved oxygen (DO) set-point in aerated activated sludge processes for nitrogen removal. This study compares proportional-integral (PI) ammonium feedback control with a DO profile created from a mathematical minimisation of the daily air flow rate. All simulated scenarios are set to reach the same treatment level of ammonium, based on a daily average concentration. The influent includes daily variations only and the model has three aerated zones. Comparisons are made at different plant loads and DO concentrations, and the placement of the ammonium sensor is investigated. The results show that ammonium PI control can achieve the best performance if the DO set-point is limited at a maximum value and with little integral action in the controller. Compared with constant DO control the best-performing ammonium controller can achieve 1-3.5% savings in the air flow rate, while the optimal solution can achieve a 3-7% saving. Energy savings are larger when operating at higher DO concentrations.

Escherichia coli avoids high dissolved oxygen stress by activation of SoxRS and manganese-superoxide dismutase

BackgroundHigh concentrations of reactive oxygen species (ROS) were reported to cause oxidative stress to E. coli cells associated with reduced or inhibited growth. The high ROS concentrations described in these reports were generated by exposing the bacteria to H2O2 and superoxide-generating chemicals which are non-physiological growth conditions. However, the effect of molecular oxygen on oxidative stress response has not been evaluated. Since the use of oxygen-enriched air is a common strategy to support high density growth of E. coli, it was important to investigate the effect of high dissolved oxygen concentrations on the physiology and growth of E. coli and the way it responds to oxidative stress.ResultsTo determine the effect of elevated oxygen concentrations on the growth characteristics, specific gene expression and enzyme activity in E. coli, the parental and SOD-deficient strain were evaluated when the dissolved oxygen (dO2) level was increased from 30% to 300%. No significant differences in the growth parameters were observed in the parental strain except for a temporary decrease of the respiration and acetate accumulation profile. By performing transcriptional analysis, it was determined that the parental strain responded to the oxidative stress by activating the SoxRS regulon. However, following the dO2 switch, the SOD-deficient strain activated both the SoxRS and OxyR regulons but it was unable to resume its initial growth rate.ConclusionThe transcriptional analysis and enzyme activity results indicated that when E. coli is exposed to dO2 shift, the superoxide stress regulator SoxRS is activated and causes the stimulation of the superoxide dismutase system. This enables the E. coli to protect itself from the poisoning effects of oxygen. The OxyR protecting system was not activated, indicating that H2O2 did not increase to stressing levels.

Spatial distribution of Greenland halibut Reinhardtius hippoglossoides in relation to abundance and hypoxia in the estuary and Gulf of St. Lawrence

AbstractAnnual bottom‐trawl surveys (1990–2010) were used to examine associations between environmental conditions, spatial distribution, and size‐specific abundance of Greenland halibut Reinhardtius hippoglossoides in the estuary and Gulf of St. Lawrence (EGSL), and to test the influence of hypoxic conditions on habitat selection. Size classes representing juvenile, immature and adult fish were used for the analyses. The highest concentrations of fish were found in the St. Lawrence estuary at both high and low levels of stock abundance. The areas occupied by 50, 75, and 95% of juvenile fish expanded with higher population abundance. However, contrary to our predictions, densities in marginal habitats did not increase at a higher rate than in optimal habitats. Fish longer than 32 cm were distributed over a broader area than juvenile fish. Their abundance explained a limited proportion of the variability in spatial distribution. The spatial dynamics of Greenland halibut in the EGSL is best described by a proportional density model where the rate of increase in local density is associated with population abundance. Habitats selected by Greenland halibut were characterized by low dissolved oxygen (DO) levels. The strong association between high fish densities and low DO concentrations indicates a high tolerance of Greenland halibut to hypoxia. It also indicates that negative effects, if present, could be compensated by other factors such as food availability and/or refuge from predation. The results of this study also clearly define the St. Lawrence estuary as the major nursery area for the EGSL population.

Gene expression profile of hepatopancreas from grass shrimp Palaemonetes pugio exposed to cyclic hypoxia

Estuarine organisms often experience periods of cyclic hypoxia characterized by hypoxia in the early morning and normoxia in the afternoon. Here we examine the genomic responses of grass shrimp, Palaemonetes pugio, exposed to cyclic hypoxia in the laboratory. Differentially expressed genes in the hepatopancreas were determined in cyclic hypoxic vs. normoxic control groups after 1, 2, 5 and 10days of exposure to cyclic hypoxia using microarrays printed with 661 annotated transcripts obtained from multiple EST (expressed sequence tag) libraries. Sampling on each day was conducted at two different time series, one in the morning (representing low concentration of dissolved oxygen (DO), designated C-AM) and one in the afternoon (representing high DO concentration, designated C-PM). Distinct differences were observed between the number and identity of specific genes that were significantly down- or up-regulated in shrimp collected at the low DO and high DO points of the cyclic DO cycle. However, cluster analysis showed that the overall response patterns of high (C-PM) and low DO (C-AM) exposures were in the same cluster at 1, 2, and 5days. In contrast, the response patterns on different days were in different clusters. Day 1 was characterized by up-regulation of 17 unknown genes in the morning and a transient down-regulation of several hemocyanin genes, which returned to normoxic control levels in the afternoon. Days 2 and 5 showed significant down-regulation of 10 (C-AM) and 15 (C-PM) unknown genes, respectively. On day 10 the high DO samples showed a dramatic increase in the number of up-regulated genes, including several distinct hemocyanin genes, and this profile did not cluster with any of the other treatment groups. Vitellogenin, cathepsin L, cytochrome c oxidase subunit III, and fatty acid binding protein 10 were the signature down-regulated genes at day 10 (C-AM). According to GO annotation, the most abundant group of genes for both cyclic low (C-AM) and high (C-PM) DO exposure was associated with transport, defense response, and metabolic process. The differentially expressed genes were mapped to KEGG metabolic and regulatory pathways according to the gene distribution in Drosophila pathway database. Cyclic high (C-PM) DO affected a broad range of pathways compared to cyclic low (C-AM) DO.

Effects of dissolved oxygen on the biooxidation process of refractory gold ores

While multiple theories exist regarding the effect of dissolved oxygen (DO) on the biooxidation of minerals, few studies have been performed the cellular or molecular scale (e.g., genetics) and the mechanism remains unclear. In this paper, the effects of DO concentration on the biooxidation process of refractory sulfide gold ores by Acidithiobacillus ferrooxidans were investigated in the experimental stirred tank bioreactors (STRs). The results indicated that higher biooxidation and cell growth rates were correlated with higher DO concentration. The biooxidation process was restricted at 1.2 ppm DO due to oxygen limitation. Furthermore, the effects of DO on cellular and molecular scale were studied for the first time. The results demonstrated that the oxygen uptake rate (OUR), the Fe(2+) oxidation activity and the rus gene expression of A. ferrooxidans all increased with the DO concentration, which might be responsible for the increase of the biooxidation rates with the DO concentration. This study provides insight into the potential impact of molecular-level mechanisms of DO in the biooxidation process of minerals.

Synergetic Effects of Ultraviolet and Microwave Radiation for Enhanced Activity of TiO2Nanoparticles in Degrading Organic Dyes Using a Continuous-Flow Reactor

A novel continuous-flow reactor was developed to investigate the synergetic effects of ultraviolet (UV) and microwave (MW) radiation on TiO2 nanoparticles for the enhancement of photodegradation of Direct Red-81 (DR-81) and Bromothymol Blue (BTB) dyes. The efficiency of the combined UV and MW radiation was higher than the sum of the isolated and corresponding thermal effects and directly proportional to the MW power. The % photodegradation of DR-81 after 105 min irradiation at ambient conditions was 40%, 68%, 72%, and 100% using UV/MW100W, UV/MW300W, UV/MW500W, and UV/MW700W methods, respectively. The % photodegradation of BTB under the same conditions was 58%, 78%, 82%, and 88%, respectively. High dissolved oxygen concentration increased DR-81 photodegradation, whereas ambient air conditions were optimum for BTB. The extent of photomineralization of both dyes was dependent on MW power. Degradation products showed that both dyes were successfully oxidized through different intermediate species. The proper...

Simulated Storm-Water Runoff Treatment by Duckweed and Algae Ponds

Constructed storm-water wetlands with different types of vegetation are capable of removing organics and nutrients from water while providing other important environmental and ecological services. The objectives of this study were to compare the efficiencies of organic and nutrient removal from a simulated storm-water runoff between the duckweed ponds (DWPs) and the algae ponds (APs) and to establish a potential link between the population of ammonia-oxidizing organisms and effluent water quality. Two replicate ponds were operated under identical conditions in which duckweeds initially thrived off the water, but they were taken over by filamentous algae after the complete removal of duckweeds. The ponds were able to remove 74±4% chemical oxygen demand (COD); 90±3%NH4+-N; 94±2%NO3−-N; and 47±7% orthophosphate in the DWPs in contrast to only 64±6% COD; 77±6%NH4+-N; 85±4%NO3−-N; and 21±6% orthophosphate in the APs. The dissolved oxygen (DO) levels were significantly different between the ponds. In the DWPs, the diurnal DO pattern (from 0.9 to 3.9 mg/L) associated with anoxic-aerobic sequencing conditions was related to the higher phosphorus (P) removal than in the APs. Archaeal and bacterial amoA abundance in the DWPs ranged from (1.1±0.2)×106 to (2.1±0.2)×109 copies/g dry soil and from (1.6±0.3)×107 to (1.1±0.4)×1010 copies/g dry soil, respectively. The hydric soil in the DWPs harbored more ammonia-oxidizing bacteria (AOB) and oligotrophic ammonia-oxidizing archaea (AOA) than any other samples in the ponds by approximately three orders of magnitude. For comparison, the high DO concentrations (an average of 5.5 mg/L) in the APs were linked to the absence of AOA, whereas the abundance of amoA from AOB ranged from (1.3±0.3)×107 to (1.6±0.2)×109 copies/g dry soil. These results suggest that the duckweeds play an important role by creating different microbial niches and cyclic anoxic-aerobic conditions and thus lead to improved organic and nutrient removal.

Effects of the DO of Nitrification Return Flow on the Nitrogen Removal of A/A-MBR Combined Process

In this study, the traditional A/A/O process was combined with MBR to create the A/A-MBR combined process. A 2.0 m3/h pilot scale study on the combined process was carried out. The influence mechanism of dissolved oxygen (DO) in the return flow on the A/A-MBR combined process was analyzed and the suitable dissolved oxygen concentration in MBR was further optimized. The results show that the combined process has the characteristics of rapid start and stable operation. Its COD, NH4+-N, TN and TP removals were 82.1%~92.4%, 93.0~98.3%, 48.4~70.7% and 93.8~97.9%, respectively. The return flow with high concentration of DO in MBR seriously affected the denitrification rate. The DO concentration of return flow increased gradually from 2.0 mg/L to 5.0 mg/L, the denitrification rate continuously decreased, the denitrification rate in the first stage decreased from 2.52 mg NO3--N/(gVSS•h) to 0.34mg NO3--N/(gVSS•h). When the DO of nitrification return liquid ascended to 5 mg/L, the denitrification ability of activated sludge was severely inhibited, and its denitrification activity was even lost. DO were controlled between 4.0±0.5 mg/L by adjusting the aeration rate in the MBR, effluent TN could be stably maintained between 10.82-13.94 mg/L with 62.6% average removal rate. The effluent COD, NH4+-N, TN and TP stably qualified to t criteria of the first level A of China’ s "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" (GB18918-2002). If the effective control of membrane fouling could be ensured, the DO in the MBR was controlled as much as possible fewer than 4.0 mg/L. This could decrease the inhibition of denitrification by high DO from the return flow and insure that effluent TN achieved the discharge standard.

Fungal Diversity of Shallow Aquifers in Southeastern Australia

The diversity of groundwater mycobiota remains relatively unknown and unchartered. As a first description of the fungal diversity in Australian aquifers we explored the distribution, abundance and diversity of fungal assemblages in samples from an alluvial (Bylong) and two sandy (Tomago; Botany Sands) unconfined aquifers in coastal catchments of NSW, Australia. A total of 89 strains were isolated with 54 Eumycotan taxa identified. The Botany Sands aquifer, with a history of industrial chlorinated hydrocarbon contamination along a hydraulic gradient, yielded the highest richness with 23 identifiable taxa, followed by Tomago with 17 and Bylong with 14. Despite differences in geology and land use, the aquifers shared similarities in their fungal assemblages with Penicillium, Rhodotorula, Paecilomyces and Cladosporium spp. common to all sites. Fungal assemblages were notably similar between the Bylong and Tomago samples and differed from the Botany samples in composition and heterogeneity. Taxa appeared to cluster into two main groups according to their association with environmental conditions; with the taxa common to the Botany aquifer correlating strongly with higher dissolved oxygen concentrations. The diversity and spatial heterogeneity of groundwater mycobiota appeared to be influenced by both anthropogenic contaminants and associated environmental variables. Based on the criteria of ubiquity, abundance and potential sensitivity to contamination, Penicillium and Rhodotorula spp. might be fitting taxa for monitoring groundwater quality.

Impact of Minimum Dissolved Oxygen Concentration on Grow‐Out Performance of Blue Catfish with Comparison to Channel Catfish

AbstractFeed intake, the feed conversion ratio (FCR), and the production of blue catfish Ictalurus furcatus and channel catfish I. punctatus were examined in 1‐acre ponds maintained at either a high or low minimum dissolved oxygen (DO) concentration (mean values of 4.29 and 2.54 ppm [55% and 32% air saturation], respectively). Two additional studies were conducted examining only blue catfish in 0.25‐acre ponds maintained at either a high (mean values of 4.43 and 4.46 ppm [56% and 55% air saturation] in the two studies) or low (mean values of 1.41 and 1.64 ppm [18% and 20% air saturation]) minimum DO concentration. Blue and channel catfish exhibited similar feed intake (13,432 versus 13,063 lb/acre), growth (1.40 versus 1.49 lb/fish), gross production (6,662 versus 6,663 lb/acre), and net production (5,935 versus 5,813 lb/acre) in the high‐DO treatments in the 1‐acre ponds. Within the low‐DO treatment, feed intake was not significantly different (13,555 versus 12,398 lb/acre for blue and channel catfish, respectively), but both gross production (6,796 versus 5,810 lb/acre) and net production (6,069 versus 4,960 lb/acre) were significantly lower in the channel catfish ponds. The FCR was similar between species (2.25 versus 2.38) and was not affected by DO treatment. In the blue catfish studies in the 0.25‐acre ponds, ponds in the high‐DO treatments had significantly higher feed intake (+23.0% and +33.4% in 2006 and 2007, respectively) and net weight gain (+38.0% versus +42.3%) than those in the low‐DO treatments; both gross production (16,898 versus 12,963 lb/acre) and net production (14,768 versus 10,855 lb/acre) were significantly higher in the high‐DO treatment in 2006. Food conversion ratios averaged 1.86 in 2006 and 2007 and were similar in fish among DO treatments in both years. Data from these and other similar controlled studies indicate that most blue catfish production variables tend to be affected less by low DO concentrations than are channel catfish.

High Rate Nitrogen Removal in an Alum Sludge-Based Intermittent Aeration Constructed Wetland

A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m(-2) d(-1). This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3-6 mg L(-1)) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.

UASB/Flash aeration enable complete treatment of municipal wastewater for reuse

A simple, efficient and cost-effective method for municipal wastewater treatment is examined in this paper. The municipal wastewater is treated using an upflow anaerobic sludge bed (UASB) reactor followed by flash aeration (FA) as the post-treatment, without implementing aerobic biological processes. The UASB reactor was operated without recycle, at hydraulic retention time (HRT) of 8 h and achieved consistent removal of BOD, COD and TSS of 60-70% for more than 12 months. The effect of FA on UASB effluent post-treatment was studied at different HRT (15, 30 and 60 min) and dissolved oxygen (DO) concentrations (low DO = 1-2 mg/L and high DO = 5-6 mg/L). The optimum conditions for BOD, COD and sulfide removal were 30-60 min HRT and high DO concentration inside the FA tank. The final effluent after clarification was characterized by BOD and COD values of 28-35 and 50-58 mg/L, respectively. Sulfides were removed by more than 80%, but the fecal coliform only by ~2 log. The UASB followed by FA is a simple and efficient process for municipal wastewater treatment, except for fecal coliform, enabling water and nutrients recycling to agriculture.

Contribution of Dissolved Oxygen to Methylene Blue Decomposition by Hybrid Advanced Oxidation Processes System

Experimental results of photocatalysis under high dissolved oxygen (DO) concentration conditions are reported. Methylene blue was used as the organic pollutant to be degraded by a novel microwave/UV/DO/TiO2photocatalyst hybrid system. The degradation rate increased with TiO2nanoparticle dosages and DO concentration. However, inhibition of photocatalysis due to bubbles produced by DO generator was also observed. When the DO generator was used to increase the DO concentration in the pollutant solution treated by the microwave-assisted UV-TiO2photocatalysis, the decomposition rate constant was highest among all the experimental conditions tested in this study. This result demonstrated that high concentration of DO can enhance the photocatalytic reaction rate by causing a synergistic effect of constituent techniques.