Search

Nitrification activities and microbial populations of ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were investigated in 10 full-scale biological nutrient removal wastewater treatment plants in Xi'an, China. Aerobic batch tests were used to determine the nitrifying activities while fluorescence in situ hybridization was used to quantify the fractions of AOB and NOB in the activated sludge. The results showed that nitrifying bacteria accounted for 1-10% of the total population. Nitrosomonas and Nitrospira were the dominant bacteria for AOB and NOB respectively. Moreover, the average percentage of AOB was 1.27% and that of NOB was 4.02%. The numerical ratios of NOB/AOB varied between 1.72 and 5.87. The average ammonium uptake rate and nitrite uptake rate were 3.25 ± 0.52 mg (NH -N)/g(VSS) h and 4.49 ± 0.49 mg (NO -N)/g(VSS) h, respectively. Correspondingly, the activity of NOB was 1.08-2.00 times higher than that of AOB. Thus, NOB was the dominating bacteria in nitrifying communities. The year-round data of Dianzicun (W6) also expressed a similar trend. Since NOB had higher activities than that of AOB, a large nitrite oxidation pool could be formed, which guaranteed that no nitrite would be accumulated. Therefore, stable nitrification could be achieved. A conceptual model was proposed to describe the population variation of AOB and NOB in a nitrifying community. [ABSTRACT FROM AUTHOR]

Abstract: Since the notable amount of particulate substrate in wastewater, the implications of particulate substrate on treatment efficiency have been a topic of major interest in the field of biological wastewater treatment. The particulate substrate has to be hydrolyzed by the extracellular enzymes, which are mainly embedded in extracellular polymeric substances (EPS) matrix of microbial aggregates, prior to consumption. Therefore, the important relevance between the particulate substrate and the characteristics of EPS can be expected. In this study, two lab-scale sequencing batch reactors were performed in parallel to investigate the effects of particulate and soluble substrate on the physicochemical characteristics of EPS in activated sludge. The results showed that the particulate substrate in the influent could significantly change the properties of activated sludge and the characteristics of EPS. More open and fluffy flocs with poorer settleability and dewaterability were formed with particulate substrate. More protein and humic compounds were introduced into the EPS matrix due to the deep involvement of protein and humic compounds in hydrolysis process of particulate substrate. The increments of protein and humic compounds then caused the slight higher molecular weight, higher hydrophobicity and lower zeta potential of EPS in particulate substrate system. The results in this study permitted for obtaining answers to understand the significant implications of particulate substrate in determining the physicochemical characteristics of EPS in biological wastewater treatment systems. [Copyright &y& Elsevier]

Hydrogenotrophic methanogens had been considered as key species for the anaerobic digestion (AD) of industrial wastewater and municipal sludge. However, how to evaluate the activity of the hydrogenotrophic methanogens was less studied. In this study, a volumetric device and a test procedure were developed for measuring the specific hydrogen utilization rate (HUR) of anaerobic sludge. Results showed that HUR values were highly influenced by sludge concentrations because of limitation on H2 mass transfer. The critical value of sludge concentration in the test bottle should not be higher than 1 gVSS/L. Under such condition, the kinetics of HUR would not be limited by H2 mass transfer and the maximal value of HUR could be obtained. Field survey confirmed that HUR exhibits a good relationship with specific methanogenic activity (SMA) and reactor performance. An anaerobic system with a relatively high HUR was found to be beneficial for maintaining H2 partial pressure in an appropriately low level. Moreover, such system was thermodynamically favourable for the syntrophic degradation of volatile fatty acids. As a crucial parameter of the anaerobic process, HUR could be used as a key indicator for evaluating and monitoring AD processes. [ABSTRACT FROM AUTHOR]

A new sensor | transverse electric (TE) polarized excite surface plasmon resonance (SPR) fiber optic biosensor is proposed. The graphene is the plasma layer. The transfer matrix method and the finite difference time domain method are applied to conduct the numerical simulation of the four layers (fiber core/photonic crystals/graphene/sample) of fiber optic biosensor. The results show that the relationship between refractive index and resonant wavelength is linear and the sensitivity of the fiber optic biosensor reaches 1942 nm/RIU. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) play a crucial role in the formation of activated sludge flocs. However, until now, the EPS are rather classified by the method used for extraction than by a theoretical consideration of their function and composition. In this paper, a new classification paradigm of EPS was proposed, which offered a novel approach to identify the role of EPS in the formation of activated sludge flocs. The current study gave an exploration to distinguish the EPS in the floc level (extra-microcolony polymers, EMPS) and in the microcolony level (extra-cellular polymers, ECPS). It was found that cation exchange resin treatment is efficient to disintegrate the flocs for EMPS extraction, however, inefficient to disaggregate the microcolonies for ECPS harvesting. A two-steps extraction strategy (cation exchange resin treatment followed by ultrasonication-high speed centrifugation treatment) was suggested to separate these two types of EPS in activated sludge flocs and the physicochemical characteristics of EMPS and ECPS were compared. The protein/polysaccharide ratio of ECPS was higher than that of EMPS and the molecular weight of proteins in EMPS and ECPS were found to be different. The ECPS contained higher molecular weight proteins and more hydrophobic substances than the EMPS contained. The result of excitation-emission matrix fluorescence spectroscopy analysis also showed that the EMPS and the ECPS have different fluorescent expressions and the components of EMPS were more diverse than that of ECPS. All results reported herein demonstrated that two different types of exopolymers exist in the activated sludge flocs and the inter-particle forces for aggregation of activated sludge flocs are not identical between the floc level and the microcolony level. It suggested that cation bridging interactions are more crucial in floc level flocculation, while the entanglement and hydrophobic interactions are more important in microcolony level cohesion. [ABSTRACT FROM AUTHOR]

Although EPS in microbial aggregates are importance in successful implementation of biological wastewater treatment systems, they also exhibit detrimental role on certain circumstance, such as excess sludge dewatering. Extensive efforts have been put into the disruption of EPS for improving the dewaterability of excess sludge and Fenton's reagent treatment has been demonstrated to be a very promising sludge conditioning method for EPS destruction. However, the information regarding detailed degradation process of EPS during Fenton's reagent treatment is limited. In this study, EPS were extracted from activated sludge and treated with different concentrations of Fenton's reagent. The physicochemical characteristic changes of EPS under different treatment were investigated in terms of components, EEM, molecular weight (MW), UV-Vis and FTIR. The results showed that EPS were prone to be disintegrated, but hard to be fully mineralized. Humic substances in EPS were more resistant to Fenton's reagent than other components. Low MW components of EPS were preferentially degraded prior to the disruption of high MW components. Besides, the disintegration of EPS into lower MW ones was accompanied by the formation of higher MW compounds caused by the bridge interaction of Fe ions. The cleavage of protein's backbone in EPS was mainly through destruction of amide II (N–H and C–N) in –CO–NH–. Fenton's reagent treatment also led to a significant increase of oxygen-containing functional groups in EPS molecules. This paper may pave a path to deeply understand the mechanisms of dewatering improvements of excess sludge by Fenton's conditioning. Image 1 • EPS were prone to be disintegrated rather than being mineralized. • Humic substances were more resistant to Fenton's reagent than other components. • High MW EPS were formed due to bridge interaction of Fe ions. • N–H and C–N was vulnerable to Fenton reagent than C=O in –CO–NH– of proteins. • More oxygen-containing groups were introduced into EPS with Fenton treatment. [ABSTRACT FROM AUTHOR]

Characteristics of extracellular polymeric substances (EPS) in activated sludge strongly depend on wastewater substrates. Proteinaceous substrates (ProS) present in heterogeneous polymeric form are intrinsic and important parts of wastewater substrates for microorganisms in activated sludge systems. However, correlations between ProS and characteristics of EPS are scarce. This study systematically explored the impacts of monomeric (Mono-), low polymeric (LoP-) and high polymeric (HiP-) ProS on compositions and functional groups of EPS in activated sludge. The results showed that the change of polymerization degree of ProS significantly altered the composition of EPS. Compared to EPS Mono-ProS , the proportion of proteins in EPS LoP-ProS and EPS HiP-ProS increased by 12.8% and 27.7%, respectively, while that of polysaccharides decreased by 22.9% and 63.6%, respectively. Moreover, the proportion of humic compounds in EPS LoP-ProS and EPS HiP-ProS were ∼6 and ∼16–fold higher than that in EPS Mono-ProS , respectively. The accumulation of humic compounds in EPS increased the unsaturation degree of EPS molecules, and thereby reduced the energy requirement for electrons transition of amide bonds and aromatic groups. Size exclusion chromatography (SEC) analyses detected more molecular clusters in EPS HiP-ProS , indicating more complex composition of EPS in HiP-ProS fed activated sludge. Spectroscopic characterization revealed the dominance of hydrocarbon, protein, polysaccharide and aromatic associated bonds in all three EPS. Nevertheless, with the increase of polymerization degree of ProS, the protein associated bonds (such as CO NH , C O, N C, N H) increased, while the polysaccharide associated bonds (such as C O C, C O H, O C OH) decreased. This paper paves a path to understand the role of ProS in affecting the production and characteristics of EPS in biological wastewater treatment systems. [ABSTRACT FROM AUTHOR]

Different from monomeric substrate, polymeric substrate (PS) needs to undergo slow hydrolysis process before becoming available for consumption by bacteria. Hydrolysis products will be available for the heterotrophs in low concentration, which will reduce competitive advantages of heterotrophs to nitrifiers in mixed culture. Therefore, some links between PS and nitrification process can be expected. In this study, three lab-scale sequencing batch reactors with different PS/total substrate (TS) ratio (0, 0.5 or 1) in influent were performed in parallel to investigate the influence of PS on nitrification process in activated sludge system. The results showed that with the increase of PS/TS ratio, apparent sludge yields decreased, while NO 3 − -N concentration in effluent increased. The change of PS/TS ratio in influent also altered the cycle behaviors of activated sludge. With the increase of PS/TS ratio from 0 to 0.5 and 1, the ammonium and nitrite utilization rate increased ∼2 and 3 times, respectively. The q-PCR results showed that the abundance of nitrifiers in activated sludge for PS/TS ratio of 0.5 and 1 were 0.7–0.8 and 1.4–1.5 orders of magnitude higher than that for PS/TS ratio of 0. However, the abundance of total bacteria decreased about 0.5 orders of magnitude from the former two to the latter. The FISH observation confirmed that the nitrifiers' microcolony became bigger and more robust with the increase of PS/TS ratio. This paper paves a path to understand the role of PS/TS in affecting the nitrification process in biological wastewater treatment systems. [ABSTRACT FROM AUTHOR]

The water quality of Feng-qing Lake, which is a landscape lake supplemented with reclaimed water, was surveyed to investigate the relationship between phytoplankton and environmental variables. A total of 29 water samples were collected to analyze temporal variations of phytoplankton and environmental factors from July 2013 to June 2014. Six phyla and 39 genera of phytoplankton were identified when the lake was supplied with reclaimed water. Among these, Cyanophyta and Chlorophyta account for 38.46% and 30.77% of phytoplankton, respectively. The dominant species in the lake are Pseudanabaena limnetica and Chlorella vulgaris , which are present the entire year. Other leading species include Cosmarium sp. and Raphidiopsis curvata . Principal component analysis (PCA) was conducted to analyze the relationship among environmental factors. Canonical correspondence analysis (CCA) was performed to investigate the relationship between environment factors and dominant species. The PCA result showed that temperature ( T ), total phosphorus (TP), total nitrogen (TN), transparency, and dissolved oxygen are the main factors that affect the eutrophication level of the lake. The CCA result revealed that TN, PO 4 3− –P, chemical oxygen demand (COD), T , and chlorophyll a exhibit a close relation with dominant species. In particular, TN, salinity, and COD influence the growth of P. limnetica ; T and COD influence the growth of R. curvata ; and T, PO 4 3− –P, NH 3 –N, and pH influence the growth of C. vulgaris and Cosmarium sp. [ABSTRACT FROM AUTHOR]

Abstract: Oxidation-ditch operation modes were simulated using sequencing batch reactors (SBRs) with alternate stirring and aerating. The nitrogen-removal efficiencies and nitrifying characteristics of two aeration modes, point aeration and step aeration, were investigated. Under the same air-supply capacity, oxygen dissolved more efficiently in the system with point aeration, forming a larger aerobic zone. The nitrifying effects were similar in point aeration and step aeration, where the average removal efficiencies of were 98% and 96%, respectively. When the proportion of anoxic and oxic zones was 1, the average removal efficiencies of total nitrogen (TN) were 45% and 66% under point aeration and step aeration, respectively. Step aeration was more beneficial to both anoxic denitrification and simultaneous nitrification and denitrification (SND). The maximum specific ammonia-uptake rates (AUR) of point aeration and step aeration were 4.7 and 4.9 mg /(gMLVSS h), respectively, while the maximum specific nitrite-uptake rates (NUR) of the two systems were 7.4 and 5.3 mg /(gMLVSS h), respectively. The proportions of ammonia-oxidizing bacteria (AOB) to all bacteria were 5.1% under point aeration and 7.0% under step aeration, and the proportions of nitrite-oxidizing bacteria (NOB) reached 6.5% and 9.0% under point and step aeration, respectively. The dominant genera of AOB and NOB were Nitrosococcus and Nitrospira, which accounted for 90% and 91%, respectively, under point aeration, and the diversity of nitrifying bacteria was lower than under step aeration. Point aeration was selective of nitrifying bacteria. The abundance of NOB was greater than that of AOB in both of the operation modes, and complete transformation of to was observed without accumulation. [Copyright &y& Elsevier]

Maternal nicotine exposure during pregnancy and lactation is associated with obesity in offspring. Brown adipose tissue (BAT) is correlated with energy metabolism and obesity. In this study, we explored the mechanism of maternal nicotine exposure on BAT changes in male offspring. Pregnant rats were randomly assigned to nicotine (1.0 mg/kg twice per day, subcutaneous administration) or control groups. In vitro, C3H10T1/2 cells were induced to differentiate into mature brown adipocytes, and 0–50 μM nicotine was given to C3H10T1/2 cells during the differentiation process. Nicotine-exposed males had white-like adipocytes and abnormal mitochondria structure in iBAT at 26 weeks. The expression of mitochondrial genes, UCP1 and AMPK-SIRT1-PGC-1α pathway were downregulated in the nicotine group at 26 weeks rather than 4 weeks. In vitro, 50 μM nicotine decreased the expression of mitochondrial genes, UCP1 and AMPK-SIRT1-PGC-1α pathway in brown adipocytes. Maternal nicotine exposure showed the "programming" effect on the decreased brown-like phenotype in BAT of adult male offspring via downregulating AMPK-SIRT1-PGC-1α pathway. This impairment of BAT may be a potential mechanism of nicotine-induced obesity in male offspring. • Maternal nicotine exposure led to the impairment of brown adipose tissue. • Nicotine exposure down-regulated the AMPK SIRT1 PGC-1α signals. • Nicotine showed the programming effect in regulating brown adipose tissue. [ABSTRACT FROM AUTHOR]