[Nitrification and Bioaugmentation of Biological Treatment System of Sewage Treatment Plant at High Temperature in Summer].

The influence of temperature (30-45℃) and ammonia-nitrogen volume load on the nitrification function and microbial community of activated sludge in an aerobic tank of a sewage treatment plant were investigated under simulated high-temperature stress in the summer. Meanwhile, the bioaugmentation effectiveness of the middle-temperature-enriched nitrifying sludge (with or without acclimation) was evaluated in two biological treatment systems under high-temperature shock. The results showed that the ammonium-nitrogen (NH4+-N) removal efficiency and the nitrifying bacteria content of the aerobic activated sludge at 30-40℃ were above 90% and up to 4.55% and decreased to 40% and 1.97% at 45℃, respectively. To quickly recover the nitrification function of the biological system under high-temperature shock in the summer, the middle-temperature-enriched nitrifying sludge was acclimated at 40℃ for 61 d and achieved (60±5) mg·(L·h)-1 nitrification activity. Then, its bioaugmentation efficiency was compared with that of the middle-temperature-enriched nitrifying sludge. In the bioaugmentation test, 10% of NH4+-N was removed in the reactor inoculated with 5% (volume fraction) of the acclimated nitrifying sludge, while the reactor needed inoculate with 10% (volume fraction) of the middle-temperature-enriched sludge to achieve the same removal efficiency. The results suggested that middle-temperature-enriched nitrifying sludge, after acclimating at 40℃, has a better enhancement effect under a high-temperature shocking load.

[Pilot-scale Experiment on Enrichment of Nitrifying Activated Sludge and Its Application in Enhancing a Wastewater Biological Treatment System Against Ammonia Shocking Loads].

Nitrifying activated sludge (NAS) was enriched in a membrane bioreactor (MBR) with pre-treated municipal wastewater and additional ammonium sulfate as the culture medium. The influences of temperature, dissolved oxygen (DO), ammonia nitrogen volumetric load, free ammonia (FA), and free nitrite (FNA) on the enrichment of NAS were investigated, the cost of the process was evaluated, and then NAS's application in enhancing a wastewater biological treatment system against ammonia shocking loads was attempted. The results showed that after 182 days of cultivation in an MBR, NAS had a nitrification activity of 98.41 mg·(L·h)-1, which was 30-times higher than that of the seeding sludge. The yield of NAS was 14.96 mg·(L·d)-1, costing 3.52 Yuan for 1 kg. Temperature was found to be a key factor affecting the sludge nitrification activity. The sludge nitrification activity was decreased to 1/3 of the maximum value at temperatures below 15.0℃, while lowering the ammonium volumetric load retarded the decrease in the sludge nitrification activity to some extent. In addition, dissolved oxygen deficiency resulted in nitrite accumulation, and thereby slowed down the NAS enrichment rate. The enriched NAS was then applied to a wastewater biological treatment pilot equipment, which had just been exposed to an ammonium shocking load. The removal rate of ammonia nitrogen in the biological system increased from 29.4% to 88.4% after 2.0% of NAS was inoculated. The enhanced biological system retained ammonia removal rates of as high as 99.0%, even as the temperature dropped to 13.3℃±1.6℃ afterwards. The above pilot-experiment results suggested that enriched nitrifying sludge is suitable for quickly increasing the start-up or recovery rates of the nitrifying function in a biological system.

[Pollution Characteristics and Emission Coefficients of Volatile Organic Compounds from the Packaging and Printing Industry in Zhejiang Province].

This paper presents the raw material composition and VOC treatment status of the packaging and printing industry in Zhejiang Province based on the survey data obtained in 2015 of 254 packaging and printing enterprises. To analyze the emission characteristics and calculate the emission coefficients of the packaging and printing industry, 100 typical enterprises were further screened according to different printing processes. The results showed that about two-thirds of packaging and printing enterprises failed to effectively dispose of VOCs; meanwhile, solvent-based materials were still commonly used in the packaging and printing industry. The main emission pollution factors of VOCs in the packaging and printing industry were ethyl acetate, isopropanol, ethanol, propyl acetate, and n-butyl acetate. The VOC emission coefficient of the packaging and printing industry in Zhejiang Province was 0.485 kg·kg-1, of which the gravure printing was the primary source with VOCs emission coefficient of 0.634 kg·kg-1. Compared with the material balance method, the error value from the emission coefficient method was less than 15%.

[Removal of Mixed Waste Gases by a Biotrickling Filter Packed with a Novel Combined Packing Material].

A pilot biotrickling filter (BTF) was set up for removal of a mixed waste gas containing toluene and ethanol. The packing material was composed of polyhedral sphere and polyhedral hollow column previously designed by our group. The results showed this BTF could successfully start up within only 8 d and the average eliminate capacities for toluene and ethanol were 97.14 and 113.10 g · (m³ · h)⁻¹, respectively. Empty bed residence time (EBRT) and the inlet concentration had effects on the removal of toluene. The maximum elimination capacity of toluene and ethanol was 123.34 and 206.36 g (m³ · h)⁻¹ under EBRT of 21.11 s, respectively. However, the effect of spray liquid density was not obvious, and the optimal value of solution and gas ratio was 6.82 L · m⁻³. The influence of unstable processing condition on its performance was also investigated. NaOH solution could effectively reduce the plugging of the filler layer, and the removal capability of pollutant could be recovered within 3 days. After the running was stopped for 10 d, the removal performance of this BTF could be quickly recovered.

[Performance evaluation of three novel biotrickling packings].

Packing is the support medium for microbial adhesion and water retention, and its characteristics are directly related to the removal of pollutants. In the present study, three novel biotrickling packings were developed: polyhedral sphere, burr sphere and polyhedral hollow column. The results showed that the structural characteristics of polyhedral sphere and polyhedral hollow column, with the specific surface area of 200 m2 x m(-3), were better than those of traditional biotrickling packings. The resistance coefficient zeta of polyhedral sphere was almost identical before and after the biofilm formation. Under the same condition, zeta of burr sphere increased much more. Investigations on the start-up time showed that the polyhedral hollow columns could contribute more to the quick biofilm formation. The performance of BTF which was packed with polyhedral sphere was better than the others. When the inlet concentrations of toluene and ethanol were 687.37 and 651.17 mg x m(-3), the removal efficiencies achieved 76.78% and 99.23%, respectively. Biomass measurements showed that the biomass adhering on these packings were more than that on the common polypropylene Bauer ring. Biofilm could be renewed and removed easily from the polyhedral sphere and the pressure drop could maintain at 51.6 Pa x m(-1) at the later stable running phase. However, the pressure drop in the BTF which used burr sphere as the packings increased much more (193.3 Pa x m(-1)), thus causing a clogging phenomenon.

[Removal of toluene from waste gas by honeycomb adsorption rotor with modified 13X molecular sieves].

The removal of toluene from waste gas by Honeycomb Adsorption Rotor with modified 13X molecular sieves was systematically investigated. The effects of the rotor operating parameters and the feed gas parameters on the adsorption efficiency were clarified. The experimental results indicated that the honeycomb adsorption rotor had a good humidity resistance. The removal efficiency of honeycomb adsorption rotor achieved the maximal value with optimal rotor speed and optimal generation air temperature. Moreover, for an appropriate flow rate ratio the removal efficiency and energy consumption should be taken into account. When the recommended operating parameters were regeneration air temperature of 180 degrees C, rotor speed of 2.8-5 r x h(-1), flow rate ratio of 8-12, the removal efficiency kept over 90% for the toluene gas with concentration of 100 mg x m(-3) and inlet velocity of 2 m x s(-1). The research provided design experience and operating parameters for industrial application of honeycomb adsorption rotor. It showed that lower empty bed velocity, faster rotor speed and higher temperature were necessary to purify organic waste gases of higher concentrations.

[Treatment of organic waste gas by adsorption rotor].

The adsorption rotor is applicable to treating organic waste gases with low concentration and high air volume. The performance of adsorption rotor for purifying organic waste gases was investigated in this paper. Toluene was selected as the simulative gaseous pollutant and the adsorption rotor was packed with honeycomb modified 13X molecular sieves (M-13X). Experimental results of the fixed adsorption and the rotor adsorption were analyzed and compared. The results indicated that some information on the fixed adsorption was useful for the rotor adsorption. Integrating the characteristics of the adsorbents, waste gases and the structures of the rotor adsorption, the formulas on optimal rotor speed and cycle removal efficiency of the adsorption rotor were deduced, based on the mass and heat balances of the adsorbing process. The numerical results were in good agreement with the experimental data, which meant that the formulas on optimal rotor speed and cycle removal efficiency could be effectively applied in design and operation of the adsorption rotor.

[Preparation and electro-catalytic characterization on La/Ce doped Ti-base lead dioxide electrodes].

Ti-base lead dioxide electrodes (Ti/PbO2) doped with rare earth La, Ce were prepared by the electrode position. The surface morphology and crystal structure of the electrodes was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), the results showed that, microstructure and crystal orientation of electrode surface changed after doping rare earth La, Ce, which made the electrode surface more dense and uniform. The electrochemical properties of the electrodes were tested by linear sweeping (LS) and cyclic voltammogram (CV), the experimental results show that, La, Ce doping improved the electrode overpotential of oxygen evolution and the peak current density, promoted the catalytic performance of the electrode. Different doping amount of modified electrodes were used to degrade methylene blue simulative dyeing wastewater, the results showed that, electrodes doped La and Ce respectively 8.0 g x L(-1) and 5.0 g x L(-1) have the best degradation efficiency and catalytic activity, for example, the removal of MB and its COD respectively researches 83.85%, 79.95% and 79.18%, 76.21%. The possible degradation pathways and mechanisms were also discussed.

[Bacterial biofilm on the apical external root surfaces of human teeth associated with chronic periradicular lesions].

OBJECTIVE: To investigate the patterns of microbial infection on the apical external root surfaces of treated and untreated teeth associated with chronic apical periodontitis and to study bacteria in the biofilm in order to find out the species, constitution and origination of bacteria in periapical biofilm. METHODS: Ten teeth with chronic apical periodontitis from patients of the Department of Stomatology of People's Hospital, Peking University: 5 untreated teeth with a radiographically visible chronic periradicular lesions and 5 teeth with extensive carious lesions, radiolucent lesions of varying sizes and attached periradicular tissues were selected for study. Using aseptic techniques and sterile instruments, bacterial samples of the root canals were taken, inoculated and separated according to usual practice. After extraction, ten teeth were fixed and the apical 5 mm portion of one root was sectioned. Root tips were dehydrated, sputter coated with gold, and then examined for the occurrence of bacteria on the apical root surfaces using scanning electron microscope. Five healthy teeth with vital pulp were used as controls. RESULTS: Microbial study showed that ten specimens yielded bacterial growth. The most prevalent bacteria were P. micros and F. nueleatum. In the 5 untreated teeth, bacterial cells were usually observed close to the apical foramen in only 1 specimen. Morphologically, these bacteria consisted of cocci. In the 5 treated teeth, a dense bacterial aggregation composed mainly of cocci and rods was observed surrounding the apical foramen of all specimens. Besides rods, other bacterial morphological types were recognized, including coaggregations of cocci and filaments, characterizing a fully developed "corn-cob". No microorganisms were found in the healthy controls. CONCLUSION: Bacterial biofilm was always present in teeth with post-treatment endodontic disease. The presence of apical bacterial biofilm is clinically important, and it may cause failure of endodontic treatment as a consequence of persistent infection.

[Prevalence of dental erosion and associated drinks in 12-year-old population of Beijing].

OBJECTIVE: To investigate the prevalence of dental erosion and associated drinks in 12-year-old adolescence of Beijing. METHODS: A random sample of 12-year-old adolescence of Beijing (n=844) was examined for dental erosion and required to fill a questionnaire of acidic drink intake. The grade criteria suitable for the survey of the dental erosion was used in the study. RESULTS: The prevalence of dental erosion was 61.8%, of which mild enamel was 74.1%, severe enamel erosion 24.9% and dentine erosion 1.0%. Statistic analysis showed that a large amount of intake of carbonated drink or juice were risk factors. CONCLUSIONS: Attention should be paid to the prevalence of dental erosion among Chinese adolescence.

[A three-dimensional finite element analysis of 0.02 taper 20# stainless steel K files during root canal instrumentation].

OBJECTIVE: To investigate the stress distribution of stainless steel K (SSK)files during root canal instrumentation. METHODS: A three-dimensional finite element model was established and analyzed under curved and torsional conditions by ANSYS 9.0. RESULTS: A finite element model of a 0.02 taper SSK 20# file was established. Under curved conditions, the stress was focused on the cutting edge when point contact occurred or the file was turned counterclockwise. The stress was focused between the cutting edges when line contact occurred or the files turned clockwise. The stress was much greater when the file contacted with the inner surface of the canal model by one point than by a line or when the file was engaged closer to the tip. CONCLUSIONS: The max pulling stress was focused on the surface of the file which indicated the starting point of the fracture.

[Clinical effects of calcium hydroxide-based sealer on chronic apical periodontitis].

OBJECTIVE: To evaluate the results of calcium hydroxide-based sealer Sealapex in the treatment of chronic apical periodontitis. METHODS: A total of 100 cases with chronic apical periodontitis were included and divided into two groups, calcium hydroxide sealer (Sealapex) group and ZOE sealer group, and Sealapex and ZOE sealer were respectively used. All cases were followed up for two years after treatment and the clinical results compared between the two groups. The evaluation was based on clinical examination and radiographic assessment using periapical index (PAI) and digital subtraction radiography (DSR) technique. RESULTS: There was no significant difference between the ZOE group and Sealapex group in overall healing rates and mean quantitative analysis at 3 months and 2 years after treatment (P = 0.206, 0.776). A correlation was found between PAI and DSR (P < 0.01, gamma = 0.58). CONCLUSIONS: Sealapex sealer could obtain satisfactory effects for the treatment of chronic apical periodontitis. The combination of DSR and PAI methods was able to monitor the radiographic bone changes of periapical disease.

Removal of dichloromethane from waste gases by a biotrickling filter.

Dichloromethane is harmful to human health and hazardous to atmospheric environment. In this study, two strains were isolated which were identified as Pseudomonas sp. and Mycobacterium sp., and utilized dichloromethane (DCM) as sole carbon and energy sources. The optimal culture conditions were temperature of 28 degrees C and pH of 6.5 for obtaining the two mixed bacterial strains. The investigation on the purification of DCM-contaminated gas was carried out in a bench-scale biotrickling filter which was inoculated with the two strains and operated under these optimal conditions. The DCM removal efficiencies varied between 72% and 99% in the biotrickling filter when empty-bed residence time was 9.6 s with the inlet concentrations ranged from 0.7 to 3.12 g/m(3) under the conditions of pH of 6.5 +/-0.5 and temperature of 28 degrees C. It was also found that NaCl accumulation in the broth would inhibit the DCM biodegradation dramatically when the accumulated NaCl concentration was over 35.1 g/L.

[The correlation between the enlargement of root canal diameter and the fracture strength and the stress distribution of root].

OBJECTIVE: To investigate the correlation between the extent of cutting of the root canal wall and the root fracture strength and the stress distribution. METHODS: Fifteen pairs of root sections were into 3 groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm respectively. The maximum load was tested required for fracture for each group through fracture test in a universal testing machine, and compared with that for the original canal. The stress and its distribution of the root with normal wall thickness (1.2 mm) and roots with 75%, 50% and 25% respectively of the normal wall thickness were examined by three-dimensional finite analysis. The maximum Von Mises stress of the root of each model was calculated. RESULTS: The mean fracture strengths of the groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm were (4 432.41 +/- 563.59) N, (4 137.43 +/- 680.29) N and (3 749.87 +/- 554.17) N respectively. The maximum load of fracture resistance is a linear function of the root canal wall thickness (r = 0.972, P < 0.001). The three-dimensional finite analysis revealed that the enlargement of root canal diameter brought on increase of stress of root canal wall, and the stress and its distribution altered with further decrease of the wall thickness. The stress of lateral loading was greater than that of vertical loading. CONCLUSIONS: The results suggests that clinical root canal treatment should be designated to remove just the infected tissue and avoid over-cutting of the hard tissue.

[Clinical effect of the restoration for pathological tooth wear].

OBJECTIVE: To investigate the effect of the restoration for pathological tooth wear. METHODS: A total of 48 pathological weared premolars and molars with restorable space in occlusal surface in 10 patients were restored by composite resins. The patients' masticatory function (biting force, masticatory efficiency, the surface electromyographic (EMG) activity of masseter muscles and anterior temporalis) were compared before and after the treatment. At the same time, the restorations were evaluated according to the modified the United States Public Health Service (USPHS) criterion. RESULTS: After the treatment, patients' clinical syndrome disappeared, the biting force was improved (P < 0.05) and the masticatory efficiency was increased significantly (P < 0.01). EMG activity, the asymmetry index and the action index of the tested muscles during different status had no significant change (P > 0.05). The composite resin restorations of the 48 teeth were all evaluated as A after three month and one year. CONCLUSIONS: Restoring the pathological weared posterior teeth with composite resins is an effective treatment to relieve the patients' syndrome, improve their masticatory efficiency and biting force.

[Establishment of the three-dimensional finite element model of the first permanent mandibular molar and its stress analysis].

OBJECTIVE: To establish more rational three dimensional finite element model (FEM) of the first permanent mandibular molar and to study the internal stress distribution. METHODS: The FEM was applied to analyze the stress distribution of the first permanent mandibular molar under various loading conditions. RESULTS: Under all five loading conditions, the maximum von-Mises stress and compressive stress in enamel were larger than that in dentin, and the tensile stress in enamel was smaller than that in dentin. When vertical force and buccal-lingual oblique force were loaded, the stresses in the enamel and dentin were minimum; when lingual-buccal oblique force was loaded, the stresses were maximum; the stresses were mainly distributed at cervical region, furcation and apical area of the mesial-lingual root canal wall. CONCLUSIONS: The stress value changes and stress distribution in the enamel and dentin were closely related with the direction of the occlusion force.

[Enamelin transcriptional expression in developing postnatal rat tooth germ].

OBJECTIVE: To observe the transcriptional expression of enamelin in developing postnatal rat first mandibular molar germs, for further studies of functions of enamelin in enamel development and mineralization. METHODS: Tissue slices of first mandibular molar germ of rat 1, 3, 7, 10, 14 days after birth were prepared. The enamelin mRNA expression was identified by in situ hybridization. RESULTS: Enamelin mRNA was observed in both ameloblast and odontoblast in 1-10 day old rat postnatal first mandibular molar germs. Enamelin mRNA appeared very weakly at 1st day, and increased through 3rd day, reached the maximum at 7th day, and reduced at 10th day and became negative at 14th day postnatally; while the expression of enamelin mRNA in odontoblast maintained lower from 1st to 10th day and negative at 14th day postnatally. CONCLUSION: Enamelin gene transcriptional expression lasts from preameloblast to maturation ameloblast, which suggests that enamelin may participate in the development of enamel and mantle dentin.