Anaerobic biodegradation of trimethoprim with sulfate as an electron acceptor

Anaerobic biodegradation of trimethoprim (TMP) coupled with sulfate reduction. Demethylation of TMP is the first step in the acclimated microbial consortia. The potential degraders and fermenters were enriched in the acclimated consortia. Activated sludge and river sediment had similar core microbiomes. Trimethoprim (TMP) is an antibiotic frequently detected in various environments. Microorganisms are the main drivers of emerging antibiotic contaminant degradation in the environment. However, the feasibility and stability of the anaerobic biodegradation of TMP with sulfate as an electron acceptor remain poorly understood. Here, TMP-degrading microbial consortia were successfully enriched from municipal activated sludge (AS) and river sediment (RS) as the initial inoculums. The acclimated consortia were capable of transforming TMP through demethylation, and the hydroxyl-substituted demethylated product (4-desmethyl-TMP) was further degraded. The biodegradation of TMP followed a 3-parameter sigmoid kinetic model. The potential degraders (Acetobacterium, Desulfovibrio, Desulfobulbus, and unidentified Peptococcaceae) and fermenters (Lentimicrobium and Petrimonas) were significantly enriched in the acclimated consortia. The AS- and RS-acclimated TMP-degrading consortia had similar core microbiomes. The anaerobic biodegradation of TMP could be coupled with sulfate respiration, which gives new insights into the antibiotic fate in real environments and provides a new route for the bioremediation of antibiotic-contaminated environments.     

Effect of 2-butenal manufacture wastewater to methanogenic activity and microbial community

The inhibition ratio sharply increased with the increasing COD. The absorbance of UV-vis at 420 nm showed a linear correlation with the SMA. The molecular structure of EPS has changed when COD was 9585 mg/L. Illumina Miseq sequencing was employed to reveal the microbial composition. The synthesis of 2-butenal, which is a vital raw material for the production of sorbic acid as a food preservative, generates some toxic by-products, so it is urgent to seek better detoxification strategies for the treatment of 2-butenal manufacture wastewater. In this study, batch experiments were carried out to investigate the inhibition effect of wastewater on the methanogenic activity. To understand the wastewater toxicity to anaerobic granular sludge, variations of the specific methanogenic activity (SMA) and extracellular polymeric substance (EPS) constituents at various wastewater CODs were investigated. Ultraviolet-visible (UV-vis) spectra and Fourier transform infrared (FT-IR) spectra were employed to analyze the structure of the EPS. The results showed that the inhibitory ratio of 2-butenal manufacture wastewater was less than 8.4% on the anaerobic granular sludge when the CODs were less than 959 mg/L. However, the inhibitory ratio increased from 36.4% to 93.6% when CODs increased from 2396 mg/L to 9585 mg/L, with the SMA decreasing from 39.1 mL CH₄/(gVSS·d) to 3.2 mL CH₄/(gVSS·d). The diversity of the microbial community under various CODs was researched by Illumina 16S rRNA Miseq sequencing and the results demonstrated that Proteiniphilum、Petrimonas and Syntrophobacter were the dominant bacteria genera in all sample. Regarding archaea, Methanobacterium was the most dominated archaea genera, followed by the Methanosaeta group in all samples. Moreover, the bacterial communities had changed obviously with increasing CODs, which indicated high CODs played a negative impact on the richness and diversity of bacterial community in the sludge samples.     

Feasibility assessment of up-flow anaerobic sludge blanket treatment of sulfamethoxazole pharmaceutical wastewater

The UASB system successfully treated sulfamethoxazole pharmaceutical wastewater. High concentration sulfate of this wastewater was the main refractory factor. UASB recovery performance after a few days of inflow arrest was studied. The optimal UASB operating conditions for practical application were determined. Treatment of sulfamethoxazole pharmaceutical wastewater is a big challenge. In this study, a series of anaerobic evaluation tests on pharmaceutical wastewater from different operating units was conducted to evaluate the feasibility of using anaerobic digestion, and the results indicated that the key refractory factor for anaerobic treatment of this wastewater was the high sulfate concentration. A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was operated for 195 days to investigate the effects of the influent chemical oxygen demand (COD), organic loading rate (OLR), and COD/SO₄^2? ratio on the biodegradation of sulfamethoxazole in pharmaceutical wastewater and the process performance. The electron flow indicated that methanogenesis was still the dominant reaction although sulfidogenesis was enhanced with a stepwise decrease in the influent COD/SO₄^2? ratio. For the treated sulfamethoxazole pharmaceutical wastewater, a COD of 4983 mg/L (diluted by 50%), OLR of 2.5 kg COD/(m³·d), and COD/SO₄^2? ratio of more than 5 were suitable for practical applications. The recovery performance indicated that the system could resume operation quickly even if production was halted for a few days.     

Analysis of antibiotic resistance of Escherichia coli isolated from the Yitong River in North-east China

The concentrations of four types of antibiotics in the Yitong River were detected. The concentration of total coliforms in summer was higher than that in spring. There was a seasonal difference in antibiotic resistance of E. coli. The E. coli in the Yitong River was found to have multiple antibiotic resistance. The Yitong River is one of the largest secondary tributaries of the Songhua River. The area where the Yitong River flows is densely populated and contains the livestock and poultry breeding areas of north-east China. These areas introduce a high risk of antibiotic contamination. In this study, the concentrations of four types of typical antibiotics including quinolones, tetracyclines, sulfonamides, and trimethoprim were determined by solid phase extraction-high performance liquid chromatography. The antibiotic resistance of Escherichia coli caused by antibiotic pollution was investigated. The concentration of total coliforms in the Yitong River was detected by the plate counting method. The antibiotic resistance of E. coli to quinolones, tetracyclines, sulfonamides, and trimethoprim was analyzed by the Kirby-Bauer method. The results showed that the concentration of total coliforms in the summer was higher than that in the spring. There was a seasonal difference in the resistance rate of E. coli to antibiotics except trimethoprim. The antibiotic resistance to fluoroquinolones was relatively low. The resistance rate to tetracyclines was higher during the summer. Moreover, resistance to several antibiotics was observed in all sections. This study provides basic data for research on pollution characteristics and prevention of antibiotic exposure in rivers.     

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline,thermal hydrolysis and ultrasonic pretreatments

Sludge digestion is critical to control the spread of ARGs from wastewater to soil. Fate of ARGs in three pretreatment-AD processes was investigated. UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process. The total ARGs concentration showed significant correlation with 16S rRNA gene. The bacteria carrying ARGs could be mainly affiliated with Proteobacteria. Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.     

Aggravation of membrane fouling and methane leakage by a three-phase separator in an external anaerobic ceramic membrane bioreactor

The existence of three-phase separator did not affect COD removal in the EAnCMBR. The existence of three-phase separator aggravated methane leakage of EAnCMBR. The existence of three-phase separator aggravated membrane fouling rate of EAnCMBR. Start-up of EAnCMBR equipped three-phase separator was slightly delayed. The three-phase separator is a critical component of high-rate anaerobic bioreactors due to its significant contribution in separation of biomass, wastewater, and biogas. However, its role in an anaerobic membrane bioreactor is still not clear. In this study, the distinction between an external anaerobic ceramic membrane bioreactor (EAnCMBR) unequipped (R1) and equipped (R2) with a three-phase separator was investigated in terms of treatment performance, membrane fouling, extracellular polymers of sludge, and microbial community structure. The results indicate that the COD removal efficiencies of R1 and R2 were 98.2%±0.4% and 98.1%±0.4%, respectively, but the start-up period of R2 was slightly delayed. Moreover, the membrane fouling rate of R2 (0.4 kPa/d) was higher than that of R1 (0.2 kPa/d). Interestingly, the methane leakage from R2 (0.1 L/d) was 20 times higher than that from R1 (0.005 L/d). The results demonstrate that the three-phase separator aggravated the membrane fouling rate and methane leakage in the EAnCMBR. Therefore, this study provides a novel perspective on the effects of a three-phase separator in an EAnCMBR.     

A comprehensive simulation approach for pollutant bio-transformation in the gravity sewer

A comprehensive pollutant transformation model for sewer systems is established. The model comprises fermentation, sulfate reduction and ammonification processes. Biochemical reactions related to distinct carbon sources are depicted in the model. Pollutant transformation is attributed to different biochemical reaction processes. Presently, several activated sludge models (ASMs) have been developed to describe a few biochemical processes. However, the commonly used ASM neither clearly describe the migratory transformation characteristics of fermentation nor depict the relationship between the carbon source and biochemical reactions. In addition, these models also do not describe both ammonification and the integrated metabolic processes in sewage transportation. In view of these limitations, we developed a new and comprehensive model that introduces anaerobic fermentation into the ASM and simulates the process of sulfate reduction, ammonification, hydrolysis, acidogenesis and methanogenesis in a gravity sewer. The model correctly predicts the transformation of organics including proteins, lipids, polysaccharides, etc. The simulation results show that the degradation of organics easily generates acetic acid in the sewer system and the high yield of acetic acid is closely linked to methanogenic metabolism. Moreover, propionic acid is the crucial substrate for sulfate reduction and ammonification tends to be affected by the concentration of amino acids. Our model provides a promising tool for simulating and predicting outcomes in response to variations in wastewater quality in sewers.     

Effect of nitrobenzene on the performance and bacterial community in an expanded granular sludge bed reactor treating high-sulfate organic wastewater

Less than 50 mg/L nitrobenzene brought little effect on anaerobic sulfate reduction. Kinetics of sulfate reduction under different nitrobenzene contents was studied. Increased nitrobenzene contents greatly changed the bacterial community structure. Genus Desulfovibrio played the key role in anaerobic sulfate reduction process. Nitrobenzene (NB) is frequently found in wastewaters containing sulfate and may affect biological sulfate reduction process, but information is limited on the responses of sulfate reduction efficiency and microbial community to the increased NB contents. In this study, a laboratory-scale expanded granular sludge bed reactor was operated continuously to treat high-sulfate organic wastewater with increased NB contents. Results successfully demonstrated that the presence of more than 50 mg/L NB depressed sulfate reduction and such inhibition was partly reversible. Bath experiments showed that the maximum specific desulfuration activity (SDA) decreased from 135.80 mg SO₄^2?/gVSS/d to 30.78 mg SO₄^2?/gVSS/d when the NB contents increased from none to 400 mg/L. High-throughput sequencing showed that NB also greatly affected bacterial community structure. Bacteroidetes dominated in the bioreactor. The abundance of Proteobacteria increased with NB addition while Firmicutes presented an opposite trend. Proteobacteria gradually replaced Firmicutes for the dominance in response to the increase of influent NB concentrations. The genus Desulfovibrio was the dominant sulfate-reducing bacteria (SRB) with absence or presence of NB, but was inhibited under high content of NB. The results provided better understanding for the biological sulfate reduction under NB stress.     

Characterization of CANON reactor performance and microbial community shifts with elevated COD/N ratios under a continuous aeration mode

COD/N at low ratios (0–0.82) improved N removals of CANON. CANON performance decreased after COD/N up to 0.82. The relative abundance of AOB decreased continuously with increasing COD/N. AOB outcompeted at a high COD load led to CANON failure. The relative abundance of AnAOB decreased and increased with increasing COD/N. The effects of increasing COD/N on nitrogen removal performance and microbial structure were investigated in a SBR adopting a completely autotrophic nitrogen removal over nitrite process with a continuous aeration mode (DO at approximately 0.15–0.2 mg/L). As the COD/N increased from 0.1 to≤0.59, the nitrogen removal efficiency (NRE) increased from 88.7% to 95.5%; while at COD/N ratios of 0.59–0.82, the NRE remained at 90.7%–95.5%. As the COD/N increased from 0.82 to 1.07, the NRE decreased continuously until reaching 60.1%. Nitrosomonas sp. (AOB) and Candidatus Jettenia (anammox bacteria) were the main functional genera in the SBR. As the COD/N increased from 0.10 to 1.07, the relative abundance of Nitrosomonas decreased from 13.4% to 2.0%, while that of Candidatus Jettenia decreased from 35% to 9.9% with COD/N<0.82 then increased to 45.4% at a COD/N of 1.07. Aerobic heterotrophic bacteria outcompeted AOB at high COD loadings (650 mg/L) because of oxygen competition, which ultimately led to deteriorated nitrogen removal performance.     

Influence of reclaimed water discharge on the dissemination and relationships of sulfonamide,sulfonamide resistance genes along the Chaobai River,Beijing

Reclaimed water threatens the ecological safety of the Chaobai River. SMX, TMP, and SDZ were the first three abundant antibiotics in the research area. SRGs and intI1 were widespread with high abundance after reclaimed water recharge. The SRGs values followed the sequence: Summer>autumn>spring>winter. Strong correlations were detected between SRGs and environmental factors. Reclaimed water represents an important source of antibiotics and antibiotic resistance genes, threatening the ecological safety of receiving environments, while alleviating water resource shortages. This study investigated the dissemination of sulfonamide (SAs), sulfonamide resistance genes (SRGs), and class one integrons (intI1) in the surface water of the recharging area of the Chaobai River. The three antibiotics sulfamethoxazole, trimethoprim, and sulfadiazine had the highest abundance. The highest absolute abundances were 2.91×10⁶, 6.94×10⁶, and 2.18×10⁴ copies/mL for sul1, sul2, and intI1 at the recharge point, respectively. SRGs and intI1 were widespread and had high abundance not only at the recharging point, but also in remote areas up to 8 km away. Seasonal variations of SRGs abundance followed the order of summer>autumn>spring>winter. Significant correlations were found between SRGs and intI1 (R² = 0.887 and 0.786, p<0.01), indicating the potential risk of SRGs dissemination. Strong correlations between the abundance of SRGs and environmental factors were also found, suggesting that appropriate environmental conditions favor the spread of SRGs. The obtained results indicate that recharging with reclaimed water causes dissemination and enrichment of SAs and SRGs in the receiving river. Further research is required for the risk assessment and scientific management of reclaimed water.     

Characteristics of two transferable aminoglycoside resistance plasmids in Escherichia coli isolated from pig and chicken manure

pRKZ3 is a non-conjugative IncQ plasmid, while pKANJ7 is a conjugative IncX plasmid. The optimal mating time of pKANJ7 varied under different conditions. Both of the two transferable ARPs had little impact on the growth of their hosts. A relatively high level of fitness cost was observed for pKANJ7. The fitness cost of ARPs depended on their hosts. Plasmid-mediated antibiotic resistance genes (ARGs) have recently become a more prominent concern in the global environment. However, the prevalence of aminoglycoside resistance plasmids in the livestock industry is under reported. In this study, two transferable aminoglycoside resistance plasmids, pRKZ3 and pKANJ7, isolated from pig and chicken manure, were characterized. Results showed that pRKZ3 (8236 bp) is a non-conjugative IncQ plasmid and contains genes encoding for plasmid replication and stabilization (repA, repB and repC), mobilization (mob), and antibiotic resistance (arr-3 and aacA). pKANJ7 (30142 bp) is a conjugative IncX plasmid which codes for a type IV secretion system (T4SS). Conjugative transfer experiments showed that the optimal mating time of pKANJ7 was 8 h under the starvation condition, but the number of tranconjugants increased with time under the nutrient condition. Statistical analysis indicated that the two plasmids had little impact on the growth of their hosts, but a relatively high level of fitness cost due to pKANJ7 was observed. We also found that the fitness cost of plasmids depended on their hosts. Compared with pKANJ7, the relative fitness cost index of pRKZ3 varied within a narrow range during the 10 days of competition. The low level of fitness cost of pRKZ3 might contribute to the persistence of the plasmid in the environment. Our study provides new information for understanding the characterizations of antibiotic resistance plasmids (ARPs) in manure sources and helps to clarify the transfer and persistence of ARPs in the environment following the application of manure.     

Effects of eggshell addition on calcium-deficient acid soils contaminated with heavy metals

The eggshell was used to remediate the contaminated soil by heavy metals. The eggshell addition decreased the available state of the heavy metals. The available calcium in the soil increased due to eggshell addition. The efficiency was investigated in different moisture conditions. In this study, effects of water conditions (flooded, wet, or dry) and eggshell dosages (0, 0.1, 1.0, and 10.0 g/kg soil, respectively) on pH variation, content of unavailable state of heavy metals, form of heavy metals, and available nutritious element calcium (Ca) in acid soils contaminated with heavy metals were investigated, respectively. The soil samples were continuously cultivated indoors and analyzed by toxicity characteristic leaching procedure and community bureau of reference (BCR) sequential extraction procedure. The results showed that the addition of eggshell could effectively improve the pH of acid soil and increase it to neutral level. Moreover, the contents of unavailable state of heavy metals Cu, Zn, and Cd increased significantly. Furthermore, when the soil was cultivated under the flooded condition with 1.0 g/kg eggshell, the unavailable state of Cu, Zn, and Cd increased the most, and these heavy metals were transformed into residual state. On the other hand, the amount of available state of Ca increased to 432.19 from 73.34 mg/kg with the addition of 1.0 g/kg eggshell, which indicated that the addition of eggshell dramatically improved the available state of Ca. Therefore, eggshell could ameliorate the soil environment as it led to the decrease of available heavy metals and improvement of fertilization effectively. In a word, this study indicates that the addition of eggshell would be a new potential method for remediation of acid field soils contaminated with heavy metals.     

Statistical modeling of radiolytic (60Co g) degradation of Ofloxacin,antibiotic: Synergetic effect,kinetic studies & assessment of its degraded metabolites

Linear, interactive and quadratic effects of process parameters were studied. Degradation of Ofloxacin (Ofx) was related with G value of irradiation process. The synergistic effect of H₂O₂ on lower dose of g-irradiation was established. The process follows pseudo first order with dose constant (d = 0.232 kGy^–1). The impact of human activities in the past few decades has paved the way for the release of pollutants due to the improper effluent treatment. Recent studies revealed that, Ofloxacin, an antibiotic as one of the major pollutant affecting surface water and ground water. In this study, the radiolytic potential of Ofloxacin was investigated. The effects of pH, dose and concentration of Ofloxacin were analyzed using One Factor At a Time (OFAT) and the interactive effects between the parameters were studied using Face Centered Central Composite Design. The statistically optimised developed model shows 30% degradation at initial antibiotic concentration of 1mM at pH 3.0 and at 2 kGy dose of gamma ray. The process efficiency was evaluated in terms of G value and its correlation with the concentration of antibiotic was also established. The process of degradation was augmented by the addition of H₂O₂ (1.5 mM). The reaction kinetics for the process was evaluated, the dose rate constant and the rate of degradation for the augmented process was found to be 0.232 kGy^-1 and 0.232 mM/kGy, respectively. The degraded metabolites of the radiolytic degradation of Ofloxacin were analyzed through change in pH, reduction in TOC and GC-MS spectrum.     

Culturomics and metagenomics: In understanding of environmental resistome

State of the art of culturomics and metagenomics to study resistome was presented. The combination of culturomics and metagenomics approaches was proposed. The research directions of antibiotic resistance study has been suggested. Pharmaceutical residues, mainly antibiotics, have been called “emerging contaminants” in the environment because of their increasing frequency of detection in aquatic and terrestrial systems and their sublethal ecological effects. Most of them are undiscovered. Both human and veterinary pharmaceuticals, including antibiotics, are introduced into the environment via many different routes, including discharges from municipal wastewater treatment plants and land application of animal manure and biosolids to fertilize croplands. To gain a comprehensive understanding of the widespread problem of antibiotic resistance, modern and scientific approaches have been developed to gain knowledge of the entire antibiotic-resistant microbiota of various ecosystems, which is called the resistome. In this review, two omics methods, i.e. culturomics, a new approach, and metagenomics, used to study antibiotic resistance in environmental samples, are described. Moreover, we discuss how both omics methods have become core scientific tools to characterize microbiomes or resistomes, study natural communities and discover new microbes and new antibiotic resistance genes from environments. The combination of the method for get better outcome of both culturomics and metagenomics will significantly advance our understanding of the role of microbes and their specific properties in the environment.     

Attached cultivation of Scenedesmus sp. LX1 on selected solids and the effect of surface properties on attachment

Attachment of Scenedesmus sp. LX1 was tested on certain materials. A criterion for selection of materials was used to choose seven materials. The amount of S. sp. LX1 attached on polyurethane foam was 51.74 mg/L. Materials’ surface influenced the attachment of microalgae. Hydrophilic and hydrophobic properties also affected the attachment of S. sp. LX1. Attached cultivation systems in the literature do not present a methodology to screen materials for microalgal growth. Hence, a method is needed to find suitable materials for attached cultivation that may enhance attachment of microalgae. In this paper, we have tested seven materials culturing Scenedesmus sp. LX1 (S. sp. LX1) to evaluate the attachment of microalgae on the material surface, its growth in suspension phase and the properties of the materials. Two materials showed attachment of S. sp. LX1, polyurethane foam and loofah sponge, and allowed microalgae to grow both in the surface of the material and suspended phase. Polyurethane foam proved to be a good material for attachment of S. sp. LX1 and the amount of attached microalgae obtained was 51.73 mg/L when adding 100 pieces/L. SEM images showed that the surface and the pore size of the materials affected the attachment of the microalgae, increasing its attachment in scaffold-like materials. Furthermore, the hydrophilic and hydrophobic properties of the materials also affected the attachment of microalgae. This research can be used as a methodology to search for the assessment of a material suitable for attachment of microalgae.     

Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic,anoxic and oxic conditions

The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al³⁺. The highest TP removal efficiency occurred under 30 mg/L of Al³⁺. EPS, PS and PN concentrations increased with the addition of Al³⁺. Sludge properties significantly changed with the addition of Al³⁺. Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al³⁺ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al³⁺ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al³⁺. The highest removal efficiency of total phosphorus (TP) was achieved at an Al³⁺ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al³⁺ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al³⁺. At the Al³⁺ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al³⁺ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al³⁺ levels (>10 mg/L) weakened microbial activity. Higher Al³⁺ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO₄^3-.     

Diagnosis of sewer pipe defects on image recognition of multi-features and support vector machine in a southern Chinese city

An image-recognition-based diagnosis system of pipe defect types was established. 1043 practical pipe images were gathered by CCTV robot in a southern Chinese city. The overall accuracy of the system is 84% and the highest accuracy is 99.3%. The accuracy shows positive correlation to the number of training samples. Closed circuit television (CCTV) systems are widely used to inspect sewer pipe conditions. During the diagnosis process, the manual diagnosis of defects is time consuming, labor intensive and error prone. To assist inspectors in diagnosing sewer pipe defects on CCTV inspection images, this paper presents an image recognition algorithm that applies features extraction and machine learning approaches. An algorithm of image recognition techniques, including Hu invariant moment, texture features, lateral Fourier transform and Daubechies (DBn) wavelet transform, was used to describe the features of defects, and support vector machines were used to classify sewer pipe defects. According to the inspection results, seven defects were defined; the diagnostic system was applied to a sewer pipe system in a southern city of China, and 28,760 m of sewer pipes were inspected. The results revealed that the classification accuracies of the different defects ranged from 51.6% to 99.3%. The overall accuracy reached 84.1%. The diagnosing accuracy depended on the number of the training samples, and four fitting curves were applied to fit the data. According to this paper, the logarithmic fitting curve presents the highest coefficient of determination of 0.882, and more than 200 images need to be used for training samples to guarantee the accuracy higher than 85%.     

Degradation of metronidazole by dielectric barrier discharge in an aqueous solution

The discharge characteristics during the degradation of MNZ by DBD were investigated. Increasing the discharge frequency can promote the degradation of MNZ. MNZ removal reaches 99.1% at the initial concentration of 40 ppm within 120 min. Coexisting organic matter inhibits the degradation of MNZ. The energy efficiency of DBD for MNZ removal is higher than other technologies. Degradation of metronidazole (MNZ) which is a representative and stable antibiotic by dielectric barrier discharge (DBD) in an aqueous solution has been studied. Effects of initial MNZ concentration, solution pH and coexisting organics on the degradation were investigated. The results illustrated that increasing the input power and the discharge frequency can improve the removal of MNZ. At low initial concentration, the removal of MNZ can reach up to 99.1%. Acidic and neutral conditions are more favorable for MNZ removal than alkaline condition in the early stage of degradation. However, the difference in MNZ removal between those in acidic or neutral media and that in alkaline one could be neglected with prolonging of the treatment time. Therefore, this method can be applied to MNZ degradation with a wide pH range. Coexisting organic matter in water can attenuate the removal to some extent. This study could provide valuable references for the degradation of nitroimidazole antibiotics by DBD.     

Comparison of CNT-PVA membrane and commercial polymeric membranes in treatment of emulsified oily wastewater

CNT-PVA membrane was fabricated and compared with polymeric membranes. The separation performance was evaluated by homemade and cutting fluid emulsions. The three membranes show similar oil retention rates. CNT-PVA membranes have higher permeation fluxes compared with polymeric membranes. CNT-PVA membrane shows higher fouling resistance. Membrane separation is an attractive technique for removal of emulsified oily wastewater. However, polymeric membranes which dominate the current market usually suffer from severe membrane fouling. Therefore, membranes with high fouling resistance are imperative to treat emulsified oily wastewater. In this study, carbon nanotube-polyvinyl alcohol (CNT-PVA) membrane was fabricated. And its separation performance for emulsified oily wastewater was compared with two commercial polymeric membranes (PVDF membrane and PES membrane) by filtration of two homemade emulsions and one cutting fluid emulsion. The results show that these membranes have similar oil retention efficiencies for the three emulsions. Whereas, the permeation flux of CNT-PVA membrane is 1.60 to 3.09 times of PVDF membrane and 1.41 to 11.4 times of PES membrane, respectively. Moreover, after five consecutive operation circles of filtration process and back flush, CNT-PVA membrane can recover 62.3% to 72.9% of its initial pure water flux. However, the pure water flux recovery rates are only 24.1% to 35.3% for PVDF membrane and 6.0% to 26.3% for PES membrane, respectively. Therefore, CNT-PVA membrane are more resistant to oil fouling compared with the two polymeric membranes, showing superior potential in treatment of emulsified oily wastewater.