Performance and mechanistic study on electrocoagulation process for municipal wastewater treatment based on horizontal bipolar electrodes

• EC modified with BPEs enhances pollutant removal and reduce energy consumption. • Increasing BPE number cannot increase flocculants yield exponentially. • Simulations help to predict the distribution of electrochemical reactions on BPEs. The design of electrodes is crucial to electrocoagulation process (EC), specifically, with respect to pollutant removal and energy consumption. During EC, the mechanisms for interaction between different electrode arrangement and electrode reactions remain unclear. This work presents an integrated EC process based on horizontal bipolar electrodes (BPEs). In the electrochemical cell, the graphite plates are used as driving cathode while either Fe or Al plates serves as driving anode and BPEs. The BPEs are placed horizontally between the driving electrodes. For municipal wastewater treatment, the pollutant removal efficiency and energy consumption in different configurations of two-dimension electrocoagulation (2D-EC) system with horizontal BPEs were investigated. The removal efficiency of turbidity, total phosphorus and total organic carbon increased significantly with the number of BPEs. Noted that the energy consumption for TP removal decreased by 75.2% with Fe driving anode and 81.5% with Al driving anode than those of 2D-EC, respectively. In addition, the physical field simulation suggested the distributions of potential and current in electrolyte and that of induced charge density on BPE surface. This work provides a visual theoretical guidance to predict the distribution of reactions on BPEs for enhanced pollutant removal and energy saving based on electrocoagulation process for municipal wastewater treatment.     

The treatment of black-odorous water using tower bipolar electro-flocculation including the removal of phosphorus,turbidity, sulfion,and oxygen enrichment

• An innovative bubble column tower BPE was designed to treat the black-odorous water. • PO₄³⁻, S²⁻ and turbidity were removed, and dissolved oxygen was enriched in the BPE. • An aluminum bipolar electrode gave the best oxygen enrichment and pollutant removal. • Changes of microorganisms confirmed the improvement in water quality achieved. The large amount of municipal wastewater discharged into urban rivers sometimes exceeds the rivers’ self-purification capacity leading to black-odorous polluted water. Electro-flocculation has emerged as a powerful remediation technology. Electro-flocculation in a bubble column tower with a bipolar electrode (BPE) was tested in an attempt to overcome the high resistance and weak gas-floatation observed with a monopolar electrode (MPE) in treating such water. The BPE reactor tested had a Ti/Ta₂O₅-IrO₂ anode and a graphite cathode with an iron or aluminum bipolar electrode suspended between them. It was tested for its ability to reduce turbidity, phosphate and sulphion and to increase the concentration of dissolved oxygen. The inclusion of the bipolar electrode was found to distinctly improved the system’s conductivity. The system’s electro-flocculation and electrical floatation removed turbidity, phosphate and sulphion completely, and the dissolved oxygen level improved from 0.29 to 6.28 mg/L. An aluminum bipolar electrode performed better than an iron one. Changes in the structure of the microbial community confirmed a significant improvement in water quality.     

Electrocoagulation process for the treatment of metal-plating wastewater: Kinetic modeling and energy consumption

The wastewater from industrial area was treated by EC via Fe and Al electrodes. Cu, Ni, Cr and Zn were highly removed at the first minutes, simultaneously. Pseudo-2nd-order was found to be more suitable for kinetics. Adsorption capacities based on kinetic modeling were observed as Cr>Cu>Ni>Zn. The chemical cost in the case of pH adjustment after EC was less as 3.83 $/m³. It is known that wastewater produced by the metal-plating industry contains several heavy metals, which are acidic in nature and therefore toxic for the environment and for living creatures. In particular, heavy metals enter the food chain and accumulate in vital organs and cause serious illness. The precipitation of these metals is mostly achieved by pH adjustment, but as an alternative to this method, the electrocoagulation process has investigated in this study using iron and aluminum electrodes. The effects of the pH adjustment on removal before and after the electrocoagulation process were investigated, and cost analyses were also compared. It was observed that a high proportion of removal was obtained during the first minutes of the electrocoagulation process; thus, the current density did not have a great effect. In addition, the pH adjustment after the electrocoagulation process using iron electrodes, which are 10% more effective than aluminum electrodes, was found to be much more efficient than before the electrocoagulation process. In the process where kinetic modeling was applied, it was observed that the heavy metal removal mechanism was not solely due to the collapse of heavy metals at high pH values, and with this modeling, it was seen that this mechanism involved adsorption by iron and aluminum hydroxides formed during the electrocoagulation process. When comparing the ability of heavy metals to be adsorbed, the sequence was observed to be Cr>Cu>Ni>Zn, respectively.     

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.     

Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation

GO/TiO₂ membrane was prepared by assembling GO nanosheets and TiO₂ nanotubes. The intercalation of TiO₂ nanotubes enlarged the space of GO interlayers and modified the surface morphology. Hydrophilic/underwater superoleophobic property of GO/TiO₂ membrane was obtained. Water permeability, hydrophilicity, oleophobicity and antifouling ability of GO-based membrane were all enhanced by intercalating TiO₂ nontubes. Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide(GO) nanosheets and titanium dioxide (TiO₂) nanotubes for oil/water separation. GO/TiO₂ membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO₂ membrane shows greater water permeability with the water flux up to 531 L/(m²·h·bar), which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO₂membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO₂ nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO₂ membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO₂ membrane in oil-water treatment.     

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.     

Shipboard bilge water treatment by electrocoagulation powered by microbial fuel cells

Reveals the synergy between microbial fuel cells and electrocoagulation. Demonstrates MFC-ECC shipboard wastewater treatment is advantageous. MFC-ECC integration enables energy neutral bilge water treatment. Ships generate large amounts of wastewater including oily bilge water, blackwater and greywater. Traditionally they are treated separately with high energy consumption. In this study we demonstrate the feasibility that these waste streams can be treated using an integrated electrocoagulation cell (ECC) and microbial fuel cell (MFC) process, which not only synergized the contaminants removal but also accomplished energy neutrality by directly powering EC with MFC electricity. Results showed that MFC stack powered ECC removed 93% of oily organics, which is comparable to the performance of an external DC voltage powered ECC. In the meantime, more than 80% of COD was removed from MFCs when fed with either acetate or municipal wastewater. Moreover, the ECC electrode area and distance showed notable effects on current generation and contaminants removal, and further studies should focus on operation optimization to enhance treatment efficiency.     

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.     

Application and mechanism of polysaccharide extracted from Enteromorpha to remove nano-ZnO and humic acid in coagulation process

Green source Ep was extracted from marine alga waste. The molecule model structure of Ep was studied and constructed. PAC-Ep coagulation system improves the efficiency of removal efficiency. Synergistic effects between NPs and HA make a big difference to enhance efficiency. Mechanism is charge neutralization, hydrogen bonding and adsorbing-complexing Enteromorpha polysaccharide (Ep) extracted from alga a novel green coagulant aid for nanoparticles (NPs) and heavy metal ions removal and the structure of EP was intensively studied in this study. The integration of Ep with polyaluminum chloride (PAC-Ep) coagulants exhibited higher coagulation performance than that of the polyaluminum chloride (PAC) because of the negatively charged NPs suspension and humic aid (HA) solution. Significant high removal efficiencies of dissolved organic matter (94.1%), turbidity (99.3%) and Zn ions (69.3%) were achieved by the PAC-Ep coagulants. The dual-coagulation properties of PAC-Ep for different pollutants was based on multiple mechanisms, including (i) Al³⁺ charge neutralization; (ii) hydroxy aluminum hydroxyl bridging formed polynuclearhydroxy complexes bridge and sweep colloidal particles; (iii) adsorption and bridging of Ep chain for the NPs and heavy metal ions. Results indicated that the destabilization of colloid was induced by the coexisting HA and higher removal was achieved as ions adsorption was enhance in the presence of HA complexation. On the basis of that, the extraction of polysaccharide is a promising candidate for its high coagulation performance in water treatment.     

Enhanced nitrification in integrated floating fixed-film activated sludge (IFFAS) system using novel clinoptilolite composite carrier

Novel carriers with favorable electrophilicity and hydrophilicity were prepared. Novel carriers had the capability of nitrification-enhancing. NH₄⁺-N removal efficiency of IFFAS process rose up to 20% with novel carriers. Nitrosomonadales and Nitrospirales were identified as the functional nitrifiers. The population of Nitrospirales increased by 4.51%. The integrated floating fixed-film activated sludge (IFFAS) process is an ideal preference for nitrification attributing to the longer sludge age for nitrifiers. However, as the core of this process, conventional carriers made of polymer materials usually exhibit negative charge and hydrophobicity on the surface, which is unbeneficial to nitrifying biofilm formation. In this study, novel clinoptilolite composite carriers with favorable hydrophilicity, positive charge and nitrification-enhancing capability were made and implemented in IFFAS system. In comparison with conventional carriers, the novel clinoptilolite composite carriers displayed positive charges on the surface (11.7±1.1 mV, pH 7.0) with increased hydrophilicity (surface contact angle dropped to 76.7°). The novel-carriers-based reactors achieved significantly better NH₄⁺-N removal efficiency at different influent concentrations, dissolved oxygen (DO) levels and shock loads (NH₄⁺-N removal efficiency rose up to 20% comparing with the control reactors filled with polyethylene (PE) carriers or activated sludge). High-throughput sequencing (HTS) results indicated the novel clinoptilolite composite carriers provided favorable niche for more types of bacteria, especially for Nitrosomonadales and Nitrospirales (the functional nitrifiers in the system). The population of Nitrospirales increased by 4.51% by using novel clinoptilolite composite carriers comparing with using PE carriers, which ensured enhanced nitrification process. This study was expected to provide a practical option for enhancing wastewater nitrification performance with the novel clinoptilolite composite carrier.     

Effective removal of Cd2+ and Pb2+ pollutants from wastewater by dielectrophoresis-assisted adsorption

Dielectrophoresis (DEP) process could enhance the removal the Cd²⁺ and Pb²⁺ with less absorbent. The removal rates of both Cd²⁺ and Pb²⁺ increased with the increase of voltage. The overall removal rate of Cd²⁺ and Pb²⁺ in the binary system is higher than that of Cd²⁺ or Pb²⁺ in the single system. DEP could cause considerable changes of the bentonite particles in both surface morphology and microstructure. Dielectrophoresis (DEP) was combined with adsorption (ADS) to simultaneously and effectively remove Cd²⁺ and Pb²⁺ species from aqueous solution. To implement the process, bentonite particles of submicro-meter size were used to first adsorb the heavy metal ions. These particles were subsequently trapped and removed by DEP. The effects of the adsorbent dosage, DEP cell voltage and the capture pool numbers on the removal rate were investigated in batch processes, which allowed us to determine the optimal experimental conditions. The high removal efficiency, 97.3% and 99.9% for Cd²⁺ and Pb²⁺, respectively, were achieved when the ions are coexisting in the system. The microstructure of bentonite particles before and after ADS/DEP was examined by scanning electron microscopy. Our results suggest that the dielectrophoresis-assisted adsorption method has a high capability to remove the heavy metals from wastewater.     

Municipal wastewater treatment in China: Development history and future perspectives

The history of China’s municipal wastewater management is revisited. The remaining challenges in wastewater sector in China are identified. New concept municipal wastewater treatment plants are highlighted. An integrated plant of energy, water and fertilizer recovery is envisaged. China has the world’s largest and still growing wastewater sector and water market, thus its future development will have profound influence on the world. The high-speed development of China’s wastewater sector over the past 40 years has forged its global leading treatment capacity and innovation ability. However, many problems were left behind, including underdeveloped sewers and sludge disposal facilities, low sustainability of the treatment processes, questionable wastewater treatment plant (WWTP) effluent discharge standards, and lacking global thinking on harmonious development between wastewater management, human society and the nature. Addressing these challenges calls for fundamental changes in target design, policy and technologies. In this mini-review, we revisit the development history of China’s municipal wastewater management and identify the remaining challenges. Also, we highlight the future needs of sustainable development and exploring China’s own wastewater management path, and outlook the future from several aspects including targets of wastewater management, policies and technologies, especially the new concept WWTP. Furthermore, we envisage the establishment of new-generation WWTPs with the vision of turning WWTP from a site of pollutant removal into a plant of energy, water and fertilizer recovery and an integrated part urban ecology in China.     

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.     

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.     

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.     

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.     

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.     

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%.