COD fractions of leachate from aerobic and anaerobic pilot scale landfill reactors

One of the most important problems with designing and maintaining a landfill is managing leachate that generated when water passes through the waste. In this study, leachate samples taken from aerobic and anaerobic landfill reactors operated with and without leachate recirculation are investigated in terms of biodegradable and non-biodegradable fractions of COD. The operation time is 600 days for anaerobic reactors and 250 days for aerobic reactors. Results of this study show that while the values of soluble inert COD to total COD in the leachate of aerobic landfill with leachate recirculation and aerobic dry reactors are determined around 40%, this rate was found around 30% in the leachate of anaerobic landfill with leachate recirculation and traditional landfill reactors. The reason for this difference is that the aerobic reactors generated much more microbial products. Because of this condition, it can be concluded that total inert COD/total COD ratios of the aerobic reactors were 60%, whereas those of anaerobic reactors were 50%. This study is important for modeling, design, and operation of landfill leachate treatment systems and determination of discharge limits.     

Thermophilic degradation of phenolic compounds in lab scale hybrid up flow anaerobic sludge blanket reactors

This Study describes the feasibility of anaerobic degradation of United States Environmental Protection Agency (USEPA) listed 4-chloro-2-nitrophenol (4C-2-NP), 2-chloro-4-nitrophenol (2C-4-NP), 2-chloro-5-methylphenol (2C-5-MP) from a simulated wastewater using four identical 7L bench scale hybrid up flow anaerobic sludge blankets (HUASBs) at five different hydraulic retention times (HRTs) under thermophilic condition (55+/-3 degrees C). The substrate to co-substrate ratios were maintained between 1:33.3 and 1:166.6. Continuous monitoring of parameters like pH, volatile fatty acids (VFAs) accumulation, oxidation reduction potential, chemical oxygen demand (COD), alkalinity, gas productions, methane percentages were carried out along with compound reduction to asses the efficiency of biodegradation. The compound reduction was estimated by using spectrophotometric methods and further validated with high-performance liquid chromatography (HPLC). Optimum HRT values were observed at 24h. Optimum ratio of substrate (phenolic compounds) to co-substrate (glucose) was 1:100. Scanning electron micrographs show that the granules were composed of thermophilic Methanobrevibacter and thermophilic Methanothrix like bacteria.     

Heavy metal leaching from aerobic and anaerobic landfill bioreactors of co-disposed municipal solid waste incineration bottom ash and shredded low-organic residues

In this study, heavy metal leaching from aerobic and anaerobic landfill bioreactor test cells for co-disposed municipal solid waste incineration (MSWI) bottom ash and shredded low-organic residues has been investigated. Test cells were operated for 1 year. Heavy metals which were comparatively higher in leachate of aerobic cell were copper (Cu), lead (Pb), boron (B), zinc (Zn), manganese (Mn) and iron (Fe), and those apparently lower were aluminum (Al), arsenic (As), molybdenum (Mo), and vanadium (V). However, no significant release of heavy metals under aerobic conditions was observed compared to anaerobic and control cells. Furthermore, there was no meaningful correlation between oxidation-reduction potential (ORP) and heavy metal concentrations in the leachates although some researchers speculate that aeration may result in excessive heavy metal leaching. No meaningful correlation between dissolved organic carbon (DOC) and leaching of Cu and Pb was another interesting observation. The only heavy metal that exceeded the state discharge limits (10mg/l, to be enforced after April 2005) in the aerobic cell leachate samples was boron and there was no correlation between boron leaching and ORP. Higher B levels in aerobic cell should be due to comparatively lower pH values in this cell. However, it is anticipated that this slightly increased concentrations of B (maximum 25mg/l) will not create a risk for bioreactor operation; rather it should be beneficial for long-term stability of the landfill through faster washout. It was concluded that aerobization of landfills of heavy metal rich MSWI bottom ash and shredded residues is possible with no dramatic increase in heavy metals in the leachate.     

Integrating an anaerobic Bio-nest and an aerobic EMMC process as pretreatment of dairy wastewater for reuse: a pilot plant study

A large dairy farm located on the island of Oahu, Hawaii was the site for an investigation for the potential integration of the existing facultative lagoon system with a cost effective pretreatment unit process. Based on the results from a laboratory study, a pilot plant was installed with two anaerobic bioreactors (10 m3 each) and one aerobic reactor (3.8 m3). Two layers of media “Bio-nest,” providing a void volume of 98%, were placed into each anaerobic bioreactor with 19% space-based on the bioreactor water volume. For better performance and reduction of shock-load, the equalization/settling tank was employed prior to the first anaerobic Bio-nest reactor. The intermediate holding tank settled effluent suspended solids from the Bio-nest reactor and adjusted the loading rate in order to improve the performance of the aerobic EMMC (entrapped mixed microbial cell) bioreactors. Based on the start-up operation of the Bio-nest system at an organic loading rate of about 1.5 g TCOD/l/day, the production rate of biogas from the first and second Bio-nest reactors was 0.64 and 0.15 l/l/day, respectively. This indicates that the anaerobic degradation of organics occurs mainly in the first Bio-nest reactor due to the low loading rate. The removal efficiency from the Bio-nest system shows TCOD removal of about 70%. The EMMC process provided further treatment to achieve a removal efficiency of TCOD at about 50% and a TN of about 35%. The cost for these pretreatments in order to be integrated with the existing lagoon system is US $1.1 per 1,000 gallons (3.8 m3) for dairy wastewater and $1.1 per 1,000 gallons (3.8 m3) for dairy wastewater and 91 for each ton of TCOD removal. This integration system provides a sustainable improvement of environment and agricultural production.     

好氧MBR污泥与厌氧MBR污泥过滤性能的比较

首先将好氧MBR污泥和厌氧MBR污泥分离成悬浮固体、胶体 溶解性物质和溶解性物质3种组分,然后通过测定污泥及各组分的比阻和压缩系数对两种MBR污泥的过滤性能进行比较研究.好氧MBR污泥的比阻明显大于厌氧MBR污泥的比阻,它们比阻的数量级都在1014~1016m/kg之间,压缩系数基本上大于0.75,说明两种MBR污泥都具有难以过滤且易于压缩的性质;在长期运行过程,好氧MBR污泥过滤性能的恶化程度明显大于厌氧MBR污泥过滤性能的恶化程度;两种MBR污泥各成分比阻大小的顺序均为:溶解性物质>胶体 溶解性物质>悬浮固体.     

Comparative performance of anaerobic reactors for treatment of sago industry wastewater

For a country like India where energy continues to be precious, with oil prices continuing to rise unlike in the West, anaerobic digestion has far greater relevance than it has to many other regions of the world. The cassava starch production in our country is mainly concentrated in small to medium scale factories, which generates 30,000–40,000 l of effluent per ton of sago produced. The effluent is acidic and highly organic in nature having chemical oxygen demand (COD) of 5,000–7,000 mg l^?1 during the season and 1,000–5,000 during the off-season. These effluents pose a serious threat to the environment and quality of life in the rural area. Since the treatment of cassava starch factory effluents through the normal biogas plants with 30–55 days retention period is very costly, attempts have been made to treat them through high-rate hybrid reactor with several hours of retention period. In Random-Packed Anaerobic Filter, the maximum COD reduction was observed (84.4 %) at 10 h hydraulic retention time (HRT). At 4 h HRT only 46.3 % COD was removed. Even though higher COD removal was achieved at 20 h, the better HRT was at 10 h as the difference between the 20 and 10 h HRT in only 0.2 %. In Up-flow Anaerobic Sludge Blanket reactor, the maximum COD removal (90 %) and total solid (TS) removal (82 %) were observed in a HRT of 30 h, whereas low COD (67 %) and TSs (64 %) removal was observed at 5 h HRT. The treatment of sago industry effluent in a hybrid reactor was studied and the HRT employed was 10, 24, 32, and 40 h. The COD removal rates were 86, 93, 94, and 95 %, and the TSs removal was 79, 85, 86, and 89 %. When the results of all these three reactors were compared, the hybrid reactor seems to be better with an optimum HRT range of 10–20 h. Hence, the anaerobic digestion has proved to be an effective method of treating the sago industry wastewater with simultaneous production of energy in the form of methane.     

Influence of leachate recirculation on aerobic and anaerobic decomposition of solid wastes

In this study, the effect of leachate recirculation on aerobic and anaerobic degradation of municipal solid wastes is determined by four laboratory-scale landfill reactors. The options studied and compared with the traditional anaerobic landfill are: leachate recirculation, landfill aeration, and aeration with leachate recirculation. Leachate quality is regularly monitored by the means of pH, alkalinity, total dissolved solids, conductivity, oxidation-reduction potential, chloride, chemical oxygen demand, ammonia, and total Kjeldahl nitrogen, in addition to generated leachate quantity. Aerobic leachate recirculated landfill appears to be the most effective option in the removal of organic matter and ammonia. The main difference between aerobic recirculated and non-recirculated landfill options is determined at leachate quantity. Recirculation is more effective on anaerobic degradation of solid waste than aerobic degradation. Further studies are going on to determine the optimum operational conditions for aeration and leachate recirculation rates, also with the operational costs of aeration and recirculation.     

Comparison of four enhancement strategies for aerobic granulation in sequencing batch reactors

Aerobic granules were developed in four identical sequencing batch reactors (SBRs) with synthetic wastewater to compare different strategies for the enhancement of granulation. The SBRs were operated by (a) increasing organic loading rate in R1; (b) reducing settling time in R2; (c) extending starvation period in R3; and (d) increasing shear force in R4. The results showed that four operational strategies were able to enhance aerobic granulation successfully in SBR, but that also showed different effect on the granulation process and characteristics of mature aerobic granules. The rapidest granulation was observed by using short settling time (R2) and the granules had higher extracellular polymeric substance (EPS) than other reactors. Extended starvation period (R3) and high shear force (R4) resulted in longer granulation period and the granules with higher integrity and smaller size. Higher organic loading rate (R1) resulted in the granules with larger size and higher K value. The maximum specific COD removal rates (q(max)) of the granules in all SBRs were at a similar level (0.13-0.16 g COD/h-g VSS) but the granules in R1 and R2 had higher apparent half rate constant (K) of 18 and 16 mg/L, than those in R3 and R4 (2.8 and 3.3 mg/L).     

Failure analysis of a pilot scale melter

Failure of the pilot-scale test melter resulted from severe overheating of the Inconel 690 (690) jacketed molybdenum electrode. Extreme temperatures were required to melt the glass during this campaign because the feed material contained a very high waste loading. Metallurgical evaluation revealed the presence of an alloy containing nickel and molybdenum in several ingots found on the bottom of the melter and on a drip which had solidified on the electrode sheath. This indicates that a major portion of the electrode assembly was exposed to a temperature of at least 1317°C, the nickel/molybdenum eutectic temperature. Small regions on the end of the 690 sheath showed evidence of melting, indicating that this localized region exceeded 1345 °C, the melting point of 690. In addition to nickel, antimony was found on the grain boundaries of the molybdenum electrode. This also contributed to the failure of the electrode. The source of the antimony was not identified but is believed to have originated from the feed material. Metallurgical evaluation also revealed that nickel had attacked the grain boundaries of the molybdenum/tungsten drain valve. This component did not fail in service; however, intergranular attack led to degradation of the mechanical properties, resulting in the fracture of the drain valve tip during disassembly. Antimony was not observed on this component.     

Removal of sulfide in integrated anaerobic–aerobic wastewater treatment system

In recent years, the stipulations fixed by regulatory bodies have become stringent to keep environmental pollution under control. Normally COD and BOD are the parameters monitored to determine the efficiency of any treatment system. But in many cases, industrial wastewater may contain sulfate along with other organic constituents. Sulfate, if present in the wastewater, will be converted to H₂S under anaerobic conditions and this is hazardous. Subsequently, if the same wastewater is treated under aerobic conditions, a part of the air supplied will be utilized for oxidation of sulfide back to sulfate which leads to reduced efficiency of the aerobic treatment. The released wastewater with high sulfate levels will be going into the environment, which is undesirable. Methods are reported in the literature for the removal of sulfate and sulfide before and after anaerobic treatment respectively. Most of these methods are chemical which are either costly or impracticable. Therefore, a novel approach for removing sulfate or sulfide in the treatment scheme is required. In the present communication, studies are undertaken by designing an innovative stripper system where sulfide is removed to the extent of 60 to 70% before aerobic treatment. The parameters involved in design and operation of the stripper, such as airflow rate, liquid flow rate, liquid to air ratio, and pH profile, are optimized. It is a physical system in which air and waste water are passed as counter currents. The treated wastewater from the stripper, which contains less sulfide, may be post-treated in the aerobic system before final discharge. Hydrogen sulfide can be efficiently removed by coupling this type of stripper to existing anaerobic systems. The system can be efficiently used in existing treatment plants or in new designs to control sulfide (free sulfide generated in an anaerobic reactor in the case of wastewaters having high sulfate inhibits methanogenesis, resulting in reduced performance of the anaerobic process) generated in anaerobic reactors and to optimize the air and oxygen requirements in the aerobic system.     

Metal elution from Ni- and Fe-based alloy reactors under hydrothermal conditions

Elution of metals from Ni- and Fe-based alloy (i.e. Inconel 625 and SUS 316) under hydrothermal conditions was investigated. Results showed that metals could be eluted even in a short contact time. At subcritical conditions, a significant amount of Cr was extracted from SUS 316, while only traces of Ni, Fe, Mo, and Mn were eluted. In contrast, Ni was removed in significant amounts compared to Cr when Inconel 625 was tested. Several factors including temperature and contact time were found to affect elution behavior. The presence of air in the fluid even promoted elution under subcritical conditions.     

Kinetics of the biodegradation of green table olive wastewaters by aerobic and anaerobic treatments

The biodegradation of the organic pollutant matter present in green table olive wastewater (GTOW) is studied in batch reactors by an aerobic biodegradation and by an anaerobic digestion. In the aerobic biodegradation, the evolution of the substrate (in terms of chemical and biochemical oxygen demand), biomass, and total polyphenolic compounds present in the wastewater are followed during the process, and a kinetic study is performed using Contois' model, which when applied to the experimental results provides the kinetic parameter of this model, resulting in a modified Contois' equation (q=3.3S/(0.31S(0)X+X), gCOD/gVSS d(-1)). Other kinetic parameters were determined: the cellular yield coefficient (YX/S=5.7x10(-2) gVSS/gCOD) and the kinetic constant of cellular death phase (kd=0.16 d(-1)). Similarly, in the anaerobic digestion, the evolution of the substrate digested and the methane produced are followed, and the kinetic study is conducted using a modified Monod model combined with the Levenspiel model, due to the presence of inhibition effects. This model leads to the determination of the kinetic parameters: kinetic constant when no inhibitory substance is present (kM0=8.4x10(-2) h(-1)), critical substrate concentration of inhibition (TP*=0.34 g/L) and inhibitory parameter (n=2.25).     

A pilot scale bioreactor using EMMC for carbon and nitrogen removal

A pilot scale (100 l reactor) of an entrapped mixed microbial cell (EMMC) process was fabricated and tested for simultaneous removal of carbon and nitrogen. Process performance, operational stability, and maintenance requirements were all determined. Two sources of actual agricultural processing wastewater containing a high concentration of chemical oxygen demand (COD) (about 800–1,000 mg/l) and domestic sewage containing a low concentration of COD (about 150–200 mg/l) were investigated in this study. Various HRT (hydraulic retention time) and aeration schedules were operated. It was found that soluble COD (SCOD) and soluble total nitrogen (STN) could be removed in the range of 40–70% and 20–90%, respectively, for domestic sewage depending on the operational conditions provided. For agricultural processing wastewater, removal efficiencies of SCOD and STN are 89–91% and 60–75%, respectively, depending on the HRTs and aeration schedules applied. Economic evaluation for the application of domestic sewage was conducted. It was found that at an HRT of 6 h with 24 h of aeration it costs U.S.$1.75 for the treatment of 1,000 gal/day (3.8 m³/day). It is apparent that the EMMC process is technically feasible for simultaneous removal of carbon and nitrogen under the operation of an alternated schedule of the aeration in one single bioreactor. Ultimately, it can replace or upgrade the existing conventional wastewater treatment plant by combining the secondary and tertiary wastewater treatment plant in one bioreactor and provides simple maintenance and operation. This will also assist in providing the high quality of treated effluent meeting current and future environmental regulation for reuse. Electronic Publication     

Bioremediation of endosulfan contaminated soil and water -- optimization of operating conditions in laboratory scale reactors

A mixed bacterial culture consisted of Staphylococcus sp., Bacillus circulans-I and -II has been enriched from contaminated soil collected from the vicinity of an endosulfan processing industry. The degradation of endosulfan by mixed bacterial culture was studied in aerobic and facultative anaerobic conditions via batch experiments with an initial endosulfan concentration of 50mg/L. After 3 weeks of incubation, mixed bacterial culture was able to degrade 71.58+/-0.2% and 75.88+/-0.2% of endosulfan in aerobic and facultative anaerobic conditions, respectively. The addition of external carbon (dextrose) increased the endosulfan degradation in both the conditions. The optimal dextrose concentration and inoculum size was estimated as 1g/L and 75mg/L, respectively. The pH of the system has significant effect on endosulfan degradation. The degradation of alpha endosulfan was more compared to beta endosulfan in all the experiments. Endosulfan biodegradation in soil was evaluated by miniature and bench scale soil reactors. The soils used for the biodegradation experiments were identified as clayey soil (CL, lean clay with sand), red soil (GM, silty gravel with sand), sandy soil (SM, silty sand with gravel) and composted soil (PT, peat) as per ASTM (American society for testing and materials) standards. Endosulfan degradation efficiency in miniature soil reactors were in the order of sandy soil followed by red soil, composted soil and clayey soil in both aerobic and anaerobic conditions. In bench scale soil reactors, endosulfan degradation was observed more in the bottom layers. After 4 weeks, maximum endosulfan degradation efficiency of 95.48+/-0.17% was observed in red soil reactor where as in composted soil-I (moisture 38+/-1%) and composted soil-II (moisture 45+/-1%) it was 96.03+/-0.23% and 94.84+/-0.19%, respectively. The high moisture content in compost soil reactor-II increased the endosulfan concentration in the leachate. Known intermediate metabolites of endosulfan were absent in all the above degradation studies.     

Influence of alkalinity on the stabilization of municipal solid waste in anaerobic simulated bioreactor

Four simulated landfill anaerobic bioreactors were performed to investigate the influence of alkalinity on the anaerobic treatment of municipal solid waste (MSW). Leachate was recirculated in all the four reactors. One reactor was operated without alkalinization. The other three were operated under alkaline conditions. Na(2)CO(3), NaHCO(3) and NaOH were added to leachate in the second, third and fourth reactor, respectively. Experimental results showed that CO(3)(2-) and HCO(3)(-) addition had a more pronounced effect on MSW stabilization while the effect of addition of OH(-) was weak. The concentration of COD, BOD(5), total nitrogen (TN), ammonium nitrogen (NH(4)(+)-N) and nitrate nitrogen (NO(3)(-)-N), etc. in leachate significantly reduced in four reactors. The removal efficiencies were 90.56%, 92.21%, 92.74% and 90.29% for COD, 66.45%, 72.38%, 68.62% and 68.44% for NO(3)(-)-N, and 96.5%, 98.75%, 97.75% and 98% for NO(2)(-)-N in the control, Na(2)CO(3), NaHCO(3) and OH(-) added reactors, respectively. The final BOD(5)/COD was 0.262, 0.104, 0.124, and 0.143, and pH was 7.13, 7.28, 7.42, and 7.24 for control, Na(2)CO(3) added, NaHCO(3) added, and OH(-) added reactor, respectively. Therefore, alkalinity addition had positive effect on the stabilization of MSW.     

Co-digestion of mixed industrial sludge with municipal solid wastes in anaerobic simulated landfilling bioreactors

In this study, the feasibility of the anaerobic co-digestion of a mixed industrial sludge with municipal solid wastes (MSW) was investigated in three simulated anaerobic landfilling bioreactors during a 150-day period. All of the reactors were operated with leachate recirculation. One of them was loaded only with MSW (control reactor); the second reactor was loaded with mixed industrial sludge and MSW, the weight ratio of the MSW to mixed industrial sludge was 1:1 (based on dry solid) (Run 1); the third reactor was loaded with mixed industrial sludge and MSW, the weight ratio of the MSW to mixed industrial sludge was 1:2 (based on dry solid) (Run 2). The VFA concentrations decreased significantly in Run 1 and Run 2 reactors at the end of 150 days. The pH values were higher in Run 1 and Run 2 reactors compared to control reactor. The differences between leachate characteristics, the biodegradation and the bioefficiency of the reactors were compared. The NH(4)-N concentrations released to leachate from mixed sludge in Run 1 and Run 2 reactors were lower than that of control reactor. The BOD(5)/COD ratios in Run 1 and Run 2 reactors were lower than that of control reactor at the end of 150 days. Cumulative methane gas productions and methane percentages were higher in Run 1 and Run 2 reactors. Reductions in waste quantity, carbon percentage and settlement of the waste were better in Run 1 and Run 2 reactors compared to control reactor at the end of 150 days. Furthermore, TN and TP removals in waste were higher in reactors containing industrial sludge compared to control. The toxicity test results showed that toxicity was observed in reactors containing industrial mixed sludge.     

Effect of copper ion on the anaerobic and aerobic metabolism of phosphorus-accumulating organisms linked to intracellular storage compounds

The shock load effect of heavy metals (Cu (II)) on the behavior of poly-phosphate-accumulating organisms (PAOs) was investigated with respect to the transformations of poly-P, intracellular polyhydroxyalkanoates (PHAs) and glycogen. The PAOs biomass was exposed to different concentrations of Cu (II) at various pH and biomass levels. The results showed that when the mixed liquor suspended solid (MLSS) concentration was 2500-4000 mg/L, the P removal was not adversely affected by spiking with 2 mg Cu(2+)/L; however, it deteriorated completely after a Cu (II) shock concentration of 4 mg/L. Nevertheless, the tolerance of PAOs biomass to Cu (II) shock could be enhanced by increasing the MLSS. Moreover, in the presence of 2 mg Cu(2+)/L, the P removal efficiency was highest at an initial pH of 6.2 and lowest at an initial pH of 6.9, indicating that the Cu inhibitory effect was reduced by increasing the pH to 7.6. The inhibition by Cu (II) was related to the transformation of intracellular storage compounds of PAOs. Specifically, poly-P degradation might be inhibited, which reduced the energy available for PHA production and eventually led to poor P removal.     

Effect of 1,3-bis(citraconimidomethyl) benzene on the aerobic and anaerobic ageing of diene rubber vulcanizates

The effect of 1,3-bis(citraconimidomethyl) benzene (Perkalink 900) has been investigated in diene rubber vulcanizates (truck-tyre tread-cap and tread-base compounds). Cure characteristics have been studied at 141 and 193 °C. Retention of physical properties after anaerobic (cured up to 2t90, 4t90 and 8t90) and aerobic ageing (aged for 1, 2, 3 and 4 weeks at 70 °C) has been found to be higher for the compounds with Perkalink 900. Heat build-up characteristics measured by Goodrich Flexometer and Martin's ball fatigue tester have been found to be lower for the Perkalink 900 compounds. Dynamic mechanical properties (tan δ) are reduced for the compounds containing Perkalink 900 even after extended cure. Fatigue to failure properties and abrasion resistance remain unaffected with the addition of Perkalink 900 in the compounds. The observed improvements in tyre-tread compound performance support the previously published mechanism of Perkalink 900. This revised version was published online in November 2006 with corrections to the Cover Date.     

Antibacterial activity of SPIONs versus ferrous and ferric ions under aerobic and anaerobic conditions: a preliminary mechanism study

In modern medicine, major attention has been paid to superparamagnetic iron oxide nanoparticles (SPIONs). Recent studies have shown the antibacterial properties of SPIONs against some Gram‐positive and Gram‐negative bacterial strains. These nanoparticles (NPs) can bind to bacterial membranes via hydrophobic or electrostatic interactions and pass through cell barriers. In this study, the authors evaluated the antibacterial activity of magnetic NPs in comparison with ferrous and ferric ions. The level of reactive oxygen species (ROS) in the treated Staphylococcus aureus and Escherichia coli bacteria were directly measured by fluorometric detection. The results showed that iron ions and SPIONs had significant dependent antimicrobial activities. SPIONs showed greater inhibitory effects than ferrous and ferric ions against the growth of treated bacterial strains under anaerobic conditions, while in aerobic conditions, ferrous showed the strongest antibacterial activity. In anaerobic conditions, they observed the greatest ROS formation and lowest minimum inhibitory concentration in the SPION‐treated group in comparison with the other groups. It seems that the release of iron ions from SPIONs and subsequent activation of ROS pathway are the main antibacterial mechanisms of action. Nevertheless, the greater antibacterial effect of SPIONs in anaerobic conditions represents other mechanisms involved in the antibacterial activity of these NPsInspec keywords: nanomagnetics, antibacterial activity, hydrophobicity, nanoparticles, superparamagnetism, biomedical materials, iron compounds, membranes, nanobiotechnologyOther keywords: ferrous ions, anaerobic conditions, superparamagnetic iron oxide nanoparticles, antibacterial properties, bacterial membranes, electrostatic interactions, bacterial strains, aerobic conditions, SPION‐treated group, antibacterial effect, cell barriers, 2′,7′‐dichlorodihydrofluorescein diacetate, reactive oxygen species, fluorometric detection, Staphylococcus aureus, Escherichia coli     

Copper bearing microalloyed ultrahigh strength steel on a pilot scale: Microstructure and properties

In the present study, copper bearing low carbon microalloyed ultrahigh strength steel has been produced on a pilot scale. Transformation of the aforesaid steel during continuous cooling has been evaluated. The steel sample has been thermomechanically processed followed by either air cooling or water quenching. Variation in microstructure and mechanical properties at different finish rolling temperatures has been studied. A mixture of granular bainite, bainitic ferrite and precipitation of nano-sized (Ti, Nb)C particles is the characteristic microstructural feature of air cooled steel. On the other hand, predominantly lath martensitic structure along with the similar type of microalloying precipitates of air cooled steels and Cu precipitates are obtained in case of water quenched steel. The best combination of strength (1364-1403 MPa) and ductility (11-14%) has been achieved for the selected range of finish rolling temperature of water quenched steel.