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     

Performance evaluation of full-scale upflow anaerobic sludge blanket reactor treating distillery spentwash

Performance of full-scale upflow anaerobic sludge blanket (UASB) reactors treating distillery spentwash was evaluated. The plant was designed to handle 650 m³ day⁻¹ of distillery spentwash having an average chemical oxygen demand (COD) concentration of 112,400 mg l⁻¹ with a HRT of 6 days. In the plant, the pH level of the influent varied from 3.50 to 4.40 but the pH of the treated effluent stabilized to a range of 7.36 to 7.68 during the study period. The operation of the reactors during study period revealed the stable conditions of the reactors, which is evident from the low COD, biochemical oxygen demand (BOD) and total solids (TS) contents in treated effluent. In the plant, the COD, BOD₅ and TS removal efficiencies were stabilized to the range of 62.19–66.59, 72.42–77.11, and 58.47–60.46%, respectively at an organic loading rate of 2.15–4.60 kg COD m⁻³ day⁻¹. The biogas production was stabilized to the range of 48,290–135,115 m³ week⁻¹ with 60% methane content. The total quantity of biogas produced ranged from 0.40 to 0.57, 1.04 to 1.71 and 0.40 to 0.56 m³ kg⁻¹ removals of COD, BOD and TS, respectively. This study concluded that the treatment of distillery spentwash using UASB reactors contributed significantly for pollution load reduction besides generating renewable in-house bio-energy.     

Effect of bio-sludge concentration on the efficiency of sequencing batch reactor (SBR) system to treat wastewater containing Pband Ni

The removal efficiency of sequencing batch reactor (SBR) system with synthetic industrial estate wastewater (SIEWW) containing Ni²⁺ or Pb²⁺ was increased with the increase of mixed liquor suspended solids (MLSS). But, the sludge volume index (SVI) of the system was increased up to higher than 100 mL/g under MLSS of up to 4000 mg/L. Also, the effluent NO₃⁻ was decreased with the increase of MLSS. The heavy metals (Ni²⁺ or Pb²⁺), BOD₅, COD and TKN removal efficiencies of SBR system with SIEWW containing 5 mg/L heavy metal (Ni²⁺ or Pb²⁺) under MLSS of 3000 mg/L were 83–85%, 96–97%, 95–96% and 83–94%, respectively. The increase of heavy metal (Ni²⁺ or Pb²⁺) concentrations of SIEWW from 5 to 50 mg/L were not significantly effected to both COD and BOD₅ removal efficiencies (they were reduced by only 4–5%), but they were strongly effected to both TKN and heavy metals removal efficiencies (they were reduced by 15 and 20–30%, respectively). Both Ni²⁺ and Pb²⁺ could repress the growth of both nitrification and denitrification bacteria. And Ni²⁺ was more effective than Pb²⁺ to reduce the heavy metals removal efficiency. The SBR system could be applied to treat the industrial estate wastewater (IEWW) containing both Pb²⁺ and Ni²⁺ even the heavy metals concentrations was up to 5 mg/L, but the removal efficiency was quite low and excess bio-sludge did not produce. However, the system efficiency could be increased with the increase of BOD₅ concentration of the wastewater. The Pb²⁺, Ni²⁺, COD, BOD₅ and TKN removal efficiencies of the system with IEWW containing 500 mg/L BOD₅, 5 mg/L Ni²⁺ and 5 mg/L Pb²⁺ under HRT of 3 days were 85.68 ± 0.31%, 87.03 ± 0.21%, 86.0 ± 0.5%, 94.04 ± 0.4% and 90.5 ± 0.9%, respectively. And the effluent SRT, SS and SVI of the system were 44.7 ± 0.6 days, 150 ± 6 mg/L and 100 mL/g, respectively.     

A pilot study of three-stage biological–chemical treatment of landfill leachate applying continuous ferric sludge reuse in Fenton-like process

This pilot study describes a three-stage continuous process for treating landfill leachate containing significant concentrations of recalcitrant organic substances. The proposed technological scheme consisted of an activated sludge pre-treatment combined with a Fenton-like process enhanced by continuous sludge reuse and followed by an activated sludge post-oxidation. Biological pre-treatment removed >99, 86, >99, 83 and 86 % of BOD₇, COD, NH₄ ⁺–N, phenols and the sum of lignin and tannins, respectively. Operational conditions in the ferric sludge-catalysed Fenton-like process stage were carefully adjusted in order to maintain the efficacy and practicability of combined treatment scheme. Although the application of ferric sludge as a catalyst in the Fenton-like oxidation reduced COD removal efficiency by 32 % as compared to the conventional Fenton process, lower process efficiency was compensated by reducing the water exchange ratio to 50 % without increasing the consumption of reagents. Moreover, an intermittent addition (added to every second treatment cycle) of fresh ferrous iron catalyst at a H₂O₂/Fe²⁺ w/w ratio of 20/1 increased the BOD₇/COD ratio from 0.04 to 0.32 and resulted in 60 % COD removal. A cyclic addition (added to every treatment cycle) of the same amount of catalyst increased the BOD₇/COD ratio from 0.09 to 0.32, and a 10 % higher COD removal efficiency as compared to intermittent catalyst addition was achieved. Finally, biological post-treatment of the leachate resulted in more than 95 % removal of each measured parameter. Overall, the combined technological scheme with continuous ferric sludge reuse in the Fenton-like stage proved promising alternative for landfill leachate treatment.     

Failure Analysis of an Effluent Treatment Plant in an Oral Care Industry

Reports of environmental pollution by industries worldwide call for an urgent need to assess wastewater treatment facilities in various industries. This study presents an assessment of a wastewater treatment plant in an oral care (toothpaste) industry. The industry was visited, facilities for wastewater treatment were assessed (based only on efficacy to remove selected environmental and human’s health-related pollutants) and measurement of essential design parameters and facility characteristics were conducted. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD₅), chemical oxygen demand (COD), suspended solids (SS), iron concentration, and total solids (TS) in the influent wastewater into the plant were 4.96 ± 0.6 m³/d; 90 ± 5 mg/L; 224 ± 8 mg/L; 1266.78 ± 10.24 mg/L; 0.31 ± 0.11 mg/L, and 2198.65 ± 20.44 mg/L, respectively. Individual efficacies were as follows: 0.49, 0.28, and 0.38% for SS, TS, and calcium, respectively. The overall efficacy of the wastewater treatment facility was found to be 0.020% which was significantly lower than expected. This indicates that no treatment was conducted on the wastewater and that the wastewater is being discharged into the environment essentially untreated. Equalization time (t _eq) was found to be 2.0 h with equivalent equalized BOD₅ concentration of 90 ± 5 mg/L, while expected volume for the equalization tank is 1.5 m³. It was concluded that failure (lower overall efficacy) of the system can be attributed to lack of an equalization tank, inadequate treatment processes, and refusal to apply standardized engineering code and practices. Although such conditions are rare in developed nations, these results demonstrate the problems in pollution control in developing communities.     

Sulfamethoxazole abatement by photo-Fenton: Toxicity,inhibition and biodegradability assessment of intermediates

The objective of this work was to study the abatement of 200 mg L⁻¹ sulfamethoxazole (SMX) solution by means of photo-Fenton process. Biodegradability of the treated solutions was followed by the ratio biochemical oxygen demand at five days/chemical oxygen demand (BOD₅/COD) and toxicity by Microtox^® and inhibition tests. Experiments with different initial concentration of H₂O₂ were carried out. The initial amount of Fe²⁺ and pH of the solution were set at 10 mg L⁻¹ and 2.8 respectively. The temperature of the reactor was kept constant in all the experiments (25 ± 0.8 °C). Photo-Fenton process is thought to be a successful treatment step to improve the biodegradability of wastewater containing SMX. The complete antibiotic removal was achieved for a H₂O₂ dose over 300 mg L⁻¹. Biodegradability (BOD₅/COD) rose from zero (SMX solution) to values higher than 0.3 (treated solutions). Toxicity and inhibition tests pointed out in the same direction: oxidized intermediates for initial H₂O₂ dose over 300 mg L⁻¹ showed no toxicity effects on pure bacteria and no inhibition on activated sludge activity.     

Failure Analysis of a Dissolved Air Flotation Treatment Plant in a Dairy Industry

Environmental pollution in Nigeria presents an urgent need to assess wastewater treatment facilities in various industries. This article presents an assessment of dissolved air flotation (DAF) operation in a dairy industry. The industry was visited, wastewater treatment facilities were assessed (based only on efficacy to remove selected environmental health-related pollutants) and measurements of essential design and characterization parameters were taken. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD₅), chemical oxygen demand (COD), suspended solids (SS) and total solids (TS) of the influent wastewater into the plant (DAF) were 3.45 L/s, 1652.37, 3304.67, 2333.82, and 4396.10 mg/L compared to effluent quality of 560.37, 1127.33, 172.33, and 1866.67 mg/L for BOD₅, COD, SS, and TS, respectively. The pH of the wastewater is being adjusted by addition of lime before the effluent equalization tank and individual efficacies of the system were 66.09, 65.89, 65.89, 57.54, 8.68, and 94.49% for BOD₅, COD, SS, TS, DS, and total nitrogen, respectively, with overall efficacy of 38.10%. It was concluded that failure (lower overall efficacy) of the system can be attributed to setting of lime in the oversized equalization tank (50 m³ instead of 16.82 m³ per 8 h shift), the lack of application of standardized engineering code and practices (provision of underground tank in the process, lack of complete coagulation processes, coagulation and flocculation units), lack of adequate aeration unit and lack of reliable systems for automatically adjusting dosage of coagulant and flocculant. Although, DAF unit is the centerpiece of a DAF-based system design, there are several other supporting systems important to optimal DAF operation. These observations, coupled with the analysis in this report, demonstrate that the facilities necessary to minimize continuous environmental pollution are lacking. Pollution will become an increasing problem unless pollution preventing codes and standards are developed; incorporated into government regulations and the regulations are enforced.     

The bioactivity and ion release of titanium-containing glass polyalkenoate cements for medical applications

The ion release profiles and bioactivity of a series of Ti containing glass polyalkenoate cements. Characterization revealed each material to be amorphous with a T _g in the region of 650–660°C. The network connectivity decreased (1.83–1.35) with the addition of TiO₂ which was also evident with analysis by X-ray photoelectron spectroscopy. Ion release from cements were determined using atomic absorption spectroscopy for zinc (Zn²⁺), calcium (Ca²⁺), strontium (Sr²⁺), Silica (Si⁴⁺) and titanium (Ti⁴⁺). Ions such as Zn²⁺ (0.1–2.0 mg/l), Ca²⁺ (2.0–8.3 mg/l,) Sr²⁺ (0.1–3.9 mg/l), and Si⁴⁺ (14–90 mg/l) were tested over 1–30 days. No Ti⁴⁺ release was detected. Simulated body fluid revealed a CaP surface layer on each cement while cell culture testing of cement liquid extracts with TW-Z (5 mol% TiO₂) produced the highest cell viability (161%) after 30 days. Direct contact testing of discs resulted in a decrease in cell viability of the each cement tested.     

Microwave enhanced Fenton-like process for the treatment of high concentration pharmaceutical wastewater

This paper explored a novel process for wastewater treatment, i.e. microwave enhanced Fenton-like process. This novel process was introduced to treat high concentration pharmaceutical wastewater with initial COD loading of 49,912.5 mg L⁻¹. Operating parameters were investigated and the optimal condition included as follows: microwave power was 300 W, radiation time was 6 min, initial pH was 4.42, H₂O₂ dosage was 1300 mg L⁻¹ and Fe₂(SO₄)₃ dosage was 4900 mg L⁻¹, respectively. Within the present experimental condition used, the COD removal and UV₂₅₄ removal reached to 57.53% and 55.06%, respectively, and BOD₅/COD was enhanced from 0.165 to 0.470. The variation of molecular weight distribution indicated that both macromolecular substances and micromolecular substances were eliminated quite well. The structure of flocs revealed that one ferric hydrated ion seemed to connect with another ferric hydrated ion and/or organic compound molecule to form large-scale particles by means of van der waals force and/or hydrogen bond. Subsequently, these particles aggregated to form flocs and settled down. Comparing with traditional Fenton-like reaction and conventional heating assisted Fenton-like reaction, microwave enhanced Fenton-like process displayed superior treatment efficiency. Microwave was in favor of improving the degradation efficiency, the settling quality of sludge, as well as reducing the yield of sludge and enhancing the biodegradability of effluent. Microwave enhanced Fenton-like process is believed to be a promising treatment technology for high concentration and biorefractory wastewater.     

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.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Combined photo-Fenton-SBR process for antibiotic wastewater treatment

The study examined combined photo-Fenton-SBR treatment of an antibiotic wastewater containing amoxicillin and cloxacillin. Optimum H₂O₂/COD and H₂O₂/Fe²⁺ molar ratio of the photo-Fenton pretreatment were observed to be 2.5 and 20, respectively. Complete degradation of the antibiotics occurred in one min. The sequencing batch reactor (SBR) was operated at different hydraulic retention times (HRTs) with the wastewater treated under different photo-Fenton operating conditions (H₂O₂/COD and H₂O₂/Fe²⁺ molar ratio). The SBR performance was found to be very sensitive to BOD₅/COD ratio of the photo-Fenton treated wastewater. Statistical analysis of the results indicated that it was possible to reduce the Fe²⁺ dose and increase the irradiation time of the photo-Fenton pretreatment. The best operating conditions of the combined photo-Fenton-SBR treatment were observed to be H₂O₂/COD molar ratio 2, H₂O₂/Fe²⁺ molar ratio 150, irradiation time 90 min and HRT of 12 h. Under the best operating conditions, 89% removal of sCOD with complete nitrification was achieved and the SBR effluent met the discharge standards.     

Application of acidogenic fixed-bed reactor prior to anaerobic membrane bioreactor for sustainable slaughterhouse wastewater treatment

High rate anaerobic treatment systems such as anaerobic membrane bioreactors (AMBR) are less popular for slaughterhouse wastewater due to the presence of high fat oil and suspended matters in the effluent. This affects the performance and efficiency of the treatment system. In this work, AMBR has been tried for slaughterhouse wastewater treatment. After the start up period, the reactor was operated with an average organic loading rate (OLR) of 4.37 kg TCOD m⁻³ d⁻¹ with gradual increase to an average of 13.27 kg TCOD m⁻³ d⁻¹. At stable conditions, the treatment efficiency was high with an average COD and BOD₅ reduction of 93.7 and 93.96%, respectively. However, a reduction in the AMBR performance was shown with the increase of the OLR to 16.32 kg TCOD m⁻³ d⁻¹. The removal efficiencies of SCOD and BOD₅ were drastically decreased to below 53.6 and 73.3%, respectively. The decrease of the AMBR performance was due to the accumulation of VFAs. Thus, a new integrated system composed of a FBR for the acidogenesis step followed by the AMBR for methanogenesis step was developed. At high ORL, the integrated system improved the performance of the anaerobic digestion and it successfully overcame the VFA accumulation problem in the AMBR. The anaerobic treatment led to a total removal of all tested pathogens. Thus, the microbiological quality of treated wastewater fits largely with WHO guidelines.     

Corrosion behavior in SBF for titania coatings on Mg–Ca alloy

TiO₂ coating was obtained by sol–gel method to improve the corrosion resistance of Mg–Ca alloy in human body environment. The corrosion behavior of Mg–1.0 Ca alloy with TiO₂ coating was investigated by electrochemical tests and immersion tests in simulated body fluid (SBF). Bare Mg–1.0 Ca alloy suffered serious attack after immersed in simulated body fluid only for 48 h. While for the Mg–1.0 Ca alloy with TiO₂ coating, the surface almost maintained intact with only several collapses after immersed in SBF for 168 h. The electrochemical test results showed that the free corrosion current (i _corr) of Mg–1.0 Ca alloy substrate was 3.3275e−2A/cm², while the i _corr of TiO₂ coating was only 1.58549e−5A/cm². Therefore, TiO₂ coating significantly improved the corrosion resistance of Mg–1.0 Ca alloy in SBF. This enhances the potential of Mg–Ca alloy used as biodegradable orthopedic material.     

Wastewater renovation using constructed soil filter (CSF): A novel approach

Constructed soil filter (CSF) also known as Soil Biotechnology (SBT) is a process for water renovation which makes use of formulated media with culture of soil macro- and microorganisms. CSF combines sedimentation, infiltration and biodegradation processes to remove oxidizable organics and inorganics of wastewater in a single facility. Operating experience shows hydraulic loading in the range of 0.05–0.25 m³/m² h and organic loading up to 200–680 g/m² d. The results show increase in dissolved oxygen levels, COD removal (from 352 mg/l to 20 mg/l); BOD removal (from 211 mg/l to 7.0 mg/l); suspended solids removal (from 293 mg/l to 16 mg/l); turbidity reduction (from 145 NTU to 5.3 NTU); iron (from 5 mg/l to 0.3 mg/l); arsenic (from 500 μg/l to 10 μg/l); total coliform and fecal coliform removal (from 145 × 10⁵ to 55 CFU/100 mL and 150 × 10⁸ to 110 CFU/100 mL respectively), with desired pathogen levels as per WHO standards, i.e. ≤10³ CFU/100 mL. CSF reveals advantages such as low HRT (0.5–2.0 h), low energy requirement (0.04 kW h/m³), no pre-treatment, high dissolved oxygen levels in the effluent, no biosludge production, no mechanical aeration and no odor, fish compatible water quality and evergreen ambience.     

Performance evaluation of a continuous bipolar electrocoagulation/electrooxidation-electroflotation (ECEO-EF) reactor designed for simultaneous removal of ammonia and phosphate from wastewater effluent

The present study aimed to evaluate the performance of a continuous bipolar ECEO-EF reactor designed for simultaneous removal of ammonia and phosphate from wastewater effluent. The reactor was comprised of two distinct units: electrochemical and separation. In the electrochemical unit, Al, stainless steel, and RuO₂/Ti plates were used. All the measurements were performed according to the standard methods. Maximum efficiency of the reactor for phosphate removal was 99% at pH of 6, current density of 3 A, detention time of 60 min, and influent phosphate concentration of 50 mg/l. The corresponding value for ammonia removal was 99% at a pH of 7 under the same operational conditions as for phosphate removal. For both phosphate and ammonia, the removal efficiency was highest at neutral pH, with higher current densities, and with lower influent concentrations. In addition to removal of phosphate and ammonia, application of the Al³⁺ plates enabled the removal of nitrite and nitrate, which may be present in wastewater effluent and are also products of the electrochemical process. The reactor was also able to decrease the concentrations of phosphate, ammonia, and COD under actual wastewater conditions by 98%, 98%, and 72%, respectively. According to the results of the present study, the reactor can be used for efficient removal of ammonia and phosphate from wastewater.     

Microstructure, mechanical, and in vitro properties of mica glass-ceramics with varying fluorine content

The design and development of glass ceramic materials provide us the unique opportunity to study the microstructure development with changes in either base glass composition or heat treatment conditions as well as to understand processing-microstructure-property (mechanical/biological) relationship. In the present work, it is demonstrated how various crystal morphology can develop when F⁻ content in base glass (K₂O–B₂O₃–Al₂O₃–SiO₂–MgO–F) is varied in the range of 1.08–3.85% and when all are heat treated at varying temperatures of 1000–1120°C. For some selected heat treatment temperature, the heat treatment time is also varied over 4–24 h. It was established that with increase in fluoride content in the glass composition, the crystal volume fraction of the glass-ceramic decreases. Using 1.08% fluoride, more than 80% crystal volume fraction could be achieved in the K₂O–B₂O₃–Al₂O₃–SiO₂–MgO–F system. It was observed that with lower fluoride content glass-ceramic, if heated at 1040°C for 12 h, an oriented microstructure with ‘envelop like’ crystals can develop. For glass ceramics with higher fluorine content (2.83% or 3.85%), hexagonal-shaped crystals are formed. Importantly, high hardness of around 8 GPa has been measured in glass ceramics with maximum amount of crystals. The three-point flexural strength and elastic modulus of the glass-ceramic (heat treated at 1040°C for 24 h) was 80 MPa and 69 GPa of the sample containing 3.85% fluorine, whereas, similar properties obtained for the sample containing 1.08% F⁻ was 94 MPa and 57 GPa, respectively. Further, in vitro dissolution study of the all three glass-ceramic composition in artificial saliva (AS) revealed that leached fluoride ion concentration was 0.44 ppm, when the samples were immersed in AS for 8 weeks. This was much lower than the WHO recommended safety limits of 1.5 ppm. Among all the investigated glass-ceramic samples, the glass ceramic with 3.85% F⁻ content in base glass (heat treated at 1040°C for 12 h), exhibits the adherence of Ca–P layer, which consists of spherical particles of 2–3 μm. Other ions, such as Mg⁺² and K⁺¹ ion concentrations in the solution were found to be 8 and 315 ppm after 8 weeks of leaching, respectively. The leaching of all metal ions is recorded to decrease with time, probably due to time-dependent kinetic modification of sample surface. Summarizing, the present study illustrates that it is possible to obtain a good combination of crystallization, mechanical and in vitro dissolution properties with the careful selection of base glass composition and heat treatment conditions.     

Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅ (ZVMN) varistor ceramics was investigated at 875–950 °C. The sintered density decreased from 5.52 to 5.44 g/cm³ and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E_{1 mA}) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (N_d) increased from 3.33 × 10¹⁷ cm⁻³ to 7.64 × 10¹⁷ cm⁻³ with the increase of sintering temperature and the barrier height (Φ_b) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE_{1 mA} = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E_{1 mA}/85 °C/24 h.     

Interfacial interaction of solid cobalt with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

Dissolution kinetics of cobalt in liquid 87.5%Sn–7.5%Bi–3%In–1%Zn–1%Sb and 80%Sn–15%Bi–3%In–1%Zn–1%Sb soldering alloys and phase formation at the cobalt–solder interface have been investigated in the temperature range of 250–450 °C. The temperature dependence of the cobalt solubility in soldering alloys was found to obey a relation of the Arrhenius type c _s = 4.06 × 10² exp (−46300/RT) mass% for the former alloy and c _s = 5.46 × 10² exp (−49200/RT) mass% for the latter, where R is in J mol⁻¹ K⁻¹ and T in K. For tin, the appropriate equation is c _s = 4.08 × 10² exp (−45200/RT) mass%. The dissolution rate constants are rather close for these soldering alloys and vary in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. For both alloys, the CoSn₃ intermetallic layer is formed at the interface of cobalt and the saturated or undersaturated solder melt at 250 °C and dipping times up to 1800 s, whereas the CoSn₂ intermetallic layer occurs at higher temperatures of 300–450 °C. Formation of an additional intermetallic layer (around 1.5 μm thick) of the CoSn compound was only observed at 450 °C and a dipping time of 1800 s. A simple mathematical equation is proposed to evaluate the intermetallic-layer thickness in the case of undersaturated melts. The tensile strength of the cobalt-to-solder joints is 95–107 MPa, with the relative elongation being 2.0–2.6%.     

Real-time control of oxic phase using pH (mV)-time profile in swine wastewater treatment

The feasibility of real-time control of the oxic phase using the pH (mV)-time profile in a sequencing batch reactor for swine wastewater treatment was evaluated, and the characteristics of the novel real-time control strategies were analyzed in two different concentrated wastewaters. The nitrogen break point (NBP) on the moving slope change (MSC) of the pH (mV) was designated as a real-time control point, and a pilot-scale sequencing batch reactor (18 m³) was designed to fulfill the objectives of the study. Successful real-time control using the developed control strategy was achieved despite the large variations in the influent strength and the loading rate per cycle. Indeed, complete and consistent removal of NH₄-N (100% removal) was achieved. There was a strong positive correlation (r² = 0.9789) between the loading rate and soluble total organic carbon (TOCs) removal, and a loading rate of 100 g/m³/cycle was found to be optimum for TOCs removal. Experimental data showed that the real-time control strategy using the MSC of the pH (mV)-time profile could be utilized successfully for the removal of nitrogen from swine wastewater. Furthermore, the pH (mV) was a more reliable real-time control parameter than the oxidation–reduction potential (ORP) for the control of the oxic phase. However, the nitrate knee point (NKP) appeared more consistently upon the completion of denitrification on the ORP-time profile than on the pH (mV)-time profile.