Final Polishing Step Research Articles

Orthodontic debonding and enamel surface integrity. A systematic review of the literature

The aim of a debonding protocol is to ensure the complete removal of composite resin without altering the enamel surface. A systematic review was conducted to analyze the effects of resin removal after the debonding of orthodontic brackets using different mechanical instruments, from both a qualitative and quantitative perspectives. An electronic search, following PRISMA guidelines, was conducted across three databases until March 2023, supplemented by a manual search. All controlled randomized studies or in vitro studies, comparing the removal of adhesive with tungsten carbide burs to other mechanical instrumentation techniques and assessing enamel surface, were included. Twenty-seven eligible articles were included, comprising two randomized studies and 25 in vitro studies, with varying bias levels. Compared to tungsten carbide burs, ultrasonic instruments and sandblasting showed similar or better results in terms of enamel loss and surface roughness. The enamel surface was equally less rough when using discs (Sof-Lex) or a fiberglass bur, or a fiberglass bur, although these techniques were time-consuming. The exclusive use of a diamond bur, stainless steel bur, or manual scaler for complete resin removal resulted in much rougher surfaces, clinically unacceptable. Preserving the enamel surface seems optimal with a two-phase protocol, involving the use of tungsten carbide burs for initial removal of most of the resin, followed by a less invasive technique for finishing resin removal. Beyond the findings of this review, a final polishing step also appears to be relevant.

Purification of recombinantly produced somatostatin-28 comparing hydrochloric acid and polyethyleneimine as E. coli extraction aids

Peptides are used for diagnostics, therapeutics, and as antimicrobial agents. Most peptides are produced by chemical synthesis, but recombinant production has recently become an attractive alternative due to the advantages of high titers, less toxic waste and correct folding of tertiary structure. Somatostatin-28 is a peptide hormone that regulates the endocrine system, cell proliferation and inhibits the release of numerous secondary hormones in human body. It is composed of 28 amino acids and has one disulfide bond, which makes it to an optimal model peptide for a whole downstream purification process. We produced the peptide in the periplasm of E. coli using the CASPON™ technology, an affinity fusion technology system that enables high soluble expression of recombinant proteins and cleaves the fusion tag with a circularly permuted human caspase-2. Furthermore, purification of the products is straight forward using an established platform process. Two different case studies for downstream purification are presented, starting with either hydrochloric acid or polyethyleneimine as an extraction aid. After release of affinity-tagged somatostatin-28 out of E. coli's periplasm, several purification steps were performed, delivering a pure peptide solution after the final polishing step. The process was monitored by reversed-phase high-performance liquid chromatography as well as mass spectrometry to determine the yield and correct disulfide bond formation. Monitoring of impurities like host cell proteins, DNA and endotoxins after each downstream unit confirmed effective removal for both purification pathways.

Heterologous Expression and Purification of Eukaryotic ALA Synthase from E. coli.

This chapter presents a method for the heterologous expression and purification of human ALA synthase from Escherichia coli. Mature ALAS is produced with an N-terminal hexahistidine affinity tag followed by a SUMO fusion tag for solubility and ease of purification. The plasmid is introduced into competent E. coli cells, and robust protein expression is induced with IPTG. The ALAS cofactor, pyridoxal 5'-phosphate, is inserted during protein production to yield an active enzyme upon purification. After cell lysis, the tagged ALAS protein is isolated via a multistep purification that involves an initial nickel-affinity step, affinity tag cleavage and removal, and a final size exclusion chromatography polishing step. Importantly, this protocol is amenable to various ALAS truncations and mutations, opening the door to understanding ALAS biology and its intersections with iron utilization across several organisms.

Selective immunoglobulin aggregates removal in antivenoms by a simple chromatographic step based on a monolithic stationary phase

Antivenom therapy is a critical intervention for treating the more than 5.000.000 envenomation accidents that occur each year around the world. These immunotherapeutic drugs are mostly produced following techniques developed more than fifty years ago with minor changes. Aggregate content has been described as one of the main causes of early adverse effects after intravenous administration of antivenoms. In this work we propose the introduction of a final polishing step to traditional antivenom manufacturing processes aimed at lowering the aggregate content in the final product. The refinement step proposed in this work is based on the selective capture of immunoglobulin aggregates by a cation exchange monolithic stationary phase. We show that this media can effectively remove aggregates in the final product under isotonic ion-strength and mildly acidic conditions following a negative chromatography strategy, thus making it a useful technique for producing higher quality products.

Unraveling microplastics removal in wastewater treatment plant: A comparative study of two wastewater treatment plants in Thailand

Wastewater treatment plants (WWTPs) are considered as a problematic pathway for microplastics (MPs) entering the oceans. This study compares the efficiency of MP removal in two different WWTPs (A1 and A2) with a conventional treatment system located in Bangkok, Thailand. WWTP-A2 is equipped with a pilot-scale ultrafiltration (UF) as a final polishing step. The number of MPs in the influent entering A1 and A2 was 16.55 ± 9.92 and 77.00 ± 7.21 MP/L, respectively. The average of 3.52 ± 1.43 and 10.67 ± 3.51 particles per L was found in the effluent discharged from A1 and A2, respectively, to nearby canals. The removal efficiency of WWTP-A2 built as a closed underground system was shown to be up to 86.14% which is more efficient than the conventional WWTP (A1). MPs were subsequently removed by a UF unit which resulted in a removal efficiency of 96.97%. However, when a large volume of treated wastewater volume is considered, a high concentration of MPs is discharged daily with the final effluent if the efficiency remains the same. The size fraction of 0.5–0.05 mm contributed to the largest proportion of MPs, and fibers were detected as the dominant group at both study sites. Results from a Fourier Transform Infrared Spectroscopy (FT-IR) confirmed that most fibers were polyethylene terephthalate (PET) derived from clothes. MPs retained in the sludge ranged from 2.63 × 104 to 4.74 × 104 particles per kilogram of dry sludge. A significant number of MPs can spread further to the environment by soil application. The results of the study indicate that the design of WWTPs and the addition of advanced tertiary treatment can improve MP removal efficiency of a WWTP. Moreover, the absence of a primary sedimentation tank in both treatment plants may influence the removal efficiency.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Adeno-associated virus process development: optimization & development of a scalable elution for polishing chromatography

In vivo gene therapy utilizing adeno-associated virus (AAV) is a rapidly developing and highly focused area of the biopharmaceutical industry. As the regulatory landscape is shaped there is an increased expectation for companies to develop manufacturing processes generating safe and efficacious AAV. A highly discussed and difficult aspect of AAV manufacturing is the separation of empty capsids from full capsids. Undesirable capsids have unknown impact on the patient’s immune system; consequently, it is desirable to remove them from the final product altogether and de-risk the potential impact to patient safety. From a process development perspective removal of undesirable capsids is challenging due to the similar quality attributes that are shared with full capsids. Anion exchange chromatography is often used as the final polishing step and is primarily used to separate empty capsids from full capsids. In order to achieve this separation a shallow increasing salt gradient with fractionation is used and these two modes of operation are not ideal for large scale manufacturing. Empty-full separation chromatography for a promising AAV8 construct underwent initial development and optimization for technology transfer to large-scale manufacturing at Precision BioSciences. This was accomplished by modifying the platform downstream process and screening both different elution conditions and resin modalities for improved resolution. The eluting peak order for this AAV8 construct is the empty capsid peak first followed by the full capsid peak and is then followed by a final impurity peak. Screening to improve resolution between the peaks created an opportunity to include an additional wash step that removes the empty capsid peak before elution occurs. This was accomplished without negative impact to product recovery and empty-full content. With the removal of the empty capsid peak the elution profile can be further optimized to not rely on a gradient fractionation at the manufacturing scale.

Application of activated effective microorganism, mudball and biosand filter for the treatment of dye wastewater

A study was carried out to evaluate the application of Activated Effective Microorganisms (AEM) solution and EM Mudballs (mixture of soil, rice bran, and EM) to wastewater generated from wool and cotton dyeing unit at Kumbeshwar Technical School (Lalitpur, Bagmati Province, Nepal). Furthermore, the AEM treated wastewater was treated through a Biosand filter as a final treatment and polishing step before discharge in a nearby sewerage system. The wastewater samples collected for 27 days were analyzed for the wastewater quality parameters such as pH, Electrical Conductivity (EC), Total Solids (TS), and Chemical Oxygen Demand (COD) using the standard methods. The average values of pH, conductivity, COD, and TS after the EM combined with Biosand (final) treatment were observed to be 7.49±1.15, 1.39±0.25 mS/cm, 1,669.4 ±858.14 mg/L, and 264±25.29 mg/L, respectively. TS and COD removal were observed to be 43.97±22.3% and 15.26±10.06%, respectively. The results show that the dye wastewater is difficult to remove by a simple biological process like the addition of EM. Combined EM and biosand filters can be an inexpensive way of treating industrial effluents. However, the existing treatment system needs to be optimized by the integration with the proper EM: water: molasses ratio, optimal feeding time and design, hydraulic retention time, solids retention time, organic loading rates in EM reactor, and COD/BOD ratio in wastewater among other important components to meet the national effluent discharge requirements.

A novel submerged photocatalytic oscillatory membrane reactor for water polishing

A submerged photocatalytic oscillatory membrane reactor was tested for micropollutants removal from water as a tertiary treatment method for water polishing. A detailed study of the system performance at various operating conditions of membrane reactor and background water matrices including humic acid (HA) and secondary wastewater effluent (SWE) was conducted. Initially, the system was evaluated using suspended nanosized TiO2 under UV illumination and antipyrine as a model pollutant. Experiments using central composite design (CCD) and response surface analysis (RSM) were used to analyze the effects of the oscillation amplitude and frequency, and airflow rate on the antipyrine removal and the membrane flux. Optimum conditions for the reactor operation were determined using a composite desirability function. These conditions were then applied for the removal of other micropollutants with varying physiochemical properties namely, diclofenac, sulfamethoxazole, and hydrochlorothiazide. Up to 90% micropollutants removal can be achieved in Milli-Q water, although, the performance was noticeably affected in presence of background organics in SWE and HA due to either catalyst blocking and/or competition of organics, as well as catalyst agglomeration. A significant process intensification can be achieved using the proposed photocatalytic oscillatory membrane reactor configuration, which could offer a promising potential as a final polishing step for water recycling.

Two Dimensional Anion Exchange-Size Exclusion Chromatography Combined with Mathematical Modeling for Downstream Processing of Foot and Mouth Disease Vaccine

The production of high-quality purified virus particles in high quantities for vaccine preparation requires a scalable purification procedure in the downstream step. A purification scheme based on combined strong anion-exchange and size exclusion chromatography (2D-AEC-SEC) was developed for the production of non-structural protein-free foot and mouth disease vaccine, and the whole procedure was accomplished with 77.9% virus yield. Additionally, a mathematical modeling and a simulation approach based on a plate model of chromatography were developed and matched with the experimental chromatography data to improve prediction of retention behavior and save time in the development of the downstream scale-up method. The purified pooled virus fraction obtained from the final polishing step had a purity higher than 85% based on analytical size exclusion analysis. Moreover, more than 90.1% of residual DNA (rDNA) was removed from the purified vaccine. The analysis of purified virus particles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), dynamic light scattering (DLS), high performance size exclusion chromatography (HP-SEC), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and transmission electron microscopy (TEM) provided clear evidence of purity and demonstrated that the final product is structurally spherical, intact particles qualified for formulation as a vaccine product.

An integrated continuous downstream process with real-time control: A case study with periodic countercurrent chromatography and continuous virus inactivation.

Integrated continuous downstream processes with process analytical technology offer a promising opportunity to reduce production costs and increase process flexibility and adaptability. In this case study, an integrated continuous process was used to purify a recombinant protein on laboratory scale in a two-system setup that can be used as a general downstream setup offering multiproduct and multipurpose manufacturing capabilities. The process consisted of continuous solvent/detergent virus inactivation followed by periodic countercurrent chromatography in the capture step, and a final chromatographic polishing step. A real-time controller was implemented to ensure stable operation by adapting the downstream process to external changes. A concentration disturbance was introduced to test the controller. After the disturbance was applied, the product output recovered within 6 h, showing the effectiveness of the controller. In a comparison of the process with and without the controller, the product output per cycle increased by 27%, the resin utilization increased from 71.4% to 87.9%, and the specific buffer consumption was decreased by 21% with the controller, while maintaining a similar yield and purity as in the process without the disturbance. In addition, the integrated continuous process outperformed the batch process, increasing the productivity by 95% and the yield by 28%.

Evaluation of BTEX adsorption in industrial effluent through the percolation method using rice husk ash as adsorbent material

The aromatic petroleum hydrocarbons (benzene, toluene, ethylbenzene and xylenes) are highly volatile and toxic to human health and the environment. Adsorption is a physical-chemical process widely used in effluent treatment in which a material called adsorbate has the capacity to retain components dispersed in an aqueous medium on its surface. Studies of waste recovery demonstrate potentialities and more noble uses than the final disposal. In this sense, the ashes generated from the combustion of rice husk can be used as a by-product with various applications; in the case of this work, as adsorbent material, due to its amorphism and its high surface area. This study aimed to evaluate the adsorption of the aromatic components of a petrochemical effluent (formation water) with the use of two types of rice husk ash generated from two different grate combustion processes in a filtration system under positive pressure. The ashes were segregated and characterized according to their physical, chemical, mineralogical, and microstructural properties. The adsorption procedure by percolation consisted of 1L of petrochemical effluent for 45 g of adsorbent material. The samples of raw effluent were analyzed by gas chromatography. The results proved that the percentage of removal of BTEX composts in the segregated ash I did not potentialize the effect of the adsorption, being higher in the raw ash, with values of 90.2; 94.9; 83.3 and 100 %, while in ash II the effect of the segregation influenced the adsorption process only for the benzene and toluene, with removal values that went from 55.08 to 69.14 % and 69.23 to 75 %, respectively, in both of the ashes studied. The results obtained were inferior to those recommended by the legislation. Thus, the different combustion temperatures of the husk influenced in the characteristics, adsorption capacity, and BTEX removal efficiency by the adsorbate. Therefore, the positive filtration system can be used as a final polishing step in the treatment of petrochemical effluents, replacing conventional systems that use activated carbon.

Recycling of wastewater from tannery industry through membrane-integrated hybrid treatment using a novel graphene oxide nanocomposite

An advanced oxidation-nanofiltration integrated hybrid process is developed in this study for treatment of leather industry wastewater to reusable criteria. The process uses a laboratory-synthesized graphene oxide-based nanocomposite in the final polishing step for ensuring high degree of purification. All investigations are done on live tannery wastewater having high level of recalcitrant pollutants such as chromium (8.2 mg L−1), COD (10,500 mg L−1), TDS (7420 mg L−1), chloride (4620 mg L−1) and sulfide (2560 mg L−1). Performance of the developed membrane is also compared with commercially available counterpart. Detailed characterization (FTIR, SEM-EDX, and BET) and experimental evidences reveal high mechanical strength, hydrophilic nature and high selectivity in removal of ionic contaminants. The integrated process successfully removes chromium (99.5%), COD (>99%) and TDS (>96%) while retaining the essential ions (Ca2+, Mg2+) substantially. A sustained high flux hovering around 200 L/ (m2 h) at 16 bar pressure over a reasonably long period (150 h) is an indicator of development of a potential new technology in effective treatment of leather industry wastewater.

Direct measurement of TEM lamella thickness in FIB-SEM.

Transmission electron microscope (TEM) specimen preparation by focused ion beam (FIB) milling requires delicate polishing of a thin window of material during the final stages of the procedure. Over or underpolishing is common and requires extra microscope resources to correct. Despite some methods for lamella thickness measurement being available, the majority of users judge the final polishing step subjectively from scanning electron microscope (SEM) images acquired between milling steps. Here we demonstrate successful thickness determination of thin silicon lamellae using calibrated secondary electron detectors in a FIB-SEM dual-beam chamber. Unlike previous thickness measurement methods it does not require long acquisition times, the use of in-chamber scanning transmission electron microscope (STEM) or energy dispersive x-ray spectroscopy detectors. The calibration aligns a SEM image to an electron energy loss spectroscopy (EELS) map of lamella thickness acquired in a TEM. This calibration reveals the greyscale-thickness dependence of two secondary electron SEM detectors: the through-lens detector (TLD) and the in-chamber electron detector (ICE). It was found that lamella thickness estimation for TLD images is accurate for areas thinner than 0.4 t/λ, whilst ICE images are most accurate for areas thicker than 0.5 t/λ up to 1.1 t/λ. The procedure presented here allows objective lamella thickness determination during the final stages of FIB specimen preparation using conventional imaging modes for common secondary electron detectors. LAY DESCRIPTION: Successful analysis of a material in a transmission electron microscope requires very thin windows of the material to be fabricated. Despite the quality of this analysis relying heavily on the thickness of the window, measuring thickness during window fabrication is not common practice. The authors show that it is possible to measure the thickness of the window directly in a focused-ion-beam chamber with a scanning electron microscope without altering the fabrication procedure, and using electron detectors common to most microscopes.

Concentration Enrichment of Fermentation Derived Acetic Acid: Transport Modeling of Forward Osmosis-Nanofiltration Integrated System

Abstract Forward Osmosis (FO)-Nanofiltration (NF) integration as the final product polishing step enables high concentration of acetic acid output through continuous dehydration of fermentation derived product. A mathematical transport model has been developed based on external and internal concentration polarization modulus of FO and extended Nernst–Plank equation for NF to capture the flux and rejection trends from those membranes. The modular designed production scheme ensured high flux (45 Lm−2 h−1), concentration (962 g L−1) and purity (>98 %) of acetic acid under non-neutralization condition. Excellent performance of the model is reflected in low relative error (<0.05), high Willmott d-index (>0.97) and high correlation coefficient (>0.98).

Efficiency of ozone microbubbles for ammonia removal from mine effluents

Several physical, chemical, and biological technologies efficiently treat ammonia nitrogen (NH3-N). However, cold temperatures and mixes of contaminants limit NH3-N removal efficiency. This study evaluated the ozone microbubbles efficiency for NH3-N removal from synthetic and five actual mine effluents. Testing was initially conducted in batch mode. Then, to confirm treatment feasibility, tests with continuous flow were performed with one synthetic and one real effluent. Results showed that the parameters of the water to be treated have significant influence on treatment efficiency. The presence of cyanides, cyanate, thiocyanate, and metals adversely influenced treatment performance. The NH3-N removal efficiency ranged from 27.8 to 99.3%. Continuous flow testing confirmed the feasibility of large-scale treatment as 99.1% of NH3-N was treated at a flow rate of 1.1 L/min over a treatment period of 570 min. Final polishing steps removed the pink color from the water after ozone microbubbles treatment, resulting in satisfactory quality of treated water.

Removal of polar micropollutants from domestic wastewater using a methanogenic – aerobic moving bed biofilm reactor system

A lab-scale system consisting of a methanogenic and an aerobic moving bed biofilm reactor (MBBR) was operated for seven months to investigate major pollutants’ and polar organic micropollutants’ removal from domestic wastewater under three different organic loading rates (OLRs). For all OLR values tested, the system achieved efficient COD (>84%) and NH4-N removal (>96%); both reactors contributed to the decrease of organic loading, while the aerobic bioreactor was exclusively responsible for the removal of ammonium nitrogen. The increase of OLR from 0.20 ± 0.10 to 2.10 ± 0.20 kg COD m−3 d−1 resulted to increase of the detected volatile fatty acids in the anaerobic reactor and increase of the produced biogas to 172.7 ± 25.3 mL L reactor−1 d−1. All target micropollutants were partially removed during different experimental phases; their removal ranged between 31% (5-methyl-1H-benzotriazole, 5TTR) and 97% (2-hydroxybenzothiazole, OH-BTH). Except benzotriazole (BTR) and OH-BTH, both reactors contributed significantly to the removal of target micropollutants, while the addition of extra aerobic MBBR as a final polishing step enhanced only OH-BTH removal. Use of experimental and literature data showed that the increase of organic loading enhanced the removal of three out of five target micropollutants, while the key factor responsible for this effect was COD concentration in influent wastewater. The modelling of micropollutants’ removal efficiency using biodegradation kinetics calculated in batch experiments showed satisfactory correlation between predicted and measured values for most target compounds.

D-Shaped POF Sensors for Refractive Index Sensing-The Importance of Surface Roughness.

In this study the influence of the surface roughness on the transmission capacities of D-shaped plastic optical fibers (POFs) and sensors performance was investigated. Five D-shaped POF sensors were produced and characterized for refractive index sensing between 1.33 and 1.41. The sensors were characterized using a low-cost optical sensing system based on the variation of the transmitted light though the POF with refractive index changes (RI). Higher surface roughness increases the scattering losses through the POF and influences the sensors’ performance; therefore, a balance must be attained. Generally, the best performance was achieved when the sensing region was polished with P600 sandpaper as a final polishing step. Polishing with sandpapers of lower grit size resulted in lower scattering, higher linearity of the sensor response and generally lower performance for RI sensing. A sensor resolution of 10−3–10−4 RIU, dependent on the value of the external refractive index, was obtained through simple and low-cost manufacturing procedures. The obtained results show the importance of surface roughness in the development of POF sensors which can be used in several applications, such as for water quality assessment.

Treatment of normal hydrocarbons contaminated water by combined microalgae – Photocatalytic nanoparticles system

Two species of microalgae (Chlorella vulgaris and Dunaliella tertiolecta) as the biological agents along with ZnO nanoparticles as the photocatalyst were used to investigate the hydrocarbon removal efficiency from oily water samples. Firstly, the toxicities of the photocatalyst, normal paraffine hydrocarbons and their combination towards the microalgae were evaluated in terms of cell growth and chlorophyll content. The capability of algae to absorb the nanoparticles in the aqueous phase was confirmed by FT-IR spectroscopy. Then, the hydrocarbon removal efficiencies of the algae, photocatalyst and the combined photocatalyst-algae system were studied by measuring the residual hydrocarbon content of the samples. Results indicated that despite of the growth inhibitory effects of n-alkanes and nanoparticles on the examined algae, both of them could survive in the system. Dunaliella tertiolecta was more affected by normal paraffins while Chlorella vulgaris was more sensitive to ZnO nanoparticles. Both of the studied species were capable of hydrocarbon removal and the efficiency of Chlorella vulgaris was superior. The combination of algae and nanoparticles was also proved to have a synergistic effect on degradation of the hydrocarbon content of the medium. The obtained removal efficiencies for initial hydrocarbon concentrations of 0.05%, 0.1% and 0.5% (v/v) were 100%, 78% and 42% for Dunaliella tertiolecta-ZnO and 100%, 93% and 88% for Chlorella vulgaris- ZnO system, respectively. It can be concluded that the examined microalgae-nanoparticle system can be considered as a final polishing step in hydrocarbons removal from oily waters.

Development of an integrated treatment strategy for a leather tannery landfill leachate

This study aimed at developing an efficient multistage treatment strategy for a complex industrial landfill leachate: a leather tannery landfill leachate. Based on the leachate physicochemical characteristics, the following treatment train was delineated and tested: (i) initial biological process for removal of biodegradable organics, ammonium and alkalinity, (ii) coagulation/flocculation process for total removal of chromium and partial removal of recalcitrant organics and suspended solids, (iii) advanced oxidation process (AOP) or electrochemical AOP (EAOP) for degradation of recalcitrant organics and biodegradability enhancement, and (iv) final biological polishing step. Two initial biological treatment configurations were applied: one comprising nitrification and the other nitrification-denitrification. Coagulation/flocculation was optimized in terms of pH, coagulant dosage (iron(III) chloride) and flocculant nature and dosage. The following AOPs/EAOPs were tested: Fenton, photo-Fenton with UVA or UVC radiation (PF-UVA or PF-UVC), anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton with UVA radiation (PEF-UVA). The biological nitrification-denitrification was beneficial not only because it avoided the need for alkalinity addition during nitrification and decreased the amount of substrate added during denitrification, as expected. Over and above that, it reduced the acid consumption in the coagulation/flocculation, avoided the application of an additional stage comprising nitrites oxidation to nitrates prior to the AOP/EAOP, and improved the efficiency of Fenton’s reaction based processes. Following nitrification-denitrification, the coagulation/flocculation was maximized at pH 3.0 and 400 mg Fe L−1 with no flocculant addition. The PEF-UVA process was the best AOP/EAOP. The final leachate fulfilled the discharge limits into waterbodies.