Production and characterization of graphene oxide-engineered biochars and application for organic micro-pollutant adsorption from aqueous solutions.

In this study, conventional and Graphene Oxide-engineered biochars were produced and thoroughly characterized, in order to investigate their potential as adsorptive materials. Two types of biomass, Rice Husks (RH) and Sewage Sludge (SS), two Graphene Oxide (GO) doses, 0.1% and 1%, and two pyrolysis temperatures, 400 °C and 600 °C were investigated. The produced biochars were characterized in physicochemical terms and the effect of biomass, GO functionalization and pyrolysis temperature on biochar properties was studied. The produced samples were then applied as adsorbents for the removal of six organic micro-pollutants from water and treated secondary wastewater. Results showed that the main factors affecting biochar structure was biomass type and pyrolysis temperature, while GO functionalization caused significant changes on biochar surface by increasing the available C- and O- based functional groups. Biochars produced at 600 °C showed higher C content and Specific Surface Area, presenting more stable graphitic structure, compared to biochars produced at 400 °C. Micro-pollutant adsorption rates were in the range of 39.9%-98.3% and 9.4%-97.5% in table water and 28.3%-97.5% and 0.0%-97.5% in treated municipal wastewater, for the Rice Husk and Sewage Sludge biochars respectively. The best biochars, in terms of structural properties and adsorption efficiency were the GO-functionalized biochars, produced from Rice Husks at 600 °C, while the most difficult pollutant to remove was 2.4-Dichlorophenol.

Effect of biochar produced from sewage sludge on tomato (Solanum lycopersicum L.) growth, soil chemical properties and heavy metal concentrations.

The addition of biochar, as shown in the literature, improves significantly the chemical and physical soil properties and plant growth. This study examined the effect of biochar, compost and the combination of them on growth, nutrient and heavy metal concentrations of tomato. Biochar (BC) was produced from sewage sludge by pyrolysis at the temperature of 300 °C. The pot trials were carried out under an open-side greenhouse for a total of four months and under four treatments. The treatments applied were: Untreated soil (Control); soil with 2% w/w biochar (BC-SS); soil with 2% w/w compost (Compost); a mixture of biochar and compost at a 2% w/w level (BC-SS + Compost). The application of biochar exhibited substantial improvement on several soil properties. Total organic carbon (TOC) of soil increased (67%-85%), as did the nitrate nitrogen (55%) and ammonium nitrogen (145%). Additionally, available phosphorus significantly increased (45.5%-54.5%) by the application of biochar with/without compost. Dry weight of the aboveground (stems) and belowground (roots) plant tissues increased as well, although tomato yield was not increased significantly. Concentration of heavy metals and trace elements in tomato tissues was quite low. Traces of chromium (Cr), nickel (Ni), and cobalt (Co) were found only in roots of those treated, while silicon (Si) was present in the roots and stems. Arsenic (As), molybdenum (Mo) and lead (Pb) were detected in all plant tissues, but their concentrations did not exceed the permissible levels established for vegetables. Furthermore, the concentration of arsenic (As) and lead (Pb) in fruits decreased by the addition of the amendments (12%-65%). In conclusion, the addition of sewage sludge biochar improved soil characteristics and plant growth. Yet, prior to its general use, factors such as the type of biomass, soil, rate of application and crop must always be taken into consideration.

Agronomic potential of biochar prepared from brewery byproducts.

This work investigated the effect of biochar produced from brewery byproducts, spent grain and surplus yeast on the physicochemical characteristics of a calcareous loam soil and plant growth of maize (Zea mays L.). Maize is a plant which needs high nitrogen fertilization, while the effect of acidic or neutral biochars on alkaline calcareous soils has only been assessed in a few studies. The effect of biochars on dry weight, as well as the level of macro- and micronutrients in soil, and above- and belowground plant tissues, were investigated, in a 30 day experiment after seedling emergence of maize (Zea mays L.), in the presence and absence of nitrogen fertilization. The results indicated that biochar from organic brewery by-products significantly increased the dry weight of the aboveground part of the plant by 59-186%, relative to the control, without the addition of inorganic N fertilization, and by 46-157% with the addition of inorganic N fertilization. The dry weight of the belowground plant tissues significantly increased by 83-92% and 46-106%, relative to the control, with or without the addition of inorganic N fertilization, respectively. Biochar addition, especially at 5% application rate individually or in a mixture, significantly increased the phosphorus content of plant tissues. The content of potassium in the plants was affected mainly by the addition of biochar derived from surplus yeast, while the concentration of calcium and magnesium in plant tissues was positively affected by spent grain biochar, in absence of inorganic nitrogen fertilization. Addition of biochars produced from brewery byproducts improved soil fertility parameters, particularly the contents of total organic carbon (by 133% and 118% with or without fertilization, respectively), total nitrogen (by 120% and 81% respectively) and available phosphorus in the studied loam calcareous soil. Overall, biochar from brewery wastes showed the potential to enhance plant growth and nutrient availability, thus it is a promising organic fertilizer for sustainable agriculture.

Adsorption of selected organic micro-pollutants on sewage sludge biochar.

In this study, biochar was produced from three differently treated sewage sludge biomasses, in three pyrolytic temperatures, 300 °C, 500 °C and 700 °C, under continuous N2 supply. The produced samples were physicochemically characterized and their initial metal concentration, along with metal leaching potential, were investigated. Moreover, the application of the biochar samples as adsorbents for the removal of seven emerging organic micro-pollutants from table water and treated wastewater matrices was investigated. The results showed that even though the biochar samples were not especially enriched in terms of physicochemical characterization, they were effective as adsorptive materials in the respective experiments. Pollutant removal was in the range of 67-99% for the table water experiments, while the removal for the wastewater experiments was 35-97%. The results of this study indicate that sewage sludge biochar has the potential to be an effective, low-cost adsorbent, providing, at the same time, a viable and environmentally friendly solution concerning the difficult task of sludge management.

The impact of biochars prepared from agricultural residues on phosphorus release and availability in two fertile soils.

Biochars have a high variability in chemical composition, which is influenced by pyrolysis conditions and type of biomass. Essential macronutrient P retained in biochar could be released and made available to plants, enhancing plant growth. This study was conducted in order to evaluate whether biochar, produced from agricultural residues, could release P in water, as well as study its potential effect on plant growth and P uptake. Biochar samples were prepared from rice husks, grape pomace and olive tree prunings by pyrolysis at 300 °C and 500 °C. These samples were used for P batch successive leaching experiments in order to determine P release in water. Subsequently, rice husk and grape pomace biochars, produced by pyrolysis at 300 °C, were applied to two temperate soils with highly different pH. A three-month cultivation period of ryegrass (Lolium perenne L.) was studied in threefold replication, while three harvests were accomplished. Treatments comprised control soils (without amendment) and soils amended only with biochar. Results of P leaching tests showed a continuous release of P from all biochars as compared to raw biomass samples, for which the highest P concentrations were detected during the first extraction. Grape pomace and rice husk biochars pyrolyzed at 500 °C showed higher levels of water-extractable P, as compared to their corresponding raw biomass. Biochars, at 500 °C, leached more P in all four extractions, compared to biochars at 300 °C, apart from olive tree prunings biochars, where both pyrolysis temperatures presented a similar trend. Concerning plant yield of ryegrass, rice husk and grape pomace biochars showed positive statistically significant effects on plant yield only in slightly acidic soil in second and third harvests. In terms of P uptake of ryegrass, grape pomace biochars depicted positive significant differences (P < 0.05) in third harvest, in slightly acidic soil, while in first and second harvests positive significant differences were observed in alkaline soil. These results suggest that biochars derived from agricultural residues may act as a source of P in agronomic applications and improve plant growth, although soil conditions may play a significant role.

Ca and Fe modified biochars as adsorbents of arsenic and chromium in aqueous solutions.

This work investigated the production of Ca and Fe modified biochars in order to use them for the removal of arsenic As(V) and chromium Cr(VI) from aqueous solutions. Rice husk was impregnated with CaO at an impregnation ratio 0.114, while both rice husk and the organic fraction of municipal solid wastes were impregnated with Fe(0) and Fe(3+) at impregnation ratios 0.114 and 0.23. The modified biochars exhibited high As(V) removal capacity (>95%), except for the case of rice husk impregnated with Fe(0), whose removal capacity reached only 58%. All modified biochars exhibited much better As(V) removal capacity compared to the non-impregnated biochars. However, the Cr(VI) removal rates were not as high as the As(V) ones. The maximum Cr(VI) removal was observed in the case of rice husk biochar impregnated with 2.3% w/w Fe(3+), whereas the majority of impregnation agents examined did not manage to enhance the biochars' Cr(VI) removal ability. The equilibrium study showed that the Freundlich model can adequately describe the sorption process for the majority of samples examined. Analysis of the amount of Fe present in the equilibrium solutions suggested that the main mechanisms of As(V) and Cr(VI) removal were possibly metal precipitation and electrostatic interactions between the modified biochars and the adsorbate.

Effluent organic matter (EfOM) characterization by simultaneous measurement of proteins and humic matter.

This work developed a method, based on the Lowry method and Frølund modification, for the simultaneous determination of proteins and humic matter in wastewater effluent samples at low concentrations. The method was based on simultaneous spectrophotometric measurements of proteins and humic matter at 750 nm in the absence and presence of CuSO4, which is responsible for increasing the absorbance only in the presence of to proteins. Statistical analysis through ANOVA showed that the response surface of the method fit the experimental measurements at significance level lower than 0.05, indicating satisfactory fit. The quantification limits of the proposed method were 0.5-30 mg/l for proteins and 2-30 mg/l for humic matter. The presence of carbohydrates did not interfere with the analysis of proteins and humic matter at carbohydrate concentrations below 35-40 mg/l. The Lowry method overestimated the concentration of the proteins because of the presence of humic substances. A carbon balance indicated that the analytical method developed could provide a satisfactory distribution of the main organic constituents in wastewater and effluents.

Coupling digestion in a pilot-scale UASB reactor and electrochemical oxidation over BDD anode to treat diluted cheese whey.

The efficiency of the anaerobic treatment of cheese whey (CW) at mesophilic conditions was investigated. In addition, the applicability of electrochemical oxidation as an advanced post-treatment for the complete removal of chemical oxygen demand (COD) from the anaerobically treated cheese whey was evaluated. The diluted cheese whey, having a pH of 6.5 and a total COD of 6 g/L, was first treated in a 600-L, pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB process, which was operated for 87 days at mesophilic conditions (32 ± 2 °C) at a hydraulic retention time (HRT) of 3 days, led to a COD removal efficiency between 66 and 97 %, while the particulate matter of the wastewater was effectively removed by entrapment in the sludge blanket of the reactor. When the anaerobic reactor effluent was post-treated over a boron-doped diamond (BDD) anode at 9 and 18 A and in the presence of NaCl as the supporting electrolyte, complete removal of COD was attained after 3-4 h of reaction. During electrochemical experiments, three groups of organochlorinated compounds, namely trihalomethanes (THMs), haloacetonitriles (HANs), and haloketons (HKs), as well as 1,2-dichloroethane (DCA) and chloropicrin were identified as by-products of the process; these, alongside free chlorine, are thought to increase the matrix ecotoxicity to Artemia salina.

Sequential treatment of diluted olive pomace leachate by digestion in a pilot scale UASB reactor and BDD electrochemical oxidation.

The efficiency of the anaerobic treatment of olive pomace leachate (OPL) at mesophilic conditions was investigated. Daily and cumulative biogas production was measured during the operational period. The maximum biogas flowrate was 65 L/d, of which 50% was methane. In addition, the applicability of electrochemical oxidation as an advanced post-treatment method for the complete removal of chemical oxygen demand (COD) from the anaerobically treated OPL was evaluated. The diluted OPL, having a pH of 6.5 and a total COD of 5 g/L, was first treated in a 600 L, pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated for 71 days at mesophilic conditions (32 ± 2 °C) in a temperature-controlled environment at a hydraulic retention time of 3 days, and organic loading rates (OLR) between 0.33 and 1.67 g COD/(L.d). The UASB process led to a COD removal efficiency between 35 and 70%, while the particulate matter of the wastewater was effectively removed by entrapment in the sludge blanket of the reactor. When the anaerobic reactor effluent was post-treated over a boron-doped diamond (BDD) anode at 18 A and in the presence of 0.17% NaCl as the supporting electrolyte, complete removal of COD was attained after 7 h of treatment predominantly through total oxidation reactions. During electrochemical experiments, three groups of organo-chlorinated compounds, namely trihalomethanes (THMs), haloacetonitriles (HANs) and haloketons (HKs), as well as 1,2-dichloroethane (DCA) and chloropicrin were identified as by-products of the process; these, along with the residual chlorine are thought to increase the matrix ecotoxicity to Artemia salina.

Arsenic and chromium removal from water using biochars derived from rice husk, organic solid wastes and sewage sludge.

Biochars derived from rice husk, the organic fraction of municipal solid wastes and sewage sludge, as well as a sandy loam soil, were used as adsorbents for As(V), Cr(III) and Cr(VI) removal from aqueous solutions. The kinetic study showed that sorption can be well described by the pseudo-second order kinetic model, while simulation of sorption isotherms gave better fit for the Freundlich model. The materials examined removed more than 95% of the initial Cr(III). However, removal rates for As(V) and Cr(VI) anions were significantly lower. Biochar derived from sewage sludge was efficient in removing 89% of Cr(VI) and 53% of As(V). Its ash high Fe2O3 content may have enhanced metal adsorption via precipitation. Soil was the most effective material for the removal of As(V), yet it could not strongly retain metal anions compared to biochars, as a significant amount of the adsorbed metal was released during desorption experiments.

Detection and fate of antibiotic resistant bacteria in wastewater treatment plants: a review.

Antibiotics are among the most successful group of pharmaceuticals used for human and veterinary therapy. However, large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics, which finally find their ways into different natural environmental compartments. The emergence and rapid spread of antibiotic resistant bacteria (ARB) has led to an increasing concern about the potential environmental and public health risks. ARB and antibiotic resistant genes (ARGs) have been detected extensively in wastewater samples. Available data show significantly higher proportion of antibiotic resistant bacteria contained in raw and treated wastewater relative to surface water. According to these studies, the conditions in wastewater treatment plants (WWTPs) are favourable for the proliferation of ARB. Moreover, another concern with regards to the presence of ARB and ARGs is their effective removal from sewage. This review gives an overview of the available data on the occurrence of ARB and ARGs and their fate in WWTPs, on the biological methods dealing with the detection of bacterial populations and their resistance genes, and highlights areas in need for further research studies.

Inactivation of Bacillus anthracis in water by photocatalytic, photolytic and sonochemical treatment.

Bacillus anthracis is one of the most dangerous and pathogenic bacterial species and its intrusion in aquatic environments is a serious threat to public health. The aim of the present study was to investigate inactivation rates of B. anthracis in water by means of photocatalytic (UVA/TiO2), photolytic (UVC) and sonochemical treatment. The effect of various operating conditions such as bacterial concentration, TiO2 loading, UV irradiation source, ultrasound power and treatment time was examined. The reference strain of B. anthracis proved to be highly resistant during photocatalytic and sonochemical treatment of aquatic samples, even in the presence of hydrogen peroxide solution, which is considered among the chemical disinfectants recommended for B. anthracis removal from aqueous suspensions. UVC irradiation was far more effective, as it achieved total inactivation in short treatment time (10 min) and at high initial concentrations (10(6) CFU mL(-1)). The effectiveness of UVC irradiation is also reinforced by the fact that no photoreactivation occurred even after 72 h of exposure under sunlight after the end of the treatment. Furthermore, the virulence of residual cells was investigated, targeting two genes carried in the plasmids pXO1 and pXO2, respectively, which are required for a fully virulent type. Interestingly, the plasmid pXO2 seems to be lost from the host after photocatalytic and photolytic disinfection, resulting in apathogenic residual strains contained in the treated sample. Overall, our results highlight the importance of B. anthracis efficient inactivation in water, as it shows considerable resistance towards effective and reliable disinfection techniques.

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design.

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30min), temperature (160-200°C), Cu(2+) concentration (250-750mgL(-1)) and H(2)O(2) concentration (0-1500mgL(-1)) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920mgL(-1), was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H(2)O(2) to reactive hydroxyl radicals. WAO at 2.5MPa oxygen partial pressure advanced treatment further; for example, 22min of oxidation at 200°C, 250mgL(-1) Cu(2+) and 0-1500mgL(-1) H(2)O(2) resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H(2)O(2) concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H(2)O(2) concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.

Boron-doped diamond anodic treatment of landfill leachate: evaluation of operating variables and formation of oxidation by-products.

Landfill leachate with a low BOD/COD ratio was electrochemically oxidized by means of a boron-doped diamond anode. In addition to organic matter removal, this study addressed the issue of formation of both chlorinated organic compounds and nitrate ions as a result of organic matter and ammonia and/or organic nitrogen electro-oxidation in the presence of chloride ions. A factorial design methodology was implemented to evaluate the statistically important operating variables: treatment time (1-4 h), pH (5-8), current intensity (6.3-8.4 A) and addition of chloride (2500-4500 mg L(-1)). The process was evaluated on COD, total nitrogen (TN) and colour removal, as well as on the formation of nitrate, nitrite and chlorinated organics. Of the four variables studied, treatment time and pH had a considerable influence on COD and colour removal. On the contrary, none of the variables had a significant effect on the elimination of TN for which an average removal of 61 mg L(-1) was obtained. The studied variables exhibited different effects on the four groups of organo-chlorinated compounds considered in this study, namely trihalomethanes (THMs), haloacetonitriles (HANs), haloketons (HKs) and 1,2-dichloroethane (DCA). Further analysis at more intense conditions, i.e. current intensity up to 18 A and reaction time up to 8 h revealed that high levels of decolourization (84%) could be achieved followed by low COD (51%) and ammonia (32%) removals. Apart from DCA, the concentration of chlorinated organics increased continuously with treatment time reaching values as high as 1.9 mg L(-1), 753 µg L(-1) and 431 µg L(-1) of THMs, HANs and HKs, respectively.

Pilot treatment of olive pomace leachate by vertical-flow constructed wetland and electrochemical oxidation: an efficient hybrid process.

A hybrid process comprising biological degradation in a vertical-flow constructed wetland (CW) and electrochemical oxidation over boron-doped diamond electrodes to decolorize, mineralize and detoxify a leachate from olive pomace processing (OPL) was investigated. Two alternative treatment schemes were compared: According to the first treatment scheme, OPL was treated by electrochemical oxidation followed by treatment in a constructed wetland pilot unit (CW-A). The second scheme comprised of treatment in a constructed wetland followed by electrochemical treatment (CW-B). The constructed wetlands units were planted with Phragmites australis (reeds) and were fed intermittently at organic loadings between 5 and 15 g COD m(-2) d(-1) and a residence time of 3 d. Electrochemical oxidation (EO) was performed for 360 min at 20 A. Treatment of OPL in the wetland at 15 g COD m(-2) d(-1) led to mean COD and color reduction of 86% and 77%, respectively; the wetland effluent with a COD of about 800 mg L(-1) was polished electrochemically for 360 min after which the overall COD and color removal of the combined process (i.e. CW-B/EO) was around 95%, while the final effluent was not toxic against the marine bacteria Vibrio fischeri. Electrochemical oxidation of the original OPL at COD values between 6250 and 14 100 mg L(-1) led to moderate COD and color reduction (i.e. less than 40%) through zero order kinetics. When this was coupled to constructed wetland post-treatment (i.e. EO/CW-A), the overall COD and color removal was 81% and 58%, respectively. The decreased efficiency may be assigned to the increased toxicity of the electrochemically treated effluent which was only partially removed in the natural treatment system.

Treatment of ink effluents from flexographic printing by lime precipitation and boron-doped diamond (BDD) electrochemical oxidation.

Effluent treatment from flexographic printing was investigated by precipitation/coagulation and electrochemical oxidation over boron-doped diamond electrodes. Precipitation with 3 g/L of lime led to complete removal of effluent turbidity (initial value of about 410 NTU) but only about 20% chemical oxygen demand (COD) decrease (initial value of about 1,900 mg/L). Higher lime dosages (up to 15 g/L) had no effect on separation. On the other hand, coagulation with alum in the range 0.05-1 mM failed to enhance the extent of solids separation achieved by gravity settling alone (i.e. about 60%). Preliminary electrochemical oxidation experiments in the presence of sulphuric acid as supporting electrolyte showed that treatment performance (in terms of COD removal and decrease in sample absorbance at 300 nm) increased with increasing applied current. The latter was more efficiently utilized at shorter treatment times and lower currents with efficiency reaching 30%. Following lime precipitation, the effluent was electrochemically oxidized at alkaline conditions for 360 min yielding 64% absorbance reduction and 50% COD removal (this corresponds to 60% overall COD removal for the combined process). The rather low electrochemical treatment performance may be attributed to limestone deposition and fouling of electrodes and other electrochemical reactor components as evidenced by the gradual drop in conductivity/current throughout the operation.

Analysis of selected pharmaceutical compounds and endocrine disruptors in municipal wastewater using solid-phase microextraction and gas chromatography.

The aim of this work was to develop a simple analytical method to determine the presence of selected pharmaceutical compounds, personal care products, and endocrine disruptors in wastewater treatment plant effluents. In this study, solid-phase microextraction (SPME) and gas chromatography with mass spectroscopy (GC-MS) were used to identify triclosan; 2,4-dichloro phenol; 2,3,4-trichloro phenol; galaxolide; tonalide; estrone; 17-beta-estradiol; 17-alpha-ethinyl estradiol; clofibric acid; and carbamazepine. Extraction parameters such as types of SPME fiber, effect of ionic strength, magnetic stirring, pH, extraction temperature, extraction time, and desorption time were investigated to optimize the SPME-GC method. Also, analytical parameters such as repeatability, linearity, and detection limits were evaluated. The method developed in this study was fast (extraction procedure and GC-MS analysis was around 100 minutes), solvent-free, and low cost. This method was used as a screening test to determine if pharmaceutical compounds, personal care products, and endocrine disruptors were present in wastewater treatment plant effluents samples from the Chania Municipal Wastewater Treatment Plant in Crete, Greece.

Boron-doped diamond anodic treatment of olive mill wastewaters: statistical analysis, kinetic modeling and biodegradability.

The electrochemical treatment of olive mill wastewaters (OMW) over boron-doped diamond (BDD) electrodes was investigated. A factorial design methodology was implemented to evaluate the statistically important operating parameters, amongst initial COD load (1000-5000 mg/L), treatment time (1-4h), current intensity (10-20A), initial pH (4-6) and the use of 500 mg/L H(2)O(2) as an additional oxidant, on treatment efficiency; the latter was assessed in terms of COD, phenols, aromatics and color removal. Of the five parameters tested, the first two had a considerable effect on COD removal. Hence, analysis was repeated at more intense conditions, i.e. initial COD values up to 10,000 mg/L and reaction times up to 7h and a simple model was developed and validated to predict COD evolution profiles. The model suggests that the rate of COD degradation is zero order regarding its concentration and agrees well with an electrochemical model for the anodic oxidation of organics over BDD developed elsewhere. The treatability of the undiluted effluent (40,000 mg/L COD) was tested at 20A for 15h yielding 19% COD and 36% phenols' removal respectively with a specific energy consumption of 96 kWh/kg COD removed. Aerobic biodegradability and ecotoxicity assays were also performed to assess the respective effects of electrochemical treatment.

Simultaneous photocatalytic oxidation of As(III) and humic acid in aqueous TiO2 suspensions.

The simultaneous photocatalytic oxidation of As(III) and humic acid (HA) in aqueous Degussa P25 TiO(2) suspensions was investigated. Preliminary photocatalytic studies of the binary As(III)/TiO(2) and HA/TiO(2) systems showed that As(III) was oxidized more rapidly than HA and the extent of photocatalytic oxidation of each individual component (i.e. As(III) or HA) increased with decreasing its initial concentration and/or increasing catalyst loading. The simultaneous photocatalytic oxidation of As(III) and HA in the ternary As(III)/HA/TiO(2) system showed that both As(III) and HA oxidation was reduced in the ternary system compared to the corresponding binary systems. The effect of operating conditions in the ternary system, such as initial As(III), HA and TiO(2) concentrations (in the range 3-20mg/L, 10-100mg/L and 50-250 mg/L respectively), initial solution pH (3.6-6.7) and reaction time (10-30 min), on photocatalytic As(III) and HA oxidation was assessed implementing a two-level factorial experimental design methodology. Seven and ten factors were found statistically important in the case of photocatalytic As(III) and HA oxidation respectively. Based on these statistically significant factors, a first order polynomial model describing As(III) and HA photocatalytic oxidation was constructed and a very good agreement was obtained between the experimental values and those predicted by the model, while the observed differences may be readily explained as random noise.

A comparative treatment of stabilized landfill leachate: coagulation and activated carbon adsorption vs. electrochemical oxidation.

This work investigated the treatment of a landfill leachate that had previously undergone biological treatment. Two treatment schemes were compared: the first one involved coagulation followed by activated carbon adsorption, whilst the second was electrochemical treatment. Coagulation with alum resulted in a 50% removal of chemical oxygen demand (COD). The optimum aluminium dose was 3 mM Al3+. Activated carbon adsorption of stabilized leachate that had been previously treated by coagulation resulted in an overall 80% removal of COD. However, a significant part of the organic matter (corresponding to 170 mg/L) was non-adsorbable. Electrochemical oxidation over a boron-doped diamond electrode led to about 90% COD removal in 240 min with the resulting stream having a COD content as low as 50 mg/L. An increase in current intensity from 15 A to 21 A had no practical effect on the overall COD removal, which followed first-order kinetics.