Use of seawater for the boron-doped diamond electrochemical treatment of diluted vinasse wastewater.

Vinasse wastewater of high organic content (COD = 131,000 mg/L) and low biodegradability (BOD5/COD = 0.11) cannot be easily managed and usually require several consecutive treatment steps. The objective of this work was to dilute vinasse wastewater with seawater and then subject them to electrochemical oxidation over boron-doped diamond (BDD) electrodes. The use of seawater is a rational and novel approach for plants close to the seashore since it may achieve the desirable levels of effluent concentration and conductivity without consuming other water resources and extra electrolytes. Experiments were conducted at initial COD values of 830-8,400 mg/L, NaCl concentrations of 34-200 mM and current densities of 70-200 mA/cm(2) for up to 5 hours. The effect of current density and NaCl concentration was marginal on the electrochemical treatment, while the single most important parameter was the initial COD concentration. The order of reaction for COD reduction appears to be 'first' at low effluent concentrations and it decreases to 'zero' at higher concentrations, denoting the importance of the ratio of organics to reactive radicals concentration. Based on COD and total organic carbon data, it is postulated that degradation occurs predominantly through total oxidation (i.e. mineralization) to carbon dioxide and water, which is characteristic of BDD anodes.

Sonochemical degradation of ofloxacin in aqueous solutions.

The use of low frequency (20 kHz), high energy ultrasound for the degradation of the antibiotic ofloxacin in water was investigated. Experiments were performed with a horn-type ultrasound generator at varying applied power densities (130-640 W/L), drug concentrations (5-20 mg/L), hydrogen peroxide concentrations (0-100 mM) and sparging gases (air, oxygen, nitrogen and argon). In general, conversion (which was assessed following sample absorbance at 288 nm) increased with increasing ultrasound energy and peroxide concentration and decreasing initial drug concentration. Moreover, reactions under an argon atmosphere were faster than with diatomic gases, possibly due to argon's physical properties (e.g. solubility, thermal conductivity and specific heat ratio) favoring sonochemical activity. Overall, low to moderate levels of ofloxacin degradation were achieved (i.e. it never exceeded 50%), thus indicating that radical reactions in the liquid bulk rather than thermal reactions in the vicinity of the cavitation bubble are responsible for ofloxacin degradation.

Synthesis and photocatalytic activity of boron-doped TiO(2) in aqueous suspensions under UV-A irradiation.

Boron-doped TiO(2) photocatalysts were synthesized employing a sol-gel method. Boric acid was used as the boron source and titanium tetra-isopropoxide as the TiO(2) precursor, both dissolved in isopropanol. Nominal boron to titanium atomic ratios were in the range 0 to 4%. After the hydrolysis step, two different procedures for the recovery of TiO(2) were followed, based on either centrifugation of the resulting reaction mixture or evaporation of the solvent under reduced pressure, both followed by a subsequent calcination step performed at 400 or 500 degrees C. The photocatalytic efficiency of the synthesized photocatalysts was assessed by measuring the photocatalytic mineralization of dichloroacetic acid in aqueous suspensions under UV-A irradiation and it was compared to the corresponding efficiency of the commercial Degussa P 25 TiO(2). Photocatalytic efficiency of the synthesized catalysts was higher for the boron-doped TiO(2) synthesized at 2% boron to titanium nominal atomic ratio, centrifuged after the hydrolysis step followed by calcinations at 400 degrees C. However, all photocatalysts synthesized in this work showed lower photocatalytic activity than Degussa P 25 TiO(2), thus highlighting the need of further improvements of the proposed method.

Ultrasonic degradation, mineralization and detoxification of diclofenac in water: optimization of operating parameters.

The 20 kHz ultrasound-induced degradation of non-steroidal, anti-inflammatory drug diclofenac (DCF) was investigated. Several operating conditions, such as power density (25-100 W/L), substrate concentration (2.5-80 mg/L), initial solution pH (3.5-11), liquid bulk temperature and the type of sparging gas (air, oxygen, argon), were tested concerning their effect on DCF degradation (as assessed measuring absorbance at 276 nm) and hydroxyl radicals generation (as assessed measuring H(2)O(2) concentration). Sample mineralization (in terms of TOC and COD removal), aerobic biodegradability (as assessed by the BOD(5)/COD ratio) and ecotoxicity to Daphnia magna and Artemia salina were followed too. DCF conversion is enhanced at increased applied power densities and liquid bulk temperatures, acidic conditions and in the presence of dissolved air or oxygen. The reaction rate increases with increasing DCF concentration in the range 2.5-5mg/L but it remains constant in the range 40-80 mg/L, indicating different kinetic regimes (i.e. first and zero order, respectively). H(2)O(2) production rates in pure water are higher than those in DCF solutions, implying that decomposition basically proceeds through hydroxyl radical reactions. Mineralization is a slow process as reaction by-products are more stable than DCF to total oxidation; nonetheless, they are also more readily biodegradable. Toxicity to D. magna increases during the early stages of the reaction and then decreases progressively upon degradation of reaction by-products; nevertheless, complete toxicity elimination cannot be achieved at the conditions in question. Neither the original nor the treated DCF samples are toxic to A. salina.

Drugs degrading photocatalytically: Kinetics and mechanisms of ofloxacin and atenolol removal on titania suspensions.

The conversion of the antibiotic ofloxacin and the beta-blocker atenolol by means of TiO(2) photocatalysis was investigated. Irradiation was provided by a UVA lamp at 3.37x10(-6)einstein/s photon flux, while emphasis was given on the effect of catalyst type and loading (50-1500mg/L), initial substrate concentration (5-20mg/L), initial pH (3-10) and the effect of H(2)O(2) (0.07-1.4mM) as an additional oxidant on substrate conversion and mineralization in various matrices (i.e. pure water, groundwater and treated municipal effluent). Conversion was assessed measuring sample absorbance at 288 and 224nm for ofloxacin and atenolol, respectively, while mineralization measuring the dissolved organic carbon. Degussa P25 TiO(2) was found to be more active than other TiO(2) samples for either substrate degradation, with ofloxacin being more reactive than atenolol. Conversion generally increased with increasing catalyst loading, decreasing initial substrate concentration and adding H(2)O(2), while the effect of solution pH was substrate-specific. Reaction rates, following a Langmuir-Hinshelwood kinetic expression, were maximized at a catalyst to substrate concentration ratio (w/w) of 50 and 15 for ofloxacin and atenolol, respectively, while higher ratios led to reduced efficiency. Likewise, high concentrations of H(2)O(2) had an adverse effect on reaction, presumably due to excessive oxidant scavenging radicals and other reactive species. The ecotoxicity of ofloxacin and atenolol to freshwater species Daphnia magna was found to increase with increasing substrate concentration (1-10mg/L) and exposure time (24-48h), with atenolol being more toxic than ofloxacin. Photocatalytic treatment eliminated nearly completely toxicity and this was more pronounced for atenolol.

Effect of key operating parameters on the non-catalytic wet oxidation of olive mill wastewaters.

The non-catalytic wet air oxidation (WAO) of olive mill wastewaters was investigated. The effect of operating conditions, such as initial organic loading (1,000 and 4,500 mg/L COD), reaction temperature (140 and 180 degrees C), treatment time (1 and 4 h), initial pH (4.8 and 7) and the use of 500 mg/L H(2)O(2) as an additional oxidant, on treatment efficiency was assessed implementing a factorial experimental design. Of the five parameters tested, the first two had a considerable effect on COD removal, while treatment time was of no significance implying that all oxidation reactions occur during the first hour of treatment. Although the level of mineralization was generally moderate, this was accompanied by nearly complete total phenols and color removal. The analysis was repeated at more intense conditions, i.e. initial COD up to 8,000 mg/L and reaction temperature up to 200 degrees C; at this level, none of the studied effects were important. However, at optimal experimental conditions (i.e. 180 degrees C, 1 h treatment and initial COD of 8,100 mg/L) WAO yielded 34, 94 and 74% removal of COD, total phenols and color respectively. Moreover, ecotoxicity to V. fischeri was slightly reduced after 2 h of treatment at the above conditions.

Electrochemical oxidation of model compounds and olive mill wastewater over DSA electrodes: 1. The case of Ti/IrO(2) anode.

The electrochemical oxidation of olive mill wastewater (OMW) and model compounds over a Ti/IrO(2) anode was studied by means of cyclic voltammetry and bulk electrolysis. Experiments were conducted at 1300 mg/L initial COD, 0-1.23V vs SHE and 1.4-1.54V vs SHE potential windows, 50 mA/cm(2) current density, 0-25 mM NaCl, 60-80 degrees C temperature and acidic conditions. The reactivity of model compounds decreases in the order phenol approximately p-coumaric acid>cinnamic acid>caffeic acid. Partial and total oxidation reactions occur with the overall rate following zero-order kinetics with respect to COD and increasing with temperature. Oxidation of OMW at 43 Ah/L, 80 degrees C and in the presence of 5mM NaCl leads to complete color and phenols removal, elimination of ecotoxicity but moderate (30%) COD reduction. Similar performance can be achieved at 6 Ah/L in the presence of 15 mM NaCl. In the absence of salt, the respective color and phenols removal (at 6 Ah/L) is less than 10%. Excessive salinity (25 mM), although does not change color, phenols and COD removal, has an adverse effect on ecotoxicity.

Ultrasound-induced inactivation of gram-negative and gram-positive bacteria in secondary treated municipal wastewater.

The effect of 24kHz, high energy ultrasound in the presence and absence of titanium dioxide particles on the destruction of different bacteria groups was studied. Applying a total of 1500W/L for 60min (this corresponds to 5400kJ/L specific nominal energy), the mean destruction of gram-negative bacteria such as total coliforms, faecal coliforms and Pseudomonas spp. was 99.5%, 99.2% and 99.7%, respectively. More recalcitrant to sonolytic inactivation were the gram-positive bacteria Clostridium perfringens and faecal streptococci with a mean removal of 66% and 84%, respectively. The presence of 5g/L TiO(2) generally enhanced the destruction of gram-negative bacteria, yielding three to five logs reduction. On the other hand, the relatively weak sonochemical inactivation of gram-positive bacteria was only slightly affected by the presence of solid particles. Inactivation was found to follow first-order kinetics regarding bacteria population and was not affected significantly by the wastewater quality. Ultrasound irradiation at 4000kJ/L specific nominal energy and in the presence of 5g/L TiO(2) achieved less than 10(3) CFU/100mL total coliforms, thus meeting USEPA quality standards for wastewater reuse.

Toxicity bioassays in core sediments from the Bay of Santander, northern Spain.

The use of Vibrio fischeri as luminescence bacteria is particularly effective in evaluating contaminated sediment. In this study, the ecotoxicity of five core sediments from the Bay of Santander, northern Spain, utilising V. fischeri as marine bacterium, was carried out. Different toxicity assay procedures were applied in order to study the influence of the mobility and bioavailability of the pollutants. Basic Solid Phase Test (BSPT) in whole sediment and acute toxicity test, using pore water and three leaching test procedures as liquid extracts, were applied. In addition, the study of the influence of the pH value on the toxicity results of the leaching tests was conducted. The obtained results show toxicity units (TU50) values in BSPT test ranging from 0.42 to 39.06 with a decrease with depth as general trend and TU50 values from 0.010 to 0.389 in the liquid extracts, where TU50 is calculated as the inverse of EC50 (%). The obtained data show the historical toxicity trends of the Bay of Santander and provides a technical database for the management of contaminated sediments. Moreover, these results showed evidence that each sediment test procedure provided independent and complementary ecotoxicological responses useful for a sediment classification. In order to analyse the correlations between chemical parameters (both organic and inorganic) and the toxicity results, the self-organising map (SOM) neural network and regression equations were applied. Satisfactory correlations (R=0.93) between chemical concentrations of sum of five heavy metals and 16 PAHs and BSPT toxicity were obtained.

Modelling of sonochemical processes in water treatment.

The mechanisms and kinetics of the sonochemical degradation of organic molecules in water are relatively complex since several parameters such as physicochemical properties, substrate concentration, water matrix, reactor geometry, ultrasound properties (frequency, power, emission system) all typically affect the process. In this work, simple kinetic models were used to predict the degradation of 2-chlorophenol and sodium dodecylbenzene sulphonate in aqueous solutions and verified against experimental data taken from previous studies. A pseudo-first order kinetic expression can adequately describe the degradation of the phenolic substrate, while a heterogeneous model based on the Langmuir-Hinshelwood equation is suitable for the surfactant degradation.

Survival of total coliforms in lawn irrigated with secondary wastewater and chlorinated effluent in the Mediterranean region.

Pregrown, two-month-old lawn was layered in 12 large square pots with an area of 0.25 m2 each, filled with a mixture of topsoil, peat, and sand. In late July, in the heart of the Mediterranean summer, the pots were divided into two groups, with six pots per group. On four different occasions, the pots in each group were sprinkled (surface irrigation) with 2 L of either secondary-treated wastewater (STW, group A) or chlorinated effluent (CHE, group B). Wastewater application always took place at 0700 hours. Samples of the surface soil and grass from each pot were collected at the following times: before irrigation, immediately after irrigation, two hours later (0900 hours), and four hours later (1100 hours). In the samples collected, the number of total coliforms per gram was measured using standard microbiological analyses. Temperature and sunlight intensity were also monitored. There was an increase in the coliforms population in soil and grass samples of both groups immediately after the wastewater application. In group A, the mean number of coliforms recorded in the soil samples reached mean values higher than 5000 cfu/g compared to 312 cfu/g recorded before application. The increase in group B was smaller but still significant. Two hours later, the number of coliforms was reduced substantially in all samples (e.g., group A, soil samples 477 cfu/g). Coliform inactivation is thought to result from the effect of temperature and mainly sunlight. However, four hours after application (1100 hours), there was a noticeable increase in the coliform number again, in all sample categories of both groups. Coliform reactivation could be a result of shadowing effect resulting from the thick foliage of the grass, where the microorganisms were protected by the sunlight radiation and regrowth in a friendly environment (especially of the soil) where moisture and nutrients were present. This, in addition to the fact that coliforms seemed to retain a sizable population between applications, results in three conclusions: (1) coliforms can survive in grass and soil for a substantial period of time, recovering from the destructive effect of chlorination, (2) use of STW, even during the Mediterranean summer, could result in a substantial "contamination" of lawns, without any proof that sun and temperature can reduce the coliform number, and (3) intense sunlight (up to 68 000 lux) was far more effective in coliform suppression than elevated temperature (up to 38 degrees C).

Sonochemical degradation of phenolic pollutants in aqueous solutions.

The sonochemical degradation of phenol, 2-chlorophenol and 3,4-dichlorophenol in aqueous solutions as a function of several operating conditions has been investigated. Experiments were performed at initial substrate concentrations of 0.1, 0.5 and 1 g l(-1), liquid phase volumes of 0.05, 0.07 and 0.08 l, electric power outputs of 125, 187.5 and 250 W, liquid bulk temperatures of 20, 35, 50 and 70 degrees C and an ultrasound frequency of 20 kHz. Substrate concentration was determined as a function of time by means of high performance liquid chromatography. At the conditions under consideration, the rate of degradation follows first order kinetics with respect to the substrate concentration and increases with increasing electric power and decreasing liquid volume. The relative reactivity appears to decrease in the order: 2-chlorophenol > 3,4-dichlorophenol > phenol. Measurements of liquid phase total organic carbon content showed that degradation by-products are more recalcitrant than the original substrate. The rate of 2-chlorophenol degradation was also found to decrease with decreasing liquid bulk temperature and increasing initial concentration. Addition of t-butanol as a hydroxyl radical scavenger only partially inhibited degradation, thus implying that degradation is likely to proceed via both radical-induced and thermal reactions. Addition of Fe2+ ions at concentrations as low as about 0.2 x 10(3) g l(-1) resulted in increased degradation rates; this is attributed to iron being capable of readily decomposing hydrogen peroxide (generated by water sonolysis) in a Fenton-like process to form hydroxyl radicals as well as being an effective oxidation catalyst. The implications of the use of ultrasound in wastewater treatment are also discussed.

Chemical treatment of an anionic surfactant wastewater: Electrospray-MS studies of intermediates and effect on aerobic biodegradability.

The effect of wet air oxidation on the aerobic biodegradability of a model wastewater containing 1000 mg L(-1) of linear alkylbenzene sulfonate (LAS) has been investigated. Semibatch oxidation experiments were performed temperature of 473 K, oxygen partial pressure of 1.3 MPa and residence times varying from 40 to 390 min, while continuous oxidation experiments were performed at a residence time of 120 min. Oxygen uptake tests were performed to assess the aerobic biodegradability of both the oxidised and the original LAS solutions using cultures that had been adapted to both LAS and oxidation intermediates. The concentration of total organic carbon, chemical oxygen demand and active detergent were followed throughout the wet oxidation and biodegradation experiments, while the main intermediates formed during wet oxidation were identified by means of Electrospray-MS and high performance liquid chromatography. It was found that LAS could be easily oxidised at 473 K to yield a group of molecules with short alkyl chains which do not behave as active detergents. Sulfonated aromatics are produced as intermediates which have had the alkyl chains shortened. The segments of alkyl chains broken off the intermediate compounds appear primarily as short chain organic acids. The original unoxidised 1000 mg L(-1) LAS solution was found to be readily biodegradable in the laboratory aerobic reactors operating at low organic loadings and substrate to microorganism concentration ratios. However, wet oxidation resulted in effluents that were less readily biodegradable than the original LAS with biodegradability decreasing with increasing degree of oxidation. These results suggest that, at the conditions under consideration, a combined chemical pre-oxidations and biological post-treatment process may be less effective in removing LAS than a single-stage biological or chemical process.

Flash freezing of erythrocyte suspensions.

Freezing whole blood in bulk usually results in severe cellular destruction through the action of ice crystals and osmotic effects in the freezing liquid. The potential of flash freezing blood aerosols onto a liquid nitrogen surface as a means of inhibiting cellular damage was studied in this work. Three commercial spraying devices were employed to spray-freeze either whole blood or concentrated erythrocyte suspensions, using hydroxyethyl starch (HES) as a cryoprotectant. The integrity and viability of the processed cells were assessed by measuring gross rheological properties and the extent of hemolysis. Cells were found to be susceptible to the very high shear stresses imposed by some of the spraying devices. Bulk freezing of blood, even in the presence of cryoprotectant, resulted in complete cellular destruction. Whereas flash freezing was capable of substantially reducing the level of hemolysis to 12.6% and preserving the cellular deformability.