Olga Gimeno

Effects of single and combined ozonation with hydrogen peroxide or UV radiation on the chemical degradation and biodegradability of debittering table olive industrial wastewaters

Abstract Chemical oxidation of debittering table olive wastewaters using ozone alone and combined with hydrogen peroxide or UV radiation has been studied. The effect of oxidant concentrations on COD, BOD, TC (total carbon), aromatic content and colour of wastewaters has been observed. COD reduction of 80 or 90% can be reached with ozone doses between 3 and 4xa0g in the presence of 10 −3 xa0M initial hydrogen peroxide concentration (2.4xa0g at the conditions investigated) or 254xa0nm UV radiation while moderate reductions of TC can be achieved (between 40 and 60%). Both the aromatic content and colour nearly completely disappear with less than 0.5xa0g of ozone applied. Along the reaction pH of wastewaters diminishes from 12 to 7.5. Biodegradability of wastewaters, measured as BOD/COD, increases from 0.16 (untreated wastewaters) to nearly 0.7 or 0.8 when using ozone combined with hydrogen peroxide (2.95xa0g O 3 fed during 2xa0h and 2.4xa0g H 2 O 2 initially charged) or UV radiation (3.98xa0g O 3 fed during 2xa0h and 2.65×10 −6 xa0Einsteinxa0s −1 ) as the oxidising systems, respectively.

Optimisation of Fenton’s reagent usage as a pre-treatment for fermentation brines

Pre-treatment of fermentation brines from green olives has been carried out by the Fe(II)/Fe(III)/H(2)O(2) system. Reagent concentration exerted a positive influence on chemical oxygen demand (COD) removal. Hydrogen peroxide uptake showed values in the range 0.3-1.6mol of COD eliminated per mol of H(2)O(2) consumed depending on operating conditions. The optimum working pH was found to be in the interval 2.0-3.5. Reaction temperature increased the COD degradation rate, although similar COD conversion values were obtained after 5h of treatment regardless of the value of this parameter. An analysis of the biodegradability of this type of effluent demonstrated the beneficial effect of the chemical pre-oxidation. According to the experimental results, it is suggested that there is an inhibitory effect of the wastewater due to its COD content and nature rather than attributable to the presence of high amounts of sodium chloride. Biodegradation efficiency increased as temperature was raised up to 30 degrees C. A further increase of this parameter up to 40 degrees C resulted in the death of the microorganisms.

Fenton-like oxidation of landfill leachate

Abstract The treatment of stabilized leachates by means of Fentons like reagent [Fe(III)–H2O2] has been studied. It has been demonstrated that the oxidation state of the catalyst does not influence the efficacy of the process in terms of chemical oxygen demand depletion profiles. The abrupt increase in temperature experienced in oxidation experiments involves a wastage of hydrogen peroxide diminishing the fraction of this reagent addressed at removing COD. If temperature is kept constant, the hydrogen peroxide uptake is 10 mg of H2O2 consumed per mg of COD abated (from 15 to 30°C). Working temperatures above 30°C does not lead to additional COD conversion, contrarily, the percentage of wasted H2O2 is increased. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of effluents.

UV-C radiation based methods for aqueous metoprolol elimination.

The endocrine disruptor metoprolol has been oxidised in aqueous solution by means of the systems UV-C, UV-C/H(2)O(2), UV-C/percarbonate, UV-C/monopersulfate, UV-C/TiO(2), UV-C/H(2)O(2)/TiO(2) and photo-Fenton. From simple photolysis experiments the quantum yield of metoprolol has been calculated (roughly 5x10(-3) mol Einstein(-1) at circumneutral pH). Addition of free radicals promoters significantly enhanced the metoprolol depletion rate. Mineralization degree was negligible when no promoter was added, while low values were achieved in the presence of either inorganic peroxides or titanium dioxide. The combination of radiation, hydrogen peroxide and TiO(2) increased the mineralization level up to values in the proximity of 45-50% under the best conditions investigated. The photo-Fenton process was the best system in terms of total oxidation (mineralization degree 70%) when optimum conditions were applied.

Wet Air Oxidation Of Wastewater From Olive Oil Mills

The oxidation of wastewater from olive oil mills has been carried out in the liquid phase at high temperatures and pressures. Synthetic urban wastewater has been used to dilute the raw effluent (dilution rate 1:10). Experiments conducted using air as the oxygen source showed a positive effect of the previous neutralization of the wastewater if compared to the oxidation conducted at the original pH of the effluent (pH = 5.3). In terms of chemical oxygen demand depletion and final biodegradability characteristics of the effluent, the use of free radical promoters, for instance hydrogen peroxide, resulted in a significant enhancement of the process. Experiments completed in the presence of two commercially available catalysts (platinum supported on alumina and copper oxide supported on active carbon) showed not only an improvement in the chemical oxygen demand removal rate but also a high degree of the mineralization of the wastewater contaminant load.

Joint treatment of wastewater from table olive processing and urban wastewater. Integrated ozonation-aerobic oxidation

Integrated ozonation-aerobic biodegradation of table olive wastewater (diluted 1:25 with synthetic urban wastewater) is presented as a suitable technology to purify this kind of effluent. Use of ozone is recommended as a pre-treatment step since it shows a high reactivity toward phenolic compounds (found in this type of wastewater) reducing, at the same time, the alkalinity of the media for further biological processing. An ozone dose of 45 mg L–1 (flow rate 20 L h–1) for a period of 35 min has been found to achieve the following goals: decrease pH, decrease phenolic content, and increase of biodegradability. The aerobic oxidation process followed first order kinetics as measured by COD depletion profiles versus time. The Arrhenius expression k = 183exp(–2214/T) was obtained for experiments of ozonated wastewater biodegradation completed at different temperatures and neutral pH.

Comparison of different advanced oxidation processes (AOPs) in the presence of perovskites.

The efficacy of the oxidation systems: O3, UV radiation, O3/UV radiation, O3/perovskite, UV radiation/perovskite, O3/UV radiation/perovskite, H2O2/UV radiation, H2O2/UV radiation/perovskite, has been investigated by using pyruvic acid as probe compound. Under the operating conditions used, the combination of UV radiation and hydrogen peroxide (with or without perovskites) leads to the fastest pyruvic acid removal while the best results in terms of mineralization degree are obtained when combining O3/UV radiation/perovskite. The effect of the variables: inlet ozone (15-75 mg L(-1)) and initial pyruvic acid (10(-3) to 10(-2)M) concentrations, catalyst load (0.01-1.5 g L(-1)) and pH (2-9) was investigated for the photocatalytic ozonation. The most influencing parameter was the ozone concentration fed to the photoreactor. A zero order was observed for pyruvic acid concentration and close to zero for catalyst load. Some deactivation is observed after reusing the catalyst, likely due to leaching of the active phase.

Pyruvic Acid Removal from Water by the Simultaneous Action of Ozone and Activated Carbon

Activated carbon (AC) has been used to catalyze the ozonation of pyruvic acid in water. Pyruvic acid conversions were found to be 9 and 37% after 90 min of single ozonation and single adsorption with 40 gL−1 AC, respectively, while 82% was reached at the same conditions during the AC catalytic ozonation. Also, for similar conditions, mineralization reached values of 67% in the AC catalytic ozonation against hardly 5% in the non-catalytic experiment. The process likely develops through both adsorption of ozone and pyruvic acid on the AC surface and generation of hydroxyl radicals that eventually is the responsible oxidizing species. Rate constants for both non-catalytic ozonation and AC-Ozone catalytic surface reaction, at 20°C and pH 7.5, were found to be 0.025 min−1 and 87.9 Lg−1s−1, respectively. For AC concentrations higher than 2.5 gL−1 gas-liquid mass transfer of ozone constituted the limiting step. At lower concentrations, internal diffusion plus surface reaction controlled the process rate.

Treatment of brines by combined Fenton’s reagent–aerobic biodegradation: II. Process modelling

Process modelling of the integrated Fentons reagent-aerobic biodegradation system has been carried out by considering a detailed reaction mechanism for the chemical oxidation step and the generalised Monod equation for the biological treatment. Chemical oxygen demand has been contemplated as a pseudo-component for simulation purposes. The proposed mechanism takes into consideration different features experimentally found. Thus, the inefficient hydrogen peroxide decomposition into oxygen and water, the influence of temperature and other operating variables and the role of oxygen have been considered. The aerobic biodegradation of the effluent after the chemical oxidation has taken place has been well simulated by Monod equation with no inhibitory terms. Dependency on temperature has been correlated by Arrhenius expression.

Co-oxidation of p-hydroxybenzoic acid and atrazine by the Fenton's like system Fe(III)/H2O2.

The system Fe(III)/H2O2 has been used to oxidise an aqueous solution of p-hydroxybenzoic acid (pHB) in the absence of light. In the process, typical operating variables such as reagent concentration exert a positive influence in the pHB degradation rate. Optimum pH has been found to be around 3. The kinetic study suggests that the mechanism involved in this system differs to some extent from that reported for the classic Fentons chemistry in pure water. Thus, formation of a complex Fe(III)-pHB seems to be a key step to initiate the oxidising mechanism. Stoichiometric measurements of the H2O2 consumption per mole of pHB degraded indicate a possible reduction of complexed Fe(III). Simultaneous oxidation of pHB (and other similar compounds such as tyrosol (Ty) or p-coumaric acid (pCu)) and atrazine have shown a synergistic effect of the first substance to remove the pesticide.