Juha Kallas

Wet oxidation of concentrated wastewaters of paper mills for water cycle closing

Experimental research into wet oxidation of concentrated wastewaters from paper mills was undertaken. Evaporation and membrane concentrates from paper mills were selected as experimental objects. The aim of the wet oxidation of the paper mill concentrates was to reduce the concentration of organics and to improve biodegradability of the concentrates. The effect of temperature, pH and the influence of homogeneous and heterogeneous catalysts on the rate of the wet oxidation process was studied. The experiments were carried out in stainless steel batch reactor at temperatures from 130 to 200°C and at pH 2, 5 and 10. The partial pressure of oxygen was maintained at 1 MPa for all experiments. The results showed COD and TOC removal increases of 50 to 80% at temperatures from 160 to 200°C. The best results with respect to the improvement of biodegradability were, however, observed under milder conditions. By the use of both homogeneous and heterogeneous catalysts, a biodegradability of 60 to 78% was achieved with wet oxidation at 150°C. Operational cost estimation for the wet oxidation process was also done and showed that the cost of wet oxidation of concentrated water by air is less expensive than an oxygen-based process.

Catalytic Ozonation of m-Dinitrobenzene

The efficiency of catalytic ozonation with homogeneous (containing dissolved ions of Fe2+, Mn2+, Cu2+, Ni2+, Co2+, V5+, Cr3+, Mo6+) and heterogeneous (MnO2, Ni2O3, Fe2O3, CuO, Al2O3, CoO, V2O5, Cr2O3, MoO3, TiO2) catalysts and non-accompanied ozonation was compared for degradation of m-dinitrobenzene (m-DNB). Several transition metals in homogeneous and heterogeneous form improved significantly the ozone performance for degradation of m-DNB. This improvement was found to be due to supplementary formation of reactive species (hydroxyl radicals) and better ozone utilization. The effects observed were found to be strongly dependent on the treatment conditions.

Modelling of Chlorophenol Treatment in Aqueous Solutions. 1. Ozonation and Ozonation Combined with UV Radiation under Acidic Conditions

Abstract Treatment of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in aqueous solutions with direct photolysis (254 nm), ozonation and ozonation with photolysis was studied. A model was developed to simulate chlorophenol treatment in a semibatch column using these processes under acidic conditions in which the chemical reactions are slow. Satisfactory results were obtained in simulating the chlorophenol and ozone concentrations, and the concentrations of an aromatic quinone, hydrogen peroxide and chloride ions formed in the course of the processes. Chlorophenol oxidation systems, however, appeared to be very complex and the formation of intermediate and final products were dependent on the reaction conditions. The degradation rate of chlorophenols was not enhanced by the combination of ozone with UV radiation compared with ozonation alone. Oxidation at low pH in both processes proceeded mainly through reactions with molecular ozone.

Advanced Oxidation Processes Against Phenolic Compounds In Wastewater Treatment

Abstract Experimental research into the oxidative treatment of aqueous solutions and wastewaters containing phenolic compounds was undertaken. Ozone, supported by short wavelength UV-irradiation, hydrogen peroxide and titanium dioxide catalyst, was selected as an oxidant in the following combinations: O3, O3/H2O2, O3/UV, O3/TiO2, O3/UV/H2O2 and O3/UV/TiO2. 5-Methylresorcinol was chosen as a model compound for the experiments with synthetic phenolic solutions. The results obtained from these experiments were compared with the results of oxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia.

Chemical oxidation of biologically treated phenolic effluents

Experimental research into the oxidative purification of biologically treated phenolic effluents of the Estonian oil shale chemical industry was undertaken. The main phenolic compounds identified in this wastewater were phenol, cresols, resorcinol and 5-methylresorcinols. For chemical oxidation of phenols different advanced oxidation methods (O3, H2O2, UV, O3/H2O2, O3/UV, H2O2/UV, O3/H2O2/UV) were tested. For tracking of the changes in the concentration of different phenols during the treatment process, HPLC and colorimetry were applied. It was shown that, in principle, phenols can be reduced almost by any oxidation method studied. Oxidation with molecular ozone has the most potential for practical application. Methods not including ozone (H2O2, UV, H2O2/UV) had, in general, lower efficiency for total phenols reduction than the methods combining ozone.

Degradation of aqueous nitrophenols by ozone combined with UV-radiation and hydrogen peroxide

Abstract The degradation of nitrophenols with ozone and ozone combined with hydrogen peroxide and/or UV-radiation was studied. These combinations accelerated the degradation of nitrophenols and decreased the ozone specific consumption mostly at low pH values. O3/UV/H2O2 combination was the most effective for the degradation of nitrophenols. According to the Daphnia magna acute toxicity test, the treatment led to complete detoxification of nitrophenols. A high degree of nitrogen mineralization was achieved.

The role of pH in aqueous photocatalytic oxidation of β-estradiol

Experimental studies of aqueous photocatalytic oxidation (PCO) of β-estradiol in TiO2 suspensions were undertaken. The dependence of PCO efficiency and adsorption of β-estradiol on pH was studied. It was found that both the adsorption of β-estradiol and the PCO efficiency increased practically linearly with increasing concentration of OH-ions. The predominant role of direct β-estradiol oxidation with positively charged holes was thus indirectly confirmed.

Coagulation as a Post-Treatment Process for Wet Oxidation of Pulp and Paper Mill Circulation Waters

The present study tested the performance of coagulation after wet oxidation (WO) as a way to improve water quality, namely colour, and establish its viability as a secondary treatment process for water cycle closing. The experiments were carried out with model TMP (Thermomechanical Pulp) water concentrated by nanofiltration. The WO runs were conducted at a temperature of 453 K and p(O 2 ) of 1 MPa. Fe 2 (SO 4 ) 3 was chosen as the coagulant for the coagulation experiments. The experimental results showed that coagulation allowed 83% colour removal and 75% lignin reduction with a coagulant dose of 0.86 g Fe 3+ /L. Recirculation of sludge to the WO system improved the performance of the WO process. The dose needed to achieve the same results for the coagulation after the recirculation loop, i.e. coagulation after wet oxidation with coagulation sludge recycled to the WO system, was 0.78 g Fe 3+ /L. The Fe ion concentration remaining after coagulation was observed to be 0.91-0.95 mg/L, which could permit sludge-free water reuse in paper mills.

Modelling of Chlorophenol Treatment in Aqueous Solutions. 2. Ozonation under Basic Conditions

Abstract Ozonation of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in basic aqueous solutions is discussed. In such conditions (pH=9.5), ozonation of chlorophenols proceeds rapidly due to the presence of the dissociated form of the phenolic compound. No ozone occurs in the bulk of the liquid and, in modelling, it becomes necessary to account for the reactions in the liquid film. Two approaches were tested: 1) the film and bulk balances were solved sequentially, and the diffusional fluxes coupling the balances were obtained by solving numerically the concentration profiles in the film; 2) the bulk mass balances were solved without the film mass balances by applying the enhancement factor calculated from existing correlations. The results of both approaches are compared with experimental data. The formation mechanism of an aromatic quinone, hydrogen peroxide and chloride ions during the ozonation appeared to differ under basic conditions from that under acidic conditions. Hy...

Pulsed corona discharge: the role of ozone and hydroxyl radical in aqueous pollutants oxidation

Ozone and hydroxyl radical are the most active oxidizing species in water treated with gas-phase pulsed corona discharge (PCD). The ratio of the species dependent on the gas phase composition and treated water contact surface was the objective for the experimental research undertaken for aqueous phenol (fast reaction) and oxalic acid (slow reaction) solutions. The experiments were carried out in the reactor, where aqueous solutions showered between electrodes were treated with 100-ns pulses of 20 kV voltage and 400 A current amplitude. The role of ozone increased with increasing oxygen concentration and the oxidation reaction rate. The PCD treatment showed energy efficiency surpassing that of conventional ozonation.