Lidia Szpyrkowicz

A Comparative study on oxidation of disperse dyes by electrochemical process, ozone, hypochlorite and fenton reagent

The results of an experimental study on the destruction of disperse dyes by chemical oxidation using ozone, hypochlorite and Fenton reagent (H2O2 + Fe2+) are compared with the data obtained by electrochemical oxidation. While the results obtained during hypochlorite oxidation were not satisfactory (only 35% reduction of colour was achieved at a dose of 6 g dm(-3)), ozonation enabled colour to be reduced by up to 90% (ozone dose 0.5 g dm(-3)). A high decolourisation degree was however accompanied by a low removal (10% efficiency) of chemical oxygen demand (COD). Trials of electrochemical oxidation proved this process much more efficient. Under the conditions of an acidic pH in 40 min of electrolysis a 79% elimination of COD was achieved at the Ti/Pt-Ir anode, which proved the best of seven different tested materials. Simultaneously 90% colour was removed. Indirect oxidation, by means of chlorine-deriving compounds, was the predominating process leading to the pollutants depletion. The best treatment results were obtained with the Fenton process, which under the optimal pH equal to 3 and hydrogen peroxide and ferrous sulphide dose of 600 and 550 mg dm(-3), respectively, resulted in a final effluent being colourless and with the residual COD equal to 100 mg dm(-3).

Electrochemical treatment of tannery wastewater using Ti/Pt and Ti/Pt/Ir electrodes

Abstract The treatment of tannery wastewater by the electrochemical method using Ti Pt and Ti/Pt/Ir electrodes is investigated. The aim of a satisfactory elimination of NH+4 from wastewaters of different strength was achieved using both types of electrodes. A Ti/Pt/Ir anode proved to have the electrocatalytical properties for NH+4 removal, but it resulted to be more sensitive to poisoning by H2S contained in the wastewater. For both types of the electrodes NH+4 removal followed pseudo-first order kinetics, with the rate decreasing in function of the presence of organic substances. A concurrent removal of COD was observed particularly with a Ti Pt anode, but its magnitude was not sufficient to ensure the discharge limits to be met while treating the raw wastewater only by the electrochemical process. In conclusion the electrochemical process can be applied successfully as a final polishing or an alternative to biological nitrification, but cannot substitute completely the traditional treatment of tannery wastewater.

Performance of electrochemical reactor for treatment of tannery wastewaters

Abstract An undivided electrochemical reactor with parallel plate Ti/Pt–Ir anode and stainless-steel cathode was used to treat tannery wastewater at constant current densities and different stirring rates. The pollutants were depleted by direct anodic oxidation and/or indirect electro-oxidation, mediated by active chlorine formed in situ, so that chemical oxygen demand, total organic carbon, tannin, sulfide, total Kjeldahl nitrogen and ammonium ion concentrations decayed with time. The results of the treatment, supported by data obtained with synthetic wastewater, showed that selectivity of the removal of different pollutants was affected by current density to a small extent. By contrast, hydrodynamic conditions strongly influenced the rates and the differential selectivity ratio of depletion of the pollutants, with the exception of tannins. The kinetics of elimination of ammonium ions, removed only via oxidation by “active chlorine”, was diminished by agitation, contrary to its effect in enhancing the removal of the other pollutants, for which direct anodic oxidation was an additional process for their destruction.

Application of electrochemical processes for tannery wastewater treatment

Tannery wastewater (real and synthetic) was treated by an electrochemical method with the principal aim of eliminating ammonium. Of various materials tested as electrodes graphite proved the best anode and steel the best cathode. Ammonium elimination was negatively influenced by the presence of organic pollutants and sulphides. The best results were obtained using electroxidation as a polishing step for the final effluents of a biological treatment plant. Ammonium elimination efficiency after 30 min of electrolysis at a current density of 0.44 A/dm2 was equal to 99%. For these conditions energy consumption for the elimination of 1 kg of NH4 + was 132 kwh. The process was less efficient when applied to raw and partially treated wastewater: to achieve the same result, electroxidation time had to be doubled and current density to be increased about threefold. COD removal was satisfactory when the initial values were relatively low (less than 300 mg/l) and only partial (about 70%) while treating wastewater wi...

Comparison of the performance of a reactor equipped with a Ti/Pt and an SS anode for simultaneous cyanide removal and copper recovery

The paper presents the results of a study on the destruction of copper complexed cyanides and the simultaneous recovery of copper in a lab-scale batch electrochemical reactor. The performance of the reactor equipped with a stainless steel (SS) plate anode is compared with the data relative to the process conducted with a Ti/Pt anode having the same overall size. Both reactors operated at various initial pH values under galvanostatic conditions. Under highly alkaline conditions in situ generation of a CuO catalyst on the anode surface was observed in both the reactors. The observed mass transport coefficient, showing both the effects of reaction kinetics and mass transfer, was a function of pH value and, only secondly, of the anode material. The highest value of (klA)obs, equal to 0.24033 cm3s−1 was obtained for a Ti/Pt anode reactor operating at the pH of 13. Under these very alkaline conditions the performance of the reactor equipped with the Ti/Pt anode at high initial Cu concentration proved slightly better than the performance with the SS anode. The energy consumption for the pH 13 was a function E=a/[Cu]+b, where a and b are the constants characteristic for each of the two reactors.

Electrochemical Destruction of Thiourea Dioxide in an Undivided Parallel Plate Electrodes Batch Reactor

Abstract The paper presents the results of a study on the electrochemical destruction of pollutants present in a spent reducing bath of a textile factory. The investigations comprised the electro-oxidation of thiourea dioxide (TUD) (the main component of the reducing bath), sulphites and urea, which are formed during oxidation of TUD. The study performed in an undivided cell parallel plate electrodes reactor, using eight different anode materials under various hydrodynamic conditions, proved that electro-oxidation can be successfully applied for treatment of spent reducing baths. The best results of TUD and SO32− electro-oxidation were obtained with a Ti/Pt electrode, which showed electrocatalytic effect for both the compounds, indicating a possibility of their direct electro-oxidation on the anode. Destruction of TUD and SO32− proceeded also via indirect electro-oxidation, mediated by chlorine evolved on the anode. The process kinetics was mass transport controlled till Re=5000. No electrocatalytic effects were observed for urea with any of the tested anode materials. The elimination of urea resulted to proceed only by indirect electro-oxidation, mediated by chlorine. For elimination of urea a Ti/Pt–Ir electrode proved to be the best anode, probably due to its high efficiency in electro-oxidation of chlorides into chlorine.

Characterization of rainwater quality from the Venice region network using multiway data analysis

Abstract The paper describes the results of an exploratory analysis of the relations between variables characterizing the quality of atmospheric precipitation in the Veneto, an Italian region with an area of ∼ 18000 km2 and a population of just over 4.5 million. A network of eight sampling stations for monitoring rainfall was set up in 1988, in line with the EMEP statements. The data consisted of 1174 observations over the period February 1989–December 1991. Principal component analysis (PCA) was used in an attempt to describe the structure of relations between the solutes in wet deposition. Some extensions of PCA (interstructure-compromise-intrastructure method) were considered in order to evaluate differences between relation structures as defined by location, season and volume of precipitations.

Nitrification and denitrification of tannery wastewaters

Abstract In this paper the studies on the dissimilative removal of nitrogen by biological means from wastewaters consisting of up to 90% chrome tannery and 10% domestic sewages are reported. Experiments were carried out over a 6 month period in a pilot plant of the modified Ludzack-Ettinger configuration. The feasibility of the biological nitrogen removal from this type of wastewaters without a preliminary chemical-physical phase or an external carbon source for denitrification was proved. The COD utilization coefficient was 12.5 mg COD for 1 mg of denitrified N. No inhibition of the process was induced by Cr or by S 2− present in the raw wastewaters. A negative effect on the denitrification rate resulted from a high ratio between the quantity of oxygen returned with the mixed liquor and the inlet COD.

Organics isolation from fresh and drinking waters by macroporous anion-exchange resins

Abstract A research on the isolation of organic pollutants from water is presented. Five macroporous anionic resins: Varion AT400, Asmit 229N, Zerolite 553N, Wofatite EA60 and Amberlite IR93 were used for humic substances and other anionic organics isolation. Varion AT400 resulted to be the best anionic resin (about 90% recovery of humic substances and a lower recovery for other anionic substances). Nearly complete desorption was achieved by NaCl/NaOH 10%/2% solution, at a volume of about 3.5 times the resin bed volume.

Treatment of herbal pharmaceutical wastewater with energy recovery

Herbal based pharmaceutical wastewater distinguishes itself because of its high content of organic pollutant and being highly acidic in nature. Adopting aerobic processes as a treatment alternative involves high capital investments, requires skilled manpower in addition to being energy intensive. On the contrary, an anaerobic system provides a low investment technology using aeration equipment, sludge disposal facility and recirculation with a prime advantage of methane recovery. The concept of immobilization technology has been incorporated in this research for biomethanation of high strength herbal based pharmaceutical wastewater. Accordingly, an investigation has been made on bench scale to assess the feasibility of an anaerobic fixed film fixed bed reactor system to treat herbal based pharmaceutical wastewater with recourse to energy recovery and to evaluate the system performance under different operating conditions.