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1

Optimization of humic acids coagulation with aluminum and iron [III] salts

100%

Libecki B. , Dziejowski J.

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2008

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tom 17

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nr 3

397-403

EN

Humic substances contained in ground and surface waters increase the degree of their pollution, give it a specific colour and contribute to the formation of toxic disinfection by-products in the process of water treatment. Coagulation is an effective method of removing organic compounds, including humic acids (HA), from water and wastewater. The proper selection of coagulants and optimization of such parameters as coagulant dose and the pH of the solution enable improvement of coagulation efficiency. The objective of the present study was to determine the efficiency of humic acids removal by coagulation, depending on the dose of Al and Fe(III) salts and pH of the analyzed solutions. A model alkaline solution and 0.2 M solutions of Al₂ (SO₄)₃ and Fe₂ (SO₄)₃ were used. The experiment was performed with and without pH adjustment, by a standard jar test procedure. COD-Cr [mg O₂ ·dm⁻³], colour – PtCo [mg·dm⁻³], turbidity – FTU [mg·dm⁻³], suspended solids – SS [mg·dm⁻³], pH and streaming potential – SP [mV] were determined during coagulation tests. In the solutions coagulated without pH adjustment and with the optimum doses of Al₂ (SO₄)₃ and Fe₂ (SO₄)₃ ,COD was at a level of 0.1 to 3% of the initial value and colour was removed almost completely. Iron(III) sulfate was found to be slightly more effective as a coagulant, in respect to COD removal. The results of electrokinetic measurements showed that the charge of molecules of humic colloids depends on the type and concentration of coagulating salt, as well as on the pH of the solution. The analysis of coagulation with pH adjustment revealed that there exists the optimum value of pH for each of the salt doses applied in the experiment. Coagulation with the use of Al₂ (SO₄)₃ and Fe₂ (SO₄)₃ proceeded at pH < 5.8 and pH < 4.2, respectively. A decrease in the pH of an HA solution allowed us to considerably (even eight-fold) reduce the dose of coagulants, maintaining high (above 94%) efficiency of humic acid removal by coagulation.

2

Interactions of aluminum and iron[III] salts with humic acids in a model alkaline solution

100%

Libecki B. , Dziejowski J.

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nr 3

681-691

EN

Both ferric and aluminum salts show good coagulation and complex-forming ability in relation to water-dissolved organic matter. The aim of this study was to characterize the reactions of aluminum salts (AlCl₃) and iron(III) salts (FeCl₃) with humic acids (HA) in a model alkaline solution as dependent on the type and concentration of coagulant. Conductometric and pH-metric titrations and coagulation jar tests were performed. Changes in COD, color and streaming potential were measured in coagulated samples. It was found that the characteristic changes in pH and electrolytic conductivity of solutions during titration with Al and Fe(III) salts are indicative of a gradual course of humic acids coagulation process. Depending on the salt used (aluminum or iron(III)), humic acids removal is a result of coagulation proceeding via various mechanisms. Precipitation was observed at a dose of 3.2 mmol dm⁻³ and pH < 6.4 in the case of AlCl₃, and at a dose of 3.0 mmol dm⁻³ and pH < 4.8 in that of FeCl₃. COD and color removal efficiency was equal to approximately 97% and 99% after coagulation with both AlCl₃ and FeCl₃. The increase in streaming potential at a salt dose of 2.4–3.6 mmol dm⁻³ was probably related to the binding of positively charged products of salt hydrolysis by the functional groups of humic acids molecules, followed by the neutralization of their charge.

PL

Sole żelaza i glinu wykazują wysoką zdolność koagulacyjną oraz kompleksotwórczą w stosunku do rozpuszczonej w wodzie materii organicznej. Celem badań było scharakteryzowanie oddziaływania soli glinu (AlCl₃) oraz żelaza(III) (FeCl₃) z kwasami huminowymi (KH) w alkalicznym roztworze modelowym w zależności od rodzaju i stężenia użytego koagulantu. Przeprowadzono miareczkowania konduktometryczne i pH-metryczne oraz testy koagulacyjne – „jar testy”. W próbach poddanych koagulacji mierzono zmiany: ChZT, barwy i potencjału przepływu. Wykazano, że charakterystyczne zmiany pH oraz przewodności elektrolitycznej roztworów podczas miareczkowania za pomocą soli Al i Fe(III) świadczą o stopniowym przebiegu procesu koagulacji kwasów huminowych. W zależności od rodzaju użytej soli – glinu lub żelaza(III) usuwanie kwasów huminowych jest wynikiem koagulacji zachodzącej wg różnych mechanizmów. Wytrącanie się osadu stwierdzono po dawce 3.2 mmol dm⁻³ przy pH < 6.4 w przypadku AlCl₃ oraz po dawce 3.0 mmol dm⁻³ i pH < 4.8 w przypadku FeCl₃. Po koagulacji za pomocą zarówno AlCl₃, jak i FeCl₃ stwierdzono ok. 97% efektywność usuwania ChZT oraz ok. 99% efektywność usuwania barwy. Zwiększenie wartości potencjału przepływu w zakresie dawek soli 2.4–3.6 mmol dm⁻³ jest prawdopodobnie wynikiem wiązania dodatnio naładowanych produktów hydrolizy soli przez grupy funkcyjne cząsteczek KH i neutralizacji ich ładunku.

3

Oddziaływanie kwasów huminowych z solami glinu

80%

Dziejowski J. , Libecki B. , Smoczyński L.

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tom Nr 11

203--205

4

The use of electrokinetic measurements in a study of pulp wastewater treatment with aluminum and iron (III) salts

80%

Dziejowski J. , Libecki B. , Smoczyński L.

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tom Vol. 7, nr 1

13-19

EN

Pulp wastewater poses a serious threat to the natural environment. It is characterized by strong coloration and a high content of organic contaminants, including compounds resistant to biochemical decomposition, often toxic to living organisms. Among a variety of physical and chemical methods of wastewater treatment, coagulation is distinguished by its simplicity and efficiency. The effectiveness of the process depends on the pH and the coagulant dose. The optimization of the process parameters can be done based on electrokinetic measurements, including: potential zeta and the streaming potential. This study examined the process of the coagulation of raw effluents from a sulfate pulp mill with aluminum and iron (III) chlorides. A standard jar test method was used. The color, turbidity, suspension and COD were determined in the samples. Tests with and without pH adjustment were conducted. Electrokinetic measurements were performed with a PCD 03 meter (Mütek Analytic Gmbh). It was found that coagulation effectiveness depended on the salts used. A correlation was also observed between the optimum pH for a determined coagulant dose and the reagent-adding sequence. Iron (III) chloride appeared more effective than aluminum chloride as regards the COD elimination. However, taking the lower optimal dose and a higher pH of coagulation into account, aluminum chloride seems to be a better coagulant for pulp wastewater treatment. The increase in the streaming potential recorded during the tests is correlated with the changes in the wastewater pH. The charge of colloids is dependent upon the pH, so different mechanisms of coagulation can be expected.