Anja Kornmüller

Anion exchange resins for removal of reactive dyes from textile wastewaters

Sorption onto an easily regenerable sorbent in fixed bed filters would be an interesting option for removal of reactive dyes from textile wastewaters. A previous screening with model solutions (Dyes Pigm 51 (2001) 111) had shown two anion exchangers (strong basic S6328a and weak basic MP62, both Bayer) to exhibit good sorption characteristics for reactive dyes. The aim of this study was to evaluate these materials more closely. Thus filter breakthrough, the behavior with original wastewater samples, and the effect of inorganic wastewater parameters as well as regeneration were studied. Breakthrough curves for both materials are relatively unfavorable with a flat gradient, but throughput until breakthrough (100-800 bed volumes) should be sufficient for technical use. With both resins dye uptake is influenced little by competition of inorganic anions (sulfate, carbonate, phosphate) and they perform well in original wastewaters. However, the weak basic type is only efficient up to pH 8. Alkaline regeneration works well for MP62, for S6328a acid regeneration works for most dyes.

Screening of commercial sorbents for the removal of reactive dyes

Sorption filters could be a relatively simple treatment step to remove reactive dyes from textile wastewater. Activated carbon is already used in some treatment plants (loadings approx. 100 mg g−1), and many non-regenerable products have been tested. This study aimed at identifying suitable sorbents for on-site regeneration. Zeolites, polymeric resins, ion exchangers and granulated ferric hydroxide (GEH) were tested with different reactive dyes (M 600–1500 g mol−1). Zeolites and microporous resins were not suitable due to extremely low sorption capacities. The macroporous resins without functional groups showed moderate maximum loadings (100–400 μmol g−1 or 100–400 mg g−1) but low affinity and were not suitable for large dyes (>1000 g mol−1). loadings on anion exchangers were high but regeneration was difficult for the strong basic type (S6328a, Bayer). The weak basic type (MP62, Bayer) showed the most favorable profile: max. loadings of 200–1200 μmol g−1 (230–900 mg g−1) and complete regeneration using alkaline methanol (10% water). With GEH moderate loadings of about 150 μmol g−1 were achieved. Catalytic oxidative regeneration of GEH is possible using H2O2.

Cucurbituril for water treatment. Part I: Solubility of cucurbituril and sorption of reactive dyes.

Cucurbituril was investigated regarding its potential as a sorbent for the removal of reactive dyes from model solutions and authentic wastewaters. The solubility of cucurbituril is low in pure water but increases in the presence of salts. When dyes sorbing onto cucurbituril are present, solubility is drastically decreased compared to dye-free media. Sorption efficiency depends on salt concentration and salt species. Moderate salt concentrations favor sorption, high concentrations lead to cucurbituril dissolution. Divalent ions have a stronger effect than monovalent ions and larger ions more than smaller ones. In tests with authentic wastewaters cucurbituril was partially (20-100%) dissolved and contaminant removal was inefficient. Because of its solubility, cucurbituril is not feasible as a sorbent in wastewater treatment unless it could be covalently fixed onto a suitable support material.

Ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions: mass transfer and reaction kinetics

The ozonation of highly condensed polycyclic aromatic hydrocarbons (PAH) was studied in oil/water-emulsions, which are comparable to poorly water-soluble PAH in industrial wastewaters and at contaminated sites. As there was a lack of knowledge about the ozonation in oil/water-emulsions, first the ozone mass transfer was studied and optimized from the gas to the water phase and from the water to the oil phase. The ratio of mass transfer and oxidation reaction was determined by the Hatta-number and revealed a slow, quasi homogeneous reaction of ozone with PAH inside the oil droplets. Because the ozone gas concentration had no influence under the optimized conditions, the selective PAH-ozonation could be described microkinetically by a direct ozone reaction of pseudo-first order regarding PAH-concentrations. The determined PAH mean reaction rate constants of 1.02 min(-1) in oil/water-emulsions are in the upper range as found for PAH dissolved in water. These results give a new insight into the ozonation in the three-phase systems and into the treatment of highly condensed, hardly biodegradable PAH.

Selective ozonation of polycyclic aromatic hydrocarbons in oil/water-emulsions

The ozonation of three to five ring condensed polycyclic aromatic hydrocarbons (PAH) was studied in synthetic oil/water-emulsions by batch experiments. PAH can be oxidized selectively in the presence of high concentrations of dodecane as an aliphatic solvent. No oxidation of dodecane, as a representative of mineral oil, could be observed during all experiments - even at pH around 11. At acid to neutral pH high oxidation rates of the PAH were achieved due to a direct reaction with ozone. In the investigated range of 20 to 40°C no influence of temperature on the ozonation of benzo(k)fluoranthene could be found. During competitive ozonation of five PAH, the reactions are completed in the sequence of acenaphthene, pyrene and finally benzo(e)pyrene, benzo(k)fluoranthene and phenanthrene almost at the same time.

Cucurbituril for water treatment. Part II: Ozonation and oxidative regeneration of cucurbituril.

In Part I it was shown, that cucurbituril has high sorption capacities for the removal of reactive dyes from textile wastewater; despite the partial dissolution of this sorbent. Ozonation has been suggested as a regeneration step for loaded cucurbituril. Ozonation of loaded and pure cucurbituril was therefore evaluated. Dissolved cucurbituril reacts with ozone forming oxidation products like nitrite, nitrate, formate, acetate and oxalate. Oxidation is enhanced at alkaline pH. Dye-loaded cucurbituril suspended in water can be decolorized by ozone, but the ozone consumption is tip to seven times higher than for ozonation of the dissolved dyes without cucurbituril. Loaded columns can be regenerated by ozone gas, but dissolution of cucurbituril results in a higher DOC content than the initial one to be removed. Therefore oxidative regeneration does not seem to be a feasible approach in this case.

Effects of Alkali and Alkaline-earth Cations on the Removal of Reactive Dyes with Cucurbituril

The sorption of reactive (textile) dyes onto cucurbituril, a cyclic polymer with hydrophobic cavity, was studied. Dye sorption is strongly enhanced by Ca 2+ or Sr 2+ concentrations up to 100 mmol/L for all studied dyes. Mg 2+ and alkaline ions had similar effects for only one dye (Reactive Red 120), and only at higher concentrations. Concentrations above 100 mmol/L- depending on cation and dye - dissolve cucurbituril and prevent dye removal. As shown in previous studies by our group loadings obtained under suitable conditions (calcium concentration between 2 and 100 mmol/L, total salt concentration not exceeding 100 mmol/L) are 1 to 1.7 mol/mol or 0.9 to 1.8 g/g. The chemical mechanism responsible for the ionic influences is still under investigation. Generally, cucurbituril is a potent sorbent for reactive dyes. However, the technical application is still limited by the lack of a support material that would allow use in fixed bed filters.

Isolation and analysis of intact polyphosphate chains from activated sludges associated with biological phosphate removal

Abstract A method is described for the isolation of various phosphate species from biological cells of different origin, such as pure and mixed cultures and sludge from wastewater treatment plants with enhanced biological phosphate removal. Extraction and fractionation of phosphates is performed without enzymatic degradation or hydrolysation of inorganic polyphosphates (polyP). Analysis of the polyphosphate was carried out by HPLC with post-column derivatization, by which the P-species could be determined separately. Two different types of phosphate chains could be distinguished: short chain polyphosphates in the range of P2 to P30 and long chain polyphosphates from P30 to above P75. Due to a lack of suitable standards above P75 the upper limit of polyphosphate polymers could not be determined. The distribution of low and high molecular weight polyP depends on the biocenosis of the sludges. Furthermore, it is demonstrated that a mass balance of those phosphate species which take part in the various processes of a biological phosphate removal is possible.

Ozonation of exhausted reactive dye-bath analogues: The use of atrazine as an OH○ probe compound

Abstract Ozonation and O3/H2O2 treatment of a spent reactive dye–bath analogue containing aminofluorotriazine type reactive dyestuffs were examined in semi–batch experiments at different pH (2, 7 and 12), bicarbonate (0.18 M at pH7) and carbonate (0.19 M at pHl2) alkalinity. Atrazine (23.2 µM) was added as an OH* – sensitive probe compound to the reactive dye–bath analogue to evaluate the individual contributions of both direct molecular (O3) and indirect radical (OH*) type reaction pathways for the treatment of spent dye–bath ingredients. From the obtained results it was evident that particularly de–aromatization (expressed in terms of UV254 and UV270 removal) kinetics were significantly retarded in the presence of HCO3, CO3 2‐ and particularly H2O2. O3 decomposition and consumption increased appreciably when H2O2 (0.125 mM at pH7) was added as compared in the presence of carbonate/bicarbonate alkalinity when H2O2 was added indicating that H2O2 and alkalinity could act as radical chain reaction promoters (carriers) and inhibitors, respectively. Atrazine degradation and UV270 abatement rates paralleled each other revealing that particularly de–aromatization of the spent dye–bath constituents mainly involves the action of OH*. Nitrate formation was distinctly higher at pH7 than at pH 12 as a consequence of the stronger OH* scavenging effect of carbonate alkalinity at pH12.