Emilia Otal

Integrated wet air oxidation and biological treatment of polyethylene glycol-containing wastewaters

The treatment of a model wastewater containing polyethylene glycol (PEG) of molecular weight 10000 in an integrated wet air oxidation–aerobic oxidation process was investigated. Partial wet air oxidation under mild operating conditions was capable of converting the original polymer to lower molecular weight compounds, such as oligomers and short-chain organic acids. The effect of molecular weight on the aerobic biodegradability of polyethylene glycol was assessed by performing shake flasks experiments with various polyethylene glycols in a molecular weight range from 200–35000 and it was found that biodegradability generally decreased with increasing molecular weight. Aqueous solutions of PEG 10000 were subjected to continuous wet air oxidation at a temperature of 423 K and a residence time of 30 min and the oxidised effluents were then subjected to subsequent continuous aerobic oxidation at residence times varying between 0·5 and 4 days. Simultaneously, continuous aerobic oxidation experiments on solutions of PEG 10000 were performed and used to compare the efficiency of the integrated treatment process with that of the direct biological treatment. Partial pretreatment by wet air oxidation under mild operating conditions resulted in effluents whose biodegradation rates were significantly higher than those of the original, unoxidised wastewater, as assessed by total organic carbon (TOC) removal rates. The original wastewater was practically non-biodegradable at a 0·5-day residence time with direct biological treatment, while an 80% TOC removal was achieved when biological treatment was coupled with a preceding wet air oxidation step. Conversely, with a 4-day residence time for the direct biological treatment the original wastewater was only partially degradable with 60–70% TOC removal recorded; with the integrated treatment process at a 4-day residence time in the bioreactor the overall TOC removal was greater than 90%.

Ammonium Ion Adsorption and Settleability Improvement Achieved in a Synthetic Zeolite-Amended Activated Sludge

Abstract Municipal wastewater treatment plants typically exhibit two classic problems: high ammonium concentration in water after conventional biological treatment and, in some cases, poor activated sludge sediment ability. Potential solutions to these problems were investigated by adding a synthetic zeolite obtained from coal fly ash to different steps of activated sludge treatment. The experimental results for ammonium removal fit well with the theoretical adsorption isotherms of the Freundlich model with a maximum adsorption capacity of 13.72 mg·g −1 . Utilization of this kind of zeolite to improve activated sludge sediment ability is studied for the first time in this work. It is found that the addition of the zeolite (1 g·L −1 ) to an activated sludge with settling problems significantly enhances its sediment ability and compact ability. This is confirmed by the sludge volume index (SVI), which was reduced from 163 ml·g −1 to 70 ml·g −1 , the V 60 value, which was reduced from 894 ml·L −1 to 427 ml·L −1 , and the zeta potential (ζ), which was reduced from −19.81 mV to −14.29 mV. The results indicate that the addition of this synthetic zeolite to activated sludge, as an additional waste management practice, has a positive impact on both ammonium removal and sludge settleability.

Solar photocatalytic treatment of landfill leachate using a solid mineral by-product as a catalyst

The treatment of municipal solid waste landfill leachate in a pilot plant made up of solar compound parabolic collectors, using a solid industrial titanium by-product (WTiO(2)) containing TiO(2) and Fe(III) as a photocatalyst, was investigated. In the study evidence was found showing that the degradation performed with WTiO(2) was mainly due to the Fe provided by this by-product, instead of TiO(2). However, although TiO(2) had very little effect by itself, a synergistic effect was observed between Fe and TiO(2). The application of WTiO(2), which produced coupled photo-Fenton and heterogeneous catalysis reactions, achieved a surprisingly high depuration level (86% of COD removal), higher than that reached by photo-Fenton using commercial FeSO(4) (43%) in the same conditions. After the oxidation process the biodegradability and toxicity of the landfill leachate were studied. The results showed that the leachate biodegradability was substantially increased, at least in the first stages of the process, and again that WTiO(2) was more efficient than FeSO(4) in terms of increasing biodegradability.

Anaerobic Treatment of Polyethylene Glycol of Different Molecular Weights

Biodegradation of high molecular weight polyethylene glycol has been found difficult under aerobic conditions. The use of a chemical treatment prior to the aerobic one was necessary to remove high molecular weight of polyethylene glycol. Anaerobic treatment of polyethylene glycol may present an alternative to integrated chemical and biological treatment for the elimination of this compound. Anaerobic biodegradation of polyethylene glycol from 200 to 10000 molecular weight was studied. It showed that, unlike aerobic treatment, the size of the molecule up to 10000 does not affect the process efficiency. The critical retention time and the optimum retention time were estimated and ranged from 10 to 14 and from 16 to 19 days, respectively. Under these operational conditions percentage of removal ranged from 85 to 90%. Thus, anaerobic degradation of polyethylene glycol presents removal percentages and hydraulic retention times similar to those of biodegradable compounds tested at the same operational conditions.

Application Of Synthetic Zeolites To The Depuration Of A Waste Landfill Leachate

In this paper the application of synthetic zeolites to the decontamination of a highly contaminated municipal waste landfill leachate has been studied. Thus, the reduction of organic matter (COD), total KjeMhal nitrogen (TKN), suspended solids and metals contents in the diluted leachate were measured after two different treatments. One of them consisted in a two-stage process: a physiochemical coagulation-flocculation treatment combined with the zeolite treatment. Two synthetic zeolites have been tested: a commercial zeolite and one obtained after a coal fly ash alkaline hydrothermal process (CV-Z). The results showed that the physico-chemical treatment using aluminium sulphate and an organic flocculent yielded an important reduction in the leachate COD, not improved by the zeolite treatment, Nevertheless, zeolites, especially CV-Z, clearly produced a strong reduction in the leachate nitrogen content. In addition, although the leachate metal concentrations are not very high, the zeolite addition also improved the metal removal. In the light of the low metal content in the leachate, a new treatment in one stage was used in a second phase. This treatment achieved an important improvement in the COD reduction, though the TKN nitrogen removal was somewhat worse than in the two stage process.

Valorisation of a by-product from the TiO2 pigment industry for its application in advanced oxidation processes

AbstractThe aim of this study was to find a recycling use for waste material (WTiO2) that results from the extraction process of TiO2 from ilmenite in the pigment industry. In view of its high TiO2 content, the photocatalytic activity of this material was tested in the degradation of humic and fulvic acid substances (HFAs) and showed low levels of photoactivity, as was the case for the commercial photocatalyst Aeroxide TiO2 P25 (P25). However, due to its high Fe3+ content, an important application was observed for WTiO2 as an HFA coagulant and catalyst in Fenton and photo-Fenton processes. A two-stage process of coagulation and photo-Fenton treatment was subsequently designed and conducted at laboratory and small pilot scale. High percentages (above 95%) were obtained in total organic carbon (TOC) removal.