I.C. Gonçalves

Batch tests for assessing decolourisation of azo dyes by methanogenic and mixed cultures.

Most of the published studies on azo dye colour removal involve anaerobic mixed cultures and there is some interest in the knowledge of how dye reduction occurs, if by facultative, strictly anaerobic or both bacterial trophic groups present in classic anaerobic digestors. This paper describes the behaviour of methanogenic and mixed bacteria cultures on the colour removal in batch systems, of a commercial azo dye, C.I. Acid Orange 7, used in paper and textile industries. The aim of this study is to demonstrate, by analysing dye decolourisation, that it occurs with mixed cultures as well as with strictly anaerobic (methanogenic) cultures. Tests were performed with a range of dye concentrations between 60 and 300 mg x l(-1). The influence of dye concentration on the carbon source removal and decolourisation processes was studied. The effect of carbon source concentration on colour removal was also analysed for both cultures. The degradation rates in mixed and methanogenic cultures were compared. The consumption of carbon source was monitored by COD analysis and dye degradation by ultraviolet-visible spectrophotometry and thin layer chromatography.

Evaluation of an integrated anaerobic/aerobic SBR system for the treatment of wool dyeing effluents

This work examined the performance of a sequencing batch reactor treating dyeing effluents from a factory that processes mainly wool and wool/polyester blends. Different operational conditions were evaluated, namely the influence of the anaerobic and the subsequent aerobic phase on the organic load removal, as well as the effect of the length of the aeration period (from 8 to 12 h) on process efficiency. A comparison between a fill stage in fast and slow modes was carried out. Results indicate that the cycle 2 conditions (fast fill and 12 h aeration time) improved the overall efficiency (85 ± 6% soluble COD and 95 ± 4% BOD5 removal yields) with a predominant COD uptake occurring in the aerobic stage. Slow, linear COD removal was observed in the anaerobic phase, in contrast with an exponential COD decrease in the oxic phase. For SS a level under 100 mg/l was general achieved in the exit of the reactor. With respect to dye degradation, a noticeable decrease of the absorbance measured in the UV–visible range was observed. This could be explained by the reduction of the azo bonds of some of the present dyes in the anaerobic step, in which ORP values lower than −400 mV were attained. Some oxidation of anthraquinone sulphonate dyes and of the aromatic amines resulting from azo bond cleavage could also have been taken place, as well as bioelimination mechanisms such as dye sorption.

A Risk Assessment Model for Water Resources: Releases of dangerous and hazardous substances

Many dangerous and hazardous substances are used, transported and handled daily in diverse situations, from domestic use to industrial processing, and during those operations, spills or other anomalous situations may occur that can lead to contaminant releases followed by contamination of surface water or groundwater through direct or indirect pathways. When dealing with this problem, rapid, technically sound decisions are desirable, and the use of complex methods may not be able to deliver information quickly. This work describes a simple conceptual model established on multi-criteria based analysis involving a strategic appraisal for contamination risk assessment to support local authorities on rapid technical decisions. The model involves a screening for environmental risk sources, focussing on persistent, bioaccumulative and toxic (PBT) substances that may be discharged into water resources. It is a simple tool that can be used to follow-up actual accident scenarios in real time and to support daily activities, such as site-inspections.

Anaerobic decolorization of an azo dye by a mixed culture

Abstract Wool dyeing wastewater contains xenobiotic compounds that can be removed by biotechnological processes. Studies on various dyes showed that anaerobic processes are suitable to alter azo dyes as a first step of the biodegradation process. These compounds are reduced by anaerobic consortia to aromatic amines and its ultimate degradation can be achieved by a further aerobic treatment. Studies on degradation rate of an wool acid dye were performed in batch systems inoculated with anaerobic biomass. A commercial diazo dye, Acid Red 73, was added to the synthetic medium in which glucose was used as sole carbon source. Results indicated that the Acid Red 73 was partially degraded by a mixed culture of anaerobic bacteria and a decolorization of 90% was obtained. Kinetics studies on removal of the colour showed that the decolorization rate was several times faster than the degradation rate of glucose for a range of dye concentrations between 60 mg/L and 400 mg/L. A first order kinetic model was used for dye concentrations up to 200 mg/L. For higher concentrations a model similar to the Michaelis‐Menten equation was better fitted to the experimental data.

Behaviour of different anaerobic populations on the biodegradation of textile chemicals

The anaerobic biodegradation of textile chemicals was evaluated with inocula grown under mesophilic (37+/-2 degrees C) or thermophilic (55+/-2 degrees C) conditions, on glucose (glucose-grown) or acetate (acetate-grown) as sole carbon sources. Wool dyebath chemicals (acetic acid, a liposomal surfactant, a synthetic amphoteric surfactant), single or as binary acetate-surfactant mixtures, were used as test carbon sources, in the presence or absence of Acid Orange 7 as model dye. First, the two mesophilic inocula (glucose- or acetate-grown) were compared relatively to lag-phase durations, specific biogas production rates, biogas yields and overall COD removal yields. In some runs, sulphide and/or the model dye were included, to test for inhibition effects. Then, the two glucose-grown inocula (mesophilic and thermophilic) were assessed in batch biodegradation tests with the same carbon feeds. The kinetics for substrate-COD and dye colour removal were described and quantified using a pseudo-first order model. The presence of dye had no effect on performance parameters for all substrates tested. Acetoclastic methanogens seemingly played an important role in biogas production from the liposomal additive, but less so from the synthetic surfactant. The association of acetate and surfactants apparently introduced mutual inhibitory effects on the rates of biogas production, substrate uptake and dye decolourisation.