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Dyeing and finishing of textile yarns and fabrics are extremely important processes in terms of both quality and environmental concerns. Among the commercial textile dyes, particularly disperse dyestuffs are of environmental interest because of their widespread use, their potential for formation of toxic aromatic amines and their low removal rate during aerobic waste treatment as well as advanced chemical oxidation. Thus, in the present paper ferrous iron coagulation, ozonation and ferrous iron-catalyzed ozonation were employed at varying pH (3-13) and Fe(II)-ion doses (0.09-18mM) for the treatment of a simulated disperse dye-bath (average initial apparent color as absorbance at 566nm=815.4m(-1); COD(0)=3784mgl(-1); TOC(0)=670mgl(-1); BOD(5,0)=58mgl(-1)) that more closely resembled an actual dyehouse effluent than an aqueous disperse dye solution. Coagulation with 5000mgl(-1) FeSO4-7H2O (18mM Fe(2+)) at pH 11 removed up to 97% color and 54% COD, whereas oxidation via ozonation alone (applied ozone dose=2300mgl(-1)) was only effective at pH 3, resulting in 77% color and 11% COD removal. Fe(II)-ion-catalyzed ozonation (3.6mM Fe(2+) at pH 3; Fe(2+):O3 molar ratio 1:14) eliminated 95% color and 48% COD and appeared to be the most attractive option among the investigated chemical treatment methods as for its applicability at the natural acidic pH of the disperse dye-bath effluent and at relatively low Fe(2+)-ion doses as compared to ferrous sulfate coagulation. However, no TOC reduction was observable for ozonation and catalytic ozonation at the investigated reaction conditions (14gl(-1) O3 at pH 3). An average six-fold enhancement in the biodegradability parameter of the synthetic dye wastewater expressed in terms of the BOD(5)/COD ratio could be achieved by the investigated chemical treatment methods.
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PMID:Treatability of a simulated disperse dye-bath by ferrous iron coagulation, ozonation, and ferrous iron-catalyzed ozonation. 1148 26

Two commercial reactive dyes, the azo dye Reactive Black 5 and the copper phythalocyanine dye Reactive Blue 21, have been treated at a concentration of 75 mg l(-1) by titanium dioxide mediated photocatalytic (TiO2/UV), dark and UV-light assisted Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) processes in acidic medium. For the treatment of Reactive Black 5, all investigated advanced oxidation processes were quite effective in terms of colour, COD as well as TOC removal. Moreover, the relative growth inhibition of the azo dye towards the marine algae Dunaliella tertiolecta that was initially 70%, did not exhibit an increase during the studied advanced oxidation reactions and complete detoxification at the end of the treatment period could be achieved for all investigated treatment processes. However, for Reactive Blue 21, abatement in COD and UV-VIS absorbance values was mainly due to the adsorption of the dye on the photocatalyst surface and/or the coagulative effect of Fe3+/Fe2+ ions. Although only a limited fraction of the copper phythalocyanine dye underwent oxidative degradation, 47% of the total copper in the dye was already released after 1 h photocatalytic treatment.
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PMID:Homogenous and heterogenous advanced oxidation of two commercial reactive dyes. 1150 5

The photocatalytic degradation of three reactive azo dyes (yellow-2, orange-16 and red-2) and one anthraquinone reactive dye (blue-19) was studied. The reactions were carried out in a reactor with recirculation using TiO2 immobilised on glass Raschig rings (system A) and compared with a batch system using the catalyst in aqueous suspension (system B). Both reaction systems were irradiated with a 125 W, lambda > 254 nm lamp. The suspended TiO2 system was also studied using a 125 W 360 nm lamp (system C). Kinetic studies indicated a rapid colour removal, following the order B > A > C. The same trend was observed in COD and TOC removal profiles. The energy consumption per order of magnitude of catalytic degradation of the dyes was lower in the batch reactor (system B) than in the reactor with recirculation and immobilised TiO2 (system A).
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PMID:Reactive dyes decolouration by TiO2 photo-assisted catalysis. 1169 59

The photocatalytic oxidation of the non-biodegradable p-nitrotoluene-o-sulfonic acid (p-NTS) in homogeneous (photo-Fenton reactions) and heterogeneous (with TiO2) solutions has been studied at a pilot-scale under solar irradiation at the Plataforma Solar de Almeria (PSA). In this study two different reactors were tested: a medium concentrating radiation system (Heliomans, HM) and a non-concentrating radiation system (CPC). Their advantages and disadvantages for p-NTS degradation have been compared and discussed. The degradation rates obtained in the CPC collector are around three times more efficient than in the HM collectors. However, in both systems, 100% of the initial concentration of p-NTS was removed. Kinetic experiments were performed in both systems using TiO2 suspensions. During the photodegradation, the disappearance of p-NTS was followed by HPLC, the mineralization of the solution by the TOC technique, the evolution of NO3-, NO2-, and SO4(2-) concentration by ionic chromatography, the toxicity by the standard Microtox test, and the biodegradability by BOD5 and COD measurements. The obtained results demonstrated the utility of the heterogeneous catalysis (using TiO2 as catalyst) as a pretreatment method that can be followed by a biological process.
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PMID:Concentrating versus non-concentrating reactors for solar photocatalytic degradation of p-nitrotoluene-o-sulfonic acid. 1169 62

Nutrients and other pollutant runoffs from streams in artificial forest areas in central Hyogo Prefecture in southwest Japan have been investigated to estimate pollutant loads since 1995. The orthophosphate and ammonium nitrogen contents were usually low and constant during the investigation. When the flowrates of the streams were normal, the concentrations of suspended solids, COD(Mn), TOC and total phosphorus were very low, and did not change much. However, when stream flows were increased by rainstorms or other precipitation, higher concentrations of these parameters occurred. Otherwise, the average concentrations of nitrate nitrogen and total nitrogen were 0.26 mg/l and 0.31 mg/l, respectively, and they were often increased by precipitation events. They changed at the same time because the ratio of nitrate nitrogen per total nitrogen was high, about 80%. The fluctuation of concentrations of total phosphorus was similar to SS concentrations, which suggested that phosphorus was discharged in the types of suspended solids from forest areas. The specific loads of the nutrients and some other pollutants did not differ among the three watersheds investigated. However, the difference among them between fine days and rainy days was fairly large. It was presumed that pollutant runoff from forest areas is strongly dependent on precipitation events.
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PMID:Runoff characteristics of nutrients in the forest streams in Hyogo Prefecture, Japan. 1172 81

Electrochemical oxidation of resorcinol for wastewater treatment in the presence of chloride was investigated. Titanium Substrate Insoluble Anode (TSIA) coated with TiO2-RuO2-IrO2 was used as an anode and graphite carbon sheet was used as a cathode. The extent of resorcinol electrochemical oxidation was determined in terms of COD removal. The Box-Behnken second order composite design was used to study the effect of operating parameters such as initial pH, chloride concentration, initial concentration of resorcinol and charge input. The experimental values were in good correlation with predicted values, and the correlation coefficient was found to be good. The effect of current density on resorcinol oxidation, the AOX level during the electrochemical treatment and TOC removal were also studied for selected conditions. It has been observed that the extended electrolysis brings down the AOX concentration to lower levels. The maximum current efficiency was observed at higher resorcinol concentration, higher chloride concentration and increasing current density.
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PMID:Electrochemical oxidation of resorcinol for wastewater treatment using Ti/TiO2-RuO2-IrO2 electrode. 1175 10

The two-stage anaerobic wastewater pre-treatment was modelled and controlled. The biological state of the reactors could be predicted using a fuzzy logic system and based upon this, proper control actions were taken automatically in order to avoid an overload. The system was designed to handle very strong fluctuations in the concentration of the substrate and the volumetric loading rate. Hydrogen concentration together with methane concentration, gas production rate. pH and the filling level of the acidification buffer tank were used as input variables for the fuzzy logic system. The manipulated variables were the flow rate from the acidification buffer tank into the methane reactor, the temperature and pH of both reactors, the circulation rate of the fixed bed reactor, back flow from the methane reactor into the acidification, and the control of the feed into the acidification buffer tank. The developed control system was successfully tested on a fully automated lab scale two-stage anaerobic digester. Different types of wastewater from food processing industries were successfully applied. Even a restart of feeding with very high COD concentrations (100 gl(-1) after several days of stand by was handled successfully. Effluent concentrations could be kept low without using TOC, COD or equivalent measurements.
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PMID:State detection and control of overloads in the anaerobic wastewater treatment using fuzzy logic. 1176 96

This work deals with the treatment of offshore oilfield wastewater from the Campos Basin (Rio de Janeiro State, Brazil). After coarse filtration, this high saline wastewater was microfiltrated through mixed cellulose ester (MCE) membranes, resulting in average removals of COD, TOC, O&G and phenols of 35%, 25%, 92% and 35%, respectively. The permeate effluent was fed into a 1-L air-lift reactor containing polystyrene particles of 2mm diameter, used as support material. This reactor was operated for 210 days, at three hydraulic retention times (HRT): 48, 24 and 12h. Even when operated at the lowest HRT (12 h), removal efficiencies of 65% COD, 80% TOC, 65% phenols and 40% ammonium were attained. The final effluent presented COD and TOC values of 230 and 55 mg/L, respectively. Results obtained by gas chromatography analyses and toxicity tests with Artemia salina showed that a significant improvement in the effluent's quality was achieved after treatment by the combined (microfiltration/biological) process.
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PMID:Oilfield wastewater treatment by combined microfiltration and biological processes. 1176 43

This is the first of two papers each dealing with a specific technological option for replacing the Fenton's reagent with simpler processes for treating industrial wastewater. In particular, the paper reports the results of an investigation aimed to check, at lab scale, the effectiveness of a chemical process (i.e., alkalinisation with or without post-ozonation) for treating tannery wastewater whose residual COD, measured after conventional biological treatment, result still higher than the Italian COD Maximum Allowable Concentration (MAC) value (i.e., 160 mgO2/L). The results have demonstrated that when the value of residual COD lies in the range 200 divided by 250 mgO2/L, a simple alkalinisation with NaOH, up to pH 12.5, allows to reach the MAC value with an alkali consumption equivalent to the acid consumption required by the Fenton treatment and with a chemical sludge production significantly lower, i.e. approximately 0.7 kg(dry)/m3 instead of approximately 1.5 kg(dry)/m3. Conversely, when the value of the residual COD lies in a higher range (i.e. 300 divided by 350 mgO2/L), in order to reach the COD MAC value, alkalinisation (from pH 8 to pH 12.5) must be followed by an ozonation post-treatment. From the chemical stand point, the paper clearly demonstrates that analyzing only simple "gross parameters" (i.e., TSS, TOC, COD, BOD5 and EC20) it is possible to get useful information about the chemical properties of the organic pollutants occurring in tannery wastewater.
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PMID:Treatment options for tannery wastewater. I: Alkalinization with or without post-ozonation. 1177 Jan 58

Ozonation of 11 naphthalene sulfonic acids (NSA) in the aqueous solution was studied by bubbling at 31 degrees C at an ozone dose rate of 5.56 mg min(-1) l(-1). COD, TOC and BOD5 of these compounds were tested. It was found that COD and TOC can be removed effectively by ozonation as expected. More than 40% COD of compounds No. I (2-amino-1-NSA), No. 5 (1-hydroxy-7-amino-5-NSA), No. 6 (6-hydroxy-1-NSA), No. 8 (6-amino-1,4-naphthalene disulfonic acid) and No. 11 (I -hydroxy-6-amino-3-NSA) has been eliminated at an ozone dosage of 5.56 mg min(-1) l(-1) for 2 h. Although TOC removal was very different, a good biodegradability was reached for NSAs with an average ozone consumption of 3.0 mgl(-1) for a TOC0 concentration of 100 mg(-1). Ozonation and biotreatment should be good alternatives for these compounds, especially after 20% TOC reduction and TOC removal were more sensitive in predicting an increase in biodegradability during ozonation, than that of COD. NSAs are similar in their behavior with reference to ozone consumption. In order to obtain a good biodegradability of NSAs at a TOC0 concentration of 100 mgl(-1), an ozone consumption between 2.0 and 4.0 mg mg(-1) ACOD is needed for this setup and 3.0 mg O3 mg(-1) TOC0 requirement may be more practical in predicting the biological behavior of naphthalene compounds.
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PMID:Ozonation of naphthalene sulfonic acids in aqueous solutions. Part I: elimination of COD, TOC and increase of their biodegradability. 1190 78


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