Chromium species behaviour in the activated sludge process (original) (raw)
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Investigation of Cr(VI) reduction in continuous-flow activated sludge systems
Chemosphere, 2004
The aim of this research was to investigate hexavalent chromium, Cr(VI), reduction by activated sludge and to evaluate the use of continuous-flow activated sludge systems for the treatment of Cr(VI)-containing wastewater. Three series of experiments were conducted using two parallel lab-scale activated sludge systems. During the first experiment, one system was used as a control, while the other received Cr(VI) concentrations equal to 0.5, 1, 3 and 5 mg l À1 . For all concentrations added, approximately 40% of the added Cr(VI) was removed during the activated sludge process. Determination of chromium species in the dissolved and particulate phase revealed that the removed Cr(VI) was sorbed by the activated sludge flocs mainly as trivalent chromium, Cr(III), while the residual chromium in the dissolved phase was mainly detected as Cr(VI). Activated sludge ability to reduce Cr(VI) was independent of the acclimatization of biomass to Cr(VI) and it was not affected by the toxic effect of Cr(VI) on autotrophic and heterotrophic microorganisms. During the second experiment, both systems were operated under two different hydraulic residence time (h equal to 20 and 28 h) and three different initial organic substrate concentration (COD equal to 300, 150 and 0 mg l À1 ). Cr(VI) reduction was favored by an increase of h, while it was limited by influent COD concentration. Finally, at the last experiment the effect of anoxic and anaerobic reactors on Cr(VI) reduction was investigated. It was observed that the use of an anoxic zone or an anaerobic-anoxic zone ahead of the aerobic reactor favored Cr(VI) reduction, increasing mean percentage Cr(VI) reduction to almost 80%.
BACTERIAL Cr (VI) REDUCTION AND ITS IMPACT IN BIOREMEDIATION
Jurnal Ilmu Lingkungan
ABSTRACTChromium is hazardous pollutant for ecosystem caused chromium especially inhexavalent form is very toxic, has high solubility and mobility, teratogenicity, mutagenicity andcarcinogenicity to living system related with its oxiding power. Remediation of soilcontaminated of heavy metals was important caused soil as medium for food producing.Conventional methods for heavy metals remediation consist of physical and chemical processbut these applications were costly and less effective. One of the remediation technologies is theusing living organisms such as microorganisms, because they have ability to reduce Cr(VI) intonon toxic form, Cr(III). The aims of this research were to evaluate the reduction activity ofrhizobacterial isolate and to identify the isolate which take a role in reducing chromiumabsorption by plant. The results showed that Isolate 39 was able to grow on LB mediumcontaining 200 ppm Cr(VI). Isolate 39 reduced Cr(VI) up to 15 ppm concentration level inminimal mediu...
Egyptian Journal of Chemistry, 2018
T HIS study aimed to emphasize the effect of hexavalent chromium Cr (VI) on the performance of a pilot scale hybrid up-flow anaerobic sludge blanket (H-UASB). The system was packed with non-woven polyester fabric (NWPF) and continuously fed with real municipal wastewater at a hydraulic retention time (HRT) 7.5 h and average organic loading rate (OLR) 1.24 Kg COD m 3 /d. The system achieved satisfactory removal rates for total suspended solids (TSS) (86.44 %), chemical oxygen demand (COD) (74.18 %) and biological oxygen demand (BOD 5) (84.8%) without the addition of Cr (VI). Results indicated that feeding the reactor with different concentrations of chromium ions ranged from 0.1-1.3 mg/l (i.e: 600 mg / m 3. d to 6000 mg / m 3. d) decreased the residual concentration of Cr (VI) in the final effluent to 0.019 mg/l, while the accumulation of chromium ion increased in the biobed (160 mg/kg) and in excess sludge (165.44 mg/kg). This was due to the biological reduction of Cr (VI) to Cr (III) by the action of sulphate and chromate reducing bacteria. Increasing the concentration of Cr (VI) up to 6000 mg / m 3. d reduce the biochemical reactions of the anaerobic microorganisms and consequently decrease the removal efficiency of TSS from 86.44% to 62.06, COD from 74.2 % to 57.07 % and BOD 5 from 84.8% to 61.92%.
2017
Background: Nowadays, different methods are applied for the removal of heavy metals from the aqueous resources that the adsorption process is one of them. The chromium VI is one of the most prevalent contaminants which create serious difficulties; so, it should be removed from the contaminated waters by an effective method before being leaved into the environment. The present research investigated the use of dried powder of activated sludge of Kavirtire wastewater treatment plant as bio sorbent for removal of chromium (VI). Methods: In the present experimental study, the effects of pH, adsorbent dose, primary concentration of metal and contact time on the removal of chromium (VI) from the aqueous solutions were studied. Then, the equations of isotherm and adsorption kinetic were specified based on the optimal conditions. The absorbent features were analyzed by SEM and EDX techniques. Results: The maximum efficiency of the removal of chromium (VI) at pH 2, optimal dose of 5 g/L, cont...
Journal of Hazardous Materials, 2010
The objectives of the present work were: (i) to analyze the capacity of activated sludge to reduce hexavalent chromium using different carbon sources as electron donors in batch reactors, (ii) to determine the relationship between biomass growth and the amount of Cr(VI) reduced considering the effect of the nitrogen to carbon source ratio, and (iii) to determine the effect of the Cr(VI) acclimation stage on the performance of the biological chromium reduction assessing the stability of the Cr(VI) reduction capacity of the activated sludge. The highest specific Cr(VI) removal rate (q Cr) was attained with cheese whey or lactose as electron donors decreasing in the following order: cheese whey ≈ lactose > glucose > citrate > acetate. Batch assays with different nitrogen to carbon source ratio demonstrated that biological Cr(VI) reduction is associated to the cell multiplication phase; as a result, maximum Cr(VI) removal rates occur when there is no substrate limitation. The biomass can be acclimated to the presence of Cr(VI) and generate new cells that maintain the ability to reduce chromate. Therefore, the activated sludge process could be applied to a continuous Cr(VI) removal process.
MODELING Cr(VI) REMOVAL BY A COMBINED CARBON ACTIVATED SLUDGE SYSTEM
2000
The chromium compounds are usually released by effluent discharge from steelworks, chromium electroplating, leather tanning and chemical manufacturing. Chromium is usually encountered in the environment as Cr(III) and Cr(VI). Each of the above oxidation states has very different biological and chemical properties; Cr(VI) is soluble and toxic, while Cr(III) is more stable and presents lower toxicity. The most commonly used
Removal of Cr (VI) by electrochemical reduction
Separation and Purification Technology, 2008
Removal of Cr (VI) from aqueous solutions by electrochemical reduction was studied using steel rods connected in unipolar mode. An aqueous solution of potassium dichromate was used as the model contaminant. Three different supporting electrolytes, viz. NaCl, NaNO 3 and Na 2 SO 4 were used during electrolysis. Only NaCl was found to be effective to arrest the passivation of electrodes by Cr (VI). The effect of initial concentration of Cr (VI) and current density on chromium removal was investigated. The rate of conversion of Cr (VI) to chromite is fast at higher current densities and the sludge is contaminated with more iron oxide. X-ray diffraction studies have revealed the formation of chromite (FeCr 2 O 4 ) as main product in the electrochemically precipitated sludge. Though chromite is a predominant species other products such as Cr 2 O 3 , Fe 2 O 3 are also formed during the process. At low current densities the electrochemical reduction of Cr (VI) was found to be initially under current control and turns to diffusion control after certain time.
Environmental factors and modeling in microbial chromium (VI) reduction
Water Environment Research, 1996
A Cr(VI)-reducing culture was enriched from an anaerobic chemos tat fed with synthetic media containing acetate and Cr(VI). The enriched culture was used for a series of batch tests to investigate several environmental factors affecting microbial Cr(VI) reduction. Under carbon-limiting conditions, the extent of Cr(VI) reduction proportionally depended on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon the initial biomass level and the type of organic compounds. The developed model predicted Cr(VI) reduction well at different Cr(VJ) concentrations. Sulfate at 120 mg SO/-IL or nitrate at 150 mg NIL slightly inhibited Cr(VI) reduction. Reduction of nitrate but not sulfate was observed along with Cr(VI) reduction. Cr(VJ) was not reduced by the aerobically growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature for Cr(VI) reduction were found to be 7.3 and 32°C, respectively. In addition, Cr(VJ) reduction was sensitive to the metal ions that may coexist with Cr(VI) in industrial wastes containing Cr(VI).
Oriental Journal of Chemistry, 2018
Present study explore the possibility of reducing toxic Cr(VI) to Cr(III) without adding acid externally to the level of regulatory norms. Trial experiments were carried out with standard solution having Cr(VI) concentration of 1976 mg/L to reveal the suitability of SnCl 2 for the reduction of Cr(VI) in the absence of mineral acid. Under the same conditions contaminated ground water from COPR dump site was examined. Complete reduction of Cr(VI) and level of total Cr to discharge limit were observed within fifteen min. for both simulated and contaminated water. This green chemistry approach and lower time duration for reduction is not reported earlier. The efficacy of the process is ascertained by analysing the other important heavy metals like Ni, Cu, Pb and Zn using AASP. Level of chloride, sulphate, BOD, TDS and pH of the treated water were also recorded. Results imply that SnCl2 effectively reduces Cr(VI) to Cr(III) in the absence of acid.
Effects of combining biological treatment and activated carbon on hexavalent chromium reduction
Bioresource Technology, 2011
The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (l obs), biomass yield (Y X/S), and specific growth substrate consumption rate (q S) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (l obs , Y X/S , q S). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.