الفهرس 
Chemistry of chromium and its compoundsOnly 14 pages are availabe for public view
 |  | from | 172 |  |  |
| | | from | 172 | | |
Abstract
In Egypt, Leather tanning industry is one of the promising industries. This sector contributes more than 300 tanneries, producing about 3.5-4.3 million cubic meters per year of wastewater. In Egypt, tannery wastewater contains organic pollutants in addition to a large amount of chromium above the permissible limits for safe discharge. The chromium is one of the most toxic metals to plants, animals and microorganisms. So, treatment of the tannery wastewater using advanced techniques to remove the harmful organics and chromium is studied in this Thesis. Here below, the main contents of the thesis and the main findings are summarized:
• A literature review covering the previous works for removal of chromium from wastewater specially tannery effluents is given in details. The different advanced oxidation processes for organics reduction are also covered. Hazardous effect of chromium as a heavy metal is refered.
• The experimental part includes the following:
Characterization of tannery effluent using inductive couple plasma (ICP), chemical oxygen demand (COD), biological oxygen demand (BOD), Surfactants and total nitrogen (TN) measurements.
Pretreatment of tannery effluent for organics removal with oxidation processes using hydrogen peroxide then it is catalyzed with ferrous sulfate as a catalyst on the bench scale experiments.
Pretreatment of tannery effluent for organics removal with advanced oxidation process (H2O2/UV) then it is catalyzed with ferrous sulfate (photo-Fenton) as a photo-catalyst in the classic photo-reactor.
A post-treatment for pretreated tannery wastewater using chemical precipitation of chromium by NaOH and MgO as precipitating agents.
Calcination of the sludge formed from the chemical precipitation stage by NaOH and MgO at different temperatures to obtain magnesium chromite.
Characterization of the end products using x-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), fourier transform infra red (FT-IR), transmission electron microscope (TEM) and thermal analyses.
• The achieved results from these experiments are summarized in the following points:
1- The tannery wastewater contains high content from magnesium (1416 ppm), chromium (560 ppm), traces of iron (1.08 ppm), chemical oxygen demand (554.5 ppm) and total nitrogen (54 ppm).
2- The obtained chemical oxygen demand removal under advanced oxidation processes indicated that the efficiency for degradation of organic pollutants present in tannery wastewater was (82.6%) in the case of fenton at the following optimum conditions: Fe2+ concentration (0.8 g/L), H2O2 concentration (35 g/L) and time 2h.
3- The obtained chemical oxygen demand removal under advanced oxidation processes (AOPs) indicated that the efficiency for degradation of organic pollutants present in tannery wastewater was (85%) in the case of H2O2/UV oxidation’s process at optimum conditions of H2O2 concentration (20 g/L) and time 2h under UV irradiation and tannery effluent alone gives (10%) as poor COD removal under UV irradiation.
4- The obtained COD removal under these AOPs indicated that the efficiency for degradation of organic pollutants present in tannery wastewater was (90.1%) in the case of photo-fenton at the optimum conditions: Fe+2 concentration (0.5 g/L), H2O2 concentration (30 g/L) and time 2h.
5- The optimum pH for precipitation agent of chromium using NaOH and MgO was ranged from 8.0 to 8.5 to give total chromium removal of 99.1 and 99.7% respectively.
6- The substitution of NaOH with MgO resulted in less sludge and shorter settling time (3h). MgO also enhanced the purity of the sludge and the total chromium removal.
7- The physicochemical characterization of the calcined sludge formed from chemical precipitation by NaOH and MgO shows the formation of cubic nano magnesium chromite at temperature of 550-650 °C with crystal size less than 27 nm.
• Finally, this work seems an excellent solution for removal of chromium as a heavy metal and degradation of organic pollutants from industrial tannery wastewater. However, this hybrid method should be up-scaled and demonstrated in continuous pilot plant unit followed by calculation the material and mass balances as well as calculation cost benfit analysis and as feasibility study.
• On the other hand, synthesis of nano magnesium chromite from precipitated sludge is a good solution for chromium reuse since nano magnesium chromite can be used as catalytic support in many reactions, thus it will be valuable refractory material for many applications.