FESO4.7H2O 98%MIN.

Description

Ferrous Sulfate is a kind of greenish-blue crystalline powder with a chemical formula of FeSO4 · 7H2O_. It is odorless and easily soluble in water but insoluble in ethanol. It will be weathered in dry air and easily oxidized to brown basic iron sulfate in moist air.

Ferrous sulfate is the sulfate salt of the divalent cation form of iron. It is an essential body mineral, that is commonly used in the treatment of iron deficiency anemia. Ferrous Sulfate is used as a nutritional supplement (iron fortifier), and fruit and vegetable coloring agent.

The coagulation/flocculation treatment using FeSO4 x 7H2O as a coagulant is evaluated in this work for the removal of organic compounds and colour from synthetic effluents simulating the cotton, acrylic and polyester dyeing wastewaters. The coagulant dose, temperature, pH, stirring speed and stirring time that maximized the removal of dissolved organic carbon (DOC) and colour for each effluent are determined for the coagulation process. The effect of the stirring speed, stirring time and the dose of flocculant (Polymer A ) on the flocculation stage is also evaluated for effluents pretreated by coagulation at the optimal conditions previously determined. The obtained results showed that the optimal operating conditions are different for each effluent, and the process (coagulation/flocculation) as a whole was efficient in terms of colour removal (-91% for cotton, -94% for acrylic effluents; polyester effluent is practically colourless). However, the DOC removal observed is not significant (33% for polyester, -45% for cotton and -28% for acrylic effluents). On the other hand, the remaining dissolved iron content is appropriate for further integrating the treatment with an iron-catalysed Fenton process, thus reducing the consumption of chemicals in the overall treatment.

Due to contact with air, most wastewaters contain dissolved oxygen and have positive Eh . This does not affect the anaerobic treatment of readily biodegradable effluents (i. e. agroindustrial wastewaters,

sewage...) because dissolved oxygen is consumed by the aerobic and facultative anaerobic bacteria present in reactor sludges (4, 5), leading to a rapid fall in redox potential. In contrast, when wastewaters contain slowly biodegradable compounds (i. e. aromatic molecules), the electron flow generated during their degradation may not be sufficient to obtain an efficient oxygen reduction by the aerobes. In that case, redox potential within digester sludges remains too high for the initiation of methanogenic fermentation preventing satisfactory reactor start-up.

When such a problem occurs, the only strategy possible consists of lowering the digester redox potential. This can be done in two ways: (i) via the addition to the wastewater of an easily metabolizable substrate like glucose in order to favour microbial oxygen consumption, or (ii) via the addition of a reducing agent in order to consume the oxygen chemically. Adequate reducing agents are sodium thioglycolate, cysteine, dithionite, sodium sulphide (3) and titanium (III) citrate (6). These agents have to be used with care since they are toxic at relatively low concentrations (3, 7) or produce very toxic oxidized derivatives when exposed to oxygen (8).

Ferrous sulphate, which is not toxic except at high concentrations (9), could replace advantageously the previous chemicals. It has no reducing power by itself; however, when fed to an anaerobic reactor, it is reduced to ferrous sulphide by the sulphate-reducing bacteria always present in reactors' inocula (10, 11). The resulting FeS is an excellent reducing agent which reacts with O2 much more rapidly than either sodium sulphide or cysteine (12). Contrarily to Na2S, it is also not toxic to methanogenic bacteria (13, 14).

Finally, FeS is characterized by a very low solubility product (Ksp = 3.7 10-19, 18°C) and a high specific gravity (4.74) leading to the formation of dense precipitates (15). For Upflow Anaerobic Sludge Bed (UASB) reactors, where the biomass is mainly located at the bottom of the digester, the FeS produced should then accumulate in the sludge bed and strongly buffer it at an adequate redox potential. Such accumulation could present a second advantage since FeS is suspected to increase the stability of sludge granules (16).

Category : WWT