Study of the Floc Produced by Chlorinated Copperas

Abstract

CONSIDERABLEinterest is being shown in the use of chlorinated copperas (ferrous sulfate) as a coagulant.The work described by Mohlman and Palmer (9) with activated-sludge coagulation and the results obtained by Hedgepeth and Olsen (3) with a highly colored water indicate the value of this material. Enslow (£) has recently presented data relating to the operating economic value of this coagulant and also concerning the reactions involved.Laboratory experiments under simulated plant conditions, as explained in a previous article (4), and using the same method of procedure, show that this reagent is a satisfactory coagulant for turbid water, being comparable to alum in this respect. A compact, easily settling floe is obtained at any pH value above 3.5. This is in sharp contrast to the value found efficient for ferric hydroxide floe (4) when using the usual iron and lime treatment.

Coagulation with Iron Compounds

“…In the acid range, the positively charged trivalent ferric and aluminum ions are likewise highly effective in precipitating the negatively charged color colloid (12). This action gives rise to "color floes" which may have absorptive properties far superior to the true iron and alum floes just mentioned (9,13). In turbidity removal it is probable that the adsorptive capacity and specific gravity of the floc particles are the important factors, although colloidal precipitation undoubtedly plays a part.…”

“…Miller (12) included ferric salts in his coagulation studies published between 1923-25. Mohlman and Palmer (13) employed them in their important investigations carried out in 1925 on the coagulation of activated sewage sludge. They found ferric chloride to be superior to all other coagulants tried for that purpose.…”

The Removal of Organic Bound Iron from Highly Colored Water

“…Dennison (31) finds silica in the soluble' sesqui-oxide state in soils. Vincent (32) finds soluble silicates de-posited in the tissues of leaves, accounting probably for the silica content in the flocculent precipitate from chlorinated copperas by Hopkins (18). Brautlecht and Parlin (23) find iron in diminution in direct proportion to the extent of soil cultivation, and bearing a relation to the vegetation thereof.…”

“…Furthermore, the laboratory results when using potassium permanganate showed that the elimination of the organic bound iron did not occur below pH 6.2 but was very effective above that point. Laboratory studies have shown that the iso-electric point of the manganese as Mn(OH)2 is in the range pH 8.8-9.8 (18). Below a pH of 8.8 pronounced swampy tastes, by far more evident than iron tastes, were produced.…”

Problems in Coagulation and Corrective Treatment

“…Coagulation with iron and lime is most efficient at pH values about 9.0 and manganese will be precipitated and adsorbed by this treatment (5,6). When using this coagulant, the ferrous sulfate must be applied to the mixing basin and given a short period of agitation before introduction of the lime.…”