Mechanism of Flocculation in the Clarification of Turbid Waters

Coagulation to remove particulate matter from turbid waters may be carried out by any of several techniques. This report attempts to discover which coagulation techniques yield comparable results, and which of these is preferable from the operator's standpoint. Because of its length, this report is divided in half. Part II, containing the results and a discussion, will appear in next month's issue.

Section: Sepmentioning

confidence: 96%

COAGULATION TESTING: A COMPARISON OF TECHNIQUES—PART 1

Tekippe¹,

Ham²

1970

“…A total of 50 ppm NaHC0 3 was added to the suspensions before the pH was adjusted with O.1N HCl or NaOH. sodium-clay suspensions were diluted with demineralized water to form the working suspensions for jar tests and mobility measurements.…”

Section: Fig 1 Mobilities Of Clays Without Alummentioning

confidence: 99%

Electrophoretic Studies of Turbidity Removal by Coagulation With Aluminum Sulfate

Black¹,

Hannah²

1961

One important factor affecting coagulation is the negative zeta potential, often referred to as the charge, that is associated with natural clay particles suspended in water. This article discusses a study of the zeta potential of clay particles that were found to be dependent on the pH and on the alum dosage. An amount of alum equivalent to several times the base‐exchange capacity of the clay suspension was required to neutralize the particle charge. Clarification was best in the range pH 7.5 – 8.5 where the particles were negative, rather than at pH values where the particle charge had been neutralized. Fair coagulation was often obtained below pH 4.5 where the particles were nearly neutral. In many instances, residual turbidities changed sharply without any accompanying change in mobility values. The eight coagulant aids used with alum all could be made to improve or inhibit coagulation by selection of dosages of alum and aid. As in the coagulation at different pH values, final particle charges could not be correlated with residual turbidities.

“…In the work conducted by Langelier and Ludwig (14), where residual turbidity was plotted against alum dosage, two general types of curves were obtained. In clays of low base-exchange capacity (20 }Le/l), shown in Fig.…”

Section: Effects Of Base-exchange Capacitymentioning

confidence: 99%

Electrophoretic Studies of Water Coagulation

Pilipovich¹,

Black²,

Eidsness³

et al. 1958

T H E importance of alum coagula-electrolytes commonly found in water, tion in removing colloidal impuri-have been the subject of many investities from water is well known. . Workers have found though much valuable experimental that good flocculation with both alum work has been done on the problems and ferric sulfate occurs within a relainvolved and although the techniques tively narrow pH range. Unfortufor coagulation with alum are well ad-nately, these results have also been vanced, the mechanisms have never considered true for the coagulation of been completely elucidated. Coagula-clay suspensions. This has led to the tion with alum, as other coagulations, belief that there is but a narrow range requires that a colloidal suspension be of coagulant dosage within which good made unstable. The two factors re-flocculation will result, and that the lated to the stability of colloidal sus-coagulant dosage for all waters must pensions are the zeta potential (some-be held within these limits. times incorrectly referred to as the Various theories have been proposed "charge") and hydration. When co-to explain the role of alum in the coagulation of a colloidal suspension oc-agulation of turbid waters. In 1948, curs, the degree of hydration or the Black (13) attempted to summarize zeta potential, or both, are insufficient existing theory as to the mechanism to maintain suspension stability. As of coagulation. He first postulated the isoelectric point is approached, the that organic color and turbidity were zeta potential and hydration decrease negatively charged colloidal particles, and coagulation may occur.or, more accurately, colloids with Most of the laboratory research that negative zeta potential. According to has been done in the past in connec-him, coagulation takes place in three tion with water clarification has been phases: in coagulation with aluminum or ferric 1. As the coagulant dissolves and the salts. The formation and properties trivalent aluminum or ferric ions become of alum and ferric floes. and the effects available, they neutralize the negative of varying the initial pH with sodium charge on the particles of color or turhydroxide or calcium hydroxide in the bidity, and ... their neutralizing power presence of different concentrations of is very great. This, in the opinion of 1467