Coagulation purification of natural water with iron oxide salts

Summary

The efficiency of using ferric chloride and ferric sulphate for coagulation purification of natural and model water depending on the turbidity, color, alkalinity of the source water and flocculation duration is considered. It is shown that for the purification of turbid water, the doses of coagulants related to the iron ion do not depend on the type of coagulant and increase with rise of the turbidity of the purified water. Power dependence of the dose of ferric chloride on the turbidity of the source water was determined. Ferric chloride is the most effective coagulant for reducing turbidity and color, simultaneously providing for the standard concentration of iron ions in purified water. The higher efficiency of ferric chloride compared to ferric sulphate is determined by the presence of polyoxychloride complexes in ferric chloride solutions. It has been established that the main contribution to the reduction of turbidity of water coagulated with iron oxide salts is made by alkalinity that determines the rate and amount of insoluble products of hydrolysis of iron oxide salts. Using the example of coagulation purification of colored waters from different water sources using iron oxide salts, it has been shown that with an increase in color and alkalinity of the source water, no clear correlation dependence of the dose and purification efficiency on these parameters is observed.

Key words

settling , turbidity , chromaticity , coagulation , flocculation , natural water , ferric sulfate , alkalinity , hydrolysis , ferric chloride

Substantiating the use of aluminium sulfate for the elimination of phosphorus from wastewater at the Saint-Petersburg wastewater treatment facilities

Summary

The article opens a series of three articles dedicated to the introduction of aluminium sulfate as a chemical for chemical removal of phosphorus compounds from wastewater. The urgency of the task of eliminating nutrients from wastewater is described; the primary concern of removing phosphorus for the protection of water bodies from eutrophication is substantiated. A short literature review including the practice of chemical removal of phosphorus from wastewater in USA and European Union is presented. Special features of the basic chemicals – calcium, aluminium and iron compounds – essential for the practical application of chemical removal of phosphorus are described. The second article will present the evaluation of the toxicity of aluminium and iron compounds; the results of investigating the impact of iron and aluminium salts on the aeration tank biocenosis and sludge mixture dewaterability will be discussed. The third final article will present a detailed report on the introduction of aluminium sulfate as a chemical for chemical removal of phosphorus compounds from wastewater at the Saint-Petersburg wastewater treatment facilities.

Key words

wastewater , aluminium sulphate , nutrients removal , chemical precipitation of phosphorus , ferric sulfate , insoluble phosphates