The REAL process--a process for recycling sludge from water works.
In order to produce drinking water, coagulants--such as aluminium salts--are widely used for precipitation and separation of impurities from raw water. The residual from the process is sludge, which presents a disposal problem. The REAL process is a method for recycling the aluminium from the sludge. In a first step, the aluminium hydroxide is dissolved in sulphuric acid. In a second step, an ultra filtration will separate all suspended matter and large molecules, leaving a concentrate of 15-20% dry solids. The permeate will contain the trivalent aluminium ions together with 30-50% of the organic contaminants. In a third step, by concentrating the permeate in a nano filter, the concentration of aluminium will be high enough to, in a fourth step, be precipitated with potassium sulphate to form a pure crystal: potassium aluminium sulphate. The potassium aluminium sulphate is comparable to standard aluminium sulphate. The process will give a residual in form of a concentrate from the ultra filtration, representing a few per cent of the incoming volume. This paper presents the results from a long time pilot-scale continuous test run at Västerås water works in Sweden, as well as calculations of costs for full-scale operations.
Stendahl
K
K
Mälarenergi AB, Business Area Water, P.O. Box 14, SE 721 03 Västerås, Sweden. kjell.stendahl@feralco.com
Färm
C
C
Fritzdorf
H
H
D000534:Alum Compounds / Q000737:chemistry* / Q000302:isolation & purification*; D000536:Aluminum Hydroxide / Q000737:chemistry*; D011232:Chemical Precipitation; D003247:Conservation of Natural Resources; D014462:Ultrafiltration; D014866:Waste Products; D018508:Water Purification / Q000379:methods*
D000534:Alum Compounds; D014866:Waste Products; C016213:aluminum oxychloride; C041524:aluminum sulfate; D000536:Aluminum Hydroxide