The REAL process - a process for recycling sludge from water works

K. Stendahl, C. Farm, I. Fritzdorf, Hans Ulmert

Research output: Contribution to journalArticlepeer-review

3 Citations (SciVal)


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 Vasteras water works in Sweden, as well as calculations of costs for full-scale operations.
Original languageEnglish
Pages (from-to)235-242
JournalWater Science and Technology
Issue number5
Publication statusPublished - 2006

Subject classification (UKÄ)

  • Water Engineering
  • Environmental Engineering


  • water treatment
  • recirculation
  • precipitation
  • aluminium
  • filtration


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