Advanced compact wastewater treatment processes are being looked for by cities all over the world as effluent standards are becoming more stringent and land available for treatment plants more scarce. In this paper it is demonstrated that a very substantial portion of the pollutants in municipal wastewater appears as particulate and colloidal matter. Pre-coagulation, therefore, gives very efficient pre-treatment that results in considerable saving in the total space required by the plant, especially when combined with a biofilm process for the removal of the soluble matter. A new biofilm process for this purpose is described. The moving bed biofilm process is based on plastic carriers, that move in the reactor, on which biomass attach and grow. The carriers are kept withinthe reactor by a sieve arrangement and biomass that is sloughing off the carriers is separated before effluent discharge. In addition to combining the moving bed biofilm process with pre-coagulation, the paper discusses also the use of a high-rate moving bed process combined with coagulation directly after the biofilm reactor in order to enhance separability. This results in very compact treatment plants for secondary treatment and possibly phosphate removal.

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