Anionic flocculants were produced by solid-phase chemical modification of starch. On the basis of their favourable properties (non-toxic, environmentally degradable), their application is very advantageous in drinking water treatment, food industry and pharmaceutical industry for removing colloid size particles from suspensions. A pilot scale plant was built for the production of the flocculant. The main part of the plant IS multifunctional batch type reactor in which all steps of the dry modification technology can be carried out. The scaling-up of the reactors requires thorough knowledge of the kinetics of the reactions taking place in the equipment. The starch modification reaction consists of the phosphorylation and degradation of the starch. The results of the kinetic investigation carried out in the laboratory and in the batch-type pilot-scale plant will be presented in this paper.