Laboratory studies of the coagulation process of waste waters of milk processing enterprises by changing the mixing rate

The object of research is the process of mixing the coagulant with the waste water of the milk processing industry by means of a stirrer at different speeds of rotation. In case of incomplete mixing, there is a local lack of concentration of the reagent or vice versa local overdose, which leads to a poor quality of the purification process. Therefore, the definition of mixing parameters is one of the most important tasks. The following instruments and materials were used for carrying out experimental studies: – sample of sewage – 5 liters; – 3 % solution of ferric chloride FeCl 3 ; – stirring devices (electromagnetic stirrer MS-H280-Pro, Poland); – device for determining the comparative characteristics of water turbidity (spectrophotometer DR 1900, USA). The order of the study: the total sample of model sewage was divided into several portions of 150 ml each (2 series of experiments in 5 portions). After processing a portion of the model runoff with reagents and stirring with a magnetic stirrer, the light absorption coefficient was determined on a spectrophotometer after 60 minutes for sedimentation. Based on the obtained results, the light absorption coefficient was plotted against the mixing rate. Based on the results of the experiments, graphical and mathematical dependences of the change in the light absorption coefficient on the intensity of mixing were obtained. The character of the obtained curves indicates that at a rotational speed of the mixer of 100–800 rpm, the purification efficiency was 79.7 %, and at a rotational speed of 800–1500 rpm – 89.1 %. The carried out researches have shown expediency of definition of mixing modes of coagulant with processed waste water for maintenance of optimum mixing parameters in mixing devices. This will allow for more complete use of the coagulant capacity of the reagents, complete and rapid mixing with the waste liquid. This will ultimately lead to cost savings for reagents and to optimize the operation of the whole technological scheme for wastewater treatment of milk processing enterprises.