ELECTROFLOTATION TREATMENT OF DAIRY WASTEWATER: CHEMICAL-TECHNOLOGICAL ASPECTS

Abstract

Experimental researches are carried out and chemical-technological laws of reagent-electroflotation treatment of sewage of dairies are established. The wastewater of the milk processing enterprise of Sumy region was selected for the study. For reagent wastewater treatment, ferric chloride FeCl3 in the form of a 5% aqueous solution is selected. To accelerate the hydrolysis of the reagent as an alkaline additive was used calcium oxide (lime) CaO in dry form and sodium hydroxide NaOH in the form of 5% aqueous solution. To accelerate the formation of sediment (sludge) used flocculant nonionic polyacrylamide (PAA) in the form of 0.05% aqueous solution. The efficiency of treatment was studied by the following indicators of wastewater: hydrogen pH, transparency and amount of ether-soluble substances. It is established that the process of extraction of ether-soluble substances largely depends on the pH of the medium and increases with increasing alkalinity of wastewater. The greatest influence of pH of the environment is observed at concentration of FeCl3 of 100-150mg / dm3. When FeCl3 is added at a concentration of 200mg / dm3, the purification effect does not depend on the pH of the medium. The most effective is the addition of ferric chloride and then lime. Initially, the addition of FeCl3 coagulates proteins and partially demulsifies the fat emulsion. After the introduction of lime into the water, hydrolysis and formation of iron hydroxide Fe(OH)3 occurs, on the surface of which contaminants are adsorbed. The greatest degree of purification from ether-soluble substances 87-88% is provided by addition of ferric chloride FeCl3 in concentration of 150-200mg / dm3 at pH of 9,5-10. It was found that when using lime to increase the pH of wastewater at a concentration of 500mg / dm3, there is a more efficient removal of ether-soluble substances and suspended solids (increased transparency), and less sediment is formed. Summarizing the obtained data, the optimal concentrations of reagents for pre-treatment of wastewater were selected – FeCl3 - 100mg / dm3, CaO - 500mg / dm3 and wastewater pH - 7.2. It is shown that the reduction of the content of ether-soluble substances to 40mg / dm3 (at the maximum permissible concentration for dairy wastewater 50mg / dm3) is possible only at high processing time (20-30 minutes) and density (0.05A / cm2) and voltage (26 V) electric current, which leads to high electricity consumption.