Laboratory investigation on the purification of food wastewater by freeze concentration

Yingjie Dai1, Hong Yan2, Sijia Zhang1, Yujie Feng3

1 School of Resources Environment, Northeast Agricultural University, Harbin 150030, China
2 College of Chemistry and Environmental Engineering, Harbin University of Science and Technology, Key Laboratory of Green Chemical Technology of College of Heilongjiang Province, Harbin, 150080, China
3 State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.

Abstract


This study was carried out to determine the feasibility of applying a freeze concentration technique to rarefy milking wastewater using either a stationary wastewater vessel (the first series of tests) or a rotary ice making machine (the second series of tests). In this study, we investigated the impact of freezing temperature, initial milking wastewater concentration and vessel depth upon the removal rate of chemical oxygen demand (COD). Results show that when the freezing temperature was decreased (from 3 C to 15 C), the freezing rate increased. The freezing rate was not significantly affected for the different concentrations of the wastewater solution. The COD removal rates at 0 25 mm of ice layer for the COD concentrations of 500 mg/L, 1000 mg/L and 2000 mg/L were 94.56%, 92.78% and 91.25% respectively at the freezing temperature of 3 C in the first test. In the second test, the milking wastewater (500 mg/L) was frozen using a rotary ice-making machine. The COD removal rates at 6 C and 15 C in the round ice (99.12% and 95.24%) and the surrounding ice (98.37% and 90.28%) were higher than the removal rate in the revolving ice (91.47% and 85.68%). Therefore, the freeze concentration method can become a powerful, simple and low cost treatment method for purifying milking wastewater in the environment.

Keywords


freeze concentration; COD; ice crystal; removal rate; wastewater

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