Study on the dewatering process for water treatment residuals: Applicability of freezing-thawing, compression, and electro-osmotic treatment

The applicability of freezing-thawing, compression, and electro-osmotic unit on dewatering water treatment residuals (WTRs) was studied through freezing-thawing conditioning followed by a pressurized electro-osmotic dewatering (PEOD) process. Results showed that 86.12% of bound water was released after freezing-thawing treatment at the optimum freezing temperature of -10 degrees C and duration of 22h. At optimized mechanical pressure of 811kPa and voltage of 30V, the subsequent PEOD could lead to a water content of 58.70% in WTRs with estimated energy consumption of 0.107kWh/kg (water removed), and free water was obviously removed by compression, while bound water content (BWC) remained stable. Moreover, freezing-thawing treatment remarkably reduced the PEOD duration from 200 to 20min. Electro-osmotic treatment could accelerate dewatering rate and improve dewatering efficiency especially for raw WTRs. Therefore, direct compression on raw WTRs could be suited to warm regions, while natural freezing-thawing treatment combined with compression/electrical compression will be selected in cold regions.