Performance of humidification-dehumidification wastewater treatment system driven by heat pump

A wastewater treatment experimental bench based on principle of humidification and dehumidification was built with using a heat pump to provide both heat and cold sources for the system. By adjusting the frequency(25-50 Hz) of circulating fan and solution pump, the effects of circulating air flow rate and wastewater flow rate on heat and mass transfer characteristics and performance parameters of wastewater treatment were emphatically studied. Experimental results showed that when the initial pH, SS and COD of wastewater were 13.51, 166 mg/L, 2 117 mg/L respectively, the pH, SS and COD of clear liquid separated by the system were 8.2, 4.0 mg/L, 53.2 mg/L respectively, which meant that water quality was greatly improved. Heat and mass transfer coefficients of packing increased with the increase of circulating air flow rate and air-side Reynolds number. Pure water production rate(PWPA) and pure water recovery rate(PWRR) also increased with the increase of circulating air flow rate. Gain output ratio(GOR) of packing increased firstly and then decreased with the increase of circulating air flow rate. Heat and mass transfer coefficients of packing increased with the increase of flow rate and Reynolds number of wastewater. PWPA also increased with the increase of wastewater flow rate, but PWRR decreased with the increase of wastewater flow rate. GOR increased gradually with the increase of wastewater flow rate, and then remained almost unchanged. Due to different influence laws of circulating air flow rate and wastewater flow rate on different performance parameters, it was necessary to select the appropriate circulating air flow rate and wastewater flow rate based on priority performance parameters.