Ultrafiltration combined with ozone for domestic laundry wastewater reclamation and reuse

Ozone was incorporated into an ultrafiltration system to produce higher quality reclaimed water from domestic laundry wastewater. Characteristics of the wastewater for initial washing waste were 488~2,847 mg/L COD, 62~674 mg/L MBAS, and 38~857 mg/L SS. The wastewater was contacted with ozone in a 10L storage tank and circulated through the membrane module for inner pressurized cross-flow filtration. The concentrate was returned back to the contact tank. The membrane used in this experiment was hollow fiber polysulfone UF membrane with MWCO 5,000 and 10,000. It has an effective filtration area of 0.06m2. The experiment was carried out in two phases with either continuous or intermittent ozone injection. For intermittent ozone injection, the mode of injection interval was changed to 5 min./5 min. and 5 min./10 min. for injection/idling. Ozone was dosed at the concentration of 1.5 mg/L. The permeate quality of UF (MWCO 5,000) was 57 mg/L as COD and 5 mg/L as MBAS at continuous ozone injection with removal of 95% in COD and 96.9% in MBAS. Using UF with MWCO 10,000, it was 93.7% and 95.5% of COD and MBAS, respectively. And using intermittent ozone injection, the removal efficiency was 93% in COD and 93.5% in MBAS without any deterioration in COD and MBAS removal. It could reduce the treatment cost. Using ozone injection, fouling of the membrane was also controlled by increasing organic degradation. The flux of UF (MWCO 5,000 and 10,000) was 0.13 and 0.20 m/d for 3 hour filtration (TMP 40≈45 kPa) without ozone injection. It was increased to 0.18 and 0.24m/d by ozone injection. The reclaimed water quality could be estimated well enough to reuse for rinsing purposes.