Demonstration of a treatment system for purification and reuse of laundry wastewater

A pre-industrial scale experimentation aimed at the demonstration of a system for purification and reuse of wastewater from an industrial laundry was carried out by means of a prototype plant installed in situ, fed with 15 m3/h of untreated wastewater. The tested treatment system consisted of: (i) physico-chemical pre-treatment (coagulation, flocculation and Dissolved Air Flotation or DAF); (ii) sand filtration; (iii) ozonation; (iv) Granular Activated Carbon (GAC) filtration and (v) cross-flow ultrafiltration (UF) on flat membranes realised in polyvinyledene fluoride (PVDF). Under the optimised treatment conditions, it was demonstrated that the outlet of the GAC filter meets the requiring law limits for discharge to surface waters in Italy, even in terms of residual content of total surfactants (<2 mg/L). The post-treatment of ultrafiltration on flat membranes further reduced the residual pollutant content, allowing reuse of the treated effluents in some washing processes of home textiles, as demonstrated by whiteness index measurements. A cost analysis was performed to assess the operating costs of each treatment step.

Under tested conditions, a purification system composed of: physico-chemical pre-treatment; sand filtration; ozonation and GAC filtration; allows to meet the requiring law limits for discharge to surface waters in Italy. A post-treatment of ultrafiltration on flat PVDF membranes allows reuse of the treated effluents in some washing processes; however, the need for a frequent membrane chemical washing has to be taken into account when considering a full scale implementation.