Microplastics removal from a hospital laundry wastewater combining ceramic membranes and a photocatalytic membrane reactor: Fouling mitigation, water reuse, and cost estimation

Abstract

The release of microplastics (MPs) through industrial laundry wastewater accounts for 35 % of global MPs emissions into the environment and it is a significant environmental problem, especially because MPs can absorb contaminants of emerging concern (CECs) from garments. This study is the first to evaluate and perform a cost estimation of the MP removal from hospital laundry wastewater (HLWW) using a combination of ceramic membranes and a pilot-scale photocatalytic membrane reactor (PMR) as a fouling mitigation strategy. The HLWW, from a hospital in Copenhagen, Denmark, contained a total organic carbon (TOC) of 345 mg L⁻¹ and 1.4 × 10⁶ MP L⁻¹, mainly of polyethylene terephthalate (PET) ranging between 100 and 200 μm in size. The pre-treatment with an ultrafiltration (UF) ZrO₂ membrane successfully removed 96 % of MPs and over 98 % of suspended solids and turbidity at an estimated cost of 0.45 US$ per m³ of permeate. In the PMR stage, ultraviolet light emitting diodes (UV LED) irradiation reduced irreversible fouling, improving permeate flow and minimizing the need for chemical cleaning. The Ce–Y–ZrO₂/TiO₂ photocatalytic membrane achieved over 99 % removal of turbidity, colour, and suspended solids, as well as 99.9 % removal of MPs, allowing the potential effluent reuse within the hospital laundry. Additionally, the retentate from the PMR process had lower TOC, easing the discharge of this concentrated stream. The cost estimation demonstrated that the photocatalytic degradation combined with traditional techniques, i.e. backflush and chemical cleaning, is more economical than using these techniques separately. Therefore, the total treatment cost was 1.09 US$ per m³ of permeate, which is lower than the cost of fresh water in Denmark. In conclusion, this innovative treatment strategy offers a sustainable and cost-effective solution for HLWW management, not only reducing water consumption by enabling water reuse in the hospital laundry but also advances towards achieving net-zero liquid discharge and contributing to the UN Sustainable Development Goals for clean water (Goal 6) and climate action (Goal 13).