Reverse osmosis (RO) reject management is a significant challenge, intensifying with the increasing industry-scale application of the RO process to treat industrial effluents. Implementing the RO process for treating textile dyeing wastewater is a common practice adopted by Common Effluent Treatment Plants (CETPs) in Tamil Nadu. Nevertheless, the limiting factor is the minimization of the reject volume. To mitigate the discharge of RO reject having an ecotoxicological effect, the necessary step is to incorporate zero liquid discharge (ZLD). The conventional membrane-based and thermal-based treatment technologies applied for reject treatment to achieve minimum liquid discharge (MLD)/ZLD are highly energy-intensive and cost-intensive. Currently, the ZLD process adopted by CETPs, in Tamil Nadu includes multiple-effect evaporator (MEE) operations to treat textile RO reject. MEE intakes high operation and maintenance and produces mixed salt brine. Operation temperature >70℃ even leads to scaling of heat transfer pipes. Additionally, the declining gain output ratio (GOR) requires adjustment with feed pre-heater or Vapor recompression (VC), which adds up expenditure.
However, microwave (MW) heating can substantiate as a novel alternative application in desalination due to its rapid, uniform, and targeted non-contact heating procedure. Furthermore, MW-induced catalytic oxidation has a widespread application in degrading organic pollutants of textile dyeing effluents, which may serve the additional purpose of pre-treatment of RO reject. Therefore, the current study focuses on applying MW heating for the twin objective of pre-treatment-desalination of RO reject from textile wastewater to substitute the conventional reject management methods.

Keywords: RO reject; Thermal-based treatment; Microwave heating; Zero liquid discharge; Textile wastewater