ero liquid discharge (ZLD) refers to a treatment process in which the plant discharges no liquid effluent into surface waters, in effect completely eliminating the environmental pollution associated with treatment. Apart from this benefit, a ZLD process also makes effective use of wastewater treatment, recycling, and reuse, thereby contributing to water conservation through reduced intake of fresh water. This chapter discusses the challenges of ZLD in a variety of process plants, such as bulk drug manufacturers, textile factories, and chemical and fertilizer plants. Creating zero discharge solutions can be accomplished by concentrating the effluent using various techniques, including membrane-based and multiple effect evaporation-based systems, and recovery and recycling of water.