Zero Liquid Discharge (ZLD) for Garment Factories: An Introduction

Zero liquid discharge (ZLD) refers to a wastewater treatment approach designed so that essentially no liquid effluent leaves the facility as discharge — instead, treated water is recovered and reused within the facility's own processes, and the residual concentrated waste stream is reduced to a solid or near-solid form for disposal, rather than discharged as liquid effluent to a water body or municipal system. This is a considerably more ambitious goal than standard ETP compliance (which focuses on treating effluent to meet a discharge standard before releasing it), since ZLD aims to eliminate the discharge itself rather than simply clean it to an acceptable level.

Bangladesh's garment and textile industry is a major export sector, and many international buyers and brands increasingly include water-stewardship and sustainability requirements — sometimes including ZLD or water-recycling targets — as part of their supplier compliance expectations, alongside Bangladesh's own Department of Environment discharge standards. This buyer-driven pressure is a distinct, additional driver for ZLD adoption beyond regulatory compliance alone, and factories serving buyers with these requirements may need to plan for ZLD capability specifically to remain a qualified supplier, independent of whether standard ETP compliance alone would otherwise be sufficient.

A typical ZLD system builds on standard ETP treatment (physical/chemical and biological treatment stages, as covered in our ETP design basics article) with additional stages specifically aimed at water recovery and volume reduction — commonly including membrane-based concentration (RO or similar, recovering additional clean water from what would otherwise be effluent), followed by thermal evaporation and crystallisation stages that further concentrate the remaining waste stream down to a manageable solid residue for disposal. Each additional stage adds capital cost, energy demand and operational complexity, which is why ZLD is a considerably larger investment than standard ETP compliance alone.

ZLD systems, particularly the thermal evaporation/crystallisation stages, are typically energy-intensive and represent a considerably higher capital and ongoing operating cost than standard ETP treatment — this is a genuine trade-off that should be assessed against the specific factory's actual buyer requirements, water costs, and sustainability commitments, rather than assumed as automatically cost-justified for every facility. Some factories pursue partial water recycling (recovering and reusing a significant portion of treated water without pursuing full zero-discharge) as a more proportionate middle-ground approach where full ZLD is not specifically required by buyers or regulation.

Before committing to a full ZLD investment, it is worth clearly establishing what is actually required — specific buyer compliance requirements (which vary between buyers and are worth confirming directly rather than assuming), applicable DoE regulatory requirements, and the factory's own water-cost economics (water scarcity or high tariff areas can make water recycling more directly cost-justified independent of any external requirement) — since these different drivers can lead to quite different appropriate levels of investment, from partial water recycling through to full zero liquid discharge, rather than treating ZLD as a single universal target regardless of the specific facility's actual situation.