Why Bangladesh Should Choose MLD Over ZLD for a Sustainable Future
Bangladesh, a rapidly industrializing nation, stands at a crossroads between environmental protection and economic survival. As pollution from factories continues to threaten rivers, groundwater, and public health, the Department of Environment (DoE) has tightened industrial discharge rules and begun promoting Zero Liquid Discharge (ZLD) — a system designed to recycle every drop of wastewater.
The goal is noble, but the method is problematic. In practice, ZLD may not be the most sustainable path for Bangladesh. Instead, a Minimum Liquid Discharge (MLD) approach — which recovers 85–90% of wastewater — offers a far more climate-resilient, cost-effective, and implementable solution.
If every industry were required to implement ZLD, it would drastically raise the country’s electricity demand, foreign exchange dependency, and greenhouse gas emissions — undermining national commitments to sustainable growth.
Scaling these figures up to the national level:
In short, the “price of the last drop” — the extra 10–15% of water recovered by ZLD — costs 24 kWh of energy, 14 kg of CO₂, and about BDT 300 per cubic meter. That is an unsustainable trade-off for a developing nation striving for both climate resilience and industrial growth.
This would increase the country’s reliance on imported LNG and refined fuels, worsen the current account deficit, and add roughly 6.3 million tons of CO₂e emissions each year — directly contradicting Bangladesh’s Nationally Determined Contributions (NDCs) under the Paris Agreement.
If Bangladesh implemented ZLD across all industries, the total setup cost would exceed USD 39–79 billion, compared to USD 8–13 billion for MLD. Even assuming a modest 70% import share, ZLD would result in an immediate foreign currency outflow of USD 18–49 billion just to buy the machinery. The replacement membranes, chemicals, and spare parts would then add recurring foreign exchange pressure every year.
In contrast, MLD systems rely mostly on RO and UF technologies already common in Bangladesh, with growing local assembly capability — helping retain value within the domestic economy.
MLD, on the other hand, produces a smaller, more manageable brine volume that can be treated, diluted, or safely discharged under controlled conditions. The goal should be “Zero Pollution,” not “Zero Liquid.”
This approach can:
Water should not be saved at the cost of burning more fossil fuel. The smarter path is Minimum Liquid Discharge, not maximum energy discharge.
Bangladesh needs Zero Pollution — not just Zero Liquid.
The goal is noble, but the method is problematic. In practice, ZLD may not be the most sustainable path for Bangladesh. Instead, a Minimum Liquid Discharge (MLD) approach — which recovers 85–90% of wastewater — offers a far more climate-resilient, cost-effective, and implementable solution.
The Scale of the Challenge
Bangladesh generates about 6 billion cubic meters of wastewater annually, including roughly 3.12 billion cubic meters from industries alone — the equivalent of 8.5 million cubic meters per day, according to the Bangladesh Bureau of Statistics (BBS). Only 19% of this wastewater is treated properly, and the rest continues to pollute rivers such as the Buriganga, Shitalakhya, and Turag.If every industry were required to implement ZLD, it would drastically raise the country’s electricity demand, foreign exchange dependency, and greenhouse gas emissions — undermining national commitments to sustainable growth.
Energy, Emissions, and Cost: The Numbers
A ZLD plant typically consumes around 6.4 kilowatt-hours (kWh) of electricity per cubic meter of treated water — more than double that of an MLD system, which averages 3.0 kWh/m³.Scaling these figures up to the national level:
- Electricity demand: MLD would consume about 9.35 terawatt-hours (TWh) per year, while ZLD would require 19.96 TWh — an additional 10.6 TWh, equal to nearly 10% of Bangladesh’s total annual power generation.
- CO₂ emissions: This extra electricity use translates into about 6.3 million tons of additional CO₂ per year, given Bangladesh’s grid emission factor of 0.593 kg CO₂/kWh.
- Power cost: At the current industrial tariff (BDT 12.39/kWh), the national energy bill for ZLD would reach BDT 247 billion annually, compared to BDT 116 billion for MLD — a difference of BDT 131 billion, or about USD 1.08 billion every year.
In short, the “price of the last drop” — the extra 10–15% of water recovered by ZLD — costs 24 kWh of energy, 14 kg of CO₂, and about BDT 300 per cubic meter. That is an unsustainable trade-off for a developing nation striving for both climate resilience and industrial growth.
Fuel Dependence and Carbon Footprint
To produce the additional 10.6 TWh required by nationwide ZLD systems, Bangladesh would need approximately 2.23 billion cubic meters of natural gas per year or, if diesel-based captive power were used, 2.86 billion liters of diesel — worth nearly BDT 292 billion annually at current prices.This would increase the country’s reliance on imported LNG and refined fuels, worsen the current account deficit, and add roughly 6.3 million tons of CO₂e emissions each year — directly contradicting Bangladesh’s Nationally Determined Contributions (NDCs) under the Paris Agreement.
Foreign Exchange Outflow: The Hidden Cost
Bangladesh does not manufacture advanced Reverse Osmosis (RO) membranes, Multiple Effect Evaporators (MEE), or crystallizers — the core components of ZLD systems. These must all be imported.If Bangladesh implemented ZLD across all industries, the total setup cost would exceed USD 39–79 billion, compared to USD 8–13 billion for MLD. Even assuming a modest 70% import share, ZLD would result in an immediate foreign currency outflow of USD 18–49 billion just to buy the machinery. The replacement membranes, chemicals, and spare parts would then add recurring foreign exchange pressure every year.
In contrast, MLD systems rely mostly on RO and UF technologies already common in Bangladesh, with growing local assembly capability — helping retain value within the domestic economy.
Environmental and Practical Concerns
ZLD does not eliminate pollution; it simply transfers it. The salts and solids extracted from wastewater — roughly 3,000 kilograms per day per 1,000 m³ of effluent — become hazardous solid waste requiring specialized disposal facilities. Bangladesh currently lacks an integrated system for managing such industrial waste, creating new environmental risks if salts are dumped illegally.MLD, on the other hand, produces a smaller, more manageable brine volume that can be treated, diluted, or safely discharged under controlled conditions. The goal should be “Zero Pollution,” not “Zero Liquid.”
A Smarter, Scalable Solution
Instead of forcing industries into expensive ZLD setups, Bangladesh should focus on high-recovery MLD systems combined with circular water management — including rainwater harvesting, water reuse, and cluster-based common effluent treatment.This approach can:
- Cut national electricity demand by over 10 TWh/year,
- Avoid 6.3 million tons of CO₂ emissions annually,
- Save BDT 131 billion per year in electricity costs, and
- Prevent USD 18–49 billion in foreign exchange loss from imported machinery.
Choose Realism Over Rhetoric
Bangladesh must pursue water security without jeopardizing its energy, economy, or climate commitments. Mandating high-efficiency MLD for all industrial zones — while reserving ZLD only for highly toxic or saline effluents — strikes the right balance between environmental protection and economic viability.Water should not be saved at the cost of burning more fossil fuel. The smarter path is Minimum Liquid Discharge, not maximum energy discharge.
Bangladesh needs Zero Pollution — not just Zero Liquid.