Minimum Liquid Discharge
Minimum Liquid Discharge — Maximise Water Recovery, Minimise Disposal Cost
Hydro Engineering Solutions designs MLD systems that drastically reduce the volume of wastewater requiring disposal — recovering water for reuse and concentrating waste streams for efficient treatment. The practical middle ground between conventional treatment and full Zero Liquid Discharge.
Water Recovery
70 – 95%
Discharge Reduction
Up to 90% vs. conventional
Core Technology
SBR · RO · Evaporation
Sectors Served
Textile · Chemical · Power
Capital Cost vs ZLD
30–50% lower
Support
AMC lifecycle contracts
How It Works
The MLD treatment sequence
MLD achieves its high recovery by cascading several treatment technologies in sequence, each recovering progressively more water from an increasingly concentrated stream — until only a minimal residual requires disposal.
Primary Treatment & Equalisation
Conventional primary treatment removes gross solids, oils, and organic load before the wastewater enters the recovery circuit. Equalisation tanks buffer flow and concentration variations to protect downstream membrane systems.
Biological Treatment (SBR)
A Sequencing Batch Reactor (SBR) provides aerobic biological treatment to break down BOD, suspended solids, and pathogens to low levels. The clarified effluent is then suitable as feed for the downstream RO concentration stage.
Reverse Osmosis Concentration
The treated biological effluent is fed to a high-recovery RO system that recovers 70–85% of the water as clean permeate for reuse. The RO concentrate — now a fraction of the original volume — advances to evaporation.
Concentrate Management
RO concentrate is either further processed by evaporation/crystallisation (approaching ZLD) or managed as a reduced-volume stream requiring permitted disposal — depending on the facility's regulatory position and economics.
Permeate Polishing & Reuse
RO permeate is polished and conditioned for process reuse — cooling tower make-up, boiler feed, or washing water — closing the water loop and reducing fresh water intake costs.
SCADA Monitoring
Online flow, conductivity, and quality monitoring tracks system performance and recovery rates in real time. Automated alerts detect membrane fouling, chemical dosing depletion, or process upsets before they escalate.
MLD vs ZLD
Which is right for your facility?
MLD and ZLD serve different compliance situations. Choosing correctly saves significant capital and operating cost without compromising your regulatory position.
Choose MLD when…
- ✓Your DoE permit allows a small residual liquid discharge
- ✓Water scarcity or effluent charges make reuse attractive
- ✓Full ZLD capital cost is prohibitive at your current scale
- ✓You are in a phased compliance journey toward ZLD
- ✓Your wastewater has moderate TDS that responds well to RO recovery
Choose ZLD when…
- →Your DoE permit or buyer audit requires zero discharge
- →You are in a water-stressed area with no discharge route
- →EU or US brand requirements mandate zero liquid discharge
- →Wastewater contains hazardous constituents that cannot be discharged
- →Long-term regulatory risk makes any discharge financially unacceptable
Technical Specifications
Design parameters
| Parameter | Typical Range |
|---|---|
| Overall Water Recovery | 70 – 95% of inlet flow |
| Discharge Volume Reduction | Up to 90% vs. conventional ETP |
| RO Recovery (within MLD) | 65 – 80% |
| SBR Effluent Quality (BOD) | < 10 mg/L |
| RO Permeate TDS | < 100 mg/L (reuse-quality) |
| Concentrate TDS | 5,000 – 50,000 mg/L (feed-dependent) |
| Capital Cost vs. Full ZLD | 30 – 50% lower |
| Operating Cost vs. Full ZLD | 20 – 40% lower |
| Footprint vs. Conventional ETP | Larger (SBR + RO added) |
| Scalability | Modular — can upgrade to ZLD |
Why Hydro Engineering Solutions
MLD designed to last — and to scale
Effluent characterisation first
MLD system performance is highly sensitive to feed chemistry. We characterise your wastewater thoroughly before designing the SBR and RO sequence to achieve your target recovery.
Upgrade path to ZLD built in
Our MLD designs are modular and ZLD-upgrade-ready — so if your compliance position or buyer requirements tighten, you can add evaporation capacity without redesigning the upstream circuit.
Water reuse integration
We design the permeate conditioning circuit for your specific reuse application — whether that is cooling tower make-up, boiler feed, or process washing — maximising the economic return on recovered water.
Transparent cost-benefit analysis
Before we design anything, we prepare a water balance and cost-benefit comparison between your current treatment cost, MLD capital and operating cost, and water saving value — so you invest with clear numbers.
Get Started
Reduce your discharge volume — significantly
Share your current treatment process and wastewater characteristics. We'll model a water balance and MLD design that shows you exactly what you can recover and what disposal cost you can eliminate.
- ✓Wastewater characterisation and water balance
- ✓Recovery target modelling (MLD vs ZLD comparison)
- ✓SBR + RO system sizing and layout
- ✓Permeate reuse circuit design
Request a Free Consultation
No obligation. Our engineering team responds within 1 business day.