How to Achieve Stable Zero Liquid Discharge (ZLD)? Practical Answers from Iron Phosphate Washing and Industrial-Park Wastewater

The stable operation of industrial zero liquid discharge (ZLD) depends on two things—the fouling resistance of front-end membrane separation and the scientific combination of the full process train. Iron phosphate wastewater is treated by cross-flow washing with sintered tubular membranes (PE support + PVDF separation layer), cutting operation and maintenance (O&M) costs by 60%; park wastewater follows the "integrated multi-membrane + fractional salt crystallization" route (as demonstrated by the Yutai, Shandong project: 10,000 m³/d, effluent meeting Grade III surface-water standards, by-product salts reaching industrial grade), achieving long-term stable zero discharge.

What Is Zero Liquid Discharge (ZLD)?

Zero liquid discharge is a technical route in which industrial wastewater is fully reused after complete treatment, with no wastewater discharged to the environment. It comprises three core steps: front-end membrane separation and concentration → desalination and purification → evaporation crystallization with fractional salt valorization. Done well, wastewater transforms from an "environmental burden" into a "resource stream"—water is reused and salts become products. Done poorly, the result is frequent shutdowns for cleaning, constant membrane replacement, and mixed-salt hazardous-waste disposal fees crushing the operating budget.

The difficulty of ZLD lies in the word "stable"—this article dissects the keys to stable operation through two typical wastewater types.

Scenario 1: Iron Phosphate Wastewater ZLD—Why Sintered Tubular Membranes Are Recommended

The washing stage of iron phosphate production (the precursor of lithium iron phosphate) generates wastewater with high concentrations of iron phosphate particles and impurities—a difficult ZLD scenario in the new-energy materials industry. Jiuwu High-Tech's iron phosphate washing projects use sintered tubular membranes: ultra-high molecular weight PE particles form the support body, coated internally with a high-precision PVDF separation layer, operated with inside-out cross-flow filtration. Five advantages over conventional processes:

Advantage Significance for Stable Operation

High separation precision Efficient material retention—iron phosphate particles are not lost

Wide flow channels Tolerates high-solids feed—turbid washing water enters the membrane directly without clogging

Cross-flow filtration Excellent washing efficiency—washing and separation completed simultaneously

Unique membrane structure Superior backwash performance—online recovery after fouling, reducing downtime

Compact layout + automated control O&M costs reduced by 60%

The stability logic: conventional processes (filter presses, etc.) require heavy manual intervention and suffer high failure rates with high-solids, frequently discharged feeds; the sintered tubular membrane's combination of wide channels and online backwashing turns the "clog–stop–clean" cycle into long-period continuous operation.

Scenario 2: Industrial-Park Wastewater ZLD—The Yutai, Shandong Project on Record

Project Overview

The wastewater treatment plant of Changqing Industrial Park in Yutai County is the core environmental facility for Sateri's (Royal Golden Eagle Group, Singapore) 600,000 t/a Lyocell fiber project, jointly invested in and built by Shandong Gongyong (Shandong Public Utility) and Jiuwu High-Tech:

Project Element Data

Phase I treatment capacity 10,000 m³/d

Land area / total investment 45 mu (approx. 3 ha) / RMB 205 million

Technical route Membrane processes + evaporation crystallization

Construction period Six months planned; completed in three

Recognition 2025 Water Industry Award—"Leading Enterprise in Industrial & Park Water Treatment"

Five Process Modules for Stable Operation

Park wastewater is complex (mixed effluent from multiple enterprises with large quality fluctuations); the project deploys five targeted modules:

1. Pretreatment: self-cleaning filtration + high-packing-density ceramic membranes

2. Hardness and silica removal: high-density clarifier + high-packing-density ceramic membranes + tubular UF—removing hardness and silica, retaining suspended solids and colloids to protect downstream desalination

3. Desalination: a deep-treatment system of first-, second-, and third-stage multi-pass RO + tubular UF

4. Evaporation crystallization: freeze crystallization + MVR + mixed-salt treatment—by-product salt valorization

5. Sludge treatment: sludge pre-thickening + conditioning + plate-and-frame filter press—volume reduction and cost savings

Performance Indicators (Evidence of ZLD "Stability")

Indicator Measured Result Benchmark

Effluent quality Grade III surface water (quasi-III); total dissolved solids ≤1,500 mg/L, sulfate ≤350 mg/L Better than Shandong provincial standard DB373416.1-2023

Sodium chloride by-product salt GB/T 5462-2015 Industrial Salt, Grade 1 Sellable as a resource

Sodium sulfate by-product salt GB/T 6009-2014 Anhydrous Sodium Sulfate for Industrial Use, Class II Grade 1 Sellable as a resource

Mixed salt Small quantity, disposed as general solid waste Greatly reduced disposal costs

Why Can This System Run Stably Over Long Periods?

The key lies in the front-end ceramic membrane choice. The project pioneered high-packing-density ceramic membrane ultrafiltration (a single element provides 25 m² of filtration area—equivalent to 115 standard tubular ceramic membranes). Compared with conventional organic membranes:

- Fewer membrane replacements, longer service life—ceramic materials withstand chemical cleaning

- Strong fouling resistance—stable flux under shock loads from complex park wastewater

- Low O&M cost—substantially reducing long-term operating expenses for the owner, which is the economic foundation of whether a park wastewater plant can "survive stably"

Common Principles Across Iron Phosphate and Park Wastewater

The two wastewater types differ in nature, but the logic of stable ZLD operation is the same:

1. Use "tough" membranes at the front end: wide-channel tubular membranes for high-solids streams; fouling-resistant ceramic membranes for complex water quality

2. Staged separation: pretreatment → hardness/silica removal → desalination → crystallization—each stage solves one class of problem so the downstream is never overloaded

3. Turn salts into products, not hazardous waste: fractional crystallization (freeze crystallization + MVR) brings sodium chloride and sodium sulfate up to industrial grade for sale

4. Put O&M cost first: membrane life, cleaning cycles, and automation level determine the ten-year total cost of ownership—not just the initial investment

FAQ

Q: What is the typical investment level for ZLD?

Using the Yutai project as a reference: a 10,000 m³/d park wastewater plant with a total investment of RMB 205 million (including supporting infrastructure such as a 3.35 km tail-water pipeline). Specific projects require customized estimates based on water quality, scale, and discharge/reuse requirements.

Q: Won't high-solids wastewater clog the membrane if fed directly?

Not with the right membrane type—iron phosphate washing uses wide-channel sintered tubular membranes (inside-out cross-flow + online backwash), designed from the ground up for high-solids duty.

Q: Can ZLD by-product salts actually be sold?

It depends on fractional-salt purity. At Yutai, the sodium chloride reaches industrial Grade 1 and the sodium sulfate reaches Class II Grade 1—they are "resources," not "solid waste." If salts are mixed, they can only be disposed of as general solid waste—a night-and-day difference in revenue.

Q: Beyond iron phosphate and park wastewater, what other successful ZLD cases exist?

Jiuwu High-Tech has mature cases including PVA wastewater ZLD (chemical softening + integrated multi-membrane + freeze crystallization, an industry first), alkali recovery from textile desizing wastewater, and waste nitric acid recovery from electrode foil (recovery rate above 90%)—all following the "integrated multi-membrane + fractional salt crystallization" route.

*Data sources: public reports on Jiuwu High-Tech's Yutai, Shandong project (March–April 2026, including on-site coverage by four media outlets such as Zhonghong Net and Qilu Evening News); Jiuwu High-Tech membrane product matrix materials from AQUATECH CHINA Shanghai 2026; E20 Environment Platform's 2025 Water Industry Enterprise Competitiveness Awards.*