[Mainland China] The "Fourth Pathway" for High-Salinity Wastewater Treatment Emerges: Solid-Liquid Synergistic Paste-Based Lithification Achieves Full-Volume Resource Recovery Without Purification or Salt Separation

2026年10月16日 of China Chemical Industry News published an article proposing the fourth technical pathway for high-salinity wastewater treatment—MLD + SLS (solid-liquid synergy) paste-like petrification. This pathway abandons evaporation crystallization and salt separation/purification, instead allowing high-salinity water to react synergistically with bulk solid wastes such as coal gangue and fly ash to produce rock-like materials for backfilling coal mine goafs. The core technology has been granted an invention patent, and 2026年3月 was assessed by the All-China Environment Federation as reaching the international advanced level.

I. Common Dilemmas of the Existing Three Pathways

After decades of technological and engineering iteration in industrial high-salinity wastewater treatment, two mainstream technical pathways have formed internationally, represented by ZLD (Zero Liquid Discharge) and MLD (Minimal Liquid Discharge) + deep well injection, while the ZLD + mixed salt landfill pathway is commonly adopted domestically. The article points out that these three pathways share common problems such as high energy consumption, high carbon emissions, poor economic viability, secondary solid waste pollution, and geological safety hazards.

II. ZLD: Converting "Water Pollution" into "Solid Waste Pollution"

ZLD is a combined process chain integrating "pretreatment—concentration—evaporation crystallization—solid-liquid separation," with decades of engineering practice in Europe, the United States, the Middle East, and other regions, mainly applied to power plant desulfurization wastewater, shale gas produced water, chemical wastewater, and other fields.

• Investment—The system equipment is complex, with comprehensive investment ranging from tens of millions to hundreds of millions of yuan.
• Energy consumption pain point—Industry data shows that the power consumption of the evaporation crystallization section reaches 40 to 80 kWh/m³, with even higher energy consumption when treating high-concentration brine, which not only drives up operating costs but also generates substantial indirect carbon emissions.
• Product dilemma—The treated product is salt and mixed salt, which may create new solid waste treatment problems, with disposal costs potentially as high as 2000 to 3000元/ton.

In other words, ZLD converts the "water pollution" problem into a "solid waste pollution" problem, and the result of enormous investment is the spatiotemporal transfer of pollution media. China's high-salinity wastewater treatment has long followed the international ZLD technical pathway, forming extensive engineering practices in coal chemical, coal, and power industries, with a typical process of "pretreatment—membrane concentration and volume reduction—evaporation crystallization—salt separation (or no salt separation)—mixed salt/miscellaneous salt—hazardous waste landfill." Coal chemical high-salinity wastewater has complex composition, and the waste salt treated through this pathway also faces problems such as sodium chloride and sodium sulfate being difficult to separate precisely, poor salt product quality, and mixed miscellaneous salt being included in the national hazardous waste list under HW category management, which both increases disposal costs and makes it difficult to achieve ideal resource utilization.

III. MLD + Deep Well Injection: Three Major Risks Remain Unresolved

MLD is an adjustment based on ZLD: after maximizing wastewater concentration, it is injected through deep well injection into deep underground saline aquifers or depleted oil and gas reservoirs for geological sequestration. However, in practical application, controversies and risks easily arise:

• Prominent geological safety risks—There have been historical cases of micro-earthquakes induced by excessive injection pressure.
• Uncertain long-term sequestration risks—The long-term migration pathways of injected fluids in deep formations are difficult to predict accurately, and reliable assessment methods for century-scale environmental risks are lacking.
• Low public acceptance—The underground pollutant injection disposal model is easily associated with negative risks such as groundwater contamination and formation damage, resulting in strong resistance to project siting and prominent social NIMBY conflicts.

IV. The Fourth Pathway: Solid-Liquid Synergy Paste-Like Petrification

Against this background, Chinese research teams and enterprises jointly proposed the MLD + SLS (solid-liquid synergy) paste-like petrification pathway. Its core is to abandon the traditional pathway of evaporation crystallization and salt separation/purification for high-salinity wastewater: after materialization treatment, high-salinity water undergoes "solid-liquid synergy" reactions with bulk industrial solid wastes such as coal gangue, fly ash, desulfurization gypsum, steel slag, and red mud, and through ambient-temperature chemical activation and multi-state, multi-phase waste synchronous solidification reactions, produces paste-like rock materials with dense structure, stable performance, and strong durability; the process paste is then pumped to geological spaces such as coal mine goafs or subsidence areas for in-situ rock-like filling and backfilling, achieving the integrated goal of "two-waste" synergistic disposal and geological hazard restoration and governance.

The authors summarize it as "a cross-disciplinary scientific process of geo-biomimetic rock formation," achieving an innovative disposal of high-salinity wastewater that involves no purification, no separation, and full resource utilization—salt ions are not treated as "separation targets" but as core functional components participating in the gelation, solidification, and material forming processes. Through a triple mechanism of physical encapsulation, chemical bonding, and ion exchange, they are stably "locked" inside the rock-like consolidated body. By applying the principles of geological biomimetics, the salts do not precipitate, leach, or migrate on geological timescales.

V. Paradigm Shifts in Four Dimensions

• Cost and Energy Consumption—From "money-burning" to "money-saving": wastewater treatment costs and solid waste disposal costs offset each other, turning "two expenditures" into "one revenue" and "environmental consumption" into "low-cost engineering raw materials."
• Products and Risks—From "mixed-salt hazardous waste" to "rock-like" stable sequestration: the concentrations of major pollutants in the leachate of the solidified body are all below the Class III water standard limits of GB/T 14848—2017.
• Spatial Utilization—From "finding land for landfill" to "creating space underground": shifting from landfill to ecological restoration of coal mine goaf and subsidence areas, completing the final disposal of "two wastes" while achieving geological disaster governance and surface subsidence control in goaf areas, turning disposal behavior into restoration behavior.
• Technology Level—Reaching "international advanced": the core technology has been granted an invention patent and was comprehensively assessed as reaching international advanced level by the All-China Environment Federation in 2026年3月.

The article also points out that this pathway achieves three transformations: first, harmful ions are converted from a "free state" to a "bound state," fundamentally changing their environmental activity and migration capability; second, an artificial material circulation system of "mine/coal-power/coal-chemical high-salinity water—backfill material—goaf/subsidence area" is constructed, shifting governance from "linear treatment" to "symbiotic circulation"; third, pollutants are transferred from surface artificial sequestration (a risk window of decades) to underground geological sequestration (stable on centennial to millennial scales).

VI. An Original Solution Adapted to China's Energy Endowment

The strategic value of this pathway lies in its adaptation to China's coal energy endowment. China's coal-producing regions highly overlap with the coal chemical and coal power industries, simultaneously generating large quantities of bulk solid waste such as coal gangue, fly ash, and desulfurization gypsum, as well as numerous coal mine goaf and subsidence areas. The solid-liquid synergistic pathway integrates three types of "burdens"—high-salinity wastewater, bulk solid waste, and goaf geological disasters—into a single governance chain, theoretically forming a closed loop of "treating waste with waste and synergistic disposal." The article positions it as a low-carbon, safe, and economical original solution, providing a brand-new technical paradigm and theoretical support for the green utilization of high-salinity wastewater.

The authors also propose future research directions: starting from key scientific questions such as the long-term evolution patterns of salt ions in cementitious systems and the durability of backfill bodies under multi-field coupling conditions, to further explore the application boundaries of such rock materials in ecological environment restoration.

VII. Three Industry Insights

First, the evaluation criteria for high-salinity wastewater treatment are shifting from "recovery rate" to "whole-system cost and risk." The approach of purely pursuing water recovery and salt crystallization purity is unsustainable in the face of energy bills and hazardous waste disposal costs; combining solid waste and wastewater treatment with mutually offsetting costs is a direction more aligned with engineering economics.

Second, "separation" is not the only prerequisite for resource utilization. The technical philosophy of traditional ZLD is to "separate everything clean," whereas the solid-liquid synergistic pathway chooses "locking stable"—making pollutants lose their migration capability on geological timescales through lattice solidification. The two philosophies correspond to different risk models and provide greater technical choice space for high-salinity wastewater treatment.

Third, cross-medium synergistic governance deserves key industry tracking. Wastewater, solid waste, and mine geological governance have long belonged to different management lines and industrial sectors, yet solutions with genuine cost advantages often emerge at the intersections. For engineering companies, whether they can develop cross-medium process packages will become one of the core competitiveness factors in the next stage.

TIANYI TECH Co., Ltd. (TIANYI LIMITED) has long been deeply engaged in the fields of wastewater treatment and reclaimed water reuse. Centering on three major directions—low-carbon processes, resource recovery, and smart operations—it provides full-chain services from solution design, equipment manufacturing, and engineering construction to operation management for municipal wastewater treatment plants, industrial parks, and various water-using entities. With the goals of "stable compliance, energy saving and consumption reduction, and resource circulation," the company continuously helps customers reduce operating costs and enhance system resilience in the green and low-carbon transition.

Source: "China Chemical Industry News," "Solid-Liquid Synergy Opens a New Frontier in High-Salinity Wastewater Treatment" (2026年10月16日), authors Yu Shujiang (Ph.D. of China University of Mining and Technology (Beijing), Chairman of Shuimu (Beijing) Energy and Environmental Protection Co., Ltd.) and Wang Kai (Senior Engineer of Shuimu (Beijing) Energy and Environmental Protection Co., Ltd.).