Water is the lifeblood of the steel industry. Scientifically promoting the recycling and reuse of water resources in the steel industry is an important part of the green development of the steel industry. With the green transformation of the steel industry, the water resource circulation system will also face new requirements, new developments, and new constructions.

Liang Siyi, chief engineer and senior engineer at China Metallurgical Group Corporation (MCC), has been deeply involved in the field of wastewater resource utilization in the steel industry for many years. Based on his years of experience in the steel industry, he pointed out: "In recent years, Chinese steel enterprises have adhered to the principle of prioritizing water conservation and increasing water sources simultaneously. The industry's water efficiency indicators have continued to improve, and some steel enterprises have reached internationally advanced levels. However, from the perspective of the industry as a whole, there is still much work that needs to be done, requiring enterprises to correctly understand, cooperate, and practically promote it."

"The in-plant water circulation system of the steel industry includes workshop-level water circulation and plant-level water circulation. At present, we should focus more on the treatment of high-concentration brine in the end of the plant-level water circulation system, avoiding the brine problem from becoming a stumbling block on the path of green development for steel enterprises." said Liang Siyi.

With the increasing awareness of environmental protection, in recent years, steel enterprises have been pursuing "zero wastewater discharge," transforming production wastewater into desalinated water for reuse after deep treatment. However, a certain amount of high-concentration brine is still produced that cannot be absorbed within the plant, and this contradiction is particularly prominent for inland steel enterprises that are not located along the coast.

The "Implementation Plan for the Recycling and Reuse of Industrial Wastewater" issued in December last year clearly proposed that by 2025, the reuse rate of industrial water in the steel industry above designated size should reach 97%.

"In this context, steel enterprises must avoid blindly launching zero wastewater discharge projects. Many projects lack effective support and guarantees, easily leading to problems such as key parameters such as the salt-nitrate ratio deviating from the actual situation, high system maintenance difficulty, and inability to dispose of crystallized salt." Liang Siyi gave an example, such as the method of using an end-stage evaporator to separate salt water. The operating costs of "zero wastewater discharge" projects in most steel enterprises are high, often resulting in projects being built but not used, becoming mere decorations.

Liang Siyi believes that zero wastewater discharge in the steel industry should not be a "one-size-fits-all" approach, but should follow the principle of "prioritizing sorting and determining use based on quality."

"Prioritizing sorting" means that enterprises must first clarify their situation through sorting, including water quantity and quality, pipeline routing, misconnections and leaks, etc., to maximize the reduction of water at the source. "Determining use based on quality" means determining the final use based on the quality of the wastewater.

"For example, for industrial wastewater with high ecological toxicity, such as desulfurization wastewater and coking wastewater in steel enterprises, it is advisable to consider setting up salt separation devices such as high-concentration brine evaporators to reduce system risks and environmental risks. For high-concentration brine in the comprehensive wastewater system of the entire plant, which is mainly composed of circulating sewage, its ecological toxicity and environmental risks are relatively low. It is recommended to use it mainly for production miscellaneous purposes and synergistic absorption. In the process of absorption in the plant area, the salt-retaining effect and silicon-oxygen tetrahedron coordination effect of steel slag and water slag should be fully utilized to stabilize and solidify the ions in the high-concentration brine. If the surface runoff in the surrounding environment of the enterprise is abundant and the environmental sensitivity is low, safe and moderate discharge should be allowed." Liang Siyi explained.

Many steel enterprises in China are integrated into cities and are important components of cities. Many cities were born because of steel and prospered because of steel.

From the perspective of water resource circulation, steel enterprises are typical large users of urban water and drainage. Local governments should organize the construction of a regional water circulation system that includes steel enterprises, and steel enterprises should assume more urban responsibilities and actively become a key link in the urban regional water circulation.

"The Guiding Opinions on Promoting the High-Quality Development of the Steel Industry, issued in February 2022, clearly requires that existing urban steel plants should focus on in-situ transformation and upgrading. In this context, we should not view the relationship between steel and cities with a fragmented or antagonistic perspective. We should make overall plans, eliminate barriers, and promote the harmonious coexistence and coordinated development of steel and cities through the scientific construction of regional water resource circulation systems. This is also a need for high-quality development of industrial-city integration." said Liang Siyi.

Liang Siyi believes that through water recycling and reuse in local units such as enterprises and communities, sewage regeneration treatment and direct use in social systems such as industry and cities, and ecological intermediary recycling and reuse of reclaimed water at the regional level, we can better promote the organic connection and coupling of water recycling and reuse at different levels and for different purposes, achieving safe and efficient use of water resources and closed-loop recycling and reuse of water resources at the regional scale.

"In addition, both internal water circulation systems and regional water circulation systems in steel enterprises are complex non-traditional water supply projects. They have the characteristics of wastewater treatment systems as well as water supply systems. All parties should fully recognize their complexity." He believes that for complex system engineering, it is even more important to pay special attention to standardization work and highlight the leading role of standards, so that executors have standards to follow and regulations to abide by.

As an expert of the ISO/TC282/SC2 International Standardization Organization Water Reuse Technology Committee, Liang Siyi also pointed out that the steel industry can fully learn from ISO international standards and accelerate the formulation and revision of national standards in this field, such as ISO 20760, ISO 20761, and ISO 23070. These standards explain the design principles and methods of water reuse systems, the design requirements and key water quality indicators of key links in water reuse, and clarify the relationship between treatment processes, pipeline transmission and distribution, and utilization pathways. The multiple evaluation index systems and methods proposed have strong reference significance for the construction of a "safe, efficient, and economical" water circulation system in China's steel industry.

"Improving and perfecting evaluation standards is an urgent task, including technical evaluation indicators and benefit evaluation indicators. In particular, risk assessment standards for the ecological utilization of industrial wastewater should be established and improved as soon as possible." Liang Siyi frankly stated.