Water Use Efficiency Assessment of Cement Production Based on Life Cycle Analysis

Abstract

In the context of increasing water scarcity, improving industrial water efficiency and resource management has become an urgent need, particularly in water-intensive sectors such as the cement industry. Based on the Water Life Cycle Assessment (WLCA) framework, in this study, a comprehensive assessment of water use, consumption, reuse, and wastewater discharge during cement production was conducted, and paths were proposed for improving water efficiency. Unlike traditional water footprint assessments, which primarily focus on measuring water consumption, the WLCA integrates a holistic analysis of the operational status of water systems. The research results show that for cement production in the Yellow River Basin, the waste heat power generation system accounts for the highest proportion of water consumption (65%), with its circulating cooling unit functioning as the core water-related subsystem. A large quantity of daily circulating cooling wastewater can be reused in production after treatment. Significant differences exist in unit product water consumption among enterprise types: clinker and cement production enterprises (0.18–0.30 m³/t) have higher water consumption than cement grinding stations (0.02–0.05 m³/t), and some enterprises hold considerable water-saving potential. Wastewater recovery and treatment technologies can markedly reduce water wastage. Meanwhile, waste heat recovery technologies improve energy utilization efficiency and indirectly lower water cooling demand. Additionally, waste co-processing technologies reduce virtual water consumption by replacing part of the coal used in cement production. This research provides practical technical solutions for water conservation and resource optimization in the cement industry, facilitating improvements in water efficiency management.

1. Introduction

With the growing challenges posed by global climate change and water scarcity, the efficient use and conservation of water resources have become core issues that need to be addressed across various industries [1]. The cement industry, being a high-water consumption sector, is particularly dependent on water resources in its production process. As a fundamental material in national economic development [2], cement not only plays an essential role in China, but also in the global economy [3,4]. Since 1985, China has become the world’s largest cement producer [5], with production reaching 1.825 billion tons in 2024, representing nearly 47% of the global market share. This enormous production scale has resulted in significant water consumption, particularly in regions where water resources are relatively scarce, putting considerable pressure on these areas. For example, the Yellow River Basin accounts for 22% of China’s total cement output, but only 3.1% of its total water resources, and coupled with severe soil erosion and insufficient water conservation capacity there, the contradiction between water supply and demand has become extremely prominent. Cement production involves various stages, including raw material preparation, coal grinding, clinker calcination, and cement grinding [6], all of which are resource and energy-intensive processes with significant environmental impacts [7]. Water consumption is involved throughout the production process, making the improvement of water use efficiency a critical issue that needs to be addressed within the cement industry.

Currently, research on the cement industry mainly focuses on the application of waste materials as substitutes in cement raw materials [8,9,10], while studies aimed at improving water use efficiency in this sector are primarily concentrated in two directions: first, the optimization of water-saving technologies in the production process, and second, the exploration of water footprint assessment methodologies. However, existing studies have three distinct gaps. First, at the technical application level, the current water-saving research is mostly limited to the optimization of single processes (e.g., cooling water treatment in the clinker calcination stage) or individual equipment [11,12,13,14], lacking a linkage analysis of the entire “water intake–water use–wastewater discharge–water reuse” chain throughout the full production process from raw material preparation and coal grinding to cement grinding. In particular, it overlooks research on the potential of serial water allocation between different production units (e.g., circulating cooling systems and raw material homogenization systems). Second, at the methodological practice level, although the ISO 14046 water footprint standard has been applied to water consumption accounting at the cement enterprise level [15,16], the existing assessments mostly remain at the statistical level of total water consumption of the entire enterprise, without refining to the measurement of unit water consumption intensity of core equipment in each production stage (e.g., rotary kiln coolers, cement mill water spray devices), nor do they include quantitative analysis of key efficiency indicators such as wastewater reuse rate and freshwater substitution rate. Third, at the system synergy level, existing studies fail to conduct a coupled analysis of water-saving technologies with energy systems (e.g., cooling water demand for waste heat power generation) and waste co-processing (e.g., accounting for additional water consumption during co-processing), resulting in proposed water-saving schemes that are difficult to adapt to the actual scenario of “resource-energy–water” multi-system synergy in cement production.

This study aims to systematically explore the characteristics of water resource flow and consumption in various production links of the cement industry, assess its water-saving potential, and propose feasible water-saving strategies in combination with advanced technologies. It will provide scientific and accurate water-saving paths for the cement industry to support its green transformation process, and meanwhile offer valuable reference bases for the formulation of relevant policies.

2. Data Collection and Methods

This research introduces an innovative water resource management approach for the cement industry, combining the Water Life Cycle Assessment (WLCA) framework with modern data analysis techniques to promote sustainable water use. Through comprehensive data collection and analysis, as well as water balance testing and precise water lifecycle assessments, systematic water resource management plans are proposed to achieve efficient use and optimization of water resources.

2.1. Data Collection

The research objects for data collection in this study are cement production enterprises. Currently, constrained by factors such as market demand and transportation conditions, cement production enterprises are mainly classified into three categories: clinker-producing enterprises, cement-producing enterprises, and cement grinding enterprises. The differences in their production processes are shown in Figure 1. Cement production includes both clinker production and cement grinding.

A survey was conducted on the cement industry in the Yellow River Basin of China, with a total of 321 sets of raw data collected. After verification and analysis, invalid samples such as concrete mixing plants (non-cement production entities) and abnormal data values (domestic water consumption exceeds industrial water consumption, etc.) were excluded, and 218 sets of valid samples were finally confirmed. It should be noted that potential errors existed during data collection—for instance, partly due to the fact that many enterprises only installed a single water meter to measure overall water consumption, making it challenging to achieve fully precise segmentation of water use across different links. The valid sample set includes 88 cement production enterprises, 34 clinker production enterprises, and 96 cement grinding stations, providing a representative dataset. The output of the sample covers more than 30% of the total output in the region. The scope of the survey data covers water usage in all links of main production, auxiliary production (such as boilers), and auxiliary production (such as greening and canteens).

2.2. Water Balance Analysis

The study conducted a water balance test on a typical cement production enterprise in the Yellow River Basin. Water balance testing is a systematic process that measures, collects, and analyzes the water volume of a water unit or system. Based on the principle of water balance, it identifies issues and suggests continuous improvement measures. China’s GB/T 12452–2022 “General Principles of Water Balance Testing” standard [17], released in July 2022, provides guidelines on water balance diagrams and equations for water-consuming units. Compared with some research methods that focus on theoretical modeling or analysis of specific links, the water balance test adopted in this study centers on the full-process water use of enterprises. It is more standardized and systematic, covering specific test procedures and data accounting requirements, and features stronger practicality. Moreover, it can directly provide targeted improvement suggestions for enterprises.

The volume of water entering (input) and discharging (output) a relatively separate or complete water system or unit is expressed in terms of the direction of water flow, independent of its chemical composition and physical state. For different categories, such as recycled water and series water, we have clearly defined their water quantity information, as shown below:

• V_cy—the input recycled water volume, measured in cubic meters (m³);
• $V_{cy}\prime$—the output recycled water volume, measured in cubic meters (m³);
• V_i—the water intake volume, measured in cubic meters (m³);
• V_s—the input series water volume, measured in cubic meters (m³);
• $V_s\prime$—the output series water volume, measured in cubic meters (m³);
• V_t—the water usage volume, measured in cubic meters (m³);
• V_co—the water consumption volume, measured in cubic meters (m³);
• V_d—the drainage volume, measured in cubic meters (m³);
• V_l—the leakage and loss volume, measured in cubic meters (m³).

The basic water balance diagram and equation are shown in Figure 2 and Formula (1).

The core of the water balance equation lies in the “balance of water inflow and outflow”, meaning that for a water-consuming unit, the total volume of water it receives (inflow) always maintains a balanced relationship with the total volume of water it discharges or consumes (outflow):

$$V_{cy} + V_i + V_s=V_{cy}\prime + V_{co}+ V_d+ V_l+ V_s\prime$$

(1)

The calculation formula for water consumption per unit product (V_ui) is as follows. In the field of industrial production, it serves as a key metric for assessing water efficiency. By quantifying the volume of water consumed to produce each unit of product, enterprises can accurately gain insight into their own water efficiency performance. Meanwhile, it can also act as a benchmark for comparing water performance among different enterprises within the same industry, thereby promoting the formation of healthy competition focused on optimizing water use among enterprises.

$$V_{ui}={\displaystyle \frac{V_i}{Q}}$$

(2)

where

• $V_{ui}$—water intake per unit production, in cubic meters per ton (m³/t);
• $Q$—total cement or clinker production in the reporting period, in tons (t).

The calculation formula for water reuse rate (R) is as follows.

$$R={\displaystyle \frac{V_{cy}}{V_{cy}+V_i}}\times 100\%$$

(3)

where

• $R$—water reuse rate (%).

The calculation formula for reuse rate of wastewater (K_w) is as follows.

$$K_w={\displaystyle \frac{V_w}{V_w+V_d}}\times 100\%$$

(4)

where

• $K_w$—reuse rate of wastewater (%).
• $V_w$—sewage reuse, in cubic meters per ton (m³/t).

The calculation formula for integrated leakage rate of water use (K_l) is as follows.

$$K_l={\displaystyle \frac{V_l}{V_i}}\times 100\%$$

(5)

where

• $K_l$—integrated leakage rate of water use, (%).

2.3. Water Life Cycle Assessment (WLCA)

As shown in Figure 3, the WLCA framework, similar to the LCA (Life Cycle Assessment) defined in ISO 14040 [18], consists of four stages.

(1) Goal and Scope Definition: similarly to LCA, this step clarifies the goal, scope, and system boundaries of the assessment. In WLCA, the goal is usually to assess and quantify the water use, consumption, reuse, and wastewater discharge during the production process. This enables comparisons of water efficiency differences between different production systems or processes, optimization of water reuse, and determination of system boundaries (e.g., whether to include the raw material collection stage and product use stage of cement production). By defining these elements, it is ensured that the assessment results can effectively support water resource management and water-saving optimization decisions.

(2) Inventory Analysis: In WLCA, inventory analysis is a more complicated link because it involves the quantitative analysis of water flow, consumption, recycling, and wastewater discharge. The water consumption, wastewater discharge, and recycled water reuse in each production process need to be presented in detail in a system diagram, and the water inflow and outflow of different operation units should be calculated. Such data can be obtained from the actual production reports of cement plants, real-time water monitoring data, and environmental discharge monitoring reports.

(3) Impact Assessment: during the impact assessment process, the focus is on calculating the water-use potential in each production link and evaluating the water efficiency loss of each subsystem. By analyzing water consumption, wastewater discharge, and the potential reuse efficiency of water, the water resource utilization efficiency in the system can be assessed.

(4) Interpretation: water resource waste and ineffective consumption in various production links can be identified, and a basis for decision-makers to improve water efficiency can be provided. This helps to formulate specific measures for optimizing production processes, improving wastewater reuse, reducing water resource waste, and minimizing environmental impacts, thereby achieving more effective management and sustainable utilization of water resources.

3. Results

The research findings are organized around the core elements of the four stages in WLCA.

3.1. System Boundary Definition

Water use in cement production includes the following parts:

(a)

Primary production system water, including raw material preparation, clinker calcination, cement grinding, etc.;

(b)

Auxiliary production system water, including power, water supply, laboratory, machine repair, warehouse, transportation, raw material yard, waste heat recovery, etc.;

(c)

Ancillary production system water, including office buildings, landscaping, employee canteens, dormitories, bathrooms, road sprinkling, etc.

Regardless of the type of cement production enterprise, its boundary includes primary, auxiliary, and ancillary production systems.

3.2. Inventory Analysis

Based on the research data calculations, for cement production enterprises, water use is differentiated across different production processes. Due to the high water consumption of the waste heat power generation system, it is listed separately. The results show that the water consumption of the primary production system (excluding waste heat power generation) accounts for approximately 20% of the total water use. The water consumption of the waste heat power generation system accounts for approximately 65%, while the auxiliary production system accounts for about 7% and the ancillary production system accounts for approximately 8%. The proportion of water use in different enterprises may vary based on actual conditions.

For example, in a cement production enterprise in the Yellow River Basin with a 4000 t/d clinker production line and a 7.5 MW waste heat power generation unit, a water balance test was conducted following the requirements of GB/T 36536–2018 [19]. Based on the actual water-use data of the enterprise, a comprehensive balance method was employed to determine the water use, water intake, water recycled, and water consumption for each stage, as shown in

Table 1. System boundary water balance analysis statistical table.

Water Category		Water Used Vi + Vcy (m3/d)	Intake Water Vi (m3/d)	Recycled Water Vcy (Vcy’) (m3/d)	Water Consumption Vd + Vl + Vco (m3/d)
Main Production Water	Mineral powder mill	240.6	0.0	240.6	240.6
	Raw material mill	443.2	0.0	443.2	443.2
	Cement mill	74.7	0.0	74.7	74.7
	Circulating cooling water	9708.3	267.3	9441.0	192.6
Auxiliary Production Water	Waste heat power generation	48,653.4	941.9	47,711.5	184.5
	Chemical water treatment station	228.0	0.0	228.0	22.8
	Wastewater treatment station	1019.4	0.0	1019.4	81.6
	Sewage treatment station	44.5	0.0	44.5	4.5
	Boiler	100.0	0.0	100.0	10.0
	Steam turbine	90.0	0.0	90.0	25.0
	Laboratory	3.8	3.8	0.0	0.4
Subsidiary Production Water	Canteen	6.8	6.8	0.0	1.0
	Staff dormitory	25.0	14.0	0.0	1.3
	Office building	10.6	10.6	0.0	1.1
	Boiler room	684.0	10.0	674.0	8.0
	Transport fleet cleaning	25.2	25.2	0.0	25.2
	Watering truck	38.1	38.1	0.0	38.1

.

Among these, the waste heat power generation circulating cooling water unit is the most important and complex system involving water. Further discussion and analysis on this are provided in the water balance for all inputs and outputs shown in Figure 4 below.

The waste heat power generation circulating cooling water unit includes important facilities such as the water spray tank, waste heat power generation circulating water pool, and waste heat power generation cooling equipment, among others. Its water system involves facilities such as the wastewater treatment station, chemical water treatment station, boiler, and steam turbine. The water intake for the waste heat power generation circulating cooling water unit consists of both fresh water and reused water. Of the fresh water, 50% of the water volume flows into the water spray tank for equipment cooling and dust control, while the remaining 50% is used to replenish the circulating water pool for waste heat power generation. Additionally, 45,000 m³/d of water is used for circulating cooling in waste heat power generation, with the circulating water pool’s daily consumption being only 98 m³/d. Furthermore, approximately 860 m³/d of wastewater from the circulating cooling water will be sent to the wastewater treatment station. After treatment, approximately 680 m³/d is primarily used for production processes, such as in mineral grinding and raw material milling, with a small portion being returned to the waste heat power generation circulating water pool. Additionally, 200 m³/d is sent to the chemical water treatment station. After further treatment at the chemical water treatment station, the wastewater is returned to the wastewater treatment station, with a portion being directed to auxiliary production equipment such as boilers and steam turbines. The boilers and steam turbines are also part of the interconnected water volume.

3.3. Water Efficiency Analysis

As shown in Figure 5, in the Yellow River Basin, the water intake per unit production for clinker enterprises is mainly between 0.18 and 0.30 m³/t, while the water intake per unit production for cement enterprises is mainly between 0.18 and 0.29 m³/t. The water intake per unit production for cement grinding enterprises ranges from 0.02 to 0.05 m³/t.

In addition, through the water balance testing, other water consumption indicators of typical cement production enterprises were analyzed, as shown in

Table 2. Analysis of water consumption indicators.

Water Consumption Indicators	Water Reuse Rate	Reuse Rate of Wastewater	Integrated Leakage Rate of Water Use
Values	97.7%	100%	2.7%

. During the test period, the total water consumption in the production process of the enterprise was 61,058.88 m³/d, with the reused water volume reaching 59,680.88 m³/d, resulting in a water reuse rate of 97.7%. The amount of wastewater and sewage generated during the production process was 1063.9 m³/d. Among them, industrial wastewater was treated in the enterprise’s wastewater treatment station, and domestic sewage was processed through the sewage treatment station. Except for the water loss of 86.1 m³/d during the sewage treatment process, all other reclaimed water was reused, with a sewage reuse volume of 977.8 m³/d, achieving a 100% wastewater reuse rate for the enterprise. In addition, the water leakage in the production process of the enterprise was 37.3 m³/d, while the total water intake for production and domestic purposes was 1378 m³/d. The integrated leakage water rate was calculated to be 2.7%, which meets the requirement for general enterprises that the comprehensive water leakage rate should be ≤3%.

4. Discussion

4.1. System Boundary and Inventory Analysis

The system boundary encompasses primary, auxiliary, and ancillary production systems because these three collectively form the enterprise’s complete production and operational framework, with each being indispensable. Primary production constitutes the core water usage process, auxiliary production provides support for it, and ancillary production serves as the essential safeguard for enterprise operations. Focusing solely on a single process would result in an incomplete water usage assessment.

From the water balance inventory data, there are significant differences in the water use characteristics of the different segments. Water intake refers to the amount of water obtained from various water sources or through different means; water consumption is the sum of the water intake and the recycled water volume of a water-use unit; water consumption (here referring to net consumption) is the amount of water that is consumed and lost in various forms during production and operation activities and cannot return to surface water bodies or underground aquifers. Under normal circumstances, the water used equals the sum of water intake and water recycled. When the water intake is zero, and the water used equals the water recycled, such as in the raw material mill and cement mill stages, it indicates that the water used in this stage comes entirely from the treatment and reuse of wastewater from other stages. When the water used equals the water intake, such as in the canteen, staff dormitories, and office buildings, it represents that the water in this stage is entirely sourced from fresh water. The recycled cooling water in the circulation cooling system amounts to 9220.5 m³/d, which is 33 times the water intake, indicating that a large volume of water is reused within the system. In contrast, when the water used exceeds the water consumption, such as in the waste heat power generation and wastewater treatment stations, it indicates that the water in these stages is consumed due to production and living activities, and the remaining water is collected and treated for reuse. When the water used equals the water consumption, such as in the cleaning of fleet vehicles and water trucks, it means the water in these stages is entirely consumed with no recovery or reuse.

The circulating cooling water unit for waste heat power generation constitutes a complex water-intensive environment, underscoring its pivotal role within the enterprise’s water management system. Not only does this unit itself consume substantial volumes of water with a high recycling rate, but through its integration with facilities such as the wastewater treatment plant and chemical water treatment station, it facilitates the cascading utilization of water resources across different production stages. This makes it a key entry point for enhancing the enterprise’s overall water efficiency.

4.2. Analysis of Differences in Water-Use Efficiency

The core operation of cement grinding enterprises is solely the grinding and processing of cement products, which does not involve water-intensive links such as high-temperature calcination or waste heat power generation. These enterprises only require a small volume of circulating water for equipment cooling, leading to relatively low unit water consumption. In contrast, the medium-to-high unit water intake range of 0.18–0.45 m³ per ton production is entirely attributed to clinker production enterprises and integrated cement production enterprises. Both types of enterprises incorporate core water-intensive processes: clinker calcination, which demands large quantities of water for cooling, and waste heat power generation, which relies on circulating water to sustain the operation of generator sets. As a result, their baseline water consumption is considerably higher than that of cement grinding enterprises.

Notably, even within the same type of enterprise (e.g., clinker production enterprises), there exists a significant gap in water use efficiency, primarily due to differences in water-saving capabilities. For instance, enterprises that fully collect, treat, and reuse wastewater can substantially reduce fresh water intake, while those with incomplete wastewater recycling systems have higher water consumption. Additionally, the choice of production process—whether dry process or wet process—also plays a key role: wet process cement production typically consumes more water for raw material slurry preparation compared to dry process cement production, further widening the efficiency gap. The water withdrawal per unit of product of some clinker and cement enterprises is as high as 0.45 m³/t, which is significantly different from the industry average, indicating that there is much room for improvement in the optimization of the water consumption process, water-saving transformation of equipment, and recycling of water resources. The typical enterprise’s 97.7% water reuse rate, 100% wastewater reuse rate and 2.7% comprehensive leakage rate (to meet the general requirements of enterprises ≤ 3%) provides the industry with a benchmark for water conservation–through improving the water recycling system, strengthening wastewater treatment and reuse and strengthening the control of leakage, water efficiency can be effectively improved. The water efficiency can be effectively improved by improving the water recycling system, strengthening the reuse of wastewater treatment and enhancing leakage control.

4.3. Suggestions and Optimization

Based on the research and data analysis of different types of cement production enterprises, the improvement of water use efficiency can be achieved through the following approaches. Furthermore, through international comparative analysis, the applicable boundaries and promotion value of the research conclusions are clarified.

4.3.1. Wastewater Recovery and Treatment

One of the most effective ways for cement plants to improve water use efficiency is through the classification, collection, treatment, and reuse of wastewater, which includes, but is not limited to, the following aspects.

In the main production processes, wastewater from the circulating water pool in clinker cement production can be directly used in cement grinding and other processes after treatment.

In auxiliary production processes, the industrial water overflow from the water spray tank serves to reduce the temperature of the water spray tank and improve the vacuum level of the steam turbine. It does not mix with other water qualities, and its water quality is essentially the same as the input industrial water quality. Therefore, it can be directly collected for use as circulating water in the waste heat power generation system. Currently, it is common to use newly added reclaimed water tanks and water pumps to collect the overflow from the water spray tank and transport it back to the circulating water pool as supplemental water for the cooling tower. In the collection process of boiler blowdown, since the temperature of the discharged wastewater is relatively high, directly discharging it would affect the quality of other wastewater. Therefore, a cooling well needs to be added to lower its temperature to an ambient temperature before collection. This can also help precipitate a small amount of sediment. Wastewater from the condensate tank, boiler blowdown, chemical water treatment plant, cooling system, and other sources can be collected together based on actual conditions. After adjustment and dosing, they can be treated together, as shown in Figure 6.

In auxiliary production processes, domestic sewage can be treated and reused for purposes such as mining water or landscaping. This classification and treatment approach not only reduces waste, but also achieves energy-saving goals.

The core logic of “classification–treatment–reuse” for wastewater is universally applicable, especially in water-scarce regions. In China, cement enterprises are dominated by large-scale new dry-process production lines (with a single-line capacity of ≥5000 t/d), which have the site and financial conditions to construct centralized wastewater treatment systems. The standardized configuration of “reclaimed water tanks + frequency-conversion water pumps” is suitable for large-scale production needs. However, for small- and medium-sized cement enterprises (with a capacity of <5000 t/d) in other countries, “integrated wastewater treatment equipment” can be used to replace centralized systems, reducing initial investment while achieving considerable water-saving benefits.

4.3.2. Waste Heat Power Generation

During the cement production process, a large amount of thermal energy is generated, especially during the high-temperature firing stage (such as in the cement kiln). If this thermal energy is not effectively utilized, it is typically wasted or discharged into the environment. Waste heat power generation technology recovers waste heat from the cement production process and converts it into electrical energy, which can effectively improve energy utilization efficiency [16,20,21]. The introduction of waste heat power generation technology helps reduce the demand for external energy.

Although the implementation of waste heat power generation technology does not directly reduce water consumption in cement plants and may even increase water consumption in some cases, it effectively reduces the demand for cooling water in external power systems, especially in traditional coal-fired power plants. In traditional power generation processes, a large amount of cooling water is used to maintain the temperature stability of generating equipment, especially under high-temperature operating conditions. By substituting for external power needs with internal waste heat power generation in cement plants, part of the external electricity demand is shifted, thereby indirectly reducing the cooling water consumption in traditional power production processes. Although water consumption within the cement plant may slightly increase, this substitution effect reflects the application of the “virtual water” concept in lifecycle assessment (LCA) [22], meaning the water resources saved in external power production.

The amount of electricity generated from waste heat in cement plants is closely related to the scale and output of the production line. The actual electricity generation is influenced by various factors, including exhaust gas temperature, flow rate, generator efficiency, and system design. Generally, the waste heat generated per ton of cement produced can be used to generate about 70–150 kWh of electricity [23]. According to the current average water efficiency of China’s thermal power industry, which is 1.22 m³/(MW·h), it is estimated that waste heat power generation per ton of cement can save approximately 0.09–0.19 m³ of virtual water. This water-saving effect indicates that the application of waste heat power generation technology in cement production is not only significant for energy conversion, but also makes a positive contribution to water resource conservation.

With over 95% of cement kilns in China being new dry-process types, the waste heat from these kilns, characterized by stable temperature and large flow, offers favorable resource support for waste heat power generation. Additionally, the technology’s core mechanism—replacing external electricity via industrial waste heat recovery—is highly applicable to thermal-power-dependent countries, enabling wide-scale promotion.

4.3.3. Co-Processing Solid Waste Treatment

As global waste solid disposal issues become increasingly severe, co-processing waste treatment technology, as an innovative method, is gradually becoming an important approach for the cement industry to reduce solid waste and optimize resource usage.

As a crucial link throughout the entire life cycle of cement production, encompassing raw material acquisition, energy consumption, and waste disposal, solid waste co-processing technology exhibits systematic and synergistic effects in optimizing water use efficiency.

From the perspective of the raw material acquisition stage, by replacing traditional mineral raw materials such as limestone and clay with municipal solid waste and industrial solid waste [24,25], co-processing not only reduces water consumption during the extraction of natural minerals (e.g., water used for dust suppression in mining and cleaning during raw material transportation), but also avoids the damage to the regional water resource conservation capacity caused by mineral resource exploitation.

In the production and energy consumption stage, the organic components in waste are converted into thermal energy required for cement production through high-temperature calcination, replacing the traditional energy supply mode of coal combustion [26,27]. This process not only reduces the indirect water use in coal mining and transportation, but also decreases the loss of cooling circulating water in the production system by optimizing the energy structure, directly improving the “net water use efficiency” of unit products (i.e., the proportion of actual effective water use after deducting indirect water use).

From the perspective of the waste disposal stage, the co-processing technology integrates solid waste that would otherwise be treated by landfilling or incineration into the cement production system. This avoids “end-of-pipe disposal water use” such as water for leachate treatment in landfills and flue gas purification in incineration plants, while also reducing the interference of landfill land occupation on the surface water resource cycle.

This model of “using production to consume waste and using waste to support production” achieves the minimization of water resource consumption throughout the entire life cycle of “raw material mining–manufacturing–waste disposal”.

Household waste is divided into kitchen waste and other waste. The other waste requires pretreatment, including processes such as crushing, screening, sorting, and iron removal, to separate it into combustible and non-combustible materials. Combustible materials (such as paper, rubber, plastics, etc.) are crushed and compressed with CaO to form new types of RDF (refuse-derived fuel) made from sorted household waste [28], which replaces part of the coal used in cement kilns. Non-combustible materials (such as bricks, ceramics, metals, etc.) are used as alternative raw materials and are ground together with the raw materials. The moisture in kitchen waste is used for pre-homogenization and no separate drying is required. After pre-homogenization, it enters the batching system. The process flow is shown in Figure 7.

Based on the concept of virtual water in water footprint theory, the changes in water consumption for cement production during the co-processing of waste were further explored. Liang et al. [29] analyzed the basic data on the resources, energy, and household waste treatment required for producing one ton of clinker under conventional production and co-processing disposal modes. In this context, conventional production represents the traditional cement (clinker) production model, while co-processing disposal refers to the situation where waste is co-processed. By combining the water intensity of various resources and energy in industrial production [30], the water consumption for different stages was quantitatively calculated, as shown in Figure 8. The results indicated that co-processing waste primarily reduces the use of coal, thereby decreasing virtual water consumption. Specifically, for each ton of clinker produced through waste co-processing, approximately 37.5 tons of coal usage can be reduced, equivalent to a reduction of 0.18 m³ of water. In addition, each ton of clinker production consumes approximately 200 kg of household waste, which requires about 0.11 m³ of water for processing at the cement plant. In contrast, the incineration of the same volume of waste for power generation requires 0.29 m³ of water. The impact of co-processing waste on the consumption of non-metallic minerals, electricity, and diesel is negligible. In summary, cement production under the solid waste co-processing model saves about 0.36 m³ of virtual water per ton (clinker) of cement produced.

China has established a sound urban domestic waste collection and transportation system, and large cement enterprises can obtain a stable supply of waste raw materials through government–enterprise cooperation mechanisms. At the same time, new dry-process technology dominates domestic cement kilns, which feature uniform and stable temperature field distribution inside the kilns and can accommodate a co-combustion ratio of waste-derived fuel (RDF) within 15%. However, traditional shaft kilns struggle to meet this technical requirement due to issues such as insufficient temperature control accuracy. In view of this, this solid waste co-disposal technology holds significant practical reference value for countries facing the dual challenges of prominent solid waste disposal pressure and energy supply shortage.

5. Conclusions

Based on the life cycle assessment framework, this study conducts a systematic evaluation of water use efficiency in the cement industry within the Yellow River Basin and proposes practical water-saving strategies.

• Through the analysis of water use indicators such as water intake per unit product at the overall level of the Yellow River Basin, the study finds that there are significant differences in water use efficiency among different enterprises, indicating substantial potential for optimization. Meanwhile, the results of water balance testing carried out on typical enterprises show that their water reuse and pipe network leakage control are in good condition.
• The application of wastewater recovery and treatment technologies is considered key to improving water efficiency. By classifying, collecting, and treating wastewater from different sources, not only can water resource waste be effectively reduced, but environmental pollution during the production process can also be minimized.
• Waste heat power generation technology not only improves energy utilization efficiency but also indirectly reduces the cooling water demand for external power generation.
• Co-processing waste treatment technology, by replacing part of the coal and natural mineral raw materials, effectively reduces virtual water consumption in the cement production process.

However, the impact of long-term climate fluctuations on water use efficiency has not been adequately addressed. The virtual water accounting relies on industry-average parameters, and errors arising from regional technological disparities require further refinement and correction. Subsequent research could establish a multi-dimensional spatiotemporal assessment system for water resource utilization efficiency within the cement industry, thereby enhancing the scientific rigor and practical applicability of the findings.

In conclusion, there is considerable room for improvement in the optimization of water resource management in the cement industry. By introducing advanced water-saving technologies and management methods, and integrating water efficiency analysis throughout the life cycle, personalized water-saving strategies can be formulated based on the water usage of different enterprises. This approach not only helps reduce water consumption, but also effectively enhances water resource utilization efficiency in the cement industry, promoting the green transformation and sustainable development of the cement sector. It provides scientific support for policymakers, helping the cement industry achieve their efficient production goals in the context of resource scarcity.