### Title: A Study on Foreign Sewage Treatment Equipment
#### Abstract
With the acceleration of global industrialization and urbanization, water pollution has become an increasingly severe environmental problem, seriously threatening human health and sustainable development. Against this background, the study of foreign sewage treatment equipment is of great significance. This paper conducts an in - depth analysis of foreign sewage treatment equipment through methods such as literature research and case analysis. The research findings show that foreign sewage treatment equipment has evolved from simple physical treatment devices in the early days to highly efficient and intelligent integrated systems today. The mainstream equipment currently in use, such as physical treatment equipment (screens, grates, sedimentation tanks), chemical treatment equipment (coagulation and flocculation units, chemical dosing systems), and biological treatment equipment (activated sludge systems, trickling filters, and biological rotating discs), each has its own characteristics and applicable scenarios. In addition, this paper discusses the technological innovation, operational issues, and future trends of foreign sewage treatment equipment, aiming to provide useful references for the development of domestic sewage treatment equipment and the improvement of sewage treatment capabilities.
#### Abstract
With the acceleration of global urbanization and industrialization, the problem of water pollution has become increasingly severe, posing serious threats to the ecological environment, human health, and sustainable social development. As an important means of solving water pollution problems, the research and development of sewage treatment equipment are crucial. This paper focuses on foreign sewage treatment equipment, systematically reviews its development history, analyzes the current mainstream equipment technologies, and looks ahead to future development trends. Through methods such as literature research and case analysis, the study finds that foreign sewage treatment equipment has evolved from simple physical treatment devices in the early days to highly efficient and integrated modern systems, with continuous technological innovation driving the improvement of treatment efficiency and environmental friendliness. Studying foreign sewage treatment equipment helps to learn from advanced technologies and experiences, providing theoretical and practical references for the optimization and development of domestic sewage treatment equipment, and contributing to global environmental protection and sustainable development.
**Keyword:** A translation of the Chinese keywords, accurately reflecting the content of the Chinese keywords.
#### 1. Introduction
##### 1.1 Global Water Resource and Pollution Status
The global water resource situation is becoming increasingly severe, with water pollution posing a significant threat to the environment, human health, and social development. According to relevant reports, water resources are unevenly distributed worldwide, and many regions face water scarcity due to population growth and climate change [[doc_refer_6]]. In addition, the discharge of untreated or inadequately treated sewage into water bodies has led to widespread water pollution, particularly in developing countries. Excessive nitrogen and organic matter in wastewater can cause eutrophication, leading to the depletion of dissolved oxygen and the death of aquatic organisms [[doc_refer_7]]. Moreover, polluted water sources directly affect human health by increasing the risk of waterborne diseases, such as cholera and typhoid fever. From a social development perspective, water pollution hinders economic growth, especially in industries dependent on clean water resources, such as agriculture and fisheries. Therefore, understanding the current status of global water resources and pollution is crucial for developing effective strategies to address this issue.
##### 1.2 Importance of Sewage Treatment
Sewage treatment plays a vital role in environmental protection, human health, and sustainable development. Through the removal of pollutants from wastewater, sewage treatment helps prevent water pollution and protect ecosystems. Advanced treatment technologies can significantly reduce the environmental impact of wastewater discharge, thus maintaining the ecological balance of water bodies [[doc_refer_4]]. From a public health perspective, efficient sewage treatment reduces the risk of waterborne diseases and improves the quality of drinking water sources, contributing to better human health outcomes. Furthermore, sewage treatment is essential for sustainable development as it promotes the circular economy by recycling water and nutrients. For example, treated wastewater can be reused for agricultural irrigation or industrial processes, alleviating water scarcity in many regions [[doc_refer_11]]. The development and application of advanced sewage treatment equipment are key to achieving these goals, as they enhance treatment efficiency and reduce operational costs. Therefore, investing in advanced sewage treatment equipment is not only an environmental necessity but also a strategic choice for long-term sustainability.
##### 1.3 Significance of Studying Foreign Sewage Treatment Equipment
Studying foreign sewage treatment equipment is of great importance for improving domestic sewage treatment capabilities and addressing water pollution challenges. Many developed countries have accumulated rich experience in sewage treatment over the past century and have developed advanced technologies and equipment. For instance, the United States, Japan, and European countries have pioneered various treatment technologies, including activated sludge systems, membrane technology, and intelligent control systems, which have significantly improved treatment efficiency and reduced environmental impacts [[doc_refer_1]][[doc_refer_2]]. By learning from these experiences, developing countries can avoid common pitfalls and adopt more efficient and sustainable treatment solutions. Moreover, studying foreign equipment provides opportunities for technology transfer and innovation, enabling domestic industries to develop tailored solutions that meet local needs. Comparative studies on domestic and foreign sewage treatment equipment have shown that there is considerable room for improvement in terms of technology integration, energy efficiency, and operational management [[doc_refer_1]][[doc_refer_2]]. Therefore, studying foreign sewage treatment equipment is not only a means of learning from best practices but also a catalyst for technological advancement and environmental protection.
#### 2. Literature Review
##### 2.1 Theoretical Basis of Sewage Treatment
Sewage treatment is a complex process that involves the removal of contaminants from wastewater using physical, chemical, and biological methods. Physical treatment principles focus on the separation of solid particles from water through processes such as sedimentation, filtration, and screening. These methods are based on the differences in size, density, and shape of pollutants, and are often used as preliminary steps in sewage treatment plants[[doc_refer_3]]. Chemical treatment principles involve the use of coagulants, flocculants, and disinfectants to neutralize or remove dissolved and colloidal impurities. The mechanisms behind chemical treatment include precipitation, oxidation-reduction reactions, and adsorption phenomena, which play a crucial role in the removal of organic and inorganic pollutants[[doc_refer_6]]. Biological treatment principles utilize microorganisms to degrade organic matter and convert harmful substances into less toxic forms. Activated sludge systems, trickling filters, and anaerobic digesters are examples of biological treatment technologies that rely on the metabolic activities of bacteria, fungi, and other microorganisms[[doc_refer_3]]. The combination of these three treatment principles forms the theoretical foundation of modern sewage treatment equipment, enabling the efficient removal of a wide range of pollutants from wastewater.
##### 2.2 Development of Foreign Sewage Treatment Equipment Research
The research and development of sewage treatment equipment in foreign countries have a long history, dating back to the 19th century when simple devices such as septic tanks and sedimentation tanks were first introduced. These early devices were designed to address the basic needs of sanitation and public health in rapidly urbanizing areas. However, they were limited in their treatment capacity and efficiency, often resulting in incomplete removal of pollutants[[doc_refer_1]]. In the mid-20th century, significant advancements were made with the development of activated sludge systems and biological filters, which marked a transition from simple physical separation to more sophisticated biological treatment processes. These technologies improved treatment efficiency and enabled the removal of dissolved organic matter and nutrients from wastewater[[doc_refer_2]]. By the late 20th century, advanced membrane technology and integrated treatment systems emerged, further enhancing the performance of sewage treatment equipment. Membrane bioreactors (MBRs) and advanced oxidation processes (AOPs) were introduced to address the challenges of treating complex wastewater streams, such as those containing high concentrations of nitrogen and phosphorus[[doc_refer_3]]. Despite the continuous improvement in treatment efficiency, each stage of development was accompanied by its own set of limitations, including high energy consumption, membrane fouling, and the need for skilled operation and maintenance personnel.
##### 2.3 Research Gaps and Trends
Despite the significant progress in sewage treatment equipment research, several gaps remain to be addressed. One of the main challenges is the development of cost-effective and energy-efficient technologies that can meet the increasing demand for water reuse and resource recovery[[doc_refer_3]]. Existing treatment systems often require high capital investment and operational costs, making them less accessible in developing countries. Additionally, the issue of membrane fouling in advanced membrane technology remains a major obstacle to its widespread application[[doc_refer_8]]. To address these gaps, current research trends are focused on the development of emerging technologies, such as intelligent control systems, integrated treatment approaches, and green and sustainable equipment. Intelligent control systems utilize automation and remote monitoring to optimize treatment processes and reduce operational costs[[doc_refer_3]]. Integrated treatment approaches aim to combine multiple treatment technologies in a single unit, thereby reducing the footprint and energy requirements of treatment plants[[doc_refer_8]]. Green and sustainable equipment focuses on the use of renewable materials and energy-efficient processes to minimize the environmental impact of sewage treatment. These trends are expected to shape the future of sewage treatment equipment research and development, leading to more efficient and environmentally friendly solutions for wastewater management.
#### 3. Development History of Foreign Sewage Treatment Equipment
##### 3.1 Early Stage (19th - Early 20th Century)
The early stage of sewage treatment equipment development in foreign countries can be traced back to the 19th century, when simple sedimentation tanks and septic tanks were widely used as primary treatment devices. Sedimentation tanks functioned based on the principle of gravity separation, where wastewater was allowed to flow through a large chamber, enabling solid particles to settle at the bottom as sludge [[doc_refer_2]]. This process effectively removed large suspended solids but had limited efficiency in addressing dissolved pollutants or pathogenic microorganisms. Septic tanks, on the other hand, utilized anaerobic microbial activity to break down organic matter present in domestic wastewater. The basic design of septic tanks included an underground chamber where wastewater was stored, allowing solids to settle and undergo partial decomposition by anaerobic bacteria [[doc_refer_11]]. While these early devices provided a rudimentary solution for sewage management, their treatment efficiencies were relatively low, and they often failed to meet the growing demands of urbanization and industrialization.
Despite their simplicity, these early treatment methods played a crucial role in mitigating the public health risks associated with untreated sewage discharge. However, their limitations became increasingly evident over time. For instance, sedimentation tanks required large land areas for construction and were prone to clogging due to the accumulation of settled solids. Septic tanks, although widely adopted in rural areas, faced issues such as odor emission, ground water contamination, and the need for frequent maintenance [[doc_refer_2]]. Moreover, the lack of standardized design guidelines and regulatory frameworks during this period further exacerbated the challenges associated with these early treatment technologies. These limitations necessitated the development of more advanced and efficient sewage treatment equipment in subsequent stages.
##### 3.2 Development Stage (Mid-20th Century - Late 20th Century)
The mid-20th century marked a significant advancement in the development of sewage treatment equipment, with the introduction of activated sludge systems and biological filters as more sophisticated treatment technologies. Activated sludge systems, first developed in the early 20th century, gained widespread adoption during this period due to their superior treatment efficiency and versatility. The working principle of activated sludge systems involves the use of aerobic microorganisms to degrade organic pollutants present in wastewater. Wastewater is mixed with a suspension of microorganisms in an aeration tank, where oxygen is supplied to promote biological oxidation processes. The treated water is then separated from the microbial biomass in a secondary sedimentation tank, and a portion of the activated sludge is recycled back to the aeration tank to maintain the microbial population [[doc_refer_1]]. This cyclic process significantly improved the removal efficiency of organic matter and suspended solids compared to earlier treatment methods.
Biological filters, another important innovation during this period, utilized fixed media such as gravel, plastic, or ceramic substrates to support the growth of microbial biofilms. Wastewater is trickled over the filter media, allowing microorganisms to adhere and form biofilms that degrade organic pollutants through aerobic metabolism. Biological filters, including trickling filters and rotating biological contactors (RBCs), offered advantages such as lower energy consumption and simpler operation compared to activated sludge systems. However, they were more susceptible to clogging and had limited capacity for handling high-strength wastewater [[doc_refer_3]]. Despite these limitations, the development of activated sludge systems and biological filters represented a major leap forward in sewage treatment technology, enabling more efficient removal of pollutants and better compliance with emerging environmental regulations.
The technological advancements during this period were driven by several factors, including the increasing awareness of water pollution impacts on public health and ecosystems, as well as the development of more robust materials and engineering techniques. For example, the introduction of synthetic materials for filter media and aeration systems enhanced the performance and reliability of treatment equipment. Additionally, the establishment of standardized design guidelines and regulatory frameworks by organizations such as the U.S. Environmental Protection Agency (EPA) and the European Union further facilitated the widespread adoption of these advanced treatment technologies [[doc_refer_1]]. These developments laid the foundation for the modernization of sewage treatment infrastructure in many countries and significantly improved the overall quality of treated wastewater.
##### 3.3 Modern Stage (21st Century - Present)
The modern stage of sewage treatment equipment development is characterized by the emergence of advanced membrane technology and integrated treatment systems, which have revolutionized the field of wastewater management. Membrane technology, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), has gained prominence due to its exceptional ability to remove a wide range of contaminants, including pathogens, suspended solids, and dissolved organic and inorganic compounds. Membrane bioreactors (MBRs), which combine biological treatment processes with membrane filtration, have become particularly popular in both municipal and industrial wastewater treatment applications. MBRs offer several advantages over conventional treatment methods, such as higher treatment efficiency, smaller footprint, and improved effluent quality suitable for reuse applications [[doc_refer_3]].
Integrated treatment systems, on the other hand, represent a holistic approach to wastewater management by combining multiple treatment processes within a single unit. These systems typically integrate physical, chemical, and biological treatment steps to achieve comprehensive pollutant removal. For example, some integrated treatment systems utilize coagulation, flocculation, sedimentation, and advanced oxidation processes (AOPs) in combination with biological treatment to address complex wastewater matrices. The advantages of integrated systems include reduced space requirements, simplified operation, and enhanced treatment flexibility. However, the high capital and operational costs associated with these technologies pose significant challenges, particularly in resource-constrained regions [[doc_refer_5]].
Despite the numerous advantages offered by advanced membrane technology and integrated treatment systems, several challenges remain. Membrane fouling, for instance, is a common issue that can lead to reduced permeability and increased operational costs. Additionally, the energy requirements of membrane processes, especially RO, are relatively high, raising concerns about sustainability and environmental impacts. To address these challenges, ongoing research focuses on the development of novel membrane materials with improved fouling resistance, as well as the optimization of treatment processes to minimize energy consumption and operational costs [[doc_refer_3]][[doc_refer_5]]. These advancements, coupled with the growing emphasis on sustainability and resource recovery, are expected to shape the future of sewage treatment equipment development.
#### 4. Analysis of Current Mainstream Foreign Sewage Treatment Equipment
##### 4.1 Physical Treatment Equipment
###### 4.1.1 Screens and Grates
Screens and grates are preliminary physical treatment devices widely used in sewage treatment plants to remove large solids from wastewater. These devices serve as the first line of defense, preventing clogging and damage to downstream equipment by intercepting floating debris, plastics, and other coarse particles [[doc_refer_3]]. Based on their structure and operation mechanism, screens can be classified into coarse screens, fine screens, and ultra-fine screens. Coarse screens typically have openings ranging from 10 to 50 mm and are designed to capture larger objects, while fine screens with openings below 5 mm are used to remove smaller particles. Grates, on the other hand, are usually installed at the inlet of treatment plants and designed to handle high flow rates, making them suitable for applications with variable water volumes [[doc_refer_8]].
The working principle of screens and grates is relatively simple yet highly efficient. Wastewater passes through the screen or grate surface, allowing liquid to flow through while retaining solids. The trapped solids are then removed through mechanical raking or washing mechanisms, which discharge the collected material for further processing or disposal. The efficiency of these devices in removing large solids is remarkable, with fine screens capable of achieving removal rates of up to 90% for particles larger than 1 mm [[doc_refer_3]]. However, their performance can be affected by factors such as the consistency of wastewater, the frequency of maintenance, and the design of the screening mechanism.
Screens and grates find application in a variety of scenarios, particularly in municipal wastewater treatment plants and industrial facilities where the removal of large solids is crucial for subsequent treatment processes. In decentralized treatment systems, such as those commonly used in North America, screens are often integrated into pre-treatment units to protect advanced treatment equipment from damage caused by large particles [[doc_refer_8]]. Additionally, their modularity and scalability make them suitable for both small-scale and large-scale treatment plants, further enhancing their versatility in different treatment contexts.
###### 4.1.2 Sedimentation Tanks
Sedimentation tanks are essential components of physical sewage treatment systems, designed to remove suspended solids through the principle of gravitational settling. These tanks play a crucial role in separating solid particles from wastewater, thereby reducing the organic load and improving the overall quality of treated effluent [[doc_refer_1]]. The working principle of sedimentation tanks is based on the difference in specific gravity between solid particles and water. As wastewater enters the tank, the flow velocity is reduced, allowing heavier particles to settle to the bottom of the tank, while lighter particles float to the surface as scum.
There are several types of sedimentation tanks, each designed to meet specific treatment requirements. Primary sedimentation tanks are typically used after screening to remove settleable solids and floating matter before biological treatment. Secondary sedimentation tanks, on the other hand, are employed after biological treatment processes to separate biomass from treated wastewater. Additionally, specialized types such as inclined plate sedimentation tanks and lamella clarifiers utilize inclined plates or parallel channels to increase settling area and improve separation efficiency [[doc_refer_3]].
The advantages of sedimentation tanks include their relatively simple design, low energy consumption, and high reliability. However, they also have certain limitations. For example, the removal efficiency of sedimentation tanks can be affected by factors such as wastewater flow rate, particle size distribution, and temperature. Additionally, the accumulation of sludge at the bottom of the tank requires regular removal and disposal, which can increase operational costs if not managed properly [[doc_refer_1]]. Despite these challenges, sedimentation tanks remain an indispensable part of many sewage treatment systems due to their effectiveness in removing suspended solids and their compatibility with other treatment processes.
##### 4.2 Chemical Treatment Equipment
###### 4.2.1 Coagulation and Flocculation Units
Coagulation and flocculation are chemical treatment processes used to remove colloidal particles and fine suspended solids from wastewater. These processes involve the addition of coagulants and flocculants to destabilize colloidal particles and promote their aggregation into larger flocs, which can then be removed through sedimentation or filtration [[doc_refer_3]]. Coagulants, such as aluminum sulfate and ferric chloride, work by neutralizing the surface charge of colloidal particles, allowing them to come into contact and form micro-flocs. Flocculants, on the other hand, are long-chain polymers that facilitate the formation of larger, more stable flocs through bridging and entanglement mechanisms [[doc_refer_7]].
The effectiveness of coagulation and flocculation in removing colloidal particles depends on several factors, including the type and concentration of coagulant and flocculant used, the pH of wastewater, and the mixing conditions. Research has shown that the optimal coagulant dosage and pH conditions can significantly improve treatment efficiency, with removal rates of up to 90% for turbidity and organic matter reported in some cases [[doc_refer_3]]. However, the selection of appropriate chemicals is crucial, as excessive dosages can lead to increased sludge production and higher treatment costs. Additionally, the environmental impacts of chemical residues in treated wastewater must be carefully considered to ensure compliance with regulatory standards [[doc_refer_7]].
Coagulation and flocculation units are commonly used in both municipal and industrial wastewater treatment plants, particularly in cases where the removal of colloidal particles is essential for meeting effluent quality requirements. In integrated treatment systems, such as those employed in European countries, these processes are often combined with advanced membrane technology to achieve high levels of pollutant removal [[doc_refer_3]]. The versatility and effectiveness of coagulation and flocculation make them indispensable components of many modern sewage treatment facilities.
###### 4.2.2 Chemical Dosing Systems
Chemical dosing systems play a critical role in sewage treatment by providing precise control over the addition of chemicals required for various treatment processes, such as coagulation, disinfection, and pH adjustment [[doc_refer_3]]. These systems typically consist of chemical storage tanks, metering pumps, mixing devices, and control panels, which allow operators to adjust chemical dosages based on real-time process conditions. The primary function of chemical dosing systems is to ensure that the correct amount of chemical is added at the right time, thereby optimizing treatment efficiency while minimizing chemical consumption and associated costs [[doc_refer_8]].
There are several types of chemical dosing systems, each designed to meet specific treatment requirements. Manual dosing systems rely on operator intervention to adjust chemical feed rates, while automatic dosing systems utilize sensors and control algorithms to achieve continuous and precise chemical addition. Intelligent dosing systems, which incorporate advanced process control technologies, can further enhance dosing accuracy by analyzing real-time data and adjusting chemical feed rates accordingly [[doc_refer_3]].
The application scenarios of chemical dosing systems are diverse, ranging from small-scale decentralized treatment systems to large-scale municipal treatment plants. In decentralized systems, such as those commonly used in Japan and South Korea, chemical dosing systems are often integrated into compact treatment units to ensure efficient operation with minimal operator intervention [[doc_refer_8]]. In larger treatment plants, chemical dosing systems are used in conjunction with other treatment processes, such as coagulation and flocculation, to achieve high levels of pollutant removal. The precise control provided by these systems not only improves treatment efficiency but also reduces the environmental impact of chemical residues in treated wastewater, making them an essential component of modern sewage treatment facilities.
##### 4.3 Biological Treatment Equipment
###### 4.3.1 Activated Sludge Systems
Activated sludge systems are widely used in biological sewage treatment due to their high efficiency in removing organic pollutants and nutrients from wastewater [[doc_refer_1]]. The working principle of activated sludge systems is based on the growth and metabolism of microorganisms, which utilize organic matter in wastewater as a source of energy for their growth and reproduction. In a typical
