【Frontiers of HaiChuan Technology】Membrane contactor technology proves its effectiveness in addressing the challenge of high-concentration ammonia nitrogen wastewater
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With the rise of ** and environmental awareness, wastewater treatment is receiving increasing attention. As an important pollution indicator in water bodies, ammonia nitrogen has given rise to various treatment processes. This article introduces a new process for treating and recovering ammonia nitrogen using Schwanno Liqui-Cel membrane contactors, known as TransMembrane ChemiSorption (hereafter referred to as the \"TMCS process\"). With the rise of ** and environmental awareness, wastewater treatment is receiving increasing attention. As an important pollution indicator in water bodies, ammonia nitrogen has given rise to various treatment processes. This article introduces a new process for treating and recovering ammonia nitrogen using Schwanno Liqui-Cel membrane contactors, known as TransMembrane ChemiSorption (hereafter referred to as the \"TMCS process\"). This article was published in the 11th issue of PROCESS, the journal dedicated to the process industry, in 2024. The original title is \"Green and Efficient Membrane Contactor Technology for the Treatment and Resource Utilization of High-Concentration Ammonia-Nitrogen Wastewater.\" The authors of this article are Wang Guihe and Wu Di, who work at Shuwanuo Company (formerly 3M Healthcare). This paper introduces the principle of using the TMCS process for treating ammonia-nitrogen wastewater, and will provide a detailed explanation through a specific case study on the selection, design, and implementation of the TMCS system. Currently, the TMCS process using Liqui-Cel membrane contactors for the treatment of ammonia-nitrogen wastewater is widely applied in various fields such as the microelectronics industry, power plants, and municipal services, enabling efficient recovery and utilization of ammonia nitrogen while meeting environmental requirements related to energy conservation and emission reduction. Ammonia nitrogen is an important indicator in water pollution monitoring, as excessive levels of it can lead to eutrophication of water bodies, promote excessive algae growth, and may have negative effects on aquatic ecosystems and human health. To address this challenge, various wastewater treatment technologies have been developed to remove ammonia nitrogen. These technologies vary depending on the specific application scenario and water quality conditions, including but not limited to biological treatment (such as nitrification/denitrification, anaerobic ammonium oxidation), chemical treatment (such as struvite precipitation, breakpoint chlorination, catalytic oxidation), and physicochemical treatment (such as stripping absorption, RO membrane separation, ion exchange, and zeolite adsorption). Among them, the TMCS-TransMembrane ChemiSorption technology developed by Shuwanuo Company (formerly 3M Healthcare) using Liqui-Cel membrane contactors represents an innovative solution that has been widely applied in various industries such as microelectronics, power generation, the chemical industry, petrochemicals, and municipal wastewater treatment. This technology can not only efficiently remove ammonia nitrogen from wastewater but also produce valuable by-products for reuse. In addition, it features modular design, compact footprint, low energy consumption and low carbon emissions, high stability, and easy maintenance.
1 Principle of the TMCS process: The TMCS process is a method for treating wastewater using membrane technology. As shown in Figure 1, this process uses a hydrophobic hollow fiber membrane as the interface; wastewater containing ammonia flows on the outside (shell side) of the hollow fiber membrane, while an acidic absorption solution flows on the inside (lumen side), with the two flowing in counterflow. Figure 2 shows the numerous nanoscale micropores created on the membrane surface through a special process. Due to the use of a hydrophobic membrane material with extremely small pore sizes, liquid water cannot wet or penetrate the membrane pores, while various volatile gases can pass through freely.
On the wastewater side, due to the higher ammonia partial pressure, free ammonia can pass through the membrane pores and migrate to the acidic side. When ammonia reaches the acidic side, it immediately reacts with the acid to form an ammonium sulfate solution. During this process, the ammonia concentration near the surface of the acidic side membrane is almost zero, thereby creating a concentration gradient of ammonia on both sides of the membrane. This concentration gradient is precisely what drives the migration of ammonia gas. As long as sufficient hydrogen ions are ensured on the acidic side to react with ammonia, and the stability of liquid contact at the membrane pore interface is maintained, an effective driving force and a stable ammonia removal efficiency can be preserved. The TMCS process is recommended over traditional gas sparging or vacuum methods for removing and recovering ammonia nitrogen from wastewater. The main reason is that ammonia has an extremely high solubility in water – tens of thousands of times higher than that of oxygen, and thousands of times higher than that of carbon dioxide. Its Henry constant is very low, which means that the partial pressure of ammonia in water is extremely low, making it difficult to remove effectively using conventional degassing methods. As shown in Figure 3, this property makes it difficult for ammonia to escape from water, and efficient removal is challenging even under gas purging or vacuum conditions.
In contrast, the TMCS process uses acid absorption as a replacement for the traditional gas purging or vacuum methods. When ammonia migrates through the membrane pores to the acidic side, it immediately reacts with the acid to form ammonium sulfate, a process that occurs almost instantaneously. This not only ensures that ammonia can be removed rapidly, but also creates the greatest driving force by maximizing the concentration difference of ammonia on both sides of the membrane, thereby improving the efficiency of ammonia nitrogen removal. Therefore, the TMCS process can more effectively address ammonia nitrogen pollution issues while enabling the recycling of resources. According to Henry’s law, only free ammonia gas can be removed; ammonium ions in water cannot be removed. However, the ammonia nitrogen parameter used for wastewater control refers to all free ammonia and ammonium ions combined. Therefore, on the water side, ammonium ions can be converted into ammonia gas through the chemical equilibrium shown in Figure 4 by adding alkali and/or raising the temperature, and then removed via the TMCS process.
To ensure the durability and long-term stable operation of the membrane modules in the TMCS process, the water side requires thorough pretreatment to meet the conditions for membrane feeding. This includes not only increasing the volatility of ammonia nitrogen by adding alkaline substances and raising the temperature appropriately, but also taking measures to prevent factors that are harmful to the membrane material from entering the system. Specifically, it is necessary to avoid oxidative damage to the membrane fibers caused by oxidizing substances such as ozone, residual chlorine, hydrogen peroxide, and hypochlorous acid ； Minimize the presence of substances with low surface tension (such as surfactants, alcohols, and other solvents) to prevent them from making the membrane filaments hydrophilic ； At the same time, efficient pre-filtering methods should be employed to reduce the level of particulate pollutants in the water entering the system, in order to prevent clogging of the membrane pores. As for the choice of absorbent solution on the acid side, there is relative flexibility; various acidic solutions such as sulfuric acid, phosphoric acid, and hydrochloric acid can be selected depending on the actual conditions (see Figure 6). When making a choice, the availability of the acid and the reuse value of the by-products should be considered. The key is to ensure that the acid solution can react fully with ammonia, thereby maintaining the driving force generated by the concentration difference of ammonia on both sides of the membrane pores. Generally, the pH value on the acid side should be maintained between 1 and 3; this allows for sufficient reaction drive while also controlling the concentration of by-products, thereby reducing the costs associated with dealing with those by-products later on.
2 TMCS Case Studies 2.1 Background This case involves a 12-inch chip manufacturing facility. In the chip production process, wet cleaning, etching, and CMP chemical-mechanical polishing all generate ammonia-nitrogen-containing wastewater. The characteristics of this wastewater are as follows: flow rate of 10 m3/h, ammonia nitrogen levels of several thousand mg/L, conductivity of several hundred µs/cm, turbidity of less than 3 NTU, pH value of 8.5, hydrogen peroxide levels of tens of thousands mg/L, and surface tension close to that of water at 72 dynes. The wastewater comes from wet cleaning and post-CMP cleaning, and therefore contains high concentrations of hydrogen peroxide and metal complexes. The target ammonia nitrogen concentration is less than 45 mg/L; the treated wastewater with low ammonia nitrogen levels is fed into the park’s pipeline network and sent to downstream wastewater treatment processes. 2.2 Water quality pretreatment analysis As described in the TMCS principle above, wastewater must have its pH increased by adding alkali or its temperature raised in order to convert ammonium ions into free ammonia gas, which can then be removed through the membrane; therefore, it is necessary to conduct an analysis of the addition of alkali to the raw water. After adding alkali, it was observed that the originally clear wastewater became turbid; when the pH value rose to 11, the turbidity reached 8 NTU, and flocs began to settle slowly at the bottom of the container. As shown in Figure 7, investigations reveal that this flocculent substance is likely to originate from complexes in the CMP slurry, and it precipitates upon increasing the pH value. The higher the pH value, the more flocculent precipitates form. As shown in Figure 8, when the pH value is <10, the increase in turbidity is not significant ； When the pH value exceeds 10, the turbidity increases significantly; therefore, pH control is important for limiting the formation of flocs.