Discussion on Ammonia Nitrogen Removal and Phosphorus Removal Technologies in Wastewater Treatment

For the removal/recycling/enrichment/purification of ammonia nitrogen in wastewater, gas-phase membrane processes can be considered (sometimes referred to as liquid membrane absorption processes, or more simply as membrane absorption or gas-phase membrane processes). The core of gas-phase membrane separation is a microporous hydrophobic membrane. On one side of the membrane, the ammonia-containing feed liquid or wastewater flows, while on the other side, an absorbing solution flows (which can be a chemically reactive substance or a physical absorbent). Ammonia diffuses from the main body of the feed liquid to the area where the membrane comes into contact with it; thereafter, it vaporizes and diffuses through the pores in the microporous hydrophobic membrane to reach the other side of the membrane, where it is chemically absorbed by the absorbing solution (for example, using sulfuric acid or salt acids as irreversible absorbents). In this way, ammonia is continuously transferred to the other side of the membrane, thereby achieving the purposes of removal, recovery, concentration, and purification simultaneously. Since the concentration of free ammonia in the absorbent is almost zero, the driving force for this process is maximized, which is beyond comparison with conventional stripping (stripping) processes. On the other hand, due to the use of hollow fiber microporous hydrophobic membranes, the specific surface area of the membrane modules is very large, typically ranging from 3000 to 6000 square meters per cubic meter, which is several times higher than that of packed towers. Characteristics of the gas-phase membrane ammonia removal process: 1. The capital investment is low, falling between that of stripping (also known as desorption or gas lift) and distillation (also known as vaporization or gas lift) ； 2. By-products can be selected as sulfuric acid, ammonium chloride, **, diammonium hydrogen phosphate, or ammonia water, ammonia gas, or even liquid ammonia. It entirely depends on the customer’s needs, allowing for flexibility ； 3. Operating costs are extremely low; if the by-product is an ammonium salt, the electricity consumption is less than 10% of that in conventional air lift processes, with no heat consumption required ； If the by-product is 5-18% ammonia water, the heat consumption is only 20-30% of that in a conventional stripping process, with almost no electricity consumption ； 4. The ammonia nitrogen level in the treated wastewater can be reduced to 50 mg/L, 15 mg/L, or even 5 mg/L, depending on the customer’s requirements ； 5. The gas-phase membrane method for ammonia removal has no specific requirements regarding the COD value, salt content, or types of salts in wastewater ； As long as the surface tension of the wastewater is high enough ； 6. Existing pretreatment techniques can raise the surface tension of wastewater to a predetermined value in order to meet the feed requirements of gas-phase membrane systems ； 7. Of course, if the wastewater is neutral or even acidic, alkaline substances need to be added to raise the pH to between 10 and 12, so that ammonia exists in molecular form, as a free substance, or as volatile ammonia. This is necessary; distillation (stripping) and desorption (stripping) also require such an increase in pH value. 8. The gas-phase membrane ammonia removal process allows slaked lime to be used in place of sodium hydroxide to raise the pH of the feed solution; by doing so, chemical costs are reduced by nearly 3 times. In the stripping process, if slaked lime is used to raise the pH, there is a risk of tower blockage caused by the reaction between calcium hydroxide and carbon dioxide in the air to form calcium carbonate precipitate ； If slaked lime is used to raise the pH during the stripping process, there is a risk of tower blockage due to the decreased solubility of calcium hydroxide at high temperatures. In the gas-phase membrane process, the feed liquid does not need to come into contact with (external, fresh) air; by adding slaked lime and then filtering, there is no issue of sediment contaminating the membrane ； 9. As long as the preprocessing is done properly and the operations are carried out correctly, the core gas membrane equipment can be used for over 2 years ； 10. Modular equipment with adjustable processing scale ； 11. Due to the moderate investment required for gas-phase membrane equipment and its extremely low operating costs, as well as its ability to overcome the problem of tower clogging caused by calcium ions, the gas-phase membrane process does not end up being a form of pseudo-environmental protection or fake environmental protection, like other ammonia removal processes.

There are cases where those that have been in operation for a long time are relatively small. The two recent projects are one with a capacity of 50 m3/d (ammonia nitrogen level of 30,000 mg/L), and the other with a capacity of 180 m3/d (ammonia nitrogen level of 6,000 mg/L). More affiliated manufacturers are waiting and observing, ready to get involved once there are positive results. After the release of the Water Ten Measures on April 16, manufacturers’ attitudes changed significantly; the second half of this year through next year should see a surge in new projects.

I have a few questions: 1. This process essentially involves releasing ammonium ions under alkaline conditions; where does the resulting ammonia gas go, and is there a market for ammonia water? 2. The quality of wastewater includes not only ammonium ions but also other organic substances; is the membrane affected by this? Are there any real-world use cases?

We have hundreds of thousands of milligrams of ammonia nitrogen – can it be treated?

Does it have no impact on the membrane either for wastewater with a high COD of over 10,000? Could you send some materials to me at 413894355@qq.com?

If the ammonia nitrogen level is in the hundreds of thousands, that means it’s 10%, 20% or higher. It should be noted that the saturated vapor pressure of 20% ammonia solution is approximately 1 atm. While the ammonia nitrogen level in the wastewater (or waste liquid) meets the specified standards, what is your target by-product? Very strong ammonia solution? Ammonia? Liquid ammonia? For this initial concentration, distillation is the most suitable method, regardless of the by-products that may be produced. Do you want to do it? What is the daily processing capacity? .

This post was last edited by yjqin1 on 2015-8-3 at 14:48. Question 1: This process essentially involves releasing ammonium ions under alkaline conditions. Where does the ammonia gas go in the end? Is there a market for ammonia water? The gas-phase membrane ammonia removal process is equivalent to desorption + absorption. It’s just more energy-efficient without spending extra on potions, saving 5-20 times more energy! By-products can be (more concentrated and purer) ammonia water, ammonium chloride, sulfuric acid, **, etc. It depends on what by-products you hope to obtain. As for the market for ammonia, whatever form of ammonia you need, I will produce it in that form – so how can you find no way to reuse it within the factory? Did that ammonia of yours come from organic or inorganic reactants? The ammonia extracted from pharmaceutical plant wastewater is reused in the fermentation process in the form of ammonium sulfate. 2. The quality of wastewater includes not only ammonium ions but also other organic substances; is the membrane affected by this? Are there any real-world use cases? Gaseous membranes have their weaknesses; they are sensitive to surfactants. So, the key is preprocessing. I have a R&D team of 14 people here, and we have been working on research and development for 6 years. To date, I have never seen anyone turn away from wastewater. It’s just that, if it weren’t for the pressure from above, no one would want to take on deamination work – it’s a sure loss with no potential profit. But right now, getting less compensation is still a gain. There are already a few examples. What industry are you in?

Gaseous membranes are not afraid of high COD levels; even values in the hundreds of thousands are no problem. Gaseous membranes are sensitive to surfactants; if 35 mg/L of sodium dodecylbenzenesulfonate is added to pure water, everything is ruined. As the saying goes, the real skill lies beyond the words; we focus our main efforts on the pre-treatment of wastewater. Ammonia-containing wastewater is classified into 7 major categories and 17 subcategories, with different pretreatment methods for each. Our company’s R&D team consists of 14 members: six are master’s graduates from Tianjin University, two are undergraduates from Nanjing University, two are high school graduates from Hengshui High School, and the rest come from reputable institutions such as Tsinghua University. One of the difficult-to-treat wastewater streams they are dealing with is FSK wastewater: it contains 15,000–35,000 mg/L of ammonia nitrogen, 80,000–100,000 mg/L of COD, 26% sodium sulfate, and 4,600 mg/L of nickel ions. The wastewater also contains phosphites, hypophosphites, malic acid, citric acid, and tartaric acid; it has oil droplets in it and emits an unpleasant odor. Using our combined process, it is possible to recycle 18% ammonia solution; hydrogen oxide nickel can be obtained for sale. The clean brine is then treated using bipolar membrane electrodialysis to yield 8% sodium hydroxide and 11% sulfuric acid solutions that can be recycled. The daily waste water volume is 10–200 tons, and the fee charged for having it collected is 3,500 yuan per ton. The manufacturers don’t want others to make money.

The membrane module used for ammonia removal by the gas-phase membrane process is a microporous hydrophobic membrane, and pollution does indeed occur during its use. Pollution arises from the following: 1. If the feed liquid or wastewater contains surfactants, the microporous hydrophobic membrane will become wetted, and leakage may even occur on both sides of the membrane. 2. There are supersaturated substances in the feed liquid or wastewater, or these supersaturated substances generated during ammonia removal gradually deposit on the membrane surface. These problems are easy to solve now. Mainly, through 25 years of continuous research, these issues have been resolved step by step. One is to make the microporous membrane more hydrophobic, one is to pre-treat the feed solution, and one is to immunize the membrane equipment.

Hundreds of thousands – among the manufacturers we’ve encountered, there are those that recycle ammonium chloride, as well as those that recycle ammonia for use in production; however, this should represent the first step in reducing ammonia nitrogen levels