How to treat inorganic wastewater with high ammonia nitrogen and high salinity?

For inorganic ammonia nitrogen (NH4), alkaline adjustment is generally used for stripping and desalination; please refer to: http://bbs.hcbbs.com/thread-440657-1-1.html

Looking at the posts posted by the moderator, the main issues are excessive ammonia nitrogen levels and pH values. Regarding the removal of ammonia nitrogen, an answer has already been given above – steam stripping can generally be used for this purpose. As for the source of steam, it can be determined based on the specific conditions of your company; typically, a reboiler needs to be installed at the bottom of the tower. The design parameters related to the tower height, trays, as well as the temperatures and pressures at the top and bottom of the tower are usually handled by design firms. After stripping, online adjustment and monitoring facilities can be installed based on the pH value of the wastewater to ensure compliant discharge

The indicators to be achieved in the processing should be specified.

Wastewater treatment must meet the Class I discharge standards specified in GB8978-1996. However, at present all wastewater is reused; there is no wastewater discharged outside. The previous process was as follows: wastewater → removal of heavy metals → pH adjustment with alkali → stripping → pH adjustment with acid → multi-effect evaporation for concentration → reuse of condensed water. ↓ ↓ Ammonia water and sodium sulfate are exported. 1. The effluent is highly acidic; to make it alkaline, a large amount of alkali is required, and later, acid is used for pH adjustment, requiring a significant amount of acid as well. 2. The steam requirement is too high, and it increases the wastewater volume by 25%, placing significant pressure on subsequent evaporation and concentration processes. 3. The salinity is too high, which makes scaling easy to occur in the system. 4. The equipment suffers from severe corrosion. Due to these problems, the cost of treating each cubic meter of wastewater is over 100 yuan; as a result, the ammonia removal system is not in operation. This post was last edited by kingwayhorn on 2009-4-16 20:30]

This post was last edited by shanyee on 2009-5-2 22:29. This wastewater seems very difficult to deal with. Actually, it’s not very difficult to sit up. Following standard procedures, someone may add liquid alkali, and then use stripping or distillation to remove ammonia nitrogen. Currently, the price of ion-exchange membrane caustic soda is around 700 yuan per ton (with a 32% concentration), while liquid ammonia costs 3,000 yuan per ton. The cost of adding chemicals to this mixture is quite high. At the same time, the salt content in the wastewater also increases, and so on. There is no need to remove ammonia nitrogen from the wastewater, as it exists in that wastewater in the form of ammonium salts. You can then adjust the pH to around 6 to keep the wastewater at a weakly acidic level, and use 5-effect evaporation for desalination purposes, in order to remove sulfuric acid, sodium sulfate, and all heavy metals; at this point, the ammonia nitrogen content in the wastewater should be below 200. If done well, it can go below 100. All the salt has been removed. The operating cost for treating wastewater is based on a rate of 120 yuan per ton of steam; thus, if the cost of treating each ton of your wastewater is 35 yuan or less, it can be handled. Reference.

There is also a misconception regarding ammonia nitrogen wastewater at present, namely blowoff and distillation. If the ammonia nitrogen in the wastewater is derived from ammonia water, there is no problem; but if it is formed from ammonium salts, doing this becomes quite troublesome. If it is very high, it is best to remove ammonia nitrogen in the form of crystals. This will also significantly reduce processing costs.

The processing cost won’t be that high; there’s no need for forced circulation evaporation, as that requires a lot of electricity. By increasing the number of evaporation stages, it’s possible to achieve at least 5 stages as you mentioned. The cost of processing will be greatly reduced. At the same time, it is not necessary to perform forced circulation in each effect. The electrical energy of the slab-type design can be reduced by over 60%. The steam utilization rate also more than doubled. For your reference. http://bbs.hcbbs.com/thread-440660-1-1.html are the types of evaporators I mentioned.

The main components of the wastewater are sodium sulfate and sulfuric acid.

By neutralizing this wastewater to a weakly acidic environment and then carrying out 5-effect evaporation, it is possible to remove salts, ammonia nitrogen, and so on. It can also reduce COD. Kills several birds with one stone.

The costs mainly include sodium hydroxide and sulfuric acid, as well as the chemicals used for removing heavy metals earlier on, plus the cost of steam. Due to the high costs, wastewater is now sent directly to the 4-effect evaporation concentration system after heavy metals have been removed from it, but this also brings about many problems. One issue is the high ammonia content in the condensate water, and the other is that the sodium sulfate that forms contains 25% sulfuric acid, which prevents it from being sold externally; as a result, it accumulates within the factory, severely affecting production. Additionally, the equipment is severely corroded and scaled, leading to ammonia leakage; as a result, the working conditions in the factory area are extremely harsh.

For this wastewater, there’s no need to add sulfuric acid anymore; simply add liquid alkali to adjust the pH to around 6. In this way, very little ammonia is produced in the wastewater containing sulfuric acid. At the same time, there is no need to remove the heavy metals; they are all removed in the solid phase. There is a high amount of ammonia in the condensate water, which indicates that the wastewater contains a significant quantity of ammonia. The pH of each stage cannot be kept at neutral or alkaline levels, as under such conditions ammonia will definitely be released; therefore, the entire process must take place under acidic conditions. Since AN sulfate is acidic in nature, if the pH is adjusted to neutral, then ammonia must be present in the wastewater. Because AN sulfate is acidic while the wastewater is neutral, it is the alkalinity of ammonia that compensates for the pH change from acidic to neutral. Therefore, there must be a high amount of ammonia nitrogen in fresh water; the source of this ammonia nitrogen is ammonia in wastewater, rather than ammonium sulfate. Hence, it is important to maintain a weakly acidic pH level. The corrosion issue with the equipment is mainly stress corrosion, I’m not sure about the material used. For this kind of wastewater, 316L is generally not a problem. Then there’s the issue of electricity costs; I assume your installed power capacity must be quite high. This is a drawback of forced circulation. For my system, which uses 6 evaporation stages to treat 100 tons of wastewater per day, the installed power capacity is only 25 kilowatts. I’m not sure what your installed power capacity is – that’s the problem related to electricity costs. Also, I estimate that the consumption of steam and the amount of water used for cooling are also significant in your case. I guess the equipment there gets clogged often too? It is also a drawback. But it can be done well. Also, when producing salt, cooling crystallization cannot be used; instead, thermal crystallization must be employed for this wastewater. I wonder how your situation is? Let’s discuss it. If it’s not convenient, you can call me at 13561343299. I have some experience in this field. All of this is for reference; I hope it will be helpful to you.

This post was last edited by shanyee on 2009-5-2 22:32. The corrosion issue with this device is not widespread; it occurs at the welds of the grating at the bottom of the evaporator, mainly due to the intense scouring effect of water flow in that area. Another reason is stress corrosion of the heat exchange tubes, which leads to tube cracking. If it’s not surface corrosion, then there’s no major problem. However, since it is a forced circulation system, maintenance is very inconvenient; the only option is to block the pipes by sealing off the ends where leaks occur. It’s difficult to operate. I guess it’s tube cracking corrosion; there shouldn’t be much of a problem with the shell side, right? I don’t know the form of corrosion, so I dare not comment rashly. Reference.

Our goal is to recycle ammonia and heavy metals; if they end up in the final solid waste, it will be even more problematic. The sodium sulfate crystals obtained after evaporation are exported; external companies use them to produce sodium sulfate. However, the environmental protection authorities have been conducting strict inspections recently, as a large amount of ammonia is released during the calcination of sodium sulfate, and these companies have been inspected by the authorities on several occasions. They require that the sulfuric acid content in sodium sulfate be below 10%; otherwise, they won’t accept our sodium sulfate. The factory area is limited; a large amount of sodium sulfate has already accumulated there. If it isn’t removed, there will be no space left to store more, and production will have to stop. Also, the daily wastewater volume is about 2,000 cubic meters, with 4 evaporation and concentration systems. This post was last edited by johncom on 2009-4-17 08:48]

The wastewater after passing through the evaporation and concentration system has a solid content of 30%; after cooling and crystallization, the solids are removed using a digger, while the supernatant is returned to the evaporation and concentration system.

It works like this: you can crystallize them all into solids, burn them, and then use water to absorb the ammonia in order to recover it.

Sulfuric acid can be decomposed at high temperatures. If liquid caustic is added for evaporation and recovery, it’s not cost-effective at all; the expenses are very high. It has to be burned anyway, so it’s better to recycle it at this time. Another issue is the sale of salt. I don’t know the situation either; it’s purely a personal bias. Please use this as some reference.

It can be directly crystallized without the need for cooling. But with things being like this, it’s unlikely that anything can be changed or done again. The key is to absorb the exhaust gases during the burning process, and water can be used for this purpose. Or reabsorb it with sulfuric acid. It’s crucial to know whether your company is able to reuse these sulfuric acid or ammonia solutions.

I learned a lot from reading the exchanges between the original poster and ipgood! I would also like to share the following personal views. First, let’s ask some questions. Can you recover heavy metals under acidic or neutral conditions? (Even so, it is possible that metal oxides or hydroxides will still precipitate under alkaline deamination conditions, which will certainly affect the normal operation of the ammonia distillation tower.) In your company’s production, is ammonia (ammonia water or liquid ammonia) or sulfuric acid the raw material, or is it neither? 1. If ammonia or liquid ammonia is used as a raw material in the manufacturer’s production process, the most feasible approach remains evaporating the ammonia after removing heavy metals. Adjusting the pH with alkali is necessary. Of course, doing this consumes alkali, acid, and steam. In that case, the focus should be on improving existing equipment and processes; for example, by first concentrating the substance threefold to 30% using multi-effect evaporation under neutral conditions, and then raising the pH value before sending it to the ammonia evaporation tower. This approach is expected to reduce the consumption of alkalis and acids, as well as steam usage. As for scaling and corrosion, it’s best to follow the advice of brother ipggod, including regarding processes and equipment. 2. If sulfuric acid AN is a raw material in the production process of the company whose post was created, I suggest you proceed as follows: remove heavy metals (is it necessary to add additional chemicals?) Would it work by raising the pH to pH=12? Precipitation and filtration are quite simple. However, when too much alkali is added, heavy metal ions tend to form complexes with free ammonia, which causes them to dissolve again. After that, the pH is raised to 12–12.5, and then a high-concentration, high-purity sulfuric acid solution is obtained using the membrane diffusion-chemical absorption method. This approach reduces the need for acids and bases (sulfuric acid is not expensive), but it eliminates the need for steam entirely. If you want to obtain solid sulfuric acid an, then please use Brother Ipgood’s efficient thermal crystallizer. We are doing something similar for a manufacturer. Of course, if one wishes to reduce the investment in membrane equipment, multi-effect evaporation concentration can be carried out under slightly acidic conditions (pH = 6–7); if the feed solution is concentrated three times, the investment in membrane equipment can be reduced proportionally. If 700 tons of concentrated brine are processed per day, the investment in membrane equipment is around 3.5 million yuan, with a daily electricity consumption of 1,000 kWh. It is easy to calculate the amount of alkali required to release ammonia and the amount of acid needed for membrane absorption. 3. If neither ammonia nor sulfuric acid is one of your raw materials, it would be best to persuade the sodium sulfide plant to install a denitrification unit; if ammonia water or liquid ammonia is readily available for sale, it can be obtained through absorption followed by distillation. If sulfuric acid AN sells well, it can be absorbed with sulfuric acid of appropriate concentration and then crystallized by thermal method. It’s not difficult either; why not do it? ! If nothing else works, your factory can simply fund the construction of a setup for them. Compared to your company’s daily treatment of 2,000 tons of water, this investment isn’t that large, is it? As for some theoretical issues: the thermal crystallization of ipgood definitely yields a mixture of sodium sulfate and anhydrous sulfate. But crystallization by the cold method isn’t much better either. The saturated solubility of sulfuric acid An at 0 degrees is around 41%, while it is 50.5% at 100 degrees. It increases monotonically with temperature, but the change is not significant. The solubility of sodium sulfate is around 4% at zero degrees, reaches its maximum of about 34% at around 33 degrees, then gradually decreases, being around 29% at 100 degrees. If sodium sulfate and sulfuric acid AN coexist in wastewater, due to the relatively small amount of sulfuric acid AN (which is in a weaker position), when the temperature drops to 0–15 degrees for the cold crystallization of sodium sulfate, what is obtained first is a eutectic salt of sodium sulfate and sulfuric acid AN in a 1:1 ratio. This also inspires us to consider performing two-step crystallization. For example, at 10 degrees, a co-crystal of ammonium salts and sodium salts is formed, with very little ammonium salt remaining in the mother liquor ； Further cooling to below 5 degrees results in the formation of sodium sulfate decahydrate (mirabilite) crystals. The co-crystalline salt is redissolved at a temperature between 30 and 60 degrees before undergoing cooling crystallization; at that point, sodium sulfate becomes the less dominant component, and the crystals obtained are mainly sodium sulfate. In this way, the ammonium content in the sodium sulfate exported will definitely be less than 10%. That highly concentrated AN sulfate solution can be used with IPGOOD’s efficient evaporation-crystallization unit to produce solid AN sulfate salts, and its market prospects should be no worse than those of sodium sulfate. This post was last edited by yjqin1 on 2009-4-18 11:36.]

First, steam-stripping ammonia is carried out to recover ammonia water, followed by concentration and crystallization to remove salts!

Put it this way, the wastewater in question is vanadium-containing wastewater. The treatment of vanadium-containing wastewater is a global challenge. In vanadium-containing wastewater, alkalis and reducing agents are used to precipitate the heavy metals; after the removal of these metals, the pH of the wastewater is around 8–9. 1. The process for vanadium production is sodiumization roasting, and the purpose of adding sulfuric acid is to precipitate vanadium. 2. The current goal is to enable the recycling of ammonia and achieve zero wastewater discharge. Your ideas and those of ipgood have been very inspiring to me; thank you! ! !