In refineries, the COD level of some wastewater is significantly above the allowed limits, making it impossible to send such wastewater to wastewater treatment plants. What should be done?
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I work at an oil refinery in the Northeast. The specific problem is as follows: The quality of the coking wastewater and the wastewater generated from crude oil electrodesalination at this refinery is very poor. Among the key parameters, the COD level is around 4000, while the acceptable standard for the inlet water quality at our plant’s wastewater treatment facility is COD below 2000. As a result, this wastewater cannot be sent to the treatment facility and must be sent out for external treatment, which incurs costs of millions per month. In this portion of the wastewater, the flow rate is generally around 800 tons per day; other parameters are within normal ranges, with a pH value of 6–8 and oil content below 100. However, the COD level is extremely high, while the B/C ratio is very low, below 0.1. What method should be used to treat this wastewater?
It can be pre-treated using the biofilm method to 2000, and then subjected to biochemical treatment. Moreover, from my experience, if this wastewater is treated separately, the COD can be reduced to around 100-200.
When COD is too high, using membrane treatment can result in very high operating costs, and the lifespan of the membranes may be very short. We have not conducted experiments on treating this type of wastewater using the biofilm method, but based on theory and experience, it is likely that this method has the aforementioned disadvantages. Could you please explain it in more detail?
Is the biofilm process still used with such a low B/C ratio? ? ? I think the biodegradability is a bit low; it might be necessary to cultivate specific bacterial strains separately
Some wastewater is severely polluted; buffer tanks can be established for storage, and blending treatment can be carried out when the processing capacity permits. For coking wastewater, there is no effective treatment method; it should be reused within the coking process as much as possible to reduce discharge.
. . 4000 is not too high. . . Pre-treat with anaerobic organisms to reduce COD to some extent, and at the same time increase the B/C ratio
Anaerobic: Hydrolytic acidification or anaerobic biological filters can be used
I think the membrane method isn’t very good; others have already mentioned its disadvantages. Could you tell me about the main components of wastewater?
This post was last edited by zfc318 on 2009-6-23 21:24. Handling wastewater depends on the quality of the wastewater and the pollutants present in it. Regarding coking wastewater, we have worked with Shougang, Shijiao, and Baogang. Although the quality of the water entering the system varies (2000 mg/L–6000 mg/L), it can generally be reduced to around 200 after treatment using biochemical and conventional physical-chemical methods; similar results are achieved for ammonia nitrogen as well. As for reaching level one, I personally think it is quite difficult to achieve without adding water or using other physical and chemical methods, so I am cautious about this. As for the B/C ratio, it is merely a reference value and not absolute. Since the microorganisms used for BOD determination are sourced from natural water bodies, they are not very effective at degrading pollutants in specific wastewater. Generally speaking, microorganisms need time to adjust their metabolic pathways in order to be effective against pollutants. This is also what is known as domestication. Of course, screening is needed first. I have personal experience with this. As for why biofilms are used, they have high stability and a high treatment load per unit volume, and a long SRT helps to retain those bacterial strains with low Y but high specificity. But choose the filler carefully, as some are actually of little help.
Hello, I know you are part of the technical team, so I’m very glad that you can answer this question; I’m truly grateful! Our wastewater, as it belongs to the pre-treatment stage before reaching the sewage treatment plant, does not have all the standard analysis parameters; only three parameters are available: COD, pH value, and petroleum content. Currently, a pH value of 6–8 and a petroleum content of 100 meet the standards for discharge into wastewater treatment plants; it is only the COD level that is too high, as it fails to reach the target of below 2000 at the entrance of the wastewater treatment plants. The volume of such coking wastewater is also very large, amounting to 600–1000 tons per day; therefore, storage or mixing methods are not suitable. At the moment, we are forced to use a desperate approach: take everything away and have someone else deal with it (in reality, what’s meant by ‘dealing with it’ is simply moving it to another facility, where they secretly mix it with other substances before discarding it). The monthly cost for this treatment amounts to over 1 million yuan, and this approach certainly isn’t sustainable in the long run; therefore, it’s necessary to find an appropriate manufacturing process. Based on the technical information I currently have, the COD levels in the wastewater from many chemical plants, paper mills, and similar facilities can reach tens of thousands of units. So, can the treatment methods used for such wastewater be applied to our own wastewater? Moreover, given the current level of technology, only biochemical treatment seems capable of solving our wastewater problems; those so-called advanced oxidation methods or catalytic oxidation methods may not be effective. So, which effective biochemical processes can be selected and optimized? And where should we start in order to resolve this sewage problem more quickly? I would be grateful for your guidance!
It’s not a problem if there is no water quality analysis; if there are process descriptions for the production unit where wastewater is generated, it is generally possible to determine what the main pollutants are. Additionally, if treatment is necessary, should it be limited to pre-treatment to reduce the level to 2000 (depending on whether the subsequent unit load is sufficient), or must emissions meet the specified standards? Are there any local emission standards? Regarding the processing process, I think that once the above issues are resolved (usually it’s necessary to check with management to see if they are interested in proceeding), a preliminary process can be developed. Then, pilot-scale process verification is necessary (it must be done, even if one has experience). Choose carefully, otherwise you’ll face continuous problems in the future). Additionally, during the pilot phase, be cautious as some companies may use various tricks, such as iron-carbon or activated carbon fillers. I’ve encountered it before, though I didn’t get it. But after running it for a few months, the system stopped working. Of course, this cannot be blamed on the owners either; after all, they are not professionals and cannot see the risks involved in the technology.
The wastewater can first be treated by air flotation to remove oil, followed by acidification and hydrolysis in order to improve its biodegradability. After that, it is processed using the activated sludge method. If the quality of the wastewater still does not meet the required standards, chemical oxidation (using chlorine dioxide) can be employed as an alternative treatment method. This is also the approach used in our plant; when the COD level of the wastewater is around 5000, it can be reduced to below 100.
The suggestion from upstairs is good. But I wonder what the cost of chemical oxidation is? What is the dosage? How is the maintenance? Especially in winter?
First of all, thank you for your active participation! The wastewater from our facility has a very complex origin and composition; the wastewater resulting from the dehydration of crude oil at the bottom of tanks contains large amounts of pollutants and minerals that are difficult to degrade, such as viscous mineral oils, high-molecular-weight polymers, surfactants, and inorganic salts ； The composition of coking electrodialysis wastewater is more complex; in addition to the aforementioned pollutants, it also contains scale removal agents made up of complexes, organic acids, and inorganic acids, as well as hard-to-degrade polyacrylamide demulsifiers ； In addition, the condensate water from the stripping steam also contains high concentrations of pollutants such as ammonia nitrogen, volatile phenols, and sulfides. Therefore, this type of wastewater is characterized by high oil content, high emulsification levels, high COD, high ammonia nitrogen, and high suspended solids; it has a complex organic composition and is toxic as well as biodegradably difficult organic wastewater. At present, through the wastewater pretreatment system we put into operation in 2005, which employs a process flow of \"water quality adjustment – sedimentation for oil removal – cyclone separation of oil and water – air flotation purification\", the problems of high oil content and high suspended solids in this type of wastewater have been initially addressed. The oil products recovered generate annual benefits of nearly 10 million yuan. However, in terms of wastewater treatment itself, the COD level remains significantly above the allowed limit, preventing the wastewater from entering the treatment plants; therefore, reducing the COD level of this wastewater is the main goal for the next step. Based on the existing process technologies, I lean toward using biochemical treatment. Because, based on the preliminary experimental results, there is a strange phenomenon with this wastewater: when oxygen or ozone is added to increase the oxygen content, the COD value actually increases, making it difficult to use advanced oxidation methods to reduce COD. On the other hand, if physical methods such as adsorption are used, firstly, high COD levels can cause the adsorbent to become deactivated rapidly, resulting in high costs. Second, the desorption of adsorbents and the disposal of used adsorbents are difficult to address. Therefore, it is more appropriate to use relatively advanced and convenient biological treatment methods. Therefore, I would appreciate it if you could provide more guidance: what biological treatment technique would be suitable for dealing with this type of wastewater? Where should I start to quickly get on the right track to solving the problem? Which domestic research institutions and companies have strong experience and capabilities in dealing with this type of wastewater? ? Thank you for the advice!
High COD levels in the coking wastewater from refineries are a common problem that is difficult to address; to date, no effective treatment methods have been reported by any facility in this field. Many large refineries use coking units for recycling and internal treatment to reduce emissions, with only a small amount of blending being required to meet the emission standards.
My factory has a higher standard; the waste must be reduced to below 500 before it can be sent to the treatment plant in the industrial park!
It seems that your wastewater presents certain challenges; in addition to the usual coking pollutants, it also contains substances such as surfactants that are difficult to biodegrade. I recommend conducting processability tests first to determine the basic processes and suitable strain selection. On this basis, pilot testing is carried out. If necessary, we can get in touch to help you conduct a processability test.
Replying to posts 17 and 18: Thank you for your enthusiasm and support! I have sent you an in-app message; I hope to get in touch with you as soon as possible to discuss further cooperation!
Hello! Friends, are you planning to mix these two types of water for treatment? What are the requirements for other parameters after treatment? The ammonia nitrogen level in coking wastewater is quite high, while the salinity of electrodialysis wastewater is relatively high. If mixing is used for treatment, it’s best to have specific guidelines regarding the salinity of the incoming water, as we primarily use biological treatment methods, which helps to reduce operating costs and investment. Ordinary biological treatment methods require a low salinity level, not exceeding 3 g/L; however, we are able to cultivate microorganisms that can tolerate a salinity level of up to 30 g/L. If you’re interested, feel free to contact me at 13589572526.
Hello: It seems quite professional from what’s been said above; it’s not difficult to reduce the physicochemical parameters of coking water to below 2000. The problem lies in the complexity of the pollutants present in the water. My suggestion is to try coagulation and sedimentation. Even when carrying out biochemical treatment, proper pretreatment is necessary. This method is easy to implement. Based on your description, it seems like a coagulation and sedimentation tank would be suitable; I can provide you with some coagulants that we have used, so that you can conduct laboratory tests. Contact 13001778622
The short service life of membrane treatment is due to the fact that a process designed for treating pure water is used with the membranes, which is why their lifespan is short. If material separation has been handled, one will know to what extent the membrane can be used.