The treatment of metal surface washing and rinse wastewaters can be a real challenge for many companies because of the high heavy metal contents in this kind of industrial effluent.
As a result of these processes, wastewaters containing raw materials and auxiliary products from the cleaning and polishing of metal goods are produced. For this reason, many manufacturing industries produce wastewater containing high chemical oxygen demand (COD) and turbidity, besides suspended solids, and heavy metals that could cause enormous environmental damages if not properly treated.
In this article we will examine the best treatment solutions and systems for these wastewaters.
What Is Metal Surface Rinse and Cleaning Process?
Metal surface rinse and cleaning is a process in the industrial field to remove impurities, such as oil stains, on the metal surface of metal goods and equipment. In this process, cleaning wastewater will be generated.
This surface cleaning wastewater generally contains surfactants, emulsified oils, corrosion inhibitors, phosphates and other inorganic substances. Salts, suspended solids, metal ions, and heavy metals.
Among them, inorganic salt concentration is high, and the biochemical properties are poor. For these reasons YASA ET developed an Electrocoagulation and Evaporation system to solve the problem of metal surface cleaning wastewater treatment.
Which Industries Produce Heavy Metal Polluted effluents?
The presence of heavy metals in wastewater has been increasing with the growth of industry and human activities, e.g., plating and electroplating industry, batteries, pesticides, mining industry, rayon industry, metal rinse processes, tanning industry, fluidized bed bioreactors, textile industry, metal smelting, petrochemicals, paper manufacturing, and electrolysis applications.
The heavy metal contaminated wastewater finds its way into the environment, threatening human health and the ecosystem. The heavy metals are non-biodegradable and carcinogenic, thus, the presence of these metals in water by improper amounts could result in critical health issues to living organisms.
Why Metal Surface Treatment, Rinse and Cleaning Wastewaters Are Difficult to Treat?
For metal surface cleaning, some products require special treatment and different companies use different processes according to their needs, thus producing very unstable metal treatment and cleaning wastewaters that contain heavy metals.
For instance, surface cleaning technologies include steam, electrolysis, ultrasonic, high-pressure cleaning method, etc. All of the above will cause differences in the composition, concentration or difficulty of treatment of metal surface rinse and cleaning wastewater.
Therefore, the choice of the correct treatment technology and chemical agents for surface cleaning wastewater is very important. The treatment of metal surface cleaning wastewater mainly involves demulsification and degreasing of wastewater, and demulsifying water treatment agents need to be used. These chemicals contribute to the demulsification and sedimentation of emulsified oil in wastewater, and also remove some metal ions to make the wastewater easy to treat.
Metal Surface Rinse and Cleaning Wastewater Treatment Disposal Precautions
In the treatment of metal surface cleaning wastewater, it should be noted that if the wastewater contains oil, the oil separation treatment should be carried out first, otherwise it may lead to an increase in the cost of wastewater treatment or obvious oil slick on the upper layer of the treated wastewater.
Due to the complexity of surface cleaning wastewater, the pre-treatment is a must have to abide to the national discharge standards. The final treatment equipment can be added to discharge the clean water into the pipe network or reuse in the production line.
Thanks to YASA ET treatment systems the manufacturing companies can discharge into the sewage network and avoid hasty sanctions. Get in touch with our team for a free consultation by clicking here.
Main Challenges in the Treatment of Surface Cleaning and Rinse Wastewater | Heavy Metals Removal
The treatment of surface cleaning and washing wastewater is problematic and costly for many enterprises since its treatment requires sophisticated project set up and high-tech equipment, specifically for removing heavy metals.
Normally, wastewater discharged from the metalworking industries is characterized by the high contents of inorganic compounds and metal ions. In these wastewaters the typical pollutants are Phosphorus, Zinc, Fluorides, and the main pollution indicator is COD. The mean values of the chemical oxygen demand (COD) typically range from 2,000 to 12,000 mg/l.
The chemical content analysis is the first step in designing a wastewater treatment system for surface cleaning wastewaters. The chemical test analysis service is performed in our laboratory, you can get in touch with us to book a test for your wastewater.
Parameters for Metal Surface Rinse and Washing Processes Wastewater Disposal
In the recent years regulations governing the disposal and discharge of industrial effluents, including metal surface rinse and washing wastewaters, have become more stringent all around the world.
Now, companies must take any and all measures necessary to ensure the safe collection and disposal of wastewater containing heavy metals. As a result, all businesses need to treat these effluents before discharging to sewers or, better, to reuse them in the production processes.
The most important parameters to consider in metal surface treatment wastewater:
Chemical Oxygen Demand (COD): Measure of the amount of oxygen that is needed to oxidize soluble and particulate organic matter in water;
Phenolic micropollutants: chloric, bromo, and nitro and alkyl are the most common phenols. Its toxicity and persistence in the environment, these phenolic compounds are considered dangerous substances;
Phosphorus, Zinc, Fluorides and other heavy metals need to be carefully monitored and removed from these wastewaters;
Depending on the country, the discharge limits for metal washing and rinsing wastewaters can vary, but the most cost-efficient wastewater treatment methods remain the same.
How to Treat Wastewater from Metal Washing Processes and Surface Treatment?
Wastewater from metal washing processes and surface treatment can be treated by various technologies, but some are more effective than others.
The most common technologies are:
Electrocoagulation and Electrooxidation;
As we can understand, an appropriate treatment system for paint rinsing wastewaters can cut down discharge volumes and cost for enterprises.
What Is the Best Wastewater Treatment Technology for Metal Surface Rinse and Cleaning Wastewaters?
Treatment and disposal options applicable to metal surface rinse and cleaning wastewaters mainly depend on the features and volume of wastewater, so the treatment solutions for a specific fluid are often difficult to determine without prior testing.
Often the best solution relies in the combination of treatment methods, so to efficiently remove pollutants from paint wastewaters and reuse the water in the production lines.
Electrocoagulation for Metal Surface Treatment and Rinse Wastewaters Treatment
The most efficient technology for metal rinse and surface treatment wastewaters often relies in the combination of different methods, such as Electrocoagulation and Electro-oxidation.
In our experience, the combination of our electrocoagulation equipment and electro-oxidations gave the best treatment results for the metal finishing and related wastewaters, especially containing heavy metals. YASA ET electrocoagulation equipment can be followed by a membrane treatment system for further polishing and pollutants removal.
Electrocoagulation and Electro-oxidation can effectively separate the pollutants and coagulate them from the water body as shown in the picture below. These technologies apply a similar treatment principle, but the final design of the equipment can affect the treatment results as explained here.
These methods can separate the most resistant contaminants by using electrochemical reactions. In case the organic content of painting wastewaters is too high, the Electrooxidation technology should be preferred since it can breakdown and remove those elements.
The contained costs of this technology, combined with the minimal use of chemicals, make it a good choice for these wastewater pre-treatment applications. More information about this technology can be found at Electrocoagulation System for Water and Wastewater Treatment.
In the case of heavy metal wastewater an electrocoagulation equipment followed by a filter press can reduce COD by 65% on average, and greatly increase the efficiency of the next treatment step, such as vacuum evaporators or membrane systems.
Now you can also test these technologies with our test equipment, click here for more info.
Metal Surface Treatment Effluents and Metal Rinse Wastewaters Treatment with Vacuum Evaporators
Wastewater evaporation has become an effective method for removing heavy metal contaminants and concentrating liquid waste from metal surface treatment and rinse processes.
A vacuum evaporation equipment, such as EVADEST, uses almost no chemicals for cleaning wastewater and thanks to its MVR technology it has much lower energy consumption when compared to other types of products on the market.
This technology can remove salts, heavy metals, and hazardous materials, reducing COD, BOD and TSS very effectively. In painting wastewater treatment, evaporators can reduce COD levels to discharge limits, and the recovery rate can reach up to 85% with the correct pre-treatment set up.
The last improvement brought by MVR evaporators make this technology the preferred choice for large volumes of metal industry wastewater.
The vacuum evaporator for the treatment of heavy metal content wastewaters can be further treated by using a crystallization equipment, such as SOLIDEST.
Cost-Effective Treatment Method For Metal Rinse and Washing Wastewaters
Normally, chemical methods are the most suitable treatment technology for heavy metal wastewaters, but it’s cost can be unsustainable for large effluent volumes.
For this reason, electro-chemical and evaporation methods are among the most cost-effective solutions for the treatment of metal rinse effluents and wastewaters with high contents of heavy metals.
In fact, electrocoagulation and electro-oxidation are among the most cost-effective solution to break down contaminants and coagulate pollutants, but the effluent requires further treatment either with evaporation or membrane filtration methods. For this reason, electrocoagulation and electrooxidation are a great choice as pre-treatment or for improving the treatment effects of evaporators and membrane equipment on metal rinse and washing wastewater treatment applications.
Finally, membrane systems are effective in further separating the pollutants from these wastewater, but the operating costs could be very high since the membranes need to be frequently replaced.
What Is The Best Treatment Technology For Metal Surface Treatment and Cleaning Wastewaters?
The best system for the treatment of wastewaters from metal surface treatment industries, combines electro-chemical, evaporative, and membrane filtration technologies.
In the past, as YASA ET we built systems for the treatment of metal surface washing wastewaters using PREDEST electrocoagulation and Electro-oxidation equipment, EVADEST vacuum evaporators and SOLIDEST crystallizers.
For more information about our solutions, you can get in touch with us at:
🌐 www.yashahuanjing.cn (中文）
📱 +86 136 3643 1077
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Removal of heavy metal ions from wastewater: a comprehensive and critical review | npj Clean Water (nature.com)