To handle oily waste liquid well, these five methods must be mastered
September 12, 2023
Frequent fines imposed on enterprises for violating pollution regulations Industrial wastewater has always been a complex issue in China's Water Treatment industry, and oily wastewater, as a member of it with a wide range of sources and complex components, has become a highly challenging water treatment task. According to incomplete statistics, China emits hundreds of millions of tons of oily wastewater annually, involving industries such as petrochemical, steel, coking, machinery manufacturing, and food processing. And the oily wastewater generated by different enterprises varies greatly in both characteristics and properties. Once untreated wastewater containing wastewater is discharged, it will have a serious impact on the ecological environment and human life. In recent years, there have been frequent incidents of companies being notified, punished, and filed for illegally discharging oily wastewater. Therefore, it is necessary and urgent to find effective, fast, and economical methods for treating oily wastewater.
It's not difficult to treat oily wastewater well! These five methods must be mastered According to the form of oil, the oil in oily wastewater can be divided into the following types: floating oil, dispersed oil, emulsified oil, and dissolved oil. Among them, floating oil and dispersed oil can reduce the oil content to below 10mg/L through physical methods such as sedimentation and flocculation. Emulsified oil and dissolved oil are evenly and stably dispersed in water with extremely small oil droplets, which have high stability and are difficult to separate. The commonly used methods for treating emulsified oil wastewater include salting out, flotation, electrochemical, membrane separation, and chemical methods. 1. Salt precipitation method Add inorganic salt electrolytes to the wastewater. The electrolyte pushes all the cations in the diffusion layer of the oil droplets into the adsorption layer, causing the double layer to be destroyed, and the oil droplets become neutral. The attraction between the oil droplets recovers and they coalesce, thus achieving the goal of demulsification. The commonly used electrolytes are salts of calcium, magnesium, and aluminum, which can neutralize charges and convert the properties of surfactants, improving the treatment effect. The salt dosage of the salting out method is generally between 1% -5%. After being treated by the salting out method, the oil content in the effluent is generally greater than 10mg/L. However, this method has slow aggregation speed, long settling and separation time, and a large equipment area. 2. Flotation method Also called air floatation method, this method is to introduce air or other gases into the water to produce micro bubbles, so that some small suspended oil droplets and solid particles in the water attach to the bubbles, float up to the water surface with the bubbles to form scum (oil-bearing foam layer), and then use an appropriate skimmer to skim the oil. This method is mainly used to treat residual water particles with a particle size of 10-60 after oil separation tank treatment μΜ The concentration of dispersed oil, emulsified oil, and fine suspended solids in the effluent can be reduced to 20-30mg/l. The air flotation process for treating oily wastewater is mature, and the oil-water separation effect is good and stable. The disadvantage is that the scum is difficult to treat. 3. Electrolysis method
The electrolysis method includes electrocoagulation and electroflotation. Electrocoagulation is the electrolysis of emulsified oil wastewater using soluble electrodes. Dissolve metal ions from the soluble anode (Fe or Al), and the metal ions undergo hydrolysis to form hydroxides for adsorption, aggregation, emulsification, and dissolution of oil, followed by sedimentation to remove oil.
This method has the advantages of small footprint, good treatment effect, and relatively less scum, and is suitable for the secondary treatment of cooling lubricants in the machining industry after chemical flocculation. The disadvantages are high power consumption, high electrode loss, and high operating costs.
4. Membrane separation method
Membrane filtration method, which uses microporous membranes to trap oil droplets and surfactants, is mainly used to remove emulsified oil and certain dissolved oils, including ultrafiltration, microfiltration, and reverse osmosis methods.
The membrane separation method is most suitable for high concentration emulsified oil wastewater with high discharge requirements and small treatment capacity. However, before using membrane separation, it is necessary to pre-treat the oily wastewater to reduce the pollutant content in the influent, so that the influent water quality can ensure the stable operation of the membrane components within a certain period of time and do not produce membrane pollution.
5. Chemical method
Also known as the chemical method, which involves adding coagulants or demulsifiers to wastewater for demulsification and oil removal, and then achieving oil-water separation through sedimentation or air flotation. Especially for oily wastewater with a large amount of emulsified oil, the next step of treatment is carried out after demulsification and oil removal.
But now, many traditional coagulants and demulsifiers cannot simultaneously reduce wastewater pollutants, or the dosage is too large to be applied in practice.
