How does a walnut shell filter work?

Regarding what you mentioned about walnut shells being hydrophilic and oleophobic, I’m not very familiar with this. If I have to offer a forced explanation, my opinion is that water itself is also oleophobic; so compared to walnut shells, does oil tend to prefer those shells? I hope experts can provide an answer! ! !

The walnut shell filter uses adsorption, filtration, and separation to remove oils and certain suspended solids from wastewater. The claim made by the original poster regarding water affinity and oil repulsion is debatable. A quick search on Baidu shows that the sound of hydrophilic materials being repelled by oil is louder than that of oil-loving materials. And most of these voices come from advertisements and product introductions of various companies. Similar views can also be found in some literature. I think it should be oil-loving. The original poster may wish to refer to the following materials: 1. “Study on the Lipophilicity and Hydrophilicity of Water Treatment Filters Using the Washburn Dynamic Method” by Yang Binwu, Chang Qing, He Chao, and Zhang Yan from the School of Environment and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070. Date of receipt: 2006203207; Date of acceptance: 2006209226. Abstract: The lipophilicity and hydrophilicity of walnut shell, magnetite, and ceramsite sand filters were studied using the Washburn dynamic method, and their surface structures were characterized. The results showed that the experimental reproducibility when using the Washburn dynamic method to determine the wettability of water treatment filters is good, indicating that this method is feasible. The lipophilicity-hydrophilicity ratios (LHR) of walnut shell, magnetite, and ceramsite sand were 76.41, 1.057, and 0.8769 respectively, suggesting that walnut shell filters have strong lipophilicity, while magnetite and ceramsite sand filters exhibit greater hydrophilicity. Consistent with the results obtained from SEM, EDS, and FTIR analyses, the differences in lipophilicity and hydrophilicity on the surfaces of walnut shell, magnetite, and ceramsite sand filters are mainly due to variations in their surface physicochemical structures. Keywords: Water treatment filters; Lipophilicity-hydrophilicity ratio; Washburn equation. Article ID: 025322468 (2006) 1121792207; Chinese Library Classification Number: X703; Document Code: A. 2. The industry standard for petroleum and natural gas in the People’s Republic of China, “Design Specifications for Treatment of Oilfield Produced Water SYT0006-1999”, also states clearly that “the greatest advantage of walnut shell filters is their excellent lipophilicity, high dirt retention capacity, resistance to breaking, and long service life.” It is widely used in oil fields such as Shengli and Daqing. ” Due to its lipophilic nature, backwashing may be problematic; perhaps people are starting to consider modifying it so as to facilitate rinsing without compromising its performance (just a guess). Merchants claiming to be hydrophilic and oleophobic may be based on this point, though it is also possible that their view is incorrect from the start. However, by nature, walnut shell filter media are indeed oil-loving. This post was last edited by Fightinghard on 2009-3-30 16:02.]

　　Walnut shell filter media is a water treatment filter material made from high-quality hickory shells, which are processed through crushing, polishing, steaming and washing, chemical treatment, and two rounds of screening. Walnut shell filter media boasts high hardness, wear resistance, and good compressive strength – with a compressive force of 23.4 kgf. It also has stable chemical properties, does not dissolve in acids or bases, exhibits strong pollution-adsorption capacity with an adsorption rate of 27–50%, is hydrophilic, and resists oil immersion. 　　Due to its hardness, ideal specific gravity, porosity, and multi-faceted structure, along with specialized physicochemical treatment that removes its pigments, fats, oils, and electroactive ions, walnut shell filter media possess excellent oil-removal capabilities, the ability to remove solid particles, and ease of backwashing. As such, it is widely used in the treatment of oily wastewater from oil fields, industrial wastewater, and domestic water. It is a next-generation filter media that replaces quartz sand filters to improve water quality and significantly reduce water treatment costs. According to tests conducted by Beijing Forestry University, the Testing Center of Shandong Academy of Sciences, and Jiangsu Institute of Environmental Protection, walnut shell particles with a particle size of 1.25–1.60 mm, which possess strong compressive strength, have an average compressive limit of 0.2295 KN (23.40 kgf). Walnut shell particles with a particle size of 0.80–1.00 mm have an average compressive strength limit of 0.165 KN (16.84 kgf). It has stable chemical properties and does not contain toxic substances; its solubility in acids, bases, and water is very low. The loss of walnut shells in hydrochloric acid solution is 4.99%, while the loss rate in sodium hydroxide solution is 3.8%, and it does not cause deterioration of water quality. http://baike.baidu.com/view/1194595.htm

“Walnut shell filter media is a water treatment filter material made from high-quality hickory shells, which are processed through crushing, polishing, steaming and washing, chemical treatment, and two rounds of screening. Walnut shell filter media boasts high hardness, wear resistance, and good compressive strength – with a compressive force of 23.4 kgf. It also has stable chemical properties, does not dissolve in acids or bases, exhibits strong pollution-adsorption capacity with an adsorption rate of 27–50%, is hydrophilic, and resists oil immersion. ” This is exactly what this post is meant to discuss. This post was last edited by Fightinghard on 2009-3-31 09:11]

Made from high-quality hickory shells, it is produced through processes such as crushing, polishing, steaming and washing, as well as chemical preservation treatment, followed by two rounds of screening. This filter media is tough, wear-resistant, and compressive (with a compressive strength of 23.4 kgf). It has stable chemical properties, strong dirt adsorption capacity (adsorption rate of 27–50%), resistance to oil immersion, and is easy to backwash and regenerate. The backwashing intensity is low (6.7 L/Sm2), the filtration rate is high (24–26 m/h), it does not compact or deteriorate, and it never needs to be replaced; only 5–10% replacement is required each year. The oil removal rate reaches 95%, with the oil content reduced to below 5 mg/g. Suitable for oil fields, fuel-saving and environmental protection equipment, etc. Test data for testing items: Oil removal rate – 90–95%; Backwashing intensity – 25 m3/m2·h; Suspended solids removal rate – 95–98%; Water flushing pressure – 0.32 MPa; Filtration speed – 20–25 m/h. Maintenance method: Add 5–10% of the original amount annually. Specific gravity – 1.5 g/cm3; Bulk density – 0.8 g/cm3. Due to its hardness, ideal specific gravity, porosity, and multi-faceted structure, along with specialized physicochemical treatment that removes impurities such as pigments, fats, oils, and electrically charged ions, walnut shell filter media exhibits excellent oil removal capabilities, as well as the ability to remove solid particles and is easy to backwash. Walnut shell filter media are widely used in the treatment of oily wastewater from oil fields, industrial wastewater, and domestic water. It is a next-generation filter media that replaces quartz sand filters to improve water quality and significantly reduce water treatment costs. According to tests conducted by Beijing Forestry University, the Testing Center of Shandong Academy of Sciences, and Jiangsu Institute of Environmental Protection, walnut shell particles with a particle size of 1.25–1.60 mm, which possess strong compressive strength, have an average compressive limit of 0.2295 KN (23.40 kgf). Walnut shell particles with a particle size of 0.80–1.00 mm have an average compressive strength limit of 0.165 KN (16.84 kgf). It has stable chemical properties and does not contain toxic substances; its solubility in acids, bases, and water is very low. The loss of walnut shells in hydrochloric acid solution is 4.99%, while the loss rate in sodium hydroxide solution is 3.8%, and it does not cause deterioration of water quality. Main markets: The above products are widely used in industrial wastewater treatment as well as in urban water supply and drainage projects across industries such as oil fields, chemicals, metallurgy, thermal power, printing and dyeing, papermaking, brewing, and leather processing. They represent the most ideal water purification filtering material for various types of filters. Last edited by zsy_lucky on 2009-3-31 20:32.]

Walnut shells have a large specific surface area, strong adsorption capacity, and high dirt-trapping capacity. Based on practical engineering experience, walnut shell filters do not achieve very satisfactory oil removal results. Currently, oil removal generally involves inclined plate oil separation plus air flotation. The concentration of oil can be removed using membranes produced by a German company. Ordinary membranes are very sensitive to oil, but foreigners mentioned in our last conversation that this type of membrane is very effective at removing oil. But the material isn’t specified