Washing post-treatment processes

The term post-treatment refers to processes vdiich are used after the principal solid-liquid separation has been achieved. The final step in the latter operation is usually some type of cake filtration which will leave a cake that may be fully saturated with liquid or partially drained and it is extremely unlikely that the solids are in an acceptable condition for any subsequent operation such as thermal drying. Thus the post treatment processes are washing and deliquoring which are concerned req>ectively with removing the soluble solids from the liquid remaining in the cake and then purging the major proportion of the liquid fi om the cake pores. 

After soil washing wash water could be reintroduced into the CHEMFIX process later for hydration purposes thus eliminating the need for any post-washing water treatment. 

Chlorite and chlorate residues were detected on pre-processed produce (0.8 and 0.5 mg/kg, respectively) that was immersed in water following ASC spray treatment for 5-10 s at 1200 mg sodium chlorite/l and pH 2.5. Residues fell to below the limit of detection of 0.1 mg/kg when a high-volume wash was applied for 30 s. In another study, conducted with various types of processed (cut up/sliced) fruits and vegetables (i.e. carrots, melons, lettuce, strawberries, onions and french fries) dipped in or sprayed with ASC at 1200 mg sodium chlorite/l, pH 2.5, for 30 s, then rinsed and held for 24 h, chlorite was detected on many of the unrinsed treated samples. However, a post-treatment wash reduced chlorite levels to below the limit of detection of 0.01 mg/kg in all cases except for ASC-dipped (but not sprayed) lettuce, on which chlorite was detected at 0.23 mg/kg. In all cases, chlorate was below 0.01 mg/kg when the produce was held for 24 h after treatment. 

Because it is primarily a surface phenomenon, bacterial devulcanisation often requires finely ground rubber powder (e.g., 200 mesh) to be most effective, as a high surface area to volume ratio is needed, and the reaction is usually carried out in a temperature-controlled bioreactor. Potential disadvantages of the process, therefore, can include the relatively high cost of the small-particle-size rubber crumb, the relatively high capital outlay, and the fact that the rubber crumb has to go through a post-treatment wash and drying process. 

In the 1970s, Solvay iatroduced an advanced TiCl catalyst with high activity and stereoregulahty (6). When this catalyst was utilized ia Hquid monomer processes, the level of atactic polymer was sufftciendy low so that its removal from the product was not required. Catalyst residues were also reduced so that simplified systems for post-reactor treatment were acceptable. Sumitomo has developed a Hquid monomer process, used by Exxon (United States), ia which polymer slurry is washed ia a countercurrent column with fresh monomer and alcohol to provide highly purified polymer (128). 

The chemical stability tests were intended to quantify etructure loss under conditions encountered in either catalyst manufacturing or post-regeneration metal redisperaion processes ("rejuvenations"). Zeolites were first calcined in dry air for two houre at 462 C, after which slurries of 20 g zeolite in 200 mL of treatment solution were prepared and stirred for two hours. The treated zeolites were collected on Buchner funnels, washed twice by reslurrying in 200 mL portions of water, dried at 110°C, and (optionally) calcined In dry air for one hour at 4B2°C. 

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