الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 111 |  |  |
| | | from | 111 | | |
Abstract
Zero Liquid Discharge technology (ZLD) is a friendly technique to the environment and reuse the wastewater which results in reducing the water consumption in the industry. This technology is used in many industrial applications especially the petrochemical industry to remove the salts (TSS) in industrial wastewater. In a traditional ZLD unit, the brine is heated with steam which evaporates the water in the brine then is concentrated in a crystallizer, that causing a problem of scaling of salts at the metal surface of the evaporator and crystallizer, which that need cleaning and shutdown of the unit. The gypsum seeds technology is used to attract the wastewater salts crystallize on the gypsum seeds instead of the metal surface of the evaporator and crystallizer. The feed wastewater is a mixture of reverse osmosis (RO) reject and softener regeneration waste, which is an actual wastewater feed to the Zero Liquid Discharge unit in a petrochemical plant. The main goal of this study is to investigate the effects of different parameters on the rate of crystallization of calcium sulfate such as preheating time before adding the wastewater, rotational speed, initial gypsum concentration, different seeding material (CaSO4.2H2O & CaCO3), particle size of seeds, pH, wastewater feed ratio (RO reject & Softener reg. waste) and mixed seeding (CaSO4.2H2O & CaCO3). The results of the present study showed that the best conditions found for the crystallization rate of the salts were 7 g/L initial gypsum concentration, 25 RPM rotational speed, without any preheating time before treatment, using larger particle size seeds, pH 10, wastewater feed ratio between RO reject & softener regeneration waste is 70:30 % volume (respectively) and using pure Terra Alba gypsum as seeding material.