Batch cleaning systems operating concentration

In the cleaning process the soil is removed by either batch or bath operation. These operations differ in solvent circulation, moisture content, detergent type, and length of wash time. The batch operation uses a fixed quantity of solvent for one operation. The solvent is not circulated during the wash cycle, while it is in the bath method. The bath operation is also known as the charged system. In the bath system, 1% to 4% concentrations of detergent and water are added into the wash tank. 

Three modes of reactor operation may be distinguished, batch, semi-batch and continuous. In a batch system all reactants are added to the tank at the given starting time. During the course of reaction, the reactant concentrations decrease continuously with time, and products are formed. On completion of the reaction, the reactor is emptied, cleaned and is made ready for another batch. 

Compeau et al. (1990) reported a full-scale slurry-phase PCP remediation. The system consisted of soil washing and screening and resulted in clean soil and wash solution. The wash solution was a slurry containing PCP and < 60-mesh-size soil particles at approximately 20% solids concentration. Slurry was treated subsequently in on-site slurry-phase bioreactors. A 50 m3 slurry reactor was operated in batch mode and inoculated by an uncharacterized PCP-mineralizing culture (107 cells/ml of slurry). After 14 days, 370mg PCP/kg slurry had been degraded to below 0.5 mg/kg. For effective biogradation to occur, inoculation was required. 

Table 1 shows that the maximum ethanol concentration in this test was 67.7 g/1, in the outlet of the third reactor, for a flow rate of 8.1 ml/h. In this condition, the TRS and glucose concentrations were 3.3 and 0.8 g/1, respectively. The system is stable for all flow rates. The lowest flow rate, 8.1 ml/h, was more difficult to control, which was what led to some more pronounced oscillation of the variable values in this condition. It was expected in the continuous run that similar results than the ones obtained in the batch run will be achieved. As in batch operation, the cycle time is considerably longer than the reaction time, if the continuous process had reached a similar performance than the one obtained with the batch run in the continuous operation, we could save cycle time (times to clean, to fill ant to empty the reactor). Therefore, from the industrial point of view, the continuous process would lead to higher productivities. 

Another parameter affecting the treatment efficiency in PMRs is the operational mode (Table 6.3).TTie PMRs can work either in batch or continuous modes. Sometimes, semi-batch systems are also applied. In batch mode, the feed tank is filled with the treated solution at the beginning of the process and no refilling of the tank before the end of the operation is done. The permeate is collected in a permeate tank and the retentate (concentrate) is recycled back to the feed tank. At the end of the batch process, a small volume of concentrate remains in the feed tank. Then the system is drained, the membranes can be cleaned if necessary, and the tank is refilled with a new batch. A modification of the batch mode is the semi-batch system. In this case the feed tank is refilled with fresh feed solution as the permeate is removed, in order to keep a constant volume in the feed tank. After a defined time, or once a predetermined concentration or flux is reached, the supply of fresh feed is stopped and the remaining solution in the tank is concentrated, as in batch mode. In continuous mode the feed solution is continuously supplied to the feed... 

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