Microbes preferred systems

Thus, one can measure the rate and extent of biodegradation or microbial utilisation of the test plastic material by using it as the sole carbon source in a test system containing a microbe-rich matrix, such as compost, in the presence of air and rmder optimal temperature conditions (preferably at 58 °C - representing the thermophilic phase). Figure 16.3 shows a typical graphical output that would be obtained if one were to plot the percent of carbon converted to CO2 as a function of time in days. 

Chlorine (or other disinfectant) is required to minimize the potential for fouling the membranes with microbes (see Chapters 8.2.1, 8.2.2, and 8.5.2.1). Once membranes are fouled with microbes, it is very difficult to remove them. A free chlorine residual of about 0.5 to 1.0 ppm in the pretreatment system is desirable. Feed water to the RO must be dechlorinated prior to the membranes because the membranes are sensitive to oxidizers, which will degrade the membrane. Sodium bisulfite is the preferred method to dechlorinate unless the RO feed water has a high organic concentration, in which case, carbon filtration at a flow rate of 2 gpm/ft is recommended. (see Chapters 8.1.4 and 8.2.3) Sodium metabisulfite is typically about 33% active, and the stoichiometic dosage of sodium metabisulfite is about 1.8 ppm per ppm free chlorine. So, the stoichiometric dosage of 33% active sodium metabisulfite is 5.4 ppm. For safety, a factor of 1.5 is used to increase the dosage of sodium metabisulfite to ensure complete elimination of free chlorine. 

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