Cocoa Processing Waste Pretreatment and Mobile Flotation Plants

A dissolved air flotation (DAF) unit was installed at a cocoa manufacturing plant in New Jersey, USA, for the pretreatment of their cocoa processing wastewater. This chapter introduces: (a) the DAF process system and literature review; (b) the cocoa and chocolate manufacturing procedures; (c) the DAF performance data for treating the cocoa processing waste, and (d) new mobile flotation plants. The constituents of the cocoa processing wastewater are mainly total suspended solids (TSS), 5-day biochemical oxygen demand (BOD5), and fats, oils, and grease (FOG). The pretreatment objective is the reduction of TSS to less than 300 mg/L, FOG to less than 100 mg/L, and BOD5 by over 85%. The pretreated water is discharged to a municipal wastewater treatment plant (WWTP). The DAF performance results have always met the industrial waste pretreatment requirements. When the DAF unit was operated under the recycle pressurization mode (66.67% recycle), using 11 mg/L of alum (as aluminum oxide) and 9.75 mg/L of organic polymer, the following were the average performance data: (a) DAF influent TSS = 144 mg/L, DAF effluent TSS = 56 mg/L (62% TSS reduction); (b) DAF influent FOG = 115 mg/L, DAF effluent FOG = 47 mg/L (59% FOG reduction). Although the influent TSS ranged from 78 to 1,460 mg/L during the operational period, the DAF effluent TSS were always less than 60 mg/L. DAF influent FOG was as high as 3,108 mg/L, but DAF effluent FOG was controlled below 100 mg/L at all times. Additional test results from an independent laboratory indicated that the target BOD5 reduction of 85% was achieved during normal plant operation. The average concentration of floated sludge was over 6%, meeting the requirement for sludge thickening. Mobile plants of DAF, dissolved air flotation–filtration (DAFF), DAF–DAF, DAF–DAFF, etc. are also developed for emergency, seasonal, or temporary services to small customers, similar to the cocoa manufacturing plant.