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The aim of this study was to investigate ammonia removal from the effluent of a full-scale biofilm reactor treating pesticide wastewater through the formation of struvite (MgNH4PO4•6H2O). The requirement of magnesium and phosphate ions for precipitation was met by adding MgO and Na2HPO4. Different NH4+:Mg2+:PO43- molar ratios were tested in batch reactors to optimize the precipitation conditions. Ammonia was reduced to 25 mg/L from an initial concentration of 210 mg/L at the highest ratio tested (1:1.2:1.3), equating to 88% removal. However, the extent of ammonia removal was only slightly affected when the N:Mg ratio was reduced from 1:1.2 to 1:0.6; dropping to 83% from 88% on a percentage basis. Struvite precipitation can be easily incorporated within the existing post-treatment section of the full-scale plant, providing the pesticide manufacturing facility with a reliable backup process for its nitrification system.

In this work, exopolysaccharide (EPS) production by the yeast Rhodotorula glutinis was investigated. The results suggest that the synthesis of EPS in batch fermentations was enhanced by using a low C/N ratio to stimulate fast cell growth during the exponential phase and by adding glucose to stationary phase cultures to provide excess carbon for EPS formation. The apparent viscosity and molecular weight of EPS were found to decrease with increasing fermentation time due to the partial hydrolysis of EPS by the acidic fermentation broth (pH 1.8). Maintaining stationary phase cultures at pH 4 was found to be effective in minimizing acid hydrolysis and producing EPS with high molecular weight and apparent viscosity.

For a distillation column under practical operation, the reflux ratio, feed location, flowrate of the top or bottom products are all very important parameters. Using the process simulation package ASPEN PLUS to solve mass balance, heat balance and phase equilibrium equations of a distillation column, the relationships between feed location and content of key components, feed location and heat loads, reflux ratio and content of key components, reflux ratio and heat loads, flowrate of the top product and content of key components, and flowrate of the top product and heat loads, can be determined. With the specifications for the content of key components as constraints, the optimal feed location, reflux ratio and flowrate of the top product can be determined. The o-xylene (OX) column in a xylene plant is optimized as a case study in this paper. Under the optimal conditions the heating utility for the reboiler can be reduced by 20%, OX can be produced by 0.8% more, and operating cost can be reduced by 2,336,000 yuan per year.