Thesis (M. Eng.) - Asian Institute of Technology, 1996

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering.

The feasibility of recovering caustic soda from bottle washers of a softdrink plant was investigated at pilot-scale using microfiltration (MF) and nanofiltration (NF). This study revealed that the MF/NF system can purify the caustic soda to a certain extent and can be reused back to the bottle washing units. Within the studied pressure ranges, the optimum applied pressure was determined as 101 kPa for MF, and 1,414 kPa for NF with corresponding permeate fluxes of 235 and 15 L/m2-h respectively. Based on these figures, a large-scale installation for the Thai Pure Drinks Ltd., Pathumthani plant was designed and a financial analysis was conducted for the system. The MF/NF system using MEMCOR hollow fiber membranes and MPS-34 (MWC0=300) gave a payback period of seven years and an IRR of 13.7%, rendering the system not financially feasible. An overall water balance was drawn to find alternatives for water purification and reuse in the plant that would lead to reduction of raw water consumption and liquid discharge into the river. It was found that reuse of microfiltered wastewater treatment plant effluent can reduce groundwater input by 40% and liquid discharged to the receiving water by 65.5%. Two proposed options for reclaiming bottle washing rinse water are treatment by reverse osmosis (RO) or purification by ion-exchange (IE). Based on theoretical considerations, an MF/RO system will recover both pure water and concentrated caustic in the process. On the other hand, IE will recover water fit for reuse in the bottle washers. The two conceptual designs have a payback period of3.2 and 3.4 years respectively, while the internal rate of return are 31.3% and 30.5%.