Waste Heat Driven Membrane Distillation for Industrial Wastewater Treatment

Abstract

The European Union has placed a high priority on reaching the goals described in the 2030 Agenda for Sustainable Development. This aim has provided added momentum to member-state environmental regulatory authorities to further tighten the discharge limits of industrial wastewater. These measures strongly influence existing industrial practices as many traditional wastewater treatment methods cannot achieve these strict release limits. Moreover, industrial sectors are encouraged to employ a zero liquid discharge strategy for advanced wastewater management, particularly for process water reuse. Emphasis is thus now placed on improved water treatment systems to recover, reuse and release water in a manner that protects natural resources, guarantees stringent regulatory constraints and ensures financial viability. In this context membrane distillation (MD) is a promising industrial wastewater treatment technology capable of meeting these requirements while utilizing low-grade heat sources.

This thesis focuses on experimental investigations and techno-economic analysis of waste heat driven MD systems for water purification in two water-intensive industries: nano-electronics facilities and cogeneration plants. Samples collected at relevant facilities were tested in an air gap MD bench unit and a semi-commercial pilot plant, with a focus on separation efficiency and potential for achieving high recovery ratios. For the techno-economic analysis of the industrial scale system, the performance of the chosen semi-commercial unit was considered to evaluate the full-scale system operation in terms of thermal energy demand and expected water purification cost. Various thermal integration approaches were investigated while considering locally available heat sources to realize the energy requirements of the specific MD system. The selected case studies include: removal of tetramethylammonium hydroxide (TMAH) from photolithography process wastewater in nano-electronics industries; treatment of chemical mechanical planarization (CMP) process wastewater in nano-electronics industries; and water recovery through advanced flue gas condensate treatment from municipal solid waste incineration and biofuel fired cogeneration plants.

The results from nano-electronics wastewater treatment tests showed that high-quality permeate could be recovered while observing good to excellent separation efficiencies of analyzed contaminants. Moreover, the proposed advanced flue gas condensate treatment is also proved successful while removing the pollutants up to the concentration levels of parts per billion. The proposed pretreatment step, pH adjustment of MD feeds, enhanced ammonia removal efficiency in all cases. Compared to current practices, the separation efficiencies of the considered MD based processes are improved. The simulation results indicate that the required thermal energy for operating large scale MD systems is readily available via internal waste heat sources of nano-electronics facilities for handling typical volumes of the mentioned wastewaters. In cogeneration plants, district heating supply and return lines are well suited as the heat source and heat sink to manage industrial-scale MD systems effectively. The process economy shows that the unit water treatment cost is mainly constrained by thermal energy cost. In case when the price of heat is considered negligible, the unit water treatment cost is significantly lower than the competing technologies.

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