Electrodialysis reversal (EDR) provides superior reuse solution for high silica wastewate
Challenge
Semiconductor device fabrication increasingly relies upon water reclamation due to economic and regulatory drivers. In such a facility, there are numerous local scrubbers that generate wastewater that could be recycled. While the local scrubber waste streams often have differing water quality and locations within the fab, there are similarities in the types of compounds requiring treatment for reclamation.
Due to the use of hydrofluoric acid (HF) to clean wafers, many local scrubber wastewater streams include high concentrations of fluoride and silica. Conventional HF Waste (HFW) treatment requires precipitation, flocculation, and sedimentation as well as substantial space (footprint) within the fab. It is well established that HFW is highly variable, which can result in instability within conventional treatment processes and potentially discharge permit violations.
Veolia has partnered with a semiconductor fabricator in Singapore to segregate and reclaim a portion of their local scrubber waste. Segregated treatment and reuse enabled plant expansion within a constrained footprint, increased the fab’s overall water recovery, and reduced environmental compliance risk.
Project Summary
End-User: semiconductor fabrication plant
Location: Singapore
Commissioned: 2016
Application: local scrubber wastewater reclamation
Technologies: electrodialysis reversal (EDR) cartridge filters, chlorine
Capacity: 150 m3/hour
Factors Impacting Technology Selection: 50-100 ppm fluoride; 65 ppm total silica in feed (after recycle implemented); SDI5min > 19, SDI1min >90, primarily silica; elevated temperature and low weight organics leading to biogrowth potential
Operational Results: effluent meets local scrubber feedwater quality requirements; 80% fluoride removal; 70% recovery; no silica fouling/removal; controlled biogrowth and 2-3 month clean-in-place interval
Winning Value Proposition: high recovery; small footprint; silica and organic tolerance; control of biogrowth; low operating cost
Keywords: microelectronics; semiconductor; local scrubber reclaim (LSR); hydrofluoric acid wastewater; wastewater reuse; industrial; fluoride; silica; electrodialysis reversal; Z.Plex* filters
Solution
Local scrubber wastewater presents some unique treatment challenges that influence the technology selection. In addition to a feed fluoride concentration of more than 50 ppm, the wastewater streams are prone to biological fouling and have a high concentration of fine silica particulates. Both biofouling and silica are known to be problematic for reverse osmosis (RO)- based systems if not adequately pre-treated.
To address these challenges, Veolia developed an integrated process flowsheet (Figure 2) that includes chlorine dosing, cartridge pre-filters (Z.Plex SWRO.Zs 50-40), and electrodialysis reversal (EDR). The combined process enables 70% recovery and reduction in fluoride concentration from 50-100 ppm to less than 28 ppm. The EDR product water is recycled to the local scrubber feed tank, where it is blended with NEWater for flow balancing.
The EDR based process has several advantages over an ultrafiltration (UF) and RO alternative, including:
- Tolerance to fine silica particles that are difficult to remove with membrane-based UF pretreatment and could foul RO membranes (since many local scrubbers do not have restrictive silica requirements, these silica particles can be returned to the scrubbers within the EDR product water)
- Ability to maintain a chlorine residual throughout the system for biogrowth control
- Reduced footprint
- Ability to achieve more than 70% recovery without the significant chemical dosing required for ion exchange and RO systems
Lower capital cost versus high pH RO systems that could include UF, ion exchange, and RO.
Result
The EDR-based system has been successfully operating since December 2016. The projected EDR membrane life is more than 7 years, and the clean-inplace frequency is only 2-3 months. Within the pretreatment system, the combined use of Z.Plex SWRO filters and a chlorine residual has increased the filter lifetime by 4-fold. This performance has enabled the customer to divert flow from the conventional HFW treatment system to the EDR-based LSR system, which required less footprint and contributed to the fab capacity expansion. An added benefit is that the conventional HFW system operates more stably without the local scrubber wastewater streams.