Nanostone
A surface water treatment plant in South Dakota, has been producing potable water with a pressurized PVDF hollow fiber MF system for over a decade. Some of the hollow fiber membranes in the plant have reached end of useful life and the owner opted to switch one of the hollow fiber membrane skids over to ceramic UF membranes. The decision was made based on a successful ceramic UF installation on site (see “High Turbidity Backwash Waste Recovery for Potable Use at Surface Water Treatment Plant” in AMTA/MTC 2018) and because the owner wanted to improve operation of the hollow fiber system with regards to fiber breakage and the poor production rates versus nameplate value of 1 MGD net production. With retrofit of 36 Nanostone CM-151 modules into this one hollow fiber skid, the skid is able to produce 1 MGD net with fewer modules and has the flexibility to increase capacity to 1.38 MGD (50 CM-151 membranes) within the existing skid footprint, by filling all available membrane slots in the future. This paper discusses the retrofit experience and methodology and also compares performance of the Nanostone Water ceramic UF to the primary MF system at the same location, running side-by-side.
Retrofit execution: The major mechanical modification during the retrofit execution, was expansion of the feed, permeate and retentate headers from 6” to 8” NPS. This step was not necessary for the 1 MGD initial phase retrofit, but was performed in anticipation of the future case of 1.38MGD production. The retrofit execution took 10 days of 8-10 hours each, from shut down of polymeric UF membranes to first production from the ceramic UF system, i.e. lost production time of 10 days. In two other Nanostone surface water and drinking water retrofit projects where skid header changes were not required, the retrofit downtimes were reduced from 10 days to 5 days. These two projects had similar 8-10hr workdays and similarly employed 2-3 team members and were slightly larger at 44 and 56 membranes changed out.
Initial system performance: The existing MF system operates with inline coagulation/prechlorination and operates at 36 gfd, 96% recovery, 10% excess recirculation, with a specific flux of 2-5 gfd/psi (TMP 7-18 psi), and a service cycle between BW of 30 minutes. Nanostone CUF system shares the same feed supply, runs in dead-end mode and achieves 125 gfd @ 97+% recovery, with a typical specific flux of 7.8 to 17.8 gfd/psi (TMP 7 – 16 psi), and a service cycle between BW of 35 mins. Production volume between maintenance cleans was extended by 5.9 times, reducing chemical cleaning cost significantly.
After simple retrofit, the first 2 months of operation showed that using a robust ceramic membrane system eliminates fiber breakage issues, improves water recovery, reduces chemical cleaning costs over 80%, operates robustly through feed upsets experienced during this time frame, while passing daily integrity tests (LRV avg 5.1 permeate side) and exceeding turbidity goals(16-18 mNTU’s), immediately at startup. For more information on Nanostone, please go to the following website: https://www.nanostone.com/
