Regenerating biological activated carbon (BAC) in drinking water treatment isn’t a new challenge, but the tools and chemistry we use for it are rapidly evolving. A recent study, published in the Journal of Water Process Engineering, suggests thermally activated persulfate (PS) might be the jumpstart your filtration media needs. This week, Water Treatment 411 dives deep into how this regeneration method performs across BAC service lifespans and why it might finally offer a practical, scalable solution.
When BAC Stops Pulling Its Weight
BAC has become a cornerstone in advanced treatment trains for good reason. It’s effective at removing a broad range of organics, including hard-to-treat micropollutants like iopamidol (IPM), while also providing biological degradation of organics that pass through ozonation or other pre-treatments. But as BAC media ages, performance degrades, not just from spent carbon but from heavy microbial colonization, extracellular polymeric substance (EPS) buildup, and pore blockage. Older BAC (up to 10 years in some DWTPs) can become so loaded with biomass and adsorbed compounds that even aggressive backwashing offers minimal performance recovery.
Traditional regeneration options like thermal reactivation or solvent-based methods are either too energy-intensive or impractical for BAC due to its biological component. Previous attempts using ultrasonic or basic thermal techniques yielded limited success. Enter thermally activated persulfate, a promising oxidant that’s gaining attention for its effectiveness and simplicity.
How Thermal PS Cleans House
This study categorized the PS regeneration process into three distinct stages:
- Microbial Inactivation and Biofilm Detachment
Over 95% of the microbial population was eliminated during the initial phase. Laser scanning confocal microscopy confirmed biofilm disintegration, especially in the outer layers. This step alone addresses a major root cause of BAC fouling.
- Oxidation of Surface-Exposed Adsorbates
With biofilm cleared, PS oxidizes pollutants adsorbed to exposed carbon surfaces. The study found increased soluble microbial products (SMPs) in the rinse water, particularly macromolecular compounds in the 2,000–50,000 kDa range, indicating breakdown of complex organic matrices.
- Carbon Skeleton Oxidation and Deep Impurity Removal
Final-stage oxidation targeted deeper impurities and partially restored pore structures, though micropore recovery remained under 5%. Despite this, surface functionality and adsorption capacity saw substantial improvement, especially for younger BAC.
Regeneration effectiveness was closely tied to media age, with 3-year-old BAC recovering 72.6% of its adsorption capacity versus just 27.4% for 10-year-old media, reinforcing that thermal PS is best used as a preventative strategy before BAC exceeds 5 years in service.
Is This Ready for Plant-Scale Rollout?
While the lab-scale results are promising, scale-up challenges remain. The study doesn’t address full-scale contact times, PS dosing logistics, or thermal energy requirements in continuous flow systems. However, compared to UV-activated or iron-activated PS systems, thermal activation is far more practical for most facilities. No special catalysts. No complex irradiation setups. Just heat and oxidant.
Operators considering implementation will need to evaluate:
- Compatibility with existing filter vessels for heating
- Neutralization of PS residuals post-regeneration
- Handling of regeneration byproducts, particularly SMPs and partially oxidized organics
A Tool, Not a Silver Bullet
Thermally activated PS is not a cure-all, with effectiveness depending heavily on timing and media age. But for utilities looking to extend BAC life, improve pollutant removal, and reduce costs associated with premature media replacement, this method offers a promising middle ground. It’s especially attractive in utilities with limited GAC disposal options or high replacement costs.
The science is sound, the results are measurable, and the process is relatively straightforward. For medium-aged BAC, the benefits are substantial. For heavily fouled media, it might be too little, too late. Either way, it’s time to start thinking about BAC not as disposable, but as regenerable — with the right chemistry.
SOURCES: Journal of Water Process Engineering
