Hexavalent Chromium Removal: Future-Proof Your Technology Investment
In California, the State Water Resources Control Board (SWRCB) recently adopted a lower Maximum Contaminant Level (MCL) of 10 parts-per-billion (ppb) for hexavalent chromium (Cr6). This regulation will take effect in October 2024. As a result, approximately 500 sites throughout the state will need to assess their Cr6 treatment plans, determine an appropriate remediation solution, and implement a compliance plan to meet the standard. This has generated considerable concern about the cost to ratepayers and taxpayers in terms of achieving compliance today and in the future should the State determine to lower the MCL.
Within the regulation, the SWRCB has identified three best available treatment (BAT) technology solutions for Cr6 removal that cities can review and evaluate. These include ion exchange (IX), reverse osmosis (RO), and reduction/coagulation/filtration (RCF) with either an on-site generated stannous, or bulk ferrous- or stannous-based reagents. Additionally, the SWRCB noted that it will periodically review the proposed 10 ppb MCL to bring it as close to the Public Health Goal (PHG) limit of 0.02 ppb. As with the setting of the current MCL, that decision will be based on the availability, cost and performance of treatment technologies.
Therefore, as cities set out to meet today’s MCL, they must consider the MCL of the future and adopt the right Cr6 treatment approach that can cost-effectively comply with a more stringent regulatory limit.
BAT Technologies: The Need to be Fit-for-Purpose
To find the most suitable Cr6 treatment approach, cities must take a set of criteria into account. These criteria include economic, environmental, and operational parameters, which are outlined in Table 1. To compare, three technologies have been evaluated against these parameters, including bulk ferrous reagent RCF, IX, and on-site generated stannous reagent RCF. Although all three solutions meet the 10 ppb MCL, some may not be suitable if the MCL is lowered in the future.
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On-Site Generated Stannous Reagent RCF: Cr6 Treatment Solution for the Present and Future
The innovative RCF technology, SafeGuard™ H2O, is based on the on-site generation of a stannous reagent. This technology has been proven to remove Cr6 down to sub-ppb residual levels, which is close to PHG of 0.02 ppb. The SafeGuard™ H2O system is highly efficient and has been used successfully in multiple field demonstrations. As a result, this technology provides cities with two unique ways to protect their Cr6 technology investment.
Cities that use SafeGuard™ H2O can reduce costs associated with treating multiple wells and implement a water blending strategy because of the technology’s ability to consistently achieve non-detect (<1 ppb) effluent levels of Cr6. Additionally, by using the SafeGuard™ H2O technology, cities can future-proof their investment and lower the presence of Cr6 as close to the PHG as possible in a cost-effective and efficient manner.
The SafeGuard™ H2O technology is highly accurate and reliable, delivering a tightly controlled dose of a stannous reagent generated onsite through an electrolytic process. The electrolytic process design consists of an electrolyzer that causes food-grade tin plates to dissolve, producing a reagent at a concentration required to meet the treatment goals of the city. Thus, meeting a treatment goal of less than 10 ppb or less than 1 ppb with SafeGuard™ H2O is merely a question of dissolving tin at a faster rate (+20%) in order toto increase the reagent dose. This means that scaling the SafeGuard ™ H2O solution to meet future MCL levels will not require more capital investment, simply an increase in tin consumption. Scaling the process would represent a minimal incremental operating cost, a testament to the investment security SafeGuard™ H2O offers cities.
In the context of the other technologies outlined in Table 1, the economic impact of lowering the MCL may vary significantly. For example, IX treatment technology may sometimes achieve less than 5 ppb. However, it will come at the expense of much more frequent media regeneration cycles needed. Also, due to multiple potential interferences, which may reduce IX media capacity and stability, costly monitoring equipment must be implemented to ensure tight treatment process control. As a result, both system capital and operational costs will increase significantly, along with a dramatic increase in toxic waste generation. The ability of a ferrous-based reagent RCF treatment system to maintain less than 5 ppb Cr6 effluent levels has been reported. However, to achieve 5 ppb, higher reagent demand is required, along with an expensive ultra-filtration polishing step. Such treatment process upgrades and modifications will result in higher treatment lifetime costs, a larger system footprint, and higher sludge generation and disposal costs.
In conclusion, cities must prioritize the implementation of Cr6 treatment solutions while protecting their investment. SafeGuard™ H2O provides a solution that ensures safety and confidence for cities. With SafeGuard™ H2O, cities can pursue a water blending strategy where appropriate and be assured of sustainable compliance if the State decides to lower the MCL.