AC25 Inevitable Role of Secondary Treatment in Direct Potable Reuse Facilities

CWEA Members: $35.00
Non-Members $45.00
CWEA Contact Hours: 1.0 contact hours towards CWEA Certifications: AWT

Presentation Description: California DPR Regulations require ozone and biological active carbon (BAC) filtration ahead of full advanced treatment consisting of reverse osmosis (RO) and advanced oxidation process (AOP). The main purpose of ozone and BAC is to address low molecular weight organic compounds some of which such as acetone, formaldehyde cannot be effectively removed by the full advanced treatment. The other purpose of ozone-BAC is to provide an additional barrier for chemical peak “averaging”. 

While Ozone-BAC can provide an effective barrier for low molecular weight compounds that are poorly removed by full advanced treatment, the capabilities of ozone-BAC is limited to relatively small chemical peaking based on North City chemical spike studies. However, one critical area has not come to closer attention of State Water Board. That is the secondary treatment. In this presentation, we will explain inevitable role of secondary treatment in a DPR train. First, an activated sludge based secondary treatment can provide excellent removal for slowly biodegradable organic compounds such as acetone, formaldehyde and all other low molecular alcohols and ketones that are poorly removed by full advanced treatment. Second, a secondary treatment can provide nitrogen control which is critical to meet nitrite and nitrate nitrogen primary MCLs of 1 and 10 mg/L, respectively. These limits may not be reliably met in RO-based full advanced treatment if no nitrogen control is provided in the upstream wastewater treatment plant (e.g., Hyperion WRP). 

Third, a good nitrogen control is essential to minimize secondary effluent nitrite concentration which creates very high ozone demand during ozonation. Last but not least, a well-designed and operated secondary treatment can provide a high-quality effluent with reduced suspended solids, phosphate and metals which can create operational challenges at downstream advanced water purification facility (AWPF).

In summary, how a robust secondary treatment along with performance requirements make DPR possible and case study examples will be presented to demonstrate how secondary process performance affects & defines AWPF design, performance & operation in a DPR train. It will provide an unmatched value for public and regulatory agencies to explore how secondary treatment that makes DPR projects more robust and resilient.
Learning Objectives:
To understand capabilities and limitations of ozone and BAC for chemical control in DPR projects
To understand role and superior benefits of activated sludge based secondary treatment in DPR
To understand how we can configure secondary treatment to make DPR projects more robust and resilient"

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