AC22 - Rethinking Secondary Treatment Design from Potable Reuse Applications

Member fee: $25.00
Non-Member fee: $35.00 

1.2 contact hours towards CWEA's: ECI, EIT Certifications 
SWRCB Waste Water CEUs: 0.1
SWRCB Drinking Water CEUs: 1.0

Presentation Description: Advancements in municipal wastewater treatment technologies started with removal of organics and nutrients (nitrogen and phosphorus) to meet stringent discharge limitations. Potable reuse is becoming an attractive option for incorporating circular economy, resiliency, water sustainability and the One Water approaches. As potable reuse projects get implemented, we have an opportunity to rethink the secondary wastewater treatment design principles and strategies. The key aspects of transforming the secondary treatment design for potable reuse applications include sewershed source control, flow equalization, consideration for scalping plants, solids retention time based on CEC removal requirements, nitrogen removal driven by nitrate MCL, phosphorus removal driven by RO fouling potential, pathogen log reduction across secondary treatment.

Sewershed source control is being required by the potable reuse regulations. Several case studies have shown that source control reduces the pollutant loads entering the WWTP. Maintaining a constant flow rate to the AWT system helps in operations and maintenance (O&M) of the system. With a constant flow operation, process performance such as pathogen log reduction and removal of CECs can be reliably achieved with greater certainty. Wastewater operators are already trained on the benefits of flow equalization on treatment performance.

AECOM is currently designing the secondary treatment for East County Advanced Water Purification Project (Padre Dam). The main purpose of the secondary treatment which receives raw wastewater diverted from the existing sewer conveyance system is to deliver a consistent water quality to MF-RO-UVAOP AWT system.

Higher safety factors are typically applied in the case of primary drinking water contaminants such as nitrate. Consequently, treatment systems are designed with a maximum allowable concentration that is close to 50% of the maximum contaminant levels (MCLs). In wastewater compliance, nitrate is a part of the total nitrogen or dissolved inorganic nitrogen discharge compliance requirements.

Quantifying and demonstrating pathogen log removal across existing treatment steps, such as secondary biological processes, eliminates the need for inclusion of new and additional pathogen inactivation barriers, which could result in substantial savings in capital and O&M costs while meeting the pathogen inactivation requirements.

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Learning Objectives:
Familiarize with the technical aspects that need to be considered when we design secondary treatment systems for potable reuse applications.
Learn how we can transform and rethink the way we design and operate the secondary treatment system to provide a consistent water quality for purified water production.
Learn how implementing source control and flow equalization can result in a reliable and cost-effective potable reuse project.

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