Achieving Stable Densification in Continuous Flow Systems through Granule Management

Presentation Description: This paper presents a comprehensive investigation into the design and operation of Continuous Flow (CF) densified wastewater treatment systems. Densifying sludge in CF systems provides a cost-effective solution to augment treatment capacity, avoiding resource-intensive and space-consuming upgrades. Despite the promise, adoption has been constrained by limited designer and decision-maker familiarity with densification techniques and uncertainty about performance benefits. The authors of this paper aimed to overcome these barriers through the Water Research Foundation (WRF) Project # 5130, which seeks to provide actionable guidance for the industry.

This study bridges the gap between Conventional Activated Sludge (CAS) and Aerobic Granular Sludge (AGS) technologies. Like AGS, the densification process employs biological and physical selection strategies to promote the formation of dense, fast-settling particles (i.e., granules). These strategies demand minor, yet pivotal modifications to CF reactor design and sludge management practices.

At the heart of the biological selection for densified sludge is the concept of an optimal selector zone. By ensuring complete uptake of rbCOD in the selector zone, we induce famine conditions in subsequent zones, thereby favoring carbon-storing, granule-forming organisms. Concurrently, physical selection is key for the retention of these granular particles formed through biological selection. Recent reports demonstrate that effective physical selection is most commonly achieved using hydrocyclones.

The centerpiece of this paper is a A full-scale demonstration DAS pilot (7 MGD) which has operated for several years. Located at the Denver Metro Water Recovery facility, this pilot combined various process configurations with physical selection (hydrocyclones) to achieve DAS.

This, coupled with additional demonstrations, provide significant insights into:

• Granule Generation: Enumerate the biological selection strategies available for different process configurations, aimed at efficient granule generation.
• Granule Retention: Elucidate tools and methodologies for operating physical selectors that maintain granule retention, despite seasonal variations.
• Granule Management: Present selection strategies that control granule size and fraction, optimizing settleability and nutrient removal performance.

This paper is designed to serve as a critical resource for designers and decision-makers, fostering confidence in CF densified systems and catalyzing their widespread adoption.