SCIENCE, RESEARCH & TECHNOLOGY
Hydrocyclone-Based Wasting and
Achieving Better Results with Fewer Resources
By Erin Tracy, P.E.; Pusker Regmi, Ph.D., P.E.; and John Millard
NUTRIENT MANAGEMENT CONTINUES TO BE ONE OF THE HOTTEST TOPICS IN WASTEWATER
treatment. New and innovative technologies for nutrient removal are being developed to both improve our ability
to meet regulatory requirements and reduce chemical and energy use. The City of Pueblo, Colorado, recently
embarked on a project to do just that by implementing full-scale hydrocyclone-based wasting at their water reclamation
facility—one of only a few mainstream hydrocyclone installations in the United States. The positive results already being
seen at Pueblo show promise for this technology to achieve better results with fewer resources.
Technology overview and benefits
Hydrocyclone-based wasting is a selective-wasting system
that yields short- and long-term benefits for treatment per-formance
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and operational improvements. A hydrocyclone is
a cone-shaped apparatus that separates a feed into a dense
underflow stream and a less-dense overflow stream. Applied
to wastewater treatment, hydrocyclone-based wasting is a
physical unit process that promotes and maintains densifica-tion
of activated sludge, which can lead to granulation. Pro-moting
the growth of aerobic granular sludge is a strategy to
improve sludge settleability and productive biomass retention
along with nutrient removal.
In hydrocyclone-based wasting, hydrocyclones are fed a portion
of the return activated sludge (RAS). The lighter, poorer-settling
solids, including bulking organisms, exit in the overflow stream
which makes up the waste activated sludge. The denser, more-desirable
fraction in the underflow is returned to the activated
sludge process. Physical selection of these dense sludge particles
provides two main benefits. First, the more orderly underflow
exhibits better settleability, effectively increasing secondary
clarifier capacity. Second, the selection of denser granules pro-motes
the retention of organisms better suited for enhanced
biological nitrogen and phosphorus removal.
While there are many potential benefits of microbial population
selection, the hydrocyclone system itself is a well-understood
physical process. From an operational and process control per-spective,
hydrocyclones are easy to operate and troubleshoot.
Similarly, the impact of hydrocyclones can be monitored with
basic settling and nutrient measurements that are already part
of the sampling regimen at many plants.
From a financial and a sustainability standpoint, hydrocyclones
offer a path for aerobic granulation as a retrofit technology that
does not require significant energy consumption, large physi-cal
footprints, or any chemical addition. In fact, hydrocyclone-based
wasting has the potential to reduce existing chemical
addition for settling aids and supplemental carbon sources.
Finally, hydrocyclones are compatible with existing activated
sludge processes and they can often be installed and commis-sioned
without major process interruptions.
Case study overview and results
The City of Pueblo recently implemented hydrocyclone-based
wasting as a retrofit to its existing activated sludge process at the
James R. Dilorio Water Reclamation Facility with two primary