Los Angeles Controlled Testing Compares Pickup Ability of Regenerative Air and Mechanical Broom Sweepers
by Ranger Kidwell-Ross
posted August 2024
In a controlled test, Elgin's RegenX regenerative air sweeper was found to be more than twice as efficient at pollutant removal than the company's Broom Bear mechanical broom sweeper. The sweepers were chosen as representative of their two technologies, regenerative air and mechanical broom. The overall study was funded by the Safe Clean Water Program (SCWP). Note that the following are preliminary results from an early part of the study and will be published as part of the final report when it is completed.
The primary goal was to evaluate the potential for increased pollutant removal and improved water quality by incorporating regenerative air sweepers into the City of Los Angeles fleet. Note: All testing was done without using water for dust suppression.
A recent study conducted by the City of Los Angeles and Larry Walker Associates has shed new light on the potential of street sweeping as a cost-effective method for reducing stormwater pollution. The study, which was intended to compare the pickup performance of mechanical broom sweepers with regenerative air sweepers, offers valuable insights for city managers looking to optimize their street sweeping and stormwater management programs.
The information about the study in this article is from a conversation with Jon Ball and Chris Minton conducted by WorldSweeper's Editor, Ranger Kidwell-Ross.
Study Background
Jon Ball, Environmental Affairs Officer for the Los Angeles Sanitation and Environment Watershed Protection Program, explained the impetus for the study: "Our LA Streets Bureau came to our group in the watershed protection program and had a question about how we can do street sweeping in a way that would optimize it for water quality benefits."
The City partnered with Larry Walker Associates to design and conduct the study. Chris Minton, Vice President of Larry Walker Associates, outlined the primary goals: "Our overarching study questions were focused on water quality, and so our study design was built around this concept of how to sweep, where to sweep and when to sweep."
Testing Methodology
The study utilized a controlled environment at a water reclamation plant, where researchers tested sweepers on different pavement types (smooth and rough) at various speeds (5, 10, and 15 mph). A standardized simulant mix was used to represent street dirt, allowing for consistent comparisons between sweeper types.
Minton described the testing process: "We used a spreader to spread out a known load of the simulant across the test area. And then one of the sweepers swept it at a controlled speed. After each sweeper pass, researchers vacuumed the surface to measure the remaining material left on the pavement surface and then conducted a grain size analysis to determine pickup efficiency for different particle sizes."
Key Findings
The study revealed a significant performance gap between regenerative air sweepers and mechanical broom sweepers. As Ball reported, "The regenerative air sweeper showed significantly higher debris pickup efficiency (75%) compared to the mechanical broom sweeper (35%)."
Minton added that "the observed efficiency differential across particle sizes between the Elgin Broom Bear mechanical sweeper and Elgin's RegenX regenerative air sweeper got larger as the particles got smaller. For the biggest particles, the difference between the pick-up efficiency (PUE) of the Broom Bear and the RegenX was only about 5-10%.
However, below 600 microns the PUE of the mechanical sweeper really tanked and the difference became very stark. With the 250-600 micron particle size class (at 5 mph), for example, you were still getting 80%+ removal with the RegenX but less than 10% removal with the mechanical. Smaller than that and the PUE of the mechanical was essentially zero while PUE for the regenerative air was above 50% down to the smallest particles. (Editor's Note: According to Wikipedia, a human hair can range from 17 to 181 microns in width; however, an average considered to be around 75 microns.)
By clicking on the following graph you may view it in a larger size. Note: That image will open into a new browser window.
You will note in the graph a higher pickup efficiency for the Broom Bear in the smallest fraction size. Here's how the testing team explained what they thought was occurring... "We hypothesized that the higher measured particle removals in the smallest particle size fraction could be attributed to fugitive dust loss. Basically, the Broom Bear removed the material from our test track but sent it into the air and surrounding area rather than into the sweeper’s hopper. There are a few observations that point towards this hypothesis:"
Pickup efficiency increased at higher speeds rather than decreased as would be normally expected.
We saw a bigger cloud of dust when the Broom Bear was operated at higher speeds, so it seems like what we’re measuring here is dirt blown off the track rather than picked up by the sweeper.
We only observed this phenomenon on the smooth surface.
Removal on the rough surface was near zero. This may be because street dirt is less easily blow off the track when it is entrained in a rough street texture.
"Importantly, what was seen was a performance difference that was most pronounced for fine particles, the sizes that typically contain higher levels of pollutants. This finding has significant implications for water quality management, as smaller particles are often more challenging to remove (via other technologies) and can carry a disproportionate amount of contaminants."
Implications for Stormwater Management
The study's results suggest that incorporating regenerative air sweepers into municipal fleets could lead to more effective pollutant removal from streets before the material can enter stormwater systems. Overall, the performance difference was most pronounced for fine particles, the sizes typically contain higher levels of pollutants. This finding has significant implications for water quality management, as smaller particles are often more challenging to remove and can carry a disproportionate amount of contaminants.
Utilizing regenerative air sweepers is an approach that could potentially reduce the need for expensive end-of-pipe treatment solutions. That fact is mirrored by studies in both Minnesota and Florida, both of which have determined picking up a pound of targeted pollutants via street sweeping appears to be as much as 5 times as cost-effective as the next most cost-effective method, catch basin cleaning/filtration.
Minton highlighted the potential cost-saving implications: "If we got this much removal for street sweeping, what would that do to our structural control costs and capacity needs? ... It may create an avenue for funding street services."
Future Directions
While the initial study focused on controlled environment testing, future phases will include real-world testing on Los Angeles streets. Ball outlined the next steps: "Where we want to take things now is out into the real life streets of LA, and do more comparison testing between sweeper types. And then also look at accumulation rates for how quickly street dirt and associated pollutants accumulate." The researchers also plan to analyze pollutant concentrations in real street dirt samples.
Challenges and Considerations
One challenge identified in the study is balancing water quality benefits with other considerations, such as air quality and operational factors. The use of water for dust suppression, for example, may negatively affect pickup efficiency although reducing fugitive dust.
Ball noted the public perception aspect: "We've gotten comments and feedback just from people we've presented to that they see the dust cloud behind a street sweeper and the obvious question is, how effective can that be?"
Conclusion
This groundbreaking study provides valuable insights for city managers looking to optimize their street sweeping programs for water quality benefits. By demonstrating the superior performance of regenerative air sweepers, particularly for fine particle removal, the research suggests a potential pathway for more cost-effective stormwater pollution control.
As the study progresses to real-world testing, it has the potential to inform decision-making processes for municipalities across the country, potentially leading to more efficient and effective urban pollution control strategies.
The following are in outline information format summarizing the preliminary findings to date:
Overview
Performance Efficiency: The regenerative air sweeper demonstrated a significantly higher street dirt pick-up efficiency (PUE) of 75% on average compared to the mechanical sweeper's 35% across all particle sizes and operating conditions. The performance gap was most pronounced for fine particles, which typically contain higher pollutant concentrations.
Pollutant Removal: The regenerative air sweeper was found to potentially remove three to six times more copper and zinc than the mechanical sweeper. This suggests a substantial improvement in pollutant removal capabilities, particularly for fine particles where pollutants are concentrated.
Operating Conditions: Testing revealed that street dirt PUE declines with increasing operating speed, with optimal efficiency achieved at or below 5 mph. The regenerative air sweeper maintained higher efficiency at higher speeds compared to the mechanical sweeper.
Surface Conditions: The regenerative air sweeper outperformed the mechanical sweeper on rough surfaces, indicating its superior ability to dislodge and collect dirt from cracks and potholes.
Testing Methodology
Controlled Environment: The testing was conducted at the Donald C. Tillman Water Reclamation Plant in Van Nuys, Los Angeles, using two test tracks representing smooth and rough street surfaces. Simulated street dirt was used to ensure consistency in testing conditions.
Variables Tested: The study evaluated the impact of sweeper type, street surface condition, and operating speed on street dirt PUE. Each sweeper was tested at speeds of 5, 10, and 15 mph on both smooth and rough surfaces.
Implications for Policy and Practice
Fleet Upgrade: The findings support the integration of regenerative air sweepers into the City's street sweeping fleet to enhance pollutant removal and improve water quality.
Operational Adjustments: The study suggests that operating sweepers at lower speeds and focusing on areas with rough surfaces could maximize street dirt and pollutant removal.
Future Research: Further phases of the study will involve real street testing and characterization of street dirt to optimize the deployment of street sweepers for maximum environmental benefit.
Overall, the controlled environment testing underscores the advantages of regenerative air sweepers over traditional mechanical sweepers, particularly in terms of pollutant removal and adaptability to various street conditions.
You can see an @ 4-minute analysis of study implications done by Ranger Kidwell-Ross in the following YouTube-hosted video. If the embed link is not working for you, the YouTube link is: https://youtu.be/9qKrprNACRo
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Jon Ball, Environmental Affairs Officer for the Los Angeles Sanitation and Environment Watershed Protection Program, explained the impetus for the study: "Our LA Streets Bureau came to our group in the watershed protection program and had a question about how we can do street sweeping in a way that would optimize it for water quality benefits."
The City partnered with Larry Walker Associates to design and conduct the study. Chris Minton, Vice President of Larry Walker Associates, outlined the primary goals: "Our overarching study questions were focused on water quality, and so our study design was built around this concept of how to sweep, where to sweep and when to sweep."
