Regenerative Air & Vacuum Sweepers: More Than Just a Pretty Face

Street and parking lot sweeping is considered a best management practice in many cities across the nation. It’s impact on our environment cannot be overstated. Not only does it make our landscapes look pretty, but it also makes our air easier to breathe, reducing instances of asthma and other respiratory diseases, as well as providing us with cleaner water.

Minnesota published a best practices resource document in 2008. They recommend, “street sweeping as a nonstructural operation provides significant benefits in achieving quality not only in the receiving water, but roadway appearance, safety, potential air quality improvement and improving structural device maintenance. Implementing a street sweeping program using higher efficiency street sweepers either alone or in combination with mechanical sweepers and coupled with sweeping frequencies reflecting the amount of roadway material generated is a prudent approach for achieving quality.”

The report suggests a minimum and maximum sweeping frequency for arterials, commercial, light industrial, heavy industrial, residential, and central business districts. The minimum suggested frequency for arterials, commercial and heavy industrial is 9 times per year, with the maximum of 16 times per year. For light industrial, they suggest a minimum of 6 times per year and a maximum of 9. They recommend 4 to 9 times per year for residential, and biweekly to 2 times per week for central business districts.

Water Quality

Over the course of a year, Seattle Public Utilities (SPU) set out to determine whether sweeping would have an effect on “preventing a significant amount of sediment and associated contaminants from being discharged to receiving waters, which not only impacts water/sediment quality but also impairs substrate quality.” One of the other possible benefits they listed was to reduce flooding as well as improved air quality and better aesthetics.

They conducted a study from 2006-2007 and published the results in a 2009 report. SPU serves an estimated 40,800 acres in the Seattle metropolitan area. This study is a response in part to the requirements of the National Pollutant Discharge Elimination System (NPDES) municipal stormwater permit, which requires cities to improve stormwater quality. NPDES is required to inspect 35,000 to 40,000 catch basins annually and to clean them when sediment depth exceeds 60 percent of the sump depth. “Catch basin inspection and cleaning constitutes nearly 60 percent of SPU’s $3.7 million drainage-related maintenance budget.”

During the testing phase, sweeping was conducted every two weeks using a Schwarze A8000 regenerative air sweeper. The study found that “the median monthly street dirt yield at the swept sites was 48, 74, and 90 percent less than the control (unswept) sites. On an annual basis sweeping removed approximately 2,200 to 3,100 pounds of material per acre of street swept.”

The test also found that sweeping has a positive affect on water. “Contaminants found in street dirt, sweeper waste, and catch basin samples included metals, petroleum hydrocarbons, and phthalates. Of these chemicals in the 55 samples analyzed, motor oil (82 percent), carcinogenic PAHs (78 percent), di-n-octylphthaltate (65 percent), bis (2-ethylhexyl)phthalate (60 percent), butylbenzylphthalate (35 percent), di-n-butylphthalate (29 percent), zinc (18 percent), and chromium (15 percent) concentrations were above the Washington state sediment/soil standards and guidelines.”

Unfortunately, there was no change in the amount or rate of sediment accumulation in the test area catch basins, meaning that the city would not benefit from savings in that area. However, the testers felt that further evaluation is needed.

The testers recommended that the city pursue “an expanded street sweeping program to reduce the amount of pollutants discharged to area receiving water bodies from city streets.”

Regenerative Air / Vacuum vs. Broom

So, what is the best sweeper for the job? “There are many tools in the tool box and you wouldn’t use a hammer for a screwdriver,” says Jim Adair, director of product management with Schwarze. “Both type sweepers overlap in the middle. A broom sweeper can pick up bulk and high volume sweeping, whereas the air machine will pick up average road debris and fine particulates. You also have fewer moving parts on an air, so there is less maintenance.”

Adair says that many of their customers have both, and some run them in tandem with the air following the broom. While most of Schwarze’s changes with the sweepers have centered around the EPA mandates, they have made other changes such as modulize sweeping heads. “You can change flaps out without removing the sweeping head, and the screens are drop down for easy cleaning,” says Adair. “Regenerative air does a better job of picking up smaller concentrates. Most cities that are bidding ask for PM 10 certified.”

For parking lots, Adair recommends regenerative air. “Regenerative air is more cost effective than broom.” But for construction areas where larger and heavier debris is present, he says that you will want a broom.

“Performance is key with Schwarze,” says Adair. “We’ve always been one of the highest performers on the market. With the higher performance and efficiency, you are able to throttle back, saving fuel and still maintain efficiency. When you need it, you can have the higher performance, but when not needed, you can reduce your RPMs and get the job done.”

“A regenerative sweeper is a versatile sweeper that lends itself to be good at many applications, such as light municipal sweeping and leaf sweeping,” says James Crockett, air sweeper products manager at Elgin Sweeper. “In other applications, due to the nature of the wide pickup head, the regenerative sweeper can transverse long and flat surfaces at an increased vehicle speed to effectively pickup foreign object debris on airport taxiways and runways.”

Unlike a regenerative sweeper, a high-power vacuum sweeper exhausts the pressure side of the blower to atmosphere. “The advantages of this configuration are its increased vacuum levels—almost double that of a regenerative system—which results in a high power density at the nozzles,” says Crockett. “This increased power density at the nozzles allows a vacuum sweeper to perform exceptionally well in other applications that a regenerative sweeper could not, such as heavy municipal sweeping, sweeping millings, restoration of porous pavement, dense dirt and gravel pickup. There are additional advantages to a vacuum sweeper and its nozzle configuration, such as a tow arm linkage, that allows the nozzles to independently trail out into the curb side of the road where the high percentage of debris resides. Unlike the regenerative system and its wide pickup head, the vacuum nozzle configuration is less susceptible to losing suction—or breaking the seal—with the road surface, because each vacuum nozzle can independently trail and conform to the contour of the road surface.”

A new configuration of the Crosswind featuring a patent pending Shared Power system has been introduced this year as part of Elgin’s new EcoInfused Technology initiative. This allows horsepower to be transparently transferred from the chassis engine to the auxiliary engine. The horsepower can come directly from the chassis engine or captured from vehicle momentum as regenerative braking. What this means is the power normally lost to heat by braking can be immediately applied to the auxiliary engine, resulting in improved performance and reduced fuel consumption.

“Elgin Sweeper made a significant investment in conducting an independent, credible, repeatable test to measure the sweeping efficiency of its sweepers,” says Crockett. “Elgin Sweeper wanted quantifiable results of what the storm water experts say about the performance of its street sweepers. We sought out Pacific Water Resources, Inc. (PWR), one of the most credible, recognized independent experts on storm water control in the United States. PWR has developed a state-of-the-art load estimation procedure called SIMPTM (simplified particulate transport model) that can quantify urban pollution loadings and accurately estimate optimum cleaning practices for streets and catch basins.”

Crockett explains that PWR, using modeling tools that accurately simulate the sediment accumulation and wash-off behaviors and their interaction with cleaning practices, designed and implemented a series of controlled street dirt pick-up performance tests for the four Elgin Sweeper models. “The purpose of the field test was to measure the efficiency of the Elgin Sweeper machines operating under conditions typically found throughout the United States,” says Crockett.

“According to PWR’s test results, Elgin Sweeper’s Crosswind NX high-performance filter regeneration sweeper with dust control removed 97.5 percent of the pollutants; the standard regenerative air Crosswind removed 96.4 percent of the pollutants; the vacuum Whirlwind removed 93.5 percent of the pollutants; and the mechanical Waterless Eagle removed 91.5 percent of the pollutants,” says Crockett. “The Waterless Eagle with water spray was also tested and removed 81.0 percent of the pollutants.”

As you can see, regenerative air and vacuum sweepers do more than just make our streets and parking lots pretty. They play a vital role in keeping our air and water clean.

For more information on the Seattle Street Sweeping Pilot Study, visit http://www.seattle.gov/util/groups/public/@spu/@drainsew/documents/webcontent/spu01_005046.pdf

For more information on the Minnesota Department of Transportation Study, visit http://www.mnltap.umn.edu/topics/sweeping/documents/sweeping.pdf

Story by Jennifer Taylor

Resources

For More Information:
Elgin, visit www.elgin.com
Schwarze, visit www.schwarze.com