Evaluation of Recycled Crushed Glass Sand Media for High-Rate Sand Filtration

Evaluation of Recycled
Crushed Glass Sand Media
for High-Rate Sand Filtration
Environmental Program
A division of the Pacific NorthWest Economic Region (PNWER)
2200 Alaskan Way, Suite 460
Seattle, WA 98121
October 1998
Aquatic Commercial Industries
This recycled paper is recyclable
Copyright © 1998 CWC. All rights reserved. Federal copyright laws prohibit reproduction, in whole or in part, in any
printed, mechanical, electronic, film or other distribution and storage media, without the written consent of the CWC.
To write or call for permission: CWC, 2200 Alaskan Way, Suite 460, Seattle, Washington 98104, (206) 443-7746.
CWC disclaims all warranties to this report, including mechanics, data contained within and all other aspects, whether expressed or
implied, without limitation on warranties of merchantability, fitness for a particular purpose, functionality, data integrity, or accuracy of
results. This report was designed for a wide range of commercial, industrial and institutional facilities and a range of complexity and
levels of data input. Carefully review the results of this report prior to using them as the basis for decisions or investments.
Report No. GL-98-1
CWC is a nonprofit organization providing recycling market development services to both businesses and
governments, including tools and technologies to help manufacturers use recycled materials. CWC is an
affiliate of the national Manufacturing Extension Partnership (MEP) – a program of the US Commerce
Department’s National Institute of Standards and Technology. The MEP is a growing nationwide
network of extension services to help smaller US manufacturers improve their performance and become
more competitive. CWC also acknowledges support from the US Environmental Protection Agency and
other organizations.
Special thanks to the following individuals, companies and agencies, whose help and support made this
evaluation possible.
Bally Total Fitness for providing their facility in Federal Way. To Mike Chapman, Steve Smith, and other
staff for their help in data collection and mechanical work.
Wayne Smith, at WMS Aquatics for his continued interest and support during this evaluation.
City of Bellingham, Washington for loaning the Hach Turbidometer for the duration of the project.
Fred Miller and the staff at TriVitro for their dedication, technical and problem solving assistance, and for
providing the glass sand media.
EXECUTIVE SUMMARY………………………………………………………………………………………………..i
1.0 BACKGROUND…………………………………………………………………………………………………….1
2.0 PLAN AND SETUP………………………………………………………………………………………………..3
3.0 FILTER EQUIPMENT…………………………………………………………………………………………..4
4.0 ADDITIONAL EQUIPMENT…………………………………………………………………………………5
5.0 ESTABLISHING THE CONTROL DATA ………………………………………………………………6
6.0 MEDIA CHANGE………………………………………………………………………………………………….8
7.0 FLOW METER PROBLEMS…………………………………………………………………………………8
8.0 GLASS SAND DATA……………………………………………………………………………………………..9
9.0 CONCLUSIONS…………………………………………………………………………………………………..12
11.0 REFERENCES…………………………………………………………………………………………………….15
Figure 1: Comparison of Average Recirculation Flow Rates
Figure 2: Comparison of Average Influent Pressures
Figure 3: Comparison of Average Effluent Filter Pressures
Figure 4: Comparison of Average Differential Filter Pressures
Figure 5: Comparison of Average Turbidity Units
Figure 6. Comparison of Backwash Time
1. Specification Sheet
© CWC 1998 i
A field test was performed to examine the potential for using finely processed recycled glass sand as a
filtration medium in high-rate sand filtration. Previous CWC studies and lab tests at Pennsylvania State
and San Jose State Universities have demonstrated that, when properly processed, recycled glass is an
effective filtration medium as a substitute for natural sand in many applications. This field test at an
athletic club swimming pool was designed to determine whether glass sand was able to attain or exceed
the clarity achieved with conventional sand and to establish how the cleaning characteristics of glass
sand media compared with sand in terms of frequency and water use. This project was also intended to
provide the filtration industry with information for economic evaluations to be made regarding the market
potential for recycled glass sand as a filtration medium.
The test was run from July 1997 to March 1998 at the Bally Total Fitness Center in Federal Way,
Washington. Three filters were used, with a filter surface area of 21.18 square feet. The maximum
design flow for the filter system, at 15 gallons per minute per square foot of filter area, was 327 gallons
per minute. Each filter contained 275 pounds of 1/8″ x 1/4″ pea gravel and 650 pounds of #20 silica
sand. Control data on turbidity, operating pressures and backwash efficiency was developed by
observing and testing the filters’ operation through four complete filter runs with conventional silica sand
media (US Sieve Standard #20 x 30).
The conventional media was removed and replaced with VitroClean™ crushed glass sand media
manufactured by TriVitro Corporation in Seattle, Washington. Again, data was collected during
repeated filter runs with the recycled glass media. This data was then compared to the control data for
silica sand.
© CWC 1998 ii
The field evaluation revealed the following trends that illustrate the performance of recycled glass sand
media compared to conventional sand media:
1. Improved water clarity shown by a 25% reduction in National Turbidity Unit (NTU) readings.
2. Increased backwash efficiency shown by a 23% reduction in water used for backwashing.
3. Approximately 20% less glass sand (by weight) required for filtration.
An anomaly in filter pressure differentials was found during the data analysis phase. While it is
unfortunate that the data on influent pressure and flow was inconsistent, other critical and positive
information regarding improved water clarity and increased backwash efficiency remains unaffected.
The data supports findings that indicate possible performance advantages in using recycled glass in highrate
sand filtration. Glass appears to be able to catch more turbid particles, thereby cleaning water
more effectively and efficiently. This may allow pool filters to be operated for fewer hours to achieve
desired water clarity, thereby saving energy and equipment life. More efficient backwashing uses less
pool water that has already been chemically treated, heated and filtered and requires less operational
and staff time.
Of particular interest is the fact that these results were achieved by using 20% less filter media by
weight. In economic terms, filter media is measured and purchased by weight; costs for filter media are
incurred in both the acquisition and disposal of media. Simply by the fact that glass is 20% less dense
than silica sand, real savings in pool operating costs can be achieved, especially when improved water
clarity and increased backwash efficiency are added considerations.
© CWC 1998 1
This study compares the performance of a recycled glass filtration medium with conventional sand in
high-rate recirculating sand filters. Previous studies sponsored by the CWC have tested glass as a
filtration medium in slow sand filtration for municipal water treatment, septic treatment sand filtration,
and monitoring well filtration. Those studies demonstrated that, when properly processed, recycled
glass is an effective filtration medium as a substitute for natural sand in many applications. This study
extends the knowledge base of effective filtration uses of recycled glass.
The water treatment and swimming pool industries have used slow-rate sand filtration for over a
century. In slow-rate filtration, water flows by gravity through a filter bed. Because the only driving
force is gravity, slow-rate filters require large amounts of filtration media and large facilities. In addition,
flocculants (broad-based polymer filtration aids) are often needed to cause particles to agglomerate for
physical removal in the filter. In order to reduce the size of filtration facilities while maintaining filtration
efficiency, gravity sand filters evolved into pressurized “rapid-sand” filters, with flow rates designed for
three to five gallons per minute per square foot (gpm/sq ft). These filters use more tightly graded
filtration media.
In the 1950’s, pressurized sand filters with filtration rates of up to 20 gpm/sq ft were introduced. These
“high-rate” sand filters did not use flocculants. The lack of flocculants, along with the higher flow rates,
made the need for high quality filtration media even more critical. These filters require very tightly
graded media, typically U.S. Standard Sieve #20 x #30 (ASTM E11 – .850mm x .600mm) silica sand,
with high uniformity of size, no clays or non-silica soils, and sub-angular grain shape.
The Northwest United States (especially Oregon and Washington) does not have natural sources of
high quality sand media for high-rate filters. This has resulted in higher costs for media because the
material must be shipped from other parts of the country.
© CWC 1998 2
TriVitro Corporation of Seattle, Washington, processes glass for a variety of uses, including tile
manufacturing, paint additives, and media for abrasive blasting. TriVitro manufactures VitroClean™,
a filter medium that has been processed specifically to meet swimming pool filter specifications. As a
result of TriVitro’s process, VitroClean™ glass sand particles have the sub-angular grain shape
required by the filter industry.
The glass used in this project was post-industrial plate glass scrap from window and door
manufacturers. The glass is processed through a series of crushers, dryers, and screens to remove
contaminants and to produce a range of uniformly sized filtration media. Post-industrial glass was
chosen for this test because it is completely free of the potential organic (sugars, labels, etc.) and
inorganic (aluminum rings, steel caps, etc.) contamination that can be present in post-consumer
container glass. The potential for these types of contamination would introduce another variable in the
analysis, and it was beyond the scope of this project to test methods for cleaning post-consumer glass.
Other studies of crushed glass filtration media for slow sand or rapid sand filters have included
“Crushed, Recycled Glass as a Water Filter Media”, by Richard Huebner, Ph.D, Penn State
University, 1994, and “Recycled Glass: Development of Market Potential”, by R. Guna Selvaduray,
San Jose State University, 1994. These studies have indicated that crushed glass media filters function
as well as conventional sand filters and may remove small turbid particles more efficiently than
conventional sand media.
The two specific issues of special interest in this study were:
1. to determine whether glass sand was able to attain or exceed the clarity achieved with conventional
sand; and
© CWC 1998 3
2. to determine how glass sand compared with conventional sand in cleaning frequency and water use.
This study examined and compared the performance of recycled glass sand media with a conventional
sand medium in high-rate sand filters during actual operating conditions. Data was first collected on the
operating characteristics of conventional sand media, then that data was compared with recycled
crushed glass sand media. The original parameters planned for evaluation of the two media included:
· Visual inspection of the pool water
· Recirculation flow rate
· Backwash flow rate
· Turbidometer readings
· Influent and effluent filter pressures
The visual inspection (by photo) was eliminated early in the evaluation because the range of changes
seen in turbidity were not observable through visual or photographic inspection. In addition, unforeseen
field conditions affected the recirculation flow rate and influent pressure readings and resulted in limiting
the conclusions that can be drawn from this project.
The Pacific West Health Club (Federal Way, WA) was chosen as the test site. Upgrades required at
the facility to facilitate this study included upsizing of a backwash pit by adding an auxiliary backwash
tank with a gravity drain to an approved sewer connection, and installation of new digital flow meters,
sight glasses, pressure gauges, and a turbidometer.
Filters used for this evaluation were “Triton” TR series filters manufactured by PacFab, Inc. These
filters are common in the swimming pool industry, with an estimated 5,000 to 7,000 filter vessels located
© CWC 1998 4
on the West Coast of the United States. Each filter contained 7.06 square feet of cross-sectional filter
area. Three filters were on one manifold, for a total of 21.18 square feet of filter surface area. The
maximum design flow for this installation, at 15 gallons per minute (gpm) per square foot of filter area,
was 327 gpm. These filters are manufactured for flow rates between 5 and 20 gpm per square foot.
Each filter contained 275 pounds of 1/8″ x 1/4″ pea gravel and 650 pounds of #20 silica sand. The
sand depth from surface to bottom drain lateral was 13.5 inches. The bottom drain laterals were
grooved to prevent sand particles larger than #30 silica from leaving the filter. Each filter was fitted
with manual air relief valves.
The backwash sight glass was not sufficient for this study, so an additional in-line sight glass was
installed on the backwash discharge line between the filters and the backwash holding tank. This sight
glass was fitted with two parallel lines, allowing a technician to evaluate the clarity of the backwash
water to determine when the filter had been sufficiently backwashed.
The size of the existing backwash holding tank was unable to hold a complete backwash discharge
from even one filter. An additional backwash holding tank with a capacity of 300 gallons was installed.
This allowed a complete backwash of three minutes per tank. The holding tank water gravity-flowed
into the sewer pit.
The recirculation flow rate and the backwash flow rate were monitored by Signet Model 5100 digital
flow meters. One was placed on the effluent recirculation line downstream of the filter, prior to chemical
© CWC 1998 5
injection points, measuring recirculation flow. The other flow meter was placed in the backwash
discharge line. To assure accuracy, the devices were installed in locations providing laminar flow (10
pipe diameters prior to measuring device and 5 pipe diameters downstream of the device of clear pipe:
no fittings, elbows, etc.).
Pressure readings were taken with stainless steel pressure gauges manufactured by Ashcroft with oil
filled cases for vibration dampening. They were located on the filter cap and the effluent filter line; six
gauges were used, two on each filter. Since the filters were manifolded, the gauge readings were
averaged to achieve consistency. The gauges chosen were 0-60 psi. In retrospect, 0-30 psi gauges
would have suited the project better. Pressure gauge readings of influent and effluent pressures were
used for the calculation of pressure differential. Differential pressure measurements provide the best
evaluation of filter bed performance with respect to collection of suspended particles, reflected by
resistance created across the filter.
Water clarity was determined from turbidity units measured by a Hach Turbidometer, model 1720A.
Measurements were recorded in National Turbidity Units (NTU’s). According to standards established
by the National Sanitation Foundation, pool water that is rated “excellent” maintains a NTU reading of
.5 or less.
Data collection sheets and procedures were developed in-house. Two National Swimming Pool
Foundation Certified Pool Operators were employed as primary and secondary technicians. Training in
data collection and backwashing procedures was completed and data collection began on July 1, 1997.
The swimming pool was intended to be the primary test site. However, since a spa system was located
in the same room, both systems were fitted with the equipment described above and comparative
evaluations were conducted. A system of valves was installed so that the Hach Turbidometer could
measure either the pool or the spa. After switching the water source, a waiting period of ten minutes
© CWC 1998 6
was established to allow the Turbidometer to adjust to the new water. The spa water often provided
skewed turbidity readings because the spa air jets introduced air bubbles that were not entirely
dissipated or removed by filtration. The air bubbles appeared as turbid particles to the turbidometer.
The original silica sand in the filters was tested by an independent test lab and rated “very good.” The
sieve size was primarily U.S. Standard #20 x 30, with a size coefficient (D60/D10) of 1.4. The size
coefficient is the ratio of the screen size through which 60% of the medium passes, divided by the screen
size through which 10% of the medium passes. The plan was to operate with the conventional sand for
no less than four complete filter runs (period between backwashes) to establish a “control database” to
which the crushed glass sand media would be compared.
There was difficulty with the backwash flow meter because debris continued to foul the transducer
paddle wheel. An in-line oversized strainer basket was installed to capture large debris and the problem
was partially solved. Data collection was resumed the following week, however, small particles
continued to clog the flow meter too often to provide reliable flow data. As a data back-up, backwash
duration (in time) was noted. While this was not as accurate as flow, it did provide a backwash
standard that could be measured and evaluated against the glass sand media.
The pool water clarity was excellent with the original conventional sand. Due to inadequate lighting for
quality photos and the subtle differences expected, the visual evaluations and recordings originally
planned were not conducted.
Collected data was consistent each day, with expected increases and decreases in pressures, flow and
turbidity readings corresponding to filter performance as the filters filled with turbid particles. The
control data phase was completed in eight weeks (see Appendix A for Figures 1 through 6).
© CWC 1998 7
The data was an average of the pressure and flow characteristics recorded each week. However,
sometimes because of staff scheduling, data was not collected and some days were interpolated from
adjacent data. According to Washington State Health and Safety Regulations, after the
recirculation flow drops 10% (approximately 25 to 30 gallons per minute), backwashes must be
scheduled to clean the filters and to re-establish the desired flow. During the analysis of the baseline
sand and glass sand media, the time between filter backwashes was seven days in all but two cases
during the 17 weeks of data collection. Seven days was a convenient schedule for backwashing, so
scheduling and data charting were established on a seven-day cycle. Figures one through five,
therefore, reflect pressure and turbidity averages for each successive day following a backwash.
The backwash flow rate measurements were somewhat skewed by flow meter problems. The average
duration (in minutes) of backwash (total of six backwashes recorded) of the conventional sand was
three minutes, twenty-one seconds. Although this was somewhat subjective, the backwash sight glass
was fitted with two black parallel lines that were to be viewed through the backwash water. When the
edges of the lines were clear, the backwash was deemed complete.
The conventional media was removed and replaced with the TriVitro crushed glass sand media. The
sand replacement took approximately one day. The 1/8″ x 1/4″ rounded pea gravel bed below the
medium was left in place. The underdrain laterals were surrounded and covered with gravel to a height
of approximately one-inch above the laterals. This gravel allowed the filter to better distribute the
backwash flow to the sand bed and is required by the National Sanitation Foundation (NSF) for the
filter’s approval at filter rates of 15 gpm (and higher) per square foot of filter area.
© CWC 1998 8
The filter manufacturer’s specifications required 6.5 cubic feet of medium for each filter (a total of 19.5
cubic feet for the system). This would have required 1,950 pounds of silica sand. However, glass is
less dense than silica sand, so only 1,560 pounds were needed, demonstrating a 20% savings in
filtration media by weight. This savings would be reflected in both raw material and shipping costs. This
difference is derived from two factors . First, the specific gravity of glass is 2.53, compared with
approximately 2.75 for sand, a 10% difference. In addition, the newly fractured glass particles appear
to not pack as tightly as the sand grains. Therefore, the interstitial spaces between the glass particles
are, on average, larger and have less rounded edges than sand grains. This confirmed previous research
at Pennsylvania State University.
Upon installation of the glass medium, the Signet flow meter equipment failed on a regular basis.
Evaluation of the recirculation flow meter transducer revealed that glass particles (estimated to be 40
micron and smaller) were passing through the filter underdrain laterals, causing the rotor to jam. After
evaluation of the glass filtration medium, it was determined that there were too many “fines” left in the
first batch of VitroClean™ sand after processing. The problem began to lessen
as repeated backwash procedures eventually removed the smaller sand particles. However, at this
point there was a question of whether the glass filtration medium as delivered in the first batch would
meet most pool owners’ satisfaction.
During the same period, TriVitro had improved its glass processing to the extent that TriVitro’s
engineers were confident that their process improvements had almost totally eliminated the fines
carryover. Therefore, it was recommended that the original glass sand be replaced and additional data
collected using this improved media product. The CWC agreed to a project extension and an
additional six weeks of testing was undertaken.
© CWC 1998 9
The final TriVitro product tested was VitroClean™ 25N, with a coefficient of uniformity of 1.40 and
effective size of .50mm. Effective size is defined as the size opening that will just pass 10% (by weight)
of a representative sample of the filter material. A specification sheet is included in Appendix B.
With the exception of the backwash duration data, the glass sand media data was collected from the
second sand media load. In fact, after four weeks of operation and backwashing and most of the “fines”
removed, the media characteristics of the “cleaned” glass sand (the first medium after
being subjected to multiple backwashes) and the new “improved” glass sand were virtually identical.
The glass sand media data is illustrated in Figures 1 through 6.
Recirculation Flow
After switching to the glass sand media, the most immediate and surprising change was the measurable
increase in recirculation flow (Figure 1). This was surprising in light of the increased influent pressure
readings (Figure 2). In general, for a centrifugal pump, it is expected that the
only way to achieve increased flow is in conjunction with decreased pressure drop. In this case, effluent
pressure was constant, as shown in Figure 3. Since influent pressures increased, the differential
pressure across the filter must have increased, as shown in Figure 4. Explaining the strange and
conflicting data in this field test is difficult.
The CWC’s project manager and the technical consultant for this project, Aquatic Commercial
Industries, share responsibility for this problem. In the first month a differential pressure increase should
have been seen along with an increased flow rate; people with experience with pump curves should
have realized there was a problem and investigated. Unfortunately, the issue was not noticed until the
curves were generated.
© CWC 1998 10
Another possible source of inaccuracy in the project was the fact that 60 psi gauges were used to take
readings as low as 3 psi. Good instrument practice requires that mechanical gauges be read within the
middle 50% of the range, in this case 15 to 45 psi. It is possible that cumulative gauge misreadings
contributed to this problem.
It is also possible that a reduction in the pump suction head (possibly stemming from a change in the
pump strainer basket and/or its maintenance) lowered the total system head, therefore allowing higher
flow as well as higher influent pressures.
Water Clarity
NTU readings actually dropped 25% with installation of the glass medium (Figure 5). This significant
drop in NTU readings indicates that glass sand media may trap finer turbid particles than conventional
sand, resulting in clearer water.
The average duration of backwash (in minutes) was 2:34 based upon ten backwashes, compared to
3:21 for silica sand based on six backwashes. Therefore, there was a reduction of as much as 23% of
water used for backwashing glass sand media compared to conventional sand.
The glass media seemed to fluidize quicker and require less water for a complete backwash. This is
probably a result of a combination of causes. First, glass sand has lower density. The lighter material
simply floats more easily with backwash flow. In addition, glass particles have a more angular shape
and relatively flatter fractured sides. This may mean that glass particles pack less densely than sand and
therefore require less backwash water to “unpack” during filter cleaning.
© CWC 1998 11
The noteworthy improvements in the backwash results in this field test were consistent with trends
identified in the San Jose State University study (Selvaduray) where measurements of the sand bed
expansion were greater with the glass sand media than with conventional sand.
In all cases, the amount of media required by weight was substantially less (approximately 20%) for the
recycled glass sand than for silica sand. In pool operations this difference would be noted twice – first
in the purchase of filter media and second in the disposal of spent media. Both are purchased by weight
rather than by volume.
The field evaluation revealed the following trends:
1. a 25% reduction in National Turbidity Unit readings;
2. a 23%+ reduction in time for backwashing; and
3. approximately 20% less glass sand (by weight) is required for filtration.
It is worthy to note that items 1, 2, and 3 were mirrored in the spa test data.
Applicability to other filter systems
Industries and governments use high rate filtration systems in a variety of settings. Findings from this and
preceding studies show strong potential for glass to be used in commercial and municipal filtration. It is
likely that the benefits concluded from this swimming pool field evaluation would be seen in other types
of filtration applications, such as stormwater, agricultural and industrial filtration.
This project was intended to be a full-scale “field test” of recycled glass for high-rate sand filtration.
The work done at San Jose State University and Pennsylvania State University showed that, in
laboratory scale, recycled glass had equal or better efficiency than conventional sand. Consistent with
© CWC 1998 12
this prior research, recycled glass sand media performed as well or better than conventional filter sand in
swimming pool filtration.
The main advantages of recycled glass sand over conventional sand are:
1. Improved Water Quality. Finer particles were removed in the filter more efficiently, reflected by
the 25% decrease in NTU’s. The findings showed repeatedly that recycled glass sand cleaned
water more effectively. Clearer water is always desired. Being able to catch smaller turbid particles
makes high-rate filtration sand even more efficient and therefore attractive over other types of
filtration media. This advantage may allow recirculation systems to be operated fewer hours in
those locations that allow pool systems to be turned off during non-use periods. This saves
electrical energy and extends equipment longevity.
2. More Efficient Backwashing. Less backwash water was required to clean the filter medium. As
these test results are duplicated in repeated future usage, the ability to backwash with over 20% less
water is a major advantage that can prove valuable both in construction and in operation. The cost
of sewer lines and holding tanks can be reduced. Most importantly, water has been saved. Beyond
the value of the water resource, pool water has an added economic value when it has been
chlorinated, pH adjusted, alkalinity adjusted, hardness adjusted, heated and filtered. The savings
through more efficient backwashing are measured both in the cost of the water consumed and then
disposed (some facilities that are charged per 100 cubic feet of water that is treated by sewage
plants). Costs for chemicals and for heating water are also reduced.
3. Less Media. Glass sand media is less dense and therefore lighter than conventional sand filter
media. Less media by weight is required. Shipping, handling and disposal costs would be saved
proportionately to the ratio of density of glass vs. silica sand media., approximately 20%.
© CWC 1998 13
The benefits described in 1 and 2 above (i.e., savings in pool operating costs, energy, water usage, etc.)
are achieved with 20% less material by weight.
It cannot be emphasized strongly enough that these results reflect a test of a specific glass
filtration medium produced by a specific processor. Although they confirm the efficacy of
properly processed glass as a recirculating water filtration medium, they do not support the
use of glass for this application from any other processor, unless that processor is able to
produce media that meets industry specifications for consistency in particle shape, size
distribution, cleanliness and uniformity.
The following recommendations are provided to those who may wish to undertake further testing in
swimming pool operations:
1. The use of ultra-sonic flow measurement devices with totalizers will allow for a more precise
measurement of filter media backwash flow and water usage. The paddle wheel units, though very
accurate, have small tolerances for particulate matter in the water and can become clogged.
2. The ability to record data seven days per week every week is important in order to monitor trends.
3. Controlling pool operating conditions at the field test facility is important. Filtration equipment
repairs or modifications and staffing changes can interfere with data collection and skew results.
4. Care must be taken to isolate and monitor changes in operating pressures due to the use of recycled
glass media. Using gauges that more accurately reflect the actual pressure conditions (see Section
4), careful evaluation of suction and discharge head condition on the recirculation pump during the
baseline evaluation and new media evaluation is important. This can be accomplished with vacuum
and pressure gauges on the suction and discharge lines of the pump.
© CWC 1998 14
5. Test designs should track filter ripening and run times. Reports from the Pennsylvania State and San
Jose State University studies showed faster ripening and longer run times. It would be valuable to
determine if these trends are readily observed in field test conditions.
© CWC 1998 15
Certified Pool Operator Handbook, National Swimming Pool Foundation, Lester
Kowalski, Editor. 1990.
Aquatic Facility Operator Handbook, National Recreation and Park Association,
Kent Williams, 1994.
Washington State Health and Safety Code, for Swimming Pools.
Crushed, Recycled Glass as a Water Filter Media, Pennsylvania State University, 1994,
Richard Heubner PhD, Project Director.
Recycled Glass: Development of Market Potential, San Jose State University, 1994,
Dr. Guna Selvaduray
Crushed Glass as a Filter Media for Onsite Treatment of Wastewater, CWC. 1995
Examination of Pulverized Waste Recycled Glass as Filter Media in Slow Sand Filtration,
NYSERDA, October 1997.
Figure 1: Comparison of Average Recirculation Flow Rates
Figure 2: Comparison of Average Influent Pressures
Figure 3: Comparison of Average Effluent Filter Pressures
Figure 4: Comparison of Average Differential Filter Pressures
Figure 5: Comparison of Average Turbidity Units
Figure 6: Comparison of Backwash Time
1. Specification Sheet
Figure 1
Comparison of Average Recirculation Flow Rates (gallons per minute)
187.5 182.5 176.7 173 168.5 162 155.5
277 272.5 268.2 265 262.5 257.5 252
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Con Sand
Figure 2
Comparison of Average Influent Pressures (pounds per square inch)
8 8.15 8.45
11 10.45
11.25 11.75 12.15
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Con Sand
Figure 3
Comparison of Average Effluent Filter Pressures (pounds per square inch)
5.8 5.4
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Con Sand
Figure 4
Comparison of Average Differential Filter Pressures (pounds per square inch)
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Con Sand
Figure 5
Comparison of Average Turbidity in National Turbidity Units (NTUs)
0.28 0.27
0.4 0.4 0.4 0.4
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Con Sand
Figure 6
Comparison of Average Backwash Time in Minutes
Week 1 2 3 4 5 6 7 8 9 10
Con Sand
Note: Conventional sand recorded for 6 weeks, Glass sand for 10 weeks.
Water Filtration Sand
An Amorphous Soda-Lime Silicon Dioxide Product
Typical Specifications
VitroClean 25N
U.S. Sieve No. % Retained on Sieve
14 0.0
16 0.2
20 4.0
25 31.5
30 46.2
40 16.5
50 0.4
pan 1.2
Effective Size 0.50mm
Coeff.Uniformity 1.40
Specific Gravity 2.53
Est. Sphericity 0.30
Est. Roundness Angular-Subangular
Other filtration sand sizes are available
Product specifications are approzimate & subject to change.
351 Elliott Avenue West
Seattle, WA 98119-4010
Sales: 360-733-2122
Plant: 206-301-0181
Fax: 206-301-0183


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