Transcript Designing for high strength wastewater

John R. Blount, P.E.
Harris County Public Infrastructure Department
Assistant County Engineer
Director, Architecture & Engineering Division
Topics
 Define high strength wastewater
 Discuss hydraulic vs. organic loading
 Explore results of Harris County high strength
wastewater studies
 Review relevant sections of 30 TAC §285
 Develop strategies for moving forward
What is high strength wastewater?
 Wastewater that has higher amounts of BOD, TSS, or
FOG than residential wastewater
Residential
wastewater
Strength < 300 mg/L BOD*
Photos: http://www.clker.com/clipart-scales-of-justice-3.html,
http://www.aediconstruction.com/sustainability/low_flow_water_fixtures.html,
http://www.bls.gov/ooh/Production/Food-processing-occupations.htm
High strength
wastewater
* Per 30 TAC §285.32(f)2
What is high strength wastewater?
 It is often highly variable
 For example, a restaurant with a lunch rush
http://www.southpaceblog.com/2012/11/06/what-to-expect-in-todays-restaurant-market/
Why should I be concerned?
 Conventional systems will not work well with high
strength wastewater due to clogging of the soil
interface.
 High strength wastewater can cause faster decline of
onsite systems without adaptations.
Photo: http://bbprof.wordpress.com/2012/03/22/a-d-in-rhetoric/
Quantity vs. Quality
 Hydraulic loading
 Water volume
 Organic loading
 Water quality
 Know what you’re dealing with- do your detective
work!
Photo: http://www.glogster.com/1jbfan/detective-work/g-6n94f14apu919am1ppmuhdh
How strong is strong?
Total Daily Load
Wastewater Flow Rates (gal per hour)
+
Wastewater quality
Overall wastewater strength
Agnoli, T. 2000. The best wastewater systems consider flow rate and waste
strength. Small Flows Quarterly, 1 (2).
Texas Restaurant Wastewater
Analysis, 2003
 Pretreatment is necessary to prevent system failure
 Highlighted the need for a design manual for
restaurants
Parameter
BOD
COD
TSS
FOG
Typical
Restaurant
domestic waste waste (average,
(range, mg/L)
mg/L)
100-400
1,202
100-300
1,717
100-350
318
16-65
131
Study funded by the Texas Onsite Wastewater Research Council
Not all restaurants are
created equal
n
6
1
4
9
1
Restaurant type
Fast food
Pizza
Chinese
Mexican
American
1
2
3
American Buffet
Steakhouse
Seafood
Typical residential
waste
BOD
TSS
FOG
mg/L, avg mg/L, avg mg/L, avg
2,137
233
102
1,856
321
183
1,364
448
241
1,254
668
190
1,063
297
147
792
601
555
195
160
229
63
77
47
100-400
100-350
16-65
Texas Restaurant Wastewater
Analysis, 2003
BOD
BOD COD TSS FOG lbs/da
n mg/L mg/L mg/L mg/L
y
Hand wash
5 2,617 2,575 366
Commercial
Dishwasher 22 1,037 1,912
Values shown are averages
418
120
30.5
153
36.9
Texas Restaurant Wastewater
Analysis, 2003
BOD
mg/L
BOD
lbs/day
Conventional fixtures
973
22
Low flow fixtures
1,309
36
Harris County Low Flow
Fixture Study, 2013
 Initiated November 2013
 Compare BOD, TSS, and FOG from an older
residential neighborhood to a new neighborhood with
low flow fixtures (and therefore, high strength
wastewater)
http://stockfresh.com/image/1722713/pending-rubber-stamp
What about NSF 40?
 Example:
 Fast food restaurant with 33 seats, loading factor of 15
gpd/seat
 According to TAC, 15 x 33 = 495. It might be assumed a
500 gpd treatment plant would suffice.
However…
What about NSF 40?
 NSF Standard 40 treatment plants assume BOD= 240
mg/L
 Harris County restaurant study
average BOD = 1202 mg/L: 5 times greater!
 Reality is this scenario would require a 2,500 gpd plant
if you look at it on an organic loading basis.
What does the TAC say?
 “(1) Tank sizing. Proprietary treatment systems that serve
single family residences, combined flows from single family
residences, or multi-unit residential developments shall be
designed using Table II in §285.91(2) of this title unless
there is an equalization tank preceding the aerobic
treatment unit. If there is an equalization tank preceding
the aerobic treatment unit, the equalization tank shall
meet the requirements set forth in §285.34(b)(4) of this
title (relating to Other Requirements) and the aerobic
treatment units can be sized using the wastewater flows in
Table III in §285.91(3) of this title.”
30 TAC §285.32(c)
Table III- Wastewater Usage Rate
 Table III ONLY applies to hydraulic loading
 “This table shall be used for estimating the hydraulic
loading rates only. Sizing formulas are based on
residential strength BOD5. Commercial/institutional
facilities must pretreat their wastewater to 140
BOD5 prior to disposal unless secondary treatment
quality is required. For design purposes, restaurant
wastewater will be assumed to have a BOD5 of at least
1,200 mg/l after exiting the grease trap or grease
interceptor.”
30 TAC §285.91(3)
What does the TAC say?
 “Proprietary units under this section have been
approved to treat flows equal to or less than their rated
capacity and with an influent wastewater strength
ranging from a 30 day average Carbonaceous Biological
Oxygen Demand (CBOD) concentration between 100
milligrams per liter (mg/l) and 300 (mg/l) and a 30 day
average TSS concentration between 100 mg/l and 350
mg/l.”
30 TAC §285.32(c)5(A)i
What does the TAC say?
 “Restaurant/food establishment sewage. When
designing for restaurants, food service establishments
or similar activities, the minimum design strength
value shall be 1,200 mg/L Biochemical Oxygen
Demand (BOD) after a properly sized grease
trap/interceptor. It is the responsibility of the designer
to properly design a system which reduces the
wastewater strength to 140 mg/L BOD prior to disposal
unless secondary treatment levels are required.”
30 TAC §285.32(f)
What does the TAC say?
 Defines residential sewage as sewage that has a
strength of <300 mg/L BOD
 Designer should consider if flow equalization is
necessary for system to work properly
30 TAC §285.32(f)2, 3
Harris County Onsite Sewage
Facility Regulations
 “Calculations for hydraulic and organic load for both
normal and peak flows on all commercial systems shall
be provided showing that both organic and hydraulic
overloading of the treatment and/or disposal method
is prevented.”
 Commercial maintenance frequency- 12 visits a year
Conclusion
 Systems that are improperly designed for the waste
stream may not protect public health and the
environment
Photo: http://science.kqed.org/quest/2012/04/27/celebrating-earth-day-in-the-age-of-man/hands-on-a-globe/
Ways to manage high
strength wastewater
1. Control at the source
 Example: scrape plates to reduce FOG
2. Treat to a higher level before discharge
 Example: install media filter
3. Adjust loading rates according to strength of
wastewater
Source: Hammerlund and Glotfelty, Maryland Department of the Environment. 2008. Onsite Sewage Disposal of High Strength Wastewater. 17th Annual Maryland Groundwater Symposium 2008.
Questions and/or Comments