Ontario's New Performance Septic Tank -- Why & How

Abstract

Removing the airspace to induce closed-conduit flow in a long, narrow, shallow septic tank results in substantially less scum and sludge formation and higher quality effluent compared to a conventional box-like tank with airspace. Introducing new technology into the environmental arena should be encouraged to reduce pollution and improve health and safety. Standards organizations and regulators need to review existing prescribed designs which may limit the treatment capabilities of the important septic tank, and to introduce performance standards and benchmarks suitable for Ontario’s climate.

Full text

Published in WEAO journal INFLUENTS, v. 5, 2009
JOWETT, Craig et al.
ONTARIO’S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
Page 1 of 8
ONTARIO’S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
E. Craig Jowett, Waterloo Biofilter Systems Inc.,
Paul Yaremko, Armtec Ltd., and
Richard Lay, Enermodal Engineering
DESIGNING FOR TREATMENT IN SEPTIC TANKS
Although 30% of sewage generated in North America passes through septic tanks, there
has been little recent study to improve the treatment efficiency of these important vessels. As
summarized by Lay et al. (2005), Jowett (2007, 2009), and D‟Amato et al. (2008), existing
literature shows that longer, narrower septic tanks improve effluent quality due to quiet, laminar
flow and minimum hydraulic „dead space‟.
Early designers such as Metcalf (1901, in Winneberger, 1984) valued long septic tanks to
produce “sedimentation by slow flow through long tanks”. However, as Winneberger (1984)
states, “…the value of long tanks became forgotten” and “probably because of construction
convenience, short, stubby tanks became common”. Entrained sludge particles settle out along
the flow path, with longer paths required for smaller particles and for deeper tanks (e.g., Novotny
et al., 1989). A long tank minimizes short-circuiting, “allowing only old water to leave the tank”
(Max Weiss, pers. comm., 2004). British standards (BS 6297, 1990) require a maximum 1000
mm water depth, resulting in a much longer, shallower tank than in Ontario.
Reducing the „dead space‟ characteristic of wider, deeper box tanks has a treatment
advantage as well. Dunbar (1907, reported in Winneberger, 1984) hung meat in septic tanks and
found that “decomposition is quicker in a tank of 12-hour capacity than one of 2-hour capacity,
but very much quicker than in a septic tank in which the sewage is stagnant”. Bailey et al. (1957)
hold stagnant flow responsible for accumulation of acidic waste products of bacterial
decomposition, which in turn “slow down or stop their growth”, and they designed their poultry
degraders with water inlets and outlets to a tile bed instead of a stagnant holding tank. Designing
a tank with efficient flow paths to remove waste products from decaying organic matter is more
desirable, from a treatment perspective, than just increasing the tank size.
„Floating scum storage‟ is a common reason for airspace in a tank, but Winneberger
(1984) states “it is a common misconception that … lighter solids … rise to surface and form a
layer of scum”. Rather, a “tough, floating mass” forms when fermentation bubbles bring up
sludge to be trapped by moulds living on the air-water interface (Metcalf and Eddy, 1930).
Tank partitions with small orifices worsen effluent quality by causing high velocity flow
and turbulence in the orifice and short-circuiting to the nearby outlet (Figure 1), as seen in dye
and solids tracing, and in the sewage testing of Rock and Boyer (1995).

JOWETT et al.
ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
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Figure 1 – Standard Ontario „box-type‟ 4500 L septic tank with 150 mm partition orifices close
to the outlet. Turbulent plumes (in orange) short-circuit untreated sewage to outlet pipe (Lay et
al., 2005).
Cold climate is an important factor in biodegradation efficiency as exemplified by the
study of decomposition of dead poultry by Bailey et al. (1957). At 38°C, decomposition was
complete after 11 days, but at 27°C only slight action was observed, and at 10°C, “the birds
were still well preserved”. As a result, they designed their heated septic tanks with 100 mm
insulation in the walls and floor to keep the tanks warmer in winter.
FROM PRESCRIPTION TO FUNCTIONALITY, IF NOT PERFORMANCE
Industry Standards
Septic tank standards that apply across Canada (CMHC, 1984; CSA, 2005) are primarily
prescriptive construction manuals for building competent tanks out of various materials.
Prescriptions are based on the established methods of the time of writing, and once they are
published and adopted by manufacturers and regulators, with time they develop a respectable and
authoritative aspect. One is naturally more hesitant to change the familiar written word, which
favours the status quo for incumbent technology and may obstruct the new.
Prescriptions set out designs that do impact sewage treatment, such as water depth, tank
length, partitions, orifice sizing, and airspace, but without benefit of performance testing to
determine what effect these requirements have on treatment. Intended functionality of these
prescriptive designs may be lost or unknown, and it is difficult for a manufacturer to demonstrate
equivalency when the function of established prescriptive technology is not apparent.
Actual benchmarks, by performance or by description of intended purpose, clarify
requirements for equivalency, and ease objective evaluation of new technology. Clear
benchmarks produce a „level playing field‟ for new environmental technologies, minimize
subjectivity, and free up the marketplace.

JOWETT et al.
ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
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Septic Tank Equivalency Benchmark
After several years of negotiation, an „Equivalency Test Protocol‟ was included in the
CSA B66 standard in 2006 to allow innovative septic tank designs into the marketplace. After
the test is successfully passed, a new tank is deemed to be „equivalent in functionality‟ to the
standard‟s prescription tanks, a phrasing developed by consensus to include a performance
aspect yet maintain its overall prescriptive nature.
The protocol requires a new tank design to be tested side-by-side with a prescriptive tank
for 12 months or more, using cold sewage of <10°C for at least 3 months. The test must be
carried out at an accredited facility using high peak flows of residential-style sewage dosed to the
tanks. Effluents are sampled at least 30 times for cBOD, COD, and TSS, and the median values
calculated for each parameter. For a new tank design to pass, not one of its three median values
can be more than 10% greater than the same parameter of the prescription tank, and more
importantly, the average of its three medians must be less than that of the prescription tank. The
protocol therefore puts a great onus on the new tank design to show that it is better than the
existing tanks in order to be included in the standard.
FIRST PAST THE POST – THE ‘WATERTUBE’ SEPTIC TANK
Two closed-conduit, laminar flow septic tanks were constructed for WATERLOO BIOFILTER
by ARMTEC in Woodstock Ontario by welding ARMTEC’S extruded „BOSS 2000‟ high-density
polyethylene pipes. Guelph-based ARMTEC is Canada‟s largest and oldest manufacturer and
supplier of high-quality corrugated steel products, corrugated HDPE pipe, and now concrete
structures for infrastructure markets. Rockwood-based WATERLOO BIOFILTER is a pioneering
innovator in decentralized sewage treatment, nutrient removal, disposal, and re-use. Kitchener-
based ENERMODAL ENGINEERING is a major player in designing LEED buildings which often
incorporate sustainable „green‟ infrastructure.
The first tank was 4500 L capacity for the tracing studies of Lay et al. (2005) (Figure 2),
and second was 5700 L fabricated in two lengths (Figure 3) to fit within the test site at the
Massachusetts Alternative Septic System Test Center (www.buzzardsbay.org/etimain.htm)
where the biochemical testing is carried out. The 5700 tank segments were connected with two
200-mm pipes to allow sludge and scum to migrate between tanks and not to act as a partition.

JOWETT et al.
ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
Page 4 of 8
Figure 2 - Closed-conduit tank limits turbulence (in orange) to the inlet area, and only 'old',
treated sewage exits the tank, depicted as laminar flow parabolic discs A to B (Lay et al., 2005).
Figure 3 - „Flooded‟ or closed-conduit flow tank of 5700 L capacity tested side-by-side with
conventional single- and double-compartment tank at Buzzards Bay test facility.
LONG-TERM SEWAGE TEST RESULTS
Since April 2005 a WATERTUBE tank has been in operation in side-by-side testing with a
single-compartment „Massachusetts‟ tank (Studies 1 & 2) fully presented in Jowett (2007, 2009)
and summarized here. Study 3 is ongoing with an „Ontario‟ tank + effluent screen.

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ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
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STUDY 1: B66 TEST PROTOCOL RESIDENTIAL-TYPE TESTING
Study 1 was carried out for 15 months and conformed to the CSA B66 test protocol
(MASSTC, 2006). In the first 3 months of operation, the conventional tank accumulated 52%
solids mainly as sludge, and the flooded A3 tank (WATERTUBE) had 15% solids with scum only
in the inlet airspace. Table 1 shows Study 1 results of cBOD, COD, and TSS for influent sewage
(DC West) and two tanks tested. The flooded A3 tank removed 24% cBOD and 78% TSS from
the sewage, and the standard single compartment F3 tank removed 15% cBOD and 73% TSS.
Table 1 – Study 1 septic tank effluent analyses following CSA B66 „Equivalency Test Protocol‟
Study 1 – 2850 L/d
April 13 2005 – July 11 2006
BOD
mg/L
COD
mg/L
TSS
mg/L
Number of QA/QC samples
51
22
76
DC West Sewage
average
209
408
197
standard deviation
61.7
133.1
83.1
cBOD
mg/L
COD
mg/L
TSS
mg/L
Number of QA/QC samples
41
39
41
A3 WATERTUBE
average
158
314
43
standard deviation
39.0
79.8
9.9
F3 Single Tank
average
178
344
53
standard deviation
51.3
87.1
17.7
Student’s t-test
A3 & F3
% confidence
96.2
89.0
99.8
WATERTUBE effluent averaged 158 mg/L cBOD and 43 mg/L TSS, and the F3 tank
averaged 178 mg/L cBOD and 53 mg/L TSS. Unpaired Student‟s t-tests indicate that the A3 and
F3 effluent populations are statistically different at the 96%, 89%, and >99% levels of
confidence, respectively. When the tank was pumped by a commercial pumper, the comments
were “It looks like 8 years of sludge buildup” in conventional tank F3, and flooded tank A3
“had a standard maintenance look” which is “3-4 years’ buildup” (MASSTC, 2006).
Grab samples were taken along tank pathways to indicate evolution of anaerobic
digestion and effluent maturity, using volatile fatty acids (VFA) and solubilization ratios of
phosphate ion versus TP and ammonium versus TKN, as suggested by Jeremy Kraemer (pers.
comm., 2005), with Table 2 as an example (see Jowett (2007, 2009) for full details).
While not comprehensive, VFA generally increase from inlet to outlet, as do alkalinity
and solubilization parameters. The performance parameters of cBOD, TSS, COD generally
decrease as expected between inlet and outlet as the sewage is being treated.

JOWETT et al.
ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
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Table 2 - Evolution along flow path on one day in Study 1 (soluble COD sample is filtered)
February 8 2006
2850 L/d
VFA
mg/L
Soluble COD
mg/L
Alkalinity
mg/L
NH3,4-N/TKN
PO4-N/TP
A3 WATERTUBE tank
A3-1 inlet
34
150
170
0.74
0.65
A3-2 end inlet segment
40
170
175
0.69
0.57
A3-3 start outlet segment
46
120
190
0.67
0.62
A3-4 outlet
51
120
195
0.76
0.75
F3 Standard tank
F3-1 inlet
48
110
190
0.72
0.73
F3-2 outlet
80
110
190
0.72
0.71
STUDY 2: LOWER HYDRAULIC LOADING RATE
Study 2 was carried out for 12 months, with flows of 2500 L/d, increasing to 2850 L/d for
the last two months. Tank A3 removed 35% cBOD and 81% TSS, and the F3 single
compartment tank removed 13% cBOD and 76% TSS (Table 3).
Table 3 –Study 2 comparison of tanks at 2500 & 2850 L/d
Study 2 – 2500 L/d 10 mo; 2850 L/d 2 mo
November 17 2006 – November 19 2007
BOD
mg/L
COD
mg/L
TSS
mg/L
Number of QA/QC samples
58
-
94
DC West Sewage
average
183
-
164
standard deviation
50.8
-
65.9
cBOD
mg/L
COD
mg/L
TSS
mg/L
Number of QA/QC samples
48
22
48
A3 WATERTUBE
average
119
243
31
standard deviation
23.0
51.8
6.5
F3 Single Tank
average
159
282
39
standard deviation
63.8
56.7
8.0
Student’s t-test
A3 & F3
% confidence
99.99
97.6
99.99
The F3 anomaly in cBOD values for days 170–230 (Figure 4) is not explained by sewage
values, and does not appear in COD or TSS values.

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ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
Page 7 of 8
Figure 4 – cBOD analyses in Study 2 showing unexplained F3 anomaly at 170–230 day period
CONCLUSIONS
Removing the airspace to induce closed-conduit flow in a long, narrow, shallow septic
tank results in substantially less scum and sludge formation and higher quality effluent compared
to a conventional box-like tank with airspace. Introducing new technology into the
environmental arena should be encouraged to reduce pollution and improve health and safety.
Standards organizations and regulators need to review existing prescribed designs which may
limit the treatment capabilities of the important septic tank, and to introduce performance
standards and benchmarks suitable for Ontario‟s climate.
REFERENCES
Bailey, W.A., Junnila, W.A., Aho, W.A. and Wheeler, W.C., 1957. A Heated Septic Tank for
Disposal of Dead Poultry. Storrs Agricultural Experiment Station, University of Connecticut,
Progress Report 21, 7 p.
BS 6297, 1990. Code of Practice for Design and Installation of Small Sewage Treatment Works
and Cesspools. British Standard Code of Practice BS 6297:1983 Amendment 6150:1990, 40 p.
CMHC, 1984. CMHC Septic Tank Standards. Central Mortgage and Housing Corporation, 25 p.
CSA, 2005. Standard B66: Design, material, and manufacturing requirements for prefabricated
septic tanks and sewage holding tanks, 7th edition. Canadian Standards Association, Mississauga
D‟Amato, V.A., Bahe, A., Bounds, T., Comstock, B., Konsler, T., Liehr, S.K., Long, S.C.,
Ratanaphruks, K., Rock, C.A., and Sherman, K., 2008. Factors affecting the performance of
primary treatment in decentralized wastewater systems. WERF 04-DEC-7 Research Digest,
Water Environment Research Foundation, Alexandria VA, 38 p. with appendices

JOWETT et al.
ONTARIO‟S NEW PERFORMANCE SEPTIC TANK – WHY & HOW
Page 8 of 8
Dunbar, W., 1907. Principles of Sewage Treatment. Translated in 1908 by H.T. Calvert. Griffin,
London.
Jowett, E.C., 2007. Comparing the performance of prescribed septic tanks to long, narrow,
flooded designs. In, WEFTEC Proceedings Technical Program 16, San Diego CA.
Jowett, E.C., 2009. Long-term comparative performance of two septic tank designs. In, NOWRA
Proceedings; Session 14: System Performance Evaluations and Modeling , Milwaukee WI.
Lay, R., Weiss, M., Pataky, K. and Jowett, C., 2005. Re-Thinking Hydraulic Flow in Septic
Tanks. Environmental Science & Engineering, 18 (1), 50–52.
MASSTC, 2006. On-site wastewater testing report “WaterTube”. Massachusetts Alternative
Septic System Test Center, Falmouth MA, 12 p.
Metcalf, L., 1901. The Antecedents of the Septic Tank. Trans. Am. Soc. Civ. Eng., XLVI
(December, 1901).
Metcalf, L. and Eddy, H.P., 1930. Sewerage and Sewage Disposal. McGraw-Hill, New York
NY.
Novotny, V., Imhoff, K.R., Olthof, M. and Krenkel, P.A., 1989. Karl Imhoff‟s Handbook of
Urban Drainage and Wastewater Disposal. Wiley, Hoboken NJ, 416 p.
Rock, C.A. and Boyer, J.A., 1995. Influence of Design on Septic Tank Effluent Quality.
Proceedings, 8th On-Site Wastewater Treatment Short Course and Equipment Exhibition, Seattle
WA, 45–62.
Winneberger, J.H.T., 1984. The Septic Tank, Septic-Tank Systems, a Consultant‟s Toolkit.
Volume II. Butterworth, Boston MA, 123 p.