Volume 13, Issue 1 - Ontario Onsite Wastewater Association

13 th Annual Onsite Wastewater Conference & Exhibition
located under the lamellar separator that, once a day, transferred sludge
produced by the EC unit to the primary reactor. Domestic wastewater was
fed into the system at a flow rate of 400 GPD by applying the NSF 40 dosing
protocol: 25% of the daily volume (Qd) from 6 a.m. to 9 a.m., 35% of Qd
from 11 a.m. to 2 p.m., and 40% from 5 p.m. to 8 p.m. Sampling over 24hour
periods was done every 2 weeks. The second approach involved a
self-cleaning UV disinfection unit used to disinfect secondary level treated
effluent. The self-cleaning UV unit consisted of a central quartz tube that
received the effluent to be treated and in which stainless steel blades
rotated to clean the quartz tube 6 times a day to overcome quartz tube
fouling (Sehnaoui,K. and Gehr, R. 2001). Two UV lamps were installed on
each side of the central quartz tube, with a parabolic reflector to maximize
UV radiation (Patented Crossfire Technology®).
This disinfection unit was extensively tested at two (2) different sites.
In both cases, the wastewater treatment unit included a septic tank
followed by an equalization tank and a rotating biological contactor in
front of the self-cleaning UV unit. The UV unit was fed by a pump at a
regulated flow rate of 15 GPM. The first system was used to service a
new subdivision of 100 homes, producing a design flow rate of 27,000
GPD. Sampling at this site was done for 24 months. The second system
treated the wastewater produced by a restaurant at a flow rate of 4,000
GPD. Its performance was evaluated over a period of 36 months.
The third approach was based on a membrane biological reactor
(MBR) that produced a tertiary level treatment, including very low
Table 1 Average concentrations (± standard deviation) for EC unit and absorbent filter system
concentrations of total phosphorus, by adding a chemical coagulant to
the treatment line. The pilot system was installed at a commercial site
(office building) equipped with an existing wastewater treatment system
that treated an average flow rate of 6,600 GPD. The MBR pilot unit
included two ultra-filtration modules (14 m² of membrane each) based on
flat sheet membranes that received septic tank effluent from the existing
system at an average flow rate of 900 GPD.
A chemical used for phosphorus removal was fed from the
equalization tank effluent to the septic tank inlet on a recirculation loop.
Results and discussion:
The results obtained with the first system (an EC unit combined with an
absorbent media-based filter) are presented at Table 1. As shown, the EC
unit removed total phosphorus to below 1.0 mg/L. Addition of an absorbent
media-based filter, after the EC unit, reduces the total phosphorus to 0.1
mg/L and all other parameters (TSS, BOD5, fecal coliforms, and turbidity)
below tertiary level treatment. The high quality of the treated effluent
meets the usual criteria for surface discharge in sensitive areas. As
described previously, the self-cleaning UV disinfection unit was
extensively tested at two (2) different sites. In both cases, the selfcleaning
UV unit was installed at the effluent of a secondary treatment
system. The performances at the first site, which treated the wastewater
from a 100-home subdivision, are presented in Tables 2 and 3.
Disinfection near detection level was obtained on a constant basis.
Parameter Units Raw wastewater Septic tank effluent EC effluent Filterv effluent n
TSS mg/L 176 ± 45 124 ± 71 38 ± 10 1.2 ± 1.8 (0.8) 23
BOD5 mg/L 195 ± 22 150 ± 51 112 ± 20 2.5 ± 0.6 (2.5) 22
Total P mg/L 9.1 ± 0.8 5.7 ± 1.6 0.6 ± 0.2 0.1 ± 0.04 (0.1) 23
Fecal coliforms (1) counts/ 715,000 408,000 5,300 67 63
Turbidity 100 mL 106 ± 41 142 ± 43 59 ± 25 0.6 ± 0.1 21
pH NTU 7.3 ± 0.1 6.9 ± 0.1 7.6 ± 0.2 6.9 ± 0.1 21
Table 2 Average concentrations at the influent of the self-cleaning UV unit (100-home subdivision)
Parameter Units Average Median Min. Max. n
TSS mg/L 14 ± 8 14 3 31 25
BOD5 mg/L 7 ± 3 6 3 17 25
Fecal coliforms counts/100 mL 1,695 (1) 3,100 30 12,000 11
UV transmissivity % 59 ± 3 59 56 67 10
(1) Geometric average
Table 3 Average concentrations at the effluent of the self-cleaning UV unit (100-home subdivision)
Parameter Units Average Median Min. Max. n
Fecal coliforms counts/100 mL 11 (1) (1) Geometric average
10 2 100 33
Tables 4 and 5 present the performance of the self-cleaning UV unit installed at the restaurant site. Again, the results obtained indicate disinfection
below detection level under all conditions tested.
Table 4 Average concentrations at the influent of the self- cleaning UV unit (restaurant)
Parameter Units Average Median Min. Max. n
TSS mg/L 21 ± 9 20 8 45 45
BOD5 mg/L 9 ± 6 8 2 30 48
Fecal coliforms counts/100 mL 823 (1) 800 230 5,300 22
UV transmissivit % 60 ± 14 57 37 92 25
(1) Geometric average
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