Wastewater treatment is a complex process that demands a combination of solutions, rather than a one-size-fits-all approach. All septic systems require oxygen so bacteria can properly convert complex molecules into basic ones like carbon dioxide (CO2), water (H2O), and nitrogen, as well as eliminate viruses like e.Coli. Therefore, the major difference between the tertiary systems is how the oxygen gets to the bacteria. Some pump air into the sewage, while others put the sewage into an area with oxygen.
All daily flow calculations start with the number of bedrooms, but this is not the case when it comes to other factors. Average daily use per person is approximately 275 L (72 gal); therefore, the maximum daily flow could be around 500 to 600 L (132 to 158 gal) per bedroom. For example in Ontario, the following Ontario Building Code (OBC) ‘bedroom rate’ guideline, provided by the Ontario Onsite Wastewater Association (OOWA), assumes for every bedroom there are two people living in a residence. For example:
- one bedroom: 750 L (200 gal);
- two bedrooms: 1100 L (317 gal);
- three bedrooms: 1600 L (422 gal);
- four bedrooms: 2000 L (528 gal); and
- five bedrooms: 2500 L (660 gal).
A professional should always be consulted for site parameters and other factors to take into consideration. In Ontario, all septic systems within a single lot and rated to accept a total daily flow rate of <10,000 L (2640 gal) must comply with OBC, while other local or provincial regulations for sizing onsite systems are in play elsewhere. Other factors to consider for water usage will be the terrain/soil site conditions, along with the fixtures used—that is, the types (low-flow, high-efficiency, or not) and number of washers (dish/laundry), faucets, showers, tubs, and floor drains used or installed on the premises.
Ever-evolving system options
For most advanced treatment systems, whether they are integrated fixed-film activated sludge treatment, trickling filter systems, extended aeration systems, or onsite membrane bioreactors (MBR), the technology easily scales up to accommodate the flows between small-scale packaged systems (as low as 1-m3 [35-cf] daily flows) and full-scale wastewater treatment plants (beyond 600 m3 [21,190 cf]). Since each system has a slightly different setup, depending on the site conditions will affect the level of maintenance willing to be undertaken.
The following are adaptive wastewater technologies that employ highly efficient treatment processes:
- effluent screening (provides pre-treatment)—septic-tank deflection devices designed to screen (down to 3-mm
[118-mil] solids) insoluble debris from wastewater to promote natural attenuate flow and sedimentation (and has a cleaned-in-place swabbing feature); - submerged aeration (typical treatment)—fine- or coarse-bubble supplementary aeration that creates a vortex circulation, mixing the liquid in the wastewater to promote removal of biological oxygen demand (BOD);
- extended aeration (typical treatment)—a complete mixed-activated treatment system utilizing submerged aerators for suspended-aeration wastewater treatment process;
- trickling filter (enhanced treatment)—automated, recirculating, pre-engineered, advanced wastewater treatment system employing a spray function to saturate textile-media;
- fixed-film technology (integrated, enhanced treatment)—submerged, oxygenated, attached growth media system
to create robust growth with naturally occurring bacteria and a nitrified/denitrified recirculation action to treat wastewater; and - membrane bioreactors (ultrafiltration)—in this strategy membranes and aeration process act as an impenetrable physical barrier to produce water filtrate that is
99.9 per cent removed of pollutants.
| ALTERNATIVE REGULATORY PATHWAYS |
For more information on alternative regulatory pathways to innovation, see:
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