What is Option B?
Option B is the Parawewa configuration for sites where natural gravity discharge is restricted. It uses the same patented biological treatment as Option A, in a hermetically sealed concrete body, and adds a heavy-duty submersible pump that lifts the treated water to the absorption point where it can be discharged safely.
Why high water table land needs a different design
In low-lying coastal and wetland areas, the ground is saturated for much of the year, and heavy monsoon rain raises the water table further. Standard concrete rings were never designed for that:
- Porous, jointed concrete can take in groundwater and fill up shortly after installation.
- Hydrostatic pressure pushing up from below can shift or float a tank, a problem known locally as “tank floating”.
- On flat or low plots there is no fall for effluent to leave the tank by gravity.
See the full engineering guide: Installing bio septic tanks in high water table lands.
How Option B is engineered for these sites
- Sealed concrete chamber. A one-piece, in-situ cast concrete chamber, rather than jointed rings or brickwork, prevents inward water infiltration even when the tank sits below the local water table.
- Discharge to the absorption point. A heavy-duty sealed pump lifts the treated water to the absorption point where gravity discharge is not possible.
- Shallow, wide geometry. Wide, shallow tank geometry avoids deep excavation into saturated ground, reducing excavation risk and dewatering cost.
- Anti-buoyancy anchoring. The installation is anchored and ballasted to resist uplift from groundwater pressure.
Where Option B is used
Option B is specified for high groundwater table lands, marshy wetlands, coastal properties and flat elevations, including areas such as Negombo, Ja-Ela, Wattala, Mathugama and Galle.
Warranty and treatment performance
Option B carries the same 10-year written manufacturer warranty as Option A, covering structural tank integrity, chamber sealing and multi-stage biological layer filtration performance. The biological treatment is the patented the Parawewa biological process (Sri Lanka Patent #16371), with effluent laboratory-tested against CEA discharge guidelines.
Option A or Option B?
If your ground is standard and your water table is normal, Option A (gravity-fed) avoids the pump and uses no electricity. If your site is waterlogged, coastal or flat, Option B is the right fit. A free site inspection confirms which applies.
| Feature | Option A – Gravity-Fed | Option B – Seal Type Parawewa System |
|---|---|---|
| Best for | Standard ground, normal soil elevation and water table | High water table, marshy, coastal and flat land |
| Discharge | Natural gravity flow | Water-sealed; treated water is lifted to the absorption point |
| Electricity | None – fully passive | Uses some electricity (less than mechanical STPs) |
| Power cuts | Keeps operating | The pump needs power to discharge |
| Treatment | Same patented biological filtration (Sri Lanka Patent #16371) | |
| Warranty | 10-year written manufacturer warranty on both options | |
