Constructed Wetland System at Mara Bushtops

Introduction

In the bush environmentally-friendly recycling and disposal of waste water is quite a challenge. Normal waste water treatment plants are highly specified constructions and have power requirements which are difficult to provide in the bush. A small exclusive camp such as Mara Bushtops does not produce sufficient waste water to justify such large treatment facilities.

Many remote camps and lodges in Kenya use a soakage pit method, however this is not regarded as an optimal solution, as waste water can eventually seep into the soil, with its potentially detrimental impact on the environment.

One alternative solution is called a constructed wetland system (CWS). This method has been developed inthe USA,where it was observed that natural swamps have the capacity to purify waste water.Based on these observations, the technology of constructed wetland systems has developed in both the USA and Europe, encouraged by an increased environmental awareness. It is only recently that CWS projects have been started in Kenya. One such large project was constructed in cooperation with the GEF SGP (GlobalEnvironmental Fund Small Grants Program) to purify waste water from Egerton University in Nakuru (see www.undp.org/kenya/GEF-SGP/ ).

Smaller constructed wetland systems have also been installed in camps and lodges. To date, the Olonana Camp is the only other camp in the greater Masai Mara area that has a constructed wetland system.

CWS at Mara Bushtops

In keeping with Mara Bushtops’ high environmental standards, a constructed wetland system was chosen as the preferred method to purify our waste water.

The CWS consists of three main elements: a septic tank, a gravel bed (also called gravel bed hydroponics, GBH) and surface ponds (also called surface cells). Initially, all waste water from the camp is collected in a septic tank. However, waste water from the kitchen is first iltered through a grease trap which removes fats, as these are difficult to break down within the CWS.

The septic tank consist sof three linked chambers, each with a volume of 12m³. Solids settle within this tank initiating an anaerobic process, which slowly digests any nutrients contained within the waste water. The last chamber of the septic tank has a pipe that flows directly into an adjacent gravel bed.

The gravel bed covers an area of approximately 200 m² into which serpentine-shaped channels have been dug, reducing the flow of the water and allowing friendly bacteria enough time to do their work. A 60 cm thick bed is graded with coarser gravel at the bottom to a finer grade at the top. Overlying the gravel is a layer of coarse sand grading to fine sand. It is in this upper layer that swamp plants with a high nutrient tolerance are planted. Indigenous sedge, reed and other aquatic plant species keep the biodiversity as natural as possible. Sedges and other swamp plants have the ability to oxygenate the soil. This allows the surface aerobic bacteria to continue the process initiated by the an aerobic bacteria below, enhancing the purification process. The plants in the gravel have been shown to absorb at least 10% of available nutrients.

Once the gravel bed is filled, water overflows via a pipe into the first surface pond. Additional serpentine channels containing stones and plants, reduce the water flow and enhance the aeration process. Indigenous algae, bacteria, invertebrates and plants further consume the remaining nutrients purifying the water. Over time more and more flora and fauna develop around these ponds further increasing the local biodiversity.

Mara Bushtops is fortunate to be located adjacent to a natural wetland. After passing through a number of surface ponds, the water enters this natural system, where a final purification takes place, after which this clean water enters the Siana and Talek catchment area.

The system is designed to use ground water as its source, which is subsequentially returned as purified waste water, allowing the hydrology of the area to be kept in balance.