Drinking Reclaimed Water in Windhoek

Most people don't know that we use reclaimed wastewater as part of our drinking water here in Windhoek. Windhoek is one of only a couple of cities in the entire world that intentionally incorporates treated wastewater (i.e. sewage) into the potable drinking water system. And they have been doing it since the 1960's. When you live in a desert, water scarce area there is no such thing as "waste" water. Karen and I have been drinking the water since January and haven't died yet.

I recently visited the Gammans Water Conditioning plant (i.e wastewater treatment plant) that is the start of the reclamation process. As most people are probably not familiar with the processes used, I will walk people through the process with the following pictures. The plant utilizes many of the same processes as found in the United States and elsewhere.

Gammans Treatment Plant

The first step is the inlet to the plant where the water goes through a grit chamber and screens to remove large, floating debris from the water.

Grit Chamber at Inlet

The water then travels through a flume to measure the quantity of water and then through a splitter box that diverts the water to a number of primary clarifiers. The clarifiers allow the heavier dirt and material to settle to the bottom of the tank while the cleaner water is siphoned off the top through a series of weirs. These initial processes are referred to as primary treatment.

Parshall Flume to Measure Water Quantity
(something by the way that was invented at Colorado State)

Divertor Box that can send water to 8 different clarifiers)

Primary Clarifier

(note weirs around circumference)

The water then is sent through another series of diversion boxes which sends the water to the secondary treatment processes. The plant utilizes biological activated sludge and trickling filter processes. They are essentially processes that try to mimic the bio-degradation processes found in natural rivers and streams. Microbes eat or consume the organic waste material in the water. So, you are converting the organic waste (i.e. "food") to living organisms - growing microscopic "bugs". The treated water then is sent to secondary clarifiers where the "bugs" settle out and the clean water is siphoned off the top through weirs.

Splitter Box that sends water to secondary treatment

Activated Sludge Basin

Aeration in Activated Sludge Basin
(purpose is to add oxygen to the water so the "bugs" can survive)

Trickling Filter Tank

Secondary Treatment Clarfier

The water in the region has a high nitrogen content caused by agricultural and industrial processes. As a result, the plant has a tertiary treatment process utilizing constructed wetlands to remove the excess nitrogen from the water (essentially, the plants absorb or uptake the nitrogen).

Constructed Wetland at Outlet
(Wildlife such as birds and fish live here as well)

After spending days slowing moving through the wetlands, the treated water is then transported directly into the drinking water treatment plant (I haven't visited that plant yet). There, the water is mixed with normal freshwater and turned into safe drinking water. It is a mixture of 60% freshwater and 40% treated wastewater that comes out of our faucets.

All of the stuff that has been removed and settled out from the wastewater (dirt, "bugs", etc.) becomes sludge that must be treated. The sludge is first sent to anaerobic digestors, which is an oxygen free environment that kills and stabilizes the "bugs". The stabilized sludge is then sent through a series of filter presses to remove the excess water. The dewatered sludge is then removed by conveyors where it is sold as fertilizer and compost.

Anaerobic Digestor Tank
(note gas collection pipes running from tank)

Filter Presses

Sludge as it collects at the end of the plant

The anaerobic digestors produced methane gases as the "bugs" decompose. The gas is collected and sent to an Bio-Gas internal combustion engine generator that produces electricity that powers part of the plant operations. So, they try to reuse all parts of the byproducts of the wastewater treatment.

Bio-Gas Generator

So, that is where we get our drinking water. The plant utilizes modern processes but you will notice that they don't exactly follow OSHA safety standards in Namibia. For anybody visiting us in Namibia, we will raise a glass of reclaimed wastewater as a toast for dinner.