Autopsy on Failed System - Ntabeni Clinic

Autopsy on Failed System - Ntabeni Clinic

Special Report Hits: 33

The original plant was installed sometime between 2003 and 2005, and the Department of Health (KZN) finally found the funds to replace it. The Wastewater Watch offered to look into the design and installation, and then submit a report on why the system failed.

Most suppliers freely advertise package plants have a life-span of 20 years and more, and that the final effluent is not only clear, odourless and inoffensive, but also legally compliant. The reason this plant was prematurely removed is that it achieved none of the above, as understood.

We believe that this type of research is unique, and just another example of how the Wastewater Watch has pioneered the reporting of water and wastewater related issues.

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Steve - WwW

Ntabeni Clinic – KZN South Coast

Picture courtesy of

This system was removed late in January 2009, from a rural clinic in the KZN South Coast. It consisted of two x 1500 litre bioreactors and a clarifier, all connected in series. This meant that all the effluent passes through the first processor, into the second and finally into the clarifier. Controlled pumping (balancing flow into the system) was done by a throttled valve in the pump sump. As understood, the duty was 5000 litres per day.

Dismantling & Removal from site

The system took four hours to disconnect and load. The electrical disconnection was simple, but as no drainage valves were fitted there was no method of emptying the system. Holes had to be drilled at the base of the tanks to empty the contents.

Once all the water had been drained, the plant was still very heavy with sludge, and both reactors weighed nearly a ton. Sludge oozed out of the reactor inlet / outlet ports.

The Autopsy

Efforts to remove the fixed media failed as the sludge buildup had made the media very heavy, and began to break up. It was decided that the top should be cut off the tank so that the configuration of the internal parts remain intact.


The top was cut open and several internal pipes were cut to allow for further inspection. The media was snugly packed inside the tank. Feed pipes, both aeration and incoming wastewater were placed on the bottom, below the media. Several plastic Coca Cola type crates were supporting the media, ensuring there was a mixing area below the media

The media was almost entirely choked with sludge, reducing the effective surface area, and therefore severely restricting the biological action. The system then became overloaded, allowing undigested sewage to further choke the system. Reports of tanks overflowing alerted the health authorities, and a solution was sought.


The media (a) used in Clear Edge systems is designed for cooling towers, and is manufactured in sheets, or slabs.

The three types of media used in package plants

Plant suppliers use it because it is very cheap, and it fills a hole. The design is flawed in that it has channels that will not allow lateral movement of water. Once water / or air has entered a channel, it can only escape at the end or top. This creates "high traffic" areas in some areas and dead areas in other areas. This is a critical flaw in that the biomass does not like to be "hurried" or "ignored".

Sludge Build-up

There will always be sludge in the reactors, which needs to be removed on a regular basis. This plant neither had facility to remove sludge, or even empty the tanks, and this is a serious design fault.

The above picture shows what clean media (left) looks like, and the media removed from the Clear Edge system (right)

Aeration System

We found this method of aeration effective. Swimming pool pumps used were a constant source of trouble, with regular failures, as understood.

Final Effluent Clarification

A 260 litre clarifier was installed at the end of the process, and was totally ineffective, both in design and in installation. Leveling of the outlet (launder) was crude, and done by means of a cable tie. The launder itself was a series of cutout scallops in 50mm pipe, neither level nor accurate.

Should this plant have had a retention period of about 13 hours, the clarifier would have had just 12 minutes to settle solids.


The system was not designed / installed to allow for servicing, maintenance or repair. The thought that went into the system indicates the manufacturer / installer either knew very little about the applied technology, or did not mind how it was installed.

The system’s failure was inevitable, due to ignorance or arrogance, or possibly both.

All in our opinion.