The evaluation of the anaerobic
baffled reactor for sanitation in dense peri-urban settlements
Report No 1248/01/06
This report presents the results and findings of Water
Research Commission project K5/1248 the
anaerobic baffled reactor for sanitation in dense peri-urban areas.
In this study, the performance of an anaerobic baffled reactor (ABR) in
the treatment of domestic wastewater was assessed by extrapolating
existing understanding of the characteristics of laboratory-scale ABRs
to design a pilot-scale reactor. The pilot-scale reactor was operated
and analysed at Umbilo and Kingsburgh wastewater treatment plants
(WWTP) where it was fed municipal wastewater. A parallel study
investigated water use and wastewater generation patterns in a
peri-urban community. A modelling study was undertaken using data from
the pilot-scale ABR from different operating periods and measured
community wastewater characteristics, and used to predict effluent
characteristics of an ABR treating domestic wastewater from a dense
peri-urban area under specified operating conditions. The cumulative
experiences and information gained in all the parts of this project
were brought together to propose improvements in ABR dimensions and
installation in Guidelines
for the design, operation and maintenance of an ABR
treating domestic wastewater. Recommendations regarding the
appropriateness of the system for different applications and
suggestions for management and maintenance strategies were made.
The provision of water and sanitation services to
previously unserved communities is a South African development
priority. No single technological solution is universally applicable to
solve this backlog and a solution for a particular community requires
that a range of technologies to be available for consideration. This
report describes the performance of the anaerobic baffled reactor (ABR)
as a possible technology for the treatment of water-borne sewage. This
system was originally developed for high-strength organic loads as
found, for example, in agro-industrial effluent. The ABR’s
particular attributes are that it provides for efficient COD removal,
does not require external power and has been shown to be resilient to
shock loads (hydraulic and organic loading).
The motivation for this project was that, in Durban, it could take
approximately 20 years for water-borne sewage to be provided to some of
the dense peri-urban communities of the Metro. Because of the lack of
availability of water, both for consumption and household use, the
wastewater produced from these areas is concentrated. Moreover, the
ambient temperatures in KwaZulu-Natal are relatively high. In this
context, it was hypothesised that the application of the ABR could
provide an immediate solution to the sanitation problem in dense
peri-urban areas, where it could be used to treat the domestic
wastewater of a small community. The density of dwelling and the
topography of these settlements negate the possibility of implementing
treatment options such as anaerobic ponds or wetlands.
eThekwini Municipality has been divided into areas where waterborne
sanitation exists, and where it does not. Within the sewered area, the
aim is to have 100% waterborne sanitation. To the sea-ward side of the
area, where possible, sewers will be built or extended where
appropriate. On the inland side of the area, however, on-site treatment
or decentralised options will be necessary.
eThekwini Municipality has adopted a policy of supplying dry sanitation
options to low-income households outside of the water-borne edge
(Macleod, 2005) However, many householders aspire to water-borne
sanitation, and there is a technology gap in water-borne sanitation
options that are sustainable, affordable and practical for these
The ABR meets several critical requirements, namely, it does not
require energy for operation; requires low maintenance; is compact and
could be mass-produced. Several ABRs could service small sub-groups
within an area and eventually connect to a sewer system for further
treatment at a WWTP. Some limitations of the ABR are: no nutrient
removal; and insufficient pathogen removal.
Objectives of the study
The aims of this project were:
These objectives were not materially altered during the course of the
project. This project has been a scoping study on many of the issues
relating to the feasibility of implementing the ABR in peri-urban,
rural or densely populated or informal communities, focussing on the
microbiological and biochemical performance of the reactor, but also
investigating community and institutional issues associated with the
- To provide an appropriate sanitation system for application
in peri-urban areas through scientific and engineering support to the
KwaZulu-Natal Business Partners for Development water and sanitation
- To develop an anaerobic baffled reactor for use in
pre-treating sewage from peri-urban areas.
- To monitor the performance of the anaerobic baffled reactor
in a peri-urban area.
- To undertake pilot studies of the anaerobic baffled reactor
at a WWTP.
- To gain scientific knowledge on the fluid mechanics and
microbiology of the anaerobic baffled reactor for the pre-treatment of
sewage from peri-urban areas.
- To contribute to the development and validation of a
computer model for anaerobic digestion.
It was not considered appropriate to implement a field ABR in a
community situation within this project since there were several
process issues that required further experimentation before the
technology could be considered ripe for implementation in the field.
The extra experimentation generated a considerable body of scientific
information which has greatly enhanced the understanding of the
dynamics of anaerobic digestion within the ABR.