The evaluation of the anaerobic baffled reactor for sanitation in dense peri-urban settlements

The evaluation of the anaerobic baffled reactor for sanitation in dense peri-urban settlements
Report No 1248/01/06

February 2006

EXECUTIVE SUMMARY

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.

1 INTRODUCTION

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 conditions.

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.

1.1 Objectives of the study

The aims of this project were:

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 project.
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.

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 project.

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.