Anaerobic digestion is increasingly being considered as an environmentally-sustainable treatment option for an extensive range of waste biomass, due to the potential for energy recovery in the form of methane production, and lower sludge volumes relative to aerobic treatment processes. When two substrates are co-digested (i.e. digested together), added benefits are foreseeable, such as increased methane production and detoxification of toxic compounds via cometabolic degradation pathways. 

In 2010, the Water Research Commission granted the WASH R&D Centre with a three year contract purposed to investigate anaerobic digestion processes and the effect of different types of industrial waste streams on the digestion performance. The overall objective of the project is to co-digest concentrated industrial effluent with sewage at the Amanzimtoti wastewater treatment works (WWTW). The Centre is providing scientific support to eThekwini Water and Sanitation (EWS). The general principle of the research being undertaken by the Centre is to capture understanding of anaerobic digestion processes and the effect of different types of industrial waste streams on the digestion performance in a computer model, being run on the WEST platform. The model will then be used to simulate the real digester and to predict how the digester will perform under different feeding scenarios, in order to effectively schedule the treatment of the effluent streams.

In order to be able to effectively model the processes, it is necessary to have a set of integrated screening experiments that may be used to generate model parameters. These model parameters may then be used to simulate digester performance and compare it to actual digester performance. The project methodology was thus devised to develop and calibrate a full-scale co-digester model and to develop and model screening experiments to provide data and parameters for this model. Once the model is developed it can be used throughout waste water treatment plants to predict the behaviour of anaerobic co-digesters and hence forms the bridge between science and practice. In addition to the Southern Wastewater Treatment Works in Amanzitoti, the study is also processing textile effluent at the Mpumalanga Works and salt loading at the Hammarsdale Waste Water Treatment Works.

The outcomes of the project are a set of operating guidelines and procedures for laboratory analyses and full-scale digester operation.

Project objectives

1. Promote better quantitative understanding of anaerobic digesters through the use of process models.
2. Promote the codigestion of concentrated industrial organic wastes in municipal digesters.
3. Demonstrate a protocol for predicting the performance of a municipal digester treating a mixed domestic / industrial effluent.
4. Demonstrate a protocol for codigestion of industrial organic concentrates in a municipal sludge digester.
5. Demonstrate the use of the protocol in maximising the amount of methane produced or maximising the amount of toxic waste treated.