K5/2001 - Co-digestion of sewage sludge and industrial concentrates

Funded by: Water Research Commission

April 2010 – June 2013; extended to June 2014

Project background

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 Pollution Research Group 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). PRG is providing scientific support to eThekwini Water and Sanitation (EWS). The general principle of the research being undertaken by PRG 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

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

The project co-digestion of high strength industrial concentrates with sewage sludge is currently being

undertaken at the Amanzimtoti Wastewater Treatment Works, south of Durban and at the laboratories of the Pollution Research Group. The type of digestion in specific is anaerobic digestion which is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. Co-digestion is the codisposal of different waste streams in the same digester. The advantage of combining these streams is that if they have complimentary characteristics it may result in a combined feed stream that is more easily digestible and generates larger amounts of biogas.

The general principle of this research is to capture understanding of the digestion processes and especially the effect of different types of industrial waste streams on the digestion in a model which is run on the WEST platform. The model is then used to simulate the real digester and to predict how the digester will perform under different feeding scenarios, in order to schedule the treatment of the effluent streams.

Future work for the co-digestion project includes the upgrade of Southern Wastewater Treatment Works, to determine the impact of industrial wastewater on anaerobic digestion at Southern WWTW and inform design of full-scale digestion process. As well as the feasibility of treating textile dye-bath effluent at the Mpumalanga

Works sludge digesters to reduce colour and salt loading at the Hammarsdale Waste Water Treatment Works.

Publications and reports

Journal Papers

Bond, T., Brouckaert, C. J., Foxon, K. M, and Buckley, C.A. 2012. A critical review of experimental and predicted methane generation from anaerobic co-digestion. Water Science & Technology. 65.1, 183-189.

Posters

11_CJB_WWT_CoDigestionPoster

Conference Papers and Presentations

Bond, T., Foxon, K. M., Brouckaert, C.J., and Buckley, C.A. 2011. The Future of Municipal Anaerobic Digestion in South Africa. Report to The Water Research Commission, Anaerobic Digestion Workshop. 17th February, 2011. Paradise Valley, Durban.

Reports and Other

Bond, T., Mukuna, F., Tecla, D., Foxon, K. M., Brouckaert, C.J., and Buckley, C.A. 2011. Operation of Laboratory-Scale Anaerobic Sequencing Batch Reactors. A Manual developed for the Water Research Commission.
Osborne, C., Brouckaert, C.J., and Foxon, K.M., 2012. Full Scale Performance and Scenario Analysis. Report to Water Research Commission.