An average WWTP, possessing anaerobic sludge treatment (fermentation), normally produces electricity in a percentage between 40 and 75 % of its own electric energy consumption. Co-fermentation with regionally available bio waste is able to improve the biogas production significantly. Including co-fermentation in its system, a WWTP can produce up to 100 % of its own electricity production or even exceed its own electricity needs.
The project was part of and funded by of the framework "Vienna Environmental 2008". The aim of the project was to analyse and assess WWTPs with mass flow balances already using co-fermentation regarding their treatment performance as well as economic performance in a first step. Subsequently a simulation model for co-fermentation was developed, which included the definition of general valid parameter values.
The big advantages of simulations are to gain a deeper knowledge about the occurring processes and the possibility to estimate and forecast the resulting gas production and its composition (CH4, H2S). With this results, design and operation strategies can be improved concerning process stability, energy production and economic efficiency.
The 3 year long project was a cooperation between H2Office and the institute for water quality, resource and waste management of the technical university of Vienna.
In a first stage, 5 municipal WWTPs which had already implemented co-fermentation, have been investigated. Periods with and without co-fermentation have been examined.
In the next step, a simulation model was developed and tested on 3 of the 5 WWTPs. In the last stage, the WWTP with the best dataset (including waste water and sludge treatment) was simulated for a period of 2 years.
A newly developed technique now helps to characterize the substrate based only on analysing techniques, which are common in wastewater treatment.
The H2S content of the gas, calculated by the model, can be especially important. Excessive H2S content in biogas can lead to fatal problems for the CHPs, in the worst case ending with a total breakdown. Therefore gas desulphurising systems can be designed on the basis of the model results.
"MODECO" is an efficient simulation tool to optimize co-fermentation facilities regarding process stability, energy production and economic output for already operating systems as well as in the design process. Furthermore the tool helps to improve the overall energy management and efficiency of a WWTP as well as to improve its combined heat power plants (CHPs).