Optimization of the MaxiFuels concept by implementation of salt removal and recovery of a high value fertilizer product

The EFP project 'Optimization of the MaxiFuels concept by implementation of salt removal and recovery of a high value fertilizer product' is conducted in the frame of the MaxiFuels project 'Pilot-testing and optimization of a fermentation concept for maximal production of bioenergy (ethanol, hydrogen and methane) from residual biomass like straw'. The aim of the MaxiFuels project is to test and further optimize the concept of 2. generation bioethanol production from lignocellulosic biomass with conversion of the fermentation residuals into biogas and valuable by-products in pilot-scale. In the present project was investigated how and to which extent the effluent from the biogas process has to be purified in order to recirculate this stream as process water in the MaxiFuels process. The project consisted of the following working tasks: i) Analysis of salt concentrations in the different process steps of the MaxiFuels process, ii) Modelling of the salt concentrations for continuous operation and recirculation of process water, iii) Identification of the highest tolerable salt concentrations for each process step, iv) Practicability, efficiency, and energy consumption for different possible processes for salt removal. The salt analysis showed that Na+ accounts for most of the salt ions in the process water due to the use of NaOH for pH adjustment. Other ions found in significant concentrations where K+, Cl-, Ca++ and P. The tolerance tests revealed the highest salt concentration without signs of inhibition to be 30 g/L. Electro dialysis showed to be the most promised method for salt removal of the respective process water. The company E2 ended its participation during the project and the company BioGasol ApS carried out most of the tasks formerly appointed to E2. Due to restructuring of the DTU Systembiology research group at Risø DTU in spring 2008, there was a lack of personnel for performing the final testing; therefore the work could not be fully completed