Abstract
Due to the rising water deficit in agriculture, digestate is increasingly being considered not only as an alternative fertiliser but also as a potential source of water. The use of recycled water for crop irrigation requires that it be treated in such a way that contaminants from the fermented biomass are not returned to the environment. Membrane processes can provide promising results in this regard. This study seeks to achieve membrane filtration using flat ceramic membranes for effective digestate liquid fraction treatment from a municipal waste biogas plant. Membranes of 1, 5, 15, and 50 kDa, and 0.14 and 0.45 µm are examined. The results obtained show that the application of a sedimentation process, as a preliminary step in the purification of the digestate, allows for a significant reduction in the content of contaminants in the solution. By analysing the effectiveness of the liquid fraction of the digestate purification in the sedimentation-membrane filtration process using flat ceramic membranes, it can be stated that all the membranes tested can be applied in the digestate purification. With an increase in the cut-off value, a deterioration in the quality of the digestate can be observed. The use of the sedimentation process before the membrane process not only improves the final quality of the digestate but also reduces the intensity of membrane fouling.
Highlights
The reasons for the change in environmental protection strategies towards so-called “clean production” are both the constantly increasing pollution of water, soil, and air and a reduction in the availability of non-renewable raw material resources
The tests were carried out using the liquid fraction of digestate from a waste biogas plant processing an organic fraction of municipal waste located in a Polish waste management plant (50◦ 530 15.5” N 17◦ 230 28.0” E)
The effectiveness of the treatment of the liquid fraction of digestate on flat ceramic membranes was evaluated by analysing the influence of the membrane cut-offs and the process parameters on the change of the Chemical oxygen demand (COD), BOD5, and Dissolved organic carbon (DOC) values
Summary
The reasons for the change in environmental protection strategies towards so-called “clean production” are both the constantly increasing pollution of water, soil, and air and a reduction in the availability of non-renewable raw material resources. A circular economy is an economic model involving growth without increasing resource consumption by changing the structure of production chains and transforming industrial systems In both municipal and agricultural biogas plants, the principles of such operation include the use of the biological fermentation process to produce biogas. This technology is seen as one of the forward-looking solutions in the waste management and renewable energy production sector [5,6,7]. Our previous study [38] determined the effectiveness of different polymeric membranes in the treatment of the digestate liquid fraction from municipal waste biogas plants. Since polymeric membranes have not shown satisfactory purification efficiency and exhibit many disadvantages, as discussed above, we decided to conduct a study to determine the suitability of ceramic membranes for this purpose with a special focus on organic matter separation
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