BioPot - Bioenergy from edible fats - Potential of mixed collected fat waste as a resource for biodiesel

Funding:

Climate and Energy Fund of the FFG in the Energy Research Programme (e!MISSION), Energy Research 2nd call for proposals

Funding period:

09/2016- 02/2018

Abstract:

The aim of this exploratory project is to determine the biodiesel potential of mixed food and fat separator waste. To this end, this waste is to be purified to the highest possible quality and the influence of storage on the quality and suitability for biodiesel production of mixed food and grease separator waste and separately collected grease separator waste is to be measured. A life cycle assessment will be used to evaluate whether the project is ecologically and economically viable.

Project partner:

Institute for Infrastructure, University of Innsbruck

Publications:

Knapp, J., Lichtmannegger, T., Robra, S., Kinzel, C. and Bockreis, A. (2018): Bioenergy from edible fats - potential of mixed fat waste as a resource for biodiesel. Final report.

Lichtmannegger, T., Kinzel, C., Müller, W., Bockreis, A. (2018): Energetic utilisation of grease separator contents - potential for the production of biodiesel and biogas. Austrian Water and Waste Management 70: 172. https://doi.org/10.1007/s00506-018-0465-9

Presentations of the project:

Life Cycle Assessment Workshop 2016, 15-16 September 2016, Pforzheim University of Applied Sciences

Poster Life Cycle Assessment Workshop

Austrian Waste Management Conference 2017 - Digitalisation in waste management. 10 - 11 May 2017, Graz

Poster ÖWAV Waste Management Conference 2017

Austrian Water Management Conference 2017 - The future of wastewater management in Austria. 04.10.-05.10.2017, Linz

Poster ÖWAV Wastewater Management Conference 2017

Contents:

Used cooking oils cause problems in wastewater and can also be a resource for the production of bioenergy if they are collected separately. Grease separators are therefore mandatory in catering establishments, not only in Austria. There are various collection systems for used cooking oil, e.g. in Tyrol the Öli system for collecting used cooking oil from households using separate collection containers. However, quantities of used cooking oil still end up in the sewage system. As a result, the energy contained in the fats cannot be utilised and the necessary increased sewer maintenance and sewage treatment plant aeration causes additional energy consumption.

Companies that process food must generally have a grease separator if they are large enough. Their maintenance and emptying is usually outsourced by the operators to private service providers. However, used cooking oil often ends up in the wastewater due to improper disposal, inadequate maintenance or the complete absence of a grease separator. There it leads to massive problems in the sewer system, such as the corrosion of pipes due to the formation of hydrogen sulphide (_H2S) or the blockage of the sewer due to the formation of mineral deposits (Dengg and Rostek, 2004). If more dissolved fats enter the sewage treatment plant, they lead to massive operational problems such as the mass proliferation of filamentous bacteria(Microthrix parvicella) and subsequently to the formation of floating sludge and foam.

Biodiesel can be produced from separately collected edible fats, as is already done in the oil system, for example. However, fats with a low proportion of free fatty acids are required for the production of biodiesel. A project is now to investigate whether a fraction of sufficiently good quality for biodiesel production can also be obtained from fat waste from combined collection systems for food waste (kitchen waste shredder and fat separator in a tank). Since fats break down into free fatty acids under certain conditions, the influence of collection and storage, such as a high water content or the presence of microorganisms, on the fat quality is to be investigated, both for pure fat separator waste and for waste from combined collection systems.

There are various established systems throughout Austria in which used cooking oils are collected separately and subsequently used for biodiesel production. Grease separator contents, on the other hand, are currently mainly used as a substrate for co-fermentation at sewage treatment plants for the production of biogas. Research projects have shown that grease separator contents can also be used as a starting substrate for biodiesel production (Canakci, 2007; Montefrio et al., 2010).

The aim of the project is to clarify whether the production of biodiesel from waste from combined collection systems for fats and other kitchen waste or from pure grease separator waste is possible, and if so, with which processes and under which conditions. Improved collection and utilisation of used cooking oils could reduce the energy consumption resulting from disposal via the sewer and increase the production of renewable energy.

Whether the production of biodiesel from the waste to be analysed makes sense in comparison to the already established production of biogas through co-digestion depends heavily on the quantity and quality of the fats that can be separated from it and the effort required for purification. Investigations should therefore show whether a fraction of sufficiently good quality for biodiesel production can be obtained from fat separator contents and waste from combined collection systems (kitchen shredder and fat separator in one tank). The most commercially widespread method today is homogeneous alkaline catalysed biodiesel production, but this method can only tolerate a very low proportion of free fatty acids (Guldhe et al., 2015; Kulkarni and Dalai, 2006). Since fats break down into free fatty acids under unfavourable storage conditions, the influence of storage on fat quality should be investigated.

Several storage tests were carried out with fat separator contents separately and mixed with food waste. The test batches were stored at 20°C and samples were taken and analysed several times a week. The fat quality was determined using various parameters, including free fatty acids (FFA). The storage tests showed that in the heavily contaminated fat separator fractions analysed, the free fatty acids increase rapidly due to the high content of water and microorganisms, in contrast to separately collected used cooking oils. In all approaches, the storage period had a negative influence on the free fatty acids. In particular, food residues from fat separators led to a rapid increase in free fatty acids (+46%). However, low concentrations of free fatty acids (<5%) are required for the alkaline-catalysed production of biodiesel. The peroxide value, a measure of fat spoilage, increased in all approaches.

The results obtained so far show that fat separator waste is not a simple starting substrate for biodiesel production. Different processing methods and optimised storage and collection systems must therefore be investigated in the further course of the project.

In order to determine the potential of grease separator contents as a resource for biodiesel production, several grease separators were analysed. Systems were sampled where the last emptying and maintenance had taken place between 30 and 190 days previously. Both the grease layer and the wastewater in the outlet of the separator were sampled.

The quality of the grease and thus its suitability for biodiesel production was determined using various parameters such as the acid number/free fatty acids. The pH value, chemical oxygen demand (COD) and total lipophilic substances were measured in the effluent samples. Combined with the water consumption data collected, this makes it possible to estimate the amount of fat lost for the production of renewable energy.

None of the separators were able to comply with the effluent limit value of 100 mg/L of low-volatility lipophilic substances. Food residues that enter the grease separator greatly reduce the yield of usable oil for biodiesel production, so no oil fraction could be recovered from two grease separators. Regular inspections of the grease separator should be carried out by the operators. In all samples analysed, the free fatty acids were above 52% (for biodiesel max. 5% advantageous). The fats obtained from the grease separator can therefore only be converted into biodiesel using special processes that tolerate high concentrations of free fatty acids.

In many cases, however, the overall process of newly developed technologies for generating renewable energies is so resource and energy-intensive that they are not ecologically viable. An important part of the project is therefore an ecological as well as an economic analysis. Whether the production of biodiesel from the waste to be analysed makes sense in comparison to the already established production of biogas through co-digestion depends heavily on the quantity and quality of the fats that can be separated from it and the effort required for purification.

References:

Canakci M. (2007). The potential of restaurant waste lipids as biodiesel feedstocks. Bioresource Technology, 98 (1), 183-190.

Dengg J., Rostek R. (2004). Fat in wastewater. Brochure on the reduction of fat input into wastewater, Abwasserverband Achental-Inntal-Zillertal.

Guldhe A., Singh B., Mutanda T., Permaul K. and Bux F. (2015). Advances in synthesis of biodiesel via enzyme catalysis: Novel and sustainable approaches. Renewable and Sustainable Energy Reviews, 41, 1447-1464.

Kulkarni M. G. and Dalai A. K. (2006). Waste cooking oil - An economical source for biodiesel: A review Industrial and Engineering Chemistry Research, 45 (9), 2901-2913.

Montefrio M. J., Xinwen T. and Obbard J. P. (2010). Recovery and pre-treatment of fats, oil and grease from grease interceptors for biodiesel production. Applied Energy, 87 (10), 3155-3161.

Contact:

University of Innsbruck
Univ-Prof. Dr.-Ing. Anke Bockreis
Technikerstrasse 13
6020 Innsbruck
anke.bockreis@uibk.ac.at