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Issue 02/2017

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From Science and

From Science and Research Biopolymers from municipal waste water treatment plants Polyhydroxyalkanoates (PHA), which are biodegradable polyesters accumulated by more than 300 different microorganisms under nutrient limited conditions are a source for bioplastic production [1, 2, 3]. Bacteria mostly use PHAs as an intracellular storage compound for energy and carbon [4]. The general chemical structure of PHA can be seen in Figure 1. Depending on the length of the side chain (R), PHAs are classified as short chain length (SCL) or medium chain length (MCL) PHAs [5]. Most material characteristics of SCL resembles polypropylene (PP) [6]. Therefore, PHAs are most likely used as a substitute for PP [7]. PHA production on municipal waste water treatment plants Pittmann and Steinmetz [8, 9] were able to show the possibilities of PHA production on waste water treatment plants (WWTP) at different processing conditions. In a two-staged production process, as shown in Figure 2, firstly short chained volatile fatty acids (VFA) are produced. The PHA production itself (Stage 2b) is based on a bacteria mixed culture selection from excess sludge of a WWTP via aerobic dynamic feeding (Stage 2a). The installed feast/famine regime for enrichment of PHA producing bacteria is state of the art and tested by many authors [10, 11, 12]. PHA producing bacteria in the WWTP’s excess sludge are able to use the polymers as a carbon- and energy source during the period of starvation (famine phase) and thus gain a selection advantage [13]. After a period of enrichment, the biomass contains a high proportion of PHA accumulating bacteria and is transferred to Reactor 2b for PHA production. The whole production process takes place in a bypass to the WWTP, and therefore without impacts on its cleaning capacity. However, the usage of primary sludge for VFA production and the further usage of these acids for PHA production removes up to 39 % of the primary sludge’s chemical oxygen demand (COD) [8]. Hence, the PHA production process competes with the biogas production on the WWTP. Results At first different raw materials of a municipal WWTP regarding VFA production were observed with primary sludge showing the best mas flux results [8]. Through variations of the process parameters temperature, pH, retention time (RT), withdrawal (WD) and the mode of operation (batch or semi-continuously) of the reactor, a maximum VFA mass flow of 1,913 with a VFA concentration of 1,653 could be achieved [8]. Afterwards experiments regarding the PHA production were conducted. Through variations of the process parameters substrate concentration, temperature, pH and cycle time, PHA concentrations up to 28.4 % of the cell dry weight (CDW) could be achieved [9]. Potential analysis On the basis of the named results and detailed data about the amounts of sewage sludge on WWTPs a potential analysis was calculated. The goal of this analysis was to determine the potential for biopolymer production on German WWTPs. The used input parameters for the calculations are shown in Table 1. After calculating the amount of the primary sludge in Germany and with respect to the fact that roughly 92 % of the people equivalents (PE) are connected to WWTPs of the classes IV and V, at which it can be assumed that these facilities produce primary sludge, the theoretical reactor size can be calculated. Now, date from the experiments can be used to calculate the possible amount of biopolymers produced at German WWTPs. The PHA production sums up to 157,000 [16]. Under consideration of By: Timo Pittmann TBF + Partner AG, Böblingen, Germany Figure 2: Scheme for production of PHA including potential calculations for German WWTPs 20 bioplastics MAGAZINE [02/17] Vol. 12

From Science and Research the stringent definition of biopolymers, introduced by Pittmann and Steinmetz [17] around 20 % of the world wide biopolymers could be produced on WWTPs in Germany. A rough estimation, with data provided by EU member states, leads to a theoretical possible PHA production on European WWTPs of nearly 880,000 [16]. This correlates to approximately 116 % of the worldwide PHA production, regarding the stringent definition. Conclusion Based on the results it can be concluded that it is possible to produce PHA out of material flows of a municipal waste water treatment plant. The presented calculations and results clearly indicate that it would be possible to produce high amounts of PHAs on WWTPs in the European Union. The potential analysis showed that waste water treatment plants could be used as a significant source for biopolymers and waste water can play an important role as a substituent for plant-based raw materials in the PHA production. With an upgraded operation more than twice of today’s worldwide biopolymer production could be produced on WWTPs in the EU and thus contribute to a recycling of the organic material contained in waste water. It has to be mentioned though that more research is necessary to verify experimental results at a larger scale. References [1] Lee, S. Y. (1996). “Plastic bacteria? Progress and prospects for polyhydroxyalkanoate production in bacteria”. In: Trends in Biotechnology 14, 431 –438. [2] Dias, J.M.L. (2006). “Recent advances in polyhydroxyalkanoate production by mixed aerobic cultures: From the substrate to the final product”. In: Macromolecular Bioscience 6, 885–906. [3] Nikodinovic-Runic, J., Guzik, M., Kenny, S., Babu, R., Werker, A., O’Connor, K., (2013). Carbon-rich wastes as feedstocks for biodegradable polymer (polyhydroxyalkanoate) production using bacteria”. In: Adv. Appl. Microbiol, 84, 13 9–200. R O [4] Chanpratreep, S. (2010). “Current trends in biodegradable PHAs”. In: Journal of bioscience and bioengineering 110, 621–632. [5] Endres und Siebert-Raths (2009). “Technische Biopolymere”. Hanser. [6] Chen, G.-Q. and Q. Wu (2005). “The application of polyhydroxyalkanoates as tissue engineering materials”. In: Biomaterials 26, 6565 –6578. [7] Wolf, O., M. Crank, M. Panel, F. Marscheide-Weidemann, J. Schleich, B. Hünsing and G. Angerer (2005). “Techno-economic Feasibility of Large-scale Production of Bio-based Polymers in Europe”. In: European Commission - Joint Research Centre EUR 22103 EN. [8] Pittmann, T. and Steinmetz, H. (2013). “Influence of operating conditions for volatile fatty acids enrichment as a first step for polyhydroxyalkanoate production on a municipal waste water treatment plant”. In: Bioresource Technology 148C, 270-276 [9] Pittmann, T. and Steinmetz, H. (2014). “Polyhydroxyalkanoate production as a side stream process on a municipal waste water treatment plant”. In: Bioresource Technology, 167, 297-302 [10] Dionisi, D., M. Majone, G. Vallini, S. Di Gregorio and M. Beccari (2005). “Effect of the applied organic load rate on biodegradable polymer production by mixed microbial cultures in a sequencing batch reactor”. In: Biotechnology and Bioengineering 93, 76–88. [11] Albuquerque, M.G.E., M. Eiroa, C. Torres, B.R. Nunes and M.A.M. Reis (2007). “Strategies for the development of a side stream process for polyhydroxyalkanoate (PHA) production from sugar cane molasses”. In: Journal of Biotechnology 130, 411–421. [12] Johnson, K., R. Kleerebezem and M.C.M. van Loosdrecht (2009). “Modelbased data evaluation of polyhydroxybutyrate producing mixed microbial cultures in aerobic sequencing batch and fed-batch reactors”. In: Biotechnology and Bioengineering 104, 50–67. [13] Pittmann, T., (2015). “Herstellung von Biokunststoffen aus Stoffstroemen einer kommunalen Klaeranlage” (production of biopolymers from streams of a municipal waste water treatment plant) Ph.D.-thesis. University of Stuttgart. [14] DWA, (2012). “Performance comparison of municipal waste water treatment plants in 2012”, dwa: German association for water, wastewater and waste. Deutsche Vereinigung fuer Wasserwirtschaft, Abwasser und Abfall e.V. Theodor-Heuss-Allee 17, 53773 Hennef, Deutschland. [15] ATV, (2000). “ATV-DVWK-A 131 – dimensioning of single-stage activated sludge plants”; DWA German association for water, waste water and waste. [16] T. Pittmann and H. Steinmetz, (2016). “Potential for polyhydroxyalkanoate production on German or European municipal waste water treatment plants”, In: Bioresource Technology 214, 9-15. [17] T. Pittmann and H. Steinmetz, (2016). “Produktion von Bioplastik auf kommunalen Klaeranlagen”, In: Wasser und Abfall 05/13, 37-41. Municipal Waste Water Treatment Plant (generic photo, no PHA production) (photo:TBF+ Partner AG) O CH CH 2 C n Figure 1: General chemical structural formula of PHA Table1: Input data used during the potential analysis. Parameter Unit Value Literature Actual connected people equivalents (PE) on German WWTPs Mio. PE 109.0 [14] Proportion of PSP*-PEs regarding total PEs in Germany % 92 [14] Amount of primary sludge per PE L/(PE · d) 1.1 [15] Total solid concentration of primary sludge/acidified material g/L 35 [13] VFA concentration g VFA /m3 7,653 [13] Retention time and withdrawal at the first production step d und %/d 4 und 25 [13] Total solid concentration in the aerobic reactors 2a /2b g/L 5.0 [13] Loading rate for PHA production kg VFA /m3 1.2 [13] Retention time and withdrawal at reactor 2 a d und %/d 2 und 50 [13] PHA proportion based on cell dry weight Gew. % 28.4 [13] *PSP = German WWTPs with preliminary sedimentation potential (PSP = more than 10.000 PE) bioplastics MAGAZINE [02/17] Vol. 12 21

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