Abstract
This work describes the production of polyhydroxyalkanoates (PHA) as a side stream process on a municipal waste water treatment plant (WWTP) and a subsequent analysis of the production potential in Germany and the European Union (EU). Therefore, tests with different types of sludge from a WWTP were investigated regarding their volatile fatty acids (VFA) production-potential. Afterwards, primary sludge was used as substrate to test a series of operating conditions (temperature, pH, retention time (RT) and withdrawal (WD)) in order to find suitable settings for a high and stable VFA production. In a second step, various tests regarding a high PHA production and stable PHA composition to determine the influence of substrate concentration, temperature, pH and cycle time of an installed feast/famine-regime were conducted. Experiments with a semi-continuous reactor operation showed that a short RT of 4 days and a small WD of 25% at pH = 6 and around 30 °C is preferable for a high VFA production rate (PR) of 1913 mgVFA/(L×d) and a stable VFA composition. A high PHA production up to 28.4% of cell dry weight (CDW) was reached at lower substrate concentration, 20 °C, neutral pH-value and a 24 h cycle time. A final step a potential analysis, based on the results and detailed data from German waste water treatment plants, showed that the theoretically possible production of biopolymers in Germany amounts to more than 19% of the 2016 worldwide biopolymer production. In addition, a profound estimation regarding the EU showed that in theory about 120% of the worldwide biopolymer production (in 2016) could be produced on European waste water treatment plants.
Highlights
Common plastic is derived from petrochemicals based on the limited natural resource petroleum
As the feast/famine ratio is more important than the overall cycle time (CT) a constant substrate concentration should ensure that the feast phases of the cycles were constant and the variation in CT resulted in a different famine phase, only. [25] stated that the feast-phase should not last longer than 20% of the overall CT to create a selection pressure on non-PHA accumulating bacteria
Around 19.3% of the worldwide biopolymers could be produced on waste water treatment plant (WWTP) in Germany considering the stringent definition, only
Summary
Common plastic is derived from petrochemicals based on the limited natural resource petroleum. Biopolymers present a possible alternative to common plastics If they are fully biodegradable [2,3] their use allows the preservation of limited resources, and suits the idea of sustainability. DDeeffiinniittiioonn ffoorr bbiiooppoollyymmeerrss,, iinncclluuddiinngg tthhee ssttrriinnggeenntt ddeeffiinniittiioonn oonn tthhee uuppppeerr rriigghhtt,, mmooddiiffiieedd aafftteerr [[44]] This definition ensures that polymers from fossil resources and non-biodegradable polymers, whicThhciasudseefiantilteioansteonnseuroefsththeamt penoltyiomneedrspfrroomblefmosss,ial rreeseoxucrlucedsedanadndnotnh-abtitohdeegterramdabbiloeppoolylymmereriss, wjuhsticuhsecdaufsoer aptolleyamsteorsn,ewohfitchheamlloenwtitohneedprpesroerbvleamtiosn, aorfeleimxciltuedderdesaonudrctehsatanthdeatlesromsubiitopthoelyidmeear oisf sjuussttauisneadbifloitryp. Material for the VFA production was shown by [13] while [14] investigated the effect of pH, sludge-retention time (RT) and acetate concentration on the PHA production from municipal waste water. A sample of all tested types of sludge was taken before and after the tests to determine the chemical oxygen demand (COD), the total Kjeldahl nitrogen(TKN) and total P
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