Angelidaki, Irini

Plósz, Benedek G.

Radovici, Maria

Valverde Pérez, Borja

Wágner, Dorottya Sarolta

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Nov 09, 2017Bioflocculation of green microalgae using activated sludge and potential for biogasproductionRadovici, Maria; Wágner, Dorottya Sarolta; Angelidaki, Irini; Valverde Pérez, Borja; Plósz, Benedek G.Publication date:2016Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Radovici, M., Wágner, D. S., Angelidaki, I., Valverde Pérez, B., & Plósz, B. G. (2016). Bioflocculation of greenmicroalgae using activated sludge and potential for biogas production. Poster session presented at 13th IWALeading Edge Conference on Water and Wastewater Technologies, Jerez da la Frontera, Spain.1. INTRODUCTION Bioflocculation of green microalgae using activated sludge and potential for biogas production  Maria Radovici, Dorottya Sarolta Wágner*, Irini Angelidaki, Borja Valverde-Pérez, Benedek Gy. Plósz Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 115, DK-2800, Kgs. Lyngby, Denmark   *e-mail: dosaw@env.dtu.dk New technologies are developed to recover wastewater resources and increase energy yields in form of biogas [1].            → Potential energy recovery using microalgae.  Available harvesting methods are costly and energy intensive [2].             Objectives: • Developing cost-efficient way of harvesting microalgae via bioflocculation using activated sludge from a short-SRT EBPR system.  • Assess the potential of energy recovery via biogas production from the harvested activated sludge-algal biomass. Table 1 – How to build a table for a poster Microalgal biomass:  Mixed green microalgal culture cultivated on effluent wastewater:  Chlorella sorokiniana   and Scenedesmus sp.  2. METHODS • An effective solution is proposed to harvest microalgal biomass and to significantly decrease the amount of polymer coagulant required; • 97% microalgal biomass recovery was reached with 16 mg polymer/g algae • Poorly settling sludge did not affect microalgal biomass recovery, however, due to bulking the biomass volume was increased; • Optimum polymer dosing depends on the mixing ratio of algae and activated sludge; • Co-digestion with biomass taken after the anaerobic phase enhanced biogas potential; • Up to 40% of the influent COD of the EBPR was recovered as methane; • Most of the COD was assimilated into biomass or mineralized to CO2 and only up to 10% is lost in the effluent of the EBPR.  5. CONCLUSIONS inspiring change References: [1] Batstone, D.J., Hülsen, T., Mehta, C.M., Keller, J., 2015. Platforms for energy and nutrient recovery from domestic wastewater: A review. Chemosphere, 140, 2–11. [2] Gerardo, M.L., Van Den Hende, S., Vervaeren, H., Coward, T., Skill, S.C., 2015. Harvesting of microalgae within a biorefinery approach: A review of the developments and case studies from pilot-plants. Algal Research 11, 248–262. [3] Valverde-Pérez, B., Wágner, D.S., Lórant, B., Gülay, A., Smets, B.F., Plósz, B.G., 2016. Short-sludge age EBPR process - microbial and biochemical process characterisation during reactor start-up and operation. Submitted to Water Research. 3. Flocculation • 27 mg polymer/g algae dosing results in 92 % microalgal recovery • Restabilization effect results in lower recovery at high polymer dosages www.iwahq.org  Activated sludge C, N, P, water N, P, water aquifer recharge         CH4    Microalgae Energy recovery Harvesting!        Biodiesel Activated sludge:   Taken from a short SRT (3.5 d) EBPR system [3]: • Solid-liquid separation after the aerobic phase (ASAE) • Solid-liquid separation after the anaerobic phase (ASAN) AS Algae Algae AS polymer 1. Flocculation experiments 2. Biomethane potential tests Mesophilic conditions (37 ºC) Digestion scenarios: I. Algae II. Algae + polymer (20 mg/g algae) III. ASAE/ASAN alone (activated sludge removed after the aerobic and after the anaerobic phase) IV. ASAE/ASAN + algae (10% ratio of algae/AS) V. ASAE/ASAN + algae + polymer (10% ratio of algae/AS, 20 mg polymer/g algae) The research was financially supported by the European Commission (E4WATER Project, FP7-NMP-2011.3.4-1 grant agreement 280756) and the Integrated Water Technology (InWaTech) project (http://www.inwatech.org.www6.sitecore.dtu.dk/).  ACKNOWLEDGEMENTS Dosing (mg coagulant / g algae)0 20 40 60 80 100 120 140 160Algal biomass recovery (%)020406080100Dosing (mg polymer/g algae)0 10 20 30 40Algal biomass recovery (%)0204060801001. Polymer dosing   100% algae + polymer 10% algae + 90% activated sludge + polymer • Microalgal recovery with activated sludge used as flocculant (strategy I) is low (40%) → we need a coagulation aid (strategy II) • 16 mg polymer/g algae dosing results in 97 % recovery SVI (ml/g)0 200 400 600 800 1000Algal biomass recovery (%)020406080100biomass volume (L)0.00.20.40.60.81.0Recovery biomass volume3. Activated sludge settleability   • Bulking events in activated sludge systems cause poorly settling sludge → The biomass volume after settling is high • The efficiency of the flocculation does not deteriorate, the microalgal recovery stays sufficient (>90%) Mixing ratio (g algae/g AS)0.0 0.2 0.4 0.6 0.8Algal biomass recovery (%)0204060801002. Mixing ratio  Algae + activated sludge + polymer (16 mg/g algae) • With increasing algae/activated sludge ratios more polymer dosing is required to reach optimal recovery • Optimum dosing should be estimated for the specific operation conditions of the process 4. Biogas potential and energy recovery Algae + ASAE + polyAlgae + ASAN + polyAlgaeASAEASANAlgae + ASAEAlgae + ASANAlgae + polyMeasured methane yield (ml CH4/gVS)200 300 400 500 600• Co-digestion of microalgae with activated sludge removed after the anaerobic phase produces significantly higher (P<0.05) methane than co-digestion of activated sludge taken after the aerobic phase → due to stored PHA by PAO in the anaerobic phase of the EBPR and balanced nutrients due to co-digestion with microalgae 1. Biogas potential of biomass   ASAN ASAECOD fraction (%)020406080100Lost as CO2EBPR effluent CH4RecalcitrantAssimilated into biomass}• Effective preservation of organic carbon via the EBPR→ up to 40% of the influent organic carbon is converted into methane • Only up to 10% of the incoming COD is lost to the effluent of the EBPR 2. Energy recovery   Flocculation strategies:  Strategy I: Flocculation of microalgae and activated sludge   Strategy II: Step 1: Coagulation of microalgae with a cationic polymer (PDADMAC)  Step 2: Flocculation with activated sludge 

Bioflocculation of green microalgae using activated sludge and potential for biogas production

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Bioflocculation of green microalgae using activated sludge and potential for biogas production

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