title: Influence of hydraulic retention time on indigenous microalgae and activated sludge process.
abstract: Integration of the microalgae and activated sludge (MAAS) process in municipal wastewater treatment and biogas production from recovered MAAS was investigated by studying the hydraulic retention time (HRT) of semi-continuous photo-bioreactors. An average total nitrogen (TN) removal efficiency (RE) of maximum 81.5 ± 5.1 and 64.6 ± 16.2% was achieved at 6 and 4 days HRT. RE of total phosphorous (TP) increased slightly at 6 days (80 ± 12%) HRT and stabilized at 4 days (56 ± 5%) and 2 days (55.5 ± 5.5%) HRT due to the fluctuations in COD and N/P mass ratio of the periodic wastewater. COD and organic carbon were removed efficiently and a rapidly settleable MAAS with a sludge volume index (SVI_10) of less than 117 mL g(-1) was observed at all HRTs. The anaerobic digestion of the untreated MAAS showed a higher biogas yield of 349 ± 10 mL g VS(-1) with 2 days HRT due to a low solids retention time (SRT). Thermal pretreatment of the MAAS (120 °C, 120 min) did not show any improvement with biogas production at 6 days (269 ± 3 (untreated) and 266 ± 16 (treated) mL gVS(-1)), 4 days (258 ± 11(untreated) and 263 ± 10 (treated) mL gVS(-1)) and 2 days (308 ± 19 mL (treated) gVS(-1)) HRT. Hence, the biogas potential tests showed that the untreated MAAS was a feasible substrate for biogas production. Results from this proof of concept support the application of MAAS in wastewater treatment for Swedish conditions to reduce aeration, precipitation chemicals and CO2 emissions.
authors.affiliation: Department of Energy, Building and Environment, Mälardalen University, SE-721 23, Västerås, Sweden. Electronic address: anbarasan.anbalagan@mdh.se.
authors.forename: Anbarasan
authors.initials: A
authors.lastname: Anbalagan
authors.affiliation: Department of Energy, Building and Environment, Mälardalen University, SE-721 23, Västerås, Sweden.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schwede
authors.affiliation: Department of Energy, Building and Environment, Mälardalen University, SE-721 23, Västerås, Sweden; ABB AB, Corporate Research, SE-721 28, Västerås, Sweden.
authors.forename: Carl-Fredrik
authors.initials: CF
authors.lastname: Lindberg
authors.affiliation: Department of Energy, Building and Environment, Mälardalen University, SE-721 23, Västerås, Sweden.
authors.forename: Emma
authors.initials: E
authors.lastname: Nehrenheim
mesh_terms: D056804:Biofuels / Q000032:analysis; D019149:Bioreactors; D002708:Chlorella / Q000378:metabolism; D019015:Geologic Sediments / Q000032:analysis; D057446:Hydrodynamics; D058086:Microalgae / Q000378:metabolism*; D044444:Scenedesmus / Q000378:metabolism; D012722:Sewage / Q000032:analysis*; D013548:Sweden; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000032:analysis*
chemical_list: D056804:Biofuels; D012722:Sewage; D062065:Wastewater
keywords: Activated sludge process; Anaerobic digestion; Hydraulic retention time; Microalgae; Nutrient removal; Thermal pretreatment