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The indigenous microalgae-activated sludge (MAAS) process during remediation of municipal wastewater was investigated by studying the influence of iron flocculation step and light intensity. In addition, availability of total phosphorous (P) and photosynthetic activity was examined in fed-batch and batch mode under northern climatic conditions and limited lighting. This was followed by a semi-continuous operation with 4 d of hydraulic retention time and mean cell residence time of 6.75 d in a photo-bioreactor (PBR) with varying P availability. The fed-batch condition showed that P concentrations of 3–4 mg L −1 were effective for photosynthetic chl. a development in iron flocculated conditions. In the PBR, the oxygen evolution rate increased with increase in the concentration of MAAS (from 258 to 573 mg TSS L −1 ) at higher surface photosynthetic active radiation (250 and 500 μmol m −2 s −1 ). Additionally, the rate approached a saturation phase at low MAAS (110 mg L −1 ) with higher light intensities. Semi-continuous operation with luxury P uptake and effective P condition showed stable average total nitrogen removal of 88 and 92% respectively, with residual concentrations of 3.77 and 2.21 mg L −1 . The corresponding average P removal was 68 and 59% with residual concentrations of 2.32 and 1.75 mg L −1 . The semi-continuous operation produced a rapidly settleable MAAS under iron flocculated condition with a settling velocity of 92–106 m h −1 and sludge volume index of 31–43 ml g −1 in the studied cases. [ABSTRACT FROM AUTHOR]

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 CO 2 emissions. [ABSTRACT FROM AUTHOR]