Nitrification and denitrification by an algal-bacterial consortium in a photo-SBR : [effects of the operational mode and ammonium loading rates]

Microalgal-bacterial photobioreactors are considered one of the sustainable wastewater treatment alternatives. An experiment was conducted for stimulating tertiary treatment from anaerobic treatment;such as an UASB to remove nitrogen from effluent. In this study, the effect of operational conditions in a photo-SBR (sequencing batch reactor) and ammonium loading rate were investigated. The SBR was operated with some different length and sequence phase. The initial mixed culture of algae species consisted of Scenedesmus quadricauda, Anabaena variabilis, Chlorella sp., Chlorococcus sp., Spirulina sp., and unidentified algae species from canal water. Nitrifying bacteria were cultured from Harnaschpolder WWTP activated sludge. The ammonium influent was increased step wise; 23, 50 and 70 and then back to 23 mg N-NH4+/l.day on three different periods.During the experiment; the highest performance was obtained during period two. The nitrification and denitrification process was successfully supported by photo-SBR setting: fill 1: 0.13h, aerobic 1: 7.3h, fill 2: 0.03, anoxic: 1.22h, aerobic 2: 1h, settles: 1.9h, and withdraw: 0.1h in two cycles per daywith the maximum nitrification rate achieved was 38 mgN-NH4+/l.d and maximum denitrification rates was 2404 mgCOD/l.d at 23.2 mgN-NH4+/l.d influent loading rate or spesific ammonium loading rate (ALR) 0.03 mgN-NH4/mgVSS.day.There were strong indicators that the nitrification and denitrification process was the main route of nitrogen removal (78%), and the effluent quality was in accordance with TIN water quality standards; below 0.6 mg/l TIN (Total Inorganic Nitrogen) on average.This study showed that microalgae could provide oxygen needed by nitrifying bacteria and sustain in the reactor. On the other hand, nitrifiers could utilize oxygen produced by algae without using external aeration to perform nitrification and heterotrophic bacteria could continue denitrify N-NO3-.Furthermore, it could be inferred that controlling operational conditions is an important factor to successfully perform nitrogen removal in photo-SBR system. Apart from light intensity, light duration and influent load (ALR) also have significant influence to the nitrogen removal performance by a microalgal-bacterial photo-SBR system