Enhanced nitrogen removal and energy saving in a microalgal–bacterial consortium treating real municipal wastewater

Abstract

The optimization of total nitrogen removal from municipal wastewater was investigated in a laboratory-scale photo-sequencing batch reactor (PSBR) operated with a mixed microalgal-bacterial consortium spontaneously acclimatized to real wastewater. No external aeration was provided in the PSBR to reduce energy consumption: oxygen was only supplied by the microalgal photosynthesis. The enhancement of total nitrogen removal was achieved through: (1) feeding of wastewater in the dark phase to provide readily biodegradable COD when oxygen was not produced, promoting denitrification; (2) intermittent use of the mixer to favor simultaneous nitrification-denitrification inside the dense flocs and to achieve 41% energy saving with respect to continuous mixing. Efficient COD removal (86 ± 2%) was observed, obtaining average effluent concentrations of 37 mg/L and 22 mg/L of total COD and soluble COD, respectively. TKN removal was 97 ± 3%, with an average effluent concentration of 0.5 ± 0.7 mg NH-N/L. Assimilation of nitrogen by heterotrophic bacteria accounted only for 20% of TKN removal, whilst the major part of TKN was nitrified. In particular, the nitrification rate was 1.9 mgN L h (specific rate 2.4 mgN gTSS h), measured with dissolved oxygen near zero, when the oxygen demand was higher than the oxygen produced by photosynthesis. Total nitrogen of 6.3 ± 4.4 mgN/L was measured in the effluent after PSBR optimization.

Real-Time Behavior of a Microalgae–Bacteria Consortium Treating Wastewater in a Sequencing Batch Reactor in Response to Feeding Time and Agitation Mode

“…+ into NO 3 − (nitrification) by AOB and NOB is followed by the biological reduction of NO 3 − into N 2 (denitrification). Hence, this process confirms that nitrification and denitrification require aerobic and anaerobic conditions [10]. Commonly, high rate algal ponds (HRAP) [20] are usually easy to design, construct, and operate.…”

“…Consequently, the AI agitation mode might enhance the microalgae multiplication, as reported [41]. On this account, the high performance of the photobioreactors under D/L was ensured by the bacterial degradation (nitrification and denitrification) [10]. It was also followed by the synergistic cooperation between the algae and bacteria from their organic and inorganic nutrient exchange through photosynthesis and respiration [38].…”

“…The development of cost-effective and efficient technologies for single-step wastewater (WW) treatment is in great demand since it can be applied as an alternative system for conventional biological WW treatment [8][9][10].…”

“…Recently, the symbiotic process of microalgae and bacteria has been significantly used for the treatment of municipal and industrial wastewater [10,13]. The microalgae-bacteria consortia maintain cost-effective aeration, sequester the greenhouse gas CO 2 , and limit the risk of pollutant volatilization [14][15][16].…”

Non-surface Attached Bacterial Aggregates: A Ubiquitous Third Lifestyle

“…Although AGS has been widely applied in wastewater treatment to replace the traditional AS, it is not an energy cost-effective process (Foladori et al, 2018). Microalgal-bacterial aggregates have been extensively investigated and regarded as a greener technology during the last two decades.…”