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

Emna Mhedhbi,Paola Foladori,Nadia Khelifi,Issam Smaali

doi:10.3390/w12071893

Abstract

A study of a microalgae–bacteria treatment system was conducted in a sequencing batch reactor (SBR) by combining a precultured native algae Nannochloropsis gaditana L2 with spontaneous municipal wastewater microorganisms. Two types of agitation, air mixing (AI) and mechanical mixing (MIX), were assessed at continuous illumination (L) and photoperiod cycle light/dark (L/D). The obtained consortium, via native microalgae addition, has a better operational efficiency compared to spontaneous control. This allows the removal of 78% and 53% of total Kjeldhal nitrogen (TKN) and chemical oxygen demand (COD), respectively. Under the (L/D) photoperiod, the optimal removal rate (90% of TKN and 75% of COD) was obtained by the consortium at 4 days of hydraulic retention time (HRT) using the AI mode. Moreover, during feeding during dark (D/L) photoperiod, the highest removal rate (83% TKN and 82% COD) was recorded at 4 days HRT using the AI mode. These results bring, at the scale of a bioreactor, new data regarding the mode of aeration and the feeding time. They prove the concept of such a technology, increasing the attraction of microalgae-based wastewater treatment.

Highlights

Conventional wastewater treatment plants are still facing several techno-economic difficulties induced by their high operational energy cost and inefficient nutrient removals [1]
We focused on the effect of the pure strain addition, the hydraulic retention time (HRT), the agitation mode, and the feeding time related to photoperiod application (L/D, L, and D/L)
As described in the diagram (Figure 2), the results were detailed for each experiment phase, considering nutrient removal rate and microscopic observation

Summary

Introduction

Conventional wastewater treatment plants are still facing several techno-economic difficulties induced by their high operational energy cost and inefficient nutrient removals [1]. 1 kWh of electricity is required to supply the oxygen needed for 1 kg of biochemical oxygen demand (BOD). For aerobic wastewater treatment plants (WWTP) [2,3]. Aeration is a costly process, presenting about 45–75% of the total energy consumption in WWTPs [4,5]. Oxygen produced from the photosynthetic reaction by microalgae can be used as a source for aerobic microbes and reduces aeration costs [6,7]. 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.

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