Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech The interactions of algae-bacteria symbiotic system and its effects on nutrients removal from synthetic wastewater Xiyan Ji, Mengqi Jiang, Jibiao Zhang ⁎ , Xuyao Jiang, Zheng Zheng Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, PR China ARTICLE INFO Keywords: Algae-bacteria consortium Nutrient removals Interactions Quorum sensing ABSTRACT The ability of Chlorella vulgaris-Bacillus licheniformis and Microcystis aeruginosa-Bacillus licheniformis consortiums to eliminate total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and soluble chemical oxygen demand (sCOD) from synthetic wastewater was studied. The highest values of dry cell weight, chlorophyll-a, and chlorophyll metabolism related genes/bacterial rRNA gene copies were obtained in the Chlorella vulgaris-Bacillus licheniformis system at Chlorella vulgaris and Bacillus licheniformis ratio of 1:3. On the 10th day, the Chlorella vulgaris-Bacillus licheniformis system at this ratio removed 86.55%, 80.28% and 88.95% of sCOD, TDP and TDN, respectively. But, the Microcystis aeruginosa-Bacillus licheniformis system at this ratio only removed 65.62%, 70.82%, and 21.56% of sCOD, TDP and TDN, respectively. Chlorella vulgaris and Bacillus licheniformis could coexist as an algae-bacteria consortia and quorum sensing substances (autoinducing peptides and bis (3′-5′) diguanylic acid) concentrations were measured. Finally, the interactions and communication patterns between Chlorella vulgaris and Bacillus licheniformis were depicted. 1. Introduction The concept of an algae-bacteria consortia was initially proposed in 1981 to study uptake of nitrogen in a flocculating algae-bacterial system (Nambiar and Bokil, 1981). There were a large number of bacteria in the natural environment that formed relationships with algae. This algae- bacteria symbiotic system was the ecological basis for natural water pur- ification. In the algae-bacteria symbiotic system, organic matter in the water body was oxidized and decomposed by aerobic bacteria to produce ammonium nitrogen (NH 3 -N), phosphate and carbon dioxide. Algae used these nutrients, along with sunlight as an energy source, to photo- synthetically synthesize cellular material. In the process, oxygen was re- leased, thereby allowing bacteria to continue oxidation of organic matter (Derry and Jacobsen, 1990). The removal efficiency of nitrogen (N) and phosphorus (P) in the environment could be improved by taking ad- vantage of the synergy between multiple species, when compared to tra- ditional single and multi-step treatments (Brenner et al., 2008). This could be achieved by combining the ability of algae to assimilate N, P, and other nutrients in sewage with the powerful ability of bacteria to decompose organic pollutants. Exploiting the joint relationship between the carbon dioxide-oxygen cycle and the material cycle created by algal-bacterial symbiosis in combination with other treatment methods might aid in de- velopment of a new technology to solve the problem of excessive N, P and organic matter that resulted in water eutrophication of urban sewage. The removal efficiencies of high-rate algal pond were higher than that of traditional stabilization pond and it was cost effective and easy to be operated. So, it was highly suitable for developing areas with relatively weak economies (Park et al., 2011). The activated algae method was developed in the 1970s and the removal rates of bio- chemical oxygen demand, chemical oxygen demand, N and P for in- dustrial-scale sewage treatment were 97%, 87%, 92% and 74%, re- spectively (Jr and Mckinney, 1972; Gomez et al., 1995). A Chlorella vulgaris-Azosprillum brasilense system was used to treat municipal was- tewater and removal efficiencies for NH 3 -N, nitrate nitrogen and P were 100%, 15% and 36%, respectively (de-Bashan et al., 2004). In contrast, single algae systems without bacteria were only able to achieve removal efficiencies of 75%, 6%, and 9%, respectively. Furthermore, wastewater treatment and biomass production could be achieved simultaneously in the algae-bacteria symbiotic system. Although the coexistence of algae and bacteria has been known for some time, little research has been conducted on algae-bacteria symbiotic systems, including N and P re- moval, biomass production and their interaction and communication mechanisms. In this study, synthetic wastewater was used as a nutrient medium for the algae-bacteria consortium of Chlorella vulgaris-Bacillus licheniformis and Microcystis aeruginosa-Bacillus licheniformis. The removal efficiencies for soluble chemical oxygen demand (sCOD), total dissolved phosphorus (TDP), and total dissolved nitrogen (TDN) were determined, along with http://dx.doi.org/10.1016/j.biortech.2017.09.074 Received 12 July 2017; Received in revised form 7 September 2017; Accepted 9 September 2017 ⁎ Corresponding author. E-mail address: jbzhang@fudan.edu.cn (J. Zhang). Bioresource Technology 247 (2018) 44–50 Available online 12 September 2017 0960-8524/ © 2017 Elsevier Ltd. All rights reserved. MARK