TopicFeasibility of using seawater in urban sanitation (implementation)
The use of seawater as secondary quality water can be a promising alternative to cope with (fresh) water scarcity. But, this practice will lead to the generation of saline wastewater. In addition, industrial wastewaters from leather, fish, pickling, and potato processing factories, also generate saline effluents. Moreover, even if no saline wastewater is used for domestic or industrial applications, saline intrusion issues along the sewer can increase the salinity in municipal wastewater collection systems. Certainly, these wastewater streams require proper treatment prior to discharge into surface water bodies. While COD and nitrogen removal can be satisfactorily achieved, the biological phosphorus removal process seems to be affected by the saline conditions. The problem exacerbates if it is taken into account that phosphorus has been pointed out as the main nutrient that drives eutrophication in surface water bodies (Yeoman et al., 1988). Recent research has shown that it is possible to perform enhanced biological phosphorus removal (EBPR) at high salinities (Welles et al., 2014). However, further research is needed under conditions closer to those potentially found in a (real) saline wastewater (e.g. higher sulfate concentrations and presence of complex organics) where the activity of sulfate reducing bacteria may be higher and could affect the EBPR process. Particularly, because the sulfate reduction processes usually led to deterioration of biological phosphorus removal due to the generation of H2S, occurrence of filamentous bulking bacteria and substrate competition (e.g. Beggiatoa spp.)(Yamamoto et al., 1991; Yamamoto-Ikemoto, 1994; Yamamoto-Ikemoto et al., 1998; Baetens et al., 2001). Nevertheless, recently, Wu et al. (2014) was able to successfully couple the biological phosphorus removal with a sulfate reduction process. While promising, the operational conditions (e.g micro-aeration of 12 h and SRT above 68d) cannot be directly applicable to existing WWTP performing EBPR. Moreover, the effluent phosphorus concentrations were above the common discharge standards criteria for surface water bodies (of less than 1 mgPO4-P/L).
This research aims to get a better understanding about the effects of the saline wastewater composition on the dominant microbial populations involved in EBPR and sulfate reduction processes (i.e. PAO and SRB) and about their potential interactions (e.g. effects of H2S on PAO, substrate competition and alternating anaerobic-aerobic conditions on SRB). This can contribute to improve and secure the satisfactory operation of EBPR WWTP temporarily exposed to saline conditions or even treating saline wastewater. This could be achieved by exploring the operating conditions that favor the dominance of PAO over SRB or even those that can lead to the co-existence of these organisms.