Cyanobacteria are viewed as promising platforms to produce fuels and/or high-value chemicals as part of so-called “biorefineries.” Their integration into wastewater treatment systems is particularly interesting because removal of the nitrogen and phosphorus in many wastewater streams is an expensive but necessary part of wastewater treatment. In this study, we evaluated strategies for cultivating Synechococcus sp. strain PCC 7002 on media comprised of two wastewater streams, i.e., treated secondary effluent supplemented with the liquid fraction extracted from sludge following anaerobic digestion. This strain is commonly used for metabolic engineering to produce a variety of valuable chemical products and product precursors (e.g., lactate). However, initial attempts to grow PCC 7002 under otherwise-standard conditions of light and temperature failed. We thus systematically evaluated alternative cultivation conditions and then used multiple methods to dissect the apparent toxicity of the media under standard cultivation conditions.

28Side-streams in wastewater treatment plants can serve as concentrated sources of nutrients 29 (i.e. nitrogen and phosphorus) to support the growth of photosynthetic organisms that ultimately 30 serve as feedstock for production of fuels and chemicals. However, other chemical characteristics 31 of these streams may inhibit growth in unanticipated ways. Here, we evaluated the use of liquid 32 recovered from municipal anaerobic digesters via gravity belt filtration as a nutrient source for 33 growing the cyanobacterium Synechococcus sp. strain PCC 7002. The gravity belt filtrate (GBF) 34 contained high levels of complex dissolved organic matter (DOM), which seemed to negatively 35 influence cells. We investigated the impact of GBF on physiological parameters such as growth 36 rate, membrane integrity, membrane composition, photosystem composition, and oxygen 37 evolution from photosystem II. At 37°C, we observed an inverse correlation between GBF 38 concentration and membrane integrity. Radical production was also detected upon exposure to 39 GBF at 37°C. However, at 27°C the dose dependent relationship between GBF concentration and 40 lack of membrane integrity was abolished. Immediate resuspension of strains in high doses of GBF 41 showed markedly reduced oxygen evolution rates relative to the control. Together, this suggests 42 that one mechanism responsible for GBF toxicity to Synechococcus is the interruption of 43 photosynthetic electron flow and subsequent phenomena. We hypothesize this is likely due to the 44 presence of phenolic compounds within the DOM. 45 46