Abstract
Microalgae and cyanobacteria are effective platforms for environmental remediation (phycoremediation), particularly of air and water. There is limited scope to deploy suspension cultures due to space, cost and maintenance challenges—driving an imperative towards biofilm-based treatment systems; however, these systems are ill-equipped for rapid and mobile deployment. In this study we explored the main technical challenges to developing cheap, accessible and low-maintenance engineered biofilm systems (biocomposites) comprising cyanobacteria (Synechococcus elongatus) immobilised to a range of textiles (n = 4) by natural or synthetic latex binders (n = 16), chitosan or shellac. Biocomposite viability (measured as net CO2 uptake) was assessed over 20 days in semi-batch trials. No maintenance was required during this period as the humidity within the reactor was sufficient to support metabolism. Two commercial natural latex binders (AURO 320 and 321) supported strong growth within the biocomposite, outperforming suspension controls. There was variation in textiles performance, with an 80/20 polyester-cotton blend performing most consistently. Biocomposite formulation was varied in terms of binder solids content and cell loading rate, with 5% solids and 2.5% cell loading the most effective combination. We demonstrate the technical feasibility of fabricating functional textile-based cyanobacteria biocomposites and discuss this within the context of developing decentralised wastewater treatment services.
Highlights
The growing global human population is placing increasing demands on water resources—demands which are unlikely to be met with current centralised treatment systems and practices (Lofrano and Brown 2010; Verstraete and Vlaeminck 2011)
The urgency for technology and process transition is heightened when viewed from a climate change context, with municipal wastewater treatment accounting for approximately 3% of global electricity consumption and 5% of non-CO2 greenhouse gas emissions (Li et al 2015)
Synechococcus elongatus PCC 7942 was grown in BlueGreen Medium (BG11) (Stanier et al 1971), and S. elongatus CCAP 1479/1A in Jaworski’s Medium (JM) (Šoštarič et al 2012) without cyanocobalamin, thiamine HCl, and biotin, in 10 L polycarbonate (Nalgene) carboys with constant air supply at 18 °C ± 2 °C, and a 16L:8D photoperiod using 30 W daylight-type fluorescent tubes (Sylvania Luxline Plus, n = 6)
Summary
The growing global human population is placing increasing demands on water resources—demands which are unlikely to be met with current centralised treatment systems and practices (Lofrano and Brown 2010; Verstraete and Vlaeminck 2011). Phycoremediation (the use of algae or cyanobacteria for environmental clean-up) is one approach that could deliver many of these requirements, with the capacity to combine wastewater and atmospheric remediation within a single treatment option, all the while generating biomass for bioprocessing (Olguín 2003; Rawat et al 2011; Kumar et al 2018; Ansari et al 2019). Due to their broad abiotic tolerances and metabolic flexibility, the use of cyanobacteria in wastewater treatment is well established (Oswald and Gotass 1957), forming an important part of mixed community activated sludge systems (Martins et al 2011). The very nature of suspension-based cultivation (generally conducted in high rate algae pond systems) remains one of the main
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