(VWR International) as previously described [16]. The electrode material was carbon fibre veil with a total area of 270 cm2 (20 g/m2) (PRF Composite Materials, Poole, UK) used in both the anode and cathode chambers. Carbon veil sheets were folded down into rectangular cuboids and connected with a nickel-chrome wire (thickness-0.45 mm) to the external circuit. The cathode electrodes were modified in 5 different experimental groups (Table 1) and included two control conditions, i.e. one control group with no electrode modification and an abiotic control (algae water) and 4 experimental groups with: a) non modified cathode electrode (algae); b) cotton string (thickness-2 mm) wrapped around the electrode (algae string); c) cellulose layer (thickness-1 mm) coating around the electrode (algae cellulose); d) stainless steel wire (type 316, thickness 0.45). The modifications were employed to support algal biofilm development on the cathode electrode and for current collection. Each experimental condition was tested in triplicate resulting in a total of 15 MFCs. No growth media, pH control or chemical pre-treatment were used.