The proximate composition of microalgae can have a major influence on the biogas productivity. For instance, lipid and protein play an important role in anaerobic digestion as they breakdown during the hydrolysis stage (Chen et al. 2008). High protein concentrations lead to the formation of ammonia compounds within the digester (Chen et al. 2008; McCarty 1964). Ammonia is produced from the bio­logical breakdown of nitrogenous matter (i. e. protein). High concentrations of ammonia being formed within the digester can lead to inhibition of the bacterial community (Buswell and Boruff 1932). Ammonia toxicity has been shown to affect the methanogenic bacteria in two separate ways. The first is by the ammonium ion directly inhibiting the methane synthesising enzyme. The second is by the hydro­phobic ammonia nitrogen (NH3-N) molecule diffusing passively into the bacterial cell causing an imbalance and/or a potassium deficiency within the microbial cell (Kayhanian 1999; Sialve et al. 2009; Ward et al. 2014). Furthermore, NH3-N in the gaseous form has been shown to be more toxic at lower concentrations than the aqueous ionised form (McCarty 1964). Ammonia is extremely toxic at levels above 3000 mg/L and can be moderately inhibitory at level of 1500-3000 mg/L (McCarty 1964). On the other hand, maintaining NH3-N concentrations between 50 and 200 mg/L have been shown to be beneficial for the bacterial population as ammonia nitrogen is an essential nutrient required by the microbial community (Parkin and Owen 1986). As the utilisation of volatile fatty acids must balance the production of volatile fatty acids by hydrolytic and acetogenic bacteria to maintain digester sta­bility, efficient digester performance is therefore dependant on maintaining the

NH3-N concentration below the inhibitory limits for all associated anaerobic digestion bacteria (McCarty 1964; Ward et al. 2014).