Efficient Anaerobic Digestion of Microalgae Biomass: Proteins as a Key Macromolecule

Abstract

Biogas generation is the least complex technology to transform microalgae biomass into bioenergy. Since hydrolysis has been pointed out as the rate limiting stage of anaerobic digestion, the main challenge for an efficient biogas production is the optimization of cell wall disruption/hydrolysis. Among all tested pretreatments, enzymatic treatments were demonstrated not only very effective in disruption/hydrolysis but they also revealed the impact of microalgae macromolecular composition in the anaerobic process. Although carbohydrates have been traditionally recognized as the polymers responsible for the low microalgae digestibility, protease addition resulted in the highest organic matter solubilization and the highest methane production. However, protein solubilization during the pretreatment can result in anaerobic digestion inhibition due to the release of large amounts of ammonium nitrogen. The possible solutions to overcome these negative effects include the reduction of protein biomass levels by culturing the microalgae in low nitrogen media and the use of ammonia tolerant anaerobic inocula. Overall, this review is intended to evidence the relevance of microalgae proteins in different stages of anaerobic digestion, namely hydrolysis and methanogenesis.

Volatile fatty acids production from protease pretreated Chlorella biomass via anaerobic digestion

“…Harvested microalgae were pretreated with Alcalase 2.5 L (Novozyme, Denmark) at a dosage of 0.585 UA g of DW −1 to hydrolyze the biomass (TS = 19.9 ± 0.4 g/L VS = 18.5 ± 1.0 g/L) and make the organic matter available to anaerobic microorganisms . Although carbohydrates have been traditionally recognized as the polymers responsible for the low microalgae digestibility, protease addition results in the highest organic matter solubilization and the highest methane production . Incubation for 5 h at 50°C and 150 rpm was performed in an IKA KS 4000 control agitator.…”

“…6,18 Although carbohydrates have been traditionally recognized as the polymers responsible for the low microalgae digestibility, protease addition results in the highest organic matter solubilization and the highest methane production. 5,18 Incubation for 5 h at 50 C and 150 rpm was performed in an IKA KS 4000 control agitator. pH was slightly alkaline (pH = 8) and it was adjusted in a Crison pH-METER Basic 20 + every 30 min by adding 0.5 M NaOH.…”

“…To overcome this drawback, a great number of pretreatments have been investigated over the last decade to facilitate cell wall disruption and promote the first hydrolysis stage of AD. Enzymatic pretreatment with proteases is a very effective method for hydrolysing microalgae cells . However, the high easily‐metabolized nitrogen content produced by proteases pretreatment provokes accumulation of VFAs and inhibition of biogas production .…”

“…Enzymatic pretreatment with proteases is a very effective method for hydrolysing microalgae cells. 5 However, the high easily-metabolized nitrogen content produced by proteases pretreatment provokes accumulation of VFAs and inhibition of biogas production. 6 During AD, proteins are degraded to total ammonia (ammonium ion + free ammonia).…”

Bioenergy production using Trichormus variabilis – a review

“…During anaerobic digestion, hydrolysis is known to be the rate limiting step which needs to be optimized via efficient pre‐treatment technologies. Owing to the composition and structural features of microalgae resulting in changes in response to the different growth conditions, it is assumed that biogas production yield will be affected by T. variabilis grown in wastewaters prior to anaerobic digestion, through expression of various proteins. However, no research has yet demonstrated the effect of these generated macromolecules, which consequently impact biodegradability of biomass during hydrolysis.…”