The rising effects of climate change and global problems of resource scarcity and environmental pollution require a change in paradigm towards sustainable energy and chemicals production. Photosynthetic microbes, including cyanobacteria and green algae, are promising raw materials for future production platforms which have high aerial productivity and don’t compete with food and feed. They are also well suited to act as chassis for the direct and continuous production of targeted fuels and chemicals, thus functioning as true biocatalysts. However, efficiencies of photoautotrophic production system need improvement before a successful shift to these platforms. 

The overall aim of this thesis is to improve efficiencies of photoautotrophic production platforms. To meet this aim, I have studied two approaches: (i) Integrative biomass-based production; and (ii) Direct biofuel/chemical production. The first approach involved the integration of wastewater treatment with biofuel production, using native Finnish microalgae. Screening revealed the native alga UHCC0027 as a suitable candidate for efficient nutrient removal and lipid accumulation. At pilot scale, UHCC0027 demonstrated robust nutrient removal performance in real wastewater of both high and low organic loading and at different temperatures, including a cold temperature relevant to Nordic conditions. Nutrient balances (C:N and N:P) were important in biomass accumulation and nutrient removal performance. Whilst Fatty acid methyl ester (FAME) profiles did not meet requirements of unblended fuel standards, workarounds such as hydrogenation may succeed in future. 

The second approach involved the immobilization of cyanobacterial and green algal cells in a novel tunable immobilization material, TEMPO oxidized cellulose nanofibrils (TEMPO CNF). This transfers the capabilities of current suspension photosynthetic cell factories to a solid-state that restricts loss of energy to biomass accumulation and enables photosynthetic cells to operate as long-living true catalysts for bioproduction. Three different construction methods were used: (i) a pure TEMPO CNF hydrogel; (ii) a Ca2+-stabilized TEMPO CNF hydrogel; and (iii) a polyvinyl alcohol (PVA) crosslinked solid TEMPO CNF film. Important outcomes were the considerably higher hydrogen yields of TEMPO CNF immobilized Chlamydomonas reinhardtii (compared to alginate controls) and the recovery and efficient hydrogen production of Anabaena sp. PCC7120 ΔhupL cells after drying. Drying was required for stable film formation and presents an opportunity for scaffold-free films in future. 

Overall, this thesis presents work demonstrating promising optimizations for improving efficiencies of microalgal wastewater treatment and biofuel (chemicals) production. Additionally, the novel employment of TEMPO CNF immobilization matrix for photobiological hydrogen production is an important step to addressing porosity and mechanical stability limitations of current immobilization techniques.