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Even with particular interest in sustainable development, due to the limited types of bioavailable carbon sources that could support heterotrophic/mixotrophic growth, microalgae-derived products still suffer from inconsistent yield and high costs. This study demonstrates a successful cocultivation of the photoautotroph Chlorella vulgaris with a hydrolytic-enzyme-abundant heterotroph, Saccharomycopsis fibuligera, enabling efficient starch upcycling from water/wastewater toward enhancing microalgae-dominant biomass and lipid production. The enzymatic activities of S. fibuligera contributed to the hydrolysis of starch into glucose, generating a 7-fold higher biomass through mixotrophic/heterotrophic growth of C. vulgaris. Further, scanning transmission electron microscopy (STEM) and quantitative analysis suggested a significantly induced accumulation of lipids in C. vulgaris. Results of meta-transcriptomics revealed the critical regulatory role of illumination in interaction shifting. Gene expression for glycolysis and lipid biosynthesis of C. vulgaris were highly activated during dark periods. Meanwhile, during illumination periods, genes coding for glucoamylase and the sulfur-related activities in S. fibuligera were significantly upregulated, leading to induced starch hydrolysis and potential increased competition for sulfur utilization, respectively. This study indicates that hydrolytic organisms could collaborate to make starch bioavailable for nonhydrolytic microalgae, thus broadening the substrate spectrum and making starch a novel biotechnological feedstock for microalgae-derived products, e.g., biofuels or single-cell protein.

Microbial protein (MP) is a promising alternative protein source with several economic and environmental advantages. Currently, there is a research trend investigating the use of residual sources for the inputs of the production process, so it becomes more circular and efficient. In this study, the residual phosphorus (P) sources struvite and precipitated calcium phosphate (PCP), recovered from wastewater, were evaluated as P sources for the production of MP using methane oxidising bacteria (MOB). The study aims to understand the P requirements of bacteria in order to optimise P dosing in the culture medium. Since phosphate is provided in excess as a buffer, its optimal supply for assimilation will have an impact on pH control. Thus, pH and buffer capacity are also monitored. Both nitrate and ammonium were used as nitrogen sources, as they have different impacts on pH. Additionally, strategies for the dissolution of struvite and PCP were assessed, as were their implications on process design. MOB were capable of growing with both PCP and struvite as a phosphorus source. However, PCP shows lower growth rates and is more difficult to dissolve efficiently. Struvite was thus the best candidate for P recovery via MP from MOB.

Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. A workshop was held in June 2015 in Leysin Switzerland to agree on common solutions to the conundrum of inconsistent BMP test results. A discussion covers actions and criteria that are considered compulsory ito accept and validate a BMP test result; and recommendations concerning the inoculum substrate test setup and data analysis and reporting ito obtain test results that can be validated and reproduced.