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Highlights • Light irradiance exhibited variability in growth response based on substrate types. • Each substrate exhibited variability of light requirement for mixotrophic growth. • Continuous light-deficient condition was adequate for effective mixotrophy from glucose. • Acetic acid exhibited better mixotrophic yield at light-sufficient condition. • Variability in photosynthetic-efficiency in mixotrophy dependent on substrate types. Abstract Current research aimed to increase mixotrophic biomass from various organic carbon sources by exploring best light conditions. Three substrates glucose, acetic acid and glycerol were studied for their effects on mixotrophic microalgae cultivation under four light conditions. Light irradiance exhibited variability in growth response and photosynthetic efficiency based on type of substrates used in mixotrophic growth. Each substrate showed variability in light requirements for their effective assimilations. From growth responses, glucose and acetic acid respectively exhibited heterotrophic and mixotrophic (better growth in light) natures. Continuous light-deficient condition was adequate for effective mixotrophic growth as well as energy saving for glucose. However, light-sufficient condition required for effective acetic acid supported mixotrophic growth. Mixotrophic benefits from glycerol and its uptake by Chlorella protothecoides was negligible in all light conditions. Investigation of heterotrophic biomass contribution by various substrates in overall mixotrophic yield, glucose offered maximum approx. 43% contribution. [ABSTRACT FROM AUTHOR]

The autotrophic removal of sulphate and nitrate in bioelectrochemical reactors was investigated at different external voltages (0.2, 0.4, 0.6, 0.8 and 1.0 V) under anaerobic conditions. Sulphate and nitrate removal, nitrite accumulation, reduction trend of nitrate and sulphate and microbial community structure were explored. Results indicate the highest removal efficiencies of nitrate and sulphate at 43.3 ± 2.8 and 7.1 ± 0.2 mg·l −1 ·d −1 when the voltage is 0.6 V. Moreover, nitrite accumulation decreases with increased voltage from 0.2 V to 1.0 V. Illumina high-throughput sequencing results show similar richness and diversity of bacterial species with increased voltage from 0.2 V to 0.8 V. However, with further increased voltage to 1.0 V, bacterial diversity and richness decrease significantly. Overall, significant differences in community compositions are observed at different voltages. [ABSTRACT FROM AUTHOR]

The aim of this study is investigate the effect of column diameter (D), height/diameter (H/D) ratio, and gas flow rate on microalgae cultivation, Haematococcus pluvialis . Bubble column reactors with various D and H/D ratio were tested to assess the hydrodynamic properties and biomass production performance. Then, H. pluvialis was cultured under outdoor autotrophic conditions using industrial flue gas. By optimizing the reactor module, reactor volume increased to 354% with minimized biomass loss. Compared to the control, developed module showed biomass and astaxanthin productivity of 0.052 versus 0.053 g/L/day, and 1.48 versus 1.47 mg/L/day, respectively. Consequently, biomass productivity was maintained with increased reactor scale, and the result is applicable to the scale up of overall microalgae cultivation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two-stage autotrophic bacterial cellulose production from C1 gases was demonstrated. • C. autoethanogenum produced ethanol and acetate from H 2 :CO:CO 2 gases. • Gas fermentation products were then converted into BC by K. sucrofermentans. • Mixotrophic BC production was also shown with gas fermentation products and glucose. • Mixotrophic BC was more robust and porous with higher crystallinity. Gas fermentation is a well-established process for the conversion of greenhouse gases from industrial wastes into valuable multi-carbon chemicals. Here, a two-stage process was developed to expand the product range of gas fermentation and synthesized the versatile biopolymer bacterial cellulose (BC). In the first stage, the acetogen Clostridium autoethanogenum was cultivated with H 2 :CO:CO 2 and produced ethanol and acetate. In the second stage, BC-synthesizing Komagataeibacter sucrofermentans was grown in the spent medium from gas fermentation. K. sucrofermentans was able to produce BC autotrophically from gas-derived metabolites alone as well as mixotrophically with the addition of exogenous glucose. In these circumstances, 1.31 g/L BC was synthesized with a major energetic contribution from C1 gas fermentation products. Mixotrophic BC characterization reveals unique properties including augmented mechanical strength, porosity, and crystallinity. This proof-of-concept process demonstrates that BC can be produced from gases and holds good potential for the efficient conversion of C1 wastes. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper was to determine the effect of two different membrane bioreactor (MBR) configurations (external/immersed) on sludge structure and microbial activity. Sludge structure was deduced from rheological measurements. The high shear stress induced by the recirculation pump in the external MBR was shown to result in decreasing viscosity due to activated sludge (AS) deflocculation. Besides, soluble microbial products (SMP) release was higher in the external MBR (5mgCOD gMLVSS −1) than in the immersed configuration (2mgCOD gMLVSS −1). Microbial activity was followed from respirometry tests by focusing on the distinction between heterotrophs and autotrophs. An easier autotrophic microbe development was then observed in the immersed MBR compared to the external one. However, the external MBR was shown to allow better heterotrophic microbe development. [ABSTRACT FROM AUTHOR]

Abstract: The granulation of nitrifying sludge in a sequencing batch reactor (SBR) fed with -N-laden inorganic wastewater was investigated. After 120-day operation spherical and elliptical granules with an average diameter of 0.32mm were observed. The hydrophobicity surface, settling velocity and specific gravity of the matured granules increased with the processing of sludge granulation. Spatial distribution of bacterial species within the autotrophic granules was analyzed with fluorescence in situ hybridization. Both ammonia- and nitrite-oxidizing bacteria were observed in the granular sludge. The Michaelis–Menten equation was used to describe their -N utilization rate, and the kinetic coefficients were calculated to be vm =18.0mg/g-VSS/h and Km =36.7mg/l. Taking into account the -N utilization rate and removal efficiency together, an -N concentration range of 100–250mg/l was found to be favourable for the operation of the SBR to cultivate nitrifying granules. [Copyright &y& Elsevier]

Abstract: This work aimed to investigate the effects of the bioreactor configurations and their design variables on the cultivation of vegetative cells Haematococcus pluvialis to achieve sustainable high cell density. The addition of vitamin B to F1 growth medium could appreciably enhance the final cell density. Employing this medium, the cultivation in the airlift bioreactor was demonstrated to outperform the bubble column at the same operating conditions. Aeration was crucial for a proper growth of the alga in the airlift bioreactor, but it must be maintained at low level to minimize shear stress. The most appropriate aeration velocity (superficial velocity) was at the lower limit of the pump, i.e. 0.4cms−1 and a smaller riser was shown to have positive influence on the cell growth. A 1% CO2 supplement to the air supply considerably enhanced the growth rate of H. pluvialis and the most suitable light intensity for the growth was at 20μmolphotonm−2 s−1. The semi-continuous culture was successfully implemented with the optimal airlift bioreactor design and under optimal conditions the harvest could be performed every four days with the specific growth rate of 0.31d−1. [Copyright &y& Elsevier]

• Main non-organic electron donors for low C/N wastewater denitrification are summarized. • Autotrophic denitrification processes for treating low C/N wastewater are highlighted. • Concerns about their potential adverse impacts in practical applications are discussed. • Combined denitrification processes for multi-contaminant removals are envisaged. Denitrification with non-organic electron donors for treating low C/N ratio wastewater has attracted growing interests. Hydrogen, reduced sulfur compounds and ferrous ions are mainly used in autotrophic denitrification, holding promise for achieving practical applications. Recently, the development of autotrophic denitrification-based processes, such as bioelectrochemically-supported hydrogenotrophic denitrification and sulfur-/iron-based denitrification assisted multi-contaminant removal, provide opportunities for applying these processes in wastewater treatment. Exploration of the autotrophic denitrification process in terms of contaminant removal mechanism, interaction among functional microorganisms, and potential full-scale applications is thus of great importance. Here, an overview of the commonly used non-organic electron donors, e.g., hydrogen, reduced sulfur compounds and ferrous ions, in denitrification for treating low C/N ratio wastewater is provided. Also, the feasibility of applying the combined processes based on autotrophic denitrification with the compounds is discussed. Furthermore, challenges and future possibilities as well as concerns about the practical applications are envisaged in this review. [ABSTRACT FROM AUTHOR]