Joeri Coppens

The use of microalgae as a high-value organic slow-release fertilizer results in tomatoes with increased carotenoid and sugar levels

The heightened awareness concerning environmental preservation, resource scarcity, food safety, and nutrition has engendered the need for a more sustainable and resource-efficient agricultural production system. In this context, microalgae offer the potential to recover nutrients from waste streams and subsequently use the microalgal biomass as a sustainable slow-release fertilizer. The aim of this study was to assess microalgal bacterial flocs treating aquaculture wastewater and marine microalgae as organic slow-release fertilizers for tomato cultivation. Comparable plant growth was observed using microalgal and commercial organic fertilizer treatments. Furthermore, the microalgal fertilizers improved the fruit quality through an increase in sugar and carotenoid content, although a lower tomato yield was obtained. An economic evaluation indicates the economic feasibility of the microalgae-based fertilizers. Further research is required to optimize the microalgae-based fertilizer composition.

Nitrification and microalgae cultivation for two-stage biological nutrient valorization from source separated urine.

Urine contains the majority of nutrients in urban wastewaters and is an ideal nutrient recovery target. In this study, stabilization of real undiluted urine through nitrification and subsequent microalgae cultivation were explored as strategy for biological nutrient recovery. A nitrifying inoculum screening revealed a commercial aquaculture inoculum to have the highest halotolerance. This inoculum was compared with municipal activated sludge for the start-up of two nitrification membrane bioreactors. Complete nitrification of undiluted urine was achieved in both systems at a conductivity of 75mScm(-1) and loading rate above 450mgNL(-1)d(-1). The halotolerant inoculum shortened the start-up time with 54%. Nitrite oxidizers showed faster salt adaptation and Nitrobacter spp. became the dominant nitrite oxidizers. Nitrified urine as growth medium for Arthrospira platensis demonstrated superior growth compared to untreated urine and resulted in a high protein content of 62%. This two-stage strategy is therefore a promising approach for biological nutrient recovery.

Photosynthetic oxygenation for urine nitrification

Human urine accounts for only a fraction of the sewage volume, but it contains the majority of valuable nutrient load in wastewater. In this study, synthetic urine was nitrified in a closed photo-bioreactor through photosynthetic oxygenation by means of a consortium of microalgae and nitrifying bacteria. In situ production of oxygen by photosynthetic organisms has the potential to reduce the energy costs linked to conventional aeration. This energy-efficient strategy results in stable urine for further nutrient recovery, while part of the nutrients are biologically recovered in the form of valuable biomass. In this study, urine was nitrified for the first time without conventional aeration at a maximum photosynthetic oxygenation rate of 160 mg O2 gVSS-1 d-1 (VSS: volatile suspended solids). A maximum volumetric nitrification rate of 67 mg N L-1 d-1 was achieved on 12% diluted synthetic urine. Chemical oxygen demand (COD) removal efficiencies were situated between 44% and 83% at a removal rate of 24 mg COD gVSS-1 d-1. After 180 days, microscopic observations revealed that Scenedesmus sp. was the dominant microalga. Overall, photosynthetic oxygenation for urine nitrification is promising as a highly electricity efficient approach for further nutrient recovery.

Kinetic exploration of intracellular nitrate storage in marine microalgae

ABSTRACT In this study, a recently developed model accounting for intracellular nitrate storage kinetics was thoroughly studied to understand and compare the storage capacity of Phaeodactylum tricornutum and Amphora coffeaeformis. In the first stage the identifiability of the biokinetic parameters was examined. Next, the kinetic model was calibrated for both microalgal species based on experimental observations during batch growth experiments. Two kinetic parameters were calibrated, namely the maximum specific growth rate and the nitrate storage rate (). A significant difference was observed for the nitrate storage rate between both species. For P. tricornutum, the nitrate storage rate was much higher ( = 0.036 m3 g−1 DW d−1) compared to A. coffeaeformis ( = 0.0004 m3 g−1 DW d−1). This suggests that P. tricornutum has a more efficient nitrate uptake ability and intracellular nitrate storage capacity and also indicates the need for determination of in order to quantify nitrate storage.