Modelling photosynthesis in shallow algal production ponds

Abstract

A mathematical model was constructed to simulate the behaviour of an open algal pond particularly with respect to CO 2 supply and utilisation. The algal pond considered takes wastewater as feed, which provides substrate for aerobic bacteria and also nutrients for the algal-bacterial consortium. CO 2-containing gas such as flue gas or biogas is considered as additional source of CO 2 to support the growth of algae which at the same time also serves the purpose of CO 2 abatement. A number of simulation studies were carried out to evaluate the performance of the system in terms of the production of algae, treatment of wastewater, and CO 2 fixation and removal. Important design and operating parameters were considered, including pond depth, hydraulic retention time, composition of the feed wastewater, flowrate and CO 2 fraction of the supplied gas flow, and the area utilised for gas flow induction. Several useful observations were made based on the simulation results, with the potential to provide guidance to the future practical development of multi-functional algal ponds.

Photosynthesis monitoring to optimize growth of microalgal mass cultures: application of chlorophyll fluorescence techniques

“…6A). RLCs of the electron transport rate vs. irradiance curve (ETR/E curve, see below) can be completed within a few minutes compared to the several hours required for SLRC (White & Critchley 1999, Ralph & Gademann 2005, Ritchie & Larkum 2012. In this experiment, the high-light adapted cultures of Chlorella show values of rETR max that are twice as high as those of low-light adapted ones (240 and 126, respectively; Fig.…”

“…In mass cultures, due to the self-shading of cells, light through the culture is attenuated exponentially with depth according to the Beer-Lambert lawfrom full sunlight at the surface to darkness at the bottom (Ritchie & Larkum 2012, Zarmi et al 2013. Several areas can be conceived in a microalgal culture exposed to solar irradiance (Tredici 2010): (1) the surface layers in which irradiance is supra-saturating and photoinhibition is taking place; (2) the deeper area, in which irradiance is saturating and a high photosynthetic rate is achieved; (3) a light-limited area, in which irradiance is used with maximum efficiency; and (4) an area below a certain irradiance intensity (the compensation point), at which photosynthetic rates are too low to compensate for respiration.…”

Phycobilisome-Deficient Strains of Synechocystis sp. PCC 6803 Have Reduced Size and Require Carbon-Limiting Conditions to Exhibit Enhanced Productivity

“…However, productivity was tested only in conical flasks and flat-panel bioreactors with a culture depth of approximately 2 cm. Under such low depths, any productivity benefits due to the effects of greater light penetration would not be observed (Ritchie and Larkum, 2012). The maximum light intensity utilized was 150 mmol photons m 22 s…”

“…Under these conditions, cells in the upper layer will receive saturating light, absorbing more energy than can be utilized by photosynthesis, with the excess being dissipated as heat or fluorescence. Net photosynthesis and biomass accumulation are reduced by photoinhibition, the direct damage of photosynthetic proteins by sunlight, and the production of reactive oxygen species, which further damages the photosynthetic machinery (Mussgnug et al, 2007;Beckmann et al, 2009;Ritchie and Larkum, 2012). Photosynthetic rates increase with the depth in the pond due to decreased photoinhibition until a maximum rate is achieved.…”

“…Photosynthetic rates increase with the depth in the pond due to decreased photoinhibition until a maximum rate is achieved. Below this depth, the light intensity is insufficient for maximal photosynthesis and yields are reduced by respiration (Ritchie and Larkum, 2012). In theory, reducing the antenna should increase biomass accumulation by decreasing energy losses and photoinhibition at the surface while allowing additional light to penetrate to lower depths, thus maximizing the percentage of cells harvesting light.…”