(10e) Design of Marine Macroalgae Photobioreactor Integrated into Building with Natural Sun Illumination

Seagriculture, which can provide offshore grown macroalgae biomass for food, platform chemicals and biofuels production will play a significant role in bioeconomy and biorefineries. Nevertheless, seagriculture development has been hindered by the lack of laboratory photobioreactors that enable fundamental macroalgae research. Here we report on the indoor macroalgae photobioreactor (MPBR) system integrated into the LEED certified building that enables maintenance and cultivation of marine macroalgae at controlled environment under natural illumination. Depending on specific reactor location, illumination varied between reactors in 238-348 µmole photons m^-2 s^-1 . The total direct energy consumption of the system was 8.15-11.45kWh during the 24 hours of operationThe total operation volume of the system was 6,400 L of seawater (salinity 3.9%, pH 8.2). Initial water stock was provided from the Tel Aviv Reading marine area and was partially (1/4-1/3) exchanged every 3 months. The compensation for evaporation was done by adding deionized water to the system to maintain the salinity at 3.9%.

The MPBR operation was been demonstrated for 6 months on continuous maintenance and cultivation of three green macroalgae species Cladophora sp., Ulva compressa and Ulva rigida isolated form the Eastern Mediterranean coast. The growth rates, protein, rhamnose, xylose, arabinose, glucose, galactose and glucuronic acid content of the cultivated species were quantified. Cladophora sp., isolated from Rosh-ha-Nikra sampling site was cultivated for 122 days. The growth rates changed from -3.66 %day^-1 to 9.78 %day^-1, with an average 3.47 %day^-1. The maximum growth was for 12 continuous days. Cladophora sp. isolated from Mikhmoret sampling site was cultivated for 122 days. The growth rates changed from 9.32%day^-1 to 95.5 %day^-1, average 36.63 %day^-1. The maximum growth was for 12 continuous days. Cladophora sp. isolated from Reading sampling site was cultivated for 97 days. The growth rates were stable at 95.47 %day^-1 during the entire period of 38 cultivation days.

Carbohydrate profiling was done for Cladophora sp. harvested at Mikhmoret site and cultivated at the system at the growing rate of 63.9%^-1 during harvesting. Rhamnose content was 3.89 µg mg_DW^-1, arabinose 30.46 µg mg_DW^-1, galactose 26.59 µg mg_DW^-1, glucose 61.72 µg mg_DW^-1, xylose 17.79 µg mg_DW^-1 and glucuronic acid 0.98 µg mg_DW^-1. The total carbohydrate yield was 14.10%. The protein content in the biomass was 11%.

U. compressa isolated from Rosh-ha-Nikra sampling site was cultivated for 187 days. The growth rates changed from -0.06% day^-1 to 3.5 %day^-1, average 1.01 %day^-1. The maximum growth was for 9 continuous days. U. compressa isolated from Mikhmoret sampling site was cultivated for 172 days. The growth rates changed from 1.46 %day^-1 to 5.51 %day^-1, average 3.65 %day^-1.The maximum growth was for 27 continuous days. U.compressa isolated from Reading sampling site was cultivated for 143 days. The growth rates were mostly negative, with the biomass loss at -82.34 %day^-1, growth rate of only 0.83 %day^-1 was observed 40 continuous days.

Carbohydrate and protein profiling was done for U. compressa harvested at Rosh-ha-Nikra site and cultivated at the system at the growing rate of 3.5% day^-1 at the time of a harvest. Rhamnose content was 48.58 µg mg_DW^-1, arabinose 0.29 µg mg_DW^-1, galactose 9.03 µg mg_DW^-1, glucose 75.13 µg mg_DW^-1, xylose 23.83 µg mg_DW^-1 and glucuronic acid 18.13 µg mg_DW^-1. The total carbohydrate yield was 17.50%. The total protein content of this biomass was 25.5%.

U. rigida isolated from Rosh-ha-Nikra sampling site was cultivated for 89 days. The growth rates changed from -3.13 %day^-1 to 19.51 %day^-1, average 4.61 %day^-1. The maximum growth was for 16 continuous days. U. rigida isolated from Haifa sampling site was cultivated for 155 days. The growth rates changed from -0.09 %day^-1 to 9.4 %day^-1, average 2.01 %day^-1. The maximum growth was for 64 continuous days.

Carbohydrate and protein profiling was done for U. rigida harvested at Haifa site and cultivated at the system at the growing rate of 1.4%/day at the time of a harvest. Rhamnose content was 37.29 µg mg_DW^-1, arabinose 0.46 µg mg_DW^-1, galactose 3.60 µg mg_DW^-1, glucose 54.84 µg mg_DW^-1, xylose 9.11µg mg_DW^-1 and glucuronic acid 16.62 µg mg_DW^-1. The total carbohydrate yield was 12.20%. The protein content from the biomass harvested was 29%.

This work provides detailed insights on the design of practical indoors photobioreactors for isolation, selection, cultivation maintenance and analysis of macroalgae species required for biorefinery feedstock development.