This body of research aimed to prove microalgal potential to utilize environmental pollutants in an effective and economic way. Ammonia gas, carbon dioxide, and wastewater were targeted as pollutants to remove in three different technical papers.

The first work, an extension of the previous paper, studied carbon dioxide effect on the microalgal ammonia scrubber system. Freshwater green algae Scenedesmus dimorphus, the same species as the previous study, were grown in a flat panel photobioreactor aerated with ammonia- and CO2-laden air. The ammonia mass loading was fixed at an optimal level found in the previous study and CO2 mass loading rates was varied in a range found in typical concentrated animal feeding operations. The data showed high ammonia and CO2 removal rate and removal efficiency and the biomass contained amino acid profiles close to the ideal protein profiles for typical animal feeds, with a high ratio of essential amino acids. Therefore, microalgae effectively mitigate ammonia and CO2 emissions, with a potential for use as an animal feed additive.

The second work was still about microalgal ammonia scrubber system using different species, Haematococcus pluvialis, known as the most productive astaxanthin producers, to enhance its economic feasibility. Currently, most H. pluvialis cultivation systems use two stage mode: optimal growth mode and stress mode to induce astaxanthin. In this study, it was hypothesized that ammonia gas can serve as both growth nutrient and stress to induce astaxanthin. Tapered bubble columns were used to avoid cell settlement because H. pluvialis cells gets bigger when they enter carotenogenesis. Before testing ammonia gas, pH and different nitrogen sources were tested because ammonia/ammonium form depends highly on pHs to compare growth performances between nitrogen sources. After confirming a good growth performance at pH 4, pH 5, and ammonium, ammonia gas was fed directly to the reactor at pH 4 and 5. Further efforts to increase astaxanthin content were made by feeding ammonia gas with different schedule or adding extra chemicals. Among all trials, only C/N ratio 1 was effective.

The third work was about treating phosphorus in wastewater (synthetic BBM medium, wastewater streams A, B, and C) using Revolving Algal Biofilm (RAB) systems. The two keys of microalgal phosphorus removal are efficient cultivation system and efficient operation design. As to prove the efficiency of RAB cultivation system, cell growth and liquid nutrient removal performances in different growth media were compared with other cultivation systems. As to design the optimal operation of the systems, phosphorus uptake kinetics and mass balance were demonstrated by analyzing bound-P, acid-soluble P (ASP), and acid-insoluble P (AISP). In continuous culture, it was shown that harvest frequency and wastewater replacement rate can be optimized according to the cellular activities.