Japanese Journal of Water Treatment Biology

Rootless duckweed Wolffia arrhiza is a promising biomass resource because it can grow rapidly and form starch-rich turions. This study examined effects of external organic compounds on the growth and turion formation of W. arrhiza. The organic compounds were investigated as possible factors to improve starch productivity. Among the tested organic compounds, certain saccharides such as sucrose, fructose, maltose and cellobiose enhanced the growth and turion formation of W. arrhiza. Although some other organic compounds inhibited its growth, glucose, citrate, pyruvate, and succinate slightly induced the turion formation of W. arrhiza. The addition of both sucrose and inorganic nitrogen promoted effectively the starch production by W. arrhiza. Results show that efficient systems which contribute to nutrient removal and starch production can be established using W. arrhiza by addition of proper organic compounds.

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In industrial contaminants, phenol is one of highly toxic substances in water treatment processes. As activated sludge (AS) is popular process for wastewater treatment, we succeeded to establish AS acclimated to high concentration (1.5 g/l) of phenol. In addition, we found that a nitrate－oxidized lignite (NOL) had a positive effect on acceleration of removal of phenol by AS. In tested NOLs, we selected NOL4 (0.4 of mixture ratio of nitrate to lignite) as the highest acceleration effector for phenol removal with the smallest amount of nitrate required in its production process. A series of culture profiling, floc size analysis, scanning electron microscopy observation, microbial community analyses with PCR－DGGE and clone sequencing suggested that NOL4 had a protective effect on microbial cells in AS and did not affect member constitution in microbial community. Furthermore, phenol degradation ability of the phenol-assimilating isolate HM2 was activated by addition of NOL4.

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