Search

The effect of periphyton propagation in paddy fields on phosphorus biogeochemical cycling has received little attention. In this phytotron study, inorganic phosphorus (P i ) accumulation by periphyton was investigated for varying inputs of calcium [Ca(II)] or ferrous‑iron [Fe(II)], and lighting conditions. Results indicated that additions of Ca(II) or Fe(II) enhanced abiotic accumulation of P i by up to 16 times, and decreased solution P i concentration by up to 50%, especially under light condition. The enhanced P i accumulation into periphyton intensified with increasing P i concentration, and P i accumulation showed a positive linear relationship with Ca or Fe accumulation. Abiotic accumulation of P i induced by Ca(II) was mainly through Ca-phosphate precipitation, and co-precipitation of P with carbonates at pH > 8. Accumulation with added Fe(II) was mainly considered to be through Fe(III) phosphate precipitation coupled with adsorption of P i by ferric hydroxides. Moreover, Fe(II) was more effective than Ca(II) in promoting abiotic accumulation of P i by periphyton. Our results indicate the potential for controlling environmental factors to enhance the role of periphyton in biogeochemical cycling and P-use efficiency in paddy rice fields and to reduce P discharged to neighboring water bodies. [ABSTRACT FROM AUTHOR]

• Sufficient P further improves biodiesel production under N starvation in glucose. • Soybean processing wastewater (SPW) is suitable for applying N and P regulation. • N-sufficient stage (stage 1) and N-starvation stage (stage 2) are naturally formed. • S. obliquus grows rapidly in stage 1 and accumulates lipids quickly in stage 2. • High fatty acids productivity in SPW verifies N and P regulation in glucose. In this study, the effects of nitrogen and phosphorus supply on biodiesel production from Scenedesmus obliquus with glucose as the carbon source were investigated. It was found that sufficient phosphorus could further improve biodiesel production under nitrogen starvation. S. obliquus was cultivated in soybean processing wastewater. The removal efficiencies of carbon oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) after 8-day cultivation were 72%, 95%, and 54%, respectively. Moreover, the fatty acid productivity after eight-day cultivation reached as high as 99.3 mg·L−1·d−1, which was 1.15 times higher than the highest efficiency using a glucose culture. This result was due to two naturally-formed stages occurring with sufficient phosphorus: nitrogen sufficiency stage for biomass and nitrogen starvation stage for lipid accumulation. It verified the conclusion of the roles of nitrogen and phosphorus obtained in the glucose culture and provided an economic and environmentally friendly choice for biodiesel production with efficient soybean wastewater treatment. [ABSTRACT FROM AUTHOR]