Cultivating Scenedesmus dimorphus in lactic acid wastewater for cost-effective biodiesel production.

The combination of lactic acid production wastewater and oil-producing microalgal culture could not only achieve harmless treatment of wastewater but also provided nutrients and significant amounts of water for microalgal culture. Thus the effects of different nutrients on the biomass yield, lipid yield of Scenedesmus dimorphus with lactic acid wastewater were investigated. Although lactic acid wastewater was very suitable for the cultivation of oil-producing microalgae, some nutrients were still needed. So 0.79 g/L NaNO3, 14 mg/L MgSO4·7H2O, 4 mg/L K2HPO4·3H2O, and trace elements needed to be added in the microalgal culture with lactic acid wastewater. In the optimized wastewater medium, the lipid yield could reach 1.54 ± 0.04 g/L, which was 48.1% higher than the level of 1.04 ± 0.06 g/L in the BG11 medium. Microalgae cells had high absorption capacity for nitrogen and phosphorus. The nitrogen, phosphorus removal rate of wastewater reached 96.31% and 90.78%, respectively, after 10 days of culture. And the treated wastewater could be used for lactic acid production for four times. These investigations laid a foundation for reducing the pollution of lactic acid wastewater, exploring a late-model for oleaginous microalgae cleaner production.

Dissolving mechanism of strain P17 on insoluble phosphorus of yellow-brown soil.

Strain P17 was a bacterial strain identified as Bacillus megaterium isolated from ground accumulating phosphate rock powder. The fermentation broth of strain P17 and the yellow-brown soil from Nanjing Agricultural University garden were collected to conduct this study. The simulation of fixed insoluble phosphorous forms after applying calcium superphosphate into yellow-brown soil was performed in pots, while available P and total P of soil were extremely positive correlative with those of groundwater. Then the dissolving effect of strain P17 on insoluble P of yellow-brown soil was studied. Results showed that Bacillus megaterium strain P17 had notable solubilizing effect on insoluble phosphates formed when too much water-soluble phosphorous fertilizer used. During 100 days after inoculation, strain P17 was dominant. Until the 120th day, compared with water addition, available P of strain P17 inoculation treated soil increased by 3 times with calcium superphosphate addition. Besides available P, pH, activity of acid and alkaline phosphatase and population of P-solubilizing microbes were detected respectively. P-solubilizing mechanism of P-solubilizing bacteria strain P17 seems to be a synergetic effect of pH decrease, organic acids, phosphatase, etc.