Short-Rotation Willows as a Wastewater Treatment Plant: Biomass Production and the Fate of Macronutrients and Metals

Evapotranspirative willow systems (EWS) are zero-discharge wastewater treatment plants that produce woody biomass and have no discharge to surface or groundwater bodies. The influence of wastewater on the growth of three clones of Salix alba (‘V 093’, ‘V 051’ and ‘V 160’) and the distribution of macronutrients and metals in a pilot EWS receiving primary treated municipal wastewater was studied under a sub-Mediterranean climate. The influent wastewater, shoot number, stem height, and biomass production at coppicing were monitored in two consecutive two-year rotations. Soil properties and the concentrations of macronutrients and metals in soil and woody biomass were analyzed after the first rotation. S. alba clones in EWS produced significantly more woody biomass compared to controls. ‘V 052’ produced the highest biomass yield in both rotations (38–59 t DM ha−1) and had the highest nitrogen and phosphorus uptake (48% and 45%) from wastewater. Nitrogen and phosphorus uptake into the harvestable woody biomass was significantly higher in all clones studied compared to other plant-based wastewater treatment plants, indicating the nutrient recovery potential of EWS. The indigenous white willow clone ‘V 160’ had the lowest biomass yield but absorbed more nutrients from wastewater compared to ‘V 093’. Wastewater composition and load were consistent with the nutrient requirements of the willows; however, an increase in salinity was observed after only two years of operation, which could affect EWS efficiency and nutrient recovery in the long term.

Bacillus promotes invasiveness of exotic Flaveria bidentis by increasing its nitrogen and phosphorus uptake

Aim The effect of exotic plants on Bacillus diversity in the rhizosphere and the role of Bacilli in exotic or native plant species remain poorly understood. Flaveria bidentis is an invasive grass in China. Setaria viridis is a native grass and occurs in areas invaded by F. bidentis. Our objectives were (i) to examine the differences in the Bacillus communities between F. bidentis and S. viridis rhizospheres soil, and (ii) to compare the effects of Bacilli from F. bidentis and S. viridis rhizospheres on the competitiveness of the invasive species. Methods Flaveria bidentis monoculture, mixture of F. bidentis and S. viridis and S. viridis monoculture were designed in the field experiment. Bacillus diversity in their rhizosphere was analyzed using 16S rRNA. One of the dominant Bacilli in the rhizosphere soil of F. bidentis was selected to test its effect on the competitive growth of F. bidentis in a greenhouse experiment. Important Findings Bacillus diversity differed in F. bidentis and S. viridis rhizosphere. Brevibacterium frigoritolerans was the dominant Bacilli in the rhizosphere of both F. bidentis and S. viridis; however, its relative abundance in the F. bidentis rhizosphere was much higher than that in the S. viridis rhizosphere. In addition, B. frigoritolerans in the F. bidentis rhizosphere enhanced the growth of the plant compared to that of S. viridis by improving the nitrogen and phosphorus levels. This study showed that F. bidentis invasion influenced Bacillus communities, especially B. frigoritolerans, which, in turn, facilitated F. bidentis growth by increasing the levels of available nitrogen and phosphorus.

Method of biochar application affects growth, yield and nutrient uptake of cowpea

Biochar produced from pyrolysis of organic materials has been found to improve plant growth by improving the physical and chemical characteristics of the soil as well as enhancing the sequestration of carbon dioxide that would release into the atmosphere through the decomposition of organic residues. However, there is scanty information on the methods used to apply biochar in order to optimize the benefits of biochar use for agricultural production. In view of this, a field study was carried out at the experimental field of CSIR – Soil Research Institute, Kumasi, to assess the effect of method of biochar application on the growth, yield and nutrient uptake of cowpea (Vigna unguiculata) in a moderately acidic sandy Ferric Acrisol. The experiment was set up using a Randomized Complete Block Design with three replications. The treatments imposed were as follows: control, broadcasting, spot and ring methods of application. The parameters assessed included growth and yield data as well as nitrogen and phosphorus uptake in shoots and grains. The data collected were subjected to analysis of variance using Genstat 12th edition. The results showed that the spot and ring methods of application significantly enhanced height, girth, nodule number and dry weight, shoot biomass and grain yield as well as nitrogen and phosphorus contents in shoots and grains when compared with the broadcasting method and control. This study therefore recommends the spot and ring methods of biochar application for adoption in cowpea production for enhanced growth, yield and nitrogen and phosphorus uptake.

Outdoor Cultivation of the Microalga Chlorella vulgaris in a New Photobioreactor Configuration: The Effect of Ultraviolet and Visible Radiation

Microalgae can be a future source of biomass with a wide range of applications, including its use to solve current environmental issues. One of the main variables for microalgal cultivation is the light supply: (i) its intensity that often does not present a uniform spatial distribution inside the culture; (ii) photoperiod; and (iii) spectrum. Therefore, this study aims to evaluate the growth of the microalgae Chlorella vulgaris in a tubular photobioreactor with compound parabolic collectors (CPCs) under outdoor conditions. The effect of ultraviolet and visible radiation on biomass productivity and nutrients (nitrogen and phosphorus) uptake was assessed. The maximum biomass productivity was (5 ± 1) × 10−3 g·L−1·h−1, and the specific growth rates ranged from (1.1 ± 0.3) × 10−2 to (2.0 ± 0.6) × 10−2 h−1. Regarding nutrient uptake, initial removal rates of (0.9 ± 0.4) mg N·L−1·h−1 for nitrogen and (0.17 ± 0.04) mg P·L−1·h−1 for phosphorus were reached. These values increased with visible and ultraviolet irradiance until certain values (143 WVIS·m−2 and 9 WUV·m−2 for biomass productivity; 101 WVIS·m−2 and 6 WUV·m−2 for nutrient removal) and then decreased for higher ones due to the photoinhibition phenomenon. Therefore, the application of CPCs to photobioreactors (PBRs) may be beneficial for microalgal culture in countries with higher latitude (with lower solar irradiance levels).