Volume 20 Issue 4

Growing food crops in gold mine tailings is limited by low nitrogen and mercury contamination. Little is known about the responses of water spinach (Ipomoea aquatica L.) to nitrogen-fixing bacteria biofertilizer. This study aimed to analyze changes in growth media properties, growth, biomass of water spinach, and mercury in both tailings-based growth media and intact plants following the application of the nitrogen-fixing Azotobacter. A liquid inoculum of Azotobacter was analyzed before the experiment. A greenhouse experiment was arranged in a randomized block design to evaluate three inoculant concentrations. Acidity and electrical conductivity of the inoculant were 7.95 and 1.74 mS/cm, respectively, while the Azotobacter count was 9.18 on a log scale. Introducing 5% and 10% inoculants increased microbial counts, total nitrogen, and acidity of the growth media, as well as shoot growth and biomass, but did not affect root length. Azotobacter did not affect mercury levels in the soil but increased mercury accumulation in intact plants. Mercury levels in soil and plants remained higher than the maximum threshold value. While soil pH and nitrogen levels showed a positive correlation with plant growth, mercury concentration in the soil exhibited a significant negative correlation. Because of high mercury accumulation, the water spinach was not safe for cultivation.

The effects of waste pulp fiber on the mechanical, physical, and technological properties of particleboard were investigated. For this purpose, 1.5%, 3%, 4.5%, and 6% were added to the middle layer of the chip blank. As an adhesive, 7% urea-formaldehyde (UF) resin was used in the middle layer and 12% in the top layer, in proportion to the dry chip weight. Chip blanks were pressed in a hydraulic press at 195 ± 5 °C, 30 kg/cm² pressure, and for 300 s, whereby test samples with dimensions of 550 x 550 x 19 mm³ and a density of 630 kg/m³ were produced. The 3% waste pulp fiber utilization provided optimum values, such as 7.3% and 27.2% improvements in bending strength and elastic modulus, respectively. However, 6.6% and 9.7% increases in thickness swelling (24 h) and water absorption (24 h) were observed. Moreover, there was a 24.6% increase in formaldehyde emissions. According to the results, it can be said that waste paper pulp fiber could be an alternative to wood raw material in particleboard production at low levels of addition.