Water Treatment Plants

Long-term ingestion of low concentrations of arsenic is detrimental to human health, yet in several countries around the world, large populations are constantly exposed to drinking water contaminated with arsenic. In Bangladesh, arsenic concentrations exceed World Health Organization guidelines in 60% of the groundwater. Arsenic can be removed by filtration and via adsorbents, such as natural zeolites, but there still is a need for simple and cost effective methods using materials that are readily available in developing countries.

Al Rmalli et al. show that the dried pulverized roots of the water hyacinth can rapidly remove arsenic from water. The method is effective for both arsenite [As(III)] and arsenate [As(V)] and requires comparatively little material (50 mikrogram of As are adsorbed per gram of roots in 24 hours). Water hyacinths grow abundantly in ponds, lakes, and rivers in Bangladesh, India, and other tropical and subtropical countries. The simplicity of the method suggests that these plants may be useful in the treatment of drinking water, particularly in rural areas. — JFU

A Star Is Reborn

As they grow old, stars with approximately the mass of our Sun experience explosive flashes just before their nuclear furnaces shut down. These flashes expel the stars’ outer shells and leave behind hot dense remnants called white dwarfs. Most of these remnants simply cool down, but some can experience a late explosion that restarts nuclear burning and expands them into giant stars again.

Hadjuk et al. (p.231;see the Perspective by Asplund) report observations and a stellar model of V4334 Sgr, a “born again” giant that reignited in 1992 and that was discovered by amateur astronomer Sakurai. The subsequent temperature drop of V4334 Sgr is 100 times faster than had been expected. The calculated mass ejection rates suggest that reignition events contribute unexpectedly large amounts of carbon and carbonaceous dust to the interstellar medium.