Daily Archives: October 25, 2014

Fulvic Acid Fouling of Ultrafiltration Membranes

Congcong Tang, Zhangwei He, Fangbo Zhao, Xiaoyang Liang, Zhanshuang Li. Effects of cations on the formation of ultrafiltration membrane fouling layers when filtering fulvic acid. Desalination Volume 352, 3 November 2014, Pages 174–180.

Fulvic acid (FA) is the main water-soluble component in humic substances which usually cause membrane fouling in the drinking water treatment process. This study investigates the ultrafiltration membrane fouling characteristics and mechanisms caused by FAs in the presence of various salt ions (Ca2 +, Mg2 +, K+ and Na+). A series of experiments had been carried out to characterize the decline of permeate flux, pollutant rejection, FA aggregates, and the morphology of the membrane’s fouling layer. Compared with pure FA solution, FA-monovalent solution containing cations (K+ and Na+) caused much lower permeate flux and smaller amount of fouling layer, which was difficult to remove by flushing with water. The presence of divalent cations (Ca2 + and Mg2 +), caused the permeate flux to noticeably increase and membrane fouling can be easily removed. Laser particle size analysis showed that the FA formed larger aggregates in the presence of Ca2 + or Mg2 + cations. Based on an atomic force microscope and scanning electron microscope analysis, results showed that monovalent cations made the colloids form a gel layer, which led to pore blocking and permeate flux decrease. And divalent cations reacted with FA and formed a cake layer of larger particles creating porous structures on the membrane surface.

Click here for full paper (fee).

Wind Turbines and Bats: Sliced and Diced

It is unfortunate that bats are dying at wind turbines. The hypothesis of this paper that bats evolved in a way that makes them fly into wind turbines or that “Darwinian evolution” has had anything to do with why bats do what they do is rather nonsensical at a macro level. A sorry state of affairs in science…More importantly, where did the bat come from in the first place? Where did the operating instructions come from for the bat “radar” to work at all? A few questions and more should be answered as well….

I have a much more plausible explanation. Bats are flying into wind turbines because the wind turbines are “just there,” in their way. This looks to be yet another reason to avoid building wind turbines.

Paul. M. Cryan, P. Marcos Gorresen, Cris D. Hein, Michael R. Schirmacher, Robert H. Diehl, Manuela M. Huso, David T. S. Hayman, Paul D. Fricker, Frank J. Bonaccorso, Douglas H. Johnson, Kevin Heist, David C. Dalton. Behavior of bats at wind turbines. PNAS, vol. 111 no. 42

Significance:
Bats are dying in unprecedented numbers at wind turbines, but causes of their susceptibility are unknown. Fatalities peak during low-wind conditions in late summer and autumn and primarily involve species that evolved to roost in trees. Common behaviors of “tree bats” might put them at risk, yet the difficulty of observing high-flying nocturnal animals has limited our understanding of their behaviors around tall structures. We used thermal surveillance cameras for, to our knowledge, the first time to observe behaviors of bats at experimentally manipulated wind turbines over several months. We discovered previously undescribed patterns in the ways bats approach and interact with turbines, suggesting behaviors that evolved at tall trees might be the reason why many bats die at wind turbines.

Abstract:
Wind turbines are causing unprecedented numbers of bat fatalities. Many fatalities involve tree-roosting bats, but reasons for this higher susceptibility remain unknown. To better understand behaviors associated with risk, we monitored bats at three experimentally manipulated wind turbines in Indiana, United States, from July 29 to October 1, 2012, using thermal cameras and other methods. We observed bats on 993 occasions and saw many behaviors, including close approaches, flight loops and dives, hovering, and chases. Most bats altered course toward turbines during observation. Based on these new observations, we tested the hypotheses that wind speed and blade rotation speed influenced the way that bats interacted with turbines. We found that bats were detected more frequently at lower wind speeds and typically approached turbines on the leeward (downwind) side. The proportion of leeward approaches increased with wind speed when blades were prevented from turning, yet decreased when blades could turn. Bats were observed more frequently at turbines on moonlit nights. Taken together, these observations suggest that bats may orient toward turbines by sensing air currents and using vision, and that air turbulence caused by fast-moving blades creates conditions that are less attractive to bats passing in close proximity. Tree bats may respond to streams of air flowing downwind from trees at night while searching for roosts, conspecifics, and nocturnal insect prey that could accumulate in such flows. Fatalities of tree bats at turbines may be the consequence of behaviors that evolved to provide selective advantages when elicited by tall trees, but are now maladaptive when elicited by wind turbines.

Full paper is here.