Impact of wastewater fouling on contact angle

Abstract

Capillary dependent systems are highly influenced by surface fouling and may degrade as material surface properties change. In anticipation of a spacecraft microgravity fluids management system exposed to highly variable wetting conditions, the impact of urine wastewater fouling on capillary contact angle was examined. The results indicate that, in general, surface fouling can decrease the contact angle when crystalline structures or biofilms form. Small crystalline growth on the order of 10 mm can lower advancing contact angles y adv by approximately 308, while biofilm growth can lower it by approximately 158. Vacuum drying of fouled surfaces increased y adv by about 88, and defects greater in height than 5% of the capillary length increased y adv by approximately 308. These trends may indicate that promotion of wastewater fouling may improve the performance of capillary dependent fluids management systems. These results may also influence terrestrial technologies, including medical catheters and sustainable wastewater treatment systems exposed to wastewater fouling.

Design considerations for sustainable spacecraft water management systems

“…Part of this concern arises from the potential for biomass to break off and into the liquid stream. As the example of a surface with relatively deep features in figure illustrates, however, the thickness of waste water fouling layers is generally less than 300 lm, and these results suggest that the fouling layer is unlikely to grow to a depth that would slough off and clog downstream hardware (Thomas and Muirhead, 2009).…”

“…In contrast, the absence of pretreatment chemicals likely results in an increased prevalence of biofilm formation and small crystalline growth, which has been shown to significantly lower the contact angle by up to 44°with 95% confidence (Thomas and Muirhead, 2009). This response can be utilized by design to increase the performance of a capillarybased wastewater management system.…”

“…Thomas and Muirhead (2009) observed that certain aspects of wastewater fouling can improve wetting characteristics. They found that although vacuum drying and large defects tended to increase H adv , crystal growth and biofilm growth actually lowered H adv .…”

“…Since it has been shown that small crystalline growth improves wetting conditions, while large crystals as well as dried and cracked surface features worsen wetting, simulating favorable fouling conditions offers an attractive alternate design strategy for capillary based systems. Specifically, by roughening a surface such that the largest defect height d and capillary length l are in ratio satisfying d/l < 0.04, a partially wetted surface will be wetted more favorably (Thomas and Muirhead, 2009). With such a capillary-based wastewater system, designers could consider integrating exposure to wastewater prior to use in flight to promote fouling layer growth to improve initial system performance.…”

“…To partially characterize which elements of a fouling layer would indeed pass through a capillary management system, particles greater than 100 lm were filtered during a 21-day test (Thomas and Muirhead, 2009). The largest particles anticipated are 1 mm, although amorphous deposits can be even larger.…”