A foam suppressor removes soap and other foaming agents from a stream of wastewater that is being treated electrolytically. This wastewater is a combination of laundry, hygiene, and urine wastewater. It is desirable to prevent foaming because foaming reduces, by about 15 percent, the efficiency of electrooxidation of waste chemical species. In the absence of foam, the electrochemical sensors used to monitor the treatment process also function more effectively and thus provide more-accurate control of the electrolytic process.
The foam suppressor contains a resin bed that sorbs soaps, detergents, and high-molecular-weight organic compounds with polar or ionic functional groups. Such materials produce large quantities of foam. Anion-exchange resins are excellent sorbents for such organics: they have large sorption capacities, preferentially sorb foaming agents, and in comparison with activated carbon, are more mechanically stable.
At the beginning of a treatment cycle, the wastewater-treatment loop (see figure) is full of raw wastewater and the electrolysis cell is off. The pump is started and circulates water through the foam suppressor. The resin bed sorbs soap, reducing the concentration of soap in the wastewater. When the concentration of soap in the wastewater becomes insufficient to cause foaming, the electrolysis cell is turned on and begins to oxidize the remaining soap along with the other waste products in the wastewater. As the concentration of soap in the wastewater decreases via electrolysis, the resin bed begins to desorb soap into the wastewater stream. The electrolysis cell oxidizes the soap that reenters the stream. Thus, the bed becomes depleted of soap; that is, regenerated.
When the concentration of soap in the water has fallen to a low value that corresponds to the equilibrium initial concentration in the resin bed, the suppressor is considered to be fully regenerated and is then bypassed. The electrolysis cell continues to operate until the waste organic content of the stream is near zero. At that point, the water is considered to be purified and can be discharged from the loop. The suppressor, with fully restored sorption capacity, is ready for a new batch of soapy wastewater. Beds have operated for 100 such cycles with no loss of foam-suppression ability.
This work was done by James R. Akse and John Thompson of Umpqua Research Co. for Johnson Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Matericals category, or circle no. 111 on the TSP Order Card in this issue to receive a copy by mail ($5 charge). MSC-22269