Environmental Engineering Reference
In-Depth Information
Semipermeable
membrane
Osmotic
pressure
Fresh
water
Salt
water
Fresh
water
Salt
water
Osmotic equilibrium
Osmosis
Concentrate
Permeate
Reverse osmosis
Figure 6.1
Description of reverse osmosis process
An important design parameter is flux, which is the volume of water that can
flow through a unit area of membrane. Flux is a function of pressure differential
between applied pressure and osmotic pressure across the membrane.
The membranes are subject to fouling. In hazardous waste management,
membranes are limited to extremely toxic materials that cannot be removed
by cost-effective technologies. Reverse osmosis is used to remove metals
from wastewater, remove dyes from textile industry, and recover oil in emul-
sified form.
2.5
Soil Vapor Extraction
Soil vapor extraction is also known as vacuum extraction, in situ volatiliza-
tion, soil venting, in situ aeration (Wong and Nolen 1997), and soil vapor
stripping (Riser-Roberts 1998). It is commonly used because it is both a
low-cost and effective hazardous waste remediation method (Wong and Nolen
1997).
The main idea of SVE is to reduce the vapor pressure within the soil to enhance
volatilization of the petroleum hydrocarbons so that they can be removed by vac-
uum extraction (Riser-Roberts 1998). Petroleum hydrocarbons in the unsaturated
zone of the soil may be in several forms: “vapor phase, dissolved phase (in pore
water), liquid phase or nonaqueous phase liquids, and adsorbed phase” (Wong
1997). Injection and extraction are both utilized to remove the volatile organic
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