Environmental Engineering Reference
In-Depth Information
3.2. Reverse Osmosis
Reverse osmosis has effectively been utilized to remove cadmium from a
metal processing waste stream (Slater et al., 1987). The system can reduce all
ionic species of cadmium by 92-98 percent of the influent concentration in
effluent water when operated at pressures greater than 50 psi and at
temperatures between 40° and 85° F. There are different types of membrane
materials available and care must be taken to ensure that operating conditions
for the specific membrane material are adhered to, especially feed water pH,
particulates and oxidants, to maintain effectiveness. Periodic testing for
percent rejection should be performed.
This technique has been effectively utilized to remove cadmium from a
metal processing waste stream. Experimentation with a thin-film composite
membrane reduced cadmium concentrations ranging from 165 to 0.003 mg/L
under elective processing conditions (Slater et al., 1987). Concentrations of
other metals and overall conductivity were rejected in the excess of 98%.
Rejection efficiency and production rate were increased by an increase in
system operating pressure. Cadmium was concentrated in a batch
concentration study while generating high quality water for process reuse.
Reverse osmosis appears to be an effective alternative to other traditional
treatment methodologies (Slater et al., 1987). The main challenge with these
techniques is cost effectiveness and periodic fouling of membrane that effects
on the functioning of the membrane.
3.3.Composting
This is a new and useful technology which can be divided into two
steps:(1) Thermocomposting, and (2) Vermicomposting. Thermocomposting is
the first and most active step in compost process and different changes occur
in it such as changes in heat, acidity, humidity and biological and pathogen
community (Jaya et al., 2005). Due to these periodic changes, the various
important results can be observed such as decrease in Carbon-Nitrogen ratio
(C:N ratio) and pathogen community, high humidity of fresh wastes and
neutralising acidity. Thermocomposting has useful effects on vermin-
composting based on better condition for earthworm activity, reproduction and
their nutrition that leads to their biomass increase, different studies by many
researchers have already proven this fact (Ndegwa.and Thompson, 2000).
Vermicomposting is the second step and is managed by earthworms causing
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