Biomedical Engineering Reference
In-Depth Information
membrane was a flexible tube resembling a thin macaroni noodle. Filtration was carried out
from outside to inside. Air was continuously injected to clean the outer membrane surface.
The rising flow of the air-water mixture produced cleaning effects along the membrane
surface. The intrinsic characteristics of the system made it feasible to operate the system at
high organic loading rate without the problems related with the poor settling properties of the
sludge or the drop in nitrogen conversion. There were no solids in the effluent as result of the
utilisation of the membrane ultrafiltration module. Ultimately, the membrane-assisted hybrid
bioreactor was successfully employed to treat a mixture of two streams generated in a fish
canning factory.
3.3. Reverse Osmosis
Reverse osmosis was developed as a water treatment method for more than 40 years ago.
The process firstly arose as a technique of desalinating seawater. Once the method's
decontaminating capabilities were recognized, reverse osmosis systems began to be
commercially produced for home water purification purposes. Such systems were installed in
homes as early as the 1970s. Reverse osmosis systems seem to be a viable option to the more
costly and energy-wasteful distillation units.
The semi-permeable membrane used in reverse osmosis contains tiny pores through
which water can flow. The small pores of this membrane are restrictive to such organic
compounds as salt and other natural minerals, which generally have a larger molecular
composition than water. These pores are also restrictive to bacteria and disease-causing
pathogens. Thus, reverse osmosis is incredibly effective for desalinating water and providing
mineral-free as well as pathogen-free water for use. In the areas with no receiving
municipally treated water or being at particular risk of waterborne diseases, reverse osmosis is
an ideal process of contaminant removal. This process requires a high pressure to be exerted
on the high concentration side of the membrane, usually 2-17 bars for fresh and brackish
water, and 40-70 bars for seawater, which has around 24 bars of natural osmotic pressure.
Nowadays, reverse osmosis has been one of the most advanced techniques for wastewater
treatment and reuse. It also widely used to reduce aster salinity for industrial applications
(Cao et al., 2007).
Walha et al. (2008) tested a reverse osmosis process for treatment of high salinity drilling
water for seafood washing and processing from The Calembo Company (seafood
conditioning, Sfax, Tunisia). The company used 50 m
3
/d of drilling water to condition
cuttlefish before freezing. The water is characterised by its high degree of hardness, high
sulphate concentration and salinity (67 g/l). Consequently, generated effluents contain a large
amount of salts and a high organic load (COD of 10-20 g/l). Treatment by reverse osmosis at
high pressure (70 bars) allows to significantly reduce the salinity of the drilling water
(permeate salinity around 2.5 g/l). Mixing reverse osmosis permeate and cuttlefish
conditioning effluent together can significantly reduce the salinity of the effluent in the view
of biological treatment with a membrane bioreactor (35 g/l or less is required).
Reverse osmosis (TFC membrane, salinity reduction: 96%) has also been employed for
recovery of marine flavor from seafood cooking juice (Vandanjon et al., 2002). Cooking juice
from buckies, shrimps and tuna have a high level of polluting load (COD of 5-40 g/l) and
have to be treated before being rejected in the environment. However, these juices seem to
