Essentials of water treatment in hemodialysis - Penn Medicine

Ahmad
Table 2 Contaminants in water and their toxic effects and maximum allowable concentrations
Maximum
Contaminant Toxic effect concentration (mg/L)
Aluminum
Known to be toxic to dialysis patients
Encephalopathy, bone disease, anemia < 0.01
Chloramines Hemolysis, anemia, methemoglobinemia < 0.10
Chlorine 0.5
Copper Hemolysis, fever, headache, hepatitis < 0.10
Fluoride Bone disease, osteomalacia < 0.20
Nitrate Cyanosis, methemoglobinemia, hypotension, nausea < 2.0
Sulfate Nausea, vomiting, acidosis 100
Zinc Anemia, nausea, vomiting, fever
Normally present in dialysate
0.1
Calcium Nausea, vomiting, weakness, headache, hypertension, malaise, cardiac problems < 2 (0.1 mEq/L)
Magnesium Nausea, vomiting, weakness, headache, hypertension, malaise, cardiac problems < 4.0 (0.3 mEq/L)
Potassium Muscle symptoms, bradyrrhythmia, death 8 (0.2 mEq/L)
Sodium Hypertension, pulmonary edema, headache, thirst, confusion, seizure, coma
Unsafe even in drinking water
70 (3.0 mEq/L)
Arsenic Nausea, vomiting, diarrhea, hepatitis, polyneuropathy, skin lesions 0.005
Barium Hypokalemia 0.1
Beryllium Pulmonary granulomatous disease with cough, weight loss 0.0004
Cadmium Bone disease, renal disease 0.001
Chromium Carcinogen 0.014
Lead Abdominal pain, neuropathy, nephropathy, encephalopathy, hypertension 0.005
Mercury Tremors, gingivitis, psychiatric symptoms 0.0002
Selenium Nausea, vomiting, diarrhea 0.09
Silver Vomiting, diarrhea, shock, coma, convulsions, death 0.005
Thallium Neuropathy 0.002
RO or mixed-bed DI. The advantages and disadvantages
of these two devices are listed in the Table 1. Some
units use both devices, either in a series, less commonly,
or more commonly, a DI as a back up for the reverse
osmosis.
Feed Water
Ca & Mg Na
Hard
Figure 3 Water softener.
Product Water
Soft
Na
Water Containing
Ca & Mg
Na
Ca Mg
Resin Beads with Na
Ca & Mg Exchanged with Na
Product Water with Na
(Ca Mg Removed)
RO SYSTEM
RO is the most cost-effective method for water purification
from both organic and inorganic solutes, including
organisms and endotoxins. This is a filtration process of
water across a very tight membrane with ionic rejection of
90% to 99%. When water is filtered across this tight
membrane, the filtered water is called ‘‘permeate’’ or
‘‘RO water’’ and water containing rejected solutes and
other substances is called ‘‘rejection,’’ ‘‘concentrate,’’ or
‘‘brine.’’ The osmolarity of brine (containing solutes) is a
lot higher than the osmolarity of permeate; normally the
water would move from permeate to brine because of
higher osmotic pressure. Enough mechanical force
(hydraulic pressure) with a pump, however, is applied
on the brine side; water is thus forced (filtered) against
the osmolar force across the membrane. RO membranes
are like dialyzer membranes except the pores are so small
that they do not even allow any solute including Na or
other ions and any organic matter (Figure 4). Three
different types of membranes, cellulosic, synthetic, and
thin composite membranes, similar to dialyzers, are fitted
130 Hemodialysis International 2005; 9: 127–134