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F. Hell and J. Lahnsteiner
nitrate content in the treated water. The number of stacks in operation is chosen
according to the water demand.
The quality of the product water is controlled by means of a conductivity
measurement. For safety reasons the product water finally passes a UV
disinfection unit.
The quality of the brine is also controlled by means of a conductivity
measurement. According to the required conductivity, the brine loop is
replenished with raw water. The circulation tank overflow is connected to the
circulation tank of the electrode rinsing loop. Thus, the concentrate serves as
electrolyte solution for rinsing the electrodes. The brine effluent on the electrode
rinsing loop flows into a buffer tank. From this buffer tank the brine is pumped
into a storage pond.
For the discharge or utilization of the brine, several possibilities were
investigated during the pilot studies (Eberhard 1993). As the most relevant
possibilities for the full-scale plant, discharge to the local sewage treatment plant
and blending with irrigation water were chosen.
The chemicals applied in the plant are polyphosphate, hydrochloric acid and
caustic soda. Polyphosphate is dosed into the brine loop as a scaling inhibitor.
Hydrochloric acid is utilized for pH adjustment in the brine loop and for regular
cleaning of the electrodialysis stacks. The spent cleaning solution is neutralised
with caustic soda. The cleaning is performed with an automatic CIP system.
Normally, the standard operation time of the treatment plant lasts from May to
October. During winter, the plant is mothballed. Therefore the plant is also
equipped with a preservation system. When the plant is mothballed, the pipes are
emptied and the tanks are drained. The pumps stay with water, and impellers are
moved from time to time so that blockage of the pumps is avoided. The EDR
stacks are connected to a small recycle tank filled with a salt solution. This salt
solution is circulated periodically through the EDR stacks by a time-controlled
pump. The total procedures for mothballing, respectively restart of the plant
require maximum 1 day each. In the conservation period the plant needs
practically no supervision. Nevertheless, maintenance works are performed during
this time.
4 Results of the Kleylehof Plant
When the plant was started, the nitrate content in the raw water was 120 mg
No3rl. At maximum applicable desalination, a nitrate concentration of as low as
25 mg N03r l was achievable. Nevertheless, according to an optimum quantity and
quality of the brine, the stack voltage was adjusted to a nitrate removal down to 40
mg N03rl. In proportion to the nitrate removal, the hardness of the drinking water
was reduced by approximately 23%. Table 1 shows an analysis for the raw water,
product water and brine.
F. Hell and J. Lahnsteiner
nitrate content in the treated water. The number of stacks in operation is chosen
according to the water demand.
The quality of the product water is controlled by means of a conductivity
measurement. For safety reasons the product water finally passes a UV
disinfection unit.
The quality of the brine is also controlled by means of a conductivity
measurement. According to the required conductivity, the brine loop is
replenished with raw water. The circulation tank overflow is connected to the
circulation tank of the electrode rinsing loop. Thus, the concentrate serves as
electrolyte solution for rinsing the electrodes. The brine effluent on the electrode
rinsing loop flows into a buffer tank. From this buffer tank the brine is pumped
into a storage pond.
For the discharge or utilization of the brine, several possibilities were
investigated during the pilot studies (Eberhard 1993). As the most relevant
possibilities for the full-scale plant, discharge to the local sewage treatment plant
and blending with irrigation water were chosen.
The chemicals applied in the plant are polyphosphate, hydrochloric acid and
caustic soda. Polyphosphate is dosed into the brine loop as a scaling inhibitor.
Hydrochloric acid is utilized for pH adjustment in the brine loop and for regular
cleaning of the electrodialysis stacks. The spent cleaning solution is neutralised
with caustic soda. The cleaning is performed with an automatic CIP system.
Normally, the standard operation time of the treatment plant lasts from May to
October. During winter, the plant is mothballed. Therefore the plant is also
equipped with a preservation system. When the plant is mothballed, the pipes are
emptied and the tanks are drained. The pumps stay with water, and impellers are
moved from time to time so that blockage of the pumps is avoided. The EDR
stacks are connected to a small recycle tank filled with a salt solution. This salt
solution is circulated periodically through the EDR stacks by a time-controlled
pump. The total procedures for mothballing, respectively restart of the plant
require maximum 1 day each. In the conservation period the plant needs
practically no supervision. Nevertheless, maintenance works are performed during
this time.
4 Results of the Kleylehof Plant
When the plant was started, the nitrate content in the raw water was 120 mg
No3rl. At maximum applicable desalination, a nitrate concentration of as low as
25 mg N03r l was achievable. Nevertheless, according to an optimum quantity and
quality of the brine, the stack voltage was adjusted to a nitrate removal down to 40
mg N03rl. In proportion to the nitrate removal, the hardness of the drinking water
was reduced by approximately 23%. Table 1 shows an analysis for the raw water,
product water and brine.