Discussion by Yair Folkman and Alberto M. Wachs
519
The authors' research relates to the special conditions prevailing in Israel, where, to date,
practically all the natural water resources have been exploited, and it is necessary to reuse sewage as a
fresh water source. On the other hand, during recent years, the nitrate level in the groundwater in
several regions of the country has risen to a level endangering their use. To remove the high nitrogen
compounds found in the sewage of this country, it was necessary to find a method that would under
the climatic conditions of Israel be cheap, so as -not to make the reused water too costly. The
method of releasing ammonia in the retention ponds appears feasible for the Dan Region Reclamation
Project located in an area of sand dunes where the weather is hot and strong winds blow. During the
winter the average water temperature is 15 C, and the average wind velocity is 17.6 km/hr; during the
summer these figures are 25°C and 10.8 km/hr, respectively. The topographical conditions allow the
construction of shallow ponds at a relatively low cost. Tertiary treatment with lime and ammonia
release can be carried out only after biological treatment ensures no nitrication will take place and that
most of the nitrogen in the effluents will appear in the form of ammonia. This tertiary treatment can
take the form of either stabilization ponds or high rate activated sludge. It is almost certain that most
of the organic nitrogen, including urea, will break up into ammonia during the biological treatment
before they reach the tertiary stage. For example, the biological treatment in the first stage of the Dan
Region Reclamation Project for a quantity of 30 million cu.m/year is based on facultative recirculating
ponds. Despite the fact that this method produced a nitrogen removal of 70% - mostly through the
removal of ammonia at 8.5 pH
1 , the rest of the ammonia must be removed. The effluent from the
recirculation ponds is then to be treated in lime reactor clarifiers where the phosphates, algae, bacteria,
viruses, B.O.D. residue, and the suspended solids will be removed together with the lime sludge. The
authors found
2 that to obtain good flocculation with lime treatment, the pH must be increased to
around 11.0, whereupon the magnesium ions in the effluents is conveyed to magnesium hydroxide
particles with a positive electrical charge acting as an efficient flocculant. A pH level of 11.0 is also
required to release the ammonia from the lime-treated effluents. True, as Mr. Potten has pointed out,
to increase the pH to 11.0, a large amount of lime is required, especially in Israel where the water is
usually hard. Furthermore, the authors discovered
3 that the amount of lime required is a function of
the ammonia concentration in the effluents, and the lower the efficiency of the ammonia removal
during the biological treatment, the greater the amount of lime required, and can vary from 500-700
mg/1. However, lime is readily available in Israel and is relatively cheap. The large quantities of lime
sludge can also be dried and regenerated.
As has been pointed out in this paper, a drop in pH takes place during the retention of the
effluents in the ammonia release ponds, and when the pH values drop to less than 9.0, they will be
channelled to percolation fields for recharging the groundwater. Surveys carried out in Israel showed
that the nitrogen in groundwater always appears as nitrates, thus demonstrating the nitrification
processes taking place during the movement of the water in the ground. Accordingly, it was found that
the removal of ammonia at the rate of 90% in the retention ponds gives a nitrate concentration in the
percolated water of less than 10 mg/1 as nitrogen.
As for the problem of the ammonia taken up from the atmosphere by other water bodies, as has
happened in very wet areas, this is not likely to occur at the Dan Region Reclamation Project owing to
the conditions prevailing in the area. The number of rainy days are few, and the strong winds disperse
the ammonia over very great distances. On the other hand, the bodies of water nearest the facilities are
the Mediterranean Sea to the west, and the Dead Sea some 150 km to the east. Losses from the
retention ponds through evaporation are expected to average 5%.
Mr. Potten has drawn attention to the printing errors appearing in the text in Eq. (27). The term
A0 should appear instead of ΔΘ.
The research described is the first stage in studying the practical approach to ammonia release in
retention ponds, and its purpose was to find a functional connection between the different
parameters, such as wind, temperature, and depth - parameters which it is possible to isolate in the
laboratory - and the ammonia release rate. In this connection it should be noted that in the experiments in tanks the samples taken 30 cm below the water surface, at mid-depth, and from the bottom
of the tank, were found to have identical concentrations, apparently because of the high diffusivity of
ammonia in water.
Results obtained on such a small scale may not be immediately applied in the field. For this reason,
a pilot plant has been constructed at the site of the plant with a capacity of 30 cu.m/hr, where an
attempt will be made to develop a more practical approach for ammonia removal. The intention here
is also to determine the accumulation rate of calcium carbonate in the retention ponds.
With regard to the exploitation of the reclaimed water for recreation the Authority responsible
for the Dan Region Sewage Reclamation Project plans to use the final retention ponds as part of a
boating, vacationing, and resort network within a recreation area to be developed in the region.
Answers to some of the questions raised by Messrs. Parker, Allen and McKendrick are included in
the reply to Mr Potter;
519
The authors' research relates to the special conditions prevailing in Israel, where, to date,
practically all the natural water resources have been exploited, and it is necessary to reuse sewage as a
fresh water source. On the other hand, during recent years, the nitrate level in the groundwater in
several regions of the country has risen to a level endangering their use. To remove the high nitrogen
compounds found in the sewage of this country, it was necessary to find a method that would under
the climatic conditions of Israel be cheap, so as -not to make the reused water too costly. The
method of releasing ammonia in the retention ponds appears feasible for the Dan Region Reclamation
Project located in an area of sand dunes where the weather is hot and strong winds blow. During the
winter the average water temperature is 15 C, and the average wind velocity is 17.6 km/hr; during the
summer these figures are 25°C and 10.8 km/hr, respectively. The topographical conditions allow the
construction of shallow ponds at a relatively low cost. Tertiary treatment with lime and ammonia
release can be carried out only after biological treatment ensures no nitrication will take place and that
most of the nitrogen in the effluents will appear in the form of ammonia. This tertiary treatment can
take the form of either stabilization ponds or high rate activated sludge. It is almost certain that most
of the organic nitrogen, including urea, will break up into ammonia during the biological treatment
before they reach the tertiary stage. For example, the biological treatment in the first stage of the Dan
Region Reclamation Project for a quantity of 30 million cu.m/year is based on facultative recirculating
ponds. Despite the fact that this method produced a nitrogen removal of 70% - mostly through the
removal of ammonia at 8.5 pH
1 , the rest of the ammonia must be removed. The effluent from the
recirculation ponds is then to be treated in lime reactor clarifiers where the phosphates, algae, bacteria,
viruses, B.O.D. residue, and the suspended solids will be removed together with the lime sludge. The
authors found
2 that to obtain good flocculation with lime treatment, the pH must be increased to
around 11.0, whereupon the magnesium ions in the effluents is conveyed to magnesium hydroxide
particles with a positive electrical charge acting as an efficient flocculant. A pH level of 11.0 is also
required to release the ammonia from the lime-treated effluents. True, as Mr. Potten has pointed out,
to increase the pH to 11.0, a large amount of lime is required, especially in Israel where the water is
usually hard. Furthermore, the authors discovered
3 that the amount of lime required is a function of
the ammonia concentration in the effluents, and the lower the efficiency of the ammonia removal
during the biological treatment, the greater the amount of lime required, and can vary from 500-700
mg/1. However, lime is readily available in Israel and is relatively cheap. The large quantities of lime
sludge can also be dried and regenerated.
As has been pointed out in this paper, a drop in pH takes place during the retention of the
effluents in the ammonia release ponds, and when the pH values drop to less than 9.0, they will be
channelled to percolation fields for recharging the groundwater. Surveys carried out in Israel showed
that the nitrogen in groundwater always appears as nitrates, thus demonstrating the nitrification
processes taking place during the movement of the water in the ground. Accordingly, it was found that
the removal of ammonia at the rate of 90% in the retention ponds gives a nitrate concentration in the
percolated water of less than 10 mg/1 as nitrogen.
As for the problem of the ammonia taken up from the atmosphere by other water bodies, as has
happened in very wet areas, this is not likely to occur at the Dan Region Reclamation Project owing to
the conditions prevailing in the area. The number of rainy days are few, and the strong winds disperse
the ammonia over very great distances. On the other hand, the bodies of water nearest the facilities are
the Mediterranean Sea to the west, and the Dead Sea some 150 km to the east. Losses from the
retention ponds through evaporation are expected to average 5%.
Mr. Potten has drawn attention to the printing errors appearing in the text in Eq. (27). The term
A0 should appear instead of ΔΘ.
The research described is the first stage in studying the practical approach to ammonia release in
retention ponds, and its purpose was to find a functional connection between the different
parameters, such as wind, temperature, and depth - parameters which it is possible to isolate in the
laboratory - and the ammonia release rate. In this connection it should be noted that in the experiments in tanks the samples taken 30 cm below the water surface, at mid-depth, and from the bottom
of the tank, were found to have identical concentrations, apparently because of the high diffusivity of
ammonia in water.
Results obtained on such a small scale may not be immediately applied in the field. For this reason,
a pilot plant has been constructed at the site of the plant with a capacity of 30 cu.m/hr, where an
attempt will be made to develop a more practical approach for ammonia removal. The intention here
is also to determine the accumulation rate of calcium carbonate in the retention ponds.
With regard to the exploitation of the reclaimed water for recreation the Authority responsible
for the Dan Region Sewage Reclamation Project plans to use the final retention ponds as part of a
boating, vacationing, and resort network within a recreation area to be developed in the region.
Answers to some of the questions raised by Messrs. Parker, Allen and McKendrick are included in
the reply to Mr Potter;