638
Discussion
2. REBHUN, M., MANKA, J. "Characterization of Organics in Secondary Effluents", Environmental
Science and Technology, 5, 606, 1971.
Reply to Discussions by M. Rebhun
The authors agree that more favourable reductions in quality parameters such as colour, COD,
hardness, etc., can be achieved by using excess lime treatment instead of aluminium sulphate. Recent
studies at Pretoria have confirmed the advantages of excess lime treatment especially where a high
quality reclaimed water is envisaged. The pilot scale investigations and full scale operations of the
reclamation plant at Springs has, however, confirmed the suitability of the alum flotation process for
this particular situation.
Choice of using alum flotation was, therefore, mainly based on economic considerations in terms
of low capital expenditure and simplicity of operation and control. Where the excess lime treatment
process would require sedimentation in a two stage process, the alum flotation is carried out in a.single
unit. Lime dosing also requires more supervision than would normally be the case with alum dosing.
L. Holland, Israel
Reflectance measurements on handsheets have been used to evaluate and compare different
methods of refining purified sewage prior to re-use of this sewage in pulp and paper manufacture. The
handsheet technique described has two shortcomings (a) it would not give any indication of the effect
of the refining method on the pulp manufacturing process, since the handsheets one made from pulp
which has already undergone complete pulping and bleaching, (b) No allowance has been made on the
effects of aging on handsheet brightness. This is particularly important since the prime effect of, for
instance, heavy metal traces on bleached pulp, is one of colour reversion, which will only be felt after
a certain time interval. The evaluation technique for selecting a suitable treatment method for refining
purified sewage for pulp and paper mill use could be improved by (1) Laboratory-scale cooking and
bleaching of pulp using the refined sewage as process water, and making of handsheets from pulp
prepared in this way. (2) Aging of a part of the pulp prior to testing; perhaps by accelerated
techniques (e.g. at 105°C or under O.V. light or strong sunlight).
Reply
The handsheet technique referred to in this paper admittedly has the shortcomings as indicated by
Mr. Holland. As a relatively simple test to differentiate between various modes of chemical pretreatment it was, however, found to be quite useful especially during the laboratory scale investigation.
L. Holland, Israel
Addition of NaOH to the refined sewage as a final treatment step to raise the pH from 6.0 to 7.2 is
almost certainly unnecessary in the case of water intended for use in the paper mill, where pH of
process water will almost certainly be less than 6.0 (if a rosin-alum sizing system is used) and addition of
caustic will simply increase the alum demand for sizing without contributing anything positive to the
papermaking process.
Reply
The main objective of adding NaOH to the refined sewage is to prevent corrosion of the pipeline
which connects the reclamation plant and the paper mill as these are situated remotely.
L. Rakosh, Israel
What is the operating pressure in the flotation process? Which poly electrolytes were used?
Reply
The operating pressure used in the flotation process is of the order 10 psig. This low aeration
requirement is probably due to the presence of synthetic detergents in the sewage effluent, and also
the fact that the total flow of water is aerated. The polyelectroly te used in the process is commercially
known as DAVCO 84.
A. Vivier, France
What do you do with your highly mineralised effluents?
Discussion
2. REBHUN, M., MANKA, J. "Characterization of Organics in Secondary Effluents", Environmental
Science and Technology, 5, 606, 1971.
Reply to Discussions by M. Rebhun
The authors agree that more favourable reductions in quality parameters such as colour, COD,
hardness, etc., can be achieved by using excess lime treatment instead of aluminium sulphate. Recent
studies at Pretoria have confirmed the advantages of excess lime treatment especially where a high
quality reclaimed water is envisaged. The pilot scale investigations and full scale operations of the
reclamation plant at Springs has, however, confirmed the suitability of the alum flotation process for
this particular situation.
Choice of using alum flotation was, therefore, mainly based on economic considerations in terms
of low capital expenditure and simplicity of operation and control. Where the excess lime treatment
process would require sedimentation in a two stage process, the alum flotation is carried out in a.single
unit. Lime dosing also requires more supervision than would normally be the case with alum dosing.
L. Holland, Israel
Reflectance measurements on handsheets have been used to evaluate and compare different
methods of refining purified sewage prior to re-use of this sewage in pulp and paper manufacture. The
handsheet technique described has two shortcomings (a) it would not give any indication of the effect
of the refining method on the pulp manufacturing process, since the handsheets one made from pulp
which has already undergone complete pulping and bleaching, (b) No allowance has been made on the
effects of aging on handsheet brightness. This is particularly important since the prime effect of, for
instance, heavy metal traces on bleached pulp, is one of colour reversion, which will only be felt after
a certain time interval. The evaluation technique for selecting a suitable treatment method for refining
purified sewage for pulp and paper mill use could be improved by (1) Laboratory-scale cooking and
bleaching of pulp using the refined sewage as process water, and making of handsheets from pulp
prepared in this way. (2) Aging of a part of the pulp prior to testing; perhaps by accelerated
techniques (e.g. at 105°C or under O.V. light or strong sunlight).
Reply
The handsheet technique referred to in this paper admittedly has the shortcomings as indicated by
Mr. Holland. As a relatively simple test to differentiate between various modes of chemical pretreatment it was, however, found to be quite useful especially during the laboratory scale investigation.
L. Holland, Israel
Addition of NaOH to the refined sewage as a final treatment step to raise the pH from 6.0 to 7.2 is
almost certainly unnecessary in the case of water intended for use in the paper mill, where pH of
process water will almost certainly be less than 6.0 (if a rosin-alum sizing system is used) and addition of
caustic will simply increase the alum demand for sizing without contributing anything positive to the
papermaking process.
Reply
The main objective of adding NaOH to the refined sewage is to prevent corrosion of the pipeline
which connects the reclamation plant and the paper mill as these are situated remotely.
L. Rakosh, Israel
What is the operating pressure in the flotation process? Which poly electrolytes were used?
Reply
The operating pressure used in the flotation process is of the order 10 psig. This low aeration
requirement is probably due to the presence of synthetic detergents in the sewage effluent, and also
the fact that the total flow of water is aerated. The polyelectroly te used in the process is commercially
known as DAVCO 84.
A. Vivier, France
What do you do with your highly mineralised effluents?