Discussion by G.E. Eden
The authors state that the use of PCBs in industry is increasing. This may be so in Japan but is
certainly not so in the United Kingdom; here the manufacturers have voluntarily agreed to discontinue
the supply of PCBs for uses which could readily contaminate the environment.
My colleagues and I are mystified by the discussion on the formation of hydrochloric acid on
irradiation. Assuming an initial concentration of PCBs of 100/Jg/l the maximum concentration of
hydrochloric acid which could be produced is 71 fJg/l This concentration added to conductivity
water would give a pH value of approximately 5.7. Is this the pH change referred to by the authors
when they say the solution became acidic by irradiation, or was acid also produced by impurities
present in the solution? presumably the identification of chloride by titration with silver nitrate was
performed after concentration, though this is not stated in the paper. Some details of the paper
Chromatographie procedure and the significance of the quoted Rf value would be welcome.
The authors have shown that by simple chemical coagulation methods using bentonite and alum
about 90 per cent removal of PCB's can be obtained. They have also shown that contact with 10 mg/1
of activated carbon can remove 74 per cent; no doubt a greater degree of removal could be achieved
by refinement of these procedures or by passing the water through granular activated carbon in a
column. To achieve a similar effect by irradiation requires a dosage of the order of 1-10 M rad.
Ballantine et al
l have shown that the cost of the energy source alone to deliver 0.1 M rad ranges
from 13 cents per 1000 gal using a reactor loop (said to be extremely speculative) to 158 cents per
1000 gal using spent fuel elements. The "most credible cost" was 104 cents per 1000 gal using Co60.
Thus the process proposed by the authors would cost at the best estimate over $10 per 1000 gal. (This
incidentally is several times the cost of distilling water.) The alternative conventional processes
mentioned by the authors would probably cost around 10 cents per 1000 gal and could be virtually
guaranteed to give a high degree of purification with the minimum of development work. Since
radiation processes for treatment of waste waters have been shown repeatedly to be uneconomic
compared with conventional processes the authors should be asked to justify their optimistic assessment of the value of radiation as a means of treating polluted water.
REFERENCES
1. BALLANTINE, D. S., MILLER, L. A., BISHOP, D. F., and ROHRMAN, F. A. The practicality of
using atomic radiation for wastewater treatment. J. Wat. Pollut. Control Fed. 41, Pt 1, 445 (March
1969)
Reply
For the identification of hydrogen chloride, to 2 liters of irradiated PCB solution, 1 ml of normal
sodium hydroxide was added, and concentrated at 50°C to 10 ml. Chlorine was determined by
titration with standard silver nitrate solution using potassium chromate as indicator.
By our estimation, the cost of irradiation treatment is 2 cents per ton, that is, about 8 cents per
1000 gallons to deliver 0.01 Mrad using Co-60.
The concentration of PCB present in the raw water of water supplies ranges from 0.1 ppb to 1.0
ppb. Such low concentration of PCB might be treated fully with 0.01 Mrad, because the lower the
concentration oi pollutants in water, the smaller dose is necessary to reduce. So irradiation treatment
seems inadequate to apply industrial waste water or sewage which has higher concentrations of
pollutants than such source water of water supplies as river or lake water.
F.L. Parker, USA
The authors do not state whether or not the design rate of reduction of PCB was also observed at
10 Mrad for concentrations of PCB at 0.1 to 1.0 ppb which are likely to be more typical values of PCB
in Japanese river waters. The data presented for all methods of treatment would have been more useful
if it also was evaluated at 10, 1, 0.1 ppb of PCB.
The authors show that 95% removal at 100 ppb at 10 Mrd occurs and that 90% removal of an
initial 100 ppb of PCB by standard methods of treatment such as coagulation 74% removal by
activated carbon and 42% removal by Fenton's reagent (all at 100 ppb of PCB). If the costs of
irradiation are an order of magnitude greater than the costs of the other treatment, then sequential
treatment by standard methods may produce an equivalent effluent at a far lower cost. We know from
the many studies that have been carried out on sewage treatment by irradiation for over 20 years that
it is technically satisfactory but that the efficiency or the costs must be improved by factors of 2 to 25
before it can economically compete with other forms of treatment.
It would also be useful if the toxicity studies were also carried out at the lower levels.
Reply
PCB is so insoluble in water that only ppb are present. We therefore examined 100~10 ppb PCB in
water solutions: 1, 0.1 ppb of PCB in water will be tried. We can remove PCB in water by standard
613
The authors state that the use of PCBs in industry is increasing. This may be so in Japan but is
certainly not so in the United Kingdom; here the manufacturers have voluntarily agreed to discontinue
the supply of PCBs for uses which could readily contaminate the environment.
My colleagues and I are mystified by the discussion on the formation of hydrochloric acid on
irradiation. Assuming an initial concentration of PCBs of 100/Jg/l the maximum concentration of
hydrochloric acid which could be produced is 71 fJg/l This concentration added to conductivity
water would give a pH value of approximately 5.7. Is this the pH change referred to by the authors
when they say the solution became acidic by irradiation, or was acid also produced by impurities
present in the solution? presumably the identification of chloride by titration with silver nitrate was
performed after concentration, though this is not stated in the paper. Some details of the paper
Chromatographie procedure and the significance of the quoted Rf value would be welcome.
The authors have shown that by simple chemical coagulation methods using bentonite and alum
about 90 per cent removal of PCB's can be obtained. They have also shown that contact with 10 mg/1
of activated carbon can remove 74 per cent; no doubt a greater degree of removal could be achieved
by refinement of these procedures or by passing the water through granular activated carbon in a
column. To achieve a similar effect by irradiation requires a dosage of the order of 1-10 M rad.
Ballantine et al
l have shown that the cost of the energy source alone to deliver 0.1 M rad ranges
from 13 cents per 1000 gal using a reactor loop (said to be extremely speculative) to 158 cents per
1000 gal using spent fuel elements. The "most credible cost" was 104 cents per 1000 gal using Co60.
Thus the process proposed by the authors would cost at the best estimate over $10 per 1000 gal. (This
incidentally is several times the cost of distilling water.) The alternative conventional processes
mentioned by the authors would probably cost around 10 cents per 1000 gal and could be virtually
guaranteed to give a high degree of purification with the minimum of development work. Since
radiation processes for treatment of waste waters have been shown repeatedly to be uneconomic
compared with conventional processes the authors should be asked to justify their optimistic assessment of the value of radiation as a means of treating polluted water.
REFERENCES
1. BALLANTINE, D. S., MILLER, L. A., BISHOP, D. F., and ROHRMAN, F. A. The practicality of
using atomic radiation for wastewater treatment. J. Wat. Pollut. Control Fed. 41, Pt 1, 445 (March
1969)
Reply
For the identification of hydrogen chloride, to 2 liters of irradiated PCB solution, 1 ml of normal
sodium hydroxide was added, and concentrated at 50°C to 10 ml. Chlorine was determined by
titration with standard silver nitrate solution using potassium chromate as indicator.
By our estimation, the cost of irradiation treatment is 2 cents per ton, that is, about 8 cents per
1000 gallons to deliver 0.01 Mrad using Co-60.
The concentration of PCB present in the raw water of water supplies ranges from 0.1 ppb to 1.0
ppb. Such low concentration of PCB might be treated fully with 0.01 Mrad, because the lower the
concentration oi pollutants in water, the smaller dose is necessary to reduce. So irradiation treatment
seems inadequate to apply industrial waste water or sewage which has higher concentrations of
pollutants than such source water of water supplies as river or lake water.
F.L. Parker, USA
The authors do not state whether or not the design rate of reduction of PCB was also observed at
10 Mrad for concentrations of PCB at 0.1 to 1.0 ppb which are likely to be more typical values of PCB
in Japanese river waters. The data presented for all methods of treatment would have been more useful
if it also was evaluated at 10, 1, 0.1 ppb of PCB.
The authors show that 95% removal at 100 ppb at 10 Mrd occurs and that 90% removal of an
initial 100 ppb of PCB by standard methods of treatment such as coagulation 74% removal by
activated carbon and 42% removal by Fenton's reagent (all at 100 ppb of PCB). If the costs of
irradiation are an order of magnitude greater than the costs of the other treatment, then sequential
treatment by standard methods may produce an equivalent effluent at a far lower cost. We know from
the many studies that have been carried out on sewage treatment by irradiation for over 20 years that
it is technically satisfactory but that the efficiency or the costs must be improved by factors of 2 to 25
before it can economically compete with other forms of treatment.
It would also be useful if the toxicity studies were also carried out at the lower levels.
Reply
PCB is so insoluble in water that only ppb are present. We therefore examined 100~10 ppb PCB in
water solutions: 1, 0.1 ppb of PCB in water will be tried. We can remove PCB in water by standard
613