April 16, 1915.

THE COLLIERY GUARDIAN.

821

as time went on. The spent gas liquor, when diluted
with 19 volumes of sewage, had, under the conditions
of the experiment, apparently no retarding influence on
the absorption by the latter; or, it would probably be
more correct to say that the sewage assisted the gas
liquor to exert its oxygen absorbing power. Still, the
experiments are sufficient to show that the biological
absorption of dissolved oxygen by highly diluted spent
gas liquor (a liquor which is capable of taking up
oxygen rapidly when it is oxidised by chemical means),
even when the dilution is made with sewage, is decidedly
slow. In other words, the inhibiting effect of the liquor
on the biological purification of polluted water is great.
The spent gas liquor from a colliery, undiluted, showed
no absorption of oxygen when kept in an Adeney
apparatus .for five days.

Other experiments on the absorption of dissolved
oxygen from water were also made, using different
volumetric methods for the determination of the oxygen.
The general results were the same.

The Commission have recently supplemented these
preliminary trials by further laboratory experiments—
extending from June 8 to July 20*, 1914—on the
biological filtration of sewage containing known
percentages of spent gas liquor. These experiments
indicate that, in warm weather, settled sewage of
moderate strength, and containing up to 3 per cent, of
strong spent gas liquor, can be readily treated on a
percolating filter at a rate of about 70 galls, per cu. yd.
per 24 hours. In cold weather purification would no
doubt be materially retarded, and, besides, out-of-door;
conditions for filtration are on the whole less favourable
than those of the laboratory. Still, it may be safely
surmised that sewage containing up to 2 per cent, of
strong spent gas liquor—a much larger proportion than
ordinary town sewages contain—would be successfully
treated on a practical scale, always provided that the
liquor was fed continuously into the sewage and the
mixture distributed on to the filter after a short settle-
ment or septic tank treatment. It would be desirable
to have some quantitative laboratory experiments made
during very cold weather.

At Oldbury, near Birmingham, great difficulty was
found in purifying the sewage, on account of the
admixture with it of about 7 to 8 per cent, of spent gas
liquor from a chemical works, although this waste liquor
was run into the sewage uniformly. Mr. H. Silvester and,
subsequently, Prof. Percy Frankland, were called in to
advise upon the matter, and they carried out a number
of experiments at the sewage works, extending, in all,
for over a - year. The general conclusion to be
drawn from those experiments was that sewage con-
taining about 7 to 8 per cent of spent gas liquor is
capable of biological purification when treated in septic
tanks, and subsequently—at somewhat low rates—upon
either contact beds or percolating filters. But even at
so moderate a rate as one filling per day, triple contact
filtration was found to be necessary for the production
of a uniformly non-putrescent effluent. No exact com-
parison can be drawn between the results obtained from
the contact beds and percolating filters, respectively,
as the volumes treated per cube yard in the two cases
were dissimilar; the actual amount of oxidation effected
on the larger volume of liquor treated by percolating
filtration was greater than that on the smaller volume
receiving contact bed treatment, but the resulting
effluent was not so well oxidised.

The sewage at Oswaldtwistle, in the Ribble water-
shed, also contains an exceptional amount of spent gas
liquor, derived from a gas liquor distillery. The volume
has not been laccurately gauged, but it amounts to
something like 3 per cent, of the total sewage flow.
The sewage is treated in a series of septic tanks, and
then on percolating filters. The effluent produced is,
as a rule, fairly good, though not of a high class.

After experimenting with his colleagues, Messrs.
Ardern and Lockett, in the laboratory of the Davyhulme
Sewage Works, Manchester, for a number of years,
mainly upon the bacterial oxidation of thiocyanates and
of phenol, and in conjunction with Air. Holton in an
out-door experiment at the Manchester Gas Works, Dr.
G. J. Fowler was empowered by the authorities to make
some large scale experiments on the treatment of the
Bradford spent gas liquor upon already existing
biological percolating filters at Frizinghall, Bradford,
Yorkshire. Previous to using the filters for this pur-
pose, he re-inoculated them with an extract of soil,
which had been covered with cow dung, and which
quickly showed a strong development of nitrate. He
states' that the Bradford Corporation are now (1914)
treating the whole of the waste liquor from the Corpora-
tion gas works in this way, with a purification of over
80 per cent., as measured by the oxygen absorbed from
permanganate in three minutes. After prolonged trial
he has come to the conclusion that it is better to allow
a dilute (though relatively strong as compared with
sewage) solution of the liquor to circulate again and
again through the filter, rather than to pass a very
highly diluted liquor through, once.

Comparing the average diluted liquor fed on to the
filters with the average final effluent discharged, Dr.
Fowler finds the respective figures for oxygen absorbed
from permanganate in three minutes to be 115 and 62.
But since only about 30,000 galls, of final effluent are
discharged per 24 hours,* the figure 62 must be com-
pared with the three minutes' figure of the original
crude liquor, viz., 450, showing an approximate puri-
fication (as judged by this test) of over 80 per cent.

Liquor from Coke Ovens.

In a few cases the spent gas liquor from coke ovens
or from power gas plants is entirely evaporated, either
by using it along with water for coke quenching, or by
means of waste heat in specially constructed evapor-
ators. When worked efficiently, both plans prevent the
discharge of any spent gas liquor into streams, but

* Excepting at week-ends, when the filters receive some
fresh water, displacing some of the liquid held up.

result in local pollution of the atmosphere with vapours
which cannot be said to be innocuous. In the
evaporator plants some of the volatile organic consti-
tuents of the spent gas liquor are no doubt burnt,’ but
in the quenching of coke .there must be much less actual
combustion, for in this latter case a volume of dense
white steam is produced, which may persist for some
time in the atmosphere.

On the occasion of a visit to a colliery where coke was
being quenched with a mixture of water and settled
spent gas liquor, the steam had a strong phenolic
smell. Since it is necessary to use an excess of water
in quenching coke, special provision has to be made
for collecting the drainage from the quenching floors,
so that it may be pumped back again for re-use.

•So far as information goes, only four special
evaporators are at present in use in England and Scot-
land. Three are used in connection with blastfurnaces
at ironworks, while the fourth is at a colliery where coke
ovens have been installed.

At works No. 76, where coal, coke, and pig iron are
produced, the oven gas is sent through tar extractors,
scrubbed with water for ammonia, then with creosote
oil for benzole, the residual gas being afterwards used
for raising steam along with either blastfurnace gas or
coal slack, or both of these. The excess of gas from the
blastfurnace is used for the evaporation of the spent
gas liquor. The latter is first settled in tanks, and
then run into a long narrow brick chamber (approxi-
mately 47 ft. by 4 ft. by 10 ft. high, partially divided
by a central wall which’ supports the roof), where it is
maintained at a depth of about 12 in. At one end of
this chamber is a firebox, into which waste blastfurnace
gas is introduced along with some air and burned, the
hot gases passing through the long chamber over the
liquor into a chimney stack at the other end. In order
to increase the rate of evaporation as much as possible,
the liquor is splashed in the chamber by means of two
paddles . driven by electric motors. The evaporator
plant deals with from 50,000 to 60,000 galls, of spent
gas liquor per day, but it is acknowledged that the plant
is being pressed very hard to accomplish this. The less
volatile substances accumulate in the bottom of the
large chamber as a reddish-brown sticky sludge, which
has to be dug out at frequent intervals.

At colliery No. 77, another form of evaporator is in
use. In this case the volume of spent gas liquor is
about 20,000 galls, per day. It is first passed through
one of two settling tanks, each having a capacity of
about 18,000 galls., and then sprayed into the top of
two brick chambers, each 15 ft. by 8 ft. by 15 ft. high,
which are strongly bound with iron bands. At the side
of the chambers there are furnace boxes, which can be
used either for burning waste gas from the coke ovens
or coal, or both, the hot gases resulting from the com-
bustion passing up through the evaporating chambers
and into a special chimney stack. In order to diminish
the rate of depreciation of the brickwork, the inside of
the chamber is kept constantly wet with an excess of
spent gas liquor which flows away from the bottom of
the evaporator, and returns to the settling tank. The
residual sludge which accumulates in the bottom of the
evaporator is dug out from time to time and . tipped.

At another ironworks (No. 78) the spent gas liquor is
run into old boilers and evaporated by means of the
waste gas from a blastfurnace. The depreciation of the
plant is in this case very high. On the occasion of the
Commission’s visit it was admitted that the plant was
not sufficiently large to cope with the whole volume of
spent gas liquor produced.

Conclusions.

The Commission conclude their observations on this
subject by pointing out the importance of constructing
evaporator plants in duplicate, so as to allow of uninter-
rupted work in the event of a breakdown. Where no
duplicate plant exists, either the profitable ammonia
recovery plant must be stopped when the evaporator
breaks down, or the spent gas.liquor must be discharged.
In some cases, waste gas liquor from collieries is dis-
charged into old pit workings.

In view of the highly noxious character of waste gas
liquor, the Commission are of opinion that in no
circumstances should it be allowed to be discharged
untreated into a stream.

When it is produced at gas works in a town, and does
not at any time exceed 2 per cent, by volume of the
sewage, it may, without serious detriment to- the
subsequent purification of the sewage, be allowed into
the sewers, always provided that there is sufficient tank
capacity at the gas works where the gas liquor is pro-
duced to ensure that it shall flow into the sewers
equably, and, as far as possible, continuously, and not in
flushes. At certain sewage works the biological
efficiency of the tanks and filters has on occasion been
seriously affected by an unexpected flush of this liquor.
It must exert, of course,, the same prejudicial effect
upon the working of a sewage farm.

When the spent gas liquor, .before being discharged
to the sewers, is subjected to partial purification, a
larger relative volume may be mixed with the sewage.
They are not aware of any method of partial purifica-
tion which is fairly successful, other than that suggested
by Dr. Fowler; and this, they think, would probably
prove more expensive than combined treatment of the
gas liquor with sewage, where sewage was available.

As at most collieries there are large spoil heaps, the
Commission recommend that these should be used for
the purification of the spent liquor by percolating filtra-
tion, as in the case of the “ bings ” at. the shale oil
works in Mid and West Lothian. This may not in al]
cases result in a satisfactory effluent, but considerable
purification will always be effected where large spoil
heaps exist. Where there are no spoil heaps, they can
only suggest, as an alternative at the present moment,
the evaporation of the. liquor.

With the exception of the filtration of the waste liquor
from shale distilling works through “ bings ” of spent
shale, which must be regarded as a somewhat special

case, the Commission know of no method by' which
spent gas liquor can be purified at reasonable cost to
such’an extent as to render it innocuous if discharged
into a stream. There are consequently no data to show
what degree of purification might reasonably be asked
for. Further work on the subject is thus required, in
order to prevent or diminish the serious ‘ injury to
streams which is at present taking place in certain
districts. ’ ’

MINING INSTITUTE OF SCOTLAND.

Annual Meeting.

The 38th annual general meeting of the Alining Insti-
tute of Scotland was held on Saturday in the rooms of
the institute, 39, Elmbank-crescent, Glasgow. Air.
James Hamilton, mining engineer, Glasgow, presided,
and there was a large attendance.

The following gentlemen were admitted to member-
ship Alessrs. Wm. Harley, mining engineer, London;
John Howatt, mining engineer, Glasgow; Wm. Logan,
mining engineer, Lugar; John W. Loudon, colliery
manager, Dunfermline; A. R. Milligan, colliery
manager, Cumnock; James Noble, mining engineer,
Whifflet.; and Gibson Reid, mining engineer, Preston.

The Council’s Report.

Mr. G. L. Kerr, on behalf of the council, submitted
the 37th annual report, from which it appeared that the
total membership now stood at 657. The arrangement
of holding the general meetings alternately in Glasgow
and Edinburgh on Saturday afternoons had been con-
tinued, and the attendances at the meetings had been
very satisfactory. The council had authorised the pre-
paration of a new catalogue of the institute library, and
it was expected that the catalogue would be printed and
issued to the members during the coming year. The
financial statement, which accompanied the report,
showed the institute to be in a sound position. — The
report was endorsed by the members.

Air. J. T. Forgie, Bothwell, in calling for a cordial
vote of thanks to the retiring president, Mr. James
Hamilton, remarked that that gentleman had been a
very hard worker indeed during his tenure of office.
Mr. Hamilton, as they all knew, was a civil and mining
engineer of great ability and experience. At the present
time he was a member of a firm which enjoyed the
reputation of. being one of the oldest firms of civil and
mining engineers in Scotland. He believed he was right
in saying that by his long connection with the firm in
question, Air. Hamilton had acquired a knowledge of
the coalfields of Scotland which he would say was
possessed by no other person at the present, moment.
Air. Forgie proceeded to eulogise the retiring president
for the initiative and. energy he displayed in raising the
money necessary as a contribution from the. Mining
Institute of Scotland towards the expense involved in
the acquisition of a Royal Charter for the Institution of
Alining Engineers.

Air. Hamilton briefly acknowledged, and said the
credit for raising the sum referred to was due to the
cordial manner in which the coal masters of Scotland
responded to the appeal from the institute. Then it
was also in large measure because of the energetic way
in which the' finance committee carried out the work
that Scotland created somewhat of.a record by having
contributed her share of the expense, while. many of
the other federated institutes were lagging behind. He
concluded by introducing the new president of the insti-
tute, Air. D. M. Mowat. He was certain of this, that
the members could not have made a wiser or a better
selection. ....

The Presidential Address.

Air. D. Al. AIowat then took the chair, and thereafter
delivered an interesting address. Speaking of the effects
of the war, he said that in the early days of the war,
through the dislocation of home industries and the
closing of many of our foreign markets, the supply, of
fuel exceeded the demand, but'recently this position
had been reversed. The supply of fuel was now- far
short of the demand, and prices had risen considerably
above the low and unremunerative level to which they
had fallen. Only since February, however, had the
price risen above the corresponding price in February of
last year. In spite of this, they found wild statements
being made by irresponsible journalists, who cried loudly
about the rapacity of the coal-owners. For example, in
an- article in the Daily News and Leader, there appeared
recently the following statements :—“ The coal trade has
■been plundering the country for eight months. That is
■a long enough innings.” If the writer of this article
had appealed to hard facts for his information, instead
of to his vivid imagination, he would have learned that
a great, many collieries had done very badly since the
beginning of the war. The recently published balance-
sheets of four Scottish companies, with an output of
three million, tons of coal, for the year ending
December 31 or January 31 last, showed that the share-
holders had not received a penny of dividend. The
authors of such statements as those already quoted were
only seeking to stir up class strife when there should be
peace, and were traitors .to their country. It seemed to
him (Air. Alowat) that the difficulties in regard to the
dearth of fuel could be got over if the conditions imposed
by the Alines (Eight Hours), Act were relaxed. Surely, if
section 4 was ever to be utilised, now was the time.
In addition, if the miners and their leaders realised the
seriousness of the national situation, the present system
of working only a part of the working week would be
suspended, and the fullest output obtained from the
men still remaining at work. Only want of a realisa-