February, 1927 I-VDUSTRIAL A N D ENGI,VEERING CHEMISTRY 24 1

The mercerizing department was next opened and the wash waters, which did not carry enough concentration of caustic soda to pay for recovery by evaporation, entered the general collection tank. The solution was then quite alkaline and a greatly increased quantity of alum was nec- essary to effect neutralization. Moreover, the clarifier tank rapidly filled with sludge, a t a time in the experience of the company when it did not know what to do with the sludge it already had. A large iron cylinder was installed to hold 66" BB. sulfuric acid, and this treatment immediately reduced the volume of sludge.

In the dyeing department there was no real difficulty in the removal of the color from the wash waters or from the used dye baths, except in few instances such as the naphthanil and basic colors, and these could be quite easily destroyed by adding bleach liquor to the concentrated dye bath be- fore discharging to the central collection tanks. Before these colors were discharged in the concentrated form they were released into the composite waste and thereafter some difficulty was experienced in clearing the color.

Water Treatment

The water used is quite hard and is softened by a zeolite treatment. In the regeneration of the zeolite beds with common salt, i t was found that magnesium chloride was

produced from the magnesium in the water. The wash water was collected in a special sump outside the filter house and was treated with caustic soda solution (60-70" Tw.) which had to be carried a considerable distance and thoroughly mixed with the effluent. This was not only very expensive but extremely inconvenient. By placing a siphon from this sump to the central sump in the basement it was possible to bring this waste in conjunction with the caustic wash waters from the mercerizing plant and have the one act against the other thus materially reducing costs.

Conclusion

The problem which this company has had to meet in the disposal of its trade waste is no doubt similar to that which confronts other textile manufacturers in the same locality if an earnest effort is made by them to produce a treated waste of equally high standard. Owing to the high cost of treat,ing its trade waste, this company is facing an unfair competition from manufacturers in other sections of the country, who are not obliged, through legislation, to give their industrial wastes special treatment. It would therefore seem advisable that some form of municipal or state system be established by which a more economical method could be devised for treating the entire industrial wastes of the section.

Effect of Temperature on Sewage Sludge Digestion','

By Willem Rudolfs

S E W JERSEY h G R I C U L T U R A L EXPBRIXENT S T A T I O N , N E W BRUNSWICK, N. J.

N A X effort to determine the effect of temperature on sludge digestion, unseeded fresh solids (raw sludge) were placed in bottles in the laboratory and subjected

to the following constant temperatures: lo", 18', 24' 29.5', and 35" C. Portions of the same fresh solids were treated with hydrated lime sufficient to produce a slightly alkaline reaction of the medium (pH 7.3). The materials were analyzed every week for total alkalinity, biochemical oxygen demand, solids, ash, total nitrogen, sulfates, and pH values. The gas was collected and analyzed for carbon dioxide, oxygen, methane, and hydrogen. Weekly counts of total bacteria and protozoa were made and the different groups of bacteria and kinds of protozoa were determined.

The complete data obtained with a thorough discussion are to be published in bulletin form from the New Jersey Agricultural Experiment Station and only some of the out- standing results are embodied in this paper.

Organic Matter Reduction and Ash Increase

I

The material digested after the least number of days is taken as a basis of comparison. Gas production from this material had practically stopped and all indications were' that further decomposition of the more resistant material would be very slow. The comparison is made after 108 days, but the sludge in question was ready for drawing in 58 days. Figure 1 shows the percentage reduction of organic matter and the percentage increase in ash of the sludges a t the differ- ent temperatures. Digestion is very slow below 10" C.

* Presented before the Division of Water, Sewage, and Sanitation Chem- istry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926.

* Paper No. 310 of the Jotirnal Series, New Jersey Agricultural Ex- periment Station, Department of Sewage Disposal

Raising the temperature a few degrees has comparatively little effect. Raising the temperature of unseeded and un- adjusted (without lime) material from 10" C. to 18" C . has far less effect during the first 108 days than would be expected. To be sure, the organic matter decreased from 17 to 19 per cent, but the ash content remained practically constant. The percentage of ash in the original material was 22.8 per cent. It was surprising to find that unseeded and unadjusted material subjected to 24" C. did not digest much more rapidly than a t 18" C., although the rate of gas production was greater at the higher temperature. Raising the temperature to 29.5" C. caused a rapid decrease in organic matter and a nearly equal rapid increase in ash content, while a temperature of 35" C. retarded the digestion processes as compared with activities a t 29.5" C.

The effect of adjusting the reaction with the aid of hy- drated lime is quite remarkable. Where a t lower tempera- tures the unlimed material liquefied to a certain extent (reduction of organic material without a comparable increase in ash) the lime-treated material mineralized nearly as rapidly as it liquefied. The plotted data are corrected for the lime added. At 29.5' C. the limed material showed less reduction in organic matter than the unlimed, but the ash increase was considerably greater. At 35' C. lime did not seem to have much effect, and it would appear from these curves to be detrimental. However, if gas production is taken into consideration, lime was at this high temperature beneficial.

Total Gas Production

The total gas production per gram organic matter in 108 days is presented in Figure 2. It should be emphasized that the total amount of gas produced from a gram organic

242 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 19, No, 2

material is not dependent upon the temperature. Recently some writers have stated that gas production increases with the temperature. If this were true the amount of gas evolved from a given amount of organic matter would be a function of temperature. However, these writers have apparently confused the rate of gas production with gas production as such or, in other words, the speed of biological activities with the activities themselves. If a given amount of organic matter found is subjected to different temperatures the ulti- mate amounts of gas will be practically the same. The amount of gas per gram organic matter varies from 250 cc. to 475 cc. depending upon the composition of the sewage, but the same sewage subjected to different temperatures will produce approximately the same volume of gas.

10 IS 24 29.6 86 Temperature 0 C.

Figure 1-Percentage Organic Matter Reduc- tion a n d Ash Increase of Sewaae Sludge Kept at Diflerent Temperatures with a n d without Lime - - - - with lime. - without lime

From Figure 2 it can be seen that the amount of gas pro- duced in the unlimed series a t 35' C. was 470 cc. per gram organic matter; at 29.5' C. during the same time it was 400 cc. In a given time the amount of gas produced from unseeded and unlimed material increased directly with the hcrease in temperature. If, however, these materials are kept for longer times a t the different temperatures the amounts of gas produced are practically the same in all cases and the material subjected to 29.5' C. reaches its maximum first. The gas produced per gram organic matter from the unseeded and limed series a t the end was between 700 and 750 cc. This increase is apparently due to the changes in reaction of the medium caused by the hydrated lime.

Bacteria and Protozoa

The average bacterial numbers (on agar plates) in units of hundred millions per gram organic matter and protozoa in thousands per gram organic matter are presented in Figure 3. It is apparent that in unadjusted sludge the aver- age numbers of bacteria do not increase with increase in temperature and in adjusted sludge they decrease with in- crease in temperature In the 19251926 report of the Sew- age Experiment Station3 the effect of lime on bacteria has been discussed in detail. Hydrated lime retards the death rate of the organisms originally present in sewage. These

: In press.

organisms are to a large extent acid-formers. At a low temperature they remain in the sludge longer than at higher temperatures, since a t higher temperatures the activities increase and the material attacked by these organisms becomes speedily exhausted. At the same time hydrated lime induces greater activities of the organisms responsible for the attack of more resistant carbohydrates (cellulose, etc.). Higher temperatures increase the rate of activities;

I.

sy

a 600 .Y 2 8 8 400

b 6 p 200

d

a

M

10 18 24 29.6 35 Temperature 0 C.

Figure 2-Total Gas Produrtion per Gram Organic Matter after 108 Days - - - - with lime. - without lime

hence these two factors together produce more gas. The composition of the gas naturally changes with the change in type of organisms. The organisms originally present in sewage sludge produce mainly carbon dioxide, whereas the organisms responsible for the decomposition of more resistant carbohydrates. etc., produce mainly methane.

The numbers of protozoa follow the numbers of bacteria rather closely. In the above-mentioned report' it is stated

I I I I I

10 18 24 29.5 35 Temperature O C.

Figure &Average Bacteria and Protozoa .per Gram Organic Matter during Period of 108 Days

without lime - - - - - with lime.

that the small flagellates which constitute the main bulk of the protozoa present are "stimulated" or derive part of their nutrition from organic acids and nitrogen compounds like amino acids. Since retardation of the bacteria responsible

February, 1927 INDUSTRIAL AND ENGINEERING CHEMISTRY 243

for the production of these products is caused by lower tem- peratures and additions of lime, the protozoa are more numerous under these conditions. At higher temperatures and additions of lime, when these bacteria are rapidly re- placed by other groups producing different intermediate compounds, protozoa numbers are necessarily low.

Proper Reaction In a previous publication4 it has been shown that exclusion

of air induces liquefaction of the organic material. This liquefaction can be changed by proper reaction and proper temperature to gasification. With the increased rate of di- gestion, odors are naturally intensified.

The digestion time in days for treated and untreated material a t different temperatures is as follows:

10°C. 18'C. 24OC. 29.5'C. 35'C. Untreated 360 200 142 61 89 Limed 325 150 108 54 108

The figures represent the minimum time necessary for di- gestion of material before sludge drawing and not until digestion is complete. It must be borne in mind that these figures are given for unseeded material. If the relation of

6 New Jersey Agr. Expt. Sta., Bull. 427.

ripe sludge and fresh solids is kept correct and constant, di- gestion time decreases again considerably.

Summary

Digestion is extremely slow a t temperatures below 10" C. Raising the temperature a few degrees above 10 has com- paratively little effect. Digestion time is materially de- creased with higher temperatures. Maximum digestion takes place at about 27-28' C . Definite quantities of organic material present in sewage produce about the same volume of gas a t all temperatures. The volume of gas produced from the same sewage sludge can be increased by changing the reaction of the medium and the composition of the gas changes due to a preponderance of different organisms.

In a given time the average number of bacteria per gram organic matter in unadjusted sludge does not increase with increase in temperature, whereas the average numbers of bacteria in lime-treated sludge decrease with the increase in temperature. In a same given time protozoan numbers (mainly small flagellates) follow t.he bacterial numbers.

Keeping the material a t the proper reaction (pH 7.3 to 7.6) decreases digestion time still further. The composition of the gas changes with the reaction of the medium.

Behavior of Formaldehyde-Tanned Hide Powder toward Chromium Compounds'

By K. H. Gustavson

WIDEN-LORD TANNINQ CO., DANVZRS, MASS.

OMPARATIVE studies of hide protein proper in the form of hide powder, of the protein in different degrees C of aggregation, and of hide powder pretreated with

other agents resulting in structural alteration of the hide protein offer a promising method of attack of problems in protein chemistry in general and the mechanism of tanning processes in particular.

This paper deals with the behavior of chromium compounds toward hide powder and toward the powder pretreated with formaldehyde.

The nature of the action of formaldehyde upon proteins is, as most problems in leather chemistry, still a much debated but unsettled problem. Of all types of tannages, the one with formaldehyde is generally considered to be purely chemical in nature. The investigations of Bergmann and his collabo- rators* in regard to the nature of reaction products between amino acid, piperazines and related structures, and formalde- hyde demonstrate the manifold possibilities of this reaction. Besides the primary amino groups, other basic groups seem to participate in the formaldehyde combination. From the view of the internal salt structure of aliphatic amino acids and types similar to diketo-piperazines as the elementary units in the protein aggregates, the action of formaldehyde may be considered to consist in a chemical combination with the basic groups and a simultaneously occurring breaking-up of the closed structure. Bjerrum3 has pointed t o the fact that the Sarensen amino acid titration is quantitative first

1 Presented before the Division of Leather and Geliitin Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 t o 11. 1926.

* Bergmann, Collegium, 1943, 210; 1914, 209; Bergmann, Jacohsohn, and Schotte, Ib id . , 1923, 345; Bergmann, Ulpts, and Carnacho, Ib id . , 1922, 352; Bergmann and Ensslin, Ib id . , 1926, 493; Bergmann and Miekeley, Bcr., 67, 662 (1924).

8 Z. physik. Chem., 104, 147 (1923).

at pH 2 9. In the isoelectric state the aliphatic amino acids exist mainly as internal complexes: hence, only a slight fixation of formaldehyde can take place in this pH range. By activation of amino groups by the formation of the sodium salt (by addition of alkali), the reaction proceeds and is quantitative a t pH 2 9. Similar considerations may be useful in the treatment of the protein-formaldehyde prob- lem. It is also a well-known fact that part of the formalde- hyde is held in reversible combination with the protein. Secondary valency phenomena and adsorption reactions are probably responsible, a t least in part, for this particular behavior.

The view of an inactivation of basic protein groups and ac- tivation of the acidic groups by the formaldehyde treat- ment is supported, among many facts, by the following findings :

The isoelectric point of gelatin after this treatment is shifted toward the acid side with reference to the original isoelectric point.'

The combining capacity of such treated hide powder toward alkali hydroxide is increased and also the stahility of the re- sultant alkali compound, a fact in harmony with the view of activation of acidic groups as resulting from combination with formaldehyde. 6

Acid dyestuffs show a marked decrease in their affinity toward formaldehyde-collagen as compared to collagen proper, indi- cating a less number of available basic protein groups for this reaction.6

Further indication of the justification of this concept is offered by the decrease in acid binding capacity of the hide powder after formaldehyde treatment, first observed by Stiasny.' His

4 Gernwross and Bach, Collegium, 1922. 350; 1923, 377. 6 Gerngross and Loewe. Ib id . , 1922, 229. I Gerngross, Ib id . 1920, 565; 1921, 169. 7 Ibid.# 1908, 132.