Sodium sulphate

Toxicity to microorganisms

Administrative data

Endpoint:

toxicity to microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Literature data

Data source

Reference

Reference Type:

publication

Title:

The effect of inorganic salts on the activated sludge process performance

Author:

Tokuz Yucel R. and Eckenfelder Wesley W. Jr.

Year:

1978

Bibliographic source:

Water Research Vol. 13. pp. 99 to 104. Pergamon Press Ltd 1979. Printed in Great Britain

Materials and methods

Principles of method if other than guideline:

37 days test with increasing concentration. The procedure for the test were the same as described in the Standard Methods (1971).

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Sodium sulphate

EC Number:

231-820-9

EC Name:

Sodium sulphate

Cas Number:

7757-82-6

Molecular formula:

H2O4S.2Na

IUPAC Name:

disodium sulfate

Test organisms

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source: the activated sludges were taken from a local municipal wastewater treatment plant.
- Acclimatation: activated sludge were acclimated to the substrate for a period of over a month.
- Feeding: the food to micro-organism ratio (F/M ratio) was approximately 0.3 mg COD/day/mg Mixed Liquor Volatile Suspended Solids (MLVSS) at the start of the experiments. The hydraulic detention time was about 2 days. Since mixed liquor solids has built up as substrate TDS level increased and since hydraulic detention time was not modified, the food to microorganism ratio decreased to about 0.1 gradually.

Study design

Test type:

static

Water media type:

freshwater

Total exposure duration:

37 d

Test conditions

Test temperature:

Kept at 20.5 ± 2°C

Dissolved oxygen:

The dissolved oxygen level in the reactors were maintained at about 8 mg/L and never dropped below 6 mg/L.

Details on test conditions:

TEST SYSTEM
- No. of replicate: three continuous flow activated sludge units were used.
- Unit volume: the total volume of each unit was 10 L of which 8 L were aeration chamber and 2 L settling basin.

No attempt was made to maintain the F/M ratio at 0.3 by wasting sludge (only wastage occurred when samples were collected for analysis), because of the problems encountered with 'deflocculating' sludge and resulting solid losses at the initial phases of the experiments. At such instances the sludge was highly dispersed and would not settle, resulting in large decreases in the concentration of sludge under aeration.

OTHER TEST CONDITIONS
Routine analyses on the cliluent included so!uble chemical oxygen demand, total suspended solids (TSS) and volatile suspended solids (VSS) determinations were performed.
Mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids were also determined daily.
Oxygen uptake rate was determined using a membrane electrode (YSI model 54A Oxygen meter, Yellow Springs Instrument Co., Yellow Springs, Ohio, U.S.A.).
- BOD of the substrate: 400 mg/L
- COD of the substrate: 1050 mg/L

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

37 d

Dose descriptor:

other: NOAEL

Effect conc.:

ca. 8 g/L

Basis for effect:

other: based on stalked ciliatcs

Effect concentrations 2

Duration:

37 d

Dose descriptor:

other: NOAEL

Effect conc.:

ca. 26 g/L

Basis for effect:

other: based on motile protozoa

Details on results:

The decrease in salinity from 25 g/L sodium chloride to less than 8 g/L improved the effluent quality greatly and subsequent switch to sodium sulphate did not cause any upset on the system even up to 30 g/L sodium sulphate concentration. The effluent remained clear and the COD removal efficiency was the same as the control unit.
Upon examination under a microscope it was observed that high salt concentrations caused filamentous micro-organisms to appear.
In the sodium sulphate system stalked ciliatcs disappeared early but even at 26 g/L sodium sulfate level, motile protozoa were observed.
The abundance of filamentous micro-organisms on the other hand did not affect the floc formation and ettling capacity of the sludge.

Applicant's summary and conclusion

Conclusions:

NOAEL at 37 days = 26 g/L based onmotile protozoa
NOAEL at 37 days = 8 g/L based onstalked ciliatcs

Executive summary:

The effect of inorganic salt sodium sulphate on the performanceof the activated sludge process was examined. Test was performed in 37 days, increasing concentration and the procedure for were the same as described in the Standard Methods (1971).

Conclusion

The effect of sodium sulphate on the system was low.

NOAEL at 37 days = 26 g/L based onmotile protozoa

NOAEL at 37 days = 8 g/L based onstalked ciliatcs