Special on : TOC

( article : TOC-E-4 )

River Monitoring

A river water monitoring, upstrean and down stream , a Chemical Plant in North of Italy

Dr.Carlo Coco

Introduction
In northern Italy operates a chemical industry which produces intermediates for dyes.
Three are the basic substances used: naphthalene, benzene, anthraquinone.
From these substances, after sulfonation, nitration and amination, it is possible to obtain intermediates :beta naphthol, alpha anthraquinonsulfonic salt and nitrobenzene are the most important from a commercial point of view.

Waste Waters Characteristics
Intermediates for dyes processing determines production of waste waters presenting high COD levels and a high salt content essentially due to salification of acids used for sulfonation and nitration.
Waste waters flow is approximately 1500 cubic meters per hour.
To the waste waters flow resulting from the industrial process , is added a new stream of approximately 100 cubic meters per hour.

This stream originates from storm waters and ground waters.
Those waters are passing through an internal dumping system that has been created since the beginnings of productive activity ( going back up the end of the 18th century) and they are also flowing through the productive area which is highly contaminated by losses of the old sewer system: in such way they are loaded up with water-soluble organics.

MONTHS ------------ upstream ----------------------------down stream
...............................mg/lof:TOC .....O2 ............................TOC ........O2

• JANUARY .....2.6..... 8.4 ......................................5.1 ..........7.6
• FEBRUARY ...3.0..... 8.2....................................... 6.0........... 7.3
• MARCH ........2.9 .....7.3 .......................................6.3........... 6.3
• APRIL ..........2.7...... 7.7...................................... 4.7 ..........5.4
• MAY ............ 2.3 ......6.9......................................4.6 ..........6.4
• JUNE ........... .2.2...... 5.7......................................4.8 ..........4.4
• JULY .............2.0 .....4.6 ......................................4.3.......... .5.8
• AUGUST .......1.9 ......4.8 ......................................4.1 ..........5.3
• SEPTEMBER .3.8..... 7.2........................................4.8 ...........5.8
• OCTOBER .....3.5 .....9.0 .......................................4.9 ............5.7
• NOVEMBER. .2.2 .....9.9 .......................................5.0 ............6.8
• DECEMBER ...1.2 ....11.6 ......................................5.2 ............6.9

Water treatment and river waters monitoring systems
Waste waters are collected in appropriate wells and drawn out by water pumps.
In order to be treated they are then sent to the waste water plant which has a chemical-physical treatment and a biologic treatment.
The biologic treatment is made of two sectors: one aerobic and one anaerobic.
This treatment plant is very effective, giving quite good results and has an high efficiency.
Nevertheless, since the water volumes to be discharged are very high, in order to monitor the effects of these wastes on the river environment, two monitoring stations have been placed, for sampling and the on-line analysis.
One has been placed 500 meters upstream the chemical plant, the other has been placed 500 meters downstream the discharge of the plant into the river water.
These two monitoring stations have a sampling system which consists of a water pump directly located in the river flow , where the river flow is measured and the sampled waters are then delivered to the monitoring station where the sample is filtered and analysed.
Inside each station are placed automatic systems for the analysis of TOC, dissolved O2, pH, temperature and salinity, a recorder and a refrigerated sampler.

Results
During a four years period every day have been collected the analytical resaults from each analyser and then the individual data have been processedt
As shown in the table, data recorded by the upstream monitoring station point out a Total Organic Carbon mean value of 2.5 mg/l approximately.
TOC values recorded downstream the industrial discharge have an average of 5 mg/l.
Also oxigen values into river waters has been monitored and evaluated : it is evident that the O2 content downstream the chemical plant is only a little bit lower then the upstream one.

Remarks
TOC and O2 values are affected by environmental changings typical of the different seasons of the year.
One parameter to be considered is also the river flow, higher during winter and lower in summer or late spring.
An other element to be considered concerns the rains that is washing away the woods facing the river, thus supplying waters with organics during winter time.
These rains, together with a low temperature of waters during the winter, promote an O2 saturation, thus reaching its highest concentration during winter months.
During the summer the TOC values are generally lower, not only because there is no soil washing away, but probably also for a raise in the temperature of water which promotes oxidation reactions of organics by dissolved oxigen.

Conclusions
TOC mean value recordered downstream the industry is highere then the one recordered upstream, pointing out the industrial activity contribution, while a little difference has been noticed regarding O2 content in both drawing points; this is due to saturation contribution of the final sedimentation tank of the tretament plant

 

	back to
	back to : a special on TOC
	©copyright STATE-OF-THE-ART®