The Nègrepelisse WTP - The performances

The Nègrepelisse WTP respects the outlet quality imposed on the BOD, COD and SS parameters. With the ponds in the treatment steps, the TKN and Pt contents are under the usual stocks.

 

Discharging quality

The treatment plant’s function is to clean up the wastewaters before discharging it in the environment.  The plant’s performances are evaluated in two forms: principal pollutants contents in the discharged water and the efficiency of eliminating these pollutants. The contents and efficiency are calculated on normalized measures with a “24 hours assessment”, ie the measurement of quantity and quality during 24 hours at the plant’s entrance and exit. In Nègrepelisse these measurements are done once a month by SATESE 82.

The joined charts give the outlet contents and the elimination efficiency of the principal pollution indicators, on average for the year and on average for the 6 summer months when the ponds are integrated on the treatment steps.  The PE column gives the average inlet pollution load calculated dividing the daily COD load with 0.120 kg, an inhabitant’s average provision. The line “Dumping Norm” gives the maximum content or the minimum efficiency according to the rules (for Nègrepelisse, no imposition on TKN, NGL, Pt)

Download the analysis results
for the SATESE 82 for 2009-201

Outlet contents

The outlet contents don’t change much from one year to another and are very under the maximum authorized. The TKN and NGL contents are weak for an intensive process.  Like usual in a constructed wetland plant the Pt contents are high regarding that the filters have little effect on this parameter.

Efficiency

The efficiency doesn’t change much from one year to another and are above the recommended minimum. The efficiency on the TKN and NGL are high for an intensive process. Like usual in a constructed wetland plant the efficiency on Pt are weak regarding that the filters have little effect on this parameter. The efficiency on TKN, NGL, and Pt are improved in summer when they pass into the ponds.

Impact on the stream

The communal treatment plant’s discharges are a lot more important than the usual natural rate of flow at the lowest water level: for 4000PE, the plant’s contributions will be 25 times more important than those of the Montrosies natural overturning basin and 2.3 times more important than those of the Courounets natural overturning basin; for 6000 PE, the plant’s contributions will be 39 times more important for the and 3.5 times more for the Courounets.

Statically, this situation happens every 5 years. The dilution is usually more important, in particular when it rains. Nevertheless, the two streams’ state will stay poor when the water is low, also because of farming pollution.

 

Capacité	WSP	Montrosies	Courounets	WSP/ Montrosies	WSP/Courounets
Wsp 4000 PE	7.6 l/sec.	0.3 l/sec.	3.3 l/sec.	25	2.3
Wsp 6000 PE	11.6 l/sec.	0.3 l/sec.	3.3 l/sec.	39	3.5

Treatment plant: average daily flow rates on dry days Streams: low water level estimated with specific flow rate Qmna5 = 0.3 l/sec

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