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Wastewater

(The text below comes from the chapter Wastewater published in yearbook Prague Environment 2006)

 

Legislation requirements for the waste water treatment in the Czech Republic

The Member States of the European Union are bound by the Council Directive 91/271/EEC of 21 May 1991 on treatment of urban waste water (Directive 91/271/EEC). In the Czech Republic regulations on water management have been harmonised with EU directives and regulations by means of the Act No. 254/2001 Code, on water and amending certain acts (hereinafter as the Water Act), which became effective on 1 January 2002 and has been amended several times since then. Pursuant to Section 38, paragraph 5 of the Water Act the Government of the Czech Republic shall establish acceptable values of pollution for the waste water discharge into watercourses and the Government established them in the Order of Government No. 61 on indicators and values of acceptable pollution of surface water and waste water, on details of the permit for the waste water discharge into surface water and into sewerage systems, and on sensitive areas, which became valid on 1 March 2003.

Just for the sake of getting oriented in the issues let us compare requirements of emission standards of the Order of the Government of the Czech Republic No. 61/2003 Code (hereinafter as the OG No. 61) and those of the EU Directive for quality of the waste water discharged.

 

Tab. Emission standards of indicators of acceptable waste water pollution pursuant to the Order of the Government of the Czech Republic No. 61/2003 Code

Source size (p.e.) BOD
[mg.l-1]
CODCr
[mg.l-1]
Insoluble matter
[mg.l-1]
N-NH4+
[mg.l-1]
Ntotal*
[mg.l-1]
Ptotal*
[mg.l-1]
p m p m p m p m p m p m

500–2000

30

60

125

180

35

70

2001–10 000

25

50

120

170

30

60

15

30

10 001–100 000

20

40

90

130

25

50

15

20

2

6

Over 100 000

15

30

75

125

20

40

10

20

1

3

The unit p.e. means the population equivalent load of one inhabitant.

* “p” values are acceptable concentrations and may be exceeded within a tolerable extent, which is established in the Annex No. 5 to the OG No. 61 (approx. in 10% of all determinations). “p*” values for Ntotal* and Ptotal* are yearly averages. “m” values are maximum concentrations, which may not be exceeded.

 

Tab. The Council Directive 91/271/EEC

Pollution source (p.e.) BOD
[mg.l-1]
CODCr
[mg.l-1]
Insoluble matter
[mg.l-1]
Ntotal*
[mg.l-1]
Ptotal*
[mg.l-1]

2000–10 000

25

125

60

10 001–100 000

25

125

35

15

2

Over 100 000

25

125

35

10

1

* Only for sensitive areas, year average is evaluated. Values of other indicators may be exceeded within a tolerable extent. The tolerable extent is the same as that in the OG No. 61, in which the table of exceedances was taken over from the Directive. The maximum values, which may not be exceeded, can attain double the values given.

It follows from the tables presented that requirements for the pollution discharged along with waste water in the EU Directive are less strict than those imposed in the Czech Republic. Therefore it can be stated that the OG No. 61 introduced very strict limit values in a uniform manner, which in turn would lead to retrofits of waste water treatment plants with capacity over 10,000 p.e., which would otherwise meet the requirements of the Council Directive 91/271/EEC (except for sensitive areas). The advantage of the Council Directive 91/271/EEC is it enables the Member States to set priorities in water protection by means of the establishing of so-called “sensitive areas” and to proceed at the revisions required every fourth year depending on, among others, their economic potential.

The Order No. 61, however, robbed the citizens of the Czech Republic of this advantage “to proceed depending on its economic potential”, which declared the whole territory of the Czech Republic as the “sensitive area” in the Agreement on the Czech Republic accession to the European Union. Even if all waste water treatment plants with capacity larger than 10,000 p.e. in the Czech Republic must comply with conditions of the OG No. 61 by 31 December 2010 at the latest, any reduction in the nitrogen and phosphorus pollution discharged from settlements lower than 10,000 p.e. may not be realistically expected without implementing further measures.

It must be recalled that a great portion of nitrogen is the input from drinking water sources. In the drinking water from the Želivka River on average 6.8 mg.l-1 total nitrogen were delivered to Prague in 2005, which accounts for approx. 66 % of the standard for average total nitrogen amount discharged. The new Water Act established that objectives for the improved state of water bodies shall be accomplished by 22 December 2015 yet the objectives are to be set on the basis of Water Management Plans of the Catchment Areas. Striving for the accelerated implementation of measures the public beneficial society of Clean Želivka River (Čistá Želivka) was established, which one of the objectives is to implement the “Set of Biotechnology Measures in the Area of the Želivka River Catchment Area”. The project with the application for support from the Cohesion Fund of the European Union includes the “Programme of Measures in the Želivka River Catchment Area” in order to provide for sustainability of the water source Želivka. The reduced content of nitrogen in drinking water should not merely bring better quality of drinking water yet also reserves in the CWWTP capacity concerning nitrogen contamination.

 

Disposal and treatment of sewage (urban waste water)

The downtown sewerage system was founded in Prague at the beginning of the last century as an integrated sewerage system taking the mixed sewage and rainwater in the same pipes. The newly built housing estates at the Prague outskirts have separated sewerage systems, which do not mix together sewage and rainwater and taking them away in separated systems. The housing estates sewerage systems are connected to main sewers of the Integrated Centralised Sewerage System in the downtown. This system disposes water to the Central Waste Water Treatment Plant (CWWTP) on the Cesar Island in Bubeneč. Besides this Central WWTP, there are other auxiliary (local) waste water treatment plants (24 in total) under operation or construction on the City territory, which mostly sewerage systems are led into (only WWTPs in Čertouzy, Miškovice, Újezd n. L., and in Kbely have integrated sewerage systems) and serve smaller parts of the City, which in the past formed separate communities. In 2005 these waste water treatment plants treated approx. 5.2 % of the urban waste water from Prague.

At present the CWWTP does not comply with the very strict requirements for discharged pollution in indicators of total nitrogen and total phosphorus pursuant to the new OG No. 61. Therefore the City of Prague has been preparing a vast retrofitting of the Central Waste Water Treatment Plant (CWWTP) at the Emperor’s Island (Císařský ostrov) in Bubeneč. On the basis of this fact the water management authority has issued on 23 June 2005 the decision on the prolongation of the current permit validity from 22 November 2000 to 31 December 2010.

Values permitted by the Department of Development of the City of Prague Re. No. MHMP-76063/2000/VYS/Tr of 22 November 2000 for purified waste water discharge from the Central Waste Water Treatment Plant Prague into the Vltava River at the river kilometre 43.3 are as follows:

 

Tab. Permitted amounts of waste water discharged

  Q24 Qday Qmax Qyear

CWWTP Prague

6,0 m3.s-1

7,0 m3.s-1

8,2 m3.s-1

189 216 000,0  m3.year-1

Value of Qmax is valid for one-hour period only

 

Tab. Permitted values of selected indicators

  BOD
[mg.l-1]
CODCr
[mg.l-1]
Insoluble matter
[mg.l-1]
N-NH4+
[mg.l-1]
Pc
[mg.l-1]
Ninorg
[mg.l-1]
p m p m p m p m p m p m

CWWTP Prague

20

40

80

140

25

70

12

18

1,8

4

22

32

For winter season

18

32

27

40

m = maximum acceptable value of concentration for analysis of simple samples of the waste water discharged
p = acceptable value of concentration for analysis of mixed samples of the waste water discharged

In 2005 the CWWTP operations were affected by failures of a great extent, the bad technical shape of low-pressure air blowers caused a year-long trouble. Due to their failures and repairs the output reserve was not in fully operational standby for a major portion of the year. Since 2006 there has been ongoing the investment for the replacement of the current blowers. The dosing station for polyflocculant into the after-settling tanks, installed in 2004, showed high failure rate in 2005 and was under limited use only. In the course of 2005 a new flocculating stations was installed before the settling tanks. Nowadays, the flocculant can be fed with higher effectiveness.

In the sludge management there was a abrupt discharge of sludge from the digester No. 7 due to the disruption of the digester jacket tightness. It was immediately shutdown and accidental repair was carried out. In September 2005 the repair of the digester tank No. 8 was started. There were still permanent troubles with screw conveyors for dewatered sludge transport into silos. Therefore the operator was compelled to pump one time a portion of digested sludge onto the sludge fields at Drasty, in order not to be forced to dump sludge on an open area. By the end of 2005 modifications were carried out to the handling tanks for pre-thickening of the excessive sludge, which enabled the simultaneous operation of the two handling tanks can be better controlled.

The Energycentre of the CWWTP generated, by biogas combustion in co-generation units, such amount of electric energy that covered approx. 73 % of the total energy consumption of then CWWTP. Despite the aforementioned troubles the operator managed to maintain effectiveness of the waste water treatment at such level that the CWWTP complied with the penalty fee limit of CODCr, which contributed to costs savings at the amount of approx. CZK 40 million. Yet the course of the year 2005 demonstrated that investments, which shall lead to the complete retrofitting of technology units and plants, must be launched.

 

Tab. Permitted and discharged annual amounts of the discharged pollutants from the CWWTP Prague in tonnes per year in 2005

CWWTP Prague BOD
[t.year-1]
CODCr
[t.year-1]
Insoluble matter
[t.year-1]
N-NH4+
[t.year-1]
Pc
[t.year-1]
Ninorg
[t.year-1]

Permitted

2 838,2

13 245,1

3 784,3

1 892,2

238,8

3 784,3

Discharged

658,0

4 463,0

1 077,0

491,0

96,0

1 842,0

The values are taken from the yearbook: Evaluation of the WWTP operations of the PVK, a. s., Prague 2006

Yet the pollution discharged from the CWWTP is not the only source of pollution to the recipient watercourses. As mentioned above in rainy periods the integrated sewerage system separates a portion of the mixed rainwater and sewage and takes the mixture directly to recipient watercourses. Yet within the total annual balance of the pollution discharged this pollution contribution is not important.

 

Tab. Maximums and averages attained at the CWWTP in 2005

Quality indicator
[mg.l-1]
Inflow
to the CWWTP
(max)
Discharge from
the CWWTP
(max)
Inflow to the CWWTP Discharge from the CWWTP
Average in 2005 Average in 2005

BOD5

410,0

21,9

238,1

5,50

COD

1 100,0

104,6

574,3

37,30

Insoluble matter

548,0

57,0

334,0

9,00

N-NH4

39,0

20,0

28,4

4,10

Ninorg

39,0

25,8

29,4

15,40

Ntotal

66,7

31,4

50,1

17,80

Ptotal

14,0

2,3

6,6

0,78

Source: PVK, a. s.

The average inflow of waste water into the CWWTP in 2005 was 3.79 m3.s-1, which means a moderate yet permanent annual decrease in inflow compared to yearly average of the previous years.

The pollution produced, which is taken out with waste water to the CWWTP, is limited by means of the Sewerage System Code. The PVK, a. s. has a department, which carries out checks of pollution producers in terms of their compliance with the Sewerage System Code.

 

Tab. Results of inspections of the Sewerage System Code compliance, 2000–2005

Industry Number of samples taken
2000 2001 2002 2003 2004 2005
Total Excd. Total Excd. Total Excd. Total Excd.  Total Excd. Total Excd.

Machinery and
electric industry

163

111

200

116

236

98

295

134

383

122

403

184

Chemical industry

61

39

86

28

89

37

56

17

66

22

56

17

Energy industry

19

6

31

11

12

1

11

1

5

1

6

1

Food industry

52

27

63

31

74

33

34

29

61

31

45

33

Printing industry

7

3

10

7

17

7

6

1

12

5

10

4

Others

82

31

129

51

244

114

24

7

42

33

164

62

Total

384

217

519

244

672

290

426

189

569

214

684

301

%

57

47

43

44

38

44

Source: PVK, a. s.

It follows from the table, that in 2005 the PVK, a. s. again increased the number of checked entities. The percentage of exceeded values in samples checked was again at the level in 2003, which confirms still persisting essential lack of discipline of respective producers in compliance with water management permit and with the Sewerage System Code.

 

Tab. Contents of selected metals in pressed digested sludge from the CWWTP in the period 1997–2005 compared to values of 1989 [mg.kg-1]

Year Chromium Lead Copper Zinc Cadmium Nickel Cobalt Mercury

1989

742,0

400,0

713,0

2 333,0

22,8

121,0

1997

73,1

191,8

338,1

1 395,0

5,3

58,4

5,2

2,7

1998

79,6

125,1

326,2

1 198,0

4,2

46,5

5,5

2,6

1999

149,6

93,3

266,0

1 144,0

4,0

42,0

8,9

3,9

2000

193,0

89,0

308,0

1 314,0

5,1

41,1

10,1

4,4

2001

227,0

81,0

298,0

1 612,0

3,8

46,5

9,3

3,8

2002

311,0

83,0

322,0

1 544,0

3,6

55,3

9,8

3,1

2003

271,0

119,0

359,0

2 424,0

6,7

67,2

8,7

4,0

2004

254,0

84,0

335,0

2 837,0

2,9

74,0

10,0

3,6

2005

92,0

124,0

332,0

1 179,0

2,8

51,0

9,8

3,0

Max 2005

190,0

470,0

370,0

1 900,0

4,3

75,0

15,0

4,6

Limit pursuant
to Czech Standard

1 000,0

500,0

1 200,0

3 000,0

13,0

200,0

10,0

Decree No. 382/01 Code

200,0

200,0

500,0

2 500,0

5,0

100,0

4,0

Note: For the sake of information there are limit values of selected metals for the permitted sludge usage given as follows:
a) for the production of industrial composts pursuant to the Czech Standard ČSN 46 5735 effective since 1 June 1991;
b) into agricultural land pursuant to the Decree No. 382/2001 Code, effective since 1 January 2002, and giving limit concentration values.

Source: PVK, a. s.

The table here above give yearly averages for respective years. Because the Decree of the Ministry of the Environment of the Czech Republic No. 382/2001 Code, on conditions of the usage of treated sludge on agricultural land, establishes limit values of concentrations of selected hazardous materials for the application onto agricultural land, their maximum values determined in 2005 are also given there just for illustration. It may be seen from the given values that the application of sludge onto agricultural land was troublesome due to the maximum concentration of lead and mercury

Print 27.6.2007 | Jiří Stach | Read: 13686 x
 
 
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