Wastewater

(the text below is based on the chapter Wastewater published in yearbook Prague Environment 2004)

Legislation requirements for the waste water treatment in the Czech Republic

Since 1 January 2002 the new Act No. 254/2001 Code, on water and amending certain acts (the water act) approved on 28 June 2001 has been effective. The act has been amended several times, last time by the Act No. 20/2004 Code and now it harmonises the Czech regulations on water management with directives of the European Union.

Even though the Water Act imposes directly a number of duties on natural and legal entities, the setting of conditions for the wastewater discharge into watercourses has remained within the responsibility of the Government of the Czech Republic (pursuant to Section 38, paragraph 5 the Government shall establish acceptable values in its Order). Therefore on 29 January 2003 the Government approved the new 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.

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. Just for the sake of getting oriented in the issues let us compare requirements of emmission standards of the Order of the Government of the Czech Republic No. 61/2003 Code (hereinafter as OG No. 61) and those of the EU Directive for quality of 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]		COD [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
501–2000	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
Nad / Over 100 000	15	30	75	125	20	40	–	–	10	20	1	3

* “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. “p*” values for N_total* and P_total* 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]	COD [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 that requirements for the pollution discharged along with waste water in the EU Directive are less strict than those imposed in the Czech Republic. The Order of the Government of the Czech Republic No. 61/2003 Code introduced very strict limit values in a uniform manner, which in turn would lead to retrofits of waste water treatment plants with capacities 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 their economic potential.

The Government of the Czech Republic, however, robbed the citizens of the Czech Republic of this advantage “to proceed depending on its economic potential” by adopting the Order No. 61 in which they declared the whole territory of the Czech Republic as the “sensitive area”. All waste water treatment plants in the Czech Republic must comply with conditions of the OG No. 61 by 31 December 2010 at the latest.

 

Disposal and treatment of sewage (urban waste water)

The downtown sewerage system was founded in Prague at the beginning of the 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 3 WWTPs have integrated sewerage systems) and serve smaller parts of the City, which were separated communities in the past.

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. 61/2003 Code. Because the intensification of the Central Waste Water Treatment Plant (CWWTP) underwent, its stage Ia was designed in 1994 when limit values for discharged pollution were adjusted to then valid the Order of the Government No. 171 /1992 Code where only ammonia nitrogen of nitrogen compounds had a limit value established. On the approval of the phase Ia the water management authorities granted the CWWTP the permission to discharge on 22 November 2000 on condition that the permission is issued for the period expiring on 31 December 2005 and till that date a new permit shall be issued in which limit values complying with the OG No. 61 /2003 Code shall be established.

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 in tables:

 

Tab. - Permitted amounts of wastewater 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 Q_max is valid for one-hour period only

 

Tab. - Permitted values of selected indicators

	BOD [mg.l-1]		COD [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
In winter season							18	32			27	40

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

At the beginning of 2003 the CWWTP operations were still slightly affected by the incorparation of the biological stage of waste water treatment as well stabilising of the digestion process in digestion tanks. The stabilisation of treatment processes was enhanced not only by a warm spell in spring yet also the feeding of aluminium iron sulphate in March and April, which was renewed in December after a break. The annual discharge of pollution from the CWWTP fell below the permitted limits in every indicator thereof.

 

Tab. - Permitted and discharged annual amounts of the discharged pollutants from the CWWTP, 2003

CWWTP Prague	BOD [t.year-1]	COD [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	1 304,0	7 655,0	3 424,0	811,0	199,0	2 802,0

Values taken from the yearbook: Evaluation of the WWTP per year in 2003 operations of the PVK, a. s., Prague 2004

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 wastewater and takes it directly to recipient watercourses. Yet within the total annual balance of the pollution discharged this way is not important.

 

Tab. - Maximums and averages attained at the CWWTP in 2003

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 2003	Average in 2003
BOD	560,0	37,0	245,0	10,0
COD	1 400,0	226,0	666,0	57,0
Insoluble matter	1 100,0	156,0	462,0	24,0
N-NH4	37,0	21,5	28,0	6,3
Ninorg	37,0	27,0	30,0	17,0
Ntotal	77,0	38,0	55,0	22,0
Ptotal	17,0	4,1	7,9	1,5

Source: PVK, a. s.

Average inflow of waste water into the CWWTP in 2003 was 4.06 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, 1998–2003

Industry	Number of samples taken
	1998		1999		2000		2001		2002		2003
	Total	Excd.	Total	Excd.	Total	Excd.	Total	Excd.	Total	Excd.	Total	Excd.
Machinery and electric industry	197	84	144	36	163	111	200	116	236	98	295	134
Chemical industry	42	30	60	28	61	39	86	28	89	37	56	17
Energy industry	22	5	21	4	19	6	31	11	12	1	11	1
Food industry	61	36	60	24	52	27	63	31	74	33	34	29
Printing industry	8	2	8	2	7	3	10	7	17	7	6	1
Others	83	19	87	18	82	31	129	51	244	114	24	7
Total	413	176	380	112	384	217	519	244	672	290	426	189
%		43		30		57		47		43		44

Source: PVK, a. s.

It follows from the table that in 2003 both the number of checked values and the number of cases when limits were exceeded increased, which confirmed still persisting essential lack of discipline of respective producers in compliance with water management permit and with the Sewerage System Code although a negligible improvement may be seen in the percentage of violations.

The table here below 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 2003 are also given there just for illustration. It may be seen from the values given that for the application onto agricultural land values determined for chromium and cadmium, which average values exceed the limit values. The use of sludge would be troublesome even for maximums found in every element monitored. Within the prepared retrofit of the CWWTO, which should comply with the conditions of the water management established by the Czech legislation harmonised with the EU legislation, it will be necessary to design principally the sludge management also for the reason of hazardous materials contents in sludge.

 

Tab. - Contents of selected metals in pressed digested sludge from the CWWTP in the period 1996–2003 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	–
1996	128,4	216,0	356,7	1 681,0	4,9	75,6	74,0	4,9
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
Max 2003	410,0	250,0	520,0	3 300,0	22,0	120,0	13,0	7,2
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:
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 concentrations.

Source: PVK, a. s.