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 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]	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 Q_max 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 COD_Cr, 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