tatjana mijuskovic - svetmovic the great importance. · 2014. 5. 14. · tatjana mijuskovic -...

The water quality prognosis of the River Drava

Tatjana Mijuskovic - Svetmovic

Faculty of Civil Engineering, University of Osijek, 31 000 Osijek,Croatia

E-mail: [email protected]

Abstract

The river Drava is the biggest drinking water supplier, as well as essential with its water foragriculture, industry, fishing, river navigation, tourism and recreation, furthermore it is usedfor energy production. Since the river is also a big waste water recipient, its protection is ofthe great importance.The waste water coming from the city of Osijek itself and neighbouring urban areas togetherwith industry waste water is discharged into the river without being treated, causing asignificant pollution, worsening the water quality, so that at this point it does not meet theprescribed II. class criteria.The paper describes the downstream water quality prognosis of the river Drava, determinedwith the classical one-dimensional Streeter-Phelps" model, that takes into account onlybiochemical processes decomposition and reaeration. Since the waste water outfall is 12.1 kmfar from the Drava river mouth in the Danube river, the complete waste water mixing withriver water does not occur, it was necessary to extend Streeter-Phelps' model with thefollowing formulas: with Lapsev's formula for the initial hydraulic dilution, Froll andRodzirel's formula for waste and belonging river water mixing coefficient (subsequentdilution) as well as Potapov's formula for turbulent diffusion coefficient.The developed model has been applied in order to predict the river water quality, Osijek wastewater discharge condition directly, without waste water treatment plant as well as todetermine waste water discharge condition using the waste water treatment plant and also toexamine seasonal discharge conditions. The required waste water treatment degree wasdetermined taking into account the river Drava ability for self-purification as well as proposedCroatian regulations for waste water discharge into the rivers and sea (according to EuropeanCommunity regulations).

1. Introduction

The river Drava springs in the south part of Tyrol, close to Dobiaca(Italy) and enters the Republic of Croatia close to the place called Ormoz on theSlovenian border, 325 km away from its well. The river Mura enters the river

Transactions on Ecology and the Environment vol 14, © 1997 WIT Press, www.witpress.com, ISSN 1743-3541

598 Water Pollution

Drava 75 km downstream and from that place till Donji Moholjac, it creates theborder between Croatia and Hungary. After 305 km of its flow, the river Dravagets into Danube close to Aljmas.

The river Drava with its water is essential for the agriculture, industry,fishing, river navigation, tourism and recreation, as well as for the energyproduction, but the waste water is also discharged into the river.

When the river Drava enters Croatia, its water quality is far from therequired one, due to the waste water discharged in Slovenia and other upper-flow developed countries, though in them we have observed considerableprogress in waste water treatment. The water quality of the river Drava is highlyinfluenced by the river Mura, whose stream getting into Croatia, can be classifiedin the class III The downstream section of the river Drava is being polluted bythe waste water from the urban areas along the river's flow, since most of theseplaces still have no waste water treatment plants.

The waste water coming from the city of Osijek and neighbouring urbanareas together with the industry waste water is discharged into the river withoutbeing previously treated, causing the significant pollution, worsening the riverwater quality so that it does not meet the class II. criteria. The city of Osijek hasalready built the biggest part of its sewerage, also the south collector - wastewater drain in the river Drava is in the process of its construction. The fact thatthe system is about to be finished and that the pollution condition of the river isquite serious, causing an urgent need to solve the problem of city waste watertreatment, together with its neighbouring urban areas. The Convention of theriver Danube protection that Croatia signed with the European Union in 1994. inSofia would hasten the solution.

This paper presents the river Drava quality prognosis on its downstream,applying classical and extended Streeter-Phelps one dimensional method. Paperalso present the degree of waste water treatment necessary, in consideration ofthe river's self-purification ability, and the prescribed regulations for the wastewater discharged into the rivers and sea for Croatia (following the existingregulations of the European community), under the condition that the waterquality of river Drava meets the class II. criteria.

2. The mathematical choice method

In order to determine the self-purification ability of the river Drava, weneeded a lot of data and indicators. Usually the violations of the prescribed waterquality regulations are the dissolved oxygen and organic presence in the water(BOD$), therefore these indicators played an important role in the model choice.

Choosing the model, we assumed that the biodegradable waste matterwould be discharged into the river, followed by the strict control of hardlybiodegradable and unbiogradable waste substance, whose concentration or/andaccumulation into the alive organisms would cause deterioration of the waterecosystem.


Water Pollution 599

The mathematical models validity, that describe processes of dilution,diffusion and biochemical degradation first and foremost depends on the numberof interdependent values, especially on the coefficients reliability, which are theresult of the water system study. Due to the nature of the distorted values, itwould be better to apply the mathematical models that describe the processeswith stochastic indicators. However the simple deterministic models are alsovery often used, because their results are very precise when we want to predictthe critical conditions and reach the right decisions.

When we want to determine model complexity we have to consider thefact that the number of the needed data (which we can obtain only by runningexpensive and long tests) increase with the model complexity . We do notusually have these data in the planning period, but we would obtain them fromtests that are the result from the beginning analysis. Therefore, in order tosimulate the Osijek downstream water quality of the river Drava, we havechosen the one dimensional model - classical Streeter-Phelps formula, that takesinto consideration only the biochemical decomposing processes and reaeration.

-KitL,=L^10 1 (1)

K2-K]

where is:

KI - deoxygenation rate (logarithmic base 10) [ day ~* ],K: - reaeration rate (logarithmic base 10) [ day ~* ],Lt - the organic material content of water expressed as BOD in time t

[mg/L],La - - the initial BOD concentration in the river, downstream of the effluent

outfall [ mg/L ],t - time of biochemical reaction [ day ],Da - the initial oxygen deficit in the stream, downstream of the effluent

outfall [ mg/L ],Dt - the dissolved-oxygen deficit in time t [ mg/L ], .

The classical Streeter-Phelps model assumes the complete mixing of thewaste water, including waste matter with the river water. However, the completemixing of the waste water and river water does not occur at the shorter distancesfrom the outfall , so that within the stream we have a "plume" of the waste waterand some river water Since the waste water outfall of Osijek should be at the12+100 km of the river Drava, 12.1 km far from the Drava river mouth in theDanube, the complete mixing of the waste water with the river water would notoccur, so we had to extend the Streeter-Phelps model with the followingformulas: with Lapsev's formula [2] for the initial hydraulic dilution (formula 3),Frol and Rodziller's formula [1,2] (formula 4) for the mixing coefficient of thewaste water and belonging river water, as well as with Potapov's formula [2],(formula 6) for the turbulent diffusion coefficient.


600 Water Pollution

(3)1-m

where is:S initial dilution,m ration of stream flow velocity to waste water flow velocity,d ration of the "plume" diameter d to outfall pipe diameter do. For the outfall

with one pipe, in the practical purpose, is used as ration of stream flowdepth H to outfall pipe diameter do.Part of stream flow which is mixed with the discharged waste water is

expressed with coefficient y, according to Frol and Rodziller [1,2] and is

equal to:

Qowhere is:a coefficient which depends on hydraulic mixing condition

(5)

cp - coefficient of the stream indentation - relation of main current streamlength Lm to straight line length from outfall to estimated cross-section Lpr;£ - coefficient depending on the outfall position (for side-bank outfall =1);E - turbulent diffusion coefficient [m"/s], according Potapov's formula forlowlands river is [2]:

200H - mean depth of river flow [m],Vp - mean stream flow velocity [m Is]

Qo - waste water flow [m* /s];QP - stream flow [m* /s];L - distance between estimated cross-section and the outfall [m].

3. Input data

Hydrological characteristics of the river Drava. The river Drava in the"downstream section" shows the valley alluvial stream characteristics. The waterlevel and the water temperature are controlled at the water gauge (thelimnograph location is 19+200 km of the river Drava) every day, but since theriver Drava is backed by the Danube close to Osijek, it is impossible to determinethe flow uniformly, applying consumption curve, so consequently we use thedata from Belisce water gauge (53+800 km of the river Drava) to estimate therelevant flow and to get information about the flow that is correct enough.


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The basis criteria for the low flow water are prescribed by our laws andregulations, defining the relevant low water as: monthly low waters with 95%certainly for unregulated streams including river Drava in the observed section.So, we analysed the low flow and the results are presented in the Table 1.

Table 1. 95 % certainty of minimal monthly, minimal monthly average, andminimal annual flows

GAUGING STATION: BELISCEPERIOD: 1962.-1993. YEARTYPE OF CURVE: LOG-PIRSON III

MONTHFLOW[t»/i]MONTH

FLOWJm/^ /

/185

JX

214

//180

X

201

///202

XI

191

IV265

XII

191

V311

VI316

min annualflow171

VII282

VIII236

min averagemonthly flow

221

Morphometncal and hydraulic characteristics . In order to determine thesevalues for the river Drava downstream from Osijek for the relevant flows, weused the data of the worst condition, regarding the diffusion and the water traveltime. These data is needed to calculate the organic decomposition, as well as theinitial and the subsequent hydraulic dilution.The accepted input data are:• mean stream flow velocity \v = 0.5 m/s• mean depth of flow H = 1.7m• channel slope 1 = 0.018 %• coefficient of the stream indentation (p = 1.067

Organic waste load. The relevant waste water flow, including the organic wasteload is accepted according to [3]:• the equivalent inhabitant number• organic waste load in relation of BODs for the

mentioned El• the mean daily flow of waste water, in the dry period• the relevant hour flow in the dry period• the mean concentration of BOD< in the waste water in

the dry period• the waste water temperature (min - max.)

The Republic of Croatia proposed regulations for the waste waterdischarge into the streams and sea according to the European Communityregulations, as well as German laws for the industrial waste water that consists ofthe biological decomposing organic waste. The regulation [4] allows the wastewater discharge in the streams of the class II., under the condition that the thirdwaste water treatment level result, before discharging into the stream, meets thecriteria of 25 mg/L 6 BOD5.

794 000 El47 640 kg/day Oo

136013 nf/day6 659 m'/h350 mg/L

12 C - 25%


602 Water Pollution

The deoxygenation rate and the reaeration rate. The deoxygenation rate K/and the reaeration rate K]' are determined on the basis of field measurements ofDrava water quality data for the period from 1980 till 1989., obtained betweentwo water sampling stations Donji Miholjac and Bistrinci (Picture 1.). Thissection is chosen because between these two sites on the observed stream, thereare no tributaries and there are no channels with waste water that would bringmore water and/or waste water.The obtained data are functioning as guidelines, since the very measuring wasperformed under different conditions than simulated by this model. Nevertheless,comparing the results, based on the data with the study results, and based on thesimilar water systems, we could choose the processes' coefficients with enoughaccuracy to preliminary estimate the river Drava water quality condition.

SAl

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Picture 1. The gauge stations situation on the river Drava downstreamsection

Reaeration rate KI [1,5] is obtained according to following formula:

(7)At LB

where is:At - time of travel [day * ],LA - BOD concentration values measured at upstream A points of the stream,LB - BOD concentration values measured at downstream B points of thestream.


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Deoxygenation rate is obtained for the temperature in the time ofsampling. For other temperature the correction is used according to formula :

K(T/c)=K(T/c)0^"^ (8)

where is:8 - a temperature coefficient which is depended of process type,Ti2 - a temperature of the water.Deoxygenation rate for the temperature of 20° C, and for the temperaturecoefficient 8= 1.047 is KI = 0.1306 I/day, which is acceptable according togreat volume of suspended solids in the Drava

Reaeration rate K.2 [1,5] is obtained according to following formula:

K K LF^2 — JVi •= —AD

D 2.3 At D(9)

where is:

L - average oxygen demand concentration in stream section,

D - average oxygen deficit in stream section,AD - change in oxygen deficit from upstream to downstream sampling points.Coefficient K? correction for the 20° C temperature is done according toformula (6), for temperature coefficient amount 8=1.0159. For the obtainedcoefficient KI, reaeration rate coefficient K is calculated and for 20 °Ctemperature is K% =0.2611 I/day.Using Fair's formula, we have f= K.2/ Ki=2.00. According to Fair's classification[6], the result is characteristic of streams falling between "large slow rivers"group and "large river with medium flow velocity" group.

physical and chemical characteristic of the river Drava. Physical and chemicalparameters of the river Drava from the sampling station Visnjevac (23+600 kmof the river Drava) ( Picture 1.) were used as the input data and they are shownin the Table 2. This sampling station is placed upstream of the waste wateroutfall - Nemetin (10+900 km of the river Drava).

Table 2. Physical and chemical parameters at the sampling station of Visnjevac

parameter

water temperature (°C)dissolved oxygen (mg/L O:)saturated oxygen (%)BODs (mg/L O:)

mm

04.4015.000.03

max

2618.60175.0012.60

average

11.899.44130.232.57

summerconditionAugust

21.38.6796.902.94

winterconditionFebruary \

2.810.7679.88298


604 Water Pollution

4.The study results

The developed model is used to predict the water quality of Drava, aswell as the Osijek's waste water discharge condition directly without beingtreated before getting into the river and also the waste water condition dischargeafter treatment in the waste water treatment plant, and also to examine differentseasons discharge conditions. The water quality prognosis is done for the dryperiod, since it describes the worst critical conditions.

Oxygen household and biochemical decomposition of the waste matterare calculated only for the waste point source, while the waste distributedsources are approximated with the waste water concentration - BODs in streamon the site immediately upstream from waste water outfall.

The necessary degree of treatment for Osijek's waste water in relationto BODs concentration, determines maximal allowed BOD< concentration in theoutlet of the waste water treatment plant which makes sure downstream - at theDrava river mouth in the Danube river - expected use of stream, respectivelylegally allowed BODs concentration for the stream class II. of 4 mg/L O?

The extended, with formula for initial and subsequent dilution, Streeter-Phelp's model results ("plume") for the mentioned conditions are moreunfavourable, and these results are shown in the Picture 2. The degrees ofOsijek's waste water treatment necessary, for single cases and conditions, areshown in Table 4.

Table 4 The degree of Osijek's waste water treatment necessary

CONDITIONmax. allowed concentration of BODg inthe waste water (mg/L 0%)- complete mixing- " plume "

necessary degree of treatment- complete mixing- " plume "

average

212.737.7

39.2389.23

mater

118.726.45

66.1092.44

summer

187.429.9

46.4691.46

5. Results discussion and the conclusion

Analysis of the waste assimilation capacity, regarding the waste waterfrom Osijek, stresses the strong necessity to install the waste water treatmentplant with the third purification level, that should be installed as soon as possible.This is extremely important since Croatia as the country that belongs to theDanube river basin, signed the Protection Convention of the river Danube.

Predicting the water quality of the river Drava, based on two indicators:dissolved oxygen and BODs, we could conclude that when we discharge wastewater using the waste water treatment plant with the BODs concentration of,according European Union guidelines and the new regulations, that would be


Water Pollution 605

passed in Croatia, 25 mg/L O] as well as for oxygen and for BODs, in the case ofthe relevant low flow, we can meet the limiting values of the stream class II. atthe Drava's mouth into Danube, 12.1 km downstream from the waste wateroutfall.

The advantage of the Drava pluvioglacial water regime, in comparison tothe rivers belonging to Sava and Adriatic river basin, is that it is rich with waterin the summer months, influencing the river water quality and acceptance abilityof the waste water

The critical period of the river Drava water quality, regarding BODs, iswinter, since at that time the required waste water treatment degree is 92,44%,close to the planned one of 93%, demanding the outfall concentration of BODsin the outlet of the waste water treatment plant 25 mg/L O:

The dissolved oxygen, due to the good stream aeration and the oxygensaturation, are not critical parameters for the river Drava water quality.Comparing the results based on the calculated complete mixing of the wastewater with the river water at the waste water outfall cross-section and the variantwith "the plume", we can see that there are significant result differences, pointingout that in order to determine the water quality we must take the hydraulicconditions in the consideration. It is extremely important since the waste wateroutflow is 12.1 km far from the river Drava mouth in the Danube, causing themixing of the waste water with some of the river water.

References:1. Tedeschi, S.: Simulation of the Sava river water quality in Zagreb area,

Water Management (Vodophvreda) 14, Belgrade, 1982., pp 279-285. (inCroatian)

2. Fedorov, N.F. and Sifrin, S.M.: Sewerage, High School, Moskva, 1968., pp240 - 277. (in Russian)

3. Preliminary study of the Nemetin's waste water treatment plant influence onthe environment, "Institution for the regional planning" - Osijek, Osijek,1993.g. (in Croatian)

4. Ahel, M. et al..: Requests for the domestic and industrial waste waterdischarging in streams and sea, pp 119-129, Conference Base of the streamand sea protection strateg)' in the Republic of Croatia, Professional basis,Opatija, 1993. (in Croatian)

5. Nemerow, N. L.: Liquid waste of industry, Addison-Wesley Publishing Co.,reading Massachusetts, 1971, pp 26-29.

6. Jolankai, G : Hydrological, chemical and biological processes of• contaminant transformation and transport in river and lake system, A state-of-the-art report, fflP-IV Project H-3.2, UNESCO, Paris, 1992.


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tatjana mijuskovic - svetmovic the great importance. · 2014. 5. 14. · tatjana mijuskovic -...

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