Water Availability and Use

The annual average per capita water availability is less than 1000 m3/cap/y (about 2000 Vcapld) and an average of 20% of this amount is used. According to different classifications (see e.g. Kulshreshtha, 1993) these values identi@ a region with marginal water vulnerability, so management is not an easy task. The situation is much worse if we consider summer low- flow periods. For instance, in August 1992 (the second driest August since 1961) the corresponding figures were 650 Vcapld and 53% usage, which spec@ a class of "water stress"

fiom the viewpoint of management.

On the availability side the runoff coefficient is smaller than for most other Slovakian rivers, and the low level of quality prohibits many water uses. This lack calls for water transfers from other regions. Public water supply relies heavily upon subsurface waters of high quality distributed from the Gabcikovo region near Bratislava.

Altogether nearly 1 m3/s is imported, about 50% from the Gabcikovo area, and the other half from Jelka and Turcek. Half of the public water is used for domestic purposes. Industry uses

12%, losses are estimated to be close to 20%, and another 20% is unaccounted for.

On the basis of data for 1992, the average water use was 3.1 m3/s (the return flow represented 67% of it). The distribution according to various sectors was 35% for industry, 6% for agriculture, 15% for energy, and 44% for households. During summer months the proportion of agricultural and household use increases (the latter up to about 50%). Water uses in industry, agriculture (reduced by 50% in 1992 due to ongoing structural changes), and energy production rely almost filly upon surface waters, while public water supply utilizes exclusively groundwater resources. In August 1992 there were several days when more than 70% of the flow monitored at the mouth had already been used. If we also consider availability and demand on smaller scales, it is evident that water management is not a straightforward task under critical low flow conditions.

Both surface and subsurface water intakes are shown (together with emissions) in Figures 3.5 and 3.6.

In summary, surface waters are used for the purposes of industry, agriculture, hydropower, and waste disposal. The quality at most of the locations is so poor that recreational usage and fishing are out of question (though the public may not be aware of the high risk of bodily contact).

3.3 Municipalities

The ratio of public water supply in the entire watershed is somewhat less than 70%. In larger municipalities the coverage is close to 100% (see Chapter 6), while it is still above 80% for settlements in the >500 population domain. The development of the (combined) sewerage network is lower by about 20% than that of supply. The situation is particularly poor in smaller settlements. For instance, wastewater collection is practically absent in villages with fewer than 4000 inhabitants. The major problem, however, is the low level of wastewater treatment (see Chapter 6 for details). Treatment plants exist in no more than eleven municipalities where about 50% of the generated wastewater is treated (see Figure 3.7

showing influent BOD-5 loads and the treated portion). As can be seen from the figure, most of the treatment plants are significantly overloaded; the average annual wastewater flow is double the design capacity. (All the treatment plants are mechanical-biological plants with the high load activated sludge process; that is, no nitrification takes place.) Thus the effluent BOD-5 value can exceed 60-70 mg/l, with only 70% (or smaller) removal rate--a very low figure (these values show one reason for the poor quality of receiving rivers). The contribution

Figure 3.5 Surface water intakes and emissions in the Nitra River basin.

of industrial discharges to municipal wastewaters is high and sometimes close to 50%. It causes problems not only due to the frequent lack of pre-treatment (which leads to difficulties such as sludge disposal), but also because of high flow fluctuations.

Municipalities contribute to about 70% of the total BOD-5 emission in the catchment. This value illustrates their crucial role in water quality management. The rest of the BOD-5 emission comes from industry; the role of agriculture is negligible.

About 70% of public drinking water is used for domestic purposes (- 200 Vcapld), while the rest is mostly for industrial uses. As indicated earlier, roughly an equal amount is used from surface intakes, again for industrial purposes. Aged infrastructures leading t o high water losses from the distribution network and infiltration to the sewer system, cause general problems in nearly all the municipalities. The needs for stormwater management and sludge treatment and disposal are also issues for most municipalities.

Figure 3.6 Groundwater intakes and emissions in the Nitra River basin.

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3.4 Industrial Emissions

INDUSTRIAL DISCHARGES

A MUNICIPAL DISCHARGES

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Larger industrial emissions of BOD-5 are displayed in Figure 3 . 8 in a similar fashion to that for municipalities. Major industrial areaslplants include Surany, Nitra, Bosany, Luzianky, Kostolany, D.Ohaj and Chynorany. Several sugar beet factories with seasonal operation (which generally starts in October) can be found in downstream regions of the watershed.

Some other industries are tanneries, chemical factories, canning, meat, milk and vegetable processing plants, and wine and spirit production plants. The thermal power plant at Kostolany which uses low-quality brown coal should be mentioned also. Its residual ash has high arsenic content, so this plant is the likely reason for the high arsenic concentrations monitored (see Chapter 7). Wastewater treatment is rather poor, and sometimes missing (e.g.

at the sugar beet factories in Surany and Mraziarne Nitra). The treatment is often only mechanical, and discharges frequently go to the municipal sewerage system. In addition to mechanical treatment, a number of mechanical-biological plants can be found. Sometimes chemical treatment steps, oil removal and neutralization are also added. The average BOD-5 contribution of industry to the catchment's total emission is about 30% (though it is somewhat higher in the "campaign" season.

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k RIVERS

TOTAL BOD LOAD EFFLUENT BOD LOAD

Figure 3.7 Municipal wastewater treatment in the Nitra River basin

3.5 W a t e r Quality

The history of the water quality monitoring network goes back to the mid-sixties (Chapter 7).

There are data available since 1976 which thoroughly cover major dischargers for 26 sampling sites (see Figures 3.2 and 3.4). These data systematically do not show a trend. The quality is permanently poor, indicating that socio-economic changes which negatively affected the environment took place prior to launching the monitoring program.

Water quality is characterized by low (and sometimes depleted) oxygen levels, high BOD-5 values (not rarely close to or above 30 mg~l--see Figure 3.9 showing maximum BOD-5 values taken from the database--characterizing biologically treated wastewater effluents), high ammonia, phosphorus, dissolved and suspended solids, and arsenic concentrations (see Chapter 7 for details). According to the existing evaluation system, the quality of the Nitra River is characterized by the two poorest classes. This is a clear consequence of high waste residuals due to old-fashioned production technologies, improperly developed water infrastructures, and insufficient industrial and municipal treatment levels as discussed before (see Chapter 6 for hrther details).

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Figure 3.8 Industrial wastewater treatment in the Nitra River basin

Groundwater quality is also rather problematic. For instance, in the Novaky/Nove Zarnky region, 98% of the samples analyzed did not meet drinking water standards. Iron, manganese, and ammonium were the components where admissable limits were surpassed most frequently (clearly indicating the absence of oxygen in the course of the filtration process).