REGARDING THE DETERMINATION OF WASTEWATER SPECIFIC FLOWS IN ROMANIA RURAL AREAS

This paper intends to inform the scientific and engineering community on the importance of wastewater treatment plants of small capacity, designed for rural settlements. By analysing the evolution of Romania’s population by towns, on 1st January 2010, the weight of urban population was 55.1 %, and the weight of the rural population was 44.9 % of the total population. The rural environment representing 44.9% of the total population is grouped into 2860 villages with a degree of connection to wastewater treatment plants of only 11.21 %. At the moment the design of treatment plants, regardless of the structure and size of the settlement, is performed in a non-differentiated way, using the same technological methods for urban and rural areas. The implementation of technical solutions that are use for urban areas in case of small and very small towns’ claims high investment costs and especially operational costs, the efficiency of these solutions being unsatisfactory, because of wrong adoption of sizing parameters, for example, the influent specific flow. From this paper will result, based on case studies, that the specific flow sizing treatment plants for rural areas is overrated, much too high, resulting in oversized treatment plants.


INTRODUCTION
A sewage treatment plant represents all technological procedures provided for the removal or restraint of polluting materials from the wastewater -by physical, chemical, biological, biochemical and microbiological processes, in order to reach the necessary purification level, and consists of mechanical purification stage, biological purification stage and tertiary purification stage.Following the calculation of the necessary purification stage for each pollutant, the necessary technological processes are chosen [1].
For the projection of the sewage treatment units, the influent wastewater flows must be determined, this representing: the average daily flow Q u.day.avr, the maximum daily flow Q u.day.max, the maximum hourly flow Q u.hour.max, and the minimum hourly flow Q u.hour.min. .According to the Romanian legislation, the determination of the household wastewater flows, pertaining to the separate sewer systems, with gravitational functioning, are determined according to the technical regulation RS (Romanian Standard) 1846-1/2006 [2], with the relations: Q u.day.averege= q u * N "PE" / 1000 [m 3 /day] ( where: q u represents the specific flow of water return [L/day, "PE"]; N "PE" -number of the population equivalent -"PE"; k day -coefficient of the daily variation; k h -coefficient of the hourly variation; p -dimensionless coefficient, depending on the number of the population equivalent of the city.
The component equipment of the mechanical purification stage is sized according to the maximum and minimum hourly flows, while the component equipment of the tertiary and biological stages are dimensioned according to the average and maximum hourly flows.However, for the calculation of all these flows, the value of the specific water flow q u must be chosen or determined.
The specific water flow represents the quantity of the consumed wastewater, transported by the sewage system and discharged in the sewage treatment unit, by one equivalent person, during 24 hours.
According to the Romanian legislation, the specific wastewater flow is chosen according to the technical regulation SR 1343/2006 [3], as follow: values between 100 and 120 L/day, "PE", for rural areas and values between 150 and 180 L/day, "PE", for the urban areas.
A few references for similar studies were conducted in Europe, for the determination of wastewater specific flow in rural areas.For example, in France, both the pollution load in wastewater and the specific water consumption differ.While in the urban area of France, the specific consumption of water is 250 L/day, "PE", in the rural area it only reaches 150 L/day, "PE".
According to the data published by the German Society for Technical Cooperation, the water consumption varies depending on the facilities of the house: in cities with a maximum number of 2000 habitants, it reaches 65 L/day, "PE", for household use and 75 L/day, "PE", for public and domestic consumption, while in cities with over 2000 habitants, the consumption raises at 85, and 95 L/day, "PE", respectively.According to the data published by the Association of 29 villages in the South-East of Vienna, the specific consumption in the rural area is 80 L/day, "PE", while in the urban areas is 120 -180 L/day, "PE".
As the specific water flow grows, the investment and operating costs of the sewage treatment units are bigger.Generally speaking, in the practice of the sewage treatment units projection it is chosen the use of the specific flow pertaining to the urban areas, where the specific water consumption is higher than in the rural areas.This is why the real choice of the specific flow value pertaining to the area served by the sewage treatment unit, is very important, taking into consideration its characteristics.

ANALYSES OF THE STUDIES REGARDING THE SPECIFIC FLOW VALUES
The specific water flows, consumed at global level, vary, for several reasons, such as the water catchment system, the treatment and distribution technologies, the type of organizing the water distribution authorities (public or private), the particularity of the served area (rural or urban) or the habit of using the water.
The habit of using the water influences the value of the specific water flow.An analysis of the "household" water consumption, for different needs, is presented in Table 1, for Seoul (South Korea), Amsterdam (Holland) and Hamburg (Germany).
According to data presented in Table 1, one can observe that the specific flow of the consumed water varies from 117 L/day, "PE", to 208 L/day, "PE", depending on the living standards of the population in the analysed areas, such as the habits of using the water for cooking, drinking, cleaning or personal hygiene.This way, although there have been analysed similar urban areas, but populated by people with different education and living manners, the specific water flows values vary in a significant way, up to 43 % [4].In Great Britain, the specific consumption in individual houses is 150 L/day, "PE", but it may grow up to 200 -380 L/day, "PE", depending on the region.
The period of time in which the specific water flow has been followed influences its value.The specific water consumption grew in time, due to the improvement of the living standard, but in the last decades, due to the efforts engaged in protecting the environment and the water resources, a decrease in the specific water consumption was observed, a tendency which will be projected in the future.
For example, in Singapore, thanks to the professional system of administrating the water supply system and the efficient manner of using the water, the specific daily water consumption decreased from 165 L/day, "PE", in 2003, to 15 L/day, "PE" and the main objective is to decrease the specific water consumption under 147 L/day, "PE", by 2020 and up to 140 L/day, "PE" by 2030 [7,8].
In the USA, in the `50s, the specific water consumption in individual houses was 113 -220 L/day, "PE".In the present, in the metropolitan areas, such as New York, the specific daily water consumption is 680 L/day, "PE".
In Germany, due to the fact that the prudent water consumption and the sustainable use of it are encouraged, the specific water consumption per head of population decreased with about 15% from 1900, in the present, being 125 L/day, "PE" [9].
In Holland, one analysis made on 1000 families proved that the development of the living standards changed the water consumption, the specific flow grew up to 135 L/day, "PE", in 1992, towards 107 L/day, "PE", in 1980 [5].
During 1993 -1999, at European urban level, the specific water consumption decreased from 104 to 99 m 3 /year, "PE".In this period, a lot of changes influencing the way of using the water took place: the growth of urbanisation, changes in the human behaviour, application of the new technologies for water supply and sewer systems, the use of alternative water resources (desalination, reuse of wastewater) [10].
The water consumption at individual level in Northern European countries is higher than in Central European countries and varies between 106 m 3 /year, "PE", in Sweden, to 267 m 3 /year, "PE", in Iceland.Some studies suggested that the higher use of the water in some countries is due to the hygiene and dish washing customs.In the Central Europe, the specific water consumption varies between 68 m 3 /year, "PE", in Germany, and 125 m 3 /year, "PE", in Ireland.These variations reflect the differences in the structures of water supply systems and the methods of applying the water conservation means.For example, in Ireland, no fee is applied to the water consumed from the public network for household needs, and this is why the specific water supply is higher.
The Baltic states, together with China, Poland and Hungary, have the lowest specific water consumption level, due to the installation of water meters, in every house, high taxation rates of water flows are established, and the rehabilitation of old water pipelines is expensive.Bulgaria, Romania and Slovenia with 294, 123 and 124 m 3 /year, "PE", have the highest degree of urban water consumption.
The high water consumption level in Bulgaria and Romania is mainly due to the high rate of failure of the water supply systems, lack of water metering in some areas and loss of water in the network [10].
The specific household water consumption, at European level, are presented din Figure 1.
Fig. 1.The specific household water consumption at European level [10].
Following the analyses of the data presented in Figure 1, a major variation of the consumed water flows can be observed.The highest values are registered in Spain (265 L/day, "PE"), followed by Norway (224 L/day, "PE"), Holland (218 L/day, "PE") and France (164 L/day, "PE"), while the lowest water consumptions at European level are registered in Lithuania (80 L/day, "PE"), Estonia (100 L/day, "PE") and Belgium (115 L/day, "PE").
Analysing the specific water flow values at global and European level, one can see that they vary significantly, both from one continent to another and from one region to another.Thus, it appears quite difficult to establish the real specific water consumption pertaining to a specific city.
The specific water flows vary depending on the methods of using the water, on the population level of education, on the means of administrating the water and sewage networks, on the means of charging the water access or on its quality.
At the same time, the specific water flows have different values for the rural areas which have a lifestyle different from the urban areas.Moreover, the water quantity used by the same population varies in time; if in the past the specific water flow grew along with the growth of the living standards, in the present, a decrease of the specific water flow is registered, due to the efforts made in order to protect the water resources and for the rational use of it.

THE ANALYSES OF THE STUDIES REGARDING THE FLOW VALUES SPECIFIC TO RURAL AREAS
In the present, for the correct determination of the water flow specific to the rural areas, studies and analyses were carried out, in collaboration with the "Water Company Someș" SA Regional Registry, of Cluj.The studies included the rural area pertaining to the county of Cluj, which comprises 69 communes and 417 villages, counting 186069 habitants, representing 27.97 % of the total number of habitants of the county of Cluj.In relation to this number of habitants, only 25517 habitants (13.7 %) benefit from access to a drinking water distribution system and 9840 habitants (5.28 %) benefit from access to a sewer and wastewater purifying system [11].According to the data of the operator, for a clearer image of the real consumption, Table 2 displays the specific flows of a series of cities, registered in 2012.For an intuitive analyses and interpretation, data of Table 2 have been transferred in Figure 2.This way, one can observe the values of the specific drinking water flows, which are far below the rated consumption, the variations being from minimal values of 24.58 L/day, "PE", up to maxim values of 96.07 L/ day, "PE", the resulting average value being 67.86 L/day, "PE".
Comparing the real values resulted from monitoring the water consumption in rural areas, with the rated consumption of 100 up to 120 L/day, "PE", results a difference of 32 % up to 43 %.Analysing the real values resulted from monitoring the real water consumption in rural areas with the ones met in the practice of projecting, of 150 L/day, "PE", results a difference of 54 %.
By projecting and executing the sewage treatment plants, without taking into consideration the present studies regarding the specific water flows, the sewage treatment units are oversized up to 54 %, resulting investment and operating costs double than the necessary ones.

CONCLUSIONS
Sizing the technological objects from the sewage treatment unit is realized on the basis of the specific flow.The higher its value grows, the higher the investment and exploitation costs will grow.This is why the real choice of the specific flow value pertaining to the area served by the sewage treatment unit is very important, taking into consideration its characteristics.
Following the studies that were carried out, one can observe that the specific water flows consumed at global and European level, vary due to several reasons, such as the water catchment system, the treatment and distribution technologies, the way of organizing the water distribution authorities (public or private), the particularity of the served area (rural or urban) or the habits of using the water.
As the hygiene standards grow, the specific water flow grows, as well.However, if a country has an environment and water supply protection policy, as well as a water supply system with decrease losses, then the flow will decrease, as well.At the same time, the specific flow values may vary a lot within the same territory, depending on the served area.The specific flow has much higher values in the urban area than in the rural one.This way, it appears difficult to establish a value for the specific water consumption pertaining to a city, studies and determinations of the specific flow being necessary, in order to result the optimal resizing of sewage treatment units, with investment and operating costs adapted to the real needs.
A similar study was carried out in collaboration with the Regional Operator "Water Company Someș" SA Regional Registry of Cluj, after which the specific flow value for sizing the specific flow of the areas pertaining to the county of Cluj, of 67.86 L/day, "PE" resulted.By using this specific flow in sizing the sewage treatment units, which is comparable to the specific flow regulated by the effective legislation to100 up to 120 L/day, "PE", a decrease up to 43 % of the investment and operating costs is realized.

Fig. 2 .
Fig. 2. The specific water consumption of rural areas from Cluj-Napoca.
The Particularity of the served areas (urban or rural) influences the specific water flow values, this being lower in the rural areas and higher in the urban ones.An example in this regard is provided by the study realized in Australia, where the specific average water consumption is 290 L/day, "PE", but it varies significantly throughout the country, from 493 L/day, "PE" in West Australia, to 221 L/day, "PE", in the state of Victoria [6].