Analysis of the current knowledge has revealed the lack of a method for increasing the cost-effectiveness of wastewater and septage treatment in plants overloaded by contamination. This was the premise for undertaking research on the process of septage pre-treatment in a subsurface vertical flow constructed wetland (SS-VF) prior to its input into the biological section of a municipal treatment plant. In previous research the authors have indicated that this allows for a significant reduction in the value of pollution indicators. The objective of this paper is to assess the cost-effectiveness of this process by means of an optimization model. The decision variable was the coefficient of septage stream distribution into the quantity directed to the SS-VF bed in relation to its total quantity. The optimization criterion was the minimization of the expected annual cost of wastewater and septage treatment. Verification of the model has shown that it is reasonable to subject all septage to the pre-treatment in a SS-VF bed for small wastewater treatment plant (WWTPs) located in rural areas. The bigger the septage pollution load is, the greater the reduction in the treatment costs. The proposed solution is less cost-effective in urban areas, where the construction of a SS-VF bed requires land purchase and additional costs of its adjustment. Optimization results largely depend on the cost function, so it is important to build it on reliable local data.
The option of using the contingent valuation method (CVM) to assess residents’ willingness to pay (WTP) for upgrading the quality of water resources in their communes is discussed in the article. Surveys were conducted using the direct interview method. The analysis included the application of CVM to examine the potential for financing projects that are focused on reducing the eutrophication process of the Baltic Sea, financing the construction of municipal sewage treatment plants in selected communes in Greece and Poland and financing the upgrade of sewage disposal and treatment standards in Śniadowo in north-eastern Poland. For authorities of a given area, the CVM is an instrument supporting the decision-making process regarding investments in water resources’ protection.
Streszczenie: Analiza jednostkowych kosztów inwestycyjnych i eksploatacyjnych stacji uzdatniania wód powierzchniowych pokazuje, że koszty te maleją wraz z wydajnością stacji. Wyższe koszty występują dla stacji pobierających wody kategorii A2 i A3, a niższe pobierające wodę kategorii A1. Jednostkowe koszty inwestycyjne stacji uzdatniania wód powierzchniowych są wielokrotnie wyższe niż w przypadku stacji uzdatniania wód podziemnych. Jednostkowe koszty eksploatacyjne stacji uzdatniania wód powierzchniowych są natomiast nieznacznie niższe niż w stacjach uzdatniania wód podziemnych stosujących procesy fizyczno-chemiczne. Analiza struktury kosztów pokazała, że amortyzacja i zużycie energii są dominującymi składnikami kosztów stacji uzdatniania wód powierzchniowych. Kolejne miejsca zajmują wynagrodzenia oraz zużycie materiałów, a koszty remontów zależą od stanu technicznego stacji.Słowa kluczowe: stacja uzdatniania wód, wody powierzchniowe, analiza kosztów, efektywność ekonomiczna.Summary: Analysis of the unit investment and operating costs of surface water treatment plants shows that these costs decrease together with the growth of the station capacity. Higher costs are incurred for the A2 and A3 category water intakes and lower costs are sustained for the A1 category. The unit investment costs of surface water treatment plants are many times higher than for underground water treatment plants. At the same time the unit operating costs are slightly lower than for underground water treatment plants using physico-chemical processes. The cost structure analysis has shown that depreciation and electricity consumption are the dominant cost components of surface water treatment plants. Salaries and material usage follow and the level of repair costs depends on the technical condition of the station.
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