Analiza efektywności kosztowej różnych wariantów technologicznych przydomowych oczyszczalni ścieków

The cost-effectiveness of a range of variants of single-house sewage treatment plants is analyzed in the article. They include plants with drainage pipe, with package drainage, with tunnel drainage, constructed wetlands, activated sludge chamber, biological filter and a hybrid plant. The analysis focuses on different ways of discharging treated wastewater, i.e. drainage pipe, package drainage, tunnel drainage, pond and soakaway. Selection of the most financially efficient system was made on the basis of the minimal rate of the average annual treatment cost. The total cost was compared with the construction costs as well as the operating costs of a holding tank. The analysis shows that, on the average, the total average annual cost of single-house sewage treatment facilities is almost 2-times lower than the cost incurred on the construction and operations of a holding tank. This ratio, however, depends largely on different prices for emptying a tank. Materials (avg. 83%) and equipment rental (avg. 12%) constitute the greatest share of the investment costs incurred on the construction of sewage treatment plants. Among the analyzed sewage treatment plant technologies the lowest investment outlays are required for drainage pipes and packages as well as constructed wetlands. The lowest treated sewage discharge costs are generated by ponds, whereas the highest by tunnel drainage. The lowest operation costs are generated by constructed wetlands, whereas the highest by holding tank, activated sludge chambers and hybrid plants. The most cost effective, characterized by the lowest average total annual cost, is constructed wetland with discharge by a pond. The greatest average annual cost of wastewater treatment is generated by hybrid plants with treated wastewater discharged into the ground by drainage tunnels. The conclusions of analysis carried out by other authors are similar to those presented in this paper. However, the presented research shows that the average annual outlays for wastewater treatment for all plants are greater. This is because additional cost factors, such as the purchase of gravel, human costs, equipment expenditures or maintenance of periodic inspections carried out by qualified personnel, were taken into account. These are costs without which it is impossible to achieve the required quality of treated sewage.