Removal efficiency-cost relationship of structural best management practices in non-point source pollution management

Nowadays, there has been a significant increase in environmental pollution, particularly in water resources as a result of rapid population growth and increasing industrial activities in the world. In parallel with this increase, the amount of water used for different purposes increased the demand for clean water. On the other hand, climate change, which has become more evident in recent years, is also another problem that has a negative impact on water resources. Considering all, the importance of water resources' conservation and their sustainable management become more clear. Thanks to the progression in treatment technologies, point pollution related to domestic and industrial sources could be controlled quite easily today. On the other hand, the elimination of non-point source pollution, which is one of the most important problems that threats the water resources, and the improvement of water quality are still among the issues that are needed to be solved. In recent years, Best Management Practices (BMPs), which are developed with the aim of combating non-point source pollution and have low cost and simple technology, have taken their place among the main technologies used for the treatment of wastewater of different types and characterization, as well as rainwater. BMP's, which can be classified in different ways based on various parameters, could be defined basically as the systems that work with the principle of preventing the transport of pollutants. Considering the widespread agricultural and animal husbandry activities in our country - particularly in rural areas- it is evident that non-point source pollution is one of the most important problems that need to be solved. Nevertheless, the real-scale use of BMP's, which is one of the most effective ways to solve this problem the country is facing, is unfortunately not very common. Determination of the cost parameter, which is one of the most important parameters for the user, is a strong driver for widening the use of these applications throughout the country. By means of this study, the sample design of the structural BMP's such as constructed wetland, stabilization pond, grassed waterway, filter strip system and animal manure storage pit was performed. The removal efficiency-cost relation of BMPs was revealed, and it was intended to assist the pre-feasibility studies and to act as a supporter for the decision-making process for the users. The cost curves were presented on an individual basis for two different sources as commissioning of the practices and one-year operation-maintenance activities. All the parameters used in the design process of the BMPs have been designed as modifiable, considering that they would vary according to various factors such as application time and the climate and geographic conditions of the region. In this regard, it was enabled users to be able to customize all design parameters according to the current situation and to make their own designs. In the first part of the study; the aim and scope of the study were emphasized and the importance of the study was explained. In the second part of the study; the concept of non-point source pollution was discussed and brief information on non-point source pollutants and sources was given. The definition, importance, and classification of the BMPs were explained, and constructed wetland, stabilization pond, filter strip, grassed waterway and animal manure pit within the scope of structural classification were examined in detail. In the third part of the study; a sample design of Vertical Flow Subsurface Wetland (VFSW), facultative stabilization pond, maturation pond, filter strip, grassed waterway, and animal manure storage pit was made based on their removal efficiencies for different pollutant parameters (TN, TP, BOD, sediment) and the related cost was calculated. The efficiency-cost relation of the practices was revealed. In the fourth part of the study; formulas and graphs related to the removal efficiency-cost relation for the Vertical Flow Subsurface Wetland (VFSW), facultative stabilization pond, maturation pond, filter strip, grassed waterway, and animal manure storage pit were presented. The cost of the systems was compared for different pollutant parameters (TN, TP, BOD, sediment) and the reasons for the differences were interpreted. In the fifth part of the study; the study was generally evaluated and suggestions were made for future studies. Results of the study indicated that the highest cost for BOD removal has occurred in the facultative stabilization pond, followed by VFSW. Considering that the stabilization ponds are used for the improvement of domestic wastewater and the filter strip system for surface flow, it would not be a realistic approach to compare the costs of the systems for TN and TP. When investigating the sediment removal, it has been found that the highest cost occurred in grassed waterway, while the lowest cost has occurred in filter strip system. When comparing all systems, it has been shown that the lowest cost has occured in filter strip system. Such a result could be explained by the lack of building material used in its construction process and its easy maintenance procedure. Obtained results also demonstrated that the pollutant that is desired to be eliminated has an important role in the selection process of the Best Management Practice to be used. Considering the results of the study, it is possible to say that the design of the filter strip when it was targeted to remove TN and TP, and the design of VSFW when it was aimed the BOD removal would decrease the cost considerably for the user. In addition to the targeted pollutant parameter to be eliminated, it is also very important to consider especially the land characteristics and climatic conditions during the selection process of the Best Management Practice to be used. For instance, although the cost of constructed wetland in BOD removal is lower compared to stabilization pond, it should be taken into consideration that removal with stabilization pond could be a more accurate choice due to their low operation and maintenance costs where the land is inexpensive or there is no shortage of area. Either, it should be taken into consideration that the stabilization ponds, which the temperature is the most important parameter for their effective work, could increase the total cost due to the low efficiency when using in the regions with cold climate, even though they were found to be low cost compared to other practices as a result of the analyzes made. Considering that the systems discussed in the study perform their functions through natural treatment, it should be kept in mind that their efficiency can change very quickly through other environmental parameters (climate, temperature, topographic structure, etc.) and different design options. The designed practices in the study are exemplary and their designing by the user in accordance with the current situation would help to make the preliminary feasibility study more accurate and thus to provide a more precise forecasting of the cost. As only the structural Best Management Practices could have been investigated in the study, it is evident that the studies related to the cost of product based and in-situ control methods in struggling with non-point source pollution which would be done in the following years would be highly supportive for the user at the decision-making point.