Modelling of the loading rate in facultative wastewater stabilization ponds and the assessment of organic matter decline

Wastewater stabilization ponds (WSPs) are natural, relatively simple, and cost-effective treatment processes that are used to stabilize the biodegradable compounds in wastewater. The present study aimed to propose a mathematical model for organic matter decline in facultative ponds (FPs). This analytical study yielded practical results, and the samples were collected from the ponds located in Yazd city, Iran. The reliability of the regression models (linear, quadratic, cubic, and exponential) was assessed and simulated by fitting the data. Initially, the data were fitted using linear and nonlinear curves. The comparative analysis of the results obtained from the models and Akaike information criterion (AIC) coefficient demonstrated that the linear model had the optimal correlations with surface loading (LS, O) and minimum average monthly air temperature (Ta) with very high percentage accountability (R2=0.939). The correlation-coefficients (R2) for the second, third, and exponential models were estimated at 0.938, 0.939, and 0.938, respectively. Therefore, it could be concluded that there was a logical association between the LS, O and Ta, which suggests that these models are able to simulate the performance of the FPs. As such, the proposed models could be used to predict the reduction of organic materials in FPs, and the linear model was statistically selected as the optimal model for this purpose. In Iran and the neighboring countries where there are similar seasonal variations in temperature in most cities, the obtained models could be widely used for designing facultative ponds.