Phosphorus Modeling in Yazd Facultative Pond

Waste stabilization ponds are simplest systems applied by human to treat thebiological degradable materials. Today, computerized tools and special mathematical modeling isused to manage environmental systems problems. System Dynamics is a system for problemsanalys is when time is a significant factor. It includes the way action and reaction of system isencountered by external thistles. After sampling and testing, phosphorus was modeled by using mathematical elationships and system Dynamics method. After making the initial model and its testing, the odel was calibrated using three months data from facultative pond in Yazd city in Iran. Algal growth rate, phosphorus settling rate and losses due to algal respiration andexcretion were from important agents. Respiration rate of herbivorous zooplankton, non living arbon hydrolysis rate and phosphorous to chlorophyll ratio were from low important agents. espiration rate of carnivorous zooplankton and phosphorous to carbon ratio were from nimportant agents. In comparison with other models, our System Dynamics Model needs low data. This s also a cheap model and we perceived good operation of it. In sensitive analysis, algal growth rate nd phosphorus settling rate were important in phosphorus removal. So, we can manage facultativepond better with increasing retention time in pond. Phosphorous to chlorophyll ratio had lowimportant role in this model. Thus, system can tolerate phosphorous variations in inlet wastewaterwith sufficient algal growth. Respiration rate of carnivorous zooplankton and phosphorous tocarbon ratio do not limit system equilibrium. Ability of the model increases with sufficient retentiontime and further data. System Dynamics ecological models give useful information for facultativeponds. It is recommended this model be used for management affairs and overall assessment offacultative ponds. For more precise assessment, it is apposite to use two or three dimensions modelssubstitute zero dimensions models.