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

Phenol is a highly toxic aromatic compound discharged into the environment through industrial effluents. The natural biological treatment process has been widely used as one of the most feasible, eco-friendly, and cost-effective options for the treatment of pollutants such as phenol. The objective of the present experimental-analytical study was to evaluate the performance of the facultative stabilization pond in removing phenol and other organic compounds from oil refinery effluents. For the purposes of this study, a pilot-scale anaerobic stabilization pond 1.2´0.6´0.55 m in size was constructed of fiberglass sheets 6 mm in thickness. The experiment was run with a hydraulic retention time of 10 days and a hydraulic loading rate of 43.5 l/d. The organic loading rate for the facultative pond was 150 kg/h. day. Samples were taken after pond operation and seeding when the pond reached its biological stability. Depending on phenol removal levels in the anaerobic stabilization pond, initial phenol concentrations at the inlet to the facultative pond were assumed to be 0-28, 30-80, 90-130, and 150-200 under warm conditions and 100-140, and 200b-260 mg/l in cool conditions. For each sample, the parameters NH3, PO4, and Phenol were measured using the Varian spectrophotometer (model UV-120-02) at the wavelengths of 425, 690, 500 nm, respectively. TCOD, SCOD, TBOD, SBOD, pH, and ORP were also measured according to the standard methods of water and wastewater. The results showed that phenol removal efficiency of the facultative pond was 71.8% for warm temperatures and 14.66% for cool temperatures. It was also found that temperature and phenol concentration significantly affected the performance of the pond. Moreover, its performance was observed to enhance with reducing phenol concentration and increasing temperature (p<0.001). Maximum phenol removal efficiency of the system was recorded at 71.8% for warm temperatures and a low phenol concentration of 0–28 mg/l while its minimum of 14.66% was recorded at a high phenol concentration of 200-260 mg/l under cold weather conditions. Based on the results obtained, it may be concluded that the pilot-scale facultative pond has a high performance in removing organic compounds with different concentrations of phenol under warm weather conditions.

One of the indexes of stabilization pond is the presence of coliform bacteria in water and wastewater. This study aimed to determine the effect of solar light on coliform variations in stabilization pond. In this experimental study, the effect of light, pH (<7, 7. 1– 8, 8. 1– 9), and temperature (10 º C and 30 º C) on facultative stabilization pond was studied for six months. The sampling was accomplished weekly. Coliform colonies were measured using the nine tube fermentation method. The coliform deterioration constant was calculated using the Maraise model. The data were analyzed using SPSS version 20. The effect of light on coliform deterioration constant was negative. Also, low pH increased the coliform death. No significant statistical difference was seen at 10 º C and 30 º C (P < 0. 05). Low temperature cannot be adherence for facultative stabilization pond. Regarding the positive effect of temperature on the coliform death, use of facultative stabilization pond in a warm climate is suggested.

The objective of this study was to identify the anoxygenic phototrophic bacteria in the anaerobic lagoons and facultative stabilization pond of the Vale do Ribeira, Cajati, Sã o Paulo, Brazil, and their correlation with physical and chemical parameters of the ponds’ water. The samples were collected seasonally (spring, summer, autumn and winter) in the sub-surface, intermediate layer and sediment-water interface. We used the PCR/DGGE with pufM 557FGC and pufM 750R primers specific to the reaction center of the photosynthetic phototrophic bacteria for their identification. The amplification products were separated by electrophoresis on denaturing gradient gel. From the bands cut out and sequenced from DGGE, the identified bacteria were Rhodopseudomonas palustris (99% similarity), Chromatium sp. (92%), Thiocapsa sp. (90%), Rhodospirillum sp. (95%), Roseobacter sp. (93%) and other uncultured bacteria.

History and Objectives: Exited sewage following mechanical methods contains pathogenic agents. Therefore, swage clearance with chlorine and other compounds is necessary. It has been reported that in fixation ponds with regard to a long-time standing, there is a high rate of clearance and there is no need of additional clearance and this reduces the costs. Therefore, this study was carried out to determine the clearance rate of fecal coliforms in fixation ponds of Shoosh sewage refinery in Tehran in 1999. Materials and Methods: The semi-experimental strategy of this study was carried out on integrated stabilization pond in all of the seasons using two feeding sewage methods The system is a combination of anaerobic and facultative ponds and then two high-performance and complementary with a total time of 20 days. Sampling was done every two weeks from inlet and outlet sewage and number of fecal coliforms was counted and data were analyzed statistically. Results: It was found out that clearance rate of fecal coliforms was greater in spring than other seasons (99.97%) and was rather great in winter (greater than 99.5%). This indicates the high performance of the system for clearance of pathogenic agents from sewage. Conclusion and Recommendations: It is concluded that combinational tixation ponds have an appropriate performance for clearance of pathogenic agents. Feeding through upward current can increase the performance, as does the facultative pond. It is recommended to carry out more studies in this field.    

Arak waste stabilization pond facilities consist of two stabilization pond systems, module 1 and module 2. The existing facilities have had several problems in their operation. The objectives of this research were to evaluate the performance of stabilization ponds in wastewater treatment of the city of Arak, because of several problems in their operation, and to prepare a scheme of its upgrading, if necessary. Within the period of May to September 2007, analyses were carried out for both raw and treated wastewaters. Results of these investigations showed that the average effluent concentrations of BOD5, COD and SS taken from primary and secondary facultative ponds of module 1 were 91.5, 169, 114; and 70, 160, 123 mg/L, respectively. These results indicated that the effluent of the primary facultative ponds of module 1 were complied with the Iranian treated wastewater standards for agricultural reuse in terms of BOD5 and COD concentrations; hence the secondary facultative ponds could be changed to other primary facultative ponds in order to increase the capacity of wastewater treatment plant. For module 2, BOD5, COD, and SS average concentrations of treated wastewater for the secondary and tertiary facultative ponds were obtained as 69, 101, 77; and 76, 127, 78 mg/L, respectively. Thus the effluent of the secondary facultative pond was complied with the considered standards in terms of all studied parameters. Consequently, the tertiary facultative pond could be changed to other secondary facultative pond to upgrade both the quality and the quantity of treated wastewater.

Waste stabilization pond (WSP) is a conventional and widely applicable wastewater treatment unit globally. This system does not require complicated mechanical operating systems but it should not be classified as a simple process at all. Facultative ponds (FP) are the heart of this system as they use the natural symbiosis of facultative bacteria and algae for organic removal. The performance of FP is very reliant on different parameters such as wastewater influent characteristics or environmental operating conditions. Nonetheless, they are simply designed and operated based on parameters like surface organic loads and hydraulic retention time (Khosravi et al. 2013). Some literatures have recently focused on the optimization of WSP layout for higher performance (Shahsavani et al. 2019; Decostere et al. 2017; Espinosa et al. 2017). For example, a question is that which form of FPs, in series or parallel, have the highest performance or operational reliability? Answering to this question is practically a challenge. There is little chance in full scale to compare the performance of FPs with the layouts in series and parallel for long term, with same source of real wastewater, similar climate and operating conditions. This research primarily evaluates and compares the performance of FPs (2008-2020) in series and parallel layout in Delijan WSP.

Background: Heavy metals have destructive and irreversible effects on the human, plants and animals. Some industries in Yazd enter industrial wastewater to municipal wastewater collection system. This can lead to high levels of heavy metals in wastewater and in turn in the wastewater treatment plant effluent.Methods: This study was carried out during four months from December 22, 2009 to May 20, 2010. The experiment was performed on the inflow, outlet of anaerobic pond and first and second facultative ponds of wastewater treatment plant and then transferred to the laboratory and measured by atomic absorption spectroscopy.Results: The results of the experiments showed that the average cadmium concentrations in the inflow, anaerobic pond outlet, and first and second facultative pond outlet were 0.0066, 0.0087, 0.0076, and 0.0083mg/l, respectively. The average amounts of chromium in the inflow, anaerobic pond outlet, and first and second facultative pond outlet were 0.0076, 0.0065, 0.0043, and 0.0056 mg/l, respectively.Cadmium concentration in the effluent was higher than standard.Conclusion: The comparison of the obtained data with Iranian standards for wastewater treatment for reuse in irrigation shows that the cadmium concentration exceeded the standard and the chromium concentration was lower than the standard. Therefore, it is not suitable for reuse in the crop farms and aquatic life.

Biological treatment method is one of the best and most cost-effective methods for the treatment of contaminated wastewaters. The purpose of this study was to evaluate the effect of retention time and temperature on the efficiency of stabilization ponds in removing organic compounds، N-N 3 and PO4 from oil refinery wastewater.Materials and Methods: The method used in the present study was of an experimental type، in which an anaerobic stabilization pond with dimensions of 1×0.2×1 m and a laboratory scale facultative pond with the capacity of 400 L were designed، set up and operated، using fiberglass sheet with a thickness of 6 mm. In this study، the hydraulic retention time of 2 and 5 days for anaerobic pond and 5 and 10 days for facultative pond were set in both hot and cold temperatures. Then، N-NH3 and PO4 parameters were measured at the wavelengths of 425 and 690 nm respectively. Also، TCOD، SCOD، TBOD، SBOD and pH of samples were measured according to the standard methods for water and wastewater tests.Results and Discussion: These results indicated that the retention time and temperature had a significant effect on the efficiency of stabilization ponds، so that the efficiency of anaerobic and facultative stabilization ponds in the removal of organic compounds was significantly increased with the increase of retention time and temperature (p<0.05). The maximum removal efficiency for COD، BOD، N-NH3 and PO4 was obtained to be 93.31، 93.66، 88.15 and 73.17 % respectively (at the retention time of days of anaerobic and 10 days of facultative and hot temperature)، and the minimum removal efficiency for the same parameters was obtained to be 41.47، 40.55، 34.26 and 22.46% respectively (at the retention time of 2 days of anaerobic and 5 days of facultative and hot temperature). Also، the single alga available in the facultative pond was formidiom and it was able to grow in high concentrations of sulfur. The results of this study showed that the pilot-scale stabilization ponds in hot temperature، if operated proprly، have the ability to remove organic compounds with a high efficiency. However، in cold weather، its efficiency is low but in acceptable level.

History and Objectives: Considering the high cost of mechanical treatment of wastewater, and the necessity to investigate more economical methods, specially the ones involving natural treatment processes, a study on efficiency of integrated stabilization pond (ISP) was conducted in Shoosh Sewage Treatment Plant during 1999.Materials and Methods: This ISP experimental study was conducted during three seasons with two types of raw sewage feedings. The system consists of an anerobic pond in combination with facultative pond in series with a high rate and a maturation samples from inflow and effluent were taken on weekly basis and COD, BaDS, TSS, total nitrogen, and Total phosphorous were checked, the resulting reduction in mentioned parameters formed the basis of a statistical evaluation.Results: Pollutants reduction eas higher in Spring compared with summer and fall. BaDS with 89% reduction showed the highest and total phosphorous with 60% showed the lowest reduction levels during the said period. The level of sewage pollutant reduction during three satges of the  study shows that the anerobic pond in combination with facultative pond register the highest percentage of pollutant removalConclusions: ISP systems are effective in treatment of sewage. Up flow of sewage in fermentation pit has a positive effect on the systems efficiency, and shows the fermentation pits considerable role in facultative ponds. Since there is little available experience about ISP in Iran, more investigation on the subject is recommended.