ABSTRACT
Partial nitrification was reported to be technically feasible and economically favorable, especially for wastewater with high ammonium concentration or low C/N ratio. In this study, the effect of dissolved oxygen [DO] and influent ratio of chemical oxygen demand to nitrogen [COD/N] ratio on biological nitrogen removal from synthetic wastewater was investigated. Experiments were conducted in moving bed biofilm reactors [MBBRs] on partial nitrification process in pilot-plant configuration for 300 days. DO levels were changed from 0.04 to 0.12 and 0.42 to 3.4 mg/l in the anoxic [R1] and aerobic [R2] reactors, respectively. The optimum DO for partial nitrification was between 1-1.5 mg/l in the aerobic reactor [R2]. Influent COD/N ratios between 20 and 2 g COD/g-N were tested by changing the nitrogen loading rate [NLR] supplied to the pilot plant. During operational conditions when the DO concentration in aerobic reactor was above 1 mg/l, near complete organic carbon removal occurred in the total MBBRs system. The effluent total nitrogen concentration in the operational conditions [1.7-2.1 mg O2/l and NH+4-N=35.7 mg N/l] was obtained in the range of 0.85-2 mg/l. The highest nitrite accumulation [50%-52%] took place at the DO concentration of 1-1.5 mg/l and increased with decreasing COD/N ratio in aerobic reactor [R2]. This study showed that the average nitrification rate at various COD/N ratios is about 0.96 gN/m[2] per day while the maximum nitrification rate is about 2 gN/m[2] per day at COD/N ratios lower than 6. The experimental COD/N ratio for denitrification was close to complete sum of NO2- and NO3- [NOx] removal efficiency [about 99%] at COD/N ratio equal 14 in the operational conditions in the anoxic reactor [R1]
ABSTRACT
In recent years, chitosan and Moringa oleifera Coagulant Protein a natural coagulant were used in order to reduce the problems occure from chemical coagulants. This investigation was done to determine effectiveness of Moringa Oleifera Coagulant Protein and Chitosan as natural coagulant aids in removal of colloidal particles and bacteria from turbid waters. In this interventional- quasi experimental study, the experiments were run by using synthetic water having low [10-20NTU], medium [100-120NTU] and high [200-220NTU] initial turbidities. In order to determine optimum pH and dosage of coagulant and coagulant aids, a conventional jar test apparatus was employed. Turbidity reading were carried out using a Hach model 2100P Turbidimeter. The samples were taken from the top four inch of the suspension for turbidity and bacteria removal measurement. Optimum dose of alum for waters with three different initial turbidities were 20, 40, and 20 mg/1, respectively. Optimum pH was between 7-7.5. Moringa oleifera Coagulant Protein and chitosan were reduced the required dosage of alum from 12.5% to 62.5% and from 50% to 87.5%, respectively, in different turbidities and residual aluminum was reduced to standard limit [0.2mg/l]. The bacteria removal efficiency were from 90% to 99.9999%. It was found when samples were stored during 24 hours; regrowth of E.coli was not observed. This study showed that natural coagulant aids can reduce the turbidity to below 5NTU without filtration in optimum condition
Subject(s)
Chitosan , Moringa oleifera , CoagulantsABSTRACT
In this research, an experimental study to evaluate nutrient removal from synthetic wastewater by a lab-scale moving bed biofilm process was investigated. Also, kinetic analysis of the process with regard to phosphorus and nitrogen removal was studied with different mathematical models. For nutrient removal, the moving bed biofilm process was applied in series with anaerobic, anoxic and aerobic units in four separate reactors that were operated continuously at different loading rates of phosphorus and nitrogen and different hydraulic retention times. Under optimum conditions, almost complete nitrification with an average ammonium removal efficiency of 99.72% occurred in the aerobic reactor. In the aerobic reactor, the average specific nitrification rate was 1.92 g NOx-N [NOx-N=NO2-N +NO3-N] produced/kg volatile suspended solids. hour [VSS.h]. Denitrification rate increased with increasing NOx-N loading in the second anoxic reactor. The aerobic phosphate removal rate showed good correlation with the anaerobic phosphate release rate. Under optimum conditions, the average total nitrogen and phosphorus removal efficiencies were 80.9% and 95.8%, respectively. As a result of the moving bed biofilm process [MBBR] kinetic analysis, the Stover-Kincannon model was chosen for modeling studies and experimental data analysis. The Stover-Kincannon model gave high correlation coefficients for phosphorus and nitrogen removal, which were 0.9862 and 0.986, respectively. Therefore, this model could be used in predicting the behavior or design of the moving bed biofilm process