RESUMO
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]
RESUMO
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