Performance of moving bed biofilm reactors for biological nitrogen compounds removal from wastewater by partial nitrification-denitrification process

In this research, the continuously operated laboratory scale Kaldnes [k1] moving bed biofilm reactors [MBBRs] under partial nitrification-denitrification process were used for treatment of synthetic wastewater containing ammonium and glucose. The Anoxic and Aerobic reactors were filled to 40 and 50% [v/v] to attach and retain biomass with k1 biofilm carriers, respectively. The favorite internal recycle ratio and hydraulic residence time [HRT] to eliminate nitrogen compounds were 300% of inflow rate and 20 hours, respectively. Optimal dissolved oxygen [DO] was 1-1.5 mg/L in the aerobic reactor. No sludge was returned into the system and only an internal recycling was performed from aerobic to anoxic reactor. The results showed that the maximum and average specific nitrification rate [SNR] in the aerobic reactor were 49.4 and 16.6 g NOx-N/KgVSS.day, respectively and the maximum and average specific denitrification rate [SDNR] as 156.8 and 40.1gNOx-N/KgVSS.day in the anoxic reactor, respectively. The results also showed that it is possible to reach a stable partial nitrification with high ratio of NO2-N/NOx-N [80% to 85%] during high load ammonium and low DO concentration [<1.5 mg/L] in the aerobic reactor. During optimum conditions, the average removal efficiency of total nitrogen [TN], ammonia and soluble organic carbon [SCOD] occurred as 98.23%, 99.75% and 99.4%, respectively. This study showed that the partial nitrification/denitrification process in the moving bed biofilm reactors system has an acceptable performance for treatment of wastewater with high load of organic carbon and organic nitrogen compounds

[Survey on possibility of disinfection of Isfahan north wastewater treatment plant effluent by low and medium pressure ultraviolet systems in pilot scale]

Today, due to health, environmental and economical problems, of chlorine application, UV radiation is better option than chlorine for disinfection of effluent. The aim of this study was disinfection of secondary effluent with UV radiation. Two types of UV disinfection system including low pressure [LP] and medium pressure [MP] was used to disinfection of Isfahan North Wastewater Treatment Plant [INWWTP] effluent without pretreatment. Single and combined lamps were operated to evaluate the removal of total and fecal coliforms [TC and FC], and fecal streptococcus [FS]. TSS, iron, hardness, UV absorption and transmittance were analyzed in order to observe the fouling of the quartz sleeves. After using LP lamp with dose of 161 mws/cm[2], TC and FC content was declined to standard level [1000 TC, and 400 FC/100ml]. In addition, disinfection with MP lamp was led to FS content of 400 MPN/100 mL. Combination of LP and MP, with dose of 460 mws/cm[2] could be met the environmental requirements of TC and FC, and the FS count was reached to 400 MPN/100 mL with dose of 237 mws/cm[2]. Maximum photo-reactivation percentage of coliforms after LP and MP lamps were appeared 15 and 3 percent respectively, while it was not observed for FS. High fluctuation in secondary effluent quality of INWWTP mainly TSS concentration was caused to decline of the UVT value. Therefore, disinfection of effluent by LP, MP and even combined both systems are not applicable in conventional UV dose. Hence, using advanced process unit before UV disinfection system is necessary for removal of TSS

Removal of cadmium and humic acid from aqueous solutions using surface modified nanozeolite A

The sorption of cadmium and humic acids from aqueous solutions using surface-modified nanozeolite A has been investigated under various examination conditions. The morphology of untreated and treated nanozeolite was studied under scanning electron microscope and transmission electron microscope. Isotherms of cadmium adsorption onto surface-modified nanozeolite A were studied at different pH, solid to liquid ratio, adsorbate concentration and interaction time. Kinetic and equilibrium studies were conducted and the equilibrium data have been analyzed using Langmuir and Freundlich isotherm models. The study revealed that experimental results were in agreement with the Freundlich model. The Langmuir monolayer adsorption capacity was found to be 1666.67 g cadmium and 6.75 g humic acid per gram of modified nanozeolite A, which is higher than that of reported value for other zeolites. The sorption ability was enhanced by surface modification and reduction in size and enabled the zeolite to adsorb cadmium. The adsorption of cadmium and humic acid on nanozeolite was found to be the highest at pH 6 and 3, respectively. Results showed that solid to liquid ratio and pH are the most important factors for cadmium and humic acid removal, respectively. Effect of competitive ions was studied and results showed that there is no competition between cadmium and humic acid sorption and presence of these ions

Decolorization and biological degradation of azo dye reactive red2 by anaerobic/aerobic sequential process

This study investigates the anaerobic treat ability of reactive Red2 in an anaerobic/aerobic sequential process. Laboratory scale anaerobic baffled reactor and fixed activated sludge reactor were operated at different organic loadings and hydraulic retention times. The effects of shock dye concentration on the chemical oxygen demand and color removal efficiencies were investigated in the anaerobic baffled reactor. The effect of hydraulic retention time on the color and chemical oxygen demand removal efficiencies were also investigated in the aerobic reactor. The studies were carried out in continuous mode and the effluent of the anaerobic baffled reactor was used as feed for the fixed activated sludge reactor. Chemical oxygen demand removal efficiency of 54.5% was obtained at HRT =1 day in the anaerobic reactor. The average color removal was 89.5%. Chemical oxygen demand removal efficiency of 69% was obtained at HRT =7 h in the aerobic fixed activated sludge reactor. A slight decrease of the color was also observed in the aerobic reactor. This investigation has shown that successful treatment of a highly colored wastewater is possible in the anaerobic baffled reactor. Also the results showed that, anaerobic biological system has higher efficiency in dye removal than fixed activated sludge system, while aerobic system has higher efficiency in chemical oxygen demand removal comparing with the anaerobic baffled reactor

Effectiveness of chitosan as natural coagulant aid in treating turbid waters

During the last decade, there has been a concern about the relation between aluminum residuals in treated water and Alzheimer disease, and more interest has been considered on the development of natural coagulants such as chitosan. Chitosan, a natural linear biopolyaminosaccharide, is obtained by alkaline deacetylation of chitin. The present study was aimed to investigate the effects of alum as coagulant in conjunction with chitosan as coagulant aid on the removal of turbidity, hardness and Escherichia coli from water. A conventional jar test apparatus was employed for the tests. The optimum pH was observed between 7 to 7.5 for all turbidities. The optimum doses of alum and chitosan when used in conjunction, were 10mg/L and 1mg/L, 5mg/L and 0.5mg/L, and 5mg/L and 0.5mg/L in low, medium and high turbidities, respectively. Turbidity removal efficiency was resulted between%74.3 to%98.2 by alum in conjunction with chitosan. Residual Al[+3] in treated water was less than 0.2 mg/L, meeting the international guidelines. The results showed that turbidity decrease provided also a primary Escherichia coli reduction of 2-4 log units within the first 1 to 2 hr of treatment. Hardness removal efficiency decreased when the total hardness increased from 102 to 476mg/L as CaCO3. At low initial turbidity, chitosan showed marginally better performance on hardness, especially at the ranges of 100 to 210 mg/L as CaCO3. In conclusion, coagulant aid showed a useful method for coagulation process. By using natural coagulants, considerable savings in chemicals and sludge handling cost may be achieved

Effects of aeration rate and detention time on thermophilic aerobic digestion of mixed sludge and its dewaterability

Thermophilic aerobic digestion [TAD] is a possible alternative for rapid sludge degradation and producing Class A biosolids. Aeration rate and detention time are two of the important parameters in TAD processes due to rapidly growing thermophilic bacteria population, limited solubility of oxygen at high temperatures and the need to prevent cooling of TAD process. Also the current knowledge and understanding of dewatering TAD biosolids are limited and incompelet.The objectives of this study were to investigate the effects of various aeration rates and detention time on some characteristics of mixed sewage sludge. Four glass-cylindrical digesters with 7 liters of sludge in each, placed in a water bath and were operated at 55 ?C with the aeration rates of 2.14, 3.00, 3.86 and 4.71 volume of air per volume of sludge per hours. It was found the increase in aeration rate decreased the required detention time in order to meet the Class A sludge regulations to reduce vector attraction. The values of Oxidation-Reduction Potential [ORP] were changed from negative values to positiv ones and the values of pH were increased from around neutral to slightly basic, but this increases were occured at different detention times. TAD affected dewaterability of mixed sewage sludge and produced biosolids with higher specific resistance to filtration [lower dewaterability] than undigested sludge. Thermophically digested sludge has a good setteling behavior and air drying on sand bed