Comparison between different models for rheological characterization of activated sludge

Activated sludge flow rheology is a very complicated phenomenon. Studies related to activated sludge tend to classify sludge as non-Newtonian fluid. Until now, several theories have been built to describe the complex behavior of activated sludge with varying degrees of success. In this article, seven different models for viscosity of non-Newtonian fluids [i.e., Power law, Bingham plastic, Herschel-Bulkley, Casson, Sisko, Carreau and Cross] were considered to evaluate their predictive capability of apparent viscosity of activated sludge. Results showed that although evaluating the constants in the four-parameter models is difficult, they provide the best prediction of viscosity in the whole range of shear rates for activated sludge. For easier prediction of viscosity at different mixed liquor suspended solids [2.74-31g/L], temperature [15-25°C] and shear rate [1-1000/s], simple correlations were proposed. Comparing the results with the experimental data revealed that the proposed correlations are in good agreement with real apparent viscosities

Application of nanofiltration membrane in the separation of amoxicillin from pharmaceutical wastewater

Separation of amoxicillin from pharmaceutical wastewater by nanofiltration [NF] membrane has been investigated in this study. For this purpose a membrane system including a polyamide spiral wound NF membrane was evaluated for the treatment of amoxicillin wastewater. The effects of operating conditions such as flow rate, pressure and concentration of amoxicillin and COD in the feed, on the efficiency of the membrane were evaluated. The permeation flux and rejection of amoxicillin and COD were the criteria for this evaluation. The rejection of the amoxicillin by the selected NF membrane was adequate and in most cases exceeded 97% whereas COD reached a maximum of 40% rejection and permeation flux was over 1.5 L/min.m[2]. The rise in pressure enhanced the transport rate of the solvents. Permeation flux of the NF membrane increased with increasing flow rates. Experimental data also indicated that concentration polarization existed in this membrane separation process. The stable permeation flux and high rejection of amoxicillin indicated the potential of NF for the recovery of amoxicillin from the pharmaceutical wastewater

Effect of heavy metals on fouling behavior in membrane bioreactors

Presence of heavy metals is considered to be a major challenge in wastewater treatment. In this research the effect of heavy metals such as nickel [Ni], chromium [Cr], and manganese [Mn] on fouling in membrane bioreactors was investigated. Fouling tendency of a cellulose acetate membrane was evaluated in MBRs with different concentrations of the mentioned elements. The concentrations of extractable extracellular polymeric substances in the mixed liquor at the steady-state condition and different concentrations of heavy metals were compared. Also the effects of concentration of heavy metals on mean floc diameter, hydrophobicity, and hence the fouling propensity of membrane was investigated. The Analysis of variance [ANOVA] method has been used to illustrate the important factors for the prediction of the fouling behavior. Results showed that different salts of the same heavy metal ion and various concentrations of heavy metals in wastewater had different effects on sludge properties and hence induced different fouling tendency of sludge

investigation on the nitrogen content of a petroleum refinery's wastewater and its removal by biological treatment

This investigation was performed on the biological removal of nitrogen from refinery's wastewater by the nitrification and denitrification process. In a petroleum refinery, removing of hydrocarbons is the main concern and nitrogen content is supposed to be negligible. The aim of this work was to search for nitrogen in Tehran Refinery wastewater and employing a biological technology to reduce this pollutant. Samplings were done in different points of wastewater treatment plant; influent to aeration unit, effluent of aeration unit and effluent of clarifiers. The results showed that despite of a high average removal efficiency of COD > 93%, the nitrogen removal during conventional activated sludge process was not efficient and sludge rising due to denitrification was observed within the clarifier. The analysis conducted in laboratory scale showed that a simultaneous nitrification and denitrification [SND] process could easily be realized in the same activated sludge plant by using the flocculating sludge and control of dissolved oxygen concentration. It was found that the higher MLSS value [10.0 g/L] and mixing rate [300 rpm] is effective in improving total nitrogen removal and overall SND performance. Our experimental results indicated that the SND process is very efficient for nitrogen removal from industrial wastewater