Removal of Emerging Contaminants from Wastewater Streams Using Membrane Bioreactors: A Review.

Water is a very valuable natural resource. As the demand for water increases the presence of emerging contaminants in wastewater has become a growing concern. This is particularly true when one considers direct reuse of wastewater. Obtaining sufficient removal of emerging contaminants will require determining the level of removal for the various unit operations in the wastewater treatment process. Membrane bioreactors are attractive as they combine an activated sludge process with a membrane separation step. They are frequently used in a wastewater treatment process and can operate at higher solid loadings than conventional activated sludge processes. Determining the level of removal of emerging contaminants in the membrane bioreactor step is, therefore, of great interest. Removal of emerging contaminants could be by adsorption onto the biomass or membrane surface, biotransformation, size exclusion by the membrane, or volatilization. Given the fact that most emerging contaminants are low molecule weight non-volatile compounds, the latter two methods of removal are usually unimportant. However, biotransformation and adsorption onto the biomass are important mechanisms of removal. It will be important to determine if the microorganisms present at given treatment facility are able to remove ECs present in the wastewater.

Atrazine Removal from Municipal Wastewater Using a Membrane Bioreactor.

As the demand for potable water increases, direct potable reuse of wastewater is an attractive alternative method to produce potable water. However, implementation of such a process will require the removal of emerging contaminants which could accumulate in the drinking water supply. Here, the removal of atrazine, a commonly used herbicide, has been investigated. Using real and synthetic wastewater, as well as sludge from two wastewater treatment facilities in the United States in Norman, Oklahoma and Fayetteville, Arkansas, atrazine removal has been investigated. Our results indicate that about 20% of the atrazine is removed by adsorption onto the particulate matter present. Significant biodegradation of atrazine was only observed under aerobic conditions for sludge from Norman, Oklahoma. Next-generation sequencing of the activated sludge revealed the abundance of Noncardiac with known atrazine degradation pathways in the Norman aerobic sludge, which is believed to be responsible for atrazine biodegradation in our study. The detection of these bacteria could also be used to determine the likelihood of biodegradation of atrazine for a given wastewater treatment facility.

Investigation into Micropollutant Removal from Wastewaters by a Membrane Bioreactor.

Direct potable reuse of wastewater is attractive as the demand for potable water increases. However, the presence of organic micropollutants in industrial and domestic wastewater is a major health and environmental concern. Conventional wastewater treatment processes are not designed to remove these compounds. Further many of these emerging pollutants are not regulated. Membrane bioreactor based biological wastewater treatment has recently become a preferred method for treating municipal and other industrial wastewaters. Here the removal of five selected micropollutants representing different classes of emerging micropollutants has been investigated using a membrane bioreactor. Acetaminophen, amoxicillin, atrazine, estrone, and triclosan were spiked into wastewaters obtained from a local wastewater treatment facility prior to introduction to the membrane bioreactor containing both anoxic and aerobic tanks. Removal of these compounds by adsorption and biological degradation was determined for both the anoxic and aerobic processes. The removal as a function of operating time was investigated. The results obtained here suggest that removal may be related to the chemical structure of the micropollutants.

Surface Modification of PVDF Membranes for Treating Produced Waters by Direct Contact Membrane Distillation.

Direct contact membrane distillation (DCMD) has been conducted to treat hydraulic fracturing-produced water using polyvinylidenedifluoride (PVDF) membranes. Tailoring the surface properties of the membrane is critical in order to reduce the rate of adsorption of dissolved organic species as well as mineral salts. The PVDF membranes have been modified by grafting zwitterion and polyionic liquid-based polymer chains. In addition, surface oxidation of the PVDF membrane has been conducted using KMnO4 and NaOH. Surface modification conditions were chosen in order to minimize the decrease in contact angle. Thus, the membranes remain hydrophobic, essential for suppression of wetting. DCMD was conducted using the base PVDF membrane as well as modified membranes. In addition, DCMD was conducted on the base membrane using produced water (PW) that was pretreated by electrocoagulation to remove dissolved organic compounds. After DCMD all membranes were analyzed by scanning electron microscopy imaging as well as Energy-Dispersive X-Ray spectroscopy. Surface modification led to a greater volume of PW being treated by the membrane prior to drastic flux decline. The results indicate that tailoring the surface properties of the membrane enhances fouling resistance and could reduce pretreatment requirements.

Designing Electric Field Responsive Ultrafiltration Membranes by Controlled Grafting of Poly (Ionic Liquid) Brush.

Electric responsive membranes have been prepared by controlled surface grafting of poly (ionic liquid) (PIL) on the commercially available regenerated cellulose ultrafiltration membrane. The incorporation of imidazolium ring on membrane surface was evidenced by FTIR (Fourier transformed infra-red) and EDX (energy-dispersive X-ray) spectroscopy. The PIL grafting resultedin a rougher surface, reduction in pore size, and enhancement in hydrophilicity. The interaction of the electric field between the charged PIL brush and the oscillating external electric field leads to micromixing, and hence it is proposed to break the concentration polarization. This micromixing improves the antifouling properties of the responsive membranes. The local perturbation was found to decrease the water flux, while it enhanced protein rejection. At a higher frequency (1kHz) of the applied electric field, the localized heating predominates compared to micromixing. In the case of a lower frequency of the applied electric field, more perturbation can lead to less permeability, whereas it will have a better effect in breaking the concentration polarization. However, during localized heating at a higher frequency, though perturbation is less, a heating induced reduction in permeability was observed. The electric field response of the membrane was found to be reversible in nature, and hence has no memory effect.