Phyto-Fenton remediation of a dichloro-diphenyl-trichloroethane contaminated site in Ha Tinh Province, Vietnam.

A field trial was conducted at a site in Cam Binh commune, Ha Tinh province, Vietnam, highly contaminated with organo-pesticides. The phyto-Fenton process was applied to remove pesticide residues in soils. In addition to magnetite (Fe3O4) materials added to the soils, fertilizers and elicitors for oxidative burst were also added in the different experimental treatments. Dichloro-diphenyl-trichloroethane (DDT) and isomers were removed in all experimental lots. The removal efficiency was highest in lot B1, a site where only iron materials were added. The removal efficiency and the final content of DDTs in B1 were 98.4% and 0.009 mg kg-1, respectively. In the presence of elicitors, the conversion of DDT to dichloro-diphenyl-dichloroethylene was more favorable. Analysis of soil properties indicated that the phyto-Fenton process can occur at neutral soil pH, and when there are only small changes in soil organic carbon content and cation exchange capacities. Shifts in the composition of the microbial communities were observed. Further studies on the interactions between materials added to soil, plants, and the soil microbiome are needed to understand the mechanism of action of the phyto-Fenton process during soil remediation.

Assessment of anti-fouling strategies for membrane coupled with upflow anaerobic sludge blanket (MUASB) process.

In this novel process, domestic wastewater was filtered by a hollow-fibre membrane coupled with an upflow anaerobic sludge blanket (MUASB) bioreactor. To improve the process sustainability and decrease energy costs, the membranes were operated under low fluxes with little, or no, shear. The efficiency of anti-fouling strategies, including relaxation, backwashing and supply of low aeration and stir rates, was assessed through detailed characterization of the fouling layers. Results indicated that backwashing was more efficient than relaxation, even when the systems were operated under the same flux productivity. In terms of shear supply, stir provided a better fouling limitation strategy compared to aeration, at similar shear stress values. Physical and chemical cleaning methods were applied to recover three fouling fractions (i.e. cake, residual and irreversible) for better characterization of the fouling layers. Under the sustainable operating conditions used in this study, most of the fouling was easily reversible by simple rinsing. In addition, permanent and irreversible fouling, resulting in the need for frequent chemical cleanings and potential membrane degradation, is limited once small shear stresses are applied. These outcomes are expected to form the basis for the future assessment of trade-off between operation, maintenance and replacement costs of membrane filtration processes used in wastewater treatment.

Advanced characterization of fouling in membrane coupled with upflow anaerobic sludge blanket process.

In this study, an advanced process based on the use of ultrafiltration hollow fibre membranes immersed in the supernatant of an upflow anaerobic sludge blanket bioreactor (MUASB) and operated under low permeate flux was proposed. Process sustainability was assessed under different operating conditions: membranes were immersed either in the supernatant or in the biomass bulk and operated under various permeate fluxes. Additionally, temporal investigation was also proposed through the advanced characterization of fouling behaviour by systematic fractionation (based on level of reversibility) and analysis by liquid chromatography-organic carbon detector. Among the various suspended solids (SS) concentrations in supernatant (10, 25, 100, and 400 mg L(-1)) and in biomass bulk (6500 mg L(-1)), higher fouling levels were observed under low SS concentrations. However, more easily reversible fouling was obtained under MUASB conditions, demonstrating potential long-term sustainability. Results of long-term operation indicated that an increase of flux leads to larger amounts of SS participating in irreversible fouling and higher irreversibility. Temporal change in fouling characteristics revealed that the most easily removable fouling layer (i.e. cake), and its relative fraction of SS, were the two main factors impacting on the overall hydraulic performance. Additionally, the development of microbial population on the membrane surface was closely related to the proteins content and the overall hydraulic resistance. Polysaccharides and other dissolved organic matters (humic substances, building blocks, and low molecular weight compounds) presented low effect on membrane fouling.