REMOVAL OF ORGANIC POLLUTANTS FROM TREATED WASTEWATER USING MICELLE-CLAY FILTERS

In countries where fresh water is abundant; treatment of wastewater is performed to sustain and protect the environment from pollution. In dry regions treatment of wastewater enables to find alternative sources for fresh water, thus overcoming in part the increased scarcity of this precious supply. Removing contaminants from wastewater can be performed using physical and chemical methods for primary treatment while, secondary wastewater treatment is accomplished by biological activity, which is designed to remove the biodegradable portion of organic constituents. Removal of recalcitrant substances as pesticides often needs advanced treatments, such as ultrafiltration, ion exchange, adsorption and reverse osmosis. In this work we evaluated how a filter based on a micelle-clay complex can be incorporated in a multi-stage procedure of wastewater cleaning to remove organic persistent pollutants. Al-Quds University plant for wastewater treatment includes biological decontamination, two ultra-filtration (UF) hollow fibre modules with cut-off of 100 and 20 kDa, respectively, an activated carbon filter, and finally a reverse osmosis membrane (RO) as reported by Kamis et al. (2009). The treated water is suitable for non-restricted irrigation. The current study investigated the purification capability of two filters (20 x 5 cm) prepared mixing a clay-micelle complex (CMC) with different excess of quartz sand (1:100, or 1:50, w/w). The filtration capacity of 1:100 and 1:50 CMC-sand columns was tested using water passed through the first UF filter (cut-off 100 kDa) forgoing the 20 kDa membrane, the activated carbon filter, and the RO stage. The micelle-clay complex was prepared as suggested by Polubesova et al. (2005; 2006) using montmorillonite and octadecyltrimetylammonium bromide (ODTMA). The CMC-sand columns were saturated with the solution permeated from the UF filter and spiked with 5 mg l-1 of tribenuron-methyl (TM – m/z 395 Da) and 5 mg l-1 of its degradation product 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (MMMT - m/z 155 Da), used as system efficiency markers for pesticide removal. After saturation the columns were eluted with the same effluent (not containing the two chemicals). Total suspended solids (TSS), total dissolved solids (TDS), turbidity, chemical oxygen demand (COD) and biological oxygen demand (BOD) were determined before and after elution in each collected 100 ml fraction using APHA standard procedures (American Public Health Association, 2006). Pesticide residues were determined by LC/MS as Chiola et al. (2010). The values of COD and BOD were reduced by an order of magnitude and 5-fold in 1:50 and 1:100 sand excess filters, respectively. In both cases, TSS and turbidity were completely removed and TDS was slightly detectable after filtration. Figure 1 shows the effect of filtration on the values of COD and BOD using the 1:50 CMC-sand filter. Tribenuron-methyl (Figure 2) was retained at 95% of added amount on the 1:100 CMC-sand filter and totally retained on the 1:50 CMC-sand column. Due to its lower molecular weigh and higher charge availability for the adsorption process, the pesticide degradation product (Figure 2) was completely removed in both cases. Table 1 reports the amounts of TM and MMMT found during the filtration process in the 100 ml fractions collected using the 1:50 CMC-sand filter. In conclusion, results indicate that the introduction in the waste water treatment system of a filter filled with a mixture of a micelle-clay complex in a sequence of purification steps could be able to achieve a high quality water avoiding further treatment stages also in the presence of pesticide residues.