Cleaning secondary effluents with organoclays and activated carbon

Background: Flocculation, adsorption and ultrafiltration, alone and in combination, were tested for tertiary treatment of Beer Sheva (southern Israel) municipal wastewater. The focus was on the adsorption of soluble organics with powdered activated carbon (PAC) and with organoclays. Results: Adsorption on 0.6 g L ^-1 octadecyltrimethylammonium bromide (ODTMA) - bentonite and flocculation with 130 mg L ^-1 FeCl ₃ reduced the dissolved organic carbon (DOC) level by 46%, and that was the highest DOC retention obtained with the organoclays. Retention achieved with 0.6 g L ^-1 PAC and 130 mg L ^-1 FeCl ₃ was 65%. Filtration through a more hydrophobic PVDF-30 membrane for 30 min resulted in 35-40% flux drop. A reasonable 6-7% flux reduction was obtained with filtration through a more hydrophilic PS-50 membrane. Conclusion: Oganoclays at low doses are a good target adsorbent for single low molecular weight molecules. On average, higher TOC retention was achieved with PAC. Introduction of adsorption as a pre-treatment step can lead to minimization of flux losses, reduced demand for flocculation and improved economics of the entire treatment.