REMOVAL OF ALUMINIUM FROM FILTER BACKWASH WATER USING ADSORBENTS AND A GEOTEXTILE

Abstract

Aluminium present in filter backwash water (FBWW) at the J. Douglas Kline Water Treatment Plant (JDKWTP), located in Halifax, Nova Scotia, represents a challenge for environmental compliance. The aluminum (Al) concentration in the FBWW sometimes exceeds the provincial regulation of guidelines of 184 (µg/L). The utilization of alum (Al2(SO4)314H2O) coagulation during treatment operations is the predominant source of this aluminum. The aim of this study is to investigate utilizing adsorbents and geotextiles to reduce total and dissolved Al concentration and total suspended solids (TSS) in the FBWW. Three adsorbents; calcium oxide (CaO), magnesium oxide (Mg0) and ferric oxide (Fe3O4) and several combinations of these adsorbents were investigated in the study. In addition, Tencate GT500 woven geotextiles were chosen as filter media to remove Al as well as to minimize TSS from the adsorbent-treated FBWW. An optimal dosage of cationic polymer was also considered to assist with the acceleration of floc formation to achieve better removal efficiency. For the testing, 1 mg/L of cationic polymer was utilized considering both pH adjustment (approx. 6.5) and without pH adjustment conditions. Adsorbent dosage was increased stepwise with an addition of 0.1~5.0 gm per liter in the FBWW resulting in removal of total Al between 95% to 98% using MgO and CaO and around 83~89% using ferric oxide. Reduction of TSS was also achieved in these trials. Geotextiles were also used to efficiently remove TSS and removal of total Al concentration was found around 95% from these treated FBWWs. An optimal (i.e. 1 g/L) dosage of a combination of 50/50 mix of CaO and iron oxide adsorbents was found to be an effective dosage resulting from the analysis which can be useful for further recommendations in future.