Reduction of ammonia from wastewater effluent using modified activated clay

Abstract

It has been noticed that effluent from wastewater treatment plants in South Africa does not comply with the minimum requirements of environmental standards of wastewater effluent for discharge into the environment. This is due to the presence of soluble, persistent organic pollutants (POPs) and other related pollutants, in particular ammonia (PakWaterCare Services, 2011). To rectify this situation, this study sought to treat wastewater effluents, initially using natural clay (bentonite and Montmorillonite). Secondly, the clay was activated by sulphuric acid to increase its adsorptive properties. The concentration of sulphuric acid ranged from 0.5M to 18.4M so that the effective concentration could be reached. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum POPs capture. The experiment was conducted two ways: 1) at first the only bentonite was used, and 2) samples were subsequently activated with H2SO4 (6M; 8M and 11M). The dosage of the coagulant into the jar tester beakers per litres of water was 0.5; 1; 1.5; 3; 5 and 10g. And then, by keeping the mixing speed (rapid mixing at 150rpm for 1min and slow mixing at 20rpm for 20min) and settling time constant (30min), the bentonite and Montmorillonite were activated by H2SO4 (0.5M; 3M; 5M; 11M and 18.4M). It was observed that for an increase in coagulant dosage, a decrease in pH was observed. This was due to an increase in acid dosage which influences the acidity of the water. The achieved results for wastewater effluents indicated that using activated clay (bentonite) as a coagulant with an optimum removal and maximum surface area for acid activation attained at 5M concentration of sulphuric acid used for activation of clay. The combinations of 5M bentonite clay to ZINPs (zero valent iron nano particles), in a mass ratio of 99:1 respectively, reduced ammonia up to 96.85% with a dosage of 61.6mg coagulant, a reduction from the raw water 277mg/L to 8.71mg/L. Most of the sample pH ranged from 6.5 to 9 as required by the Department of Water Affairs and Forestry. The samples’ conductivities were below the standard 2500μs/cm; the 5M+ZVINPs at 60.1mg had a conductivity of 259μs/cm. Hence, this treatment is not only effective and economical, but also ecologically acceptable.