Urban Institute Ireland Research Collection

Aluminium-based water treatment residual (Al-WTR) is the most widely generated residual from water treatment facilities worldwide. It is regarded as a by-product of no reuse potential and landfilled. This study assessed Al-WTR as a potential phosphate-removing substrate in engineered wetlands for wastewater treatment. Results indicate the specific surface area ranged from 28.0 m2 g-1 to 41.4 m2 g-1 and this increased with increasing particle size. X-ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy all indicate that the Al-WTR is mainly composed of amorphous aluminium which influences its phosphorus (P) adsorption capacity. The pH and electrical conductivity ranged from 5.9 - 6.0 and 0.104 dS m-1 - 0.140 dS m-1 respectively, and both showed that it should suitably support plant growth. Batch tests showed a maximum P adsorption capacity of 31.9 mg-P g-1 and significant P removal was achieved in column tests. Overall, results showed that Al-WTR can be a low-cost, easily and locally available substrate for enhanced P removal in engineered wetlands and it carries the benefits of reuse of a by-product that promotes sustainability.

Excess phosphorus (P) in wastewaters promotes eutrophication in receiving waterways. A cost-effective method such as use of novel low-cost adsorbents for its adsorptive removal would significantly reduce such impacts. Using batch experiments, the intrinsic dynamics of P adsorption by waste alum sludge (an inevitable by-product of drinking water treatment plants) was examined. Different models of adsorption were used to describe equilibrium and kinetic data, calculate rate constants and determine the adsorption capacity. Results indicate that the intraparticle rate constant increased from 0.0075 mg g-1 min-1 at 5 mg L-1 to 0.1795 mg g-1 min-1 at 60 mg L-1 indicating that more phosphate is adsorbed per gram.min at higher P concentration. Further analyses indicate involvement of film and particle diffusion mechanisms as rate controlling steps at lower and higher concentrations respectively. Mass transfer coefficient obtained ranged from 1.7 × 10-6 to 1.8 × 10-8 indicating a rapid transportation of phosphate molecules onto the alum sludge. These results further demonstrates that alum sludge – hitherto thought of as undesirable waste, can be used as novel adsorbent for P removal from wastewater through various applications, thus offsetting a portion of the disposal costs while at the same time improving water quality in sensitive watersheds.