AbstractThe Urban Waste Water Treatment Directive increases government regulatory pressure required to ensure phosphate discharged by Waste Water Treatment Works (WWTWs) meet consent. Bricks from construction waste have been viewed as an alternative treatment medium for phosphate. This thesis examines the use of recycled bricks and novel brick-like materials to afford an opportunity for the provision of a green solution to issues associated with phosphate removal and recovery.
This thesis builds on existing studies on the use of recycled bricks, firstly eliminating the problem associated with use of powdered form of clay material by pelletising these materials. The pellets developed performed better than conventional brick dust. The composition of pelletised material was modified to ascertain the extent of phosphate adsorption. Optimization of pelletised material was carried out in batch studies, and phosphate removal was found to vary with elemental composition and increase with treatment time among other factors. The maximum adsorption capacity was 42.37 mg/g, 70.42 mg/g and 52.91 mg/g for AlMFCP, CaMFCP and FeMFCP respectively. The modified pellets show a faster kinetic that was up to five times faster than FCP signifying that the modified pellets will require a reactor that was five times smaller in size than FCP. Physisorption was the dominant adsorption mechanism supported by some pore diffusion for AlMFCP and FeMFCP but the dominant mechanism for adsorption using CaMFCP was chemisorption supported by some physical diffusion processes. Acidic pH favoured adsorption using FeMFCP, and slightly acidic pH for AlMFCP while adsorption using CaMFCP was favoured at acidic and neutral pH. Phosphate adsorption achieved using materials of this study was compared to materials of other studies through the comparison of adsorption isotherms. Pellets modified with calcium carbonate showed the best performance and was consequently used in further studies. Phosphate adsorption involved different mechanisms at different stages but tending to physisorption as the dominant mechanism.
Fixed bed column study performed on the pellets showed the practicability of a full-scale application in a wastewater treatment plant. Increase in bed height and column diameter improved adsorption capacity due to longer empty bed contact time (EBCT) between the adsorbent and phosphate in solution. Higher flow rate hindered adsorption as a result of shorter contact between adsorbent and phosphate in solution. The column with column diameter of 2 cm, bed height of 10 cm and influent phosphate concentration of 20 mg/L showed the shortest retention time of 1.75 minutes, followed by the column with a bed height of 10 cm, column diameter of 5 cm and influent phosphate concentration of 20 mg/L.
Phosphate sorbed to materials in this study was recycled as a slow release fertilizer for agricultural production. The spent adsorbent compared favourably with yield obtained from KH2PO4fertilizer. The yield increased with increase in application rate of phosphate with 382.17 kgP/ha producing the highest yield. The performance of pots with P added in the form of phosphate sorbed to CaMFCP was similar to pots with P added in the form of KH2PO4when germination rate, plant height and WM yield were considered while pots with added KH2PO4showed a better DM yield than pots with P added in the form of phosphate sorbed to CaMFCP. Relative effectiveness of fertilizer showed improvement as growth progressed. At the latter stages, yield using phosphate from spent filter materials surpassed KH2PO4fertilizer. This demonstrated that spent fired clay pellets could be used as a slow release fertilizer for agricultural purpose thereby offering a green and cost effective option for phosphate removal in wastewater and the management of the resultant waste pellets.
|Date of Award
|Augustine Ifelebuegu (Supervisor) & Adrian Wood (Supervisor)