Phosphorus removal from sewage by flocculated foamed lightweight aggregate: Performance optimisation, adsorption kinetics and mechanisms

In this paper flocculated foamed lightweight aggregate (FFLA) with polymeric ferric sulfate (PFS) as flocculant was proposed to replace traditional aggregate to improve phosphorus removal efficiency of pervious concrete. The effect and the mechanism of PFS on the basic physical properties, phosphorus removal efficiency evaluation and adsorption kinetics were studied. The results showed that with the increase of PFS content, the loose bulk density, cylinder compressive strength and softening coefficient of FFLAs decreased, and the water absorption through time increased because PFS promoted the foaming of hydrogen peroxide and the correlation coefficients between loose bulk density and cylinder compressive strength and softening coefficient exceeded 0.93. The highest removal rates of TP and PO43--P were 87.71% and 96.49% by FFLAs. According to the correlation coef-ficient R2 of adsorption kinetic models, TP removing could be reflected by Pseudo-first order and Intraparticle diffusion models. So the diffusion and flocculation or precipitation played major roles in kinetic mechanism. There was no evident effect of 60-day phosphorus-removal soaking on FFLA composition according to FTIR and DTG-TG results, which could effectively ensure the durability of pervious concrete. P2O5 could be clearly seen in the XRF results, so the porous structure of FFLA could effectively adsorb phosphorus.

Automated summary

This study proposed the use of flocculated foamed lightweight aggregate (FFLA) with polymeric ferric sulfate (PFS) as a replacement for traditional aggregate in order to enhance the phosphorus removal efficiency of pervious concrete. The effect and mechanism of PFS on the physical properties, phosphorus removal efficiency evaluation, and adsorption kinetics were investigated. The results showed that increasing PFS content led to decreased loose bulk density, cylinder compressive strength, and softening coefficient of FFLAs, while increasing water absorption over time due to the promotion of foaming by PFS. FFLAs achieved the highest removal rates of TP and PO43--P, which were 87.71% and 96.49%, respectively. The results also suggested that diffusion and flocculation or precipitation played major roles in the kinetic mechanism.