Lead (Pb²⁺) adsorption by means of pristine and prewashed residual Moringa oleifera Lam. seed husk biomass for water treatment applications

Moringa oleifera Lam. (MO) seed husk waste was used to remove Pb during batch and filtration processes, from lead-containing water. MO husk biomass was used in its pristine (i.e. unwashed) and prewashed forms. Adsorption was described by the Dubinin-Radushkevich model (q_m 3.719 [mg Pb/g MO husk], K = 1.116×10⁻⁷ [mol²/J²]). A new developed model (Bulk Balance Filtration Model-BBFM) correlated better to 15-cm bed height continuous experiments (q_F  = 730.9 [mg/L] and k_B  = 0.00189 [L·mg⁻¹·min⁻¹]–pristine husk, and q_F  = 528.7 [mg/L] and k_B = 0.001921 [L·mg⁻¹·min⁻¹]–prewashed husk). BBFM and classic models adjusted well to the 30-cm bed data, while the classic models correlated better to the 45-cm bed filter. In general, prewashing was inefficient to improve metal removal and prewashed husk revealed an unfavourable change in its morphology. The adsorption process resembles to be purely physical in accordance to the isotherm parameters and FTIR spectra. SEM-EDS results corroborate the presence of adsorbed lead in MO husks. Pristine MO husk waste exceeded 91% Pb removals, water usage was minimum and no chemicals were added. Pristine MO husk without a prewashing step provides a green, practical and cheap solution to rural communities’ households and may serve as a business opportunity for families dedicated to growing and harvesting MO.