Development of a biosorption column utilising seaweed based biosorbents for the removal of metals from industrial waste streams

Abstract Development of a biosorption column utilising seaweed based biosorbents for the removal of metals from industrial waste streams. Richard K. Walsh. A range of seaweed species were screened (in live and dried form) for Cu2+, Pb2+ and Cr3+ removal properties including; (Rhodophytes) Polysiphonia lanosa, Porphyra umbilicalis, Gigartina stellata, Palmaria palmata, Corallina officinalis, Gracilaria verrucosa, (Chlorophytes) Ulva intestinalis, Ulva compressa, Ulva lactuca, (Phaeophytes) Ascophyllum nodosum and Fucus vesiculosus. Waste Ascophyllum Product (WAP), from an industrial process, was also screened. Results of batch tests indicated dried seaweed was preferable for utilisation in a biosorption column with WAP, F. vesiculosus and P. lanosa removing 1.50 mg Cu/g biosorbent, 1.69 mg Cu/g and 1.31 mg Cu/g respectively. Pre-exposure of a seaweed species to a metal in live form enhanced the removal of that particular metal when the seaweed was subsequently exposed in dried biomass form. Dried forms of WAP, F. vesiculosus and P. lanosa were each immobilised in agar, K-carrageenan and sodium alginate (all seaweed derivatives) prior to application in a fixed bed biosorption column in order to resist compacting due to hydrostatic pressure hindering flow-through. The agar and carrageenan seaweed biosorbents were formed into 15 mm x 5 mm x 10 mm blocks and the Na alginate seaweeds biosorbents formed 5 mm spheres. The fixed bed packed biosorption column, constructed from 304 grade heat treated SS with a PTFE interior coating, measured 70 mm internal Ø. The biosorbent bed height was 170 mm with a packing density of 260 g L-1. Each biosorbent was tested separately (4 replicates) in a column by running a 10 mg L-1 Cu2+ solution continuously for a period of 3 hours at 25ml min-1. The 5% agar/7.5% WAP biosorbent demonstrated the highest removal efficiency (RE) of 98%. Protonated biosorbents showed no significant difference in RE. Further testing of the 5% agar/7.5% WAP biosorbent showed overall metal removal values (W) of 269 mg Pb/ g, 91.3 mg Cu/ g and 57.4 mg Cr/ g. Breakthrough points (TB) were 6, 124 and 1.2 hours with exhaustion points (TE) of 96, 218 and 70 hours for Cu, Pb and Cr III respectively. After evaluation of column operation time and overall capacity, the 5% agar/7.5% WAP biosorbent was most suitable for the removal of Pb from a waste stream followed by Cu but was not practicable for the removal of Cr III