“Hypol FHP 2002™”, hydrophilic polyurethane (HPU) was used as a pre-polymer for foam formation. To produce HPU foam, the pre-polymer was heated to 40 °C in a water bath before mixing with the aqueous solutions. An amount of 670 g of pre-polymer was mixed with 1675 g of water to initiate foam reaction. Different additives: dry powder XL388 biomass (prepared according to ), clay and PAC were incorporated in the foam medium by adding a weighed amount of each additive into the aqueous media before mixing with pre-polymer. Polymerization process was performed in a 2 l plastic beaker, where the solution was vigorously mixed for 20 s using a mechanical stirrer and then poured into a rectangular glass aquarium (16 × 25 × 40 cm). As the foaming reaction progressed, the PU foam expanded to fill the mold. The foam was left for at least 30 min to reach its maximal strength, before the mold was removed. The thin impermeable “skin” layer that formed on the outer surface of the foam was removed by an electrical foam cutter (Bosch GSG 300). The foam was cut into cubes with average side dimension of 1 cm2. The four different foam compositions prepared are shown in Table 1. The foam specimens were washed by submerging them in deionized water for 15 min, squeezing and releasing several times. This washing procedure was repeated four times, after which the foam specimens were either oven-dried at 70 °C for 24 h to form dry foams, or submerged in water for 30 min, squeezed to remove the excess water, and dried by paper towels, to form pre-hydrated foams .