The nutrient assimilative capacity of maerl as a substrate in constructed wetland systems for waste treatment

This study evaluated the performance of maerl (calcified seaweed);Is a subs trate for artificial wetland waste treatment systems. Pilot scale artificia l wetlands were set up in the laboratory; three planted with Phragmites aus tralis and three unplanted, and fed with a synthetic sewage solution. The e ffluent from the tanks was monitored over a period of 9 weeks for chemical oxygen demand, total nitrogen. total phosphorus, ammonium-N, total oxidised nitrogen, soluble reactive phosphorus, dissolved oxygen, pH and temperatur e. The data were analysed using repeated measures ANOVA to look for signifi cant differences between treatments, and within treatments, over time. A ba tch incubation experiment was also carried out to ascertain the maximum ads orption capacity of maerl for phosphorus. Results obtained were compared wi th those in the literature for other substrates. Variability within and bet ween treatments was high, but it was found that maerl effectively removed t otal phosphorus (98%). Nitrogen removal was less effective, with the tanks producing ammonium-N. The low nitrogen removal shown in the tanks was a fac tor of the short duration of the experiment; but ammonification did decreas e in the planted tanks over time. Performance at removing nitrogen was norm al when compared with figures in the literature, but phosphorus removal by maerl was considerably higher than gravel bed wetlands, and comparable with the very best figures given for artificial wetlands based on novel substra tes such as shales and slags. This trial showed that maerl has great potent ial as a constructed wetland substrate, due to its high phosphorus-adsorbin g capacity. (C) 2000 Elsevier Science Ltd. All rights reserved.