To improve the performance efficiency of subsurface constructed wetlands (CWs), a variety of media have been tested. Recently, there has been a rising interest in biochar. This research aims to develop the effectiveness of sand media amended with biochar and two plants species (Melaleuca quinquenervia and Cymbopogon citratus) in removing phosphorus from sewage effluent in CWs. The experimental design consisted of vertical flow (VF) mesocosms with seven media treatments based on the proportions of biochar in the sand media which ranged from 0 to 25% by volume. During the first 8months, the mesocosms were loaded with secondary clarified wastewater (SCW) then septage was used for the remaining 8months. Inflow and outflow were monitored for total phosphorus (TP) and PO4-P. Plants were harvested at the end of the experiment and TP biomass was determined. Removal efficiencies of TP in the mesocosms loaded with SCW and septage ranged from 42 to 91% and 30 to 83%, respectively. Removal efficiencies of PO4-P ranged from 43 to -92% and 35 to 85% for SCW and septage, respectively. The results revealed that the sand media performed better than the biochar-amended media; increasing the proportion of biochar in the media decreased removal efficiency of phosphorus. However, after flushing due to major rain event, there was no significant difference between sand and sand augmented with 20% biochar. Total plant P ranged from 1.75g in the 20% biochar mesocosm to 2.10g in the sand only mesocosm. Plant uptake of P, at least in part, may be accredited for the better P removal efficiency in the sand media compared to the biochar-amended media.

In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake Markermeer were high, viz. on average ca. 1,000 g m -2 day -1 . The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with its large surface area (dynamic ratio = [H(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most of the lake's sediment bed. Indeed, near-bed currents can easily reach values [10 cm/s. Measurements of the thickness of the settled ''mud'' layer, as well as 137 Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics were investigated in preliminary laboratory experiments in a small ''micro-flume'', applying increasing water currents onto five Lake Markermeer sediments. Sediment resuspension started off at 0.5-0.7 cm/s and showed a strongly exponential behaviour with respect to these currents.

Biochar has been identified as a media amendment to improve nutrient removal from wastewater, and N retention and plant growth in agroforestry. It therefore has the potential for treating domestic wastewater. The aim of this research was to compare nitrogen removal and plant growth in pure sand and sand amended with biochar, in wetland mesocosms (240 L) receiving sewage. There were seven media treatments based on the proportions of biochar in the sand media (100% sand, sand and coir peat, 5, 10, 15, 20, 25% biochar). The plant species were Paperback tree (Melaleuca quinquenervia) and Lemongrass (Cymbopogon citratus). The mesocosms were continuously loaded for 8 months with secondary clarified wastewater (SCW) (16 L/day). Septage was then intermittently loaded (20 L/2 days) for a further 8 months. Inflow and outflow samples were monitored for TN, NH 4-N, and NO x-N. All treatments showed good nitrogen removal efficiency. Average removal efficiencies of TN, NO x-N and NH 4-N in the mesocosms loaded with SCW ranged from 71 to 87%, 81 to 93% and 65 to 79%, for 100% Sand to 25% Biochar respectively. For septage, the removal efficiencies ranged from 63 to 81%, 69 to 87% and 66 to 81%, for 100% Sand to 25% Biochar respectively. Significant differences of nitrogen outflow concentrations were observed between pure sand and sand amended with biochar. Physical chemical properties of the biochar would have facilitated microbial processes and adsorption. Strong positive correlations were observed between biochar content in the media and nitrogen removal rates. The increased nitrogen removal may be attributed to higher mineralisation of organic nitrogen and NH 4-N, especially in the case of septage where strong correlation was observed between BOD 5 and TN removal. Total N biomass in the plants harvested after 21 months ranged from 13.4-14.0 g N. The addition of biochar did not increase plant N biomass in either species.