No abstract

No abstract

No abstract

Mass balance performance data from side by side studies of planted and unplanted gravel-bed treatment wetlands with horizontal subsurface-flow are compared. Planted systems showed enhanced nitrogen and initial phosphorus removal, but only small improvements in disinfection, BOD, COD and suspended solids removal. Direct nutrient uptake by plants was insufficient to account for more than a fraction of the improved removal shown by planted systems. Roles of plants as ecosystem engineers are summarised, with organic matter production and root-zone oxygen release identified as key factors influencing nutrient transformation and sequestration.

Ammoniacal nitrogen (ammonia and ammonium) in agricultural wastewaters can promote eutrophication of receiving waters and be potentially toxic to fish and other aquatic life. Zeolites, which are hydrated aluminum-silicate minerals, have an affinity for ammonium ions (NH 4 + ) and are, therefore, potentially useful in removing this contaminant from wastewaters. The major objectives of this study were to evaluate the capacity of two natural New Zealand zeolites (clinoptilolite and mordenite) to remove NH 4 + from a range of wastewaters under both batch and flowthrough conditions. Effects of two zeolite particle size ranges (0.25-0.50 mm and 2.0-2.83 mm) on NH 4 + removal performance were also investigated. Results obtained from the batch adsorption experiments indicated that both zeolites tested, regardless of their particle sizes, were equally effective (87-98%) -3 of wastewater throughput, which equates up to 5.8-6.5 g NH 4 -N kg -1 zeolite. In contrast, at a faster loading flow rate (15.9 mm min -1 ), the breakthrough was almost immediate (1 BV) for coarse zeolites and after 22 BVs for fine zeolite. The NH 4 + breakthrough capacity for fine mordenite was 2.0-4.4 g NH 4 -N kg -1 zeolite. Fine zeolites were more effective than coarse zeolites in removing wastewater NH 4 + (95% and 55% removal, respectively), even after receiving 64 BV of wastewater.

No abstract

No abstract

No abstract