Recycling of wastewater nutrients in a wetland filter

• This thesis demonstrates the possibility of using wastewater nutrients for plant biomass production and concomitantly achieving year-round wastewater treatment. As part of a joint research project, the emphasis in this thesis is on nutrient recycling capacity relative to treatment efficiency.An artificial wetland system was studied in experimental field lysimeters. Wastewater was infiltrated into soil planted with reed sweetgrass (Glyceria maxima). In natural stands of this grass, harvesting two or three times per year had a negative impact on biomass yields. This was attributed to a reduced amount of carbohydrates stored in the rhizomes, resulting in the formation of thinner shoots in harvested stands. In contrast to this, high biomass yields were obtained with two harvests per year in the wetland filter.Crop removal of nitrogen and phosphorus amounted to a maximum of 55% and 28% of the amount applied during a growing season. Year-round wastewater application would decrease the relative removal because no plant uptake occurrs during the winter months. However, applied nutrients are also transferred to the soil, thus contributing to the nutrient recycling capacity of the system. This may determine the longevity of a wet! and filter as a method of wastewater treatment, since the soil is gradually saturated with phosphorus. Another factor of importance for the long-term limitations is the observed decrease in soil permeability.Treatment efficiency of phosphorus and BOD7 met the required limits for wastewater emissions in Sweden. An average 60% removal of nitrogen was achieved, which is significantly more than in a conventional tertiary treatment plant. The costs for reaching this treatment level were estimated to be lower for a wet land filter than for the existing treatment systems for urban areas up to 1000 inhabitants. The feasibility for this conceptual change of better resource management with regard to present Swedish wastewater treatment strategy is discussed.

Ämnesord

SAMHÄLLSVETENSKAP  -- Annan samhällsvetenskap -- Tvärvetenskapliga studier inom samhällsvetenskap (hsv//swe)

SOCIAL SCIENCES  -- Other Social Sciences -- Social Sciences Interdisciplinary (hsv//eng)

Nyckelord

INTERDISCIPLINARY RESEARCH AREAS

TVÄRVETENSKAPLIGA FORSKNINGSOMRÅDEN

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