Removal of organic pollutants and nutrients from olive mill wastewater by a sand filter.

Effects of wastewater discharge on microbial populations and enzyme activities in mangrove soils

The use of willow vegetation /lters for wastewater treatment is gaining interest in Sweden. A study was conducted in order to determine reasonable rates of wastewater application to such vegetation /lters. NO 3-N leaching loads and N-uptake by the plants were quanti/ed in relation to nitrogen application rate, irrigation rate, shoot growth, and soil type during three years after planting of willow (Salixviminalis ) in sixteen 1200-l lysimeters /lled with clay or sand soil. Nitrogen was applied at rates corresponding to 110 –244 kg N=ha yr combined with irrigation of 3–6 mm=day during 100 –110 days each growing season. NO3-N leaching loads were very high the /rst year after plant establishment (on average 341 kg N =ha from clay and 140 kg N=ha from sand lysimeters). However, NO3-N leaching loads decreased and were low or negligible during the second (43 from clay and 17 kg N=ha from sand lysimeters) and third year (3 kg N=ha from clay and less than 1 kg N=ha from sand lysimeters). Harvest of the plants after the second growing season did not seemingly a8ect NO3-N leaching loads during the third year. Soil type and N application rate strongly in9uenced NO3-N leaching loads, whereas irrigation rate had only a slight e8ect, and thus, dosing of wastewater should be based on N-amounts. Assuming an annual shoot growth of 10 tonnes (dry weight)=ha in a willow vegetation /lter, wastewater could be applied at rates corresponding to 160 –190 kg N =ha without substantial NO3-N leaching losses. c 2001 Elsevier Science Ltd. All rights reserved.

Nitrate leaching from lysimeter-grown short-rotation willow coppice in relation to N-application, irrigation and soil type

The progress of research on the magnitude of denitrification has been restricted by the difficulties involved in making accurate field measurements. Numerous laboratory studies have provided useful information on the factors affecting denitrification in soils but these findings cannot be used to predict the extent of denitrification in the field. In recent years, increased interest in the efficiency of nitrogen (N) use in agriculture and the impact of fertilizer N on the environment have spurred research on the development of field methods for measurement of denitrification loss (Rolston et al. 1976, 1978, Focht 1978, Ryden et al. 1978, 1979a,b, Denmead 1979, McKenney et al. 1978, Matthias et al. 1980).

R. G. Gilbert

Papers

Denitrifying Bacteria Populations and Nitrogen Removal in Soil Columns Intermittently Flooded with Secondary Sewage Effluent 1