CONSTRUCTED WETLANDS FOR WASTE-WATER TREATMENT IN ESTONIA

In Estonia many natural/semi-natural wetlands have been used for munic ipal or agricultural wastewater. During the last 6 years twelve constr ucted wetlands for wastewater purification were established. Budgets o f organic matter (BOD), total-N and total-P of three systems (a sand/p lant filter with vertical flow, established in 1992, area 90 m(2), loa ding 3.8 g BOD m(-2) d(-1); a combined overland flow-vertical flow roo t-zone system on a Phalaris arundinacea-slope, 1989, 2400 m(2) ha, 1 g BOD m(-2) d(-1); an aquatic macrophyte channel (bioditch), 140 m(2), 40 g BOD m(-2) d(-1)), located in southern Estonia, are analyzed. Exce pt for nitrogen, the efficiency of the sand/plant filter was found sat isfactory: 82%, 36%, and 74% for BOD5, total-N, and total-P, respectiv ely. The poor performance with respect to nitrogen may be caused by we ak vegetation. In the Phalaris-system, 65% of organic matter, 67% N, a nd 80% P was removed. The average output concentrations of this system were always lower than the recommended limits (BOD5 < 10 mg l(-1) tot al-N <10 mg l(-1), and total-P <2 mg l(-1)). Due to the high input loa d, the BOD5, total-N, and total-P values in the outlet of the bioditch were high and extremely variable: 5-100, 6-16, and 1-4 mg l(-1), resp ectively. To guarantee the recommendable output values from the biodit ch, either a significant decrease of input load or an enlargement of t he area of the wetlands would be needed. All results show that compare d to other seasons the winter performance was not reduced. (C) 1997 IA WQ. Published by Elsevier Science Ltd.