Multipurpose plant systems for renovation of waste waters

Abstract

Two promising aquatic macrophytes Lemna minor (Duckweed) and Eichornia crassipes (Water Hyacinth); were used to test their cleaning ability for domestic waste waters in lagoons with one entry point and three outlets in 1996 (floatation rate 110 m(3)/day; BOD5 130-170 mg/l; pH 13.5). E. crassipes plants (5+ 5 roots, 25 cm long) were cultured in two lagoons and L. minor in one lagoon. Both species failed to grow due to a high pH. In 1997 the pH of water was neutralized to 6-7 before plant introduction in to the lagoons. L. minor plants did not grow due to overgrowth of rushes. However, E. crassipes grew very well and a total of 3 100 and 3400 roots were counted after 90 days with average heights of 70-75 cm, during this year. These plants showed high absorptive capacity. The dry weight of the harvested plants showed a parallelism to the prevalence with 80.160 kg dry weight. Phenological observations revealed that 80-90% of the plants covering the lagoon surface bloomed and water coming from the outlet became clear enough with a BOD5 value of 30-40 and 50-80 mg/l. In a later experiment L. minor (20 plants) was cultured in a tank in May 2001 (BOD5 130, COD 170, suspended matter 35.2 mg/l). In all 1100 plants/m(2) were counted at the end of 90 days. After harvesting Lemna plants, water analysis showed that BOD5 was 39.27, total nitrogen content 43, phosphorus 2, potassium 1.67, Pb 0.02, Cd 0.005, and Cr 0.05 mg/l. Renovated and non-renovated waters were used for irrigation of lawns covered by the grass species like Lolium perenne and L. italicum. These species behaved better when sprayed with 100% renovated water than mixed or non-renovated waters.