Effect of synthetic wastewater on young Kandelia candel plants growing under greenhouse conditions

Abstract

A greenhouse experiment was performed to evaluate the effects of synthetic wastewater in three different strengths, NW, MW and CW, on the growth of the one-year old Kandelia candel (L.) Druce plants. NW had the characteristics and strength similar to natural municipal wastewater while MW and CW contained five and ten times of the nutrients and heavy metals in NW, respectively. Artificial seawater was used as the control. During one year wastewater treatment experiment, Kandelia were found to withstand wastewater of high strength and toxic symptoms were not detected in all plants. Synthetic wastewater with strength similar to the natural municipal sewage (NW) stimulated plant growth. The plants treated with NW had significantly higher aerial and root biomass, taller stem than those found in the CW, MW and the control. Maximum growth, in terms of both stem height and total biomass, of all plants occurred in summer months, from June to September. With respect to the physiological and biochemical activities, CW and MW treated plants had significantly lower levels of chlorophyll a, total chlorophyll and catalase activity than those found in NW and control groups. In contrast, the proline content of plants treated with wastewater was similar to that of the control. These results suggest that normal wastewater (NW), attributed to its nutrients and trace elements, enhanced plant growth. The medium (MW) and concentrated wastewater (CW) supported similar amount of plant growth as the control but the physiological and biochemical parameters indicate that these treated plants might have been exposed to some kind of stress, probably due to the excess heavy metals present in MW and CW.