Abstract

Constructed wetlands (CW) have been considered as a waste and a stormwater treatment systems for small communities or for areas with unsteady sewage flow conditions. Several investigations were undertaken for estimation suspended solids, organic matter and nutrients efficiency removal but only few focused on retention of microorganisms in constructed wetlands. In this review mechanisms of elimination of viruses, indicator bacteria as well as helmith eggs and protozoan parasites are discussed. Generally the retention and the removal efficiency of microorganisms in the wetlands systems can be attributed to the combination of filtration, sorption and inactivation, which are controlled by the retention time and the flow condition. Filtration depends on the beds' matrix and involves the physical blocking of movement through the pores smaller then microorganisms. Binding between the solid surfaces and the microorganisms (especially bacteria cells) is mainly affected by the chemistry of the bed particles and the properties of the microbial organisms. The rate of microorganisms inactivation is probably also influenced by abiotic and biotic factors. The majority of allochtonic microorganisms die off after introduction to the "natural" treatment systems such as wetlands because of the abiotic stress. But even subpopulations better suited for survival and colonization, can also be eliminated because of predation. The bacterial phages, protozoa and nematodes as well as inhibitory substances secreted by other bacteria may also be a reason of reduction of the enteric bacteria in the wetland conditions. Also macrophytes in the wetland system are regarded as an essential in hygienisation of wastewater. However bacterial elimination in constructed wetlands is regarded as a highly efficient (>99,9%), the final number of bacteria in the treated sewage can still affect the environmental ecosystems.

Authors (5)