Substrate effect on bacterial communities from constructed wetlands planted with Typha latifolia treating industrial wastewater

Abstract

Constructed wetlands (CWs) have been recognized as being able to effectively treat wastewater from municipal and industrial sources. This study focused on the effect of different substrates and long-term operation of horizontal subsurface flow CWs treating tannery wastewater on the bacterial communities. The CWs were planted with Typha latifolia in three types of substrate: two units with different types of expanded clay aggregates and one unit with fine gravel. Another unit with expanded clay was left unvegetated. Changes in the bacterial community related to the type of substrate, different hydraulic loading rates and along CW operation were examined using denaturating gradient gel electrophoresis (DGGE). Bacterial enumeration was also performed and several bacterial isolates were retrieved from the CWs. Phylogenetic affiliations of those isolates were obtained on the basis of 16S rRNA gene sequences and revealed that they were closely related to the genera Bacillus (TM1S1, TM1R3, TNR1 and TAR1), Paracoccus (TM1R2), Pseudomonas (TM1R1) and Halomonas (TM1S2). The type of substrate and the presence of T. latifolia had a major effect on the species richness and the structure of bacterial communities as inferred by numerical analysis of DGGE profiles.

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

“…These properties will influence the development of the biota which the substrate provides support for. In fact, it has been observed that some particular materials seem to be preferable media for some plant species and microorganisms strains [81][82][83]90]. On the other hand, the development and activity of the biotic elements may over time affect and modify the support matrix characteristics.…”

“…In the past, much of the design of CWS has been done with little knowledge of (or consideration for) the roles played by each component and how their effects could be enhanced and optimized. However, over the most recent years some accumulated knowledge has been increasingly applied in the construction and operation of new systems, which results in a much greater variety of plant species, support matrix materials and constructed wetland designs being seen, studied and introduced in newly set up CWS [35,42,43,58,60,[73][74][75][76][77][78][79][80][81][82][83][84][85]. The goals of the target contaminants to remove in those CWS have also become increasingly more ambitious.…”

“…Populations of microorganisms develop naturally in CWS and are exposed to some similar factors as those affecting their development in WWTPs. These microbial communities are very diverse and one can find an array of bacteria, fungi, protozoa, algae, etc., among the microorganisms that thrive in wetlands, which provide adequate environmental conditions for their growth and development but whose characteristics are also pronouncedly influenced by the type of vegetation and the support matrix materials [35,58,[81][82][83]. The characteristics of these microbial populations can additionally be modified by inoculation of the CWS with strains that are more suitable for the purpose of the system.…”

“…The nature and activity of the biotic CWS components is also strongly correlated to the support matrix pH, which has a particularly profound effect on the microbial community composition and the development of plants. Different gradients of redox, nutrients availability, and environmental conditions, such as pH and temperature create variable niches throughout the wetland systems, in which different biochemical processes take place which can be determinant for the treatment efficiency [81][82][83]90].…”

“…Temperature, pH, oxygen, presence of toxic substances and nutrients available within the CWS are expected to play a very important role in the removal efficiency [72,[81][82][83]90].…”