Biological treatment of saline municipal wastewater

Project co-ordinator: Prof. Dr. Boris Kompare
Faculty of civil engineering and geodesy

Many Slovenian and other coastal cities have sewerage systems that are influenced by the tide. Even the best-constructed sewerage pipelines can have elements that may provide seawater intrusion. The consequence is that the municipal WWTP has to cope with additional loads from both the in hydraulic, as well as the qualitative point of view (salt, chlorides). The hydraulic loads can be solved by engineering measures, while the successful treatment of saline water usually poses great problems. The microorganism (MO) community may adapt to certain levels of salinity, provided that there are no oscillations. In municipal sewerage salinity often oscillates daily (wastewater production, tidal effects), and thus the MO cannot adapt. The consequence is a considerable reduction in the efficiency of wastewater treatment, which can be much lower than that required by legislation.

The aim of this WP is to try to find MOs that are more tolerant to salinity oscillations and then develop suitable technologies for biological wastewater treatment to obtain the desired treatment efficiency – i.e. comparable to continental WWTP's without the influence of salinity. It is foreseen that such MOs could consist of halotolerant fungi, able to grow at fluctuating salinity and degrade pollutants under these circumstances. This also means development of biomass carriers and at the same time protection of the biomass against unfavourable conditions that still have to be investigated.

The research will be conducted in several phases:

(1)Isolation of suitable MOs at a pilot WWTP, that will be erected at a municipal WWTP site which has salinity problems.

(2)Isolation of enriched selected halophilic and halotolerant fungi from natural hypersaline environments (Sečovlje salt pans), where they are already selectively enriched

(3)Taxonomic identification of cultivable microfungi through a polyphasic approach: morphology, metabolic profiles, and genomic characteristics (sequences).

(4)Physiological characterisation of microbial halotolerance with emphasis on adaptation to broad salt ranges (from 0 -32% NaCl).

(5)Investigation of adaptation mechanisms at the level of metabolism and growth of the selected targeted MO. In the selected MOs, differentially expressed genes and their protein products will be studied as a response to the presence of pollutants in salinised community waste waters, in comparison with non-saline waters. We will try to identify and characterise the mechanisms of action of the key proteins involved in the degradation of pollutants at high salinity. This knowledge should enable engineering of proteins with improved characteristics.

(6)Construction of a suitable pilot WWTP, that will optimise conditions for the growth of MOs and at the same time fulfil the wastewater treatment criteria. Simultaneously we will study the possibility of enrichment of the actual microbial consortium, unadapted to increased salinity, with adequate eurihaline microfungi and potentially also bacteria, optimally adjusted to saline conditions.