Pathogens can be categorised as bacteria, viruses, protozoa and helminths (Awuah, 2006). The most common pathogen found in wastewater is Salmonella. However, there are many other pathogens harmful to human health, such as E. coli, Pseudomonas, Shigella, Vibrio, Mycobacterium, Clostridium, Leptospira, Yersinia, Giardia, Cryptosporidium, intestinal worms, Norwalk virus and rotavirus (Marsalek et al., 2002).
Since identification and quantification of all pathogens is impractical, too expensive and time consuming, a few organisms are used as indicators of water quality, such as coliform indicators (total coliform, fecal coliform and E. coli), fecal streptococci, enterococci, Clostridium perfringens and Aeromonas. The methods for their quantification, which have been the same for the past 30 years for the examination of water and wastewater (APHA, 2005) and are not standard, are adapted according to the varying conditions. However, it should be kept in mind that no single indicator guarantees that the water is free of pathogens (APHA, 2005). Coliforms are usually used as indicator because it is rare to isolate bacterial enteric (intestinal) pathogens without fecal contamination (APHA, 2005). Moreover, coliforms usually outlast most common pathogenic bacteria during natural die-off. However, they do not always survive viruses and other organisms (Awuah, 2006). Moreover, the general believe that by removing fecal coliforms, all other pathogens would also be removed to a satisfactory level is no longer sufficient, because recent technologies and methodologies can qualify and quantify more resistant pathogens (Crockett, 2007).
Removal of pathogens might be harder that it seems due to the adaptive processes of the microbial cells of the organism, which might include modification of enzyme synthesis to take-up growth limiting nutrients or re-routing of metabolic pathways (Awuah, 2006).
Algae have been reported to enhance pathogens growth, but also to have a bactericidal effect on them. Chlorella vulgaris has been reported to compete with heterotrophic bacteria for glucose, especially at neutral conditions. Under stress conditions, including high pH, Chlorella vulgaris will produce toxins of long chain fatty acids, which will selectively destroy pathogens (Awuah, 2006).
Natural die-off is one of the most important factors for removal of faecal coliforms (Awuah, 2006). Other factors include: temperature, pH, oxygen, sunlight (UV radiation), Attachment/adhesion of pathogens to the host tissues, Competition for nutrients and predation of bacteria by viruses, protozoa and bacteria themselves.
The commonly available technologies for pathogens removal include: reverse osmosis, UV disinfection, ozonation and membrane filtration. However all these technologies are still very expensive, therefore not very sustainable in a close cycle approach as the one to be implemented at NIOO.
The source separated black water (BW) of the NIOO building will be treated on-site, as presented in Fig. 1, in order to remove the excess of nutrients, ensuring a final effluent that can be discharged to surface water without environmental and public health risk.
It is known that the effluents of anaerobic wastewater treatment reactors are high in pathogens due to its favourable growing conditions in terms of temperature, pH and oxygen levels (van der Steen et al., 1999). Therefore, in this project we intend to evaluate the pathogens resilience throughout the proposed treatment scheme and to define ways for removing them.
The work plan consists of:
- Determining which indicators for pathogens should we analyse
- Determining what is the concentration of indicator pathogens in:
- raw BW
- digested BW from UASB operated at mesophilic conditions
- digested BW from UASB operated at thermophilic conditions
- accumulate in digester’s sludge
- after solids removal (still have to see if it will be needed to remove SS and how)
- accumulated in algae
- effluent of algae photobioreactor (PBR).
At the end we will be able to give insight on the pathogens removal efficiencies of the:
- UASB thermophilic
- UASB mesophilic
- Algae photobioreactor.
APHA. (2005) Standard Methods for the Examination of Water and Wastewater. 21st edn ed.
American Public Health Association, Washington DC.
Awuah E. (2006) Pathogen Removal Mechanisms in Macrophyte and Algal Waste Stabilization Ponds,
Wageningen University / UNESCO-IHE Institute for Water Education, The Netherlands, Delft.
Crockett C.S. (2007) The Role of Wastewater Treatment in Protecting Water Supplies Against
Emerging Pathogens. Water Environment Research 79:221-232.
Marsalek J., Schaefer K., Exall K., Brannen L., Aidun B. (2002) Water reuse and recycling, CCME
Linking Water Science to Policy Wirkshop Series, Canadian Council of Ministers of the
Environment, Winnipeg, Manitoba. pp. 39.
van der Steen P., Brenner A., van Buuren J., Oron G. (1999) Post-treatment of UASB reactor effluent
in an integrated duckweed and stabilization pond system. Water Research 33:615-620