2.3. Limitations regarding microbiological
indicators
Regarding the microbiological indicators, low
faecal coliform removal efficiencies have been
reported in anaerobic reactors, usually amounting to around only 1 log-unit (Chernicharo
et al. 2001c; von Sperling et al. 2002, 2004; von
Sperling & Mascarenhas 2004). Regarding other
types of microorganisms, such as viruses and
protozoans (mainly Giardia and Cryptosporidium), there are few references covering their
reduction or elimination in anaerobic reactors.
The removal of helminth eggs in anaerobic
reactors, particularly in UASB reactors, has
been reported as amounting to 60–90%
(Chernicharo et al. 2001c; von Sperling et al.
2002, 2004), being therefore insufficient to produce effluents that may be used in irrigation.
However, it should be mentioned that these
limitations are not exclusive of anaerobic reactors, but are a characteristic of most compact
wastewater treatment systems.
As the risk of human contamination by ingestion or contact with water containing pathogenic
organisms is high, many times it may be necessary to disinfect the effluents. This fact becomes
even more serious due to the poor sanitary conditions in developing countries. On the other
hand, the low investments in health and sanitation make the population of these countries bearers of several diseases that can be transmitted by
faeces and, consequently, by the sewage generated by this population.
Although the domestic sewage is an unquestionable source of contamination by pathogenic
organisms, it is worth of mention that the agents
used in the disinfection processes can also cause
harm to human health and the aquatic environment. It is then concluded that the decision to
either disinfect or not sewage should be taken
from a careful evaluation, based on the specific
characteristics of each situation. In other words,
there are no universal guidelines ruling sewage
disinfection requirements. The decision on the
need to disinfect the sewage of a certain locality
involves (USEPA 1986)