Water is a vital resource to every living thing on the earth. Once the water is contaminated (physically, chemically, biologically, or radiologically), it brought negative impacts to the living thing. This paper provides a brief review of the characterization of biological pollutants in drinking water and their effects on human health. Some biological contamination was detected in water resources such as pathogenic bacteria (Escherichia coli, Vibrio cholerae, Salmonella, etc.), viruses (hepatitis A virus, hepatitis E virus, rotavirus, etc.), parasites (Giardia, Entamoeba, Cyclospora, etc.), and parasitic worm (Ascaris lumbricoides, Ancylostoma duodenale, Strongyloides stercoralis, etc.). The diseases were significantly prevalent in developing countries due to limited access to clean water and poor sanitation. Most of the diseases had common symptoms such as diarrhea, fever, and body and muscle aches that were transmitted to humans through the fecal–oral route. About 1.7 billion children were affected by diarrhea each year and about 525,000 of the children died each year. Besides, nearly 1 million adults were killed by diarrhea every year. Some treatment was implemented to remove the biological contamination in drinking water, such as oxidation treatment, ultraviolet radiation, distillation, biologically active carbon filtration, electrochemical, and nanotechnology.

Treatment of domestic wastewater in a pilot-scale upflow anaerobic hybrid (AH) reactor (0.9 m³) in combination with downflow hanging sponge (DHS) system (1.3 m³) was investigated. The combined system was operated at a hydraulic retention time (HRT) of 6.0 h for AH and 3.2 h for DHS system. The total process achieved a substantial reduction of CODₜₒₜₐₗ resulting in an average effluent concentration of only 39 ± 12 mg/l. Moreover, 90 ± 7 % of ammonia was eliminated in the DHS system. Nitrate and nitrite data revealed that 49 ± 3.2 % of the ammonia removal occurred through nitrification process. The removal efficiency of total coliform (TC), fecal coliform (FC), and fecal streptococci (FS) was relatively low in the AH reactor. The major portion of TC, FC, and FS was removed in the DHS system resulting to an average count of 1.7 × 10⁵ ± 1.1 × 10²/100 ml for TC, 7.1 × 10⁴ ± 1.2 × 10²/100 ml for FC, and 7.5 × 10⁴ ± 1.3 × 10²/100 ml for FS in the final effluent. Likely, the combined system was very efficient for the removal of protozoological species such as sarcodins (Entamoeba cysts), flagellates (Giardia cysts), and ciliates (Balantidium cysts). This was not the case for coccidia (Cryptosporidium oocysts), where 36.4 and 27.3 % were detected in the effluent of AH and DHS system, respectively. Only 10 % of intestinal nematode and cestode ova were recorded in the effluent of AH reactor and were completely removed in the DHS system.