Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

Abstract

Conventional onsite wastewater treatment systems (OWTSs) could potentially contribute to the transmission of infectious diseases caused by waterborne pathogenic microorganisms and become an important human health concern, especially in the areas where OWTSs are used as the major wastewater treatment units. Although previous studies suggested the OWTSs could reduce chemical pollutants as well as effectively reducing microbial contaminants from onsite wastewater, the microbiological quality of effluents and the factors potentially affecting the removal are still understudied. Therefore, the design and optimization of pathogen removal performance necessitate a better mechanistic understanding of the hydrological, geochemical, and biological processes controlling the water quality in OWTSs. To fill the knowledge gaps, the sources of pathogens and common pathogenic indicators, along with their major removal mechanisms in OWTSs were discussed. This review evaluated the effectiveness of pathogen removal in state-of-art OWTSs and investigated the contributing factors for efficient pathogen removal (e.g., system configurations, filter materials, environmental and operational conditions), with the aim to guide the future design for optimized treatment performance.

A Sustainable and Low-Cost Soil Filter Column for Removing Pathogens from Swine Wastewater: The Role of Endogenous Soil Protozoa

“…Protozoan grazing also affects the interactions between bacteria and other microorganisms in the soil [35,39]. Numerous studies have documented that predation mechanisms play a significant role in reducing the bacteria in water and wastewater filtration systems [23,33,47,[49][50][51][52]. This study showed that the presence of bacterivorous protozoa in the soil columns stimulated a more stable removal efficiency of fecal bacteria, than that in the absence of protozoa predation (Figure 3B).…”

“…A report cited by Schlimme et al (1997), showed protozoa consumption rates of 9-266 bacteria per hour for a flagellate and 200-5000 per hour for a ciliate [54]. Bacterivorous protozoa were documented to have different feeding rates, depending on their species and prey density [49,54,65]. Although predation by protozoa was revealed as the mechanism of bacterial destruction [46,47,52], there is little information available to support the percentage of bacteria removal by protists in a filtration system.…”

“…With increasing environmental concern and awareness of the health risks in connection with the Clean species were observed as major predators in removing pathogenic parasitic protozoa in aquatic environments [48]. Protozoa predation was considered as the main mechanism for bacterial removal in onsite wastewater treatment systems [23,33,47,[49][50][51]. Retained, immobilized, and biofilm-associated bacteria in biosand filters were eliminated by protozoa [47,52,53].…”

“…Decamp et al (1999) reported that the moderate grazing rate of protozoa ranged from 9.5 to 49 bacteria/protozoa/hour for a planted and unplanted bed wetland [41]. An extensive review highlighted that the grazing rates of free-living protozoa were 10 3 to 10 5 bacteria/ciliate/hour and increase with increasing prey density [49]. Another study cited by Schlimme et al (1999) reported that flagellate and ciliate protozoa have different grazing rates [54].…”

Effect of Wastewater Treatment on Bacterial Community, Antibiotic-Resistant Bacteria and Endoparasites

“…Helminths are also often considered as the primary constraint for the reuse of wastewater in agriculture because of their low infective dose and prolonged survival rate in the environment [ 18 , 19 , 20 ]. Developmental stages of endoparasites have been found in raw wastewater [ 20 ].…”