Systematic Review of Microorganism Removal Performance by Physiochemical Water Treatment Technologies

Access
to safe drinking water is crucial for public health necessitating
the use of effective water treatment processes. We conducted a systematic
literature review on microorganism removal by physical treatment processes
used in drinking water treatment systems with the aim of providing
current summary data to update the World Health Organization’s
Guidelines for Drinking Water Quality (GDWQ) and to reflect on the
data available for comparison of treatment technologies. We reviewed
peer-reviewed articles reporting original data that were published
between 1997 and March 2022 on the following physical treatment technologies:
roughing filters, storage reservoirs, bank filtration, conventional
and high-rate clarification, dissolved air flotation, lime softening,
granular media filtration, slow sand filtration, precoat filtration,
membrane filtration, granular activated carbon, ceramic membrane filtration,
and soil aquifer treatment. The literature search was conducted in
several databases including Web of Science and PubMed. Data from 165
articles were included in the analysis and used to calculate Log Reduction
Values (LRVs) for each technology by microbial contaminant type (bacteria,
virus, or protozoa). The quantity and quality of data ranged widely
for each technology. We found granular media, membranes (microfiltration
(MF), ultrafiltration (UF), and reverse osmosis (RO)), and precoat
filtration to remove the most protozoa with average LRVs of 3.0 (95%
CI 2.8–3.3), 5.7 (95% CI 5.4–6.0), and 4.4 (95% CI 4.1–4.7),
respectively. Bacteria was removed most effectively by membrane filtration
(MF, UF, RO) with average LRVs of 4.5 (95% CI 3.9–5.1) and
moderately by dissolved air flotation, lime softening, and soil aquifer
treatment with average LRVs of 2.7, 2.6, and 2.4 respectively. Viruses
were removed most effectively by reverse osmosis membrane filtration
with an average LRV of 4.9 (95% CI 4.0–5.7). This data provides
valuable information on pathogen reduction and areas of needed research.
The variation in results underscores the importance of further consideration
when selecting technologies to use and the need for standardized reporting
in both lab and field studies. It is important to consider variables
in water quality and technology operation that may impact treatment
effectiveness when selecting treatment options for use. The findings
contribute to ongoing efforts to revise the WHO’s GDWQ, offering
updated insights into LRVs for different water treatment technologies.