13 research outputs found
Effects of Backwashing on Granular Activated Carbon with Ammonium Removal Potential in a Full-Scale Drinking Water Purification Plant
Granular activated carbon (GAC) has been widely introduced to advanced drinking water purification plants to remove organic matter and ammonium. Backwashing, which is the routine practice for GAC maintenance, is an important operational factor influencing the performance of GAC and its microbial biomass. In this study, the effects of backwashing on the ammonium removal potential of GAC were evaluated. In addition, abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) on GAC were analyzed. GAC samples before and after backwashing were collected from a full-scale drinking water purification plant. Samplings were conducted before and after implementation of prechlorination of raw water. The results showed that the ammonium removal potential of the GAC increased by 12% after backwashing before prechlorination (p < 0.01). After implementing the prechlorination, the ammonium removal potential of the GAC decreased by 12% even after backwashing (p < 0.01). The AOA was predominant on the GAC in the two samplings. Regardless of prechlorination, the amounts of the AOA and the AOB remained at the same level before and after backwashing. Analysis of the backwashing water indicated that the amounts of the AOA and AOB washed out from the GAC were negligible (0.08%⁻0.26%) compared with their original amounts on the GAC. These results revealed the marginal role of backwashing on the biomass of ammonia oxidizers on GAC. However, the results also revealed that backwashing could have a negative impact on the ammonium removal potential of GAC during prechlorination
Changes in Dissolved Organic Matter Composition and Disinfection Byproduct Precursors in Advanced Drinking Water Treatment Processes
Molecular changes in dissolved organic
matter (DOM) from treatment
processes at two drinking water treatment plants in Japan were investigated
using unknown screening analysis by Orbitrap mass spectrometry. DOM
formulas with carbon, hydrogen and oxygen (CHO–DOM) were the
most abundant class in water samples, and over half of them were commonly
found at both plants. Among the treatment processes, ozonation induced
the most drastic changes to DOM. Mass peak intensities of less saturated
CHO–DOM (positive (oxygen subtracted double bond equivalent
per carbon (DBE–O)/C)) decreased by ozonation, while more saturated
oxidation byproducts (negative (DBE–O)/C) increased and new
oxidation byproducts (OBPs) were detected. By Kendrick mass analysis,
ozone reactions preferred less saturated CHO–DOM in the same
alkylation families and produced more saturated alkylation families
of OBPs. Following ozonation, biological activated carbon filtration
effectively removed <300 Da CHO–DOM, including OBPs. Following
chlorination, over 50 chlorinated formulas of disinfection byproducts
(DBPs) were found in chlorinated water samples where at least half
were unknown. Putative precursors of these DBPs were determined based
on electrophilic substitutions and addition reactions. Ozonation demonstrated
better decomposition of addition reaction-type precursors than electrophilic
substitution-type precursors; over half of both precursor types decreased
during biological activated carbon filtration