Antimicrobial Properties of a Biocide Based on Quaternary Ammonium Compounds plus Polyhexamethylene Guanidine and Possible Methods for Its Deactivation

Abstract

Biocidal agents (BAs) are widely used in environmentally safe toilet complexes (ESTC) of passenger railcars to suppress microbial activity in fecal sludge (FS). The subsequent disposal of BA-containing FS at municipal sewage treatment facilities adversely affects their work due to the loss of activated sludge. The antimicrobial properties of BAs based on quaternary ammonium compounds (QAC) and polyhexamethylene guanidine (PHMG), as well as methods for its neutralization, have been studied. It was confirmed that BAs based on QAC and PHMG have an antimicrobial effect on various groups of bacteria, reducing their number by 10-100 or more times. It was found that FS contains two groups of microorganisms with different sensitivities to BA. Methods for the deactivation of BA antimicrobial action in FS were tested with (1) a deactivating agent; (2) incubation with thermophilically digested wastewater sludge as a source of the methanogenic microbial community; and (3) chemical deactivation via acidification or alkalization. The highest efficiency was obtained from thermophilic anaerobic digestion with the pretreatment of FS with a strong acid.

Didecyldimethylammonium Chloride- and Polyhexamethylene Guanidine-Resistant Bacteria Isolated from Fecal Sludge and Their Potential Use in Biological Products for the Detoxification of Biocide-Contaminated Wastewater Prior to Conventional Biological Treatment

“…This means that after pretreatment with bacterial products, FS become less harmful to the activated sludge of WWTP and can be disposed of without undesirable consequences. It should be noted that the isolated bacteria most probably do not use these biocides as a carbon source, but developing in its presence, they shift the pH of the medium to alkaline (final pH was around 8.7–8.9, data not shown), contributing to the decomposition of QAC and guanidine derivative [ 42 ]. Furthermore, apparently, the decomposition of toxic substances could be caused by the activity of A. faecalis , which are known for their ability to degrade various biocides.…”

“…One of the new uses for these biocidal agents is as a component of a chemical toilet additive designed to deodorize fecal waste and control microbial activity. The combined use of QAC and PHMG as biocides to prevent the biodegradation of human waste products by saprotrophic microorganisms and eliminate an unpleasant odor in fecal sludge (FS), for example, in environmentally safe toilet complexes (ESTC) of passenger railcars, has the task of preserving human waste products until their subsequent processing or disposal [ 42 , 43 ]. However, when disposed of in municipal wastewater treatment plants (WWTPs), such waste poses a potential threat, as it negatively affects activated sludge, inhibiting the processes of nitrification, denitrification, and biochemical oxygen demand (BOD) [ 44 , 45 ].…”

“…There is still very little development in this area. Previously, Litti et al [ 42 ] proved the effectiveness of the deactivating agent and chemical neutralization by strongly acidifying or alkalizing the medium to deactivate QAC and PHMG. However, the use of additional chemicals increases processing costs.…”