Spatiotemporal Dynamic Change Of Microbiota And Odor Generation Of Household Front-Loading Washing Machine

Black stains and malodor inside washing machines are common and unresolved problems.Front-loading washing machines,due to their water-saving and better cleaning performance,are gradually occupying a larger share of the global washing machine market.However,the non-removability of front-loading washing machines makes it difficult to clean the interior,and the formation of biofilms cannot be observed and removed in time,with malodors being more pronounced.This work focuses on the changes in microbial communities and the sources of malodor production during the use of washing machines.By tracking the microbial contamination of two new washing machines through one year,typical microbial biofilm components and odor production from the isolated stains were investigated,as well as common cleaning measures.The main researches are as follows:（1）Two new washing machines were sampled continuously for one year at the door rubber seal,inside wall of outer drum,and drain outlet,and were subjected to metagenomic testing.The results showed that the phyla with the highest bacterial abundance at the three locations were all Proteobacteria,with the drain outlet having the most abundant species.The most abundant bacterial genera in the washing machines were Sphingobium,Acinetobacter,Brevundimonas,Acinetobacter,Pseudomonas,Stenotrophomonas,and Rhizobium.Sphingobium was the main dominant bacterial genus at the rubber seal,Rhodotorula and Meyerozyma were the main dominant fungal genera,and Acinetobacter was the main dominant bacterial genus on the drum wall.The drain outlet had a more complex bacterial composition,with Cupriavidus as the characteristic bacterial genus.The dominant fungal phylum in the washing machine was Ascomycota,and the dominant fungal genera were Meyerozyma and Rhodotorula.（2）The biofilms and origin of malodors inside the washing machines were analyzed.C₂H₆S₂ was the main source of malodor in the washing machine.Gas production analysis of typical isolated bacterial strains from the washing machine showed that Cupriavidus metallidurans,Sinorhizobium Chen,Pseudomonas putida,and Acinetobacter junii were the strongest producers of C₂H₆S₂.The components and peak area ratios of the gases produced by the isolated strains were significantly different between normal culture and culture in medium containing laundry wastewater,and other malodor components such as alkanes,alcohols,ketones,and benzothiazoles were also detected.The composition of the biofilms of four typical isolated strains,P.putida,Sphingobium yanoikuyae,Chryseobacterium hispalense,A.junii was determined,and the results showed that the extracellular DNA content is rich in the biofilms of A.junii and P.putida,while the protein content of the biofilms of C.hispalense and S.yanoikuyae was abundant.（3）The effectiveness of commonly used antibacterial methods for cleaning washing machines was analyzed through cleaning practice.The results showed that high-temperature washing and sterilization methods were effective for sterilizing all three locations,with the most significant effects on the door rubber seal and drain outlet.Silver ions were not effective for killing already-formed biofilms,and completely failed to inhibit the growth of P.putida and Meyerozyma guilliermondii on the culture medium.The antibacterial performance of isothiazolinone was excellent and environmentally friendly,with a minimum inhibitory concentration of 32.25 mg·L^-1,and it could significantly destroy the cell structure of P.putida.