Microbial degradation of various types of dissolved organic matter in aquatic ecosystems and its influencing factors

Interactions between chemodiverse dissolved organic matter(DOM)and biodiverse microbes are governed by a myriad of intrinsic and extrinsic factors which are not well understood.Here,we update and bridge the gap of this interdisciplinary theme comprehensively.At an ecosystem level,aquatic ecosystems dominated by algae-sourced DOM(e.g.,eutrophic lake or coastal upwelling areas)harbor more biolabile DOM,such as directly assimilable monomers and readily hydrolysable biopolymers.However,other ecosystems prevailed by DOM supply from soil and vascular plants(e.g.,river or wetland)have more biorefractory DOM,such as low molecular weight(LMW)residue of aliphatic C skeletons and geopolymers.A variety of heterotrophic bacteria,archaea,fungi,phagotrophic protists,and even photoautotrophic phytoplankton shows genomic and/or culturing experimental evidence of being able to process a diverse type of organics.The various biodegradable organics have different chemical structures and chemical bonds such as carbohydrates,amino acids,proteins,lignins,lipids,carboxylic acids,humic acids,hydrocarbons,and nanoplastics.Meanwhile,bio-production of metabolism intermediates and/or biorefractory organics(e.g.,carboxyl-rich alicyclic molecules,CRAM)is observed despite general decay of bulk dissolved organic carbon(DOC)during bioassay experiments.In particular,emerging evidence shows that archaea contribute significantly to biomass in the marine mesopelagic zone and subsurface environments and their abundance often increases with depth in sediments.Furthermore,not only intrinsic factors(e.g.,DOM composition and structure),but also extrinsic ones(e.g.,sunlight and dissolved oxygen)play important roles in interplays between DOM and microbes.

Using fluorescence surrogates to track algogenic dissolved organic matter(AOM) during growth and coagulation/flocculation processes of green algae

Tracking the variation of the algogenic organic matter(AOM) released during the proliferation of green algae and subsequent treatment processes is crucial for constructing and optimizing control strategies. In this study, the potential of the spectroscopic tool was fully explored as a surrogate of AOM upon the cultivation of green algae and subsequent coagulation/flocculation(C/F) treatment processes using ZrCl_4 and Al_2(SO_4)_3. Fluorescence excitation emission matrix coupled with parallel factor analysis(EEM-PARAFAC) identified the presence of three independent fluorescent components in AOM, including protein-like(C1), fulvic-like(C2) and humic-like components(C3). Size exclusion chromatography(SEC) revealed that C1 in AOM was composed of large-sized proteins and aromatic amino acids. The individual components exhibited their unique characteristics with respect to the dynamic changes. C1 showed the highest correlation with AOM concentrations(R^2= 0.843) upon the C/F processes. C1 could also be suggested as an optical predictor for the formation of trihalomethanes upon the C/F processes. This study sheds a light for the potential application of the protein-like component(C1) as a practical surrogate to track the evolution of AOM in water treatment or wastewater reclamation systems involving Chlorella vulgaris green algae.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge:Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products(SMP)with the shift of the substrate condition from a feast to a famine phase in biological treatment systems.This study demonstrated that the formation of SMP could be suppressed by up to 75%during the famine phase with the addition of essential nutrients.In contrast,presence of electron acceptor did not play any significant role during the stress condition,showing the similar amounts of SMP(r=0.98,p<0.05)formation between the bioreactors supplied with air and N2.The SMP formed in the famine phase was more biorefractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition(R^2>0.95).The fluorescence excitation-emission matrix coupled with parallel factor analysis(EEM-PARAFAC)revealed the presence of four different fluorescent components,including two protein-like(C1 and C4),fulvic-like(C2),and humic-like(C3)components,in the SMP and bEPS formed at different conditions.Both C1 and C4 showed increasing trends(R^2>0.95)with the length of starvation in the bioreactors without essential nutrients.Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers.This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules(particularly proteins),which typically exert many environmental concerns to effluent organic matter quality.

Enhancing the total organic carbon measurement efficiency for water samples containing suspended solids using alkaline and ultrasonic pretreatment methods

In this study,we investigated the effect of sample pretreatments(ultrasonication and alkaline extraction)on total organic carbon(TOC)measurements for water samples containing suspended solids(SS)of four different origins(algae,soil,sewage sludge,and leaf litter)to more clearly assess the impact of particulate organic carbon(POC)in water.The effects each of ultrasonication(power,pulse,etc.)and alkaline extraction condition(concentration,time,etc.)on the TOC recovery and precision were investigated,and the results were compared with those of a new sample pre treatment method combining both methods.Alkaline treatment(0.01 mol/L NaOH)showed higher precision than ultrasonication(100/5 on/off pulse),and notably,the differences among the measured TOC values in samples of different origins were also further reduced in the alkaline treatment.This suggests that the ultrasonic pretreatment results can be mainly attributed to the increase in POC recovery through particle size reduction,whereas the alkaline treatment results are achieved through the enhancement of POC solubilization.It is also particularly noteworthy that a higher TOC recovery of 87.6%±7.4%with a higher precision of 8.4%could be obtained using the combined method,compared to each treatment(ultrasonic:TOC recovery 34.7%,relative standard deviation 63.1%;alkaline:49.6%and 23.0%,respectively).Thus,simultaneous pretreatment with ultrasonication and alkaline extraction is expected to increase the oxidation rate of organic matter and the homogeneity of the samples,minimizing the loss of POC measurement values,and thereby improving the reliability of the TOC measurements of water samples containing SS.

Mortality rates of pathogen indicator microorganisms discharged from point and non-point sources in an urban area

This research measured the mortality rates of pathogen indicator microorganisms discharged from various point and non-point sources in an urban area. Water samples were collected from a domestic sewer, a combined sewer overflow, the effluent of a wastewater treatment plant, and an urban river. Mortality rates of indicator microorganisms in sediment of an urban fiver were also measured. Mortality rates of indicator microorganisms in domestic sewage, estimated by assuming first order kinetics at 20℃ were 0.197 day^-1, 0.234 day^-1, 0.258 day^-1 and 0.276 day^-1 for total coliform, fecal coliform, Escherichia coli, and fecal streptococci, respectively. Effects of temperature, sunlight irradiation and settlement on the mortality rate were measured. Results of this research can be used as input data for water quality modeling or can be used as design factors for treatment facilities.