Excitation-emission Matrix Analysis Research Articles

Effects of earthworms on nitrification and ammonia oxidizers in vermicomposting systems for recycling of fruit and vegetable wastes

Although it is known that earthworms enrich the nitrate content in their final products, the detailed mechanisms behind this are not well understood, and this is important for determining the agricultural value of vermicomposting. Hence, this study aimed to investigate the effects of earthworms on ammonia oxidization and to clarify the functions of ammonia-oxidizing bacteria and archaea (AOB and AOA) during vermicomposting of fruit and vegetable wastes (FVWs). For this, two dry systems using dry FVWs and a fresh system using fresh FVWs were adopted and compared during 60days of vermicomposting. Each system included two treatments, with earthworms and without earthworms. The results revealed that vermicomposting could facilitate the stabilization of FVWs, forming high value-added products. Based on the results of fluorescent excitation-emission matrix analysis, humification indices of the dry and fresh vermicomposts were 4.0 and 4.2, respectively. Moreover, compared to the minus net nitrification rates in groups without worm treatment, the net nitrification rates of 17.5mgN/kg/d and 9.3mgN/g/d, respectively, were found in dry and fresh vermicomposting systems, indicating that earthworms could significantly accelerate the nitrification process. Compost treated with earthworms exhibited elevated numbers of ammonia oxidizers (AOA and AOB) and greater community diversity in final products, compared to the counterparts without earthworms. Final vermicompost products were abundant in the AOB members of Nitrosomonas and Nitrosospira along with AOA groups including Crenarchaeota and Thaumarchaeota. By contrast, AOA were the dominate members completing ammonia oxidization during vermicomposting of dry and fresh FVWs. This study suggests that earthworms facilitate the ammonia oxidization process by promoting both numbers and diversity of AOA and AOB during vermicomposting of FVWs.

Microwave-assisted digestion and NaOH treatment of waste-activated sludge to recover phosphorus by crystallizing struvite

ABSTRACTA number of studies of waste-activated sludge (WAS) pretreatments, aimed at releasing phosphorus (P) from WAS and increasing the amount of P that can be recovered, have been performed. Here, a microwave-assisted digestion and NaOH treatment (MWs & NaOH) coupled crystallizing struvite, to promote the solubilization, transformation, and recovery of P from WAS, is proposed. Microwaves (MWs) can cause cavities to form in WAS, weakening the bonds between extracellular polymeric substances and the solid phase. Irradiating with MWs significantly increased the efficiency at which P was dissolved (i.e. transferred from the solid to the liquid phase) and the efficiency at which organic P was hydrolyzed and transformed into inorganic P when the NaOH treatment was performed. The P solubilization and transformation characteristic achieved in different treatments was examined by scanning electron microscopy and three-dimensional excitation emission matrix analysis. The MWs & NaOH method released 34.20–43.73% of total P from WAS, and 23.48–32.07% of the total P was recovered by crystallizing struvite at pH 9.5 and Mg:P ratio of 1.5:1. It would cost about USD 85–103 per ton of dry WAS to treat WAS using the MWs & NaOH method.

Role of polarity fractions of effluent organic matter in binding and toxicity of silver and copper

This study evaluates the effect of the physicochemical properties of effluent organic matter (EfOM) from industrial and sewage wastewater treatment plants (WWTPs) on the binding and toxicity of Ag and Cu. EfOM was isolated into hydrophobic, transphilic, and hydrophilic fractions depending on its polarity, and was characterized by elemental, specific ultraviolet absorbance, and fluorescence excitation-emission matrix analyses. Our results suggest that the EfOM consists of microbially derived non-humic substances that have lower aromaticity than the Suwannee River natural organic matter (SR-NOM). The Freundlich model was better at explaining the binding of Ag and Cu onto both SR-NOM and EfOM than the Langmuir model. In particular, the hydrophilic fractions of sewage EfOM showed higher binding capacities and affinities for Ag and Cu than the corresponding hydrophobic fractions, resulting in better reduction of the acute toxicity of Ag and Cu towards Daphnia magna. However, in the case of both SR-NOM and industrial EfOM, the hydrophobic fractions were more efficient at reducing metal toxicity. These findings suggest that the EfOM has different physicochemical properties compared with NOM and that the binding and toxicity of heavy metals are largely dependent on the polarity fractions of EfOM.

Performance and mechanism of phycocyanin removal from water by low-frequency ultrasound treatment

Ultrasonication pretreatment of raw water with high content of algal cells might cause an increase in dissolved organic nitrogen (DON) and proteins, which must be removed effectively before coagulation. In this study, the efficiency of sonication treatment in removing typical proteins derived from algal cells was investigated by applying ultrasonic waves at 20, 40, 60, 80, and 100kHz, and the influencing factors and removal mechanism were discussed. The results showed that low-frequency sonication could degrade phycocyanin to some extent, achieving about 95% removal rate after 150min of sonication. However, excitation emission matrix analysis indicated that ultrasonication could not entirely degrade phycocyanin into inorganic nitrogen, and many proteins and nitrogen-containing organics were found in the samples after sonication. While the total nitrogen concentration remained consistent during the entire sonication process (240min), the total inorganic nitrogen concentration increased from 0.6 to 1.3mg/L, indicating that only 33.3% of DON was oxidized into inorganic nitrogen. Nevertheless, sonication could significantly attenuate the interference of phycocyanin in coagulation and enhance coagulation. The mechanical effects and free-radical oxidation resulting from cavitation collapse could be responsible for the degradation of phycocyanin and proteins following sonication. In all, the use of ultrasonic treatment as a posttreatment following sonication to remove algal cells from raw water may not be beneficial.

Natural organic matter fouling behaviors on superwetting nanofiltration membranes

Nanofiltration has been widely recognized as a promising technology for the removal of micro-molecular organic components from natural water. Natural organic matter (NOM), a very important precursor of disinfection by-products, is currently considered as the major cause of membrane fouling. It is necessary to develop a membrane with both high NOM rejection and anti-NOM fouling properties. In this study, both superhydrophilic and superhydrophobic nanofiltration membranes for NOM removal have been fabricated. The fouling behavior of NOM on superwetting nanofiltration membranes has been extensively investigated by using humic acid (HA) as the model foulant. The extended Derjaguin−Landau−Verwey−Overbeek approach and nanoindentor scratch tests suggested that the superhydrophilic membrane had the strongest repulsion force to HA due to the highest positive total interaction energy (ΔGTOT) value and the lowest critical load. Excitation emission matrix analyses of natural water also indicated that the superhydrophilic membrane showed resistance to fouling by hydrophobic substances and therefore high removal thereof. Conversely, the superhydrophobic membrane showed resistance to fouling by hydrophilic substances and therefore high removal capacity. Long-term operation suggested that the superhydrophilic membrane had high stability due to its anti-NOM fouling capacity. Based on the different anti-fouling properties of the studied superwetting membranes, a combination of superhydrophilic and superhydrophobic membranes was examined to further improve the removal of both hydrophobic and hydrophilic pollutants. With a combination of superhydrophilic and superhydrophobic membranes, the NOM rejection (RUV254) and DOC removal rates (RDOC) could be increased to 83.6% and 73.3%, respectively.

Effect of a solar Fered-Fenton system using a recirculation reactor on biologically treated landfill leachate

The effects of electrochemical oxidation (EO), Fered-Fenton and solar Fered-Fenton processes using a recirculation flow system containing an electrochemical cell and a solar photo-reactor on biochemically treated landfill leachate were investigated. The most successful method was solar Fered-Fenton which achieved 66.5% COD removal after 120min treatment utilizing the optimum operating conditions of 47mM H2O2, 0.29mM Fe2+, pH0 of 3.0 and a current density of 60mA/cm2. The generation of hydroxyl radicals (OH) are mainly from Fered-Fenton process, which is enhanced by the introduction of renewable solar energy. Moreover, Fe2+/chlorine and UV/chlorine processes taking place in this system also result in additional production of OH due to the relatively high concentration of chloride ions contained in the leachate. The energy consumption was 74.5kWh/kg COD and the current efficiency was 36.4% for 2h treatment. In addition, the molecular weight (MW) distribution analysis and PARAFAC analysis of excitation emission matrix (EEM) fluorescence spectroscopy for different leachate samples indicated that the organics in the leachate were significantly degraded into either small molecular weight species or inorganics.

Treatment of landfill leachate using electrochemically assisted UV/chlorine process: Effect of operating conditions, molecular weight distribution and fluorescence EEM-PARAFAC analysis

Leachate, a highly polluted wastewater, is generated from landfill containing complex compositions which have great impact on the environment. The advanced treatment of biochemically treated landfill leachate using electrochemically assisted UV/chlorine process (UEC) in a flow reactor was investigated. The effects of pH and current density on COD and NH3-N removal by UEC process were evaluated. At the pH value of 5.0, current density of 60mA/cm2, the removal efficiencies for COD and NH3-N were observed as 77% and 87%, respectively. The electrochemical process alone (EC) could obtain relatively high NH3-N removal but very low COD removal, compared with which, the UEC process significantly promoted the removal efficiency of COD while that of NH3-N increased to a very limited extent. Most of NH3-N was converted into N2 and little nitrogen compounds and chloramines were remained in the leachate after 8h treatment. Moreover, the variations of active chlorine and chloride ions were monitored in the EC and UEC systems, and a possible mechanism was proposed for the UEC process. The in situ electro-generated active chlorine and photo-generated radical species should be responsible for the efficient degradation of landfill leachate. The total energy consumption and current efficiency were 216.5 (kWh/kg COD) and 17.5%, respectively, for 8h treatment. In addition, the molecular weight (MW) percentage distribution analysis and PARAFAC analysis of excitation emission matrix (EEM) fluorescence spectroscopy indicated that the organic matters in the leachate were significantly degraded into the fractions with small molecular weight.

Benefit of adding adsorbent in submerged membrane microfiltration treatment of wastewater

In this study, the effect of coupling ion-exchange resin (purolite) and powdered activated carbon (PAC) in a submerged membrane reactor was investigated in terms of (i) removal of different classes of organic matter and (ii) reduction of membrane fouling. The degree of fouling in a membrane hybrid system was modelled in terms of transmembrane pressure development and organic removal efficiency using a simple semi-empirical model. Among these three absorbents, PAC was the most effective with higher removal efficiency for DOC (almost 100% reduction of hydrophobic organic compounds). Excitation–emission matrix analysis and LC–OCD were employed for the detailed organic characterisation.

Treatment of Actual Chemical Wastewater by a Heterogeneous Fenton Process Using Natural Pyrite

Wastewater from chemical plants has remarkable antibiotic effects on the microorganisms in traditional biological treatment processes. An enhanced Fenton system catalyzed by natural pyrite was developed to degrade this kind of wastewater. Approximately 30% chemical oxygen demand (COD) was removed within 120 min when 50 mmol/L H2O2 and 10 g/L natural pyrite were used at initial pH from 1.8 to 7. A BOD5/COD enhancement efficiency of 210% and an acute biotoxicity removal efficiency of 84% were achieved. The COD removal efficiency was less sensitive to initial pH than was the classic Fenton process. Excessive amounts of pyrite and H2O2 did not negatively affect the pyrite Fenton system. The amount of aniline generated indicated that nitrobenzene reduction by pyrite was promoted using a low initial concentration of H2O2 (<5 mmol/L). Fluorescence excitation emission matrix analyses illustrated that H2O2 facilitated the reduction by natural pyrite of organic molecules containing an electron-withdrawing group to electron-donating group. Thus, the Fenton-like process catalyzed by pyrite can remediate wastewater containing organic pollutants under mild reaction conditions and provide an alternative environmentally friendly method by which to reuse natural pyrite.

The pollutants removal and bacterial community dynamics relationship within a full-scale British Gas/Lurgi coal gasification wastewater treatment using a novel system

The novel system of EBA (based on external circulation anaerobic (EC) process–biological enhanced (BE) process–anoxic/oxic (A/O) process) was applied to treat the British Gas/Lurgi coal gasification wastewater in Erdos, China. After a long time of commissioning, the EBA system represented a stable and highly efficient performance, particularly, the concentrations of COD, NH4+-N, total organic carbon, total nitrogen and volatile phenols in the final effluent reached 53, 0.3, 18, 106mg/L and not detected, respectively. Both the GC–MS and fluorescence excitation–emission matrix analyses revealed significant variations of organic compositions in the effluent of different process. The results of high-throughput sequencing represented the EBA system composed 34 main bacteria which were affiliated to 7 phyla. In addition, the canonical correspondence analysis indicated high coherence among community composition, wastewater characteristics and environmental variables, in which the pH, mixed liquid suspended solids and total phenols loading were the most three significant variables.

Removal of fluorescent dissolved organic matter in biologically treated textile wastewater by ozonation-biological aerated filter

Ozonation-biological aerated filter (O3-BAF) has been proven effective for the biologically treated textile wastewater. However, little information on the behavior of dissolved organic matter in the process was available. In this study, a pilot scale O3-BAF was set up to treat the biologically treated textile wastewater, and both fluorescent excitation–emission-matrix (EEM) and HPLC with multi-excitation/emission fluorescence scan were applied to study the removal characterization of fluorescent dissolved organic matter (DOM). The results showed that with the improvement of biodegradability by ozonation, the combination of ozonation and BAF could low the COD of the effluent below 50 mg/L, meeting the Chinese Discharge Standard. EEM analysis showed that the removal of the triple-excitation peaks at Em460 was the dominant mechanism of high removal efficiency of color and UV254 during ozonation process. In addition, during the ozonation process, the fluorescent DOM species were decomposed in the order of humic substances with Em at 460 nm (HS-Em460-Ex3), the hydrophobic aniline-like species, humic substances with Em at 430 nm (HS-Em430-Ex2) and the hydrophilic aniline-like species. This study provided better understanding on the decoloration mechanism of ozonation and helps to build automatic optimization systems in advanced treatment of textile wastewater.

Effects of membrane orientation on fouling characteristics of forward osmosis membrane in concentration of microalgae culture

Application of forward osmosis (FO) membrane to microalgae cultivation processes enables concentration of microalgae and nutrients with low energy consumption. To understand fouling characteristics of FO membrane in concentration of microalgae culture, we studied flux decline, flux recovery by cleaning, and foulants characteristics, in different membrane orientation of active-layer-facing-feed-solution (AL-FS) and active-layer-facing-draw-solution (AL-DS) modes. Batch concentration of Chlorella vulgaris was conducted with a cellulose-triacetate FO membrane. Rapid flux decline and lower flux recovery was observed in AL-DS mode because of inner-membrane fouling including internal pore clogging, adsorption and internal concentration polarization in the support layer. A proportion of polysaccharides in extracellular polymeric substances to soluble microbial products were larger in chemical cleaning effluent than physical one in AL-DS mode, although those were not significantly different in AL-FS mode. Excitation-emission matrix analysis revealed that proteins and humic-like substances were also possible irreversible foulants both in AL-DS and AL-FS modes.

Chlorination of Microcystis aeruginosa: cell lyses and incomplete degradation of bioorganic substance

The frequent occurrence of blue-green algae bloom in recent years has raised a series of troubles in water treatment processes, and has become a global common concern. We investigated the lethal effect of chlorine, one common chemical algicide, to inactivate Microcystis aeruginosa in the process. Multiple methods were employed to investigate the chlorination effect of M. aeruginosa, including cells calculation with fluorescent staining, photosynthetic pigment contents determination, organic carbon analyses, and fluorescence excitation–emission matrix analyses. The results indicated that even more significant lethal effect of cells with higher chlorine exposure, and chlorophyll-a could hardly be a competent indicator for cell inactivation. Meanwhile, incompletely degraded characteristic of bioorganic substance was reflected during chlorination. Our results offer insight into the lethal effect of M. aeruginosa by chlorination, which will be valuable for understanding both inactivation mechanisms of M. aeruginosa and degradation process of bioorganic substance.

Bacterial growth during the start-up period of pilot-scale biological activated carbon filters: Effects of residual ozone and chlorine and backwash intervals

This study aimed to evaluate the effects of residual ozone and chlorine and the backwash intervals on bacterial activities and density in pilot-scale biological activated carbon (BAC) filters by employing adenosine triphosphate (ATP) measurement and flow cytometry. The BAC filters received water treated by full-scale coagulation–filtration–ozonation processes. The attached bacterial density on the BAC increased rapidly in the first few weeks. The residual chlorine in the influent water caused ca. 1-log reduction of ATP-per-cell in the bacteria attached on the BAC and in the effluent and backwash waters. Extending the backwash interval made the bacteria attached on the BAC more resistant to ozone and chlorine, as suggested by the higher ATP-per-cell of the attached bacteria and the higher percentage of high-nucleic-acid intact bacteria in the backwash water. However, the attached bacterial density was higher for the shorter backwash interval operation than for the longer one during the high-ozone period. Although no significant difference in DOC removal rates was observed between the two BAC filters, fluorescence excitation–emission matrix analysis revealed that high residual ozone decreased the removal of aromatic proteins and soluble microbial product-like compounds.

Impact of dataset diversity on accuracy and sensitivity of parallel factor analysis model of dissolved organic matter fluorescence excitation-emission matrix.

Parallel factor (PARAFAC) analysis enables a quantitative analysis of excitation-emission matrix (EEM). The impact of a spectral variability stemmed from a diverse dataset on the representativeness of the PARAFAC model needs to be examined. In this study, samples from a river, effluent of a wastewater treatment plant, and algae secretion were collected and subjected to PARAFAC analysis. PARAFAC models of global dataset and individual datasets were compared. It was found that the peak shift derived from source diversity undermined the accuracy of the global model. The results imply that building a universal PARAFAC model that can be widely available for fitting new EEMs would be quite difficult, but fitting EEMs to existing PARAFAC model that belong to a similar environment would be more realistic. The accuracy of online monitoring strategy that monitors the fluorescence intensities at the peaks of PARAFAC components was examined by correlating the EEM data with the maximum fluorescence (Fmax) modeled by PARAFAC. For the individual datasets, remarkable correlations were obtained around the peak positions. However, an analysis of cocktail datasets implies that the involvement of foreign components that are spectrally similar to local components would undermine the online monitoring strategy.

A method for in-gel fluorescent visualization of proteins after native and sodium dodecyl sulfate polyacrylamide gel electrophoresis

We have developed a simple one-step 30-min method for fluorescent visualization of proteins in native and sodium dodecyl sulfate polyacrylamide gel electrophoresis (PAGE) gels. The method is based on formation of strong fluorophores via potassium ferricyanide-provoked oxidation of tryptophan (Trp). Following PAGE, gels are soaked in water solution of potassium ferricyanide (100mM) and NaOH (1M) and are kept in the dark for 30min. Gels are then transferred to water and scanned. The sensitivity of the method was slightly lower compared with standard Coomassie Brilliant Blue (CBB) staining. The method can be useful when rapid acquisition of data is of the essence. After preview, gels can be post-stained using the CBB protocol for further analysis. The intensity of fluorescence is dependent on Trp number, so the protocol might find application in the quantification of Trp residues as illustrated here. Importantly, there is room for improvement of the method. Namely, according to excitation–emission matrix analysis of stained protein bands, maximal fluorescence intensity (at 345/460nm) was 3.5-fold higher compared with the settings that were available on a commercial imager (395/525nm). As a supplement, we present an upgrade of the previously described method for in-gel detection of non-heme iron-binding proteins that also employs potassium ferricyanide.

Two-stage mesophilic anaerobic digestion from waste activated sludge enhanced by low-temperature thermal hydrolysis

Two-stage mesophilic anaerobic digestion of waste activated sludge was conducted to enhance methane production by low-temperature thermal hydrolysis. Two steady stages were evaluated: the first acidogenic stage was operated at sludge retention times of 2 d, and the second methanogenic stage was controlled at hydraulic retention times of 8 d. Thermal hydrolysis results showed that more chemical oxygen demand, proteins and carbohydrates were released from sludge as temperature increased from 50 to 120°C. Protein-like substances were major components from three-dimensional (3D) excitation–emission matrix analysis, and their fluorescence intensities were matched with temperatures. Sludge extracellular structure was disintegrated from scanning electron microscope analysis when the temperature was beyond 80°C. The volatile fatty acids (VFAs) and methane production had positive relation to the soluble organic matters after low-temperature hydrolysis. About 100°C was the suitable temperature for sludge digestion, and corresponding VFAs and biogas productions were 1,672 mg/L and 123 mL/gVSS, respectively.

Comparison of three-dimensional fluorescence analysis methods for predicting formation of trihalomethanes and haloacetic acids

This work investigated the application of several fluorescence excitation–emission matrix analysis methods as natural organic matter (NOM) indicators for use in predicting the formation of trihalomethanes (THMs) and haloacetic acids (HAAs). Waters from four different sources (two rivers and two lakes) were subjected to jar testing followed by 24hr disinfection by-product formation tests using chlorine. NOM was quantified using three common measures: dissolved organic carbon, ultraviolet absorbance at 254nm, and specific ultraviolet absorbance as well as by principal component analysis, peak picking, and parallel factor analysis of fluorescence spectra. Based on multi-linear modeling of THMs and HAAs, principle component (PC) scores resulted in the lowest mean squared prediction error of cross-folded test sets (THMs: 43.7 (μg/L)2, HAAs: 233.3 (μg/L)2). Inclusion of principle components representative of protein-like material significantly decreased prediction error for both THMs and HAAs. Parallel factor analysis did not identify a protein-like component and resulted in prediction errors similar to traditional NOM surrogates as well as fluorescence peak picking. These results support the value of fluorescence excitation–emission matrix–principal component analysis as a suitable NOM indicator in predicting the formation of THMs and HAAs for the water sources studied.

Simultaneous monitoring of biofilm growth, microbial activity, and inorganic deposits on surfaces with an in situ, online, real-time, non-destructive, optical sensor

Deposits on surfaces in water-bearing systems, also known as ‘fouling’, can lead to substantial losses in the performance of industrial processes as well as a decreased product quality. Early detection and localization of such deposits can, to a considerable extent, save such losses. However, most of the surfaces that become fouled, for example, in process water pipes, membrane systems, power plants, and food and beverage industries, are difficult to access and analyses conducted on the water phase do not reveal the site or extent of deposits. Furthermore, it is of interest to distinguish biological from non-biological deposits. Although they usually occur together, different countermeasures are necessary. Therefore, sensors are required that indicate the development of surface fouling in real-time, non-destructively, and in situ, preferably allowing for discrimination between chemical and/or biological deposits. In this paper, an optical deposit sensor is presented which fulfills these requirements. Based on multiple fluorescence excitation emission matrix analysis, it detects autofluorescence of amino acids as indicators of biomass. Autofluorescence of nicotinamide adenine dinucleotide + hydrogen is interpreted as an indicator of biological activity, thus it acts as a viability marker, making the method suited for assessing the efficacy of disinfection treatments. Scattering signals from abiotic deposits such as calcium carbonate or corrosion products can clearly be distinguished from biotic substances and monitored separately. The sensor provides an early warning of fouling, allowing for timely countermeasures to be deployed. It also provides an assessment of the success of cleaning treatments and is a promising tool for integrated antifouling strategies.

Characterisation of foulants in membrane filtration of biorefinery effluents

Effluents from biorefineries are highly coloured and carry a large organic load. Traditional treatment options, such as anaerobic and aerobic digestions are capable of reducing the biological oxygen demand, but cannot remove the residual chemical oxygen demand (COD) nor decolourise the effluent. Membrane filtration has been increasingly used for water recovery from industrial effluents, such as from these biorefineries. Different grades of membranes can be used to remove particular contaminants, such as suspended solids, organic macromolecules and salts from these effluents. Effluents were filtered by ultrafiltration (UF) and nanofiltration (NF) membranes and samples were analysed for traditional parameters, such as COD, dissolved organic carbon (DOC) and colour. While UF was capable of only partial removal of colour, COD and DOC, NF was shown to be capable of removing close to 100% of the organic content of the molasses and lignocellulosic effluents. Use of advanced analytical techniques, such as fluorescence excitation emission matrix analysis and liquid chromatography, helped to illustrate the difference between organic compounds found within molasses and lignocellulosic effluents. This was also useful in explaining the difference in membrane separation performance between the two effluents.