Total Extracellular Polymeric Substances Content Research Articles

Performance and mechanism of Chlorella in swine wastewater treatment: Roles of nitrogen-phosphorus ratio adjustment and indigenous bacteria

The effects of adjusting the nitrogen-phosphorus (N/P) ratio of wastewater and indigenous bacteria on swine wastewater treatment by Chlorella sp. HL were investigated. The optimal N/P ratio of Chlorella in swine wastewater was 20 by adjusting the phosphorus concentration. The participation of indigenous bacteria increased total extracellular polymeric substances content, which was beneficial to maintain the stability of the algal-bacterial consortium, and improved the algal density and the removal rate of total nitrogen, total phosphorus, and chemical oxygen demand by 47.8%, 24.0%, 30.7%, and 326.7%, respectively. Proteobacteria was the dominant phylum with the relative abundance of 71.58% in the algal-bacterial system at optimal N/P ratio, and Brevundimonas, Chryseobacterium, and Pseudomonas played positive roles in the establishment of symbiotic systems at the genus level. These results provide a theoretical basis for the construction of an efficient algal-bacterial symbiotic system in swine wastewater treatment and support for commercial scale-up.

Organic degradation and extracellular products of pure oxygen aerated activated sludge under different F/M conditions

This study aimed to investigate the effect of food to microorganisms rate (F/M) on organic removal, extracellular polymeric substances (EPS) and soluble microbial products (SMP) of the pure oxygen aerated activated sludge running in batch mode. The F/M rates were controlled by adjusting the MLSS concentrations (2000, 5000, 8000 mg/L) and/or the initial TOC concentrations (100, 500 mg/L). Results showed that at high F/M rate (0.25 kg TOC/kg MLSS), the substrate degradation rate in the oxygen aerated reactor could reach 1.347 mg TOC/(L·min)), much higher than that in the air aerated reactor (0.640 mg TOC/(L·min)). The SMP concentrations with oxygen aeration were also higher than those with air aeration under high F/M conditions. The total EPS contents in the pure oxygen aerated sludge were significantly lower regardless of the different F/M rates. High F/M condition would lead to more amount of polysaccharides synthesis rather than proteins synthesis in EPS.

Application of submerged membrane bioreactor technology for the treatment of high strength dairy wastewater

Abstract In this study, an aerobic submerged membrane bioreactor (sMBR) was used for the treatment of dairy wastewater at 15 h of hydraulic retention time (HRT) and 40 d of sludge retention time (SRT) with constant permeate flux (9.5 L.m-3.d-1(LMH)). The COD, ammonia-nitrogen (NH3-N) and orthophosphate (PO4-P) removal efficiencies were 98.2%, 95.4% and 88.9%, respectively. The results demonstrated that sMBR was a suitable and effective treatment for removal of organic matter and nutrients for treating dairy wastewater. The properties of the activated sludge, such as extracellular polymeric substances (EPS) and soluble microbial products (SMP) concentration, protein and carbohydrate, relative hydrophobicity, zeta potential and floc size distribution were also investigated. According to the results obtained, the total EPS content was lower than that of domestic wastewater treatment by MBR technology.

Study of extracellular polymeric substances in the biofilms of a suspended biofilter for nitric oxide removal.

The extraction and quantitative analysis of extracellular polymeric substances (EPS) have been frequently reported in studies of activated sludge. However, little is currently known about the EPS in the biofilms of biofilter systems. This study investigates the EPS in biofilms of Chelatococcus daeguensis TAD1 established in a suspended biofilter for nitric oxide (NO) removal under thermophilic conditions. Polysaccharide was the main EPS component under all experimental operation conditions of the aerobic biofilter, although the EPS contents and components varied under different operating conditions. As the concentration of the inlet NO varied from 200 to 2000mg/m3, the EPS and protein contents generally increased. At the highest inlet concentration (2000mg/m3), the EPS and protein contents reached 0.118 and 0.055mg/g, respectively (representing increases of 7.3 and 35%, respectively, over the inlet concentration of 200mg/m3). In contrast, the polysaccharide content was quite stable against inlet NO concentration. Decreasing the empty bed residence time increased the EPS and polysaccharide contents, but exerted little effect on the protein content. Varying the pH of the circulating fluid from 4 to 8 changed the EPS and its components in complex ways. We also found a strong correlation between the total EPS content and the NO removal efficiency. Therefore, it is possible to take EPS into consideration for biofilter control.

Variation of extracellular polymeric substances (EPS) and specific resistance to filtration in sludge granulation process to the change of influent organic loading rate

Four sequencing batch reactors (SBRs) were operated to evaluate the effects of changing the influent chemical oxygen demand (COD) loading rate (F/M ratio) on various components of EPS and their relationship with other physicochemical characteristics of granular sludges in the SBR system. F/M ratio in R-1, R-2, R-3, and R-4 was 0.11, 0.21, 0.32, and 0.43 kg COD/kg mixed liquor suspended solids (MLSS)·d, respectively. The sludge fed with higher F/M ratio enhanced the granulation process and produced more polysaccharides (PS) and proteins (PN) than the sludge run with lower COD loading rate while humic substances and uronic acids did not show any profound difference in their contents. The total EPS contents in the granular sludges were higher at the beginning of experiment as compared to their values noted at the end of studies. The granular sludge settleability was positively correlated with the F/M ratio and EPS contents. Specific resistance values at the end of studies were 2.37 × 108, 1.38 × 108, 1.86 × 108, and 9.32 × 108 s2/g in R-1, R-2, R-3, and R-4, respectively, to that of seed sludge (6.80 × 109 s2/g). The higher values of specific resistance in R-4 were due to raised contents of PS compared to other reactors. EPS particularly PS were found to be positively correlated with settleability and negatively with dewatering characteristics of sludges.

Using graphene oxide to enhance the activity of anammox bacteria for nitrogen removal

Graphene oxide (GO) was applied in this study to enhance the activity of anaerobic ammonium oxidation (anammox) bacteria for nitrogen removal. A GO dose-dependent effect on anammox bacteria was observed through batch tests. The results showed that the activity increased as the GO dose was varied within 0.05–0.1gL−1. A maximum 10.26% increase of anaerobic ammonium oxidizing activity was achieved at 0.1gL−1 GO. Analysis of extracellular polymeric substances (EPS) indicated that the highest carbohydrate, protein, and total EPS contents (42.5, 125.7, and 168.2mg (g volatile suspended solids)−1, respectively) were obtained with 0.1gL−1 GO. Appropriate GO dose stimulated EPS production to promote the activity of anammox bacteria. Transmission electron microscopy showed the large surface area of GO benefited cell attachment. These findings proved that the application of GO was an effective approach to enhancing the activity of anammox bacteria.

Extraction and analysis of extracellular polymeric substances in membrane fouling in submerged MBR

The extraction and analysis of EPS in active biomass and membrane fouling were performed to investigate the influence of extracellular polymeric substances (EPS) on membrane fouling of MBR. The new membrane and fouling membrane surface morphology was characterized by EDX analysis. The results show that membrane contaminant is mainly composed of organic compounds. EPS in active biomass and membrane pollutant were extracted by method of alkaline regular centrifugation. Most of EPS were found to have high molecular weight over 12,000 D, which is very difficult to degrade. The total EPS contents in the extracted solution and the contents of polysaccharide protein and DNA in EPS were respectively analysed with TOC analysis and by phenol-sulfuric acid method, modification of the Bradford method and the fluorometric method. The analytical results indicate that the content of EPS in membrane fouling is about four times as much as that in active biomass, and polysaccharide is the most important pollutant on membrane, as well as protein’s role in membrane fouling is not negligible, whereas the DNA is not important in membrane fouling because of its content (non-dialysis) in membrane contaminant being less than that in the active biomass. In addition, the results in electrophoresis experiment provide the information about the concentrated distribution of molecular weight of large fragment DNA in both membrane contaminant and the biomass.

Surface properties of sludge and their role in bioflocculation and settleability

The influence of sludge retention time (SRT) on the extracellular polymeric substances (EPS) and physicochemical properties (hydrophobicity and surface charge) of sludge was studied using laboratory-scale sequencing batch reactors (SBRs) fed a synthetic wastewater containing glucose and inorganic salts. Sludge surfaces were more hydrophobic (larger contact angle) and less negatively charged at higher SRTs (16 and 20 d) than at lower SRTs (4 and 9 d). The ratio of proteins to carbohydrates within the EPS of the sludges increased as the SRT increased from 4 to 12 d corresponding to the changes in the physicochemical properties of the sludge. The protein : carbohydrate ratio remained constant at SRTs of 16 and 20 d. A transition in sludge properties appeared to occur between the upper range of low- (9 d) and lower range of high- SRTs. The total EPS content, however, was independent of the SRT. A higher sludge volume index (SVI), an indication of poorer settleability or compression, was associated with a larger amount of total EPS but no significant correlation between SVI and the surface properties of sludge was observed. A more hydrophobic and less negatively charged surface corresponded to lower levels of ESS. These results indicate that it is the surface properties, hydrophobicity, surface charge and composition of EPS , of sludge, rather than the quantity of EPS, that govern bioflocculation. In contrast, the EPS content is more important in controlling the settleability of sludge.