Characterization of phosphorus species distribution in waste activated sludge after anaerobic digestion and chemical precipitation with Fe3+ and Mg2+

Given the great concern about phosphorus (P) resource depletion, it's promising to recover P from waste activated sludge (WAS) especially for agricultural application. To this end, it's necessary to understand the P speciation and fractionation within the sludge before and after stabilization and precipitation. In this study, we systematically studied P species and distribution within WAS after anaerobic digestion and chemical precipitation using liquid state P-31 nuclear magnetic resonance (NMR) spectroscopy, sequential extraction method as well as XRD Technology. P transformation and bioavailability were also discussed with the obtained results. Inorganic P was found to be dominant in WAS before (67.6%) and after digestion (77.2%). Vivianite seems to dominate among the P-containing minerals both in the raw and digested sludge from XRD spectra. In the NMR spectra, the orthophosphate (Ortho-P) and polyphosphate (Poly-P) were two dominant species in the raw sludge. However, the Poly-P peak vanished after anaerobic digestion, indicating Poly-P was released and degraded under anaerobic environment. Fe3+ addition and Mg2+ addition with pH adjustment displayed comparable P removal efficiencies. No significant differences on P distribution by sequential extraction test was observed after P precipitation. Considering that no pH adjustment was needed, it might be more cost efficient to recover P by iron addition

The Study of Serum Vitamin D and Insulin Resistance in Chinese Populations with Normal Glucose Tolerance

Objectives. The aim of this study was to investigate the relationship between serum vitamin D and insulin resistance in Chinese subjects without diabetes mellitus. Methods. Serum 25(OH)D was measured in 897 individuals with normal glucose tolerance (NGT). Oral glucose tolerance tests (OGTTs) were conducted to exclude cases with diabetes, impaired fasting glucose (IFG), and impaired glucose tolerance (IGT). Metabolic parameters were measured and compared between the highest and lowest 25(OH)D quartiles. The relationship between serum 25(OH)D and homeostatic model assessment-insulin resistance (HOMA-IR) was analyzed. Results. Indexes, such as HOMA-IR, FINS, and SBP, were negatively correlated with serum 25(OH)D concentrations. Compared with the lowest quartile, individuals in the highest group had decreased Lg (HOMA-IR), Lg (FINS), and SBP. Pearson correlation analyses showed that serum 25(OH)D was negatively associated with age, BMI, Lg (HOMA-IR), and Lg (FINS). Multivariate linear regression analysis confirmed the negative correlation of Lg (HOMA-IR) and 25(OH)D. Conclusions. This study showed that serum 25(OH)D could be regarded as an independent predictor of insulin resistance for subjects without diabetes mellitus in China. Adequate vitamin D supplementation may improve multiple metabolic disturbances

Waste into treasure: New insight to inhibit scale generation in industrial circulating cooling water

The present study investigated the inhibitory role of ginkgo fallen leaves on scale generation in industrial circulating cooling water (ICCW), and the dual scale inhibition mechanism was revealed to demonstrate the ICCW engineering application potential of ginkgo fallen leaves treatment. The results showed that pH, alkalinity and turbidity decreased from 8.68, 295.74 mg/L and 2.482 NTU to 7.27, 111.23 mg/L and 0.483 NTU, respectively, after adding 7.5 g/L fallen leaves in 2 h. The ascorbic acid released by the fallen leaves not only decreased the ICCW alkalinity, but also complexed with the residual Ca2+ to form calcium ascorbate, which combined to inhibit the ICCW scale generation. Finally, compared to other chemical scale inhibition methods, fallen leaves treatment could save 0.34–850 CNY/ton in agent costs. Also, no additional building area was required, saving infrastructure costs. Therefore, turning fallen leaves waste into treasure provided the green and sustainable innovative strategy for scale inhibition in the ICCW, and has significant potential for engineering applications

New insight into enhanced production of short-chain fatty acids from waste activated sludge by cation exchange resin-induced hydrolysis

Recently, the production of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has received increasing attention. Although several pretreatment methods had been investigated, sludge hydrolysis through depletion of multivalent cations has rarely been reported. In this work, cation exchange resin (CER) was used for enhancing WAS hydrolysis and subsequent SCFAs production at various dosages of 0 to 3.5 g/g SS. With the addition of CER, the multivalent cations and trace metal elements (e.g. Ca2+, Mg2+, Fe3+, Zn2+, etc.) were removed from sludge through CER-mediated ion exchange, leading to disruption of extracellular polymeric substance (EPS), while triggering cell lysis which was evidenced by remarkable leakage of cellular DNA. This CER-mediated cyclic release-removal of multivalent cations resulted in substantial sludge hydrolysis with release of biodegradable organic matters. At the optimal CER dosage of 1.75 g/g SS, soluble COD (SCOD) was dramatically increased to 5944 mg/L (SCOD/TCOD = 34.7%) against 1440 mg/L in the control after 2-day fermentation. Meanwhile, a considerable SCFAs of 334.5 mg COD/g VSS was produced within the first 4 days of anaerobic fermentation, which was 3.3 times higher than that in the control. It was found that the acetic and propionic acids accounted for 57.4–65.4% of SCFAs produced in CER-assisted anaerobic fermentation. Compared to pretreatment with potassium ferrate, surfactant and enzymes, a much higher SCFAs concentration was obtained in this study with CER. In fact, used CER could be recovered and reused, without harsh chemicals left in fermented sludge. This indeed created an environmentally and economically beneficial situation with considerably saved pretreatment agents.This work was supported by the National Natural Science Foundation of China – China (No.51778179)

Enhancing volatile fatty acids production from waste activated sludge by a novel cation-exchange resin assistant strategy

This study developed a novel strategy for enhancing volatile fatty acids production from waste activated sludge by cation-exchange resin assistant anaerobic fermentation. The process condition was optimized by response surface methodology. Considerable sludge disintegration degree (40.9%) and volatile fatty acids yield (4619.6 mg COD/L) were achievable at the proposed process conditions, i.e. cation-exchange resin dosage = 2.05 and 1.78 g/g SS, fermentation time = 4.97 and 6.46 d, and stirring strength = 246.9 and 261.2 rpm, respectively. Grey relational analysis revealed that cation-exchange resin dosage, fermentation time, and stirring strength presented similarly significant effects on sludge disintegration. The reusability tests showed that NaCl solution had the best effect on cation-exchange resin regeneration, and the performance of regenerated resin was comparable with the original resin on volatile fatty acids production. Compared with conventional pretreatment methods, the proposed cation-exchange resin assistant strategy revealed obvious advantages of saved pretreatment agents, easy operation, none chemical residual in sludge and small footprint. Total volatile fatty acids recovery can reach 1.46 × 108 tons chemical oxygen demand annually in terms of China's context, which could offset one third of carbon gap in China's wastewater treatment plants. The proposed cation-exchange resin assistant strategy indeed sheds lights on the direction for WAS treatment in a close alignment with process viability and engineering feasibility.This work was supported by the National Natural Science Foundation of China e China (No.51778179) and Research and Development Program in Key Areas of Guangdong Province (2019B110209002)

Effect of NaCl concentration on microbiological properties in NaCl assistant anaerobic fermentation : hydrolase activity and microbial community distribution

Previous studies have demonstrated that sludge hydrolysis and short-chain fatty acids (SCFAs) production were improved through NaCl assistant anaerobic fermentation. However, the effect of NaCl concentrations on hydrolase activity and microbial community structure was rarely reported. In this study, it was found that α-glucosidase activity and some carbohydrate-degrading bacteria were inhibited in NaCl tests, owing to their vulnerability to high NaCl concentration. Correspondingly, the microbial community richness and diversity were reduced compared with the control test, while the evenness was not affected by NaCl concentration. By contrast, the protease activity was increased in the presence of NaCl and reached the highest activity at the NaCl concentration of 20 g/L. The protein-degrading and SCFAs-producing bacteria (e.g., Clostridium algidicarnis and Proteiniclasticum) were enriched in the presence of NaCl, which were salt-tolerant.Published versio

An innovative alkaline protease-based pretreatment approach for enhanced short-chain fatty acids production via a short-term anaerobic fermentation of waste activated sludge

This study reported a novel pretreatment approach with combination of alkaline protease (AP) and pH 10 for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge (WAS). Through the AP-based pretreatment, WAS flocs were disintegrated with cell lysis, leading to release of biodegradable organic matters. At the external AP dosage of 5%, SCOD of 5363.7 mg/L (SCOD/TCOD = 32.5%) was achievable after 2-h pretreatment. More than 66% of SCOD was composed of proteins and carbohydrates. Considerable SCFAs of 607 mg COD/g VSS was produced over a short-term anaerobic fermentation of 3 days, which was 5.4 times higher than that in the control. Acetic and propionic acids accounted for 74.1% of the SCFAs. The AP-based approach increased endogenous protease and ?-glucosidase activities, facilitating biodegradation of dissolved organic matters and SCFAs production. Such approach is promising for WAS disposal and carbon recovery, the produced SCFAs might supply 60% of carbon gap in wastewater

Breakage–reflocculation implemented by two-stage shear for enhancing waste-activated sludge dewaterability: Effects of shear condition and extracellular polymeric substances

<p>The conditioning of waste-activated sludge (WAS) before dewatering is crucial for enhancing sludge dewaterability. The breakage–reflocculation that was implemented by two-stage shear (drastic first-stage shear for breakage and moderate second-stage shear for reflocculation utilizing the bioflocculation function) which was proposed as a novel WAS conditioning method with several advantages (simple operation, lower cost, and none added reagent) compared to traditional methods. Effects of the shear condition and extracellular polymeric substances (EPS) on breakage–reflocculation were orderly investigated. Two equations were developed by response surface methodology for predicting breakage–reflocculation conditioning performance. Analysis of variance (ANOVA) indicated that individual effects of first-stage shear rate (<i>G</i>₁), second-stage shear rate (<i>G</i>₂), second-stage shear time (<i>t</i>₂), and interactive effect of <i>G</i>₁<i>G</i>₂ were significant. More compact WAS flocs with better dewaterability and larger floc size formed through breakage–reflocculation. This was reflected in that the capillary suction time decreased by 16.9% and mean floc size increased by 24% under the optimum shear condition. In addition, the loosely bound EPS was revealed to be closely negatively correlated with breakage–reflocculation conditioning performance, indicating its adverse role in breakage–reflocculation. The breakage–reflocculation could be used as an independent conditioning method with low cost or a part of combined method.</p