Qinglian Wu

Enhancement of volatile fatty acid production by co-fermentation of food waste and excess sludge without pH control: The mechanism and microbial community analyses.

The study provided a cost-effective and high-efficiency volatile fatty acid (VFA) production strategy by co-fermentation of food waste (FW) and excess sludge (ES) without artificial pH control. VFA production of 867.42mg COD/g-VS was obtained under the optimized condition: FW/ES 5, solid retention time 7d, organic loading rate 9g VS/L-d and temperature 40°C. Mechanism exploration revealed that the holistic biodegradability of substrate was greatly enhanced, and proper pH range (5.2-6.4) was formed by the high buffering capacity of the co-fermentation system itself, which effectively enhanced hydrolysis yield (63.04%) and acidification yield (83.46%) and inhibited methanogenesis. Moreover, microbial community analysis manifested that co-fermentation raised the relative abundances of hydrolytic and acidogenic bacteria including Clostridium, Sporanaerobacter, Tissierella and Bacillus, but suppressed the methanogen Anaerolineae, which also facilitated high VFA production. These results were of great guiding significance aiming for VFA recovery from FW and ES in large-scale.

Adsorption of p-nitrophenols (PNP) on microalgal biochar: Analysis of high adsorption capacity and mechanism

Biochars derived from three microalgal strains (namely, Chlorella sp. Cha-01, Chlamydomonas sp. Tai-03 and Coelastrum sp. Pte-15) were evaluated for their capacity to adsorb p-nitrophenols (PNP) using raw microalgal biomass and powdered activated carbon (PAC) as the control. The results show that BC-Cha-01 (biochar from Chlorella sp. Cha-01) exhibited a high PNP adsorption capacity of 204.8mgg-1, which is 250% and 140% higher than that of its raw biomass and PAC, respectively. The adsorption kinetics and equilibrium are well described with pseudo-second-order equation and Freundlich model, respectively. BC-Cha-01 was found to contain higher polarity moieties with more O-containing functional groups than PAC and other microalgae-derived biochars. The strong polarity of binding sites on BC-Cha-01 may be responsible for its superior adsorption capacity. The biochars from Chlorella sp. Cha-01 seem to have the potential to serve as a highly efficient PNP adsorbent for wastewater treatment or emergency water pollution control.

Enhanced sulfamethoxazole ozonation by noble metal-free catalysis based on magnetic Fe3O4 nanoparticles: catalytic performance and degradation mechanism

In this research, Fe3O4 nanoparticles were prepared by a low-cost route free of other agents, and applied in the catalysis of sulfamethoxazole (SMX) ozonation. It was proven that Fe3O4 nanoparticles significantly enhance SMX ozonation. Using a kinetics analysis, when Fe3O4 particles were added to the ozonation process, the reaction rate constant increased by 51% when the pH was 5. Moreover, we also identified that Fe3O4 enhanced the SMX ozonation removal rate by changing the degradation pathway. It was found that addition of Fe3O4 improved the production of Lewis acid active sites in SMX. These kinds of site in SMX are much easier to attack, which leads to a higher SMX removal rate and lower operational costs for the Fe3O4-based catalytic ozonation process compared to an O3 oxidation process. Finally, the SMX degradation pathways were classified for the first time, based on ozone oxidation types to give a guide for the quick and direct oxidation of SMX and other pollutants.

Enhanced volatile fatty acid production from excess sludge by combined free nitrous acid and rhamnolipid treatment

VFA production from excess sludge (ES) was greatly enhanced by a low-cost and high-efficient treatment: 0.67mg/L free nitrous acid (FNA) pretreatment combined with 0.04g/g TSS rhamnolipid (RL) addition (FNA+RL), which significantly shortened fermentation time to 3days and increased VFA production to 352.26mgCOD/g VSS (5.42 times higher than raw ES). Propionic and acetic acids were the two leading components (71.86% of the total VFA). Mechanism investigation manifested FNA+RL improved the biodegradability of ES, achieved positive synergetic effect on solubilization, hydrolysis and acidification efficiencies, and inhibited methanation. Microbial community distribution further explained the above phenomena. The bacteria related to polysaccharides/protein utilization and VFA generation, including Clostridium, Megasphaera and Proteiniborus, were mainly observed in FNA+RL, whereas gas-forming bacteria Anaerolineae and acid-consuming bacteria Proteobacteria were assuredly suppressed. Besides, Propionibacterineae associated with propionic acid generation was exclusively enriched in sole RL and FNA+RL.

Economical evaluation of sludge reduction and characterization of effluent organic matter in an alternating aeration activated sludge system combining ozone/ultrasound pretreatment.

An ozone/ultrasound lysis-cryptic growth technology combining a continuous flow anaerobic-anoxic-microaerobic-aerobic (AAMA+O3/US) system was investigated. Techno-economic evaluation and sludge lyses return ratio (r) optimization of this AAMA+O3/US system were systematically and comprehensively discussed. Economic assessment demonstrated that this AAMA+O3/US system with r of 30% (AAMA+O3/US2# system) was more economically feasible that can give a 14.04% saving of costs. In addition to economic benefits, a 55.08% reduction in sludge production, and respective 21.17% and 5.45% increases in TN and TP removal efficiencies were observed in this AAMA+O3/US2# system. Considering the process performances and economic benefits, r of 30% in AAMA+O3/US2# system was recommended. Excitation-emission matrix and Fourier transform infrared spectra analyses also proved that less refractory soluble microbial products were generated from AAMA+O3/US2# system. Improvement in 2,3,5-triphenyltetrazolium chloride electron transport system (TTC-ETS) activity in AAMA+O3/US2# further indicated that a lower sludge lyses return ratio stimulated the microbial activity.

Optimization of ultrasonic pretreatment and substrate/inoculum ratio to enhance hydrolysis and volatile fatty acid production from food waste

A new method of combinating ultrasonic (US) pretreatment and substrate/inoculum ratio (S/I) adjustment was applied to enhance hydrolysis and volatile fatty acid (VFA) production from food waste. The maximum VFA production was obtained at an US of 1 W mL−1 and S/I 6, which was four times greater compared to that without pretreatment and S/I adjustment.

Enhancing sludge biodegradability and volatile fatty acid production by tetrakis hydroxymethyl phosphonium sulfate pretreatment

A new pretreatment method based on tetrakis hydroxymethyl phosphonium sulfate (THPS) biocide was tried to enhance sludge disintegration, and improved sludge biodegradability and subsequent volatile fatty acid (VFA) production. Sludge activity decreased to less than 10% after 2 days pretreatment using 20mg/g-TSS THPS, which also obviously destroyed EPS and cell membrane, and dissolved more biodegradable substances (48.8%) than raw sludge (19.7%). Moreover, 20mg/g-TSS THPS pretreatment shortened fermentation time to 4days and improved VFA production to 2778mg COD/L (4.35 times than that in control). Therein, the sum of n-butyric, n-valeric and iso-valeric acids unexpectedly accounted for 60.5% of total VFA (only 20.1% of that in control). The more high molecular weight VFAs (C4-C5) than low molecular VFAs (C2-C3) resulted from THPS pretreatment benefited to subsequent medium-chain volatile acids (C6-C12) generation to realize the separation and recovery of organic carbon more efficiently.

Biosorption of cadmium by a lipid extraction residue of lipid-rich microalgae

The present study investigates the performances and mechanisms of biosorption of cadmium (Cd) ions using a lipid extraction residue from three strains of lipid production microalgae. The adsorption performance was determined by batch biosorption experiments and kinetic modeling. The algae cell in the whole growth period and lipid extraction residue both exhibited desirable adsorption performance. The lipid extraction residue from the strain of Coelastrum sp. PTE-15 had the highest capacity of Cd sorption, which was 32.8 mg g−1. FTIR data suggested that the functional groups acting as binding sites on the microalgae surface which participate in biosorption were carboxylic, hydroxyl, and amino. The biosorption properties and maximum adsorption capacity of the lipid extraction residue from three microalgal strains were determined by equilibrium modeling. The adsorption process followed the Langmuir isotherm model with a high value of correlation coefficients (≥0.99) and biosorption capacity being estimated to be 36.1 mg g−1.

Enhancement of volatile fatty acid production using semi-continuous anaerobic food waste fermentation without pH control

This study proposed a cost-effective and high-yield volatile fatty acid (VFA) production strategy using anaerobic food waste (FW) fermentation without pH control, which could be recommended for practical scale VFA production and FW treatment. Efficient hydrolysis, high VFA production (867.42 mg COD per g of VS) and VFA/SCOD (88.65%), and slight methane production (20.56 mL per g of VS, only 5.34% of theoretical value) were obtained via semi-continuous anaerobic FW fermentation under the optimized conditions, which were a substrate to inoculum ratio of 5, a temperature of 40 °C, a solid retention time of 7 d and an organic loading rate of 9 g VS per L per d. The highly-efficient VFA production was mainly attributed to the proper pH, which was not adjusted artificially and was maintained at 5.2–6.4 by the neutralization effect of ammonia release. And both the kinetic model and the carbon mass balance analysis showed that the substrate was adequately utilized to produce VFA under the optimized conditions. These results were of great guiding significance for the practical continuous recovery of VFA from FW.

Upgrading liquor-making wastewater into medium chain fatty acid: Insights into co-electron donors, key microflora, and energy harvest

Ethanol and lactate are considered suitable electron donors (EDs) for chain elongation (CE); however, their respective shortcomings still limit the substrate conversion ratio and medium chain fatty acid (MCFA) production. To address this limitation, different EDs and electron acceptors (EAs) were combined to compare their CE performances, and to investigate whether the combination of ethanol and lactate could further enhance the MCFA production based on the complementary characteristics of ethanol and lactate. The results verified, for the first time, ethanol and lactate as the co-EDs formed a cooperative relationship to largely promote the conversion of substrates into MCFA. The co-EDs of ethanol and lactate stimulated the transformation of dispersive lactate-carbon flux from the competing acrylate pathway into n-heptylate. Additionally, the coexisting by-products (H2 and CO2) from ethanol and lactate also contributed to the supererogatory MCFA generation. The key microbial taxa that distinguished the co-EDs from their single action were the preponderant species from class Negativicutes and family Ruminococcaceae. In addition, the co-EAs of acetate, n-butyrate, and n-caproate also promoted MCFA generation. Low concentration of n-caproate could be directly elongated into n-caprylate, while n-caproate concentration exceeding the toxic limit was unsuitable as an EA. This research provided a guide for substrate selection and collocation for CE technology. Chinese liquor-making wastewater (CLMW) was subsequently used as a substrate for MCFA production since it contains abundant lactate, ethanol, and short-chain fatty acids. In this study, a MCFA selectivity of 80.34 ± 5.26%, a slightly higher selectivity which is in the range of previously reported ones, was obtained. This study paves a way for the sustainable development of Chinese liquor industry by recycling the high-output CLMW into MCFA.