Meizhen Wang

Improving production of volatile fatty acids from food waste fermentation by hydrothermal pretreatment.

Food waste (FW) was pretreated by a hydrothermal method and then fermented for volatile fatty acid (VFAs) production. The soluble substance in FW increased after hydrothermal pretreatment (⩽200 °C). Higher hydrothermal temperature would lead to mineralization of the organic compounds. The optimal temperature for organic dissolution was 180 °C, at which FW dissolved 42.5% more soluble chemical oxygen demand than the control. VFA production from pretreated FW fermentation was significantly enhanced compared with the control. The optimal hydrothermal temperature was 160 °C with a VFA yield of 0.908 g/g VSremoval. Butyrate and acetate were the prevalent VFAs followed by propionate and valerate. FW fermentation was inhibited after 200 °C pretreatment. The VFAs were extracted from the fermentation broth by liquid-liquid extraction. The VFA recovery was 50-70%. Thus, 0.294-0.411 g VFAs could be obtained per gram of hydrothermally pretreated FW (in dry weight) by this method.

Ecological roles and release patterns of acylated homoserine lactones in Pseudomonas sp. HF-1 and their implications in bacterial bioaugmentation.

To enable development of a better bacterial bioaugmentation system for tobacco wastewater treatment, the roles and release patterns of acylated homoserine lactones (AHLs) in Pseudomonas sp. HF-1 were evaluated. Swarming was found to be induced by N-hexanoyl-homoserine lactone (C(6)-HSL) and N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C(6)-HSL); the formation of extracellular polymeric substances (EPS) was induced by 3-oxo-C(6)-HSL, C(6)-HSL and N-3-oxo-octanoyl-homoserine lactone (3-oxo-C(8)-HSL); and biofilm formation was induced by C(6)-HSL and 3-oxo-C(8)-HSL. When the culture conditions were 25°C, pH 5-6, 3% inoculum, 1.5 g L(-1) nicotine and 1% NaCl, the amount of AHLs released was sufficient for quorum sensing of swarming and EPS formation for strain HF-1, which was beneficial to the startup stage during bioaugmentation. When strain HF-1 was cultured at pH 8 in the presence of 1.2-1.8 g L(-1) of nicotine and 1% NaCl, the threshold for quorum sensing of biofilm formation was reached and the bioaugmentation system showed an efficient performance.

Where are signal molecules likely to be located in anaerobic granular sludge

Quorum sensing is a concentration-sensing mechanism that plays a vital role in sludge granulation. In this study, the regularities of distribution of different signal molecules, including intra- and interspecific signal molecules (diffusible signal factor, DSF), interspecific signal molecules (autoinducter-2, AI-2) and intraspecific signal molecules (acyl-homoserine lactones, AHLs), from three types of anaerobic granular sludge were investigated. The results showed that 70-90% of DSF was distributed in sludge, while AI-2 in the Water phase accounted for over 80% of the total content. Interestingly, there was a positive correlation between DSF and AI-2, which played opposite roles in granulation. Moreover, more than 55% of short and medium acyl chain AHLs tended to spread in aqueous water, while the long acyl chain AHLs were closer to granular sludge than the short and medium acyl chain AHLs. With the exception of one type of sludge, the percentage of long acyl chain AHLs in the sludge phase was greater than 70%. The different distributions of signal molecules were primarily determined based on their physicochemical properties, including molecular weight and solubility in water or organic solutions. In addition, the basic properties of sludge, such as the granular level or the production of EPS, were closely related to the diversity, distribution and concentration of signal molecules. As a medium in granulation, extracellular polymeric substances production was regulated by different signal molecules from different parts of anaerobic granular sludge. This study provides a foundation for investigation of quorum sensing in the system of anaerobic granular sludge.

The effect of C/N ratio on nitrogen removal in a bioelectrochemical system

The effect of C/N ratios of 2, 2.7, and 3.5 on nitrogen removal in a bioelectrochemical system (BES) was investigated. Starch was used as a carbon source for the electrogenesis phenomenon we observed in a previous study. The results showed that an increased C/N ratio helped the BES to remove nitrate and depress nitrite accumulation but did not increase autotrophic denitrification. Nitrate and total nitrogen removal were increased from 0.69±0.02gm(-3)h(-1) to 1.09±0.16gm(-3)h(-1), and from 0.52±0.08gm(-3)h(-1) to 0.97±0.06gm(-3)h(-1), respectively, when the C/N ratio was increased from 2.0 to 3.5. However, the autotrophic denitrification ratio decreased from 72.74% to 50.23% with the same increase in the C/N ratio. High C/N ratios postponed the excretion of soluble microbial products and increased electrogenesis, but did not improve the anode transformation efficiency.

Bioaugmentation of activated sludge with Acinetobacter sp. TW enhances nicotine degradation in a synthetic tobacco wastewater treatment system.

Bioaugmentation (BA) using Acinetobacter sp. TW with high nicotine-degrading efficiency was applied in a bioreactor receiving a load of COD (3,200 ± 50 mg/L) and nicotine (1.0 ± 0.1g/L). The results showed that because of the colonization of strain TW, the COD removal was stable at 80-90%, while nicotine removal reached 98% in the BA system. Furthermore, according to PCR-DGGE fingerprinting, compared with the originally activated sludge, more bacteria existed in the BA systems while some bacteria disappeared from the non-BA system. In terms of the quorum sensing, short chain AHLs increased to assist colonization of strain TW, and long chain AHLs were secreted and helped to resist the nicotine toxicity. Compared with the non-BA system, the amounts of ROS, protein carbonyls and 8-OHdG were significant lower in the BA systems, which suggested that strain TW played an important role in eliminating the nicotine toxicity from the bioreactors.

The effect of carbon sources on nitrogen removal performance in bioelectrochemical systems.

In order to ascertain the effects of different carbon sources (methanol, glucose, starch and NaHCO(3)) on denitrification in BESs, the experiment was conducted in a constant current, 3.5 of chemical oxygen demand to nitrate ratio in a greenhouse. Among the four carbon sources investigated in BESs, NaHCO(3) showed the highest nitrite accumulation and the ratio of soluble microbial products to soluble chemical oxygen demand (SMP/SCOD) with a value of 3.68 ± 0.68 mg/L and 94%, respectively. And the addition of organic substrates could reduce SMP production and enhance the denitrification process. In the constant voltage experiment, it was observed that the organics could be used by microbes to generate electrons at the anode. And a maximal current value of 11.0 mA in the BESs fed with starch indicated that the complex carbon source was easier to be used by microorganisms to generate electricity than the simple carbon source.

Electrical Stimulation Improves Microbial Salinity Resistance and Organofluorine Removal in Bioelectrochemical Systems

ABSTRACT Fed batch bioelectrochemical systems (BESs) based on electrical stimulation were used to treat p-fluoronitrobenzene (p-FNB) wastewater at high salinities. At a NaCl concentration of 40 g/liter, p-FNB was removed 100% in 96 h in the BES, whereas in the biotic control (BC) (absence of current), p-FNB removal was only 10%. By increasing NaCl concentrations from 0 g/liter to 40 g/liter, defluorination efficiency decreased around 40% in the BES, and in the BC it was completely ceased. p-FNB was mineralized by 30% in the BES and hardly in the BC. Microorganisms were able to store 3.8 and 0.7 times more K+ and Na+ intracellularly in the BES than in the BC. Following the same trend, the ratio of protein to soluble polysaccharide increased from 3.1 to 7.8 as the NaCl increased from 0 to 40 g/liter. Both trends raise speculation that an electrical stimulation drives microbial preference toward K+ and protein accumulation to tolerate salinity. These findings are in accordance with an enrichment of halophilic organisms in the BES. Halobacterium dominated in the BES by 56.8% at a NaCl concentration of 40 g/liter, while its abundance was found as low as 17.5% in the BC. These findings propose a new method of electrical stimulation to improve microbial salinity resistance.

Enhancement of acidogenic fermentation for volatile fatty acid production from food waste: Effect of redox potential and inoculum

The aim of this study was to explore the effects of redox potential (ORP) and inoculum on volatile fatty acids (VFAs) production from food waste by acidogenic fermentation. Four experimental conditions with two ORP levels were tested: limited aeration conditions with ORP level of -100 to -200mV inoculating anaerobic sludge (LA+AnS) or aerobic sludge (LA+AeS), and anaerobic conditions with ORP level of -200 to -300mV inoculating anaerobic sludge with 2-bromoethanosulfophate (AN+BES) and without BES (AN). The maximal VFA yield (0.79g COD/g VS) was attained in LA+AnS reactor due to enhanced hydrolysis of substrates, especially proteins (degradation efficiency 78.3%). A higher frequency of phylum Firmicutes under limited aeration conditions (42.2-48.2%) was observed than that under anaerobic conditions (21.1%). The microbial community was more diverse in LA+AnS reactors than LA+AeS. We conclude that appropriate ORP level (from -100 to -200mV) and inoculum play essential roles in VFA production.

Stimulative mineralization of p-fluoronitrobenzene in biocathode microbial electrolysis cell with an oxygen-limited environment

p-Fluoronitrobenzene (p-FNB) is a toxic compound and tends to accumulate in the environment. p-FNB can be effectively removed and defluorinated in a single-chamber bioelectrochemical system (BES). To verify the suppositionally integrated reductive and oxidative metabolism mechanism in the BES, an oxygen-limited environment was used, with pure oxygen and nitrogen environments used as two controls. Under the oxygen-limited condition, the most excellent performance was achieved. The defluorination rate and mineralization efficiency were 0.0132h(-1) and 72.99±5.68% after 96h, with 75.4% of fluorine in the form of the fluoride ion. This resulted from the unique environment that allowed conventionally integrated reductive and oxidative catabolism. Moreover, the oxidation-reduction potential (ORP) had a significant effect on microbial communities, which was also an important reason for performance diversity. These results provide a new method for complete p-FNB treatment and a control strategy by ORP regulation for optimal system performance.

Acidogenic fermentation characteristics of different types of protein-rich substrates in food waste to produce volatile fatty acids

In this study, tofu and egg white, representing typical protein-rich substrates in food waste based on vegetable and animal protein, respectively, were investigated for producing volatile fatty acids (VFAs) by acidogenic fermentation. VFA production, composition, conversion pathways and microbial communities in acidogenesis from tofu and egg white with and without hydrothermal (HT) pretreatment were compared. The results showed HT pretreatment could improve the VFA production of tofu but not for egg white. The optimum VFA yields were 0.46g/gVS (tofu with HT) and 0.26g/gVS (egg white without HT), respectively. Tofu could directly produce VFAs through the Stickland reaction, while egg white was converted to lactate and VFAs simultaneously. About 30-40% of total protein remained in all groups after fermentation. Up to 50% of the unconverted soluble protein in the HT groups was protease. More lactate-producing bacteria, mainly Leuconostoc and Lactobacillus, were present during egg white fermentation.