Apr 2021, Volume 15 Issue 2

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    Dongjie Shang, Jianfei Peng, Song Guo, Zhijun Wu, Min Hu

    • Characteristics and interannual variation of aerosol pollution are illustrated.

    • Mechanisms of secondary aerosol formation in winter haze of North China are reviewed.

    • Directions in future studies of secondary aerosol formation are provided.

    Severe haze pollution occurs frequently in the winter over the Beijing-Tianjin-Hebei (BTH) region (China), exerting profound impacts on air quality, visibility, and human health. The Chinese Government has taken strict mitigation actions since 2013 and has achieved a significant reduction in the annual mean PM2.5 concentration over this region. However, the level of secondary aerosols during heavy haze episodes showed little decrease during this period. During heavy haze episodes, the concentrations of secondary aerosol components, including sulfate, nitrate and secondary organics, in aerosol particles increase sharply, acting as the main contributors to aerosol pollution. To achieve effective control of particle pollution in the BTH region, the precise and complete secondary aerosol formation mechanisms have been investigated, and advances have been made about the mechanisms of gas phase reaction, nucleation and heterogeneous reactions in forming secondary aerosols. This paper reviews the research progress in aerosol chemistry during haze pollution episodes in the BTH region, lays out the challenges in haze formation studies, and provides implications and directions for future research.

    Ting Chen, Yingying Zhao, Xiaopeng Qiu, Xiaoyan Zhu, Xiaojie Liu, Jun Yin, Dongsheng Shen, Huajun Feng

    • Economics of food waste treatment projects at 29 pilot cities in China was examined.

    • Roles of location, population size, processing technique, and income were studied.

    • Economic benefits were limited with a profit to cost ratio of 0.08±0.37.

    • Service population size affects construction economics significantly (P = 0.016).

    • Choice of food waste processing technique affects operating economics notably.

    This study examines the economic benefits of food waste treatment projects in China and factors affecting them. National-level pilot projects for food waste treatment located in 29 cities were selected as samples. The economics of food waste recycling from the investors’ perspective, in terms of investment during the construction phase and cost and benefit during the operation phase, was assessed. Results indicate that the average tonnage investment of food waste treatment projects was RMB 700.0±188.9 thousand yuan, with a profit to cost ratio of 0.08±0.37. This ratio increased to 0.95±0.57 following the application of government subsidies. It highlights the limited economic benefits of food waste treatment facilities, which rely on government subsidies to maintain their operations in China. Further analysis using a multi-factor analysis model revealed that regional location, service population size, processing techniques, and urban income exerted varying impacts on the economy of food waste treatment. Population size exerted the highest impact (P = 0.016) during the construction stage, and processing techniques notably influenced the project economy during the operation stage. The study highlights the need to prioritize service population size and processing techniques during economic decision-making and management of food waste recycling projects. The results of this study can serve as a valuable practical reference for guiding future policies regarding food waste treatment and related planning.

    Guoliang Zhang, Liang Zhang, Xiaoyu Han, Shujun Zhang, Yongzhen Peng

    • PN-A was start-up under low inoculation amount and a higher NRR was achieved.

    • PN-anammox system was successfully restored by aggressive sludge discharge.

    • Increase in granular sludge was the important factor to rapid recovery.

    • Enrichment of AOB and AnAOB in granular sludge favors the stable operation.

    Partial nitritation (PN)-anaerobic ammonium oxidation (anammox) is a promising pathway for the biological treatment of wastewater. However, the destruction of the system caused by excessive accumulation of nitrate in long-term operation remains a challenge. In this study, PN-anammox was initialized with low inoculation quantity in an air-lift reactor. The nitrogen removal rate of 0.71 kgN/(m3·d) was obtained, which was far higher than the seed sludge (0.3 kgN/(m3·d)). Thereafter, excess nitrate build-up was observed under low-loading conditions, and recovery strategies for the PN-anammox system were investigated. Experimental results suggest that increasing the nitrogen loading rate as well as the concentration of free ammonium failed to effectively suppress the nitrite oxidation bacteria (NOB) after the PN-anammox system was disrupted. Afterwards, effluent back-flow was added into the reactor to control the up-flow velocity. As a result, an aggressive discharge of sludge that promoted the synergetic growth of functional bacteria was achieved, leading to the successful restoration of the PN-anammox system. The partial nitritation and anammox activity were in balance, and an increase in nitrogen removal rate up to 1.07 kgN/(m3·d) was obtained with a nitrogen removal efficiency of 82.4% after recovery. Besides, the proportion of granular sludge (over 200 mm) increased from 33.67% to 82.82%. Ammonium oxidation bacteria (AOB) along with anammox bacteria were enriched in the granular sludge during the recovery period, which was crucial for the recovery and stable operation of the PN-anammox system.

    Jiangbo Jin, Yun Zhu, Jicheng Jang, Shuxiao Wang, Jia Xing, Pen-Chi Chiang, Shaojia Fan, Shicheng Long

    • The calculation process and algorithm of response surface model (RSM) were enhanced.

    • The prediction errors of RSM in the margin and transition areas were greatly reduced.

    • The enhanced RSM was able to analyze O3-NOx-VOC sensitivity in real-time.

    • The O3 formations were mainly sensitive to VOC, for the two case study regions.

    Quantification of the nonlinearities between ambient ozone (O3) and the emissions of nitrogen oxides (NOx) and volatile organic compound (VOC) is a prerequisite for an effective O3 control strategy. An Enhanced polynomial functions Response Surface Model (Epf-RSM) with the capability to analyze O3-NOx-VOC sensitivities in real time was developed by integrating the hill-climbing adaptive method into the optimized Extended Response Surface Model (ERSM) system. The Epf-RSM could single out the best suited polynomial function for each grid cell to quantify the responses of O3 concentrations to precursor emission changes. Several comparisons between Epf-RSM and pf-ERSM (polynomial functions based ERSM) were performed using out-of-sample validation, together with comparisons of the spatial distribution and the Empirical Kinetic Modeling Approach diagrams. The comparison results showed that Epf-RSM effectively addressed the drawbacks of pf-ERSM with respect to over-fitting in the margin areas and high biases in the transition areas. The O3 concentrations predicted by Epf-RSM agreed well with Community Multi-scale Air Quality simulation results. The case study results in the Pearl River Delta and the north-western area of the Shandong province indicated that the O3 formations in the central areas of both the regions were more sensitive to anthropogenic VOC in January, April, and October, while more NOx-sensitive in July.

    Chen Wang, Jun Wang, Jianqiang Wang, Meiqing Shen

    • K+ hinder the structural degradation of Cu/SAPO-34 under humid condition<100°C.

    • K+ on Cu/SAPO-34 brings lower acidity and inferior SCR activity at high temperature.

    • Fe/Beta was used to compensate the low activity of Cu/SAPO-34 at high temperature.

    • The hybrid catalysts with KCu/SAPO-34 and Fe/Beta show a great potential for using.

    K ions were introduced onto Cu/SAPO-34 catalysts via the ion-exchange process in order to improve their stability under low-temperature hydrothermal aging. The changes in structure and copper-species contents of these catalysts upon hydrothermal aging were probed in order to investigate their effects on selective catalytic reduction (SCR) activity. For the fresh Cu/SAPO-34 catalysts, K ions had little influence on the chabazite framework but effected their acidities by exchanging with acid sites. After hydrothermal aging, the structural integrity and amount of active sites decreased on pure Cu/SAPO-34. While the K-loaded catalysts showed improved chabazite structure, acidity, and active site conservation with increasing K loading. However, although the 0.7 wt% K catalyst maintained the same crystallinity, active site abundance, and low-temperature SCR activity as the fresh catalyst upon aging, an apparent decrease in SCR activity at high temperature was observed because of the inevitable decrease in the number of Brönsted acid sites. To compensate for the activity disadvantage of K-loaded Cu/SAPO-34 at high temperature, Fe/Beta catalysts were co-employed with K-loaded Cu/SAPO-34, and a wide active temperature window of SCR activity was obtained. Thus, our study reveals that a combined system comprising Fe/Beta and K-loaded Cu/SAPO-34 catalysts shows promise for the elimination of NOx in real-world applications.

    Chi Zhang, Wenhui Kuang, Jianguo Wu, Jiyuan Liu, Hanqin Tian

    • China’s rural industrial land (RIL) area quadrupled from 1990 to 2015.

    • RIL expansion cost 9% of China’s crop production and threatened human/ecosystem safety.

    • The underprivileged population bears a disproportionally large share of the risks.

    China’s rural industrialization has been a major driver for its rapid economic growth during the recent decades, but its myriad environmental risks are yet to be fully understood. Based on a comprehensive national land-use data set, our study shows that the area of China’s rural industrial land (RIL) quadrupled during 1990–2015, reaching 39000 km2 in 2015, comparable to urbanization in magnitude but with a much greater degree of landscape fragmentation which implies stronger ecological and environmental impacts. About 91% of the protected areas in the central China were within 50 km from rural industrial land, thus exposed to industrial disturbances. Accelerated rural industrial land expansion, particularly in regions under high geo-hazard risks, led to dramatically increased environmental risks, threatening the safety and health of both rural industrial workers and residents. Moreover, negative effects from rural industrial land expansion could partially offset the crop production growth in recent decades. The underprivileged rural population in the west bears a disproportionally large share of the increased environmental risks. China urgently needs to design and implement sustainable policies to restrict and reshape its rural industrialization. This study aims to inspire policy makers and researchers to rethink the current model of industrial expansion and improve rural industrial land planning, which is important for achieving the sustainable development goals of China.

    Yue Hu, Ding Dong, Kun Wan, Chao Chen, Xin Yu, Huirong Lin

    • Bacterial release from aged pipe sections under extreme conditions was quantified.

    • Released bacterial community structure exhibited large variation after transition.

    • Risks from transition reduced significantly with cleaner source.

    As a result of pollution in the present water sources, cities have been forced to utilize cleaner water sources. There are few reports regarding the potential shift of bacterial community structure driven by water source switching, especially that of corrosion-related bacteria. Three types of finished water were used for simulation, the polluted source water from the Qiantang and Dongtiaoxi Rivers (China) was replaced by cleaner water from Qiandao Lake (China). Here, we discussed the transition effects through three simulated reactors. The bacterial characteristics were identified using the high-throughput sequencing and heterotrophic plate count method. It was observed that the level of culturable bacteria declined by 2–3 orders of magnitude after water source switching. The bacterial community released from the pipeline reactor was significantly different under different finished water, and it exhibited large variation at the genus level. Porphyrobacter (58.2%) and Phreatobacter (14.5%) clearly replaced Novosphingobium, Aquabacterium, and Cupriavidus as new dominant genera in system A, which could be attributed to the lower carbon and nitrogen content of the new water source. Although corrosion-inhibiting bacteria decreased after switching, they still maintained dominant in three reactors (6.6%, 15.9%, and 19.7%). Furthermore, potential opportunistic pathogens such as Sphingomonas were detected. Our study shows that after transition to a high quality water source, the total culturable bacteria released was in a downtrend, which leads to a great reduction in the risk of bacterial leakage in the produced drinking water.

    Reza Katal, Mohammad Tanhaei, Jiangyong Hu

    • Photocatalytic activity was improved in TiO2 thin film by rapid thermal annealing.

    • Photoreactor was designed for TiO2 thin film.

    • Considerable reusability and durability of prepared photocatalysts were studied.

    Un-biodegradable pharmaceuticals are one of the major growing threats in the wastewaters. In the current study, TiO2 thin film photocatalysts were designed by nanocrystal engineering and fabricated for degradation of the acetaminophen (ACE) in a photocatalytic reaction under UV light irradiation in batch and continuous systems. The photocatalyst was prepared by sputtering and then engineered by thermal treatment (annealing at 300℃ (T300) and 650℃ (T650)). The annealing effects on the crystallinity and photocatalytic activity of the TiO2 film were completely studied; it was found that annealing at higher temperatures increases the surface roughness and grain size which are favorable for photocatalytic activity due to the reduction in the recombination rate of photo-generated electron-hole pairs. For the continuous system, a flat plate reactor (FPR) was designed and manufactured. The photocatalytic performance was decreased with the increase of flow rate because the higher flow rate caused to form the thicker film of the liquid in the reactor and reduced the UV light received by photocatalyst. The reusability and durability of the samples after 6 h of photocatalytic reaction showed promising performance for the T650 sample (annealed samples in higher temperatures).

    Shengjie Qiu, Jinjin Liu, Liang Zhang, Qiong Zhang, Yongzhen Peng

    • Sludge fermentation liquid addition resulted in a high NAR of 97.4%.

    • Extra NH4+-N from SFL was removed by anammox in anoxic phase.

    • Nitrogen removal efficiency of 92.51% was achieved in municipal wastewater.

    • The novel system could efficiently treat low COD/N municipal wastewater.

    Biological nitrogen removal of wastewater with low COD/N ratio could be enhanced by the addition of wasted sludge fermentation liquid (SFL), but the performance is usually limited by the introducing ammonium. In this study, the process of using SFL was successfully improved by involving anammox process. Real municipal wastewater with a low C/N ratio of 2.8–3.4 was treated in a sequencing batch reactor (SBR). The SBR was operated under anaerobic-aerobic-anoxic (AOA) mode and excess SFL was added into the anoxic phase. Stable short-cut nitrification was achieved after 46d and then anammox sludge was inoculated. In the stable period, effluent total inorganic nitrogen (TIN) was less than 4.3 mg/L with removal efficiency of 92.3%. Further analysis suggests that anammox bacteria, mainly affiliated with Candidatus_Kuenenia, successfully reduced the external ammonia from the SFL and contributed approximately 28%–43% to TIN removal. Overall, this study suggests anammox could be combined with SFL addition, resulting in a stable enhanced nitrogen biological removal.

    Shanwei Ma, Hang Li, Guan Zhang, Tahir Iqbal, Kai Li, Qiang Lu

    • N-doped activated carbon was prepared for catalytic pyrolysis of walnut shell.

    • Alkylphenols were selectively produced from catalytic pyrolysis process.

    • The alkylphenols yield increased by 8.5 times under the optimal conditions.

    • Formation mechanism of alkylphenols was proposed.

    Alkylphenols are a group of valuable phenolic compounds that can be derived from lignocellulosic biomass. In this study, three activated carbons (ACs) were prepared for catalytic fast pyrolysis (CFP) of walnut shell to produce alkylphenols, including nitrogen-doped walnut shell-derived activated carbon (N/WSAC), nitrogen-doped rice husk-derived activated carbon (N/RHAC) and walnut shell-derived activated carbon (WSAC). Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were carried out to reveal the influences of AC type, pyrolytic temperature, and AC-to-walnut shell (AC-to-WS) ratio on the product distributions. Results showed that with nitrogen doping, the N/WSAC possessed stronger capability than WSAC toward the alkylphenols production, and moreover, the N/WSAC also exhibited better effects than N/RHAC to prepare alkylphenols. Under the catalysis of N/WSAC, yields of alkylphenols were significantly increased, especially phenol, cresol and 4-ethylphenol. As the increase of pyrolytic temperature, the alkylphenols yield first increased and then decreased, while high selectivity could be obtained at low pyrolytic temperatures. Such a trend was also observed as the AC-to-WS ratio continuously increased. The alkylphenols production achieved a maximal yield of 44.19 mg/g with the corresponding selectivity of 34.7% at the pyrolytic temperature of 400°C and AC-to-WS ratio of 3, compared with those of only 4.67 mg/g and 6.1% without catalyst. In addition, the possible formation mechanism of alkylphenols was also proposed with the catalysis of N/WSAC.

    Miao Li, Jian Li, Yuchen Lu, Cenyang Han, Xiaoxuan Wei, Guangcai Ma, Haiying Yu

    • A predictive model for storage lipid/water distribution coefficient was developed.

    • The model yields outstanding fitting performance, robustness, and predictive ability.

    • Hydrophobic and electrostatic interactions and molecular size dominate log Klip/w.

    • The model can be used in a wide application domain to predict log Klip/w values.

    The distribution of organic compounds in stored lipids affects their migration, transformation, bioaccumulation, and toxicity in organisms. The storage lipid/water distribution coefficient (log Klip/w) of organic chemicals, which quantitatively determines such distribution, has become a key parameter to assist their ecological security and health risk. Due to the impossibility to measure Klip/w values for a huge amount of chemicals, it is necessary to develop predictive approaches. In this work, a quantitative structure-property relationship (QSPR) model for estimating log Klip/w values of small organic compounds was constructed based on 305 experimental log Klip/w values. Quantum chemical descriptors and n-octanol/water partitioning coefficient were employed to characterize the intermolecular interactions that dominate log Klip/w values. The hydrophobic and electrostatic interactions and molecular size have been found to play important roles in governing the distribution of chemicals between lipids and aqueous phases. The regression (R2 = 0.959) and validation (Q2 = 0.960) results indicate good fitting performance and robustness of the developed model. A comparison with the predictive performance of other commercial software further proves the higher accuracy and stronger predictive ability of the developed Klip/w predictive model. Thus, it can be used to predict the Klip/w values of cycloalkanes, long-chain alkanes, halides (with fluorine, chlorine, and bromine as substituents), esters (without phosphate groups), alcohols (without methoxy groups), and aromatic compounds.

    Om Prakash, Stefan J. Green, Pooja Singh, Puja Jasrotia, Joel E. Kostka

    Rhodanobacter spp. are dominant in acidic, high nitrate and metal contaminated sites.

    • Dominance of Rhodanobacter is likely due to tolerance to low pH and heavy metals.

    • High organic content increases stress tolerance capacity.

    • Longer incubation time is critical for accurate assessment of MIC (various stresses).

    This work examines the physiologic basis of stress tolerance in bacterial strains of the genus Rhodanobacter that dominate in the acidic and highly metal contaminated near-source subsurface zone of the Oak Ridge Integrated Field Research Challenge (ORIFRC) site. Tolerance of R. denitrificans to levels of different stresses were studied in synthetic groundwater medium and R2A broth. Two strains of R. denitrificans, strains 2APBS1T and 116-2, tolerate low to circumneutral pH (4–8), high Uranium (1 mmol/L), elevated levels of nitrate (400 mmol/L) and high NaCl (2.5%). A combination of physiologic traits, such as growth at low pH, increased growth in the presence of high organics concentration, and tolerance of high concentrations of nitrate, NaCl and heavy metals is likely responsible for dominance of Rhodanobacter at the ORIFRC site. Furthermore, extended incubation times and use of low carbon media, better approximating site groundwater conditions, are critical for accurate determination of stress responses. This study expands knowledge of the ecophysiology of bacteria from the genus Rhodanobacter and identifies methodological approaches necessary for acquiring accurate tolerance data.

    Xianke Lin, Xiaohong Chen, Sichang Li, Yangmei Chen, Zebin Wei, Qitang Wu

    • Indirect use of sludge in ditches alongside plants was tested in field experiments.

    • The dried and stabilized sludge in ditches was recovered with heavy metals.

    • Cd, Pb, Cu and Zn in the planted soil were all in a safe range.

    • The indirect use of sludge increased plant yield, soil N content and C storage.

    The treatment and disposal of municipal sewage sludge (MSS) is an urgent problem to be resolved in many countries. Safely using the nutrients within MSS to increase crop yield and enhance the fertility of poor soil could contribute to achieving sustainable development. An indirect use of MSS in ditches alongside Pennisetum hybridum plants was studied in field plots for 30 months and the contents of heavy metals and macronutrients were monitored in soil, sludge and plant samples. We found that the yield of P. hybridum was significantly increased by 2.39 to 2.80 times and the treated plants had higher N content compared with no sludge. In addition, the organic matter (OM) and N contents in the planted soil increased significantly compared with the initial soil. The OM content in the planted soil of the MSS treatment was 2.9 to 5.2 times higher than that with no sludge, and N increased by 2.0 to 3.8 times. However, MSS had no significant effect on the N, P and K contents in the soil at the bottom of the MSS ditch, and the content of heavy metals (Cd, Pb, Cu and Zn) were also within the safe range. Moreover, the moisture content and phytotoxicity of MSS after this indirect use were reduced and the heavy metal contents changed little, which is favorable to the further disposal of recovered MSS. Therefore, this indirect use of MSS is beneficial to agricultural production, soil quality and environmental sustainability.

    Huibin Guo, Ning Wang, Xiang Li

    • Metformin consumes O2−• and OH• induced by PM are proposed.

    • OH• dominated the oxidation of metformin compared with O2−•

    • Metformin can prevent the harm of ROS induced by PM to human health.

    • Antioxidative potential of metformin was first proposed to provide measures.

    Exposure to particulate matter (PM) can lead to the excessive accumulation of reactive oxygen species (ROS), which causes oxidative stress and endangers human health. In this study, the effects of metformin on PM-induced radicals were investigated, and the antioxidation reaction mechanism of metformin was analyzed by the density functional theory (DFT) method. The corresponding results revealed that the consumption rate of dithiothreitol (DTT) increased as the metformin concentration (0–40 mmol/L) increased under exposure to PM active components. Moreover, the OH radical content decreased as the metformin concentration increased. This result may be related to the consumption of PM-induced OH radicals by metformin, which promotes the DTT consumption rate. Additionally, because the initiation reaction has a high barrier, the oxidation reaction rate between metformin and •O2− is not very fast, although various catalysts may be present in the human environment. Importantly, we found that the barrier of metformin induced by OH radicals is only 9.6 kcal/mol while the barrier of metformin induced by oxygen is 57.9 kcal/mol, which shows that the rate of the •OH-initiated oxidative reaction of metformin is much faster and that this reaction path occurs more easily. By sample analysis, the mean OH radical generation was 55 nmol/min/g (ranging from 5 to 105 nmol/min/g) on haze days and 30 nmol/min/g (ranging from 10 to 50 nmol/min/g) on non-haze days. Moreover, OH radical generation was higher on haze days than on neighboring non-haze days. Taken together, all data suggest that metformin could consume the PM-induced radicals, such as OH radicals and •O2−, thereby providing health protection.

    Weichuan Qiao, Rong Li, Tianhao Tang, Achuo Anitta Zuh

    • PFOS was removed by soil adsorption and plant uptake in the VFCW.

    • Uptake of PFOS by E. crassipes was more than that of C. alternifolius.

    • PFOS in wastewater can inhibit the removal of nutrients.

    • Dosing with PFOS changed the soil microbial community in the VFCW.

    A vertical-flow constructed wetland (VFCW) was used to treat simulated domestic sewage containing perfluorooctane sulfonate (PFOS). The removal rate of PFOS in the domestic sewage was 93%–98%, through soil adsorption and plant uptake, suggesting that VFCWs can remove PFOS efficiently from wastewater. The removal of PFOS in the VFCW was dependent on soil adsorption and plant uptake; moreover, the percentage of soil adsorption was 61%–89%, and was higher than that of the plants uptake (5%–31%). The absorption capacity of Eichhornia crassipes (E. crassipes) (1186.71 mg/kg) was higher than that of Cyperus alternifolius (C. alternifolius) (162.77 mg/kg) under 10 mg/L PFOS, and the transfer factor of PFOS in E. crassipes and C. alternifolius was 0.04 and 0.58, respectively, indicating that PFOS is not easily translocated to leaves from roots of wetland plants; moreover, uptake of PFOS by E. crassipes was more than that of C. alternifolius because the biomass of E. crassipes was more than that of C. alternifolius and the roots of E. crassipes can take up PFOS directly from wastewater while C. alternifolius needs to do so via its roots in the soil. The concentration of 10 mg/L PFOS had an obvious inhibitory effect on the removal rate of total nitrogen, total phosphorus, chemical oxygen demand, and ammonia nitrogen in the VFCW, which decreased by 15%, 10%, 10% and 12%, respectively. Dosing with PFOS in the wastewater reduced the bacterial richness but increased the diversity in soil because PFOS stimulated the growth of PFOS-tolerant strains.

    Karla Ilić Đurđić, Raluca Ostafe, Olivera Prodanović, Aleksandra Đurđević Đelmaš, Nikolina Popović, Rainer Fischer, Stefan Schillberg, Radivoje Prodanović

    • Mutations in Lignin peroxidase Trp171 environment improved azo dyes degradation.

    • Expression on yeast cell surface and cell lysis allowed reusability of biocatalyst.

    • Aga2-LiP chimeric variants were characterized.

    The enzymatic degradation of azo dyes is a promising alternative to ineffective chemical and physical remediation methods. Lignin peroxidase (LiP) from Phanerochaete chrysosporium is a heme-containing lignin-degrading oxidoreductase that catalyzes the peroxide-dependent oxidation of diverse molecules, including industrial dyes. This enzyme is therefore ideal as a starting point for protein engineering. Accordingly, we subjected two positions (165 and 264) in the environment of the catalytic Trp171 residue to saturation mutagenesis, and the resulting library of 104 independent clones was expressed on the surface of yeast cells. This yeast display library was used for the selection of variants with the ability to break down structurally-distinct azo dyes more efficiently. We identified mutants with up to 10-fold greater affinity than wild-type LiP for three diverse azo dyes (Evans blue, amido black 10B and Guinea green) and up to 13-fold higher catalytic activity. Additionally, cell wall fragments displaying mutant LiP enzymes were prepared by toluene-induced cell lysis, achieving significant increases in both enzyme activity and stability compared to a whole-cell biocatalyst. LiP-coated cell wall fragments retained their initial dye degradation activity after 10 reaction cycles each lasting 8 h. The best-performing mutants removed up to 2.5-fold more of each dye than the wild-type LiP in multiple reaction cycles.

    Huan He, Qinjin Yu, Chaochao Lai, Chen Zhang, Muhan Liu, Bin Huang, Hongping Pu, Xuejun Pan

    • An innovative bubble column tower BPE was designed to treat the black-odorous water.

    • PO43, S2 and turbidity were removed, and dissolved oxygen was enriched in the BPE.

    • An aluminum bipolar electrode gave the best oxygen enrichment and pollutant removal.

    • Changes of microorganisms confirmed the improvement in water quality achieved.

    The large amount of municipal wastewater discharged into urban rivers sometimes exceeds the rivers’ self-purification capacity leading to black-odorous polluted water. Electro-flocculation has emerged as a powerful remediation technology. Electro-flocculation in a bubble column tower with a bipolar electrode (BPE) was tested in an attempt to overcome the high resistance and weak gas-floatation observed with a monopolar electrode (MPE) in treating such water. The BPE reactor tested had a Ti/Ta2O5-IrO2 anode and a graphite cathode with an iron or aluminum bipolar electrode suspended between them. It was tested for its ability to reduce turbidity, phosphate and sulphion and to increase the concentration of dissolved oxygen. The inclusion of the bipolar electrode was found to distinctly improved the system’s conductivity. The system’s electro-flocculation and electrical floatation removed turbidity, phosphate and sulphion completely, and the dissolved oxygen level improved from 0.29 to 6.28 mg/L. An aluminum bipolar electrode performed better than an iron one. Changes in the structure of the microbial community confirmed a significant improvement in water quality.