The integration of cyanide hydratase and tyrosinase catalysts enables effective degradation of cyanide and phenol in coking wastewaters

A combined process model for wastewater treatment based on hydraulic retention time and toxicity inhibition

Hydraulic retention time (HRT), as an important parameter in the wastewater treatment process, has a great impact on water quality and energy consumption. With the rapid advances in computer technology and deepened understanding of in microbial metabolism, a series of activated sludge models (ASMs) have been developed and applied in wastewater treatment. However, ASMs simulation based on the nexus of HRT, water treatment process, water quality and energy consumption has yet to be verified. In this study, HRT was creatively linked to water treatment process variation. And a novel combined process model (CPM) was developed based on the operational data and treatment performance data from 4 full-scale coking wastewater treatment processes. In the CPM, an array of biological treatment processes were represented by setting the HRT in respective treatment units of the anaerobic-oxic-hydrolytic & denitrification-oxic (A/O/H/O) process. The relationships between HRT, effluent quality and energy consumption were systematically analyzed. Results showed that: (i) for A/O/H/O process, the HRT of first oxic (O1) reactor has a key effect on the effluent water quality and energy consumption, while the impact of the anaerobic (A) reactor HRT was limited; (ii) the O/H/O process has a clear advantage in treating coking wastewater due to the carbon removal and detoxification function of O1 reactor; (iii) the lowest energy consumption (with the total system HRT below 210 h) to meet the biological effluent quality requirements (COD = 200 mg/L, TN = 50 mg/L) is 4.429 kWh/m³. Since the CPM could effectively work out the optimal process configuration and break the boundaries between HRT and process variation, it has enormous potential to be extended to the design of other wastewater treatment processes.

Catalytic ozonation of hard COD in coking wastewater with Fe2O3/Al2O3-SiC: From catalyst design to industrial application

Development of robust, reactive, and inexpensive catalyst for pollutants abatement with catalytic ozonation is of great significance. Herein, the effect of a robust and easy-recovery catalyst, Fe₂O₃/Al₂O₃-SiC, for the catalytic ozonation of hardly biodegradable COD (hard COD) in coking wastewater had been explored. Al-O-Si bond formed on modified SiC through the substitution of hydrogen in surficial Si-OH groups by Al³⁺. The Lewis acid sites improved the adsorption of ozone and facilitated the formation of ·OH and O₂·^-. For coking wastewater treatment, the removal ratio of hard COD and the generation speed of hydroxyl radical (R_ct) in the catalytic ozonation process were 71% and 253% higher than those in the ozonation group, respectively. Ozone utilization increased from 0.44 g COD removed/g O₃ in the ozonation group to 1.42 g COD removed/g O₃ in the Fe₂O₃/Al₂O₃-SiC catalytic ozonation group. In a full-scale application, Fe₂O₃/Al₂O₃-SiC catalytic ozonation decreased the consumption of O₃ to 60 mg L^-1 and decreased the operation cost by 50%. These results provided an approachable way for sharing the extraordinary capacity of ozone for contaminants remediation in industrial applications.

Recent Progress in the Production of Cyanide-Converting Nitrilases—Comparison with Nitrile-Hydrolyzing Enzymes

Nitrilases have a high potential for application in organic chemistry, environmental technology, and analytics. However, their industrial uses require that they are produced in highly active and robust forms at a reasonable cost. Some organic syntheses catalyzed by nitrilases have already reached a high level of technological readiness. This has been enabled by the large-scale production of recombinant catalysts. Despite some promising small-scale methods being proposed, the production of cyanide-converting nitrilases (cyanide hydratase and cyanide dihydratase) is lagging in this regard. This review focuses on the prospects of cyanide(di)hydratase-based catalysts. The current knowledge of these enzymes is summarized and discussed in terms of the origin and distribution of their sequences, gene expression, structure, assays, purification, immobilization, and uses. Progresses in the production of other nitrilase catalysts are also tackled, as it may inspire the development of the preparation processes of cyanide(di)hydratases.

Immobilized enzymes and cell systems: an approach to the removal of phenol and the challenges to incorporate nanoparticle-based technology

The presence of phenol in wastewater poses a risk to ecosystems and human health. The traditional processes to remove phenol from wastewater, although effective, have several drawbacks. The best alternative is the application of ecological biotechnology tools since they involve biological systems (enzymes and microorganisms) with moderate economic and environmental impact. However, these systems have a high sensitivity to environmental factors and high substrate concentrations that reduce their effectiveness in phenol removal. This can be overcome by immobilization-based technology to increase the performance of enzymes and bacteria. A key component to ensure successful immobilization is the material (polymeric matrices) used as support for the biological system. In addition, by incorporating magnetic nanoparticles into conventional immobilized systems, a low-cost process is achieved but, most importantly, the magnetically immobilized system can be recovered, recycled, and reused. In this review, we study the existing alternatives for treating wastewater with phenol, from physical and chemical to biological techniques. The latter focus on the immobilization of enzymes and microorganisms. The characteristics of the support materials that ensure the viability of the immobilization are compared. In addition, the challenges and opportunities that arise from incorporating magnetic nanoparticles in immobilized systems are addressed.

Application Potential of Cyanide Hydratase from Exidia glandulosa: Free Cyanide Removal from Simulated Industrial Effluents

Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN−). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN to the much less toxic formamide, have been considered for a mild approach to wastewater decyanation. However, few data are available to evaluate the application potential of CynHs. In this study, we used a new CynH from Exidia glandulosa (protein KZV92691.1 designated NitEg by us), which was overproduced in Escherichia coli. The purified NitEg was highly active for fCN with 784 U/mg protein, kcat 927/s and kcat/KM 42/s/mM. It exhibited optimal activities at pH approximately 6–9 and 40–45 °C. It was quite stable in this pH range, and retained approximately 40% activity at 37 °C after 1 day. Silver and copper ions (1 mM) decreased its activity by 30–40%. The removal of 98–100% fCN was achieved for 0.6–100 mM fCN. Moreover, thiocyanate, sulfide, ammonia or phenol added in amounts typical of industrial effluents did not significantly reduce the fCN conversion, while electroplating effluents may need to be diluted due to high fCN and metal content. The ease of preparation of NitEg, its high specific activity, robustness and long shelf life make it a promising biocatalyst for the detoxification of fCN.

Partial oxidation of phenol in supercritical water with NaOH and H2O2: Hydrogen production and polymer formation

The catalytic supercritical water partial oxidation of phenol using H₂O₂ as oxidant in the presence of NaOH was explored to enhance hydrogen production and inhibit phenol polymerization. The results indicated that H₂ production was enhanced in the presence of NaOH when phenol supercritical water oxidation was controlled at a lower O/C ratio. Compared with the individual catalytic partial oxidation of phenol, the reaction with NaOH and H₂O₂ simultaneously enhanced H₂ production and inhibited polycyclic polymer generation at O/C ratios below 0.5. A peak hydrogen gasification efficiency value of 62.35% was observed at an O/C ratio of 0.3 with 1.0 wt% NaOH, and a phenol removal efficiency of nearly 75% was reported. Phenol polymerization was effectively inhibited for reaction times limited to 50 s. Moreover, other phenol reaction pathways reported in the literature were compared with the partial oxidation of phenol in supercritical water with NaOH and H₂O₂.

Application and Mechanism of Sludge-Based Activated Carbon for Phenol and Cyanide Removal from Bio-Treated Effluent of Coking Wastewater

The toxic pollutants phenol and cyanide in the bio-treated effluent of coking wastewater still need advanced treatment to meet environmental requirements. In this study, activated carbon prepared from municipal sludge and bamboo waste (SBAC) was used for simultaneous adsorption of phenol and cyanide from bio-treated effluent of coking wastewater. The results showed that the optimum removal efficiencies of volatile phenol (69.7%) and total cyanide (80.1%) were observed at a SBAC dosage of 8 g/L, a pH value of 8.0, and a contact time of 80 min. The physical and chemical properties of SBAC were analyzed using Brunauer–Emmett–Teller (BET) surface area (SBET), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. SBAC had high SBET (289.58 m2/g) and rich mesoporous structure (average pore diameter of 3.688 nm), and carboxylic groups on SBAC surfaces were enhanced due to the addition of bamboo waste. In addition, a kinetic model of pseudo-first-order fitted well with the experimental data of volatile phenol, while the adsorption of total cyanide onto the SBAC was better described by a pseudo-second-order kinetic model.

Polymerization and oxidation of phenols in supercritical water

The treatment of toxic and difficult-to-degrade phenolic compounds has become a key issue in the coking, pharmaceutical, and chemical industries. Considering the polymerization and oxidation of phenolic compounds in supercritical water partial oxidation/supercritical water oxidation (SCWPO/SCWO), the present study reviewed the removal efficiency and reaction pathway of phenolic compounds and phenolic waste/wastewater under different reaction conditions. Temperature is the dominant factor affecting the SCWO reaction. When the oxidizing ability is insufficient, the organics polymerize to form phenolic compounds. The gradual increase of oxidant equivalent causes the intermediate product to gradually oxidize to CO₂ and H₂O completely. Finally, the free radical reaction mechanism is considered to be a typical SCWO reaction mechanism.

Synergic effect of adsorption and biodegradation enhance cyanide removal by immobilized Alcaligenes sp. strain DN25

A high efficiency and stability polyurethane-foam (PUF)-immobilized cell system was constructed to remove cyanide based on simultaneous adsorption and biodegradation (SAB). The performance of the PUF-immobilized system was evaluated by comparison with the freely suspended cell system. The SAB system exhibited more effective and robust, and could still remain degradation activity even at 40 °C or pH 11.0. The SAB system completely removed 500 mg CN^-/L within 8 h at 30 °C, pH 8.0, and 120 rpm, whereas 12 h were required for the free cells system. Moreover, the SAB system showed apparent superiority in removing higher concentration cyanide up to 1200 mg CN^-/L. A continuously stirred tank bioreactor (CSTR) was successfully designed and steadily operated with approximately 85% of the total average removal efficiency for 52 days at an influent cyanide concentration of 100-200 mg/L, which demonstrated a favorable reliability. Cyanide removal process could be well described using a pseudo first-order model, and the higher apparent rate constants (k) of the immobilized cells showed the synergic effect of adsorption and biodegradation significantly enhanced cyanide removal. Preliminarily, it was found that the foam characteristic might play a not negligible role on the cyanide-degrading enzyme expression of strain DN25 in the SAB system.

Application of surface modification using sodium hypochlorite for helping flotation separation of acrylonitrile-butadiene-styrene and polystyrene plastics of WEEE

Acrylonitrile-butadiene-styrene (ABS) and polystyrene (PS), as important fractions of Waste from Electric and Electronic Equipment (WEEE) plastics, show great significances to the recycling of WEEE. The objective of this study is to develop a simple, practical and efficient surface modification method using sodium hypochlorite (NaClO) for separation of waste ABS and PS plastics by the aid of froth flotation. After surface modification, more hydrophilic groups are introduced on ABS surface than that of PS, enhancing its surface hydrophilicity clearly and reducing its recovery in floated products. Single parameter experiments demonstrate NaClO concentration, treatment temperature, treatment time are key parameters in surface modification. Optimization of conditions for surface modification of ABS was conducted by Response Surface Methodology with a Box-Behnken design, and a predicting model was obtained also. The optimum conditions are NaClO concentration of 0.05 M/L, temperature of 67.50 °C, treatment time 59.50 min and stirring rate of 200 rpm. Under optimum conditions, ABS and PS with different particle sizes can be separated efficiently with recovery of 99.18% and 99.47%, and purity of 99.45% and 99.18% respectively. The application of surface modification using sodium hypochlorite can facilitate efficient flotation separation of waste ABS and PS plastics for the recycling of WEEE.

Biotransformation of phenol in synthetic wastewater using the functionalized magnetic nano-biocatalyst particles carrying tyrosinase

Low conversion efficiency and long-processing time are some of the major problems associated with the use of biocatalysts in industrial processes. In this study, modified magnetic iron oxide nanoparticles bearing tyrosinase (tyrosinase-MNPs) were employed as a magnetic nano-biocatalyst to treat phenol-containing wastewater. Different factors affecting the phenol removal efficiency of the fabricated nano-biocatalyst such as catalyst dosage, pH, temperature, initial phenol concentration, and reusability were investigated. The results proved that the precise dosage of nano-biocatalyst was able to degrade phenol at the wide range of pHs and temperatures. The immobilized tyrosinase showed proper phenol degradation more than 70%, where the substrate with a high concentration of 2500 mg/L was subjected to phenol removal. The nano-biocatalyst was highly efficient and reusable, since it displayed phenol degradation yields of 100% after the third reuse cycle and about 58% after the seventh cycle. Moreover, the immobilized tyrosinase was able to degrade phenol dissolved in real water samples up to 78% after incubation for 60 min. It was also reusable at least seven cycles in the real water sample. The results proved the effectiveness and applicability of the fabricated nano-biocatalyst to treat phenol-containing wastewaters in a shorter time and higher efficiency even at high phenol concentration. The developed nano-biocatalyst can be promising for the micropollutants removal and an alternative for the catalysts used in traditional treatment processes.

Influence of Integrated Membrane Treatment on the Phytotoxicity of Wastewater from the Coke Industry

In this paper, coke wastewater that had passed through biological and integrated membrane processes (filtration on sand bed-reverse osmosis) was chosen to assess the phytotoxicity of selected industrial wastewater with regard to the test plant-Vicia faba. An innovative research technique in vitro test was conducted in a large scale phytothrone chamber on two matrices: cotton and Murashige and Skoog Basal Medium (MSBM). The toxicity of wastewater was evaluated for samples: (1) treated in the treatment plant by biological processes, (2) filtrated through a sand bed and filtrated (3) reverse osmosis (RO) membrane. The results showed that there is a noticeable correlation between increasing concentrations of wastewater and seed germination of the test plant. Although the wastewater collected from the coke plant was treated biologically, it showed very high levels of germination inhibition (90-98% for cotton matrix and 92-100% for MSBM matrix) and strong toxic effects. The wastewater collected from the coke plant showed a significantly greater phytotoxic effect compared with those obtained from the effluent treated on a sand bed and in RO. However, wastewater, even after treatment on a sand bed (reduction of COD-39%, TN-46%, TOC-42%, TC-47%, SS-50%, 16PAHs-53%), was still toxic and germination inhibition was in the range of 24-48% for the cotton matrix and 14-54% for the MSBM matrix. The toxicity of wastewater treated in the membrane process was the lowest (reduction of COD-85%, TN-95%, TOC-85%, TC-86%, SS-98%, 16PAHs-67%). The germination inhibition was in the range of 4-10% for the cotton matrix and 2-12% for the MSBM matrix. These samples are classified as non-toxic or slightly toxic to the model plant. The present study highlights the necessity of monitoring not only the basic physical and chemical indicators (including the level of toxic substances as PAHs), but also their effect on the test organisms in wastewater samples.

A novel strategy for the efficient removal of toxic cyanate by the combinatorial use of recombinant enzymes immobilized on aminosilane modified magnetic nanoparticles

Cyanase detoxifies cyanate by transforming it to ammonia and carbon dioxide in a bicarbonate-dependent reaction, however, dependence on bicarbonate limits its utilization in large-scale applications. A novel strategy was therefore developed for overcoming this bottleneck by the combined application of cyanase (rTl-Cyn) and carbonic anhydrase (rTl-CA). The synergistic effect of rTl-Cyn and rTl-CA could reduce the dependence of bicarbonate by 80%, compared to using rTl-Cyn alone. Complete degradation of cyanate (4 mM) was achieved with buffered conditions and 85 ± 5% degradation with industrial wastewater sample, when 20 U of rTl-Cyn was applied. Furthermore, a similar percentage of degradation was achieved using 80% less bicarbonate, when rTl-Cyn and rTl-CA were used together under identical conditions. In addition, rTl-Cyn and rTl-CA were immobilized onto the magnetic nanoparticles and their catalytic activity, stability and reusability were also evaluated. This is the first report on the synergistic biocatalysis by rTl-Cyn and rTl-CA, for cyanate detoxification.