Optimization of the reaction conditions for enzymatic removal of phenol from wastewater in the presence of polyethylene glycol

The effect of the additive, polyethylene glycol (PEG), on the horseradish peroxidase (HRP) catalysed removal of phenol from wastewater has been studied over the phenol concentration range of 1–10 mM (0.1–1.0 g/l). The optimum pH, HRP concentration, PEG concentration and the molar ratio of hydrogen peroxide and phenol have been investigated in the presence of PEG at room temperature in order to achieve the maximum phenol removal efficiency with the minimum cost. The effect of concentrations of HRP and PEG on reaction time was also investigated. Experimental results showed that the addition of PEG had significant protective effect on the activity of HRP. The amount of peroxidase required was reduced 40- and 75-fold less than that required without PEG for 1 and 10 mM phenol solutions, respectively. The higher the phenol concentration, the more effective was the addition of PEG. In the presence of PEG, the optimum pH is 8.0 and the optimum molar ratio of hydrogen peroxide and phenol is around 1.0. The minimum doses of HRP and PEG required for at least 95% removal were determined for several phenol concentrations and two empirical models are proposed to predict the minimum HRP and PEG doses required for 95% removal over the entire phenol concentration range of 1–10 mM. Under the optimum reaction conditions described above, the reaction times for at least 95% removal from 1 and 10 mM phenol solutions were 5 and 3 h, respectively. An increase in HRP concentration significantly reduced the reaction time; however, an increase in PEG concentration showed negligible influence.     

Removal of phenols from a foundry wastewater using horseradish peroxidase

Horseradish peroxidase (HRP) catalyses the oxidation of phenols by hydrogen peroxide resulting in the formation of water-insoluble polymers which can be separated by coagulation and sedimentation. The feasibility of the enzyme process to treat a foundry wastewater containing 3.5 mM of total phenols (330 mg/l as phenol) was examined. Two enzyme stocks of different purities were used but total phenols removal was independent of enzyme purity. For both stocks, 97 to 99% of the phenolic contaminants were removed, despite the presence of other contaminants such as organic compounds and iron in the waste matrix. The quantity of HRP required for this degree of treatment was in the same range as for the treatment of a synthetic wastewater containing an equal amount of pure phenol. Polyethylene glycol, a chemical additive, reduced enzyme inactivation, allowing a 22-fold reduction in the amount of HRP required for 99% removal of phenols from the foundry waste. Residual chemical oxygen demands (COD) varied depending on the enzyme source. The high purity HRP achieved more than 65% removal of COD, but due to a high concentration of other organic matter present in the low purity HRP, no reduction in COD was achieved with this enzyme source. A comparison was made between enzyme treatment and oxidation using Fenton's reagent. Enzyme cost must be significantly reduced in order to make the enzyme treatment process economically competitive.     

Oxidation of aromatic compounds by haemoglobin

Klibanov et al. have recently developed new methods for the elimination of phenols and aromatic amines. These involve two enzyme systems. Polyphenol oxidase with oxygen and horseradish peroxidase (HRP) with hydrogen peroxide, which permit the precipitation of these pollutants from wastewaters. Another study, using HRP, has shown that phenols at the low concentration usually found in drinking water, can be removed but with no apparent precipitate. However, these processes seem to be limited by the cost of the catalyst. In this work, the possibilities for oxidation of a phenolic compound such as methoxyphenol, by free or immobilized HRP, haemoglobin or blood haemolysate, in the presence of hydrogen peroxide, were investigated. Results indicate that haemoglobin can replace HRP with regard to its activity and cost. Removal of phenol was studied with free blood-haemolysate. More than 90% of this aromatic compound disappeared. Two conversion products were identified, 4,4′- and 2,2′-dihydroxybiphenyl, but not in sufficient quantity to account for all phenol removed.Nearly complete removal of benzidine and o-dianisidine, two carcinogenic aromatic amines often found in surface water, was obtained with immobilized blood haemolysate.Enzymatic oxidation by haemoglobin appear to be efficient and useful in the removal of micropollutants from drinking water.     

Degradation of phenol using tyrosinase immobilized on siliceous supports

The degradation of phenol by tyrosinase immobilized on chemically modified sodium aluminosilicate (NaA), calcium aluminosilicate (CaA), and silica gel was studied. Phenol conversion by immobilized tyrosinase ranged between approximately 15% and 60%, depending upon the initial phenol concentration, pH, and enzyme loading. Tyrosinase immobilized on CaA and on NaA could be re-used repeatedly without any decrease in performance. However, in studies at pH 8.0, significant enzyme inhibition was observed, since phenol conversion was rapid for approximately 20 min, then reached a plateau. The inhibition was reversible; activity was restored upon placing the immobilized enzyme in fresh substrate. Reducing the pH to 6.8 from 8.0 led to higher conversion of phenol, and decreased the inhibition of the immobilized enzyme.     

Degradation of 2,4,6-trinitrotoluene by immobilized horseradish peroxidase and electrogenerated peroxide

This paper presents horseradish peroxidase (HRP)-catalyzed removal of 2,4,6-trinitrotoluene (TNT) by an electrochemical packed-bed flow reactor operated in a circulating batch mode with the help of in situ generated hydrogen peroxide. HRP immobilized on the reticulated vitreous carbon electrode was prepared for the cyclic voltammetry of 2,4,6-TNT. Effects of pH and temperature on the TNT electroreduction in 0.2M phosphate buffer saturated with oxygen were examined. HRP immobilized carbon electrode was capable of catalyzing the oxidation and detoxification of 44 microM TNT in aqueous solution under optimized conditions. The removal rate of TNT for the electroenzymatic method was much greater than for electrochemical and biochemical methods. Stoichiometric and kinetic studies indicated that the hydrogen peroxide was utilized more effectively in the electroenzymatic method. Denitrification as intermediate reaction was also investigated.     

Multifunctional biomagnetic capsules for easy removal of phenol and bisphenol A

This paper reports fabrication, optimization and characterization of multifunctional biocapsules with immobilized enzyme using a layer-by-layer configuration and their application for removal of phenol and bisphenol A (BPA). The method is based on the combined use of enzymatic oxidation of the BPA and subsequent binding of the reaction product onto a chitosan core biopolymer. This platform has multiple functions including: (1) enzymatic degradation of BPA, (2) adsorption of the degraded compound within the core material, (3) colorimetric quantification and (4) magnetic capabilities. We examined various configurations of core/shell structures of alginate and chitosan and determined the stability and the optimum conditions in which these structures provide the most effective removal capacity. The amount of BPA that can be removed per capsule is 5.6 ppm while phenol can be removed up to 10 ppm per capsule within 15 h.     

Laccase-catalyzed removal of bisphenol-A from water: protective effect of PEG on enzyme activity

The feasibility of using the enzyme laccase to treat synthetic wastewater containing bisphenol-A (BPA) was examined. Optimization of pH, laccase concentration, polyethylene glycol (PEG) as an additive for >95% conversion and precipitation of BPA over 3 h of reaction period was determined through colorimetric assay and HPLC. PEG reduced enzyme inactivation, allowing a 5.2-fold reduction in the amount of laccase required for >95% removal of BPA in the range of 0.1-1 mM over 3 h. The fate of PEG after the reaction was also monitored. Linear relationships were found between the concentration of BPA (0.1-1 mM) and the optimum concentrations of laccase and PEG. Little PEG remained in the solution when up to 75 mg/L of PEG was used to treat 0.5 mM BPA. Beyond this level, PEG concentration increased linearly in the supernatant. It is inferred that an interaction between PEG and the polymeric products resulted in the protection of laccase.     

固定化酶酸化反应器/UASB处理黄浆废水的研究

针对现有两相厌氧反应器微生物易流失以及单方面延长酸化相的停留时间导致的过酸化影响后续甲烷化过程的现象，开发了一套新型两相厌氧处理系统，其酸化相是采用大孔树脂固定化酶作生物载体的水解酸化反应器，产甲烷相则是接种了经长期驯化培养的高温厌氧污泥的UASB。采用该装置处理玉米加工过程中产生的富含蛋白质废水（黄浆废水），考察了进水COD浓度和负荷、C／N值等因素对系统处理效能的影响。结果表明：该装置运行稳定，在低C／N值和低负荷条件下，酸化相的酸化率（VFA／COD）即可达30％以上，其出水pH值稳定在6．7～7．0；产甲烷相对COD的去除率为91．3％，进水C／N值对产甲烷相去除COD有明显影响。     

Removal of arsenic(III) from aqueous solutions using fresh and immobilized plant biomass

The ability of Garcinia cambogia, an indigenous plant found in many parts of India, to remove trivalent arsenic from solution was assessed. Batch experiments were carried out to characterize the As(III) removal capability of fresh and immobilized biomass of G. cambogia. It was found that the kinetic property and uptake capacity of fresh biomass were significantly enhanced by the immobilization procedure. The uptake of As(III) by fresh and immobilized biomass was not greatly affected by solution pH with optimal biosorption occurring at around pH 6--8. The presence of common ions such as Ca and Mg at concentrations up to 100mg/l had no effect on As(III) removal. However, the presence of Fe(III) at 100mg/l caused a noticeable drop in the extent of As(III) removal but the effect was minimal when Fe(III) was present at 10mg/l. The adsorption isotherms quantitatively predicted the extent of As(III) removal in groundwater samples collected from an arsenic-contaminated site in India. Immobilized biomass loaded with As(III) was amenable to efficient regeneration with NaOH solution. Column studies showed that immobilized biomass could be reused over five cycles of loading and elution. The excellent As(III) sequestering capability of fresh and immobilized G. cambogia biomass could lead to the development of a viable and cost-effective technology for arsenic removal in groundwater.     

Biodegradation of phenol by Synechocystis sp. in media including triacontanol hormone

Phenol removal levels of Synechocystis sp. were investigated in BG11 media with 10 mg/L triacontanol (TRIA) and without it to test whether the hormone could increase the removal efficiency by increasing biomass. The assays were performed to determine the effect of light on degradation, in media with 119.0–492.8 mg/L phenol under light and dark conditions. At increasing phenol concentrations, the degradation ranged between 98.5 and 100% regardless of a dark or a light condition. Experiments were carried out under light to determine the optimum pH for effective degradation. Optimum pH was found to be 6.5 at 200 mg/L phenol with or without TRIA. Phenol degradation was investigated in the 120.2–826.9 mg/L range. Although 377.4 mg/L phenol was completely degraded in hormone controls within 120 h, degradation was increased by TRIA, and the process was completed in 96 h. These data suggest that Synechocystis sp. has potential for use in the treatment of wastewaters containing phenol.     

Natural and synthetic hormone removal using the horseradish peroxidase enzyme: temperature and pH effects

The primary objective of our research was to establish the technical feasibility of using the horseradish peroxidase (HRP) enzyme for natural and synthetic estrogens-estrone (E1), 17beta-estradiol (E2), estriol (E3), and 17alpha-ethinylestradiol (EE2)-removal. The effects of temperature and pH on enzymatic treatment kinetics were investigated. Residual estrogen concentrations were quantified by liquid chromatography, coupled with mass spectrometry analysis. In a synthetic solution at pH 7 and 25+/-1 degrees C, the HRP enzyme-catalyzed process was capable of achieving 92-100% removal of E1, E2, E3, and EE2 within 1h of treatment with an HRP activity of 0.017 U/ml. The influence of the pH (5-9) and temperature (5-35 degrees C) on estrogen removal was observed to be significant, with the optimum pH near neutral conditions. The results also showed that wastewater constituents significantly impact the HRP-catalyzed estrogen removal. The experimental research proved that the HRP-catalyzed system is technically feasible for the removal of the main estrogens present in the environment at low concentrations.     

强化常规工艺对苯酚污染的应急处理技术研究

分析了苯酚去除技术的优缺点,在综合考虑水厂现有条件及可操作性的情况下,分别采用水厂常规工艺及相关强化技术在去除苯酚方面进行了对比试验研究.试验结果表明:常规工艺去除苯酚的能力有限,而同时增加粉末活性炭吸附和高锰酸钾复合药剂氧化,可大大增强常规工艺对苯酚的去除效果,苯酚去除率高达99.85%.当苯酚含量为0.068 3 mg/L时,投加30 mg/L粉末活性炭和4 mg/L高锰酸钾复合药剂,就可保证砂滤出水苯酚含量达标(<0.002 mg/L).     

高级氧化+SBR工艺处理聚乙二醇废水试验研究

研究了高级氧化+SBR组合工艺处理高浓度聚乙二醇(PEG)废水的效果及其影响因素。结果表明,采用芬顿试剂作为高级氧化剂,当FeSO4.7H2O投加量为800 mg/L,H2O2投加量为30 mL/L,反应时间为3.5 h时,CODCr去除率可达到50.5%;生化处理阶段所需采用两级SBR工艺,污泥浓度均为4 000 mg/L,一、二级厌氧及好氧反应时间分别为12和10 h;芬顿试剂氧化和厌氧处理对提高PEG废水的可生化性有明显效果;该组合工艺的出水水质可以达到《污水综合排放标准》(GB 8978—1996)中的二级排放标准。     

Heterotrophic activity compromises autotrophic nitrogen removal in membrane-aerated biofilms: results of a modeling study

A 1-d multi-population biofilm model was constructed to study the effect of heterotrophic activity on completely autotrophic ammonium (NH4+) removal in membrane-aerated (counter-diffusion) versus conventional biofilm systems (co-diffusion). Growth of heterotrophic bacteria (HB) was supported either solely by biomass decay products or by organic carbon (as chemical oxygen demand (COD)) in the influent. Three scenarios were considered: influence of HB growing on biomass decay products on steady-state performance (total nitrogen (TN) removal efficiency); influence of the influent COD/N ratio on steady-state performance (supplying COD in the influent); and impact of dynamic changes in the influent COD/N ratio on TN removal efficiency. The results revealed that the TN removal efficiency in the counter-diffusion biofilm was significantly different when HB were included in the simulations at NH4+ surface loads of LNH4>2.7 g - N m(-2) d(-1). Influent COD significantly altered the microbial community composition in the counter-diffusion biofilm and anaerobic NH4+ oxidation could not be sustained at COD/N>2. The co-diffusion system, however, was less affected and more than 50% of the TN removal originated from anaerobic NH4+ oxidation at those ratios. Perturbation experiments showed that step increases to influent COD/N ratios of 2 or higher over a period of 50 d or longer caused a loss of anaerobic NH4+ oxidation capacity which could not be regained within a reasonable time frame (>1000 d) in the counter-diffusion system. In contrast, simulating a 1-d sloughing event only caused a disturbance of 200 d although a maximum biofilm loss of 90-95% occurred. These results clearly indicate the importance of heterotrophic activity in autotrophic N removal biofilms, especially in counter-diffusion systems where they may compromise N removal capacity.     

固定化小球藻去除污水中氮、磷的试验研究

采用海藻酸钙对蛋白核小球藻进行固定,并用于去除污水中的氮磷。氮磷比试验结果表明,固定化小球藻对氮磷的去除受氮磷比的影响,氮磷比越小则对氨氮的去除率也就越高,但去除量与初始浓度有关;氮磷形态试验结果显示,固定化小球藻对不同形态氮的去除能力顺序为：氨氮〉简单有机氮〉硝酸盐氮〉亚硝酸盐氮,对不同形态磷的去除能力顺序为：正磷酸盐〉偏磷酸盐〉焦磷酸盐〉有机磷酸盐。     

太阳能固定膜光催化反应器降解苯酚中试

以结构简单、光能利用率高的复合抛物面采光板为采光元件,以采用溶胶凝胶法负载在比表面积大、化学性质稳定的玻璃纤维网上的高活性TiO2固定催化剂制备催化组件,并选用长寿命冷阴极低压汞灯作为人工辅助光源,研制成功结构简单、可全天候运行的太阳能光催化反应器.采用其处理低浓度苯酚配水的中试结果表明,该装置传质效果好,当循环流量＞5 L/min（Re=491）时即可消除传质限制作用;苯酚的降解呈表观一级反应,当光强介于12.4～25.9 W/m^2时,表观反应速率常数与光强呈线性关系;当采用电光源时,对苯酚的降解是光催化和直接光分解综合作用的结果.此外,该装置对自来水中的苯酚也具有较高去除效率,具有广阔的应用前景.     

A comparative study on treatment of wastewaters with various biodegradability and various pH values using single‐chamber microbial fuel cells

This work assessed the performance of a single‐chamber microbial fuel cell (MFC) with various substrates. Primary settled domestic wastewaters were used to simulate wastewaters of high biodegradability; while phenol‐based wastewaters and benzene‐based wastewaters were used to simulate wastewaters of low biodegradability. Experiments were performed at initial pH values of 6, 7 and 8. The maximum voltage production, power density and removal of substrate were obtained using primary settled domestic wastewater, whereas the lowest values were obtained using phenol‐based wastewater. The maximum chemical oxygen demand removal efficiency, phenol removal efficiency and benzene removal efficiency were 80.8, 63.3 and 77.8%, respectively. The performance of the MFC was enhanced by increasing the influent pH. The lowest coulombic efficiencies were obtained from phenol‐based wastewater and benzene‐based wastewater, which indicated that electrogenic bacteria were not the primary microorganisms responsible for the biodegradation of low biodegradable wastewater.     

Immobilization of rapeseed press-cake in an alginate matrix for the sorption of atrazine

Due to residual oil retained within it, rapeseed press-cake has been shown to be effective for the removal of atrazine from water through an absorption mechanism. However, it is difficult to put this into practice due to the hygroscopic nature of the press-cake resulting in considerable swelling, together with the formation of a thick paste which hinders phase separation. In order to overcome this, press-cake has been immobilized in an alginate matrix. The kinetics and sorption efficiency of this immobilized press-cake to absorb the model pesticide atrazine, has been studied. The results show that the rate of atrazine removal is slower than for free press-cake, although the total amount of atrazine removed is the same (K(pc/w)=0.25). Phase separation was greatly simplified. The alginate immobilized press-cake could be dried, in order to reduce volume and weight, with no adverse effect on atrazine removal kinetics or sorption properties.     

Photodegradation of phenol using TiO<Subscript>2</Subscript>, ZnO and TiO<Subscript>2</Subscript>/ZnO catalysts in an annular reactor

In recent years the incorporation of ZnO as a semiconductor into other catalysts, for enhancing photodegradation processes, has gained attention. This paper describes the synthesis of a blend of metal oxide (TiO₂/ZnO) photocatalyst and subsequent testing of the catalyst for the degradation of phenol in an annular photoreactor. The concentration of phenol before and after degradation was determined using Ultra-Violet-Spectroscopy (UV-Vis). Calcined TiO₂/ZnO composite material with a mass loading ratio of 1: 1 exhibited the highest percentage phenol removal compared to the unblended TiO₂ and ZnO systems at pH 7.2 and temperature of 25°C. It was shown that about 98% phenol degradation could be achieved at initial phenol concentration of 10; 20 and 50 ppm, except for 100 ppm which gave less than 50% degradation. Thus, TiO₂/ZnO blend as photocatalyst can be used for degradation of phenol in water. The pseudo-first order reaction kinetics fitted well the Langmuir-Hinshelwood model in almost all concentration ranges tested.     

砾间接触氧化/水平潜流人工湿地净化微污染河道水

以微污染河道水为处理对象,研究了砾间接触氧化/水平潜流人工湿地复合工艺对水质的净化效果。经过26 d改变进水配比、曝气方式等的调控运行,成功启动复合工艺模拟装置,砾间接触氧化区(简称砾石区)的COD、NH4⁺-N去除率均稳定在75%左右,TN去除率在45%~60%。为进一步强化净化效果,探讨了砾石区水力停留时间(HRT)和砾石曝气区与非曝气区(O/A)分段进水配比对砾石区及后置潜流人工湿地出水水质的影响。当砾石区HRT为5 h时,砾石区对污染物的去除效果较好,COD、NH4⁺-N、TN平均去除率分别可达72%左右、75.28%、67.79%,人工湿地对三者的去除率分别为31%、43%、28%;当O/A区分段进水配比为1∶1时,对COD、NH4⁺-N的平均去除率较高,分别为77.39%和84.91%,分段进水配比为1∶2时,对TN的去除率最高,达到68.5%,人工湿地对TN的去除率为24.47%。因此,砾石区HRT为5 h为较佳参数,分段进水配比可根据进水污染状况灵活选择,研究结果可为实际工程应用提供理论支撑。