污水处理厂苯系物暴露风险评价及控制对策

对污水处理厂6个处理单元逸散出的苯系物进行了采集和分析,研究了苯、甲苯和二甲苯在不同季节和不同处理单元的浓度变化规律,并对夏季逸散出的苯系物的致癌和非致癌风险进行了评价,提出了苯系物等挥发性物质的控制对策。结果表明:3种苯系物的气相浓度由高到底均为夏春秋冬。夏季初沉池散逸的苯、甲苯、二甲苯最多,气相浓度分别为83、99和172μg/m3。苯系物在春、秋和冬季的平均浓度为其夏季浓度的97.6%、94.0%和87.7%。苯系物对人体以致癌风险为主,长期工作在污水处理厂处理单元附近的工作人员存在轻微的致癌风险。通过减少污水紊流、优化污泥回流过程、采用合理的曝气方式、减少暴露年限和对处理单元加盖密封等方法可以从源头减少苯系物等挥发性物质的逸散。     

新疆石河子市污水处理厂BIOLAK工艺改造

新疆石河子市污水处理厂原BIOLAK工艺曝气采用表曝机,因冬季寒冷导致曝气池温度骤降,曝气池MLSS值难以达到设计要求,出水难以达标排放。结合旱寒区地理气候特点、运行经验,在保证充分利用现有构筑物的前提下提出增加水解池容积、改用BIOLAK专用曝气链、改造后稳定池等措施,改造后出水水质良好,达到《城镇污水处理厂污染物排放标准》(GB 18918—2002)的二级标准。     

一株苯系物降解真菌筛选及降解特性

采用逐量分批驯化的方法以污水处理厂污泥作为菌源,苯、甲苯、二甲苯为唯一碳源,驯化、分离、筛选能够有效降解苯系物的真菌,命名为B1。采用单因素以及正交实验方法并对真菌降解环境影响因素及降解效率进行了测定和研究。结果表明:真菌B1对苯系物降解的最佳条件为C∶N=5∶1,pH5,温度30℃,菌种接种量为5.5ml(50ml培养基)。采用GC对初始液相浓度0～90mg/L范围内的苯系物降解效果进行测定,未发现苯系物对真菌降解活性产生抑制作用。真菌对苯系物的降解效率为:甲苯>苯>二甲苯,最高降解效率分别达到87.39%,85.21%,81.47%。混合物降解效果略高于单一底物的降解效果。     

CASS工艺中PAC强化除磷试验研究

南方某污水处理厂采用CASS工艺,冬季时其出水总磷浓度不能满足《城镇污水处理厂污染物排放标准》(GB 18918—2002)的一级A标准。通过投加PAC和CFD(计算流体力学)模拟,对PAC强化除磷的效果及其对污泥活性的影响进行了研究。结果表明,在距曝气池末端约1/2处,于曝气停止前30 min投加4 mg/L的PAC能使出水TP浓度满足一级A标准要求;短期内连续投加4 mg/L的PAC对污泥活性有一定的抑制作用,但不会对出水指标产生不利影响。     

气质联用法测定工业废水中的五种挥发性有机化合物

建立了顶空气相色谱-质谱检测工业废水中三氯甲烷、四氯甲烷、三氯乙烯、四氯乙烯、三溴甲烷五种挥发性有机化合物残留量的方法,选择离子扫描模式(SIM)检测,方法的检出限为1.2μg/L,在10²00μg/L范围内呈现良好的线性关系,相关系数均为0.9992,在加标回收实验中,三氯甲烷、四氯甲烷、三氯乙烯、四氯乙烯、三溴甲烷的加标回收率分别为99.2%,100.1%,95.9%,99.1%,96.7%,该方法灵敏度高,分离效果良好,能有效地消除复杂基质带来的干扰,可以作为工业废水中三氯甲烷、四氯甲烷、三氯乙烯、四氯乙烯、三溴甲烷残留量的检测和确证方法。     

ABR/高负荷生物滤池污水处理工艺的设计及运行

对ABR/曝气/高负荷生物滤池污水处理工艺的设计和运行进行了分析。工程实践表明,该工艺具有污泥产量小、运行能耗低的特点,但冬季运行时出水效果不理想。将中间曝气池改为接触氧化池后,冬季出水水质可以达到《城镇污水处理厂污染物排放标准》(GB18918—2002)的二级标准,在其他季节出水水质可以达到一级B标准。     

A2/O和MBR组合工艺在寒冷地区污水处理中的应用

以内蒙古赤峰市喀喇沁旗锦山污水处理厂新建工程为例,探讨了A²/O+MBR组合工艺在寒冷地区的适用性以及设计经验。该工程近期处理规模为2×10⁴m³/d,采用三段回流式A²/O+MBR组合工艺。因冬季设计水温为9℃,故采用应对寒冷地区的保温设计,将所有建筑物和构筑物增加框架围护结构或彩钢板进行保温。实践结果表明,在冬季运行时,保持较高的污泥浓度(缺氧池污泥浓度控制在8 g/L左右)和适当提高曝气量(好氧池末端DO控制在4 mg/L以上),可使出水水质指标稳定达到并优于《城镇污水处理厂污染物排放标准》(GB 18918—2002)中的一级A标准。     

气相色谱法分析天然气中苯系物含量

苯系物(BTEX)通常包括苯、甲苯、乙苯和二甲苯等芳香族化合物,一般天然气中含有微量的苯系物。在天然气生产和加工环节,检测苯系物组分含量对预测天然气烃露点/烃含量具有重要意义。通过实验,建立了采用气相色法分析苯系物含量的方法,各苯系物定性重复性RSD_(7(定性))不超过0.01%;苯和甲苯定量重复性RSD_(7(定量))不超过2.5%,乙苯和二甲苯定量重复性RSD_(7(定量))为7%～11%;各组分最低检测限可达约2×10~(-10) g/s;对二甲苯和间二甲苯的分离度达到2.2。分析实际天然气样品,验证了该方法的可行性和适用性。获得的结论对准确检测天然气中苯系物含量提供了技术参考,为使用天然气组成数据准确预测烃露点/烃含量提供了可靠的完整数据,计算获得的烃露点/烃含量对天然气处理厂脱烃装置工艺设计和输气管道的安全运行提供数据支持。     

青冈污水处理厂CASS工艺的设计与运行

青冈污水处理厂近期处理规模为1.3×104m3/d,冬季水温12℃。污水厂二级生化处理采用CASS工艺,运行方式灵活,能够较好地适应青冈地区的冬季低温环境。该工艺可保证冬季低温条件下生产运行的稳定,确保出水达到《城镇污水处理厂污染物排放标准》(GB 18918—2002)中的一级B标准。详细介绍了该工程的工艺流程、设计参数和技术特点。     

萧山城市污水处理厂脱氮除磷升级改造实践

萧山城市污水处理厂利用原有处理设施进行提标改造,采用A/A/O工艺,包括新建曝气池和曝气沉砂池,使整个处理流程具备了脱氮除磷功能,出水水质达到《城镇污水处理厂污染物排放标准》(GB18918—2002)的一级B标准。介绍了改造工程的处理工艺、改造措施及运行情况,可为一些传统污水处理厂升级改造提供参考。     

Chlorinated organics from chlorine used in water treatment

The contribution from impurities in chlorine to levels of chlorinated organics found in potable water after chlorination was investigated. Techniques for sampling of chlorine and gas chromatography (GC) determination of chlorinated organics in chlorine are described. The detection limits were better than 1 ppm for each of chloromethane, dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, hexachloroethane, hexachloropropane and hexachlorobenzene in chlorine. With the exception of chloroform which occasionally accounted for nearly 1 μg l⁻¹ in water, the levels of the nine compounds in chlorine accounted for less than 0.1 μg l⁻¹ of each compound in chlorinated water from 10 Canadian treatment plants. The occurrence of these nine and 28 additional chlorinated organics previously detected in water supplies was determined by aid of liquid-liquid extraction of water samples. Seven compounds, including chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethylene were detected, usually at levels ranging from 0.1 to 1 μg l⁻¹ in chlorinated water from the treatment plant.     

Volatile and semi-volatile organochlorine compounds in tap and riverine waters in the area of influence of a chlorinated organic solvent factory

The study of volatile and semi-volatile organochlorinated compounds, VOC and SVOC, respectively, in the river and tap water of an area under the influence of a chlorinated organic solvent factory has shown that the industrial activities are reflected in the composition of the river waters, namely by the presence of chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, penta and hexachlorobenzene and octachlorostyrene as major pollutants, but that the tap waters are free from products which can be related to this origin. However, the potable water contains significant concentrations of species derived from chlorination, namely chloroform, bromodichloromethane, dibromochloromethane and bromoform, as well as pesticides of wide use in agriculture, α- and γ-hexachlorocyclohexane. The VOC and SVOC compositions in these tap waters are very similar to that found in the waters of Barcelona, a reference urban area which is not under the influence of large organochlorine solvent factories.     

A study of the concentrations of selected organic vapors in the ambient atmosphere of suburban and rural New Jersey locations

Data were collected on a selected group of volatile organic compounds including aromatic, chlorinated aromatic, and halogenated one‐ and two‐carbon compounds at three sites in the state of New Jersey. Sampling took place at South Amboy, Rutherford and Batsto Village during 1979 and continued in 1980 at the latter two sites. Studies were also carried out on the correlation of the concentration data obtained with wind direction during sampling.

The most frequently detected pollutants include the aromatic compounds, benzene, toluene, xylenes and chlorobenzene, as well as trichloroethylene and tetrachloroethylene. Concentration levels found were usually in the low part‐per‐billion range for Rutherford and South Amboy, with levels in Batsto averaging at least a factor of three lower. Correlation of wind direction with average concentration shows no significant trends for Rutherford or Batsto, but does indicate a general effect of industrial area pollution on South Amboy.     

Treatment of VOCs in high strength wastes using an anaerobic expanded-bed GAC reactor

The potential of the expanded-bed granular activated carbon (GAC) anaerobic reactor in treating a high strength waste containing RCRA volatile organic compounds (VOCs) was studied. A total of six VOCs, methylene chloride, chlorobenzene, carbon tetrachloride, chloroform, toluene and tetrachloroethylene, were fed to the reactor in a high strength matrix of background solvents. Performance was evaluated. The reactor was found to effect excellent removal of all VOCs (97%). Chloroform, while itself removed at levels in excess of 97%, was found to inhibit the degradation of acetate and acetone, two of the background solvents. Without any source of chloroform in the feed, excellent COD removals were obtained in addition to near-complete removal of all the VOCs.     

Enumeration of aromatic oxygenase genes to evaluate monitored natural attenuation at gasoline-contaminated sites

Monitoring groundwater benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations is the typical method to assess monitored natural attenuation (MNA) and bioremediation as corrective actions at gasoline-contaminated sites. Conclusive demonstration of bioremediation, however, relies on converging lines of chemical and biological evidence to support a decision. In this study, real-time PCR quantification of aromatic oxygenase genes was used to evaluate the feasibility of MNA at two gasoline-impacted sites. Phenol hydroxylase (PHE), ring-hydroxylating toluene monooxygenase (RMO), naphthalene dioxygenase (NAH), toluene monooxygenase (TOL), toluene dioxygenase (TOD), and biphenyl dioxygenase (BPH4) genes were routinely detected in BTEX-impacted wells. Aromatic oxygenase genes were not detected in sentinel wells outside the plume indicating that elevated levels of oxygenase genes corresponded to petroleum hydrocarbon contamination. Total aromatic oxygenase gene copy numbers detected in impacted wells were on the order of 10(6)-10(9)copies L(-1). PHE, RMO, NAH, TOD, and BPH4 gene copies positively correlated to total BTEX concentration. Mann-Kendall analysis of benzene concentrations was used to evaluate the status of the dissolved BTEX plume. The combination of trend analysis of contaminant concentrations with quantification of aromatic oxygenase genes was used to assess the feasibility of MNA as corrective measures at both sites.     

Effect of ethanol on BTEX biodegradation kinetics: aerobic continuous culture experiments

The use of ethanol as an automotive fuel oxygenate represents potential economic and air-quality benefits. However, little is known about how ethanol may affect the natural attenuation of petroleum product releases. Chemostat experiments were conducted with four pure cultures (representing archetypes of the known aerobic toluene degradation pathways) to determine how ethanol affects benzene, toluene, ethylbenzene, and xylene (BTEX) biodegradation kinetics. In all cases, the presence of ethanol decreased the metabolic flux of toluene (measured as the rate of toluene degradation per cell). This negative effect was counteracted by an ethanol-supported increase in biomass, which is conducive to faster degradation rates. When the influent total organic carbon (TOC) of the toluene-ethanol mixture was kept constant, the metabolic flux of toluene was proportional to its relative contribution to the influent TOC. This empirical relationship was used to derive a mathematical model that simulated effluent benzene concentrations as a function of the influent mixed-substrate composition, the dilution rate, and Monod kinetic coefficients. Under carbon-limiting conditions (1 mg/L influent benzene), the data and model simulations showed an increase in benzene removal efficiency when ethanol was fed at low concentrations (ca. 1 mg/L) because its positive effect on cell growth outweighed its negative effect on the metabolic flux of benzene. High ethanol concentrations, however, had a negative effect, causing oxygen limitation and increasing effluent benzene concentrations to higher levels than when benzene was fed alone. The slower BTEX degradation rates expected at sites with high ethanol concentrations (e.g., at gasohol-contaminated sites) could result in longer BTEX plumes and a greater risk of exposure.     

Adsorption of chlorinated organic compounds on activated carbon from water

The adsorption capacities and rates of seven principal chlorinated organic compounds for six commercial GACs were investigated. All the adsorption isotherms were expressed by the Freundlich equation, and the isotherms for the chloroethylenes such as trans - 1,2-dichloroethylene, trichloroethylene and tetrachloroethylene could be shown by the modified Freundlich equation Q′ = k′ (C/C_s)^l/n for each GAC. The magnitude of adsorption of the chlorinated organic compounds was in the order of: tetrachloroethylene > trichloroethylene > trans - 1,2-dichloroethylene > 1,1-dichloroethane > carbontetrachloride > 1.1,1-trichloroethane > chloroform. The value of k for a certain GAC could be predicted from the quantity of pores smaller than 2 nm in diameter. The adsorbed amounts were decreased by 10–20% when humic substances coexisted. The working periods of a fixed bed adsorber before regeneration were predicted by calculating breakthrough curves for various influent concentrations of trichloroethylene and tetrachloroethylene at the space velocities of 5 or 10 h⁻¹, and it was certified that the adsorption method by GAC was feasible for removing these compounds from water.     

Organic air pollutants inside and outside residences in Shimizu, Japan: levels, sources and risks

Concentrations of 38 organic air pollutants including aromatic hydrocarbons (AHCs), carbonyl compounds (CCs), volatile organic halogenated compounds (VOHCs), and organophosphorus compounds (OPCs) were measured in indoor and outdoor air in an industrial city, Shimizu, Shizuoka Prefecture, Japan. Levels of pollutants tended to be higher indoors than outdoors in both summer and winter except for benzene, carbon tetrachloride, trichloroethylene, tetrachloroethylene, and dichlorvos (DDVP). This trend was especially pronounced for CCs such as formaldehyde and acetaldehyde. For the organic air pollutants, the concentrations of AHCs and VOHCs substantially increased in winter, but not those of CCs and OPCs; the trends were similar for both indoors and outdoors. We investigated possible indoor sources of pollutants statistically. Multiple regression analysis of corresponding indoor and outdoor concentrations and the responses to our questionnaire showed that indoor concentrations of certain AHCs were significantly affected by their outdoor concentrations and cigarette smoking. For formaldehyde, indoor concentrations were significantly affected by house age and the presence of carpet or pets. For p-dichlorobenzene (pDCB), the concentrations in bedroom trended to be higher than those in other indoors and outdoors, suggested that mothballs for clothes present in bedrooms are the principal indoor source of pDCB. We compared indoor and outdoor pollutant concentrations to acceptable risk limits for 11 organic air pollutants. In indoors without smoking samples, the geometric mean concentrations of benzene, formaldehyde, acetaldehyde, carbon tetrachloride, pDCB, and DDVP exceeded the equivalent concentration representing the upper bound of one-in-one-hundred-thousand (1x10(-5)) excess risk over a lifetime of exposure.     

Investigation of BTEX removal efficiency using the electrolytic oxidation and Fenton’s reaction

The removal of benzene, toluene, ethyl benzene, and xylene (BTEX) using the electrolytic oxidation or Fenton’s reaction has been studied. The value of current and pH value were shown to produce a significant effect on electrolytic oxidation of BTEX. More than 95% of BTEX could be removed at 500 mA current within 8 hours. In the case of Fenton’s reaction it was established that more than 95% of BTEX could be removed at pH 4 with an addition of hydrogen peroxide in the amount of 12 mg/dm³. The treatment cost based on electrolytic oxidation amounted to between $0.04 and $5.1 USD/m³. For Fenton’s reaction, the treatment cost was between $0.16 and $0.65/m³. The costs of electrolytic oxidation and Fenton’s reaction were similar to the cost of electrodialysis and cheaper than the freeze–thaw and evaporation; however, these costs were higher than for air flotation and the use of anoxic/aerobic granular activated carbon.