Performance of a sub-surface flow constructed wetland in polishing pre-treated wastewater-a tropical case study

This paper reports on the performance of three units of a sub-surface horizontal flow constructed wetland (CW) pilot plant in polishing effluent from the upflow anaerobic sludge blanket (UASB) reactor plant. Studies on the use of UASB for on-site wastewater pre-treatment were initiated in Tanzania for the first time in 1993, while initial research works on the application of CW for polishing effluent from UASB, the results of which are reported in this paper began in 1999. In this study the UASB reactor plant received and pre-treated part of the wastewater from the student's hostels at the University College of Lands and Architectural Studies in Tanzania. Out of the three units, unit B was planted with Phragmites mauritianus, unit C with Typha latifolia and A was used as a control. Both P.mauritianus and T.latifolia have been extensively researched in Europe and USA as suitable species of vegetation in CW. However, very limited studies on the suitability of these wetland plants have been reported under tropical climate. The studied parameters were chemical oxygen demand (COD), nitrate (NO(3)-N), nitrite (NO(2)-N), ammonium (NH(4)-N), faecal coliforms (FC), total coliforms (TC), pH, temperature and dissolved oxygen (DO). The study was carried out at an average hydraulic retention time of 1.93 days (1.85 in unit A, 1.96 in unit B and 1.99 in unit C) obtained as a ratio of the volume of wastewater in the wetland and the volumetric flow rate of wastewater through the wetland unit while taking into consideration the porosity of the media. Better performance for the vegetated units B and C were obtained compared to the control unit A. Nutrients were least removed in all units (NH(4)-N 11.2%, 25.2% and 23% in units A, B and C, respectively, NO(3)-N 32.2%, 40.3% and 44.3% for units A, B and C, respectively, and NO(2)-N 23.9%, 38.5% and 23.1% for units A, B and C, respectively). The COD removal rate was 33.6%, 56.3% and 60.7% for units A, B and C, respectively. The study also indicated that pH increased from the influent to the effluent and that DO increase was related to the decrease of temperature. FC and TC removal ranged from 43% to 72%, with the least removal in unit A.     

The quest for safe drinking water: an example from Guinea-Bissau (West Africa)

While humans require water for life, one-sixth of our species lives without access to safe water. In Africa, the situation is particularly acute because of global warming, the progression of the Sahara desert, civil unrest and poor governance, population growth, migration and poverty. In rural areas, the lack of adequate safe water and sanitary infrastructures leaves millions with doubtful water quality, increasing the harshness of daily life. In this paper, a pilot study was conducted during the wet season on Bolama Island (Guinea-Bissau, West Africa), a UNESCO Man and the Biosphere Reserve. Twenty-eight shallow wells, supplying water to most of the population, were sampled for microbiological, physical and chemical water quality characteristics. A ten-parameter water quality index (WQI) adapted to tropical conditions was applied to compare the different wells. About 79% of the wells showed moderate to heavy fecal contamination. From the surveyed parameters, it was found that chemical contamination was less important, although all samples were acidic, with the pH averaging 5.12+/-0.08. The WQI was 43+/-4% (0%-worst; 100%-best quality), showing that the water from the majority of wells was polluted but should be suitable for domestic use after appropriate treatment. At the onset of the wet season, diarrhea represented 11.5% of all medical cases, 92.5% of which were children aged <15. This paper suggests inexpensive steps to reduce the fecal contamination and control the pH in order to increase the potability of the well water and, concomitantly, to raise the living standards of the population in one of the poorest countries of the world.     

Occurrence, molecular characterization and antibiogram of water quality indicator bacteria in river water serving a water treatment plant

Water pollution by microorganisms of fecal origin is a current world-wide public health concern. Total coliforms, fecal coliforms (Escherichia coli) and enterococci are indicators commonly used to assess the microbiological safety of water resources. In this study, influent water samples and treated water were collected seasonally from a water treatment plant and two major water wells in a Black Belt county of Alabama and evaluated for water quality indicator bacteria. Influent river water samples serving the treatment plant were positive for total coliforms, fecal coliforms (E. coli), and enterococci. The highest number of total coliform most probable number (MPN) was observed in the winter (847.5 MPN/100 mL) and the lowest number in the summer (385.6 MPN/100 mL). Similarly E. coli MPN was substantially higher in the winter (62.25 MPN/100 mL). Seasonal variation of E. coli MPN in influent river water samples was strongly correlated with color (R² = 0.998) and turbidity (R² = 0.992). Neither E. coli nor other coliform type bacteria were detected in effluent potable water from the treatment plant. The MPN of enterococci was the highest in the fall and the lowest in the winter. Approximately 99.7 and 51.5 enterococci MPN/100 mL were recorded in fall and winter seasons respectively. One-way ANOVA tests revealed significant differences in seasonal variation of total coliforms (P < 0.05), fecal coliforms (P < 0.01) and enterococci (P < 0.01). Treated effluent river water samples and well water samples revealed no enterococci contamination. Representative coliform bacteria selected by differential screening on Coliscan Easygel were identified by 16S ribosomal RNA gene sequence analysis. E. coli isolates were sensitive to gentamicin, trimethoprim/sulfamethazole, ciprofloxacin, vancomycin, tetracycline, ampicillin, cefixime, and nitrofurantoin. Nonetheless, isolate BO-54 displayed decreased sensitivity compared to other E. coli isolates. Antibiotic sensitivity pattern can be employed in microbial source tracking.     

Faecal-Indicator Budgets for Recreational Coastal Waters: A Catchment Approach

This paper explores the application of a catchment faecal-indicator budget approach to the examination of faecal-indicator sources impacting on coastal recreational water quality. This involves (i) the characterization of water quality in sewage effluent and riverine inputs, and (ii) measurement and estimation of input flows; the product of these components yields the input flux of indicator organisms from each source. The impact of sewage-treatment scenarios on budgets is also investigated.     

Simultaneous effects of environmental factors on motile Aeromonas dynamics in an urban effluent and in the natural seawater

Seasonal dynamics of motile Aeromonas in a treated urban effluent and in natural seawater along the Sfax coast (Mediterranean sea, Tunisia) were measured over a year concurrently with seven environmental factors, and compared with those of faecal coliforms. Counts for Aeromonas from a standard plate count method, ranged from 1.48 x 10(5)CFU.100 ml(-1) to 2.2 x 10(8)CFU.100 ml(-1) in the effluent and from 7.9 x 10(3)CFU.100 ml(-1) to undetectable level in the surface marine waters. Contrary to faecal coliforms, the Aeromonas dynamics exhibited a seasonal distribution in seawater which was inverse of the seasonal distribution in the sewage: From the end of November 1998 to April 1999 (cold period), Aeromonas counts increased in the treated effluent, while it decreased very rapidly in seawater. From May to October (warm period), Aeromonas abundance decreased in the effluent but showed an increasing fluctuating trend in the marine waters with a maximum in late summer/early autumn when the temperatures were around 22-23 degrees C. Multiple correlation and regression analyses suggest, by the coefficient of determination (R(2)), that 42% of variance in Aeromonas number changes in the treated effluent, may be explained by only turbidity, radiation and Aeromonas density in the previous sample, while 37% of variance in marine ecosystem were explained by radiance and conductivity. Furthermore, the t statistics and their p values and the coefficient of partial determination (r(2)) indicated that radiance contributed the most (r(2)=0.3184, t=-3.2, p=0.0041) to the dynamics of motile Aeromonas in seawater, when combined with conductivity.The models relevant for changes in faecal coliforms abundance incorporated turbidity, radiance in the effluent and conductivity, pH, radiance, turbidity in coastal marine environment. These models explain 66% and 73% of the observed cell number fluctuation, with turbidity (r(2)=0.529, t=5.08, p=0.0001) and conductivity (r(2)=0.5407, t=4.97, p=0.0001) as dominant factors in the multivariate model proposed, respectively, for the two sampling sites. The results presented here suggest that the combination of negative effects of sunlight and conductivity in natural seawater mainly affects the colony-forming capacity and make the motile Aeromonas nonrecoverable during cold months.     

Cost and effluent quality controllers design based on the relative gain array for a nutrient removal WWTP

The main objective of this work was the design of different effluent quality controllers and a cost controller for WWTPs. This study was based on the relative gain array (RGA) analysis applied to an anaerobic/anoxic/aerobic (A²/O) configuration of a simulated WWTP, with combined removal of organic matter, nitrogen and phosphorus. The RGA analysis was able to point out the best pairing amongst the input and the output control variables of the plant to design low order and decentralized effluent quality controllers, such as proportional-integral controllers for each variable of interest (ammonium, nitrate and phosphate). In a second step, a cost controller to automatically search for the most economic setpoints of the effluent quality controllers was implemented based on the best decentralized control structure tested. The simulated plant was operated under different control modes that chronologically represent control configurations becoming gradually more complex: (i) in open loop; (ii) with dissolved oxygen (DO) control in the last aerobic reactor only; (iii) with the effluent quality controllers active; (iv) with the effluent quality controllers active and automatically receiving the setpoints from a cost controller. The effluent quality controllers alone and the cost control together with effluent quality controllers could save up to 42,000 Euros/year and 225,000 Euros/year, respectively, when compared to the operating costs of the plant operating with DO control (a reduction of 2.5% and 13% of the operating costs, respectively). The cost controller proved to be a good tool for automating the search of the most profitable setpoints of the effluent quality controllers for a given cost setpoint.     

Effect of pre- and post-UV disinfection conditions on photoreactivation of fecal coliforms in wastewater effluents

Photoreactivation of microorganisms following UV disinfection can represent a disadvantage to using UV technology for wastewater treatment since recovery may, in some cases, reach several logs. Thus, decreasing photoreactivation can lead to considerable savings in capital and operating costs. Objectives of this study were to determine pre- and post-UV irradiation conditions which could decrease fecal coliform (FC) photoreactivation in wastewater effluents. Results indicated that delaying exposure to photoreactivating light for 3 h suppressed photoreactivation after relatively low UV doses of 10 and 20 mJ/cm². Moreover, at least 440 lux (0.065 mW/cm²) of visible light was needed to initiate photoreactivation. Additionally, photoreactivation decreased significantly when samples were exposed to visible light simultaneously or prior to UV irradiation. This was more significantly observed for winter samples, where photoreactivation decreased by nearly 50%. Finally, summer FC populations were more sensitive to inactivation and less able to photoreactivate than winter populations. The effect of visible light on photoreactivation levels may be explained by several photo-mechanisms of FC photolyase, such as photodecomposition of the MTHF co-factor and reduction of FAD.     

混凝沉淀/兼氧/CASS工艺处理抗生素生产废水

采用混凝沉淀／兼氧／CASS工艺处理抗生素生产废水,经过6个多月的试运行,出水水质稳定达标,混凝沉淀、兼氧、CASS处理单元对COD的平均去除率分别大于47％、61％、92％,吨水投资为5500元,运行费用为1．75元／m^3。工程验收监测结果表明,系统出水水质达到《污水综合排放标准》（GB8978-1996）的一级标准,COD去除率为97．8％,SS去除率为97．1％,氨氮去除率为99．6％。     

MIBR/纳滤组合工艺用于再生水回用工程

以生活污水为对象,采用膜固定化微生物反应器（MIBR）／纳滤组合工艺进行再生水回用处理,出水水质达到《生活饮用水卫生标准》（GB5749-2006）中“农村小型集中式供水和分散式供水部分水质指标及限制”标准。该组合工艺流程简单、投资省、出水水质好、自动化程度高,为严重缺水地区（尤其是铁路沿线站点）解决洗衣、洗浴等用水提供了新思路。     

水解酸化/好氧/混凝气浮工艺处理染整废水

为扩大生产规模和提高出水水质,某染整厂对原处理工艺进行了改造,采用水解酸化/好氧/混凝气浮组合工艺处理染整废水.实践结果表明,对SS、BOD5、COD、色度的总去除率分别达到63.6%、93.4%、92.3%、92.9%,出水水质全部达到〈纺织染整工业水污染物排放标准〉（GB 4287-92）的一级标准.     

Combined permeable pavement and photocatalytic titanium dioxide oxidation system for urban run‐off treatment and disinfection

Permeable pavement systems (PPS) are frequently associated with high removal efficiencies for water quality parameters. Their effluent can, therefore, be recycled, for example, for sprinkling onto gardens. Nevertheless, some stakeholders fear that potentially pathogenic organisms within the treated run‐off could be too high, and therefore they request disinfection before recycling. The aim of this paper is, therefore, to assess the efficiency of a batch flow combined titanium dioxide (TiO₂) and ultraviolet (UV) light photocatalytic reactor in removing water‐borne microbial contaminants from the effluent of PPS. Combined TiO₂ and UV photocatalytic reaction times between 80 and 100 min were required for the complete removal of Escherichia coli, total coliforms and faecal Streptococci, which had mean initial counts of 1.5 × 10⁷, 4.4 × 10⁶ and 6.9 × 10⁵ colony‐forming units (CFU) per 100 mL, respectively. In comparison, UV disinfection alone resulted in insignificant microbial removal. Suspended TiO₂ powder was more effective than small immobilised TiO₂ crystals.     

含炭高密度沉淀池/超滤工艺处理污水厂二级出水

采用含炭高密度沉淀池/超滤组合工艺处理污水厂二级出水,考察了其对常规指标和微量有机污染物的去除效能,并对膜污染特性进行了分析。结果表明,组合工艺对浊度的去除率高达99.9%,出水浊度在0.01 NTU左右;对DOC、UV(254)、TP、氨氮和TN的平均去除率分别为41.02%、49.82%、60.44%、23.34%和10.90%;三维荧光光谱分析表明,组合工艺能有效去除水中的腐殖质和蛋白质类有机物;通过LC-MS/MS检测水中微量有机污染物发现,组合工艺可以使水中的微量有机污染物含量下降66%以上;同时含炭高密度沉淀池预处理能有效减轻膜污染,使跨膜压差增长速度减缓。     

SEASONAL VARIATION OF BACTERIOLOGICAL AND CHEMICAL QUALITY OF DRINKING WATER: A CASE STUDY IN A PALESTINIAN DISTRICT

Evaluation of drinking water quality for Jenln district in Palestine was carried out for the years 1997, 1998, and 1999, respectively. Only 53.1 %, 85.4% and 69.6% of the drinking water samples tested for free chlorine residual, total coliforms and faecal coliforms, respectively are within the limits of the Palestinian and International standards. The seasonal variation of bacteriological and chemical quality of drinking water was investigated. It was found out that the summer season has the best quality and the winter has the worst. There remains some ignorance in testing the drinking water in the villages and towns in Jenin district. Huge efforts are required to improve the drinking water quality in Jenin district, as well as other Palestinian districts, through public awareness, training of governmental Inspectors, in addition to a strict monitoring system for water quality.     

稳定塘工艺深度处理污水厂二级出水的研究

采用CAST/稳定塘组合工艺以实现城镇污水处理的功能提升。分析了该组合工艺在冬、夏两季最大处理水量时的运行效果,结果表明:稳定塘系统可有效去除二级处理出水中的氮、磷和悬浮物,冬季(HRT=6.4 d)对TN、氨氮、TP、COD和SS的去除率分别为40%、70%、55%、50%、70%,夏季(HRT=5.4 d)对上述指标的去除率分别为56%、97%、76%、55%、68%,处理效果优于冬季。两种工况下稳定塘系统的出水水质均可达到《城镇污水处理厂污染物排放标准》(GB18918—2002)的一级A标准,可有效降低受纳水体的营养负荷。第一和第二单元去除了原水中大部分的污染物,其净化机理以微生物分解和物理化学作用为主,二者对去除污染物的总贡献率>70%;第三单元进水中的污染物浓度已经很低,主要作为系统出水水质的屏障。因此,CAST/稳定塘组合工艺用于提升城镇污水处理功能是可行的。     

沸石生物滤池/混凝沉淀/超滤工艺处理微污染源水

微污染源水中的污染物以有机物和氨氮为主,采用传统工艺处理时其出水水质难以达到《生活饮用水卫生标准》(GB 5749—2006)的要求。将沸石作为生物滤池的填料,与混凝沉淀、超滤组合后用于处理微污染地表水,考察了其对污染物的去除效果。结果表明:该组合工艺对氨氮有较好的去除效果,出水氨氮在0.5 mg/L以下,去除率可达90%;对有机物也有较好的去除效果,出水CODMn在2 mg/L左右,去除率约为60%,出水水质达到了《生活饮用水卫生标准》(GB 5749—2006)的要求。该工艺对氨氮的去除主要由沸石生物滤池完成,而沸石生物滤池、混凝沉淀及超滤均能去除CODMn,贡献率分别为49.6%、30.9%、19.5%。     

Influence of inter-annual variations in climatic factors on fecal coliform levels in Mississippi Sound

Information on the effects of inter-annual variations in climatic factors on fecal coliform levels in coastal waters is scarce. We used 11 years (1990–2001) of rainfall, water temperature, Pearl River stage and salinity data to assess the effects of the 1991–1992 and 1997–1998 El Niño events on fecal coliform levels in Mississippi Sound. El Niño-Southern Oscillation had major effects on Pearl River stage and water quality in the Sound. The geometric mean fecal coliform number differed among years (P=0.0001), being highest during 1991–1992 El Niño years (14.22 MPN per 100 ml) and lowest during 1999–2000 La Niña years (<1.8 MPN per 100 ml). Mean salinity varied among years (P=0.0001) from 9 ppt (1991–1992) to 21 ppt (1999–2000). Mean water temperature was lowest in 1997–1998 (14.5 °C) and highest in 1998–2000 (19.4 °C). Pearl River stage differed among years (P=0.0001), ranging from 1.96 m (1999–2000) to 3.57 m (1997–1998). Inverse relationships were observed between fecal coliform levels and salinity (r²=0.74; P=0.001) and water temperature (r²=0.69; P=0.001), whereas positive relationships were obtained with total rainfall (r²=0.52; P=0.013) and Pearl River stage (r²=0.90; P=0.0001). These relationships are useful for evaluating the potential effects of climate change on water quality and classification of shellfish growing waters in order to protect humans from consuming contaminated shellfish in shallow river-influenced estuaries.     

磷回收提高生物除磷效果的验证

在前期的模拟试验中曾预测，磷回收介入生物营养去除（BNR）工艺，不仅有利于提高生物除磷效果，而且可以降低生物除磷所需的进水COD／P值。为了证实这一预测，以传统A^2／O工艺作为主要流程进行试验。结果表明，当侧流比达到20％时，满足排放标准（TP〈1mg／L）的最低COD／P值从原来的35降低到25，此时对磷的有效回收率为34％。这意味着，在生物除磷过程中可节约25％～30％的碳源。     

EGSB的后续处理工艺选择

考察了与厌氧污泥膨胀床（EGSB）串联的厌氧生物滤池、好氧生物滤池和活性污泥法等3种工艺的除污性能。结果表明，厌氧生物滤池出水COD浓度较高，好氧生物滤池出水水质不够稳定，而采用活性污泥法作为EGSB的后续工艺，则出水水质良好且运行稳定。     

ABR-BAF工艺处理采油废水的中试研究

进行了利用折流板厌氧反应器（ABR）-曝气生物滤池（BAF）工艺处理江汉油田马-25污水处理站采油废水的中试研究，主要考察了ABR的除油效果、提高废水可生化性的作用以及BAF的运行参数、处理效果等。研究结果表明：当废水流量为0．3m^3／h时，ABR反应器对油的去除率平均为83．5％，对COD的去除率平均为40．8％，出水BOD，／COD值提高了24．8％。ABR一方面去除了采油废水中的大部分油，另一方面提高了采油废水的可生化性。当BAF的水力负荷为0．6m／h、进水COD平均为203．5mg／L时，出水COD平均为85．7mg／L，平均去除率为57．9％；对SS的去除率为82．7％。组合工艺对油、COD、BOD，和SS的总去除率分别为96．1％-96．9％、58．2％～75．1％、80．0％-93．1％和80．7％～87．1％。扫描电镜（SEM）观察结果显示：生物膜结构紧密，并且观察到裂口虫，生物相非常丰富。ABR-BAF工艺能够很好地处理采油废水，出水水质满足污水二级排放标准。     

混凝/化学氧化/曝气生物滤池深度处理垃圾渗滤液

随着垃圾渗滤液的老龄化,常规的生化处理已经不能使出水达标排放,需要进行深度处理。采用混凝／化学氧化／曝气生物滤池联合工艺深度处理垃圾渗滤液,进水COD为700mg／L左右,出水COD〈100mg／L,去除率〉85％,排放口水质达到《生活垃圾填埋污染控制标准》（GB16889--1997）一级标准。