Occurrence and fate of heavy metals in the wastewater treatment process

The occurrence and the fate of heavy metals (Cd, Pb, Mn, Cu, Zn, Fe and Ni) during the wastewater treatment process were investigated in the wastewater treatment plant (WTP) of the city of Thessaloniki, northern Greece, operating in the activated sludge mode. For this purpose, wastewater and sludge samples were collected from six different points of the plant, namely, the influent (raw wastewater, RW), the effluent of the primary sedimentation tank (primary sedimentation effluent, PSE), the effluent of the secondary sedimentation tank (secondary sedimentation effluent, SSE), sludge from the primary sedimentation tank (primary sludge, PS), activated sludge from the recirculation stream (activated sludge, AS), and the digested/dewatered sludge (final sludge, FS).

The distribution of metals between the aqueous and the solid phase of wastewater was investigated. Good exponential correlation was found between the metal partition coefficient, logK_p, and the suspended solids concentration. The mass balance of heavy metals in the primary, secondary and the whole treatment process showed good closures for all metal species. The relative distribution of individual heavy metals in the treated effluent and the sludge streams indicated that Mn and Cu are primarily (>70%) accumulated in the sludge, while 47–63% of Cd, Cr, Pb, Fe, Ni and Zn remain in the treated effluent.     

洗车废水处理技术现状与展望

洗车废水中含有泥砂、油乳化液、有机物及洗涤剂类污染物质。在分析中 ,对洗车废水的水质进行了分类 ,并针对不同的水质 ,对国内的大型洗车场的处理工艺和小型洗车行的洗车废水回用工艺进行了介绍和分析 ,对国外采用膜工艺处理洗车废水的相关研究也进行了简要的介绍 ,同时提出了洗车废水的污泥处理问题。从社会、经济效益来看 ,洗车废水回用是必然趋势。现行的洗车废水回用处理工艺回用率低、处理效果不理想 ,采用高效、简单、实用、经济的原则进行设计 ,满足社会对洗车水回用的需求是未来洗车废水处理技术发展的要求     

洗浴废水循环再利用技术的探讨和分析

在我国 ,洗浴废水达到城市生活污水量的 30 %。本文针对目前洗浴废水通常作为一次性用水的现象 ,参考各国在污水再利用方面所做的工作 ,结合国内外对洗浴废水处理的研究成果 ,探讨了把洗浴废水处理为浴池补给用水的经济、技术、政策和公众接受观念的可行性 ,分析了现有对洗浴废水的处理方法及其工艺流程。提出将洗浴废水处理为浴池直接的补给水的思路 ,同时 ,通过对洗浴废水的成分分析、各种处理工艺的优缺点比较及处理后水回用的适用场所的讨论 ,论述洗浴废水经处理后达到《生活饮用水卫生标准》的可能性 ,可以安全地用作为浴池补给用水。     

Optimization and treatment of wastewater of crude oil desalting unit and prediction of scale formation

In this article, one of Iran’s southwest oil fields that produces 3200 barrels per day (bbl/d) of wastewater from oil and gas processing was investigated. Experimental analysis of oil reservoir water and desalting wastewater disposal of crude oil desalting unit was performed. First, water was treated with a reverse osmosis membrane. As a result, the purified water, with lower total dissolved solids (TDS) and pH, was a suitable candidate for injection into the adjacent wells of the crude oil desalting unit. The effectiveness and compatibility of this wastewater to the formation water of the oil field wells were simulated. Finally, we studied and identified the formation, the amount, and the type of mineral scale deposits. These are the most important problems during water injection into the wells. The analysis shows that the refined water from the reverse osmosis (RO) process was a suitable and low-cost economical option for injection in onshore and offshore fields, due to the low amount of salts, the concentration of susceptible ions in scaling formation, and the appropriate pH. This oil field, which is in the second half of life, requires enhanced oil recovery methods (EOR) for the maintenance of pressure and an increase in oil recovery.

     

Treatment of greenhouse wastewater using constructed wetlands.

Five wetland designs, based on conventional surface flow (SF) and subsurface flow (SSF) approaches, were assessed for nitrogen and phosphorus removal from greenhouse wastewater. Results indicated none of the individual designs assessed was capable of providing the highest treatment effect for all nutrients of concern; however, the SF wetland emerged as the most appropriate design for the treatment of greenhouse wastewater. The highest mean phosphorus reduction of 65% was observed in the unplanted SF wetlands. Peak nitrate reductions of 54% were observed in the 15-cm deep SF wetlands and ammonia removal of 74% was achieved in the unplanted SF wetlands. Nitrate concentration in the greenhouse effluent can be reduced to acceptable levels for the protection of freshwater aquatic life (i.e., less then 40 ppm) using a loading rate of 1.65 g NO3-N/m2/day and a design water depth of 30 cm or greater. Based on available literature and the results of this research project, a multistage design, consisting of an unplanted pre-treatment basin followed by a 25 to 35 cm deep surface flow marsh with open water components, is recommended.     

Biodegradation of wastewater nitrogen compounds in fractures: laboratory tests and field observations

Throughout several coastal regions in the Mediterranean where rainfalls rarely exceed 650 mm per year municipal treated wastewater can be conveniently reused for soil irrigation. Where the coastal aquifer supplies large populations with freshwater in such area, an assessment of ground water quality around spreading sites is needed. In this study, the efficacy of natural filtration on nitrogen degradation in wastewater spreads on the soil covering the Salento (Southern Italy) fractured limestone was quantified by using laboratory tests and field measurements. In the laboratory, effluent from municipal wastewater treatment plants was filtered through a package of fractures made by several slabs of limestone. An analysis of wastewater constituent concentrations over time allowed the decay rates and constants for nitrogen transformation during natural filtration to be estimated in both aerated and non-aerated (i.e., saturated) soil fractures. A simulation code, based on biodegradation decay constants defined in the laboratory experiments, was then used to quantify the total inorganic nitrogen removal from wastewater injected in an aquifer in the Salento region (Nardò). Here the water sampled in two monitoring wells at 320 m and 500 m from the wastewater injection site and downgradient with respect to groundwater flow was used to verify the laboratory nitrification and denitrification rates.     

The occurrence of cyanide formation in six full-scale publicly owned treatment works.

This paper presents results from an intensive monitoring program implemented at six full-scale publicly owned treatment works (POTWs) to investigate the fate and formation of cyanide in wastewater treatment processes, with a focus on chlorination and dechlorination processes. A review of historical monitoring data for cyanide species in these POTWs was also conducted. This POTW monitoring program provided a database for the investigation of cyanide formation in wastewater secondary treatment. Data from participating POTWs showed evidence of cyanide formation in this 1-year monitoring effort, although the cyanide formation pattern varied significantly from one plant to another and among seasons. Generally, the chlorination of thiocyanate (SCN-) seems to be the most important mechanism for the formation of cyanide in wastewater treatment processes, especially in chlorination and dechlorination. This hypothesis is supported by the findings of a related laboratory study of mechanisms of cyanide formation in POTWs. It is recommended that POTWs monitor SCN in influent and secondary effluent to identify its presence and adjust chlorine dose appropriately.     

Improvement of DOC removal by multi-stage AOP-biological treatment

The single and multi-stages advanced oxidation process (AOP)-biological treatments were evaluated to apply for drinking water treatment, especially for the water containing less susceptible dissolved organic carbon (DOC) to ozone, comparing with the ozonation-biological treatment. Minaga reservoir water and the secondary effluent from a Municipal wastewater treatment plant were used as dissolved organic matter (DOM) solutions. DOC removals after 60 min AOP-biological treatment were 62% and 41% in the Minaga reservoir water and the secondary effluent, respectively, whereas those in the ozonation-biological treatment only 40% and 15% of DOC were removed, respectively. The result indicated that the single-stage AOP-biological treatment could improve DOC removal in comparison with the single-stage ozonation-biological treatment. This is because the AOP mineralized both biodegradable dissolved organic carbon (BDOC) produced in the early stage of oxidation and non-biodegradable dissolved organic carbon (NBDOC), whereas only BDOC was mineralized by further ozonation and NBDOC was not oxidized in the ozonation-biological treatment. The multi-stage treatment could not improve DOC removal in comparison with the single-stage treatment in the ozonation-biological treatment for the secondary effluent containing less susceptible DOC to ozone. However, the multi-stage AOP-biological treatment significantly reduced DOC and achieved 71% of DOC removal by 4 times repetition of 15 min oxidation, whereas DOC removal was 41% in the single-stage AOP-biological treatment for the same oxidation time. The improvement of DOC removal by the multi-stage AOP-biological treatment was due to BDOC removal as a radical scavenger by subsequent biological treatment in the early stage of oxidation and direct mineralization in the latter stage of oxidation.     

不同深度处理工艺去除污水处理厂出水中氮磷的比较研究

城市污水厂出水直接进入天然水体、或经过深度处理后回用于灌溉、补充景观水体和回灌地下水,均需要进行安全性评价.针对北京市北小河污水处理厂出水经过深度处理后回用于奥运公园的安全性,比较了不同深度处理工艺对营养盐(氮、磷)总量和不同形态的去除效果.研究表明,二级处理本身对氮磷的去除效果十分有限,回用水需经过深度处理.在所研究的生物活性炭吸附、微滤、超滤、反渗透以及上述技术的组合工艺中,使用超滤和反渗透联用的工艺路线对脱氮除磷的效果较为理想,其他工艺对去除氮磷的效果十分有限.     

ClO2对医院高浓度含氰废水处理的试验研究

以医院排放的高浓度含氰废水为研究对象,采用"硫酸亚铁+曝气"初级化学处理和ClO2二级深度氧化处理相结合的处理模式,不仅使含氰废水实现无毒化处理,而且使高浓度含氰废水实现资源化回收利用.试验表明,处理后的废水中CN-浓度达到国家排放标准GB8978-1996中的一级标准,为医院高浓度含氰废水的治理提供了一种新的方法.     

直接过滤-臭氧-生物活性炭工艺用于城市污水二级处理出水深度处理的研究

采用砂滤-臭氧-生物活性炭工艺在北京市某污水处理厂开展了以污水再生回用为目的的城市污水深度处理中试研究.在臭氧消耗量5 mg/L,接触时间20 min,生物活性炭空床停留时间(EBCT)为20 min的条件下,出水浊度为1.5 NTU左右,色度接近0,UV254从0.162 cm-1降低到0.08 cm-1,DOC和CODMn分别从10.1 mg/L和12.8 mg/L降低到6 mg/L左右.由于对生物活性炭柱进行了曝气供氧,NH4 -N从40 mg/L降低到5 mg/L左右.     

直接过滤-臭氧-生物活性炭工艺用于城市污水二级处理出水深度处理的研究

采用砂滤-臭氧-生物活性炭工艺在北京市某污水处理厂开展了以污水再生回用为目的的城市污水深度处理中试研究。在臭氧消耗量5mg／L，接触时间20min，生物活性炭空床停留时间（EBCT）为20min的条件下，出水浊度为1．5NTU左右，色度接近0，UV254从0．162cm^-1降低到0．08cm^-1，DOC和CODMn分别从10．1mg／L和12．8mg／L降低到6mg／L左右。由于对生物活性炭柱进行了曝气供氧，NH4^- N从40mg／L降低到5mg／L左右。     

不同深度处理工艺去除污水处理厂出水中氮磷的比较研究

城市污水厂出水直接进入天然水体、或经过深度处理后回用于灌溉、补充景观水体和回灌地下水,均需要进行安全性评价.针对北京市北小河污水处理厂出水经过深度处理后回用于奥运公园的安全性,比较了不同深度处理工艺对营养盐（氮、磷）总量和不同形态的去除效果.研究表明,二级处理本身对氮磷的去除效果十分有限,回用水需经过深度处理.在所研究的生物活性炭吸附、微滤、超滤、反渗透以及上述技术的组合工艺中,使用超滤和反渗透联用的工艺路线对脱氮除磷的效果较为理想,其他工艺对去除氮磷的效果十分有限.     

偶氮二异庚腈生产废水处理试验和工程调试

偶氮二异庚腈的生产过程中产生大量的废水,其有机物和氨氮含量高,生化性差.为解决其处理达标问题,采用氨氮吹脱-上流式厌氧污泥床(UASB)-A/O- NaOCl强氧化-接触氧化的组合工艺对其进行了试验研究.结果表明,该工艺对COD、氨氮的去除率分别达到99％、98％以上.并在此试验研究的基础上,投资建设了一个污水处理站,采用氨氮吹脱-UASB-A/O-二级好氧-NaOCl强氧化-接触氧化-气浮池的组合工艺,经过一年多的运行,出水水质稳定,对COD、氨氮的去除率分别为99％、98％以上,出水水质达到《污水综合排放标准》(GB 8978-1996)的一级标准.     

Making chlorine greener: performance of alternative dechlorination agents in wastewater

The residual chlorine in chlorine-disinfected and dechlorinated wastewater was characterized using a liquid chromatograph that was switched between reversed-phase separation and flow injection analysis modes, permitting measurement of fractionated and total residual chlorine, respectively. Residuals were detected in the effluent of an operating wastewater treatment plant employing chlorine disinfection and sulfite dechlorination. Despite dechlorination, an estimated total residual chlorine of 3 microM (0.2 ppm as Cl2) was detected in the effluent. To improve dechlorination effectiveness, four alternative agents (ascorbic acid, iron, sulfite plus iodide mediator, thiosulfate) were compared to sulfite on laboratory-chlorinated wastewater. Listed in order of decreasing relative effectiveness, we found: iron metal > sulfite plus iodide approximately = thiosulfate > sulfite > ascorbic acid. Only the iron metal column was completely effective at rapidly removing all traces of residual chlorine.     

氯化铁处理AB工艺二级出水中的磷

铁盐混凝剂因其高电荷、安全无毒、易于控制等优点,在城市污水厂除磷方面得到了进一步的发展和应用。为了考察FeCl3除磷的作用特征,探讨除磷效率随pH值、FeCl3投加量等混凝参数的变化规律,以氯化铁(FeCl3)为除磷剂,某城市污水处理厂二级出水为实验水样,进行了实验研究。研究结果表明,水样的硬度对混凝剂除磷性能有较大影响,在最佳工艺条件———不调节水样pH值、FeCl3投加量为75 mg/L时,可将废水中的总磷含量从4.95 mg/L降至0.44 mg/L以下,处理出水可达《城镇污水处理厂污染物排放标准》(GB 18918-2002)中的一级A排放标准(GB18918-2002)(TP<0.50 mg/L)。     

Is the evaluation of “traditional” physicochemical parameters sufficient to explain the potential toxicity of the treated wastewater at sewage treatment plants?

Water scarcity is one of the most important environmental and public health problems of our century. Treated wastewater reuse seems to be the most attractive option for the enhancement of water resources. However, the lack of uniform guidelines at European and/or Mediterranean level leaves room for application of varying guidelines and regulations, usually not based on risk assessment towards humans and the environment. The benefits of complementing the physicochemical evaluation of wastewater with a biological one are demonstrated in the present study using Cyprus, a country with extended water reuse applications, as an example. Four organisms from different trophic levels were used for the biological assessment of the wastewater, namely, Pseudokirchneriella subcapitata, Daphnia magna, Artemia salina and Vibrio fischeri. The physicochemical assessment of wastewater based on “traditional” chemical parameters indicated that the quality of the wastewater complies with the limits set by the relevant national guidelines for disposal. The ecotoxicological assessment, however, indicated the presence of toxicity throughout the sampling periods and most importantly an increase of the toxicity of the treated wastewater during summer compared to winter. The resulting poor correlation between the physicochemical and biological assessments demonstrates that the two assessments are necessary and should be performed in parallel in order to be able to obtain concrete results on the overall quality of the treated effluent. Moreover, a hazard classification scheme for wastewater is proposed, which can enable the comparison of the data sets of the various parameters deriving from the biological assessment in a comprehensive way.     

A/O1/H/O2工艺处理焦化废水硝化过程的实现及其抑制

针对焦化废水中的有毒污染物会对敏感易受干扰的硝化细菌产生不利影响从而破坏硝化过程稳定性的现象,采用A/O1/H/O2工艺处理焦化废水的实际工程为研究对象,根据工程运行的水质监测数据分析,发现几种主要污染物的浓度变化会对二级好氧段的硝化过程产生抑制影响。序批式毒性抑制实验结果表明,苯酚、硫氰化物和喹啉对硝化过程具有毒性抑制作用,半抑制浓度EC50分别为34.26、278.5和73.24 mg/L。当二级好氧工艺段运行正常时（C/N约4.3/1,pH8～8.5,DO 4～4.5 mg/L）,出水氨氮浓度可低于5 mg/L,是由于焦化废水经厌氧/好氧/水解工艺后毒物浓度大幅下降,毒性得到削减,表明焦化废水生物处理A/O1/H/O2组合流化床工艺具有较强抵抗毒物抑制并实现高效的硝化作用。     

Sources and fate of nitrosodimethylamine and its precursors in municipal wastewater treatment plants.

To assess the occurrence and fate of nitrosodimethylamine (NDMA) and its precursors in wastewater treatment plants, samples from wastewater treatment plants and industrial sources were analyzed for NDMA, total NDMA precursors, and dimethylamine (DMA). The median concentration of NDMA in untreated wastewater was approximately 80 ng/L, with maximum concentrations up to 790 ng/L presumably occuring because of sources unrelated to domestic wastewater. Concentrations of DMA in untreated wastewater ranged from approximately 50 to 120 microg/L and accounted for a majority of the NDMA precursors. The removal of NDMA during secondary biological treatment exhibited considerable variability, with overall removal ranging from 0 to 75%. In contrast, removal of NDMA precursors and DMA generally exceeded 70%. The median concentration of NDMA in secondary effluent before disinfection was 46 ng/L. Although DMA was removed during secondary treatment, other NDMA precursors in wastewater effluent will result in formation of additional NDMA upon disinfection with chloramines.