The effect of primary sedimentation on full-scale WWTP nutrient removal performance

Traditionally, the performance of full-scale wastewater treatment plants (WWTPs) is measured based on influent and/or effluent and waste sludge flows and concentrations. Full-scale WWTP data typically have a high variance which often contains (large) measurement errors. A good process engineering evaluation of the WWTP performance is therefore difficult. This also makes it usually difficult to evaluate effect of process changes in a plant or compare plants to each other. In this paper we used a case study of a full-scale nutrient removing WWTP. The plant normally uses presettled wastewater, as a means to increase the nutrient removal the plant was operated for a period by-passing raw wastewater (27% of the influent flow). The effect of raw wastewater addition has been evaluated by different approaches: (i) influent characteristics, (ii) design retrofit, (iii) effluent quality, (iv) removal efficiencies, (v) activated sludge characteristics, (vi) microbial activity tests and FISH analysis and, (vii) performance assessment based on mass balance evaluation. This paper demonstrates that mass balance evaluation approach helps the WWTP engineers to distinguish and quantify between different strategies, where others could not. In the studied case, by-passing raw wastewater (27% of the influent flow) directly to the biological reactor did not improve the effluent quality and the nutrient removal efficiency of the WWTP. The increase of the influent C/N and C/P ratios was associated to particulate compounds with low COD/VSS ratio and a high non-biodegradable COD fraction.     

Low-temperature inhibition of the activated sludge process by an industrial discharge containing the azo dye acid black 1

A municipal wastewater treatment plant (WWTP) receiving industrial dyeing discharge containing acid black 1 (AB1) failed to meet NH(3) and BOD(5) discharge limits, especially for NH(3) during the winter. Dyeing discharge was combined with domestic sewage in volumetric ratios reflecting the range received by the WWTP and fed to sequencing batch reactors at 22 and 7 degrees C. Analysis of the various nitrogen species revealed complete nitrification failure at 7 degrees C with more rapid nitrification failure as the dye concentration increased. Slight nitrification inhibition occurred at 22 degrees C: NH(3) removal decreased from 99.9% for the control compared to only 97.0% removal with dye addition. Dye-bearing wastewater also reduced COD removal by half at 7 degrees C and by one-fifth at 22 degrees C, and increased effluent TSS nearly three-fold at 7 degrees C. Activated sludge quality at 7 degrees C deteriorated after exposure to AB1, as indicated by excessive foaming and the presence of filamentous bacteria and by a decrease in endogenous and exogenous oxygen uptake. Decreasing AB1 loading resulted in partial activated sludge recovery. Eliminating the dye-bearing discharge to the full-scale WWTP led to improved performance bringing the WWTP into compliance with discharge limits.     

Biological removal of 17α-ethinylestradiol by a nitrifier enrichment culture in a membrane bioreactor

Increasing concern about the fate of 17α-ethinylestradiol (EE2) in the environment stimulates the search for alternative methods for wastewater treatment plant (WWTP) effluent polishing. The aim of this study was to establish an innovative and effective biological removal technique for EE2 by means of a nitrifier enrichment culture (NEC) applied in a membrane bioreactor (MBR). In batch incubation tests, the microbial consortium was able to remove EE2 from both a synthetic minimal medium and WWTP effluent. A maximum EE2 removal rate of 9.0 μg EE2 g⁻¹ biomass-VSS h⁻¹ was achieved (>94% removal efficiency). Incubation of the heterotrophic bacteria isolated from the NEC did not result in a significant EE2 removal, indicating the importance of nitrification as driving force in the mechanism. Application of the NEC in a MBR to treat a synthetic influent with an EE2 concentration of 83 ng EE2 L⁻¹ resulted in a removal efficiency of 99% (loading rates up to 208 ng EE2 L⁻¹ d⁻¹; membrane flux rate: 6.9 L m⁻² h⁻¹). Simultaneously, complete nitrification was achieved at an optimal ammonium influent concentration of 1.0 mg NH₄⁺-N L⁻¹. This minimal NH₄⁺-N input is very advantageous for effluent polishing since the concomitant effluent nitrate concentrations will be low as well and it offers opportunities for the nitrifying MBR as a promising add-on technology for WWTP effluent polishing.     

Simulation of closed double‐sludge retention time anoxic‐oxic process in wastewater treatment: case study for a utility model process

The ‘closed double‐sludge retention time anoxic‐oxic (SRT AO) process’ is a utility model designed by the Shanghai Urban Construction Design and Research Institute. It can quantitatively control the nitrification level by adjusting wastewater distribution and mixed sludge return during wastewater treatment, and can thus considerably reduce construction investment and operation costs. However, mixed sludge return from the sedimentation tank may dilute the concentration of nitrobacteria because the heterotrophic bacteria propagate faster. In this paper, the closed double‐SRT AO process was modelled and simulated based on its application at the Zhuyuan Second Wastewater Treatment Plant (WWTP). The distribution ratio was found to have a significant influence on the nitrobacteria's concentration but does not eliminate the existence of nitrobacteria in the system. Extension of sludge age enhanced the heterotrophic bacteria concentration and to a greater extent the nitrobacteria concentration, thus attenuated the dilution of nitrobacteria. Mixed liquid recycling showed little effect on nitrobacteria concentration. The closed double‐SRT AO process in Zhuyuan Second WWTP had enough capacity for complete nitrification, but the shortage of organic matter in the influent impeded the nitrogen removal.     

应用工艺智能优化控制系统降低污水厂能耗

生物工艺智能优化系统（BIOS）是一个前馈优化系统，通过获得A／O工艺实时的在线数据（如氨氮、硝酸盐氮、进水流量、混合液悬浮物浓度），BIOS系统不断进行模拟计算，然后按照生物反应器进水的污染物负荷状况来提供最佳的DO设定值；同时为达到最佳的TN去除率，BIOS系统还对好氧区回流至缺氧区的内回流比（IRQ）进行了优化。BIOS系统在美国康涅狄格州En-field污水厂的实际应用情况表明，该系统能提高脱氮效率36％，同时降低曝气量19％。     

Global sensitivity analysis in wastewater treatment plant model applications: Prioritizing sources of uncertainty

This study demonstrates the usefulness of global sensitivity analysis in wastewater treatment plant (WWTP) design to prioritize sources of uncertainty and quantify their impact on performance criteria. The study, which is performed with the Benchmark Simulation Model no. 1 plant design, complements a previous paper on input uncertainty characterisation and propagation (Sin et al., 2009). A sampling-based sensitivity analysis is conducted to compute standardized regression coefficients. It was found that this method is able to decompose satisfactorily the variance of plant performance criteria (with R² > 0.9) for effluent concentrations, sludge production and energy demand. This high extent of linearity means that the plant performance criteria can be described as linear functions of the model inputs under the defined plant conditions. In effect, the system of coupled ordinary differential equations can be replaced by multivariate linear models, which can be used as surrogate models. The importance ranking based on the sensitivity measures demonstrates that the most influential factors involve ash content and influent inert particulate COD among others, largely responsible for the uncertainty in predicting sludge production and effluent ammonium concentration. While these results were in agreement with process knowledge, the added value is that the global sensitivity methods can quantify the contribution of the variance of significant parameters, e.g., ash content explains 70% of the variance in sludge production. Further the importance of formulating appropriate sensitivity analysis scenarios that match the purpose of the model application needs to be highlighted. Overall, the global sensitivity analysis proved a powerful tool for explaining and quantifying uncertainties as well as providing insight into devising useful ways for reducing uncertainties in the plant performance. This information can help engineers design robust WWTP plants.     

Pharmaceutical compounds in the wastewater process stream in Northwest Ohio

In order to add to the current state of knowledge regarding occurrence and fate of Pharmaceutical and Personal Care Products (PPCP's) in the environment, influent, effluent and biosolids from three wastewater treatment facilities in Northwest Ohio, USA, and a stream containing effluent discharge from a rural treatment facility were analyzed. The three WWTP facilities vary in size and in community served, but are all Class B facilities. One facility was sampled multiple times in order to assess temporal variability. Twenty compounds including several classes of antibiotics, acidic pharmaceuticals, and prescribed medications were analyzed using ultrasonication extraction, SPE cleanup and liquid chromatography-electrospray ionization tandem mass spectrometry. The highest number of compounds and the greatest concentrations were found in the influent from the largest and most industrial WWTP facility. Short-term temporal variability was minimal at this facility. Many compounds, such as clarithromycin, salicylic acid and gemfibrizol were found at concentrations more than one order of magnitude higher than found in the effluent samples. Effluent waters contained elevated levels of carbamazepine, clindamycin and sulfamethoxazole. Differences in composition and concentration of effluent waters between facilities existed. Biosolid samples from two different facilities were very similar in PPCP composition, although concentrations varied. Ciprofloxacin was found in biosolids at concentrations (up to 46 mug/kg dry mass) lower than values reported elsewhere. Diclofenac survived the WWTP process and was found to persist in stream water incorporating effluent discharge. The low variability within one plant, as compared to the variability found among different wastewater treatment plants locally and in the literature is likely due to differences in population, PPCP usage, plant operations and/or local environment. These data are presented here for comparison with this emerging set of environmental compounds of concern.     

某市贾第鞭毛虫和隐孢子虫污染现状

利用免疫荧光分析技术对南方某市饮用水源水、自来水厂出水和污水处理厂进、出水中贾第鞭毛虫和隐孢子虫(两虫)的污染状况进行了调查,并就自来水厂常规处理工艺对两虫的去除特性进行了研究.结果显示:该市饮用水源水中的两虫密度分别为2～120个/100L和0～24个/100 L,自来水厂出水分别为0～12个/1000 L和0～8个/1000 L,污水处理厂进水中的两虫密度分别为7 200～18 300个/L和69～1 210个/L,二级处理出水的分别为6～153个/L和1～46个/L;混凝沉淀和过滤对两虫有较好的去除效果.     

Dynamic modelling of nitrification in an aerated facultative lagoon

Faced with the need to improve ammonia removal from lagoon wastewater treatment plants (WWTPs) operated in Quebec, Canada, mechanistic modelling has been proposed as a tool for explaining the seasonal nitrification phenomenon and to evaluate optimization and upgrade scenarios. A lagoon model that includes a modified activated sludge biokinetic model and that assumes completely mixed conditions in the water column and sediments has been applied to simulate 3 years of consecutive effluent data for a lagoon from the Drummondville WWTP. Successful prediction of results from this plant indicates that the seasonal nitrification is determined by temperature, dissolved oxygen (DO) concentrations, hydraulic retention time (HRT) of the water column and washout driven by a well-mixed water column. Results also indicate that sediments contribute to the ammonia load in the lagoon effluent, particularly in spring and early summer. Sensitivity analyses performed with the model indicate that the nitrification period could be prolonged by increasing DO concentrations in the lagoon and that bioaugmentation would be particularly effective in spring and early summer. Limitations of the model are discussed, as well as ways to improve the hydraulic model.     

Evaluation of the fate of perfluoroalkyl compounds in wastewater treatment plants

Recent studies have shown that the wastewater treatment plant (WWTP) is a significant source of perfluoroalkyl compounds (PFCs) in natural water. In this study, 10 PFCs were analyzed in influent and effluent wastewater and sludge samples in 15 municipal, 4 livestock and 3 industrial WWTPs in Korea. The observed distribution pattern of PFCs differed between the wastewater and sludge samples. Perfluorooctane sulfonate (PFOS) was dominant in the sludge samples with a concentration ranging from 3.3 to 54.1 ng/g, whereas perfluorooctanoic acid (PFOA) was dominant in wastewater and ranged from 2.3 to 615 ng/L and 3.4 to 591 ng/L in influent and effluent wastewater, respectively. Principal component analysis (PCA) results provided an explanation for this variation in PFC distribution patterns in the aqueous and sludge samples. The fates of PFCs in the WWTPs were related with the functional groups. The PFOS concentrations tended to decrease after treatment in most WWTPs, whereas PFOA increased. The different fates of PFOA and PFOS in WWTPs were attributed to the higher organic carbon-normalized distribution coefficient of perfluoroalkylsulfonate (PFASs) than that of the carboxylate analog, indicating the preference of PFASs to partition to sludge. Although industrial WWTPs contained high concentration of PFCs, they are not the main source of PFCs in Korean water environment because of their small release amount. WWTPs located in big cities discharged more PFCs, suggesting household sewage is one of the significant sources of PFCs contamination in the environment.     

化工农药废水处理提标改造工程设计与实践

湖南某化工农药产业基地污水处理厂提标改造工程处理规模为2.0×10^4 m^3/d,在充分分析现有污水厂处理工艺、进出水指标以及运行状况的基础上,采用高级氧化前置预处理+强化生化+后置高级氧化+深度处理工艺进行提标改造,出水水质稳定达到《城镇污水处理厂污染物排放标准》(GB 18918-2002)的一级A标准,直接运行费用为8.004元/m^3。     

Redistribution of wastewater alkalinity with a microbial fuel cell to support nitrification of reject water

In wastewater treatment plants, the reject water from the sludge treatment processes typically contains high ammonium concentrations, which constitute a significant internal nitrogen load in the plant. Often, a separate nitrification reactor is used to treat the reject water before it is fed back into the plant. The nitrification reaction consumes alkalinity, which has to be replenished by dosing e.g. NaOH or Ca(OH)₂. In this study, we investigated the use of a two-compartment microbial fuel cell (MFC) to redistribute alkalinity from influent wastewater to support nitrification of reject water. In an MFC, alkalinity is consumed in the anode compartment and produced in the cathode compartment. We use this phenomenon and the fact that the influent wastewater flow is many times larger than the reject water flow to transfer alkalinity from the influent wastewater to the reject water. In a laboratory-scale system, ammonium oxidation of synthetic reject water passed through the cathode chamber of an MFC, increased from 73.8 ± 8.9 mgN/L under open-circuit conditions to 160.1 ± 4.8 mgN/L when a current of 1.96 ± 0.37 mA (15.1 mA/L total MFC liquid volume) was flowing through the MFC. These results demonstrated the positive effect of an MFC on ammonium oxidation of alkalinity-limited reject water.     

Xenobiotic removal efficiencies in wastewater treatment plants: residence time distributions as a guiding principle for sampling strategies

The effect of mixing regimes and residence time distribution (RTD) on solute transport in wastewater treatment plants (WWTPs) is well understood in environmental engineering. Nevertheless, it is frequently neglected in sampling design and data analysis for the investigation of polar xenobiotic removal efficiencies in WWTPs. Most studies on the latter use 24-h composite samples in influent and effluent. The effluent sampling period is often shifted by the mean hydraulic retention time assuming that this allows a total coverage of the influent load. However, this assumption disregards mixing regime characteristics as well as flow and concentration variability in evaluating xenobiotic removal performances and may consequently lead to biased estimates or even negative elimination efficiencies.The present study aims at developing a modeling approach to estimate xenobiotic removal efficiencies from monitoring data taking the hydraulic RTD in WWTPs into consideration. For this purpose, completely mixed tanks-in-series were applied to address hydraulic mixing regimes in a Luxembourg WWTP. Hydraulic calibration for this WWTP was performed using wastewater conductivity as a tracer. The RTD mixing approach was coupled with first-order biodegradation kinetics for xenobiotics covering three classes of biodegradability during aerobic treatment.Model simulations showed that a daily influent load is distributed over more than one day in the effluent. A 24-h sampling period with an optimal time offset between influent and effluent covers less than the half of the influent load in a dry weather scenario. According to RTD calculations, an optimized sampling strategy covering four consecutive measuring days in the influent would be necessary to estimate the full-scale elimination efficiencies with sufficient accuracy. Daily variations of influent flow and concentrations can substantially affect the reliability of these sampling results. Commonly reported negative removal efficiencies for xenobiotics might therefore be a consequence of biased sampling schemes. In this regard, the present study aims at contributing to bridge the gap between environmental chemistry and engineering practices.     

Input characterization of perfluoroalkyl substances in wastewater treatment plants: source discrimination by exploratory data analysis

This paper presents a methodology based on multivariate data analysis for identifying input sources of perfluoroalkyl substances (PFASs) detected in 37 wastewater treatment plants (WWTPs) across more than 40 cities in the state of Minnesota (USA). Exploratory analysis of data points has been carried out by unsupervised pattern recognition (cluster analysis), correlation analysis, ANOVA and per capita discharges in an attempt to discriminate sources of PFASs in WWTPs. Robust cluster solutions grouped the database according to the different PFAS profiles in WWTP influent. Significantly elevated levels of perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) and/or perfluorooctane sulfonate (PFOS) in influent have been found in 18 out of 37 WWTPs (49%). A substantial increase in the concentrations of PFHxA and/or PFOA from influent to effluent was observed in 59% of the WWTPs surveyed, suggestive of high concentration inputs of precursors. The fate of one precursor (8:2 fluorotelomer alcohol) in WWTP was modeled based on fugacity analysis to understand the increasing effluent concentration. Furthermore, population-related emissions cannot wholly explain the occurrence and levels of PFASs in WWTPs. Unusually high influent levels of PFASs were observed in WWTPs located in specific industrial areas or where known contamination had taken place. Despite the restriction on the production/use of PFOA and PFOS, this paper demonstrates that wastewater from industrial activities is still a principal determinant of PFAS pollution in urban watersheds.     

Fate of dissolved organic nitrogen in two stage trickling filter process

Dissolved organic nitrogen (DON) represents a significant portion of nitrogen in the final effluent of wastewater treatment plants (WWTPs). Biodegradable portion of DON (BDON) can support algal growth and/or consume dissolved oxygen in the receiving waters. The fate of DON and BDON has not been studied for trickling filter WWTPs. DON and BDON data were collected along the treatment train of a WWTP with a two-stage trickling filter process. DON concentrations in the influent and effluent were 27% and 14% of total dissolved nitrogen (TDN). The plant removed about 62% and 72% of the influent DON and BDON mainly by the trickling filters. The final effluent BDON values averaged 1.8 mg/L. BDON was found to be between 51% and 69% of the DON in raw wastewater and after various treatment units. The fate of DON and BDON through the two-stage trickling filter treatment plant was modeled. The BioWin v3.1 model was successfully applied to simulate ammonia, nitrite, nitrate, TDN, DON and BDON concentrations along the treatment train. The maximum growth rates for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria, and AOB half saturation constant influenced ammonia and nitrate output results. Hydrolysis and ammonification rates influenced all of the nitrogen species in the model output, including BDON.     

HPB工艺用于污水厂提标扩容改造的生产性试验研究

基于HPB工艺中试研究结果,为进一步验证HPB工艺在提标扩容实际生产工况下的处理效果和可实施性,在湖南某水质净化厂进行了生产性试验。试验期间,在总进、出水量保持不变的条件下,进行HPB工艺改造,将现状两组生化池(A2/O)切换为单组运行,处理水量提升1倍,总停留时间缩短为5. 0 h以下。通过复合粉末载体的投加及排泥过程中载体和附着微生物的回收循环,实现了"双泥龄",克服了脱氮菌和除磷菌的污泥龄矛盾,提高了脱氮除磷效率。试验结果表明,生化池混合液浓度控制在10 000 mg/L左右,在厂区进水水量和水质变化较大(K_Z≥1. 3)、水温低于冬季设计温度时,HPB工艺系统运行稳定,主要出水水质指标COD <30 mg/L、NH3-N <1. 5 mg/L、TN <10 mg/L、TP <0. 3 mg/L,能够实现高效、稳定达标。     

Field evaluation of the treatability of type A zeolite in a trickling filter plant

Type A zeolite is a synthetic aluminosilicate which can be used as a builder in laundry detergents. The treatability of this zeolite in wastewater was evaluated in a trickling filter plant under field conditions. The normal performance of the plant was established during a baseline period of three months, after which the zeolite was added to the raw wastewater for 7 months. The removal of the zeolite by the plant averaged 81% or more at an influent concentration of 10 mg 1⁻¹. Of the zeolite that passed into the secondary effluent, 92% was removed by a dual-media filter. Removal from raw influent to tertiary effluent was thus 99%. The presence of the zeolite in the wastewater had no effect on the performance of the plant, the production of gas by the anaerobic digester or the concentrations of Pb, Zn and Ni in the effluent.     

腈纶纱染色废水预处理工程的设计与运行

为使厂内处理水质达到接管标准,采用水解／塔式生物滤池和混凝沉淀工艺作为腈纶纱染色废水预处理工艺。工程运行表明,原水COD≤1600mg／L时,适当增大回流量,水解／塔式生物滤池对COD的去除率可达57％;再经混凝沉淀处理,可去除45％的COD,出水COD〈380mg／L,能满足接管要求。另外,出水色度、SS也优于接管标准。因此,采用上述工艺对腈纶纱印染废水进行预处理在技术上是可行的,经济上也是可以接受的（运行费用为1．82元／m^3）。