Role of aquatic plants in wastewater treatment by artificial wetlands

This report describes investigations using artificial wetlands which quantitatively assess the role of each of three higher aquatic plant types, Scirpus validus (bulrush), Phragmites communis (common reed) and Typha latifola (cattail), in the removal of nitrogen (via sequential nitrification-denitrification), BOD and TSS from primary municipal wastewaters. During the period August 1983–December 1984, the mean ammonia concentration of 24.7 mg l⁻¹ in the primary wastewater inflow (hydraulic application rate = 4.7 cm day⁻¹) was reduced to mean effluent levels of 1.4 mg l⁻¹ for the bulrush bed, 5.3 mg l⁻¹ for the reed bed and 17.7 mg l⁻¹ for the cattail bed, as compared to a mean value of 22.1 mg l⁻¹ for the unvegetated (control) bed. For all three vegetated beds, the mean effluent ammonia values were significantly below that for the unvegetated bed and for the inflow. The bulrushes and reeds (in that order) proved to be superior at removing ammonia, both with mean effluent levels significantly below that for the cattail bed. The high ammonia-N (and total N) removal efficiencies shown by the bulrush and reed beds are attributed to the ability of these plants to translocate O₂ from the shoots to the roots. The oxidized rhizosphere so formed stimulates sequential nitrification-denitrification. Similarly BOD removal efficiencies were highest in the bulrush and reed beds, both with mean effluent BOD levels (5.3 and 22.2 mg l⁻¹, respectively) significantly below that for the unvegetated bed (36.4 mg l⁻¹) and equal to or better than secondary treatment quality (30 mg l⁻¹). Our results demonstrate that higher aquatic plants can indeed play a significant role in secondary and advanced (N removal) wastewater treatment by wetland systems, a role that is completely distinct from that associated with their pollutant uptake capacity.     

Energetics of single-sludge nitrogen removal

Energetic considerations were used to predict several parameters of the single sludge nitrogen removal system. Experimental results from bench-scale studies using a synthetic feed served to evaluate the proposed method. Based on observed sludge yields the energy utilization efficiency was estimated at 20 and 40% for heterotrophs and nitrifiers, respectively, at SRT ranging from 7 to 17 days. For a constant nitrogen/COD removal ratio of 0.14 the predicted nitrifiers fraction in the sludge was 0.077. Based on viable cell counts the nitrifiers fraction varied between 0.125 and 0.206 averaging 0.153. The calculated specific nitrification rate based on total nitrifiers mass ranged from 37 to 63 mg N g VSS⁻¹ h⁻¹ with an average of 46 mg N g VSS⁻¹ h⁻¹. Based on viable cells counts the specific activity was determined between 937 and 1660 mg N g VSS⁻¹ h⁻¹ with an average of 1219 mg N g VSS⁻¹ h⁻¹. Results of this study suggest the thermodynamic approach can be used successfully in determining several parameters of the single sludge process. However, its applicability to predict such parameters as nitrifiers fraction and specific nitrifraction rate is dependent on prior knowledge of the energy utilization efficiency and microbial viability.     

Effect of plants and filter materials on bacteria removal in pilot-scale constructed wetlands

Due to the lack of testing units or appropriate experimental approaches, only little is known about the removal of bacteria in constructed wetlands. However, improved performance in terms of water sanitation requires a detailed understanding of the ongoing processes. Therefore, we analyzed the microbial diversity and the survival of Enterobacteriaceae in six pilot-scale constructed wetland systems treating domestic wastewater: two vertical sand filters, two vertical expanded clay filters and two horizontal sand filters (each planted and unplanted). Samples were taken from the in- and outflow, from the rhizosphere, and from the bulk soil at various depths. Colony-forming units of heterotrophic bacteria and coliforms were analyzed and the removal of bacteria between the in- and outflow was determined to within 1.5-2.5 orders of magnitude. To access the taxon-specific biodiversity of potential pathogens in the filters and to reduce the complexity of the analysis, specific primers for Enterobacteriaceae were developed. While performing PCR-SSCP analyses, a pronounced decrease in diversity from the inflow to the outflow of treated wastewater was observed. No differences were observed between the bulk soil of planted and unplanted vertical filters. Some bands appeared in the rhizosphere that were not present in the bulk soil, indicating the development of specific communities stimulated by the plants. The fingerprinting of the rhizosphere of plants grown on sand or expanded clay exhibited many differences, which show that different microbial communities exist depending on the soil type of the filters. The use of the taxon-specific primers enabled us to evaluate the fate of the Enterobacteriaceae entering the wetlands and to localize harboring in the rhizosphere. The most abundant bands of the profiles were sequenced: Pantoea agglomerans was found in nearly all samples from the soil but not in the effluent, whereas Citrobacter sp. could not be removed by the horizontal unplanted sand and vertical planted expanded clay filters. These results show that the community in wetland system is strongly influenced by the filtration process, the filter material and the plants.     

城市污水生物脱氮除磷应用技术

对近年来国内外城市污水生物脱氮除磷工艺机理的研究成果进行了综述 ,介绍了几种常见的生物脱氮除磷工艺 ,并从生物脱氮除磷系统内微生物群体动态平衡的角度详细论述了生物脱氮除磷工艺的影响因素 .     

Nitrogen and phosphorus removal from plant nursery runoff in vegetated and unvegetated subsurface flow wetlands

Subsurface horizontal flow reed beds are being evaluated for Nitrogen (N) and Phosphorus (P) removal from plant nursery runoff water in New South Wales Australia. The need to include plants (Phragmites australis), the effect of reaction time (3.5 v 7.0 d) and dissolved organic carbon (DOC) on N and P removal in batch fed gravel wetland tubs (55 L) was studied over 19 months. Simulated nursery runoff water containing N (10.1 mg L(-1), 74% as NO3) and P (0.58 mg L(-1), 88% as PO4) and DOC (2-5 mg L(-1)) was used. The planted wetland tubs removed >96% TN and TP over most of the 19-month study period while unplanted tubs were inefficient (<16% N and <45% P removal) and occasionally discharged nutrients. Doubling the reaction time to 7.0 days had no effect on nutrient removal. Plant nutrient uptake accounted for most of the N (76%) and P (86%) removed while roots and rhizomes were the dominant sink (N 58%, P 67%). The addition of methanol (C:N-3:1) to unplanted tubs achieved 81-98% N removal. In Carbon limited low nutrient nursery runoff, plants were essential to a gravel-based wetland to achieve efficient nutrient removal with effluent TN and TP concentrations of <1 mg L(-1) and 0.05 mg L(-1), respectively with a 3.5 day reaction time.     

氧化沟的脱氮除磷

阐述了氧化沟脱氮除磷的特点、机理、影响氧化沟脱氮除磷的因素及各种形式氧化沟的脱氮除磷,最后提出了氧化沟的未来发展方向,以期既节约能源又买现最佳的除磷脱氮效果。     

Single sludge nitrogen removal in an oxidation ditch

Activated sludge systems of the oxidation ditch configuration are uniquely suitable for the single-sludge nitrification and denitrification process. This is due to the high recycle flow generated by the aeration system. Existing systems, originally designed for carbonaceous organic removal and nitrification, can be modified to the complete nitrogen removal mode, through the control of oxygen supply. This paper discusses the conditions required for such modification along with the necessary calculation procedures. A case study of a full-scale industrial plant is presented. Calculations based on the principles outlined herein illustrate the capability of the existing system to operate successfully under the single-sludge mode. Actual data over a 15 months period support these results.     

Evaluation of Methods for Nitrogen and Phosphorus Control in Sewage Effluents

The design parameters for the City of Copenhagen sewage-treatment works were established on an experimental basis, and parallel studies of six pilot plants were made over a two-year period. The key parameters are (a) the rate of nitrification and denitrification, (b) temperature, and (c) BOD: N ratio in the influent. The data obtained from different methods had to be normalized with respect to the fraction of nitrifiers, temperature, and concentrations of substrates in order to achieve consistent results. The results indicated a substantial inhibition of the nitrifiers, i.e. a 20–30% reduction of the reaction rate. Significant savings were made possible by a comprehensive analysis of the temperature conditions.     

Dynamics of sulphur compounds in horizontal sub-surface flow laboratory-scale constructed wetlands treating artificial sewage

The knowledge regarding the dynamics of sulphur compounds inside constructed wetlands is still insufficient. Experiments in planted (Juncus effusus) and unplanted horizontal sub-surface-flow laboratory-scale constructed wetlands fed with artificial wastewater were carried out to evaluate the sulphate reduction, the composition and dynamics of generated sulphur compounds, as well as the influence of carbon load and plants on processes of sulphur transformation.In planted and unplanted wetlands, the addition of organic carbon (TOC of about 120 mg L⁻¹) immediately affected the transformation of up to 90% of the incoming sulphate (150 mg L⁻¹), directing it mainly towards elemental sulphur (30%) and sulphide (8%). During this experimental period, nearly 52% of the transformed sulphate-sulphur was calculated to be immobilized inside the planted wetland and 66% inside the unplanted one.In subsequent experiments, the deficiency of organic carbon inside the planted wetlands favoured the decrease of elemental sulphur in the pore water coupled to retransformation of depot-sulphur to dissolved sulphate. Nearly 90% of the deposited and reduced sulphur was found to be reoxidized. In principle, the results indicate a substantial improvement of this reoxidation of sulphur by oxygen released by the helophytes. Surplus of organic carbon promotes the ongoing sulphate reduction and the stability of deposed and dissolved reduced sulphur compounds.In contrast, inside the unplanted control wetland, a relative stability of the formed sulphur depots and the generated amount of dissolved sulphur compounds including elemental sulphur could be observed independently of the different loading conditions.     

Investigation of bacterial removal during the filtration process in constructed wetlands

In this study, bacterial removal efficiencies of planted and unplanted subsurface vertical flow constructed wetlands are compared. Indicator organisms such as faecal coliforms (Escherichia coli, total coliforms) and enterococci, and a number of heterotrophic bacteria (heterotrophic plate counts) have been analysed from the influent and effluent of the constructed wetlands as well as at different depths (water and substrate samples). Furthermore dry matter content and total organic carbon (TOC) have been analysed and correlated. The investigated systems show a high removal rate for indicator organisms (a log removal rate of 2.85 for HPC, 4.35 for E. coli, 4.31 for total coliforms and 4.80 for enterococci was observed). In general no significant difference in the removal efficiency of planted and unplanted vertical flow beds could be measured. Only enterococci measured in the substrate samples of the main layer of the filter could a statistically significant difference be observed.     

新型生物脱氮工艺--CANON工艺

介绍了新型生物脱氮工艺———CANON工艺的基本原理及特征,详述了该工艺的研究进展,并展望了其发展前景。     

污水处理厂低碳源条件下的强化脱氮措施

某市政污水处理厂的生物处理系统采用改良A/A/O工艺,针对运行中出现的定期(国家法定节假日)进水碳源不足的问题,提出了可行的强化脱氮措施.在小长假期间,进水有机碳源略有降低,通过提前将运行模式调整为脱氮A/O模式,可保证生物处理系统的脱氮效果;在长假期间,尤其是国庆节和春节期间,进水有机碳源会大幅降低,且持续时间相对较长,为确保出水总氮浓度达标,除提前调整运行模式外,必须辅助投加葡萄糖作为碳源.实践效果表明,以上强化脱氮措施可有效保证出水总氮浓度的稳定达标.     

Denitrification in a natural wetland receiving secondary treated effluent

The potential of a natural wetland as a site for nitrogen removal from secondary treated effluent was examined by investigating the distribution of denitrification rates and activity in soils and decaying plant material. Field measurements of soil Eh, pH and temperature showed that the effluent inflow favours denitrification by lowering Eh, maintaining pH 6.4–6.7, and raising soil temperature. Analysis of soil concentrations of nitrate plus nitrite and ammonium ions shows that the effluent inflow increased the concentrations of inorganic nitrogen in the soil, and encouraged higher rates of denitrification. Denitrification rates measured by an acetylene blockage technique were highest in soil samples from downstream of the effluent inflow, with the maximum rates being recorded in soils from 0 to 60 cm and in decaying plant material lying on the soil surface. Both nitrate plus nitrite concentration and denitrification activity declined rapidly below 6 cm in upstream and downstream soil samples. Denitrification rates in the natural wetland are increased by the addition of secondary treated effluent, and make a year-round contribution to the removal of nitrogen from the wastewater. Rates of nitrogen removal in the wetland could be increased by encouraging greater spatial and temporal interaction of the effluent amended water with the sites of highest denitrification activity.     

A comparative study of Cyperus papyrus and Miscanthidium violaceum-based constructed wetlands for wastewater treatment in a tropical climate

The treatment efficiencies of constructed wetlands containing Cyperus papyrus L. (papyrus) and Miscanthidium violaceum (K. Schum.) Robyns (synonymous with Miscanthus violaceum (K. Schum) Pilg.) were investigated in a tropical climate (Kampala, Uganda). Papyrus showed higher ammonium-nitrogen and total reactive phosphorus (TRP) removal (75.3% and 83.2%) than Miscanthidium (61.5% and 48.4%) and unplanted controls (27.9% ammonium-nitrogen). No TRP removal was detected in control effluent. Nutrients (N and P) were significantly higher (p<0.015) in papyrus than Miscanthidium plant tissues. Plant uptake and storage was the major factor responsible for N and P removal in treatment line 2 (papyrus) where it contributed 69.5% N and 88.8% P of the total N and P removed. It however accounted for only 15.8% N and 30.7% P of the total N and P removed by treatment line 3 (Miscanthidium violaceum). In addition, papyrus exhibited a significantly larger (p=0.000) number of adventitious roots than Miscanthidium. Nitrifying bacteria attached to papyrus (2.15 x 10(6)+/-1.53 x 10(5) MPN/g DW) and Miscanthidium roots (1.30 x 10(4)+/-8.83 x 10(2) MPN/g DW) and the corresponding nitrification activities were consistent with this finding. Epiphytic nitrifiers appeared more important for total nitrification than those in peat or suspended in water. Papyrus root structures provided more microbial attachment sites, sufficient wastewater residence time, trapping and settlement of suspended particles, surface area for pollutant adsorption, uptake, assimilation in plant tissues and oxygen for organic and inorganic matter oxidation in the rhizosphere, accounting for its high treatment efficiency.     

污水脱氮除磷处理中的化学药剂投加

污水处理厂脱氮除磷处理中,在各个工艺环节需要投加化学药剂。着重介绍了反硝化的碳源、生物除磷中挥发性脂肪酸、碱度、化学除磷药剂中的各种药剂投加方法的基本原理、投加量计算、操作要求以及投加量的控制。     

生物膜与活性污泥结合工艺脱氮除磷研究

常规生物脱氮除磷工艺存在相互影响和制约的因素,因此脱氮和除磷效果难以同时达到最佳。根据研究提出了生物膜与活性污泥结合的新工艺,可同时高效地脱氮、除磷和去除有机物。试验结果表明,氨氮去除率达９９％以上,ＴＮ、ＴＰ和ＣＯＤ的去除率分别达到８５％、９５％和９５％。     

双污泥脱氮除磷工艺用于老厂达标改造

阐述了双污泥脱氮除磷（PASF）工艺的处理流程及特点,并与常规AAO单污泥系统进行了比较,介绍了该工艺在老厂达标改造中的应用.结果表明,相对于传统的处理工艺,双污泥脱氮除磷处理工艺在出水水质、基建投资、运行费用及运行管理方面均有较大的优势,适合老污水处理厂达标改造.     

Effect of pathogen concentrations on removal of Cryptosporidium and Giardia by conventional drinking water treatment

The presence of waterborne enteric pathogens in municipal water supplies contributes risk to public health. To evaluate the removal of these pathogens in drinking water treatment processes, previous researchers have spiked raw waters with up to 10(6) pathogens/L in order to reliably detect the pathogens in treated water. These spike doses are 6-8 orders of magnitude higher than pathogen concentrations routinely observed in practice. In the present study, experiments were conducted with different sampling methods (i.e., grab versus continuous sampling) and initial pathogen concentrations ranging from 10(1) to 10(6) pathogens/L. Results showed that Cryptosporidium oocyst and Giardia cyst removal across conventional treatment were dependent on initial pathogen concentrations, with lower pathogen removals observed when lower initial pathogen spike doses were used. In addition, higher raw water turbidity appeared to result in higher log removal for both Cryptosporidium oocysts and Giardia cysts.     

The persistence and removal of enteric pathogens in constructed wetlands

Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256log(10)day(-1) and 0.151log(10)day(-1), respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345log(10)day(-1) and 0.312log(10)day(-1), respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397log(10)day(-1) and 0.107log(10)day(-1), respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198log(10)day(-1) and 0.054log(10)day(-1), respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029log(10)day(-1) and 0.37log(10)day(-1), respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment.     

乌鲁木齐河东污水厂的脱氮除磷运行效果分析

对乌鲁木齐河东污水处理厂AB工艺的实际脱氮除磷效果进行了监测分析。结果表明：AB工艺处理鸟鲁木齐城市污水的除磷效果优于脱氮效果，对TP的去除率平均为80％；A段对TN的去除率平均为44．7％，经过B段后NH4^＋—N含量升高，使AB工艺对TN的总去除率降至35．7％左右。A段厌氧污泥进入B段可以取得稳定的除磷效果，去除率平均为96．2％；B段污泥进入A段对AB工艺的脱氮除磷效果没有产生明显影响。B段出现NH4^＋-N升高的主要原因是该段的水力停留时间未达到硝化所需时间的要求。