Environmental aspects of the use of NTA as a detergent builder

The behaviour, fate and significance of the detergent builder nitrilotriacetic acid (NTA) has been reviewed with particular reference to the removal of NTA during wastewater treatment and the effects of NTA on heavy metal solubility both during treatment and in the receiving environment. It is concluded that NTA removal during secondary biological treatment is subject to considerable variation, both temporal and between works as a result of changes in NTA load, temperature, water hardness and treatment process parameters. As a result of such variability, effluent NTA concentrations may be sufficient to mobilise heavy metals resulting in metal contamination of receiving waters and potable waters, particularly in areas of low effluent dilution and high water re-use. Removal of NTA during primary sedimentation and septic tank treatment is concluded to be predominantly due to adsorption to the sludge solids while removal in anaerobic sludge digestion is subject to operational characteristics of the treatment works. Disposal of NTA contaminated sludge to land may contaminate groundwaters and affect heavy metal speciation, while the disposal of contaminated sludge or sewage to sea may result in toxic algal blooms, in addition to effects on metal speciation.     

造纸污泥堆肥对葡萄的肥效及其重金属风险评价

通过田间试验,考察了造纸污泥堆肥及其复合肥对葡萄的肥效及重金属污染风险.结果表明,施加造纸污泥堆肥和复合肥可以显著提高葡萄的生物量,改善葡萄果实品质,且果实重金属含量符合国家食品卫生标准,对葡萄园土壤的重金属含量也无明显影响,不存在明显的重金属风险.因此,土地施用污泥堆肥及复合肥是合理处置造纸污泥的重要途径.     

An inventory of heavy metals inputs to agricultural soils in England and Wales

An inventory of heavy metal inputs (Zn, Cu, Ni, Pb, Cd, Cr, As and Hg) to agricultural soils in England and Wales in 2000 is presented, accounting for major sources including atmospheric deposition, sewage sludge, livestock manures, inorganic fertilisers and lime, agrochemicals, irrigation water, industrial by-product 'wastes' and composts. Across the whole agricultural land area, atmospheric deposition was the main source of most metals, ranging from 25 to 85% of total inputs. Livestock manures and sewage sludge were also important sources, responsible for an estimated 37-40 and 8-17% of total Zn and Cu inputs, respectively. However, at the individual field scale sewage sludge, livestock manures and industrial wastes could be the major source of many metals where these materials are applied. This work will assist in developing strategies for reducing heavy metal inputs to agricultural land and effectively targeting policies to protect soils from long-term heavy metal accumulation.     

Chemical partitioning and remobilization of heavy metals from sewage sludge dumped in Dublin Bay

During the disposal of sewage sludge to the marine environment, chemical changes may alter the mobility of trace elements, thus affecting their potential toxicity and availability to marine organisms. Primary sludge from the Ringsend treatment plant in Dublin receives both domestic waste and trade wastes which contain heavy metals, and approx. 250,000 tons per annum is periodically dumped in Dublin Bay. The purpose of this study was to determine changes which may occur in the chemical partitioning of heavy metals in the sludge during disposal. Samples of sludge were collected from the treatment plant in July 1987. Sequential chemical extraction of heavy metals (Cu, Pb, Cd, Zn, Fe, Mn) was carried out in a nitrogen-filled glove box using 1 M ammonium acetate, 1 M sodium acetate, 0.1 M hydroxylamine HCl (pH 2), 0.2 M ammonium oxalate (pH 3), 30% hydrogen peroxide and concentrated HNO₃. Seawater-extractable metal was determined by mixing subsamples of sludge with filtered seawater from Dublin Bay for 2 h. Chemical partitioning of heavy metals among solid phases in the sludge residue was redetermined by sequential chemical extraction. Both sludge and dumpsite sediments were analysed for total heavy metal content and organic content. The sludge was found to be only slightly anaerobic with a water content of 88% and significant concentrations of some metals, notably copper and zinc. Most of the non-residual copper, lead and cadmium was found in the organic/sulphidic fraction of the sludge (hydrogen peroxide extract), while the dominant phase for zinc was the moderately reducible fraction (ammonium oxalate extract) and only iron and manganese had substantial proportions of metal in more labile phases. Agitation with seawater mobilized cadmium and manganese to a significant extent (56 and 43%, respectively) but negligible amounts of copper or lead (0 and 2%, respectively). However, significant changes in solid-phase partitioning of lead and zinc occurred resulting in mobilization from stronglybound to more labile fractions. No deleterious effects were found at the dumpsite but localized effects are possibly due to the increased mobility of zinc, lead and particularly cadmium.     

Musk fragrances, DEHP and heavy metals in a 20 years old sludge treatment reed bed system

The Sludge Treatment Reed Bed (STRB) technology is a cost-efficient and environmentally friendly technology to dewater and mineralize surplus sludge from conventional wastewater treatment systems. Primary and secondary liquid sludge is loaded onto the surface of the bed over several years, where it is dewatered, mineralized and turned into a biosolid with a high dry matter content for use as an organic fertilizer on agricultural land. We analysed the concentrations of five organic micropollutants (galaxolide, tonalide, cashmeran, celestolide and DEHP) and six heavy metals (Pb, Ni, Cu, Cd, Zn and Cr) in the accumulated sludge in a 20-year old STRB in Denmark in order to assess the degradation and fate of these contaminants in a STRB and the relation to sludge composition. The results showed that the deposited sludge was dewatered to reach a dry matter content of 29%, and that up to a third of the organic content of the sludge was mineralized. The concentrations of heavy metals generally increased with depth in the vertical sludge profile due to the dewatering and mineralization of organic matter, but in all cases the concentrations were below the European Union legal limits for agricultural land disposal. The concentrations of fragrances and DEHP ranged from 10 to 9000 ng g⁻¹ dry mass. The attenuation of hydrophobic micropollutants from the top to the bottom layer of the reed bed ranged from 40 to 98%, except for tonalide which increased significantly with sludge depth, and consequently showed an unusual depth distribution of the galaxolide/tonalide ratio. This unexpected pattern may reflect changes imposed by a long storage time and/or different composition of the fresh sludge in the past. The lack of a significant decreasing DEHP concentration with sludge age might indicate that this compound is very persistent in STRBs. In conclusion the STRB was a feasible technology for sludge treatment before its land disposal.     

Fate of organotins in sewage sludge during anaerobic digestion

Adsorption onto sewage sludge is an important process for the elimination of tributyltin (TBT) from wastewater. However as the disposal of sewage sludge to agricultural land is a significant route for recycling biosolids, there exists an issue as to whether the potential long-term build-up of organotins in agricultural soil is acceptable, from a human health and environmental point of view. For the sustainable use of biosolids in agriculture it is essential to control and reduce the quantities of persistent pollutants such as organotins in sewage sludge. In this study, a sampling program was designed to establish the levels of TBT (and other organotins) in sewage sludge and their reduction during anaerobic treatment and processing prior to disposal. Experiments were also undertaken to assess the fate of TBT in laboratory scale anaerobic digesters where the influence of digester operating parameters could be evaluated. Organotin concentrations were determined using capillary gas chromatography with flame photometric detection. The results demonstrated that the majority of TBT remained concentrated in the solid phase (sewage sludge). Concentrations of TBT in sewage sludge were approximately 18 mg kg(-1) (dry weight) and both laboratory experiments and fieldwork demonstrated that degradation of TBT during anaerobic digestion of sludge was minimal.     

对《城镇污水处理厂污泥处置农用泥质》的思考

2008年制订了<城镇污水处理厂污泥处置农用泥质>标准,对污泥农用时重金属浓度指标实行分级控制.根据作物试验结果,并结合我国农田土壤的实际情况,对毒性强、危害大的重金属元素从严控制,对毒性和污染风险小的锌和铜,则适当放宽限制;对种植非食用农作物的农田,也适当放宽重金属浓度的限制.另外,增加了污泥中有机污染物、病原菌、腐熟度和污泥施用时间、施用量、禁用区域等方面的具体规定.     

厌氧条件下硫酸盐对重金属形态的转化作用

对城市污水处理厂污泥厌氧消化过程中不同浓度的硫酸盐对铜、锌、镍三种重金属化学形态变化所起的作用进行了分析研究 .结果表明 ,硫酸盐的存在能够促进污泥中重金属向稳定的硫化物形态转变     

OUR和INT-ETS表征污泥活性的比较

为探寻能快速评价重金属对污泥活性影响的方法,开展了抑制污泥OUR和INT-ETS活性的试验研究.结果表明,OUR反映重金属毒性作用的灵敏性高于INT-ETS;当活性污泥受到重金属污染后,其OUR降低情况与COD的相似,而INT-ETS活性受到的抑制作用相对较小;各重金属离子表现出了不同的毒性作用,以OUR为评价参数时毒性顺序为:Hg2 ＞Cu2 ＞Ag ＞Cd2 ＞Zn2 ＞Ni2 ＞Pb2 ,以INT-ETS活性为评价参数时则为:Hg2 ＞Ag ＞Cu2 ＞Cd2 ＞Zn2 ＞Ni2 ＞Pb2 .OUR是表征污泥活性受重金属影响的较佳参数.     

Metal supplementation to UASB bioreactors: from cell-metal interactions to full-scale application

Upflow anaerobic sludge bed (UASB) bioreactors are commonly used for anaerobic wastewater treatment. Trace metals need to be dosed to these bioreactors to maintain microbial metabolism and growth. The dosing needs to balance the supply of a minimum amount of micronutrients to support a desired microbial activity or growth rate with a maximum level of micronutrient supply above which the trace metals become inhibitory or toxic. In studies on granular sludge reactors, the required micronutrients are undefined and different metal formulations with differences in composition, concentration and species are used. Moreover, an appropriate quantification of the required nutrient dosing and suitable ranges during the entire operational period has been given little attention. This review summarizes the state-of-the-art knowledge of the interactions between trace metals and cells growing in anaerobic granules, which is the main type of biomass retention in anaerobic wastewater treatment reactors. The impact of trace metal limitation as well as overdosing (toxicity) on the biomass is overviewed and the consequences for reactor performance are detailed. Special attention is given to the influence of metal speciation in the liquid and solid phase on bioavailability. The currently used methods for trace metal dosing into wastewater treatment reactors are overviewed and ways of optimization are suggested.     

不同污泥处置方法中重金属的迁移规律

污泥中含有的重金属是污泥处置及其资源化利用中的主要限制因素，从污泥的土地利用、焚烧及制作建材三方面，论述了污泥中重金属的迁移规律及其影响因素，评价了上述3种污泥处置方法的安全性，提出了污泥资源化利用中需注意的问题。     

对《农用污泥中污染物控制标准》中几个问题的商榷

系统的、科学的污泥农用标准是监控污泥土地利用和防止污泥污染的重要前提.根据城市污泥农用过程中重金属、病原菌、有机污染物、杂草种子、蚊蝇滋生及盐分、N、P的流失等方面存在的环境风险问题,重点分析了<农用污泥中污染物控制标准>(GB 4284-84)在标准名称、施用范围、污染物限定值以及标准的可操作性等方面存在的问题,并提出了相应的修改意见和建议.     

The Impact of EU and UK Environmental Pressures on the Future of Sludge Treatment and Disposal

Current and future production of sludge in the UK is estimated, and it is predicted that recycling to agricultural land and incineration (with energy recovery) will be the major disposal options for sludge in the future. Environmental pressures on sludge recycling to land may lead to restrictions on applications in terms of nitrogen content and more stringent limits for metals in soils. Attention to sludge quality and the development of quality management practices in utilization or disposal operations will help to minimize environmental concerns and facilitate sludge disposal to all outlets. Focal points for quality assurance in sludge recycling operations are listed, and environmental pressures on sludge use in agriculture are discussed in detail. Use in agriculture involves recycling a secondary resource, and calling the resource 'biosolids' is part of promoting this excellent example of good environmental management.     

Potential Impact of Draft Proposals to Revise the EC Directive Controlling Sewage-Sludge Applications to Land

The EC Directive which controls the application of sewage sludge to agricultural land, in particular, the reduction in permitted concentrations of heavy metals in sludge and sludge-amended soils, is being reviewed by the European Commission. The implications for sludge recycling in Scotland are examined, and it is estimated that the available land bank would be reduced to about 50% of its present area. In addition, the land area which is required would have to significantly increase because of the proposed lower application rates. These scenarios cast doubt on the long-term viability of the sludge-recycling option in Scotland.     

Operating a High-Rate Digester: The Southern Water Experience

Southern Water has implemented a large capital-investment programme in order to meet the requirements of the EU Urban Wastewater Treatment Directive. Within Southern Water, the Directive will result in a doubling in the quantity of wastewater sludge to be treated. In order to minimise the amount of sludge to be transported and produce a stabilised sludge which is suitable for recycling to agricultural land, the company's sludge strategy is based on treatment by mesophilic anaerobic digestion.
This paper (a) highlights some of the consequences of operating a high-rate digestion plant, and (b) focuses on areas such as depositions in thickened sludge digester feed lines, the start-up procedures for high-rate digesters, foaming, hair and fibre build-up problems and treatment failure caused by toxicity inhibition. All these problems have been corrected or controlled and have resulted in Southern Water revising and updating its design manuals and standards, to prevent such future difficulties.     

Influence of anaerobic digestion on the carbon footprint of various sewage sludge treatment options

This paper describes the results of a model set up to determine carbon footprints for sludge treatment solutions with and without standard or advanced anaerobic digestion. Complete and 'gate' (up to the point the sludge leaves the sewage works gate) footprints were calculated. The lowest carbon footprints corresponded with advanced digestion options, which reduced downstream energy and transport (hence carbon) requirements regardless of the endpoint of the sludge. The lowest complete carbon footprint solution coincided with advanced digestion, followed by drying with energy recovery. However, this option had the highest gate carbon footprint. In terms of gate carbon footprint, land application of an advanced digested sludge cake had the smallest footprint, followed by land application of dried pellets and finally incineration.     

Environmental assessment of anaerobically digested sludge reuse in agriculture: Potential impacts of emerging micropollutants

Agricultural application of sewage sludge has been emotionally discussed in the last decades, because the latter contains organic micropollutants with unknown fate and risk potential. In this work, the reuse of anaerobically digested sludge in agriculture is evaluated from an environmental point of view by using Life Cycle Assessment methodology. More specifically, the potential impacts of emerging micropollutants, such as pharmaceuticals and personal care products, present in the sludge have been quantified. Four scenarios were considered according to the temperature of the anaerobic digestion (mesophilic or thermophilic) and the sludge retention time (20 or 10 d), and they have been compared with the non-treated sludge.From an environmental point of view, the disposal of undigested sludge is not the most suitable alternative, except for global warming due to the dominance (65-85%) of the indirect emissions associated to the electricity use. Nutrient-related direct emissions dominate the eutrophication category impact in all the scenarios (>71.4%), although a beneficial impact related to the avoidance of industrial fertilisers production is also quantified (up to 6.7%). In terms of human and terrestrial toxicity, the direct emissions of heavy metals to soil dominate these two impact categories (>70%), and the contribution of other micropollutants is minimal. Moreover, only six (Galaxolide, Tonalide, Diazepam, Ibuprofen, Sulfamethoxazole and 17α-ethinyloestradiol) out of the 13 substances considered are really significant since they account for more than 95% of the overall micropollutants impact.     

电动力修复技术去除城市污泥中的重金属研究

分析了城市污水处理厂污泥中重金属的形态，重点考察了不同形态的Cd、Zn在电动力作用下的去除率。结果表明，污泥经电动力作用5d后，对Cd、Zn的总去除率分别为64．50％、65．02％，其中对易被植物吸收的非稳态（可交换态、碳酸盐结合态和铁锰氧化物结合态）Cd、Zn的去除效果尤为明显，去除率分别高达68．60％、75．73％。可见，应用电动力修复技术去除污泥中的重金属是可行的，修复后的污泥可进行土地利用。     

Attenuation of heavy metal toxicity of the activated sludge process by treatment with ferric chloride

Industrial wastes containing heavy metals can interfere with the normal operation of municipal wastewater treatment plants utilizing biological treatment processes. It is well known, however, that activated sludge can become acclimated to toxic levels of heavy metals if the dosages are increased gradually. Although such an acclimation procedure could prevent inhibitory effects of slug loads of toxins, the use of toxic heavy metals for normal plant operation is too perilous for consideration. It is, however, acceptable to utilize a nontoxic metal that may give general tolerance to toxic metals.

Laboratory experiments were conducted to examine the use of ferric chloride acclimation for treatment against heavy metal toxicity of an activated sludge process. The oxygen uptake of acclimated and unacclimated seed was measured by respirometry to determine the inhibitory effects of Ag and Pb.

The toxic effects of Ag and Pb were greatly reduced for acclimated seed. The experimental data area utilized in kinetic rate equations, and families of curves are developed to show the inhibition of Ag and Pb at a range of concentrations when the activated sludge is acclimatized at different concentrations of Fe(III).     

污泥堆肥化对重金属生物可利用性的影响

通过重金属形态分析及在模拟雨水、酸雨淋溶条件下重金属迁移实验和理论分析，研究了堆肥化处理对污泥中重金属生物可利用性的影响。结果表明：堆肥化处理使重金属的不稳定形态含量降低，原污泥在酸雨淋溶下重金属已经迁移到约16厘米深的土柱中，而经过处理后的污泥淋出液中的重金属含量很低，仅有少量污泥中含量较高的元素向土柱深层迁移。迁移量及深度明显低于未处理的原污泥。实验及理论分析均证明了堆肥化处理可以降低污泥中重金属在土壤中的迁移性，使重金属的生物可利用性降低。