Antibiotic resistance of E. coli in sewage and sludge

The aim of the study is the evaluation of resistance patterns of E. coli in wastewater treatment plants without an evaluation of basic antibiotic resistance mechanisms.Investigations have been done in sewage, sludge and receiving waters from three different sewage treatment plants in southern Austria. A total of 767 E. coli isolates were tested regarding their resistance to 24 different antibiotics. The highest resistance rates were found in E. coli strains of a sewage treatment plant which treats not only municipal sewage but also sewage from a hospital.Among the antimicrobial agents tested, the highest resistance rates in the penicillin group were found for Ampicillin (AM) (up to 18%) and Piperacillin (PIP) (up to 12%); in the cephalosporin group for Cefalothin (CF) (up to 35%) and Cefuroxime-Axetil (CXMAX) (up to 11%); in the group of quinolones for Nalidixic acid (NA) (up to 15%); and for Trimethoprime/Sulfamethoxazole (SXT) (up to 13%) and for Tetracycline (TE) (57%).Median values for E. coli in the inflow (crude sewage) of the plants were between 2.0 x 10(4) and 6.1 x 10(4)CFU/ml (Coli ID-agar, BioMerieux 42017) but showed a 200-fold reduction in all three plants in the effluent. Nevertheless, more than 10(2)CFU E. coli/ml reached the receiving water and thus sewage treatment processes contribute to the dissemination of resistant bacteria in the environment.     

城市污水厂污泥处置技术分析及福州市污泥处置的思考

本文对城市污水厂污泥处理处置主要技术进行分析,并阐述了国外污泥处置技术发展趋势,提出了污泥处理处置工作急需解决的问题。结合当前的污泥处置技术发展趋势,通过对福州市污水厂污泥处置现状及存在问题分析,提出了福州市今后的污泥处置技术路线:将厌氧消化做为有效减容、减量的手段,对污染物指标达到国家土地利用标准的污泥考虑土地利用,污染物指标不符合国家土地利用标准的污泥考虑焚烧和建材利用。     

Microwave-induced pyrolysis of sewage sludge

This paper describes a new method for pyrolyzing sewage sludge using a microwave furnace. It was found that if just the raw wet sludge is treated in the microwave, only drying of the sample takes place. However, if the sludge is mixed with a small amount of a suitable microwave absorber (such as the char produced in the pyrolysis itself) temperatures of up to 900 degrees C can be achieved, so that pyrolysis takes place rather than drying. Microwave treatments were also compared with those carried out in a conventional electric furnace, as well as the characteristics of their respective carbonaceous solid residues.     

The decomposition of sewage sludge in seawater

Laboratory experiments were conducted over a 12 week period to follow the decomposition of sewage sludge in seawater and in sediment-seawater mixtures under aerobic and anaerobic conditions at 4° and 21°C. Results showed that the sewage sludge decomposed more rapidly in the presence of oxygen. Dissolved organic carbon, a major carbon source in sewage sludge, abruptly decreased to very low concentrations in 3–4 weeks in aerobic systems; concentrations of particulate carbon decreased only gradually during the 12 week period. Aerobic conditions at the sewage sludge dump site in the New York Bight apex can promote rapid decomposition of sewage sludge if it is distributed evenly over an area of at least 5.2 km² (2 miles).     

固化污泥压缩特性研究

固化技术是污泥进行填埋处置常用的处理技术之一,固化污泥的压缩参数是进行填埋场库容计算和稳定性评价的重要指标。选用水泥作为固化材料,开展了不同材料添加量和不同养护时间条件下固化污泥的压缩特性研究,并从固化污泥水分形态和转化角度对压缩性变化机理进行了探讨。结果表明,即使水泥添加量达到30%,固化污泥的压缩指数也高达0.71,是一种高压缩性的土。水泥的添加量在10%~20%时,固化污泥压缩指数降低显著,但是超过20%以后,压缩指数变化趋于稳定。其原因主要在于污泥中的水分具有较高的结合势能,过多的水泥并不能获得更多的自由水发生水化反应。固化污泥的压缩指数随着养护时间的增加而降低,当达到14 d时趋于稳定,但60 d以后压缩指数又出现降低趋势,其原因主要是微生物逐步分解污泥结合水中的碳氢化合物,有机质含量下降,导致压缩指数降低。     

Application of microwaves for sewage sludge conditioning

The article focuses on the effect of microwave treatment on the de-waterability of sewage sludge. The specific resistance to filtration, capillary suction time, and dry matter content in centrifuged sludge cake were measured. The quality of sludge liquor obtained after microwave processing was also analysed. It was found out that microwaves improve sludge de-waterability. The quantitative improvement depends on sludge type-better effect of microwave processing were observed in the primary sludge compared to mixed or digested sludges. If microwave treatment is followed by polyelectrolyte conditioning, the effects are considerably better than while these conditioning methods are used separately. Microwave conditioning increased burden of organic matter (BOD(5), COD) in the sludge liquor.     

Lignite aided dewatering of digested sewage sludge

Mechanical dewatering is commonly used to increase the solids content of municipal sludge prior to its disposal. However, if the rate of filtration is slow, mechanical dewatering can be expensive. In this study, the use of lignite to improve the sludge dewatering is investigated. The effectiveness of lignite conditioning of polyelectrolyte-flocculated sludge is examined using mechanical compression tests. Results show that lignite conditioning in conjunction with polyelectrolyte flocculation gives much better dewatering than the polyelectrolyte flocculation alone. Using Darcy's filtration theory, the specific cake resistance and permeability of the compressed cakes are obtained. Both of these parameters are significantly improved after lignite conditioning. Mercury porosimetry tests on compressed cakes show that the porosity of the lignite-conditioned sludge cake is much higher than that of the polyelectrolyte-flocculated sludge and it increases with increasing doses of lignite. The mercury porosimetry results show that the lignite pore volume of pores greater than 0.5 μm are reduced with increasing sludge ratio indicating that sludge is trapped within these pores, whereas smaller pores are unaffected. The yield stress curves for sludge, lignite and sludge-lignite mixtures show that the sludge filter cake is very compressible, but the lignite-conditioned cake has a range of compressibility which although more than lignite indicate that the cake is relatively incompressible at low pressures. Thus, lignite conditioning acts to maintain the permeability of the filter cake during compression dewatering by resisting cake compression. This leads to a trade-off between the rate of dewatering and the solids content of the compressed cake. With lignite conditioning, the dewatering rate can be increased by a factor of five for the same degree of water removal.     

Statistical modelling anaerobic digestion for process optimisation and bench‐marking: a case study of E. coli inactivation across all Thames Water conventional sewage sludge treatment sites

Untreated sewage sludge potentially contains a wide range of enteric pathogens that present a risk to human health. Mesophilic anaerobic digestion (MAD) is the most‐favoured process for sewage sludge treatment in the United Kingdom. It is a well‐established approach to sludge stabilisation, but the mechanisms responsible for pathogen removal are poorly understood. Operational data collected by Thames Water from conventional MAD sites were statistically scrutinised to examine the effects of primary and secondary digestion on the removal of the enteric indicator bacteria, Escherichia coli, by using the IBM SPSS statistical software package for ANOVA, post‐hoc and multiple regression analysis. The results showed that the process temperature conditions at the MAD plants were equivalent to or exceeded the minimum estimated by the analysis necessary to comply with the 2 log₁₀ removal standard for E. coli. The results also showed that primary digestion conditions (specifically temperature) sublethally damaged E. coli and increased decay in secondary digestion and therefore over the whole digestion process.     

Geotechnical and hydrochemical properties of sewage sludge

The geotechnical and geochemical properties of sewage sludge from Kaunas city, Lithuania, were investigated to assess whether it could form a low permeability landfill cover. New sludge, sludge stored or kept in the atmosphere and old sludge were studied. It was found that over time the strength of the sewage sludge increased due to self-consolidation and destruction of organic material. The concentration of metals in the sewage extract was considerably lower than in the landfill leachate. It was concluded that if kept in an open polygon for 1–2 years, the sewage sludge can be used as a low permeability landfill cover.     

Determination of sorption of seventy-five pharmaceuticals in sewage sludge

Sorption of 75 active pharmaceutical ingredients (APIs) to three different types of sludge (primary sludge, secondary sludge with short and long sludge age respectively) were investigated. To obtain the sorption isotherms batch studies with the APIs mixture were performed in four nominal concentrations to water containing 1 g of sludge. The range of APIs concentrations was between ng L⁻¹ to μg L⁻¹ which are found in the wastewater effluents. Isotherms were obtained for approximately 45 of the APIs, providing distribution coefficients for linear (K_d), Freundlich (K_f) and Langmuir (K_L) isotherms. K_d, K_f and K_L ranging between 7.1 × 10⁴ and 3.8 × 10⁷, 1.1 × 10⁻² and 6.1 × 10⁴ and 9.2 × 10⁻³ and 1.1 L kg⁻¹, respectively. The obtained coefficients were applied to estimate the fraction of APIs in the water phase (see Abstract Graphic). For 37 of the 75 APIs, the predicted presence in the liquid phase was estimated to >80%. 24 APIs were estimated to be present in the liquid phase between 20 and 80%, and 14 APIs were found to have <20% presence in the liquid phase, i.e. high affinity towards sludge. Furthermore, the effect of pH at values 6, 7 and 8 was evaluated using one way ANOVA-test. A significant difference in K_ds due to pH changes were found for 6 of the APIs (variation 10-20%).     

污水处理厂污泥脱水性研究

对城市污水厂未消化污泥进行了絮凝脱水试验,用L9正交表对影响絮凝沉淀的各种因素进行了比较,结果表明,高价态盐的混凝效果要好于低价态,而混凝剂加药量及混凝时间等因素也对结果有很大影响。     

Time-trends of metals and organic contaminants in sewage sludge

The occurrence of chemicals in sludge from sewage treatment plants (STPs) is of concern for human health and the environment. Legislations and regulations are put in place to minimize the release of harmful chemicals into the environment and arable land, e.g. via application of sewage sludge. Temporal trends analysis of sludge contaminants can be used to assess the effectiveness of such actions. Such analyses can be performed retrospectively, using sludge stored in environmental specimen banks, to investigate new or emerging environmental contaminants. The present study provides data from time-trend analyses of metals, persistent organic pollutants, pharmaceuticals, personal care products, and other organic compounds in sludge from Swedish. The analysis showed that sludge is a suitable matrix for time-trend studies and it can take on average 12 years (range, 5-26 years) to track an annual change of ±10% (with a power of 80%). Statistically significant trends were found for 18 out of the 77 compounds subjected to analysis, of which 75% showed decreasing trends. Triclosan and the antibiotic norfloxacin followed the same trend as the national recorded usage and decreased annually by 65% and 60%, respectively. The opposite was true for the methylsiloxanes, which showed an annual average increase of about 30%. A downward trend (about 20% year⁻¹) was observed for the polybrominated diphenylethers (PBDEs 154 and 183), while PBDE 209 increased by 16%. Further measurements are required to determine if the substitution of PBDEs by chlorinated paraffins or organophosphorus compounds have resulted in increased concentrations of the latter in sludge.     

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.     

污水处理厂污泥填埋技术研究

分析了我国污水厂污泥的处理现状和污泥填埋面临的困难,介绍了系统化的污泥干化填埋技术方案,实现了污泥的科学填埋,对促进污水处理行业的可持续发展具有积极的推动作用。     

污水处理厂污泥资源化利用技术分析

生活及工业中产生的污水量不断增加,污水处理厂处理后产生的污泥量也随之增大。目前,我国污泥的主要主要处理方法为填埋和焚烧。本文介绍了污水处理厂污泥组成、传统污泥处理方法、污泥资源化处理方法,并对污泥资源化处理案例进行分析,发现未来的污泥处理应侧重于资源回收、减少影响环境及节约经济成本等方向。     

Uncertainties in stormwater E. coli levels

Although water-quality monitoring programs have been widely used to identify and understand the level of pollution in urban stormwater systems, these data are often used without due consideration of the inherent uncertainties contained within these measurements. This study focuses on the uncertainties associated with the monitored levels of Escherichia coli, a common microbial indicator, in urban stormwater. Four sites located in Melbourne, Australia, were used to assess the uncertainty of six stormwater flow and E. coli variables: (1) discrete E. coli concentration, (2) stormwater flow rate, (3) stormwater event volume, (4) event mean concentration (EMC) of E. coli (i.e. a flow-weighted average of an event's E. coli concentrations), (5) E. coli load for each measured event, and (6) site mean E. coli concentration (SMC) (i.e. a volume-weighted average of the E. coli EMCs). Uncertainties of discrete E. coli samples were greater than 30%, while the uncertainty in stormwater flow measurements averaged greater than 97%, mainly due to the high uncertainties in measurements of very low flows. Propagation of these uncertainties, through their respective formulas, found that E. coli EMC uncertainties varied between 10% and 52% and that uncertainties relating to SMC estimates ranged from 35% to 55%. These results show the importance of considering uncertainty when using monitored data sets for any application, including those relating to stormwater management decisions. Suggestions are made about how to increase the accuracies of E. coli monitoring in urban stormwater and how to balance the different sources of uncertainties so that the overall combined uncertainties are minimised while keeping costs at a minimum.     

Long-term changes in sewage sludge stored in a reed bed

The problem of the utilization and management of sewage sludge originating from small wastewater treatment plants is still unsolved. A common approach is to store the sludge in plots which in time turn into grassland. This investigation was aimed at evaluating the influence of the storage time in plots on the chemical properties of sewage sludge deposited there. Tests were carried out on samples obtained from discrete layers of stratified sludge that had lain in a hydrophyte facility disused for 7 years after 23 years of continuous sludge discharge. The age of the sludge was established by the lead-210 method. Moisture, organic matter, total nitrogen and total phosphorus contents were measured in samples of dated sewage sludge. The composition of the stored biosolids stabilized with respect to phosphorus, nitrogen and organic matter within 11, 15 and 17 years, respectively.     

城镇污水污泥的处理处置现状分析

根据我国污水污泥的处理情况,分析了填埋、填海、焚烧、堆肥、建材资源化等污泥处置方式的优缺点,认为填埋、填海、堆肥、焚烧等处置方式未来将会受到更多的限制,而建材资源化利用将会成为污泥处置的重要方式。     

Palestinian experience with sewage sludge utilizing reed beds

Management of sewage sludge is one of the main environmental problems in Palestine. More than 400 m³/day of aerobic sludge and 5000 m³/year of anaerobic sludge are disposed of randomly in the Gaza Strip, creating several environmental and health problems. Because of the political–economic situation, a low cost system for sludge treatment has to be adopted. The results of a pilot project using a reed bed system in the Gaza Strip are promising. Sludge that accumulated in a reed bed system over a 3-year period was found to be well mineralized and composted, and suitable for land application. The water that drained from the reed bed was found to contain very low concentrations of suspended solids (SS) and chemical oxygen demand (COD). This paper presents the results of a 3-year project using a reed bed for sewage sludge treatment in Gaza – Palestine. The quality of drained water and the quality and quantity of accumulated sludge were monitored in two drying beds, one planted with reeds and the other left as a conventional drying bed.