Priority and emerging pollutants in sewage sludge and fate during sludge treatment

This paper aims at characterizing the quality of different treated sludges from Paris conurbation in terms of micropollutants and assessing their fate during different sludge treatment processes (STP). To achieve this, a large panel of priority and emerging pollutants (n = 117) have been monitored in different STPs from Parisian wastewater treatment plants including anaerobic digestion, thermal drying, centrifugation and a sludge cake production unit. Considering the quality of treated sludges, comparable micropollutant patterns are found for the different sludges investigated (in mg/kg DM – dry matter). 35 compounds were detected in treated sludges. Some compounds (metals, organotins, alkylphenols, DEHP) are found in every kinds of sludge while pesticides or VOCs are never detected. Sludge cake is the most contaminated sludge, resulting from concentration phenomenon during different treatments. As regards treatments, both centrifugation and thermal drying have broadly no important impact on sludge contamination for metals and organic compounds, even if a slight removal seems to be possible with thermal drying for several compounds by abiotic transfers. Three different behaviors can be highlighted in anaerobic digestion: (i) no removal (metals), (ii) removal following dry matter (DM) elimination (organotins and NP) and iii) removal higher than DM (alkylphenols – except NP – BDE 209 and DEHP). Thus, this process allows a clear removal of biodegradable micropollutants which could be potentially significantly improved by increasing DM removal through operational parameters modifications (retention time, temperature, pre-treatment, etc.).     

污水处理固体废弃物污泥的处置方法研究

从生活污水处理工艺出发介绍污泥产生的环节,探究污泥传统处置方法和资源化处置方法,同时对污泥源头减量化方法做了详细论述,最后分析了污泥处置成本的影响因素,对污泥环保处置提供参考与帮助.     

Life cycle assessment of sewage sludge co-incineration in a coal-based power station

A life cycle assessment was conducted to evaluate the environmental and economic effects of sewage sludge co-incineration in a coal-fired power plant. The general approach employed by a coal-fired power plant was also assessed as control. Sewage sludge co-incineration technology causes greater environmental burden than does coal-based energy production technology because of the additional electricity consumption and wastewater treatment required for the pretreatment of sewage sludge, direct emissions from sludge incineration, and incinerated ash disposal processes. However, sewage sludge co-incineration presents higher economic benefits because of electricity subsidies and the income generating potential of sludge. Environmental assessment results indicate that sewage sludge co-incineration is unsuitable for mitigating the increasing pressure brought on by sewage sludge pollution. Reducing the overall environmental effect of sludge co-incineration power stations necessitates increasing net coal consumption efficiency, incinerated ash reuse rate, dedust system efficiency, and sludge water content rate.     

The usability of the IR,RAC and MRI indices of heavy metal distribution to assess the environmental quality of sewage sludge composts

To assess the environmental quality of compost, it is insufficient to use only total metal concentration. Therefore in this study, the stability of metals in compost and the environmental risk they pose were assessed by three indices that have been proposed for soils or sediments: the I_R, the RAC and the MRI. In mature composts, the highest bonding intensity was for Ni (0.79 < I_R < 0.93), then for Cu (0.56 < I_R < 0.65) and Pb (0.55 < I_R < 0.73), and the lowest for Zn (0.19 < I_R < 0.25). Although, both the I_R and the RAC are useful indices for evaluating the mobility of metals, they do not take into account their toxicity. Therefore, the overall classification of compost should also include the MRI, at which metal toxicity from the most available fractions is considered. Based on the MRI ranged between 10.0 and 11.6, all composts evaluated posed a low risk.     

Composting in small laboratory pilots: performance and reproducibility

Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed the performance of composting considering the transformations of organic matter. Moreover, composting at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and the reproducibility of composting has rarely been reported. The objectives of this study are to design an innovative small-scale composting device safeguarding self-heating to drive the composting process and to assess the performance and reproducibility of composting in small-scale pilots. The experimental setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The performance of the process was assessed by monitoring the temperature, O₂ consumption and CO₂ emissions, and characterising the biochemical evolution of organic matter. A good reproducibility was found for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments, excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility of the process and the quality of the final compost make it possible to propose the use of this experimental device for research requiring a mass reduction of the initial composted waste mixtures.     

Greenhouse gases emissions accounting for typical sewage sludge digestion with energy utilization and residue land application in China

About 20 million tonnes of sludge (with 80% moisture content) is discharged by the sewage treatment plants per year in China, which, if not treated properly, can be a significant source of greenhouse gases (GHGs) emissions. Anaerobic digestion is a conventional sewage sludge treatment method and will continue to be one of the main technologies in the following years. This research has taken into consideration GHGs emissions from typical processes of sludge thickening + anaerobic digestion + dewatering + residue land application in China. Fossil CO₂, biogenic CO₂, CH_4, and avoided CO₂ as the main objects is discussed respectively. The results show that the total CO₂-eq is about 1133 kg/t DM (including the biogenic CO₂), while the net CO₂-eq is about 372 kg/t DM (excluding the biogenic CO₂). An anaerobic digestion unit as the main GHGs emission source occupies more than 91% CO₂-eq of the whole process. The use of biogas is important for achieving carbon dioxide emission reductions, which could reach about 24% of the total CO₂-eq reduction.     

Feasibility of composting combinations of sewage sludge,olive mill waste and winery waste in a rotary drum reactor

Representative samples of the following biowastes typically generated in Castilla La Mancha (Spain) were composted using a pilot-scale closed rotary drum composting reactor provided with adequate control systems: waste from the olive oil industry (olive mill waste; OMW), winery–distillery waste containing basically grape stalk and exhausted grape marc (WDW), and domestic sewage sludge. Composting these biowastes was only successful when using a bulking agent or if sufficient porosity was supported. OMW waste composting was not possible, probably because of its negligible porosity, which likely caused anaerobic conditions. WDW was successfully composted using a mixture of solid wastes generated from the same winery. SS was also successfully composted, although its higher heavy metal content was a limitation. Co-composting was an adequate strategy because the improved mixture characteristics helped to maintain optimal operating conditions. By co-composting, the duration of the thermophilic period increased, the final maturity level improved and OMW was successfully composted. Using the proposed reactor, composting could be accelerated compared to classical outdoor techniques, enabling easy control of the process. Moisture could be easily controlled by wet air feeding and leachate recirculation. Inline outlet gas analysis helped to control aerobic conditions without excessive aeration. The temperature reached high values in a few days, and sufficient thermal requirements for pathogen removal were met. The correct combination of biowastes along with appropriate reactor design would allow composting as a management option for such abundant biowastes in this part of Spain.     

Effect of composting process on phytotoxicity and speciation of copper, zinc and lead in sewage sludge and swine manure

The concentration and bioavailability of heavy metals in composted organic wastes have negative environmental impacts following land application. Aerobic composting procedures were conducted to investigate the influences of selected parameters on heavy metal speciation and phytotoxicity. Results showed that both of sewage sludge (SSC) and swine manure (SMC) composting systems decreased the pH, the content of organic matter (OM) and dissolved organic carbon (DOC), and total amounts of Cu, Zn and Pb. Sequential extraction showed that readily extractible fractions of exchangeable and carbonate in Cu and Zn increased during SSC composting but decreased during SMC composting, thus their bioavailability factors (BF) enhanced in SSC but declined in SMC. The fraction of reducible iron and manganese (FeMnOX) of Cu and Zn in SSC and FeMnOX-Cu in SMC decreased, but FeMnOX-Zn in SMC gradually increased in the process of compost. In contrast, the changes of Pb distributions were similar in two organic wastes. Pb was preferentially bound to the residual fraction and its BF decreased. The evolution of heavy metal distributions and BF depended on not only total metal concentrations but also the other properties, such as pH, decomposition of OM and decline of DOC. The germination rate (RSG), root growth (RRG) and germination index (GI) of pakchoi (Brassica Chinensis L.) increased during the composting process. Linear regression analysis demonstrated that GI, which could represent phytotoxic behavior to the plants, could be poorly predicted by BF or total amount of metals, i.e., BF-Zn, T-Cu. However, the inclusion of other physicochemical parameters (pH, OM and DOC) could enhance the linear regression significances (R).     

Utilization of river sediment,sewage sludge and wheat straw as the primary raw material in sintered-shale bricks

Journal of Material Cycles and Waste Management - China produces large amounts of sewage sludge and agricultural waste every year. In line with the concepts of economic and environmental...     

Gasification of dried sewage sludge: status of the demonstration and the pilot plant

The disposal of sewage sludge from municipal waste water treatment plants is suffering from raising costs.The gasification is an alternative way of treatment, which can reduce the amount of solid residues that must be disposed from a water treatment plant. The produced gas can be used very flexible to produce electrical energy, to burn it very cleanly or to use it for upgrading.The gasification in the fluidised bed and the gas cleaning with the granular bed filter has shown successful operation. A demonstration plant in Balingen was set up in 2002 and rebuilt to a larger throughput in 2010. As a next step a demonstration plant was built in Mannheim and is now at the end of the commissioning phase. Nowadays the product gas is blended with biogas from sludge fermentation and utilized in a gas engine or combustion chamber to produce heat. In the future the process control for a maximized efficiency and the removal of organic and inorganic impurities in the gas will be further improved.     

Co-combustion of dried sewage sludge and coal in a pulverized coal boiler

More than 1.1 million tons of municipal and industrial sewage sludge is produced annually in Poland. Most of this sewage sludge is landfilled or used for recultivation and fertilization of soil. After accession of Poland to the EU, large investments are planned for wastewater treatment, so it is expected that the amount of sewage sludge produced in Poland will grow in the near future. It is well known that the combustion of sewage sludge is becoming a more and more popular utilization method of such waste. Unfortunately, the current situation in Poland makes it impossible to incinerate the sewage sludge because of a lack of incinerators. One possible solution for Poland is the co-firing of dried sewage sludge in existing coal-fired utility boilers. This article presents results of initial Polish industrial trials of dried municipal sewage sludge and hard coal co-combustion in an OP-230 pulverized coal boiler. Such a solution was shown to be technically viable and not to require changes to the existing technological system. Cocombustion of sewage sludge with coal in power plants seems to be the best solution for sludge utilization in the near future in Poland.     

Reuse of sewage sludge ashes (SSA) in cement mixtures: the effect of SSA on the workability of cement mortars

The influence of sewage sludge ash (SSA) on workability of cement mortars has been studied. The irregular morphology of SSA particles produced a decrease of mortar workability. A nonlinear reduction of workability in mortars containing SSA was observed, but when SSA content in mortars was increased the workability reduction was less significant. A superplasticizer is used in order to compensate the decrease of workability produced by SSA. When SSA sized fractions were used, only significant differences in workability for mortars prepared with high water volumes or with the presence of superplasticizer were observed.     

Sewage sludge composting: Influence of initial mixtures on organic matter evolution and N availability in the final composts

The influence of bulking agents on organic matter (OM) stability and nitrogen (N) availability in sewage sludge composts was investigated. The same sludge was composted on an industrial plant with different mixtures of bulking agents. The composting process included an active phase and a curing phase, both lasting 6 weeks, separated by the screening of composts. The OM evolution was characterised by carbon (C) and N mass balances in biochemical fractions. The OM stability and N potential availability of final composts were measured during soil incubations. During composting, the C and N losses reached more than 62% of the initial C and more than 45% of the initial N, respectively, due to C mineralisation or N volatilisation and screening. The bulking materials mostly influenced OM evolution during the active phase. They contributed to the mitigation of N losses during the active phase where N immobilisation through active microbial activity was favoured by bulking agents increasing the C:N ratio of the initial mixtures. However, the influence of bulking agents on OM evolution was removed by the screening; this induced the homogenisation of compost characteristics and led to the production of sludge composts with similar organic matter characteristics, C degradability and N availability.     

High-solids anaerobic co-digestion of sewage sludge and food waste in comparison with mono digestions: Stability and performance

System stability and performance of high-solids anaerobic co-digestion of dewatered sludge (DS) and food waste (FW) in comparison with mono digestions were investigated. System stability was improved in co-digestion systems with co-substrate acting as a diluting agent to toxic chemicals like ammonia or Na⁺. For high-solids digestion of DS, the addition of FW not only improved system stability but also greatly enhanced volumetric biogas production. For high-solids digestion of FW, the addition of DS could reduce Na⁺ concentration and help maintain satisfactory stability during the conversion of FW into biogas. System performances of co-digestion systems were mainly determined by the mixing ratios of DS and FW. Biogas production and volatile solids (VSs) reduction in digestion of the co-mixture of DS and FW increased linearly with higher ratios of FW. A kinetic model, which aimed to forecast the performance of co-digestion and to assist reactor design, was developed from long-term semi-continuous experiments. Maximum VS reduction for DS and FW was estimated to be 44.3% and 90.3%, respectively, and first order constant k was found to be 0.17 d^?1 and 0.50 d^?1, respectively. Experimental data of co-digestion were in good conformity to the predictions of the model.     

Integrated drying and incineration of wet sewage sludge in combined bubbling and circulating fluidized bed units

An original integrated drying and incineration technique is proposed to dispose of sewage sludge with moisture content of about 80% in a circulating fluidized bed. This system combines a bubbling fluidized bed dryer with a circulating fluidized bed incinerator. After drying, sewage sludge with moisture less than 20% is transported directly and continuously from the fluidized bed dryer into a circulating fluidized bed incinerator. Pilot plant results showed that integrated drying and incineration is feasible in a unique single system. A 100 t/d Sewage Sludge Incineration Demonstration Project was constructed at the Qige sewage treatment plant in Hangzhou City in China. The operational performance showed that the main operation results conformed to the design values, from which it can be concluded that the scale-up of this technique is deemed both feasible and successful.     

Treatment of sludge containing nitro-aromatic compounds in reed-bed mesocosms - Water, BOD, carbon and nutrient removal

Since the mid-1970s, Sweden has been depositing 1 million ton d.w sludge/year, produced at waste water treatment plants. Due to recent legislation this practice is no longer a viable method of waste management. It is necessary to improve existing and develop new sludge management techniques and one promising alternative is the dewatering and treatment of sludge in constructed wetlands. The aim of this study was to follow reduction of organic carbon, BOD and nutrients in an industrial sludge containing nitro-aromatic compounds passing through constructed small-scale wetlands, and to investigate any toxic effect such as growth inhibition of the common reed Phragmites australis. The result showed high reduction of all tested parameters in all the outgoing water samples, which shows that constructed wetlands are suitable for carbon and nutrient removal. The results also showed that P. australis is tolerant to xenobiotics and did not appear to be affected by the toxic compounds in the sludge. The sludge residual on the top of the beds contained low levels of organic carbon and is considered non-organic and could therefore be landfilled. Using this type of secondary treatment method, the amount of sludge could be reduced by 50-70%, mainly by dewatering and biodegradation of organic compounds.     

Comparative assessment of municipal sewage sludge incineration,gasification and pyrolysis for a sustainable sludge-to-energy management in Greece

For a sustainable municipal sewage sludge management, not only the available technology, but also other parameters, such as policy regulations and socio-economic issues should be taken in account. In this study, the current status of both European and Greek Legislation on waste management, with a special insight in municipal sewage sludge, is presented. A SWOT analysis was further developed for comparison of pyrolysis with incineration and gasification and results are presented. Pyrolysis seems to be the optimal thermochemical treatment option compared to incineration and gasification. Sewage sludge pyrolysis is favorable for energy savings, material recovery and high added materials production, providing a ‘zero waste’ solution. Finally, identification of challenges and barriers for sewage sludge pyrolysis deployment in Greece was investigated.     

Stabilization of sewage sludge in the presence of nanoscale zero-valent iron (nZVI): abatement of odor and improvement of biogas production

The potential benefits of nanoscale zero-valent iron (nZVI) on sludge stabilization, either the abatement of odor or the improvement of biogas production, were investigated in this study. Two commercial-grade microscale iron powders were also utilized for comparison. Adding 0.10 wt% of nZVI in sludge during anaerobic incubation significantly reduced the concentration of H₂S in biogas by 98.0 % (96.2–98.9 %), probably attributed by reactions between sulfides and the neo-formed hydrous Fe(II)/Fe(III) oxides layer at the surface of ZVI nanoparticles. Meanwhile, the percentage of P in bioavailable fractions decreased from 76.8 to 52.5 %, possibly due to the formation of vivianite [Fe₃(PO₄)₂]. Furthermore, 0.10 wt% of nZVI in anaerobic digestion for 17 days enhanced the concentration of CH₄ in biogas by 5.1–13.2 % and improved the production of biogas and methane by 30.4 and 40.4 %, respectively. The amendment of iron nanoparticles during anaerobic digestion can not only effectively reduce H₂S in biogas, but also potentially boost methane production significantly.     

江苏省火电机组节能减排在线监测系统的开发及应用

阐述了江苏省火电机组节能减排在线监测系统的监测模型、系统架构及应用功能开发情况,分析了系统的特点及其推广应用情况。该系统以实现多种类型火电机组节能减排监管业务数据的实时在线监测为目标．基于电力调度数据网络,利用J2EE分布式多层系统应用架构技术,依据MVC模式的设计思路进行技术的选型及应用的开发,包括机组状态实时监控、统计分析等功能,已在全省270余家电厂应用,保障了脱硫（硝）电价等节能减排政策落到实处。     

Pyrolysis of mixtures of sewage sludge and manure: a comparison of the results obtained in the laboratory (semi-pilot) and in a pilot plant

A pilot-scale pyrolysis process was carried out for the treatment of a mixture of two types of waste, sewage sludge and cattle manure, comparing the results with others obtained under laboratory conditions (semi-pilot scale). The aim of this study was to obtain the energetic valorization of the products. Owing to the specific characteristics of the plant, two products were obtained from the process: gas and carbonized solid. As no liquid fraction was obtained, the gas fraction is a greater percentage made up of both condensable and non-condensable compounds, which were obtained separately at the laboratory scale. The pilot plant was designed so that the gases produced by thermolysis were burnt continuously in a combustion chamber, while the carbonized fraction was fed in batches for co-combustion. To determine composition and combustion ability, the gas and solid products from the pilot process were characterized by chromatographic analysis of the gaseous fraction and chemical analysis and programmed-temperature combustion of the carbonized solid. The composition of the combustion gases, rich in light hydrocarbons, and the carbon present in the carbonized fraction enable the energetic valorization of these products. The combustion gases were subjected to a cleaning process and their composition analysed twice: before and after the gas cleaning treatment. The study led to a positive assessment of the possible use of the process products as fuel, provided that the combustion gases are treated. As most of the sulphur and chlorine from the original waste are mainly concentrated in the solid fraction, the use of char as a fuel will depend on the effectiveness of clean-up techniques for combustion gases. During gas cleansing, neutralizing with sodium bicarbonate proved effective, especially for the acidic compounds HCl, HF and SO(2).