Removal of DEHP in composting and aeration of sewage sludge

The potential of composting and aeration to remove bis(2-ethylhexyl) phthalate (DEHP) from municipal sewage sludge was studied with two dewatered sludges: raw sludge and anaerobically digested sludge. Composting removed 58% of the DEHP content of the raw sludge and 34% of that of the anaerobically digested sludge during 85 days stabilisation in compost bins. A similar removal for the anaerobically digested sludge was achieved in a rotary drum in 28 days. Less than 1% of DEHP was removed with the compost leachate. Although DEHP removal was greater from raw sludge compost than anaerobically digested sludge compost, the total and volatile solids removals were on the same level in the two composts. In the aeration of raw sludge at 20 degrees C the DEHP removals were 33-41% and 50-62% in 7 and 28 days, respectively. Both composting and aeration are concluded to have the potential to reduce the DEHP contents typically found in sewage sludges to levels acceptable for agricultural use.     

Impact of drying and composting procedures on the concentrations of 4-nonylphenols, di-(2-ethylhexyl)phthalate and polychlorinated biphenyls in anaerobically digested sewage sludge

Enhanced treatments of sewage sludge produce a more manageable product for agricultural use by stabilizing the material, removing water, and reducing the possibility of pathogen transfer. We investigated the impact of pilot-scale composting and drying of sludge on physicochemical characteristics and on the concentrations of some organic contaminants. During the 143 day composting procedure, organic matter fell 22% and moisture by half. Concentrations of 4-nonylphenols (4-NPs) fell by 88% and di-(2-ethylhexyl) phthalate (DEHP) by 60%; losses continued throughout the procedure. Losses of total polychlorinated biphenyls (PCBs) were 11%, mostly from the lower molecular weight congeners, suggesting volatilization as the most likely loss mechanism. The drying process was much shorter, 40 days, yet organic matter content decreased by 27% and moisture by 85%. Losses of 4-NPs (39%) and DEHP (22%) were less than in composting and stopped when moisture content became constant. There were no losses of PCBs. Both treatments are simple, practical procedures that reduce the volume of waste and are applicable in situ on farms. Composting would be the method of choice for reducing organic contaminants but requires much longer times than drying.     

Leaching of heavy metals and alkylphenolic compounds from fresh and dried sewage sludge

Reusing sewage sludge as a soil fertiliser has become a common alternative to disposal. Although this practice has a few benefits, it may contribute to the medium- and long-term contamination of the trophic chain because sewage sludge may contain heavy metals and organic contaminants. As the leaching of contaminants may depend on the sludge pre-treatment, the leaching of heavy metals (Cu, Ni, Pb, Zn and Cr) and alkylphenolic compounds (APCs) (octylphenol (OP), nonylphenol (NP), nonylphenol-mono-ethoxylate (NP₁EO)) was investigated in five fresh and 40 °C dried sewage sludge samples from north-eastern Spain. FT-IR analyses and full-scan GC-MS chromatograms showed that sludge drying changed the nature of organic compounds leading to changes in their solubility. Moreover, sludge drying led to a higher relative contribution of dissolved organic carbon than the particulate organic carbon in the leachates. Leaching of Pb, Zn and Cr was below 5 % in both fresh and dried sludge samples, whereas Cu and Ni leached at rates up to 12 and 43 %, respectively, in some of the dried sludge samples. The leaching yields of OP, NP and NP₁EO ranged from 1.3 to 35 % for fresh samples, but they decreased from 0.8 to 3.4 % in dried samples. The decrease in the leachability of APCs observed in dried sludge samples might be attributed to the fact that these compounds are associated with particulate organic matter, with significantly lower concentration or even absent in dried sludge than in fresh sludge samples. Therefore, it is recommended to dry the sludge before its disposal.     

Effects of lime amendment on availability of heavy metals and maturation in sewage sludge composting

A batch composting study was performed to evaluate the feasibility of co-composting sewage sludge with lime, aiming at reducing the availability of heavy metals in the sludge compost. Sewage sludge with sawdust as bulking agent was amended with lime at 0, 0.63, 1.0, and 1.63% w/w, and composted for 100 days in laboratory batch reactors. The changes in temperature, pH, electrical conductivity (EC), and extractable heavy metal contents were measured while compost maturity was determined by C/N(organic) and cress seed germination during the composting period. Liming raised pH of compost effectively at the initial stage of composting and caused a decrease in EC through precipitation of soluble ions. Lime amendment also significantly reduced water-soluble and Diethylene triamine pentracetic acid (DTPA)-extractable metal contents. The maximum reductions were 60 and 40% for Cu, 80 and 40% for Mn, 55 and 10% for Zn, and 20 and 25% for Ni at the end of the composting period for the lime-amended sludge as compared to the control. In spite of the inhibitory effect of lime amendment on the decomposition activity of sewage sludge, all treatments reached maturation after 63 days of composting as indicated by the results of C/N(organic) ratio and cress seed germination test results. A lime amendment of < or =1.0% is recommended to co-compost with sewage sludge.     

湿污泥在流化床中干燥特性

在鼓泡流化床干燥器内,床料采用0～1 mm的石英砂,以热空气作为干燥介质,对城市污水污泥的流态化干燥特性进行实验研究。通过控制送风温度、流化风量、加料量、污泥粒径等参数,研究在不同工况条件下床温以及干污泥含水率的变化情况。结果表明,随着送风温度的升高,床温升高,干污泥含水率下降,最终趋向于一个稳定值8%。床温随流化风量的增加先是减小而后升高,干污泥的含水率随流化风量的增加先是降低而后增大。当加料量从11 kg/h增加到13kg/h时,干污泥的含水率基本没有变化,当加料量超过13 kg/h时,干污泥的含水率从8.1%开始呈递增趋势。随污泥粒径的增大,床温升高,干污泥含水率也随之升高。     

Utilization of urban sewage sludge: Chinese perspectives

Purpose

Urbanization and industrialization in China has resulted in a dramatic increase in the volume of wastewater and sewage sludge produced from wastewater treatment plants. Problems associated with sewage sludge have attracted increasing attention from the public and urban planners. How to manage sludge in an economically and environmentally acceptable manner is one of the critical issues that modern societies are facing.

Methods

Sludge treatment systems consist of thickening, dewatering, and several different alternative main treatments (anaerobic digestion, aerobic digestion, drying, composting, and incineration). Agricultural application, landfill, and incineration are the principal disposal methods for sewage sludge in China. However, sewage sludge disposal in the future should focus on resource recovery, reducing environmental impacts and saving economic costs.

Results

The reuse of biosolids in all scenarios can be environmentally beneficial and cost-effective. Anaerobic digestion followed by land application is the preferable options due to low economic and energy costs and material reuse.

Conclusion

It is necessary to formulate a standard suitable for the utilization of sewage sludge in China.     

Speciation of heavy metals during co-composting of sewage sludge with lime

During composting the humification of organic matter will have a significant effect on the physicochemical form of existence of heavy metals. Therefore the present study was conducted to investigate the effect of co-composting sewage sludge with lime on heavy metal speciation and the changes in DTPA extractable metals. Metal speciation was conducted to evaluate the redistribution of Cu, Mn, Ni, Pb and Zn in sewage sludge composted with lime. Sewage sludge was mixed with sawdust in 2:1 (w/w fresh weight) and then composted with lime at 0%, 0.63%, 1% or 1.63% (dry weight) for 100 days. The lime addition did not cause any changes in the different forms of Cu and Mn, but the composting process caused transformations of residual form of Cu and Mn into oxidizable and reducible form, respectively. For Ni, the reducible form was mainly transformed into residual form and lime addition decreased this transformation. Major transformation of different forms of Pb was not found, however the residual form of Pb increased with lime addition. The predominant residual form of Zn was mainly transformed into oxidizable form and the lime addition reduced this transformation. Addition of lime to sewage sludge during composting resulted in lower DTPA extractable metal contents. Therefore, lime is a suitable material to co-compost with sewage sludge to reduce the availability of heavy metals.     

电渗透脱水对污泥热干燥特性的影响

以污水厂机械脱水后的污泥作为研究对象,提出了采用电渗透-热干燥结合进行深度脱水的方法。通过对原泥以及电渗透脱水至不同含水率(67%、71%和76%)的污泥在热干燥过程中含水率和干燥速率的测定,分析电渗透脱水对污泥热干燥特性的改善规律。结果表明,经电渗透脱水至含水率为67%和71%的污泥在热干燥过程中的传热传质速率及干燥速率有明显提高,且干燥温度越高,电渗透后污泥的干燥速率与原泥的干燥速率差距越大。相同电压梯度及相同温度下电渗透至67%后进行热干燥耗能最少。实际应用中应结合能耗分析选择合适的电渗透程度及干燥温度,以达到最优效果。     

调理剂对堆肥产品重金属生物有效性的影响

城市污泥中重金属含量及其生物有效性是限制污泥农用的主要因素,因此,研究污泥堆肥化处理过程中重金属生物有效性,对污泥的农用具有重要意义。实验以城市污泥为原料,以菌菇渣和秸秆为调理剂,设置4个处理:A(污泥∶菌菇渣∶秸秆=1∶0.4∶0.025)、B(污泥∶菌菇渣∶秸秆=1∶0.3∶0.025)、C(污泥∶秸秆=1∶0.12)和D(污泥∶秸秆=1∶0.09),进行好氧堆肥实验,采用BCR顺序提取法测定各种形态的重金属,研究堆肥前后重金属形态的变化规律。结果表明,城市污泥中Cu、Ni、Pb和Cr主要以可氧化态及残渣态存在,生物有效性较低,而Zn和Cd主要以酸溶态和可还原态存在,生物有效性较高;堆肥过程显著降低了Cu、Zn、Ni和Pb的生物有效性,并改变了Cu、Zn、Ni、Pb、Cr和Cd的形态分布,使污泥中的Cu、Zn、Ni、Pb和Cd向着更稳定的可氧化态或残渣态转变;污泥经过堆肥处理后,Cu、Zn和Ni 3种重金属生物有效性关系为:ABCD,与其他处理相比,处理A残渣态的Pb和Cr增加比例较多,综合来看,处理A对重金属生物有效性的降低最为明显,重金属钝化效果最佳。     

城市污水污泥处置方式的温室气体排放比较分析

针对我国现在主流的城市污水污泥处置方法:填埋,焚烧,堆肥。用IPCC中推荐的方法和缺省值,对处置过程中产生的温室气体的直接排放、间接排放和替代排放做了计算和分析。填埋过程计算排放的温室气体有CH4,焚烧过程计算排放的有温室气体CO2和N2O,堆肥过程计算的排放的有温室气体CO2和N2O,最终比较的结果都折算成CO2的排放。结果表明,污泥填埋、焚烧、堆肥所产生的CO2的净排放量分别为695.847 kg CO2/t、443.643 kg CO2/t、511.817 kgCO2/t。由于考虑了堆肥以后的有机肥利用,从减排以及污泥资源化的角度分析,得出堆肥是相对好的污泥处置方式。     

城市污水厂污泥的浸泡油炸

提出了一种利用餐厨废油为热交换介质，在常压下对城市污水厂污泥进行油炸干化制成固体燃料，以实现城镇两大废弃物一污泥和餐厨废油综合处置的方法。以大豆油模拟餐厨废油，研究了污泥油炸干燥特性及过程影响参数。实验结果表明，污泥经油炸干化后，干基含水率从初始的4．56kg／kg降低至0．05kg／kg，干基含油率升为0．37～0．47kg／kg，干污泥热值达到21．551～24．082MJ／kg，是一种高热值固体燃料。油温对污泥油炸干化过程影响显著，当油温从120℃升至180℃时，污泥干燥时间从28min缩短至4min。实验条件下，1t餐厨废油可处理约8．3t湿污泥。     

污泥好氧堆肥预处理混合破碎机实验研究

针对污泥高温好氧堆肥技术对粒径和含水率的要求,研制开发出了污泥混合破碎机。该破碎机采用螺旋式布置弯刀,实现污泥和辅料(包括熟料和平菇渣)的混合、破碎和输送三重功能,并能连续作业。实验表明:通过调节污泥与辅料的混合比,可以满足堆肥所需的混合料粒径(20 mm)和含水率(60%左右)要求;采用V熟:V平=1∶1作辅料,破碎机污泥处理量小于7 t/h时,满足粒径和含水率要求所需的污泥/辅料体积比R为1∶(2.5~3.5);分别采用平菇渣和熟料作辅料,结果表明,与污泥混合后都可以满足堆肥要求;平菇渣起到膨松作用,需要的量相对少。     

Sequential extraction of heavy metals during composting of sewage sludge

The major limitation of soil application of sewage sludge compost is the total heavy metal contents and their bioavailability to the soil-plant system. This study was conducted to determine the heavy metal speciation and the influence of changing the physico-chemical properties of the medium in the course of composting on the concentrations, bioavailability or chemical forms of Cu, Zn, Pb and Ni in sewage sludge. Principal physical and chemical properties and FTIR spectroscopical characterization of sludge compost during treatment show the stability and maturity of end product. The total metal contents in the final compost were much lower than the limit values of composts to be used as good soil fertilizer. Furthermore, it was observed by using a sequential extraction procedure in sludge compost at different steps of treatment, that a large proportion of the heavy metals were associated to the residual fraction (70-80%) and more resistant fractions to extraction X-NaOH, X-EDTA, X-HNO3 (12-29%). Less than 2% of metals bound to bioavailable fractions X-(KNO3+H2O). Heavy metal distribution and bioavailability show some changes during composting depending on the metal itself and the physico-chemical properties of the medium. Bioavailable fractions of all elements tend to decrease except Ni-H2O. Zn and mainly Cu present more affinity to organic and carbonate fractions. In contrast, Pb is usually preferentially bound to sulfide forms X-HNO3. Nickel shows a significant decrease of organic form. Significant degrees of correlation were found between heavy metal fractions and changes of some selected variables (e.g. pH, ash, organic matter, humic substance) during the course of composting. Mobile fractions of metals are poorly predictable from the total content. The R2 value was significantly increased by the inclusion of other variables such as the amount of organic matter (OM) and pH.     

Changes of polycyclic aromatic hydrocarbons during composting of sewage sludges with chosen physico-chemical properties and PAHs content

The aim of the experiment was to determine changes in the PAH content during sewage sludge composting. The extent was evaluated to which sewage sludge properties influences on PAHs losses during composting. Five municipal sewage sludges were studied from sewage treatment plants located in the south-east of Poland, i.e. in Stalowa Wola, Kra?nik, Lublin, Zamo?? and Bi?goraj. The treatment plants selected were characterised by their differentiation with catchments area as well as the industrial character of the areas. Sludge composting was carried out in aerobic conditions in plastic containers for a period of 76 days. The content of 14 polycyclic aromatic hydrocarbons (PAHs) and some physical-chemical (TOC, Nt, TOC/Nt, CEC, BS, TEB, pH, available potassium and phosphorus, total forms of cations) sewage sludge properties were monitored. In the present study correlations between PAHs losses (during various phases of composting) and physical-chemical properties of sewage sludges and composts were also evaluated. The sewage sludges were characterised both by differentiated properties and by PAH content. The total PAH content (the sum of 14 PAHs from the EPA List with exception of naphthalene and acenaphthene) in the sludges ranged from 3674 to 11236 microg kg(-1). Four- and three-ring compounds were predominant in the sewage sludges. Almost all of the sludges were characterised by differentiated content levels of both individual PAHs groups and PAHs sum. After 76 days of composting, a significant lowering of the PAH content was observed in all sludges as compared to the beginning of the experiment. The range of total observed PAH losses was from 15.8% to 48.6%, depending on the sewage sludge. The largest lowering of the PAH content was observed in the sludge with the lowest concentration of the xenobiotics studied. The largest losses in individual PAHs were observed in the case of five- and six-rings compounds, and were probably related to strong pollutant binding by other components of the sewage sludge. The few significant relationships showed that PAH losses during composting were only slightly determined by the analysed physical-chemical properties.     

Evolution of heavy metal speciation during the aerobic composting process of sewage sludge

The contents of heavy metals and their bioavailability to the soil-plant system were the major limitation to the application of sewage sludge compost in soil. This study was conducted to determine the evolution of heavy metal speciation in the course of an aerobic composting, and investigate the influence of changes of composting process parameters including pH, temperature and organic matter (OM) content on distribution of heavy metal speciation in composted sludge. The sequential extraction procedure developed by Tessier et al. was used in sludge compost to determine the heavy metal speciation. Results showed that, during composting, (1) the contents of the residue fraction for Pb, Zn and Cd were decreased but those for Ni and Cr were increased; the Cu residue fraction was almost constant; (2) the contents of the total mobile fractions (including fractions 1-4) for Zn and Pb were significantly increased, but the increase of those for Cu and Ni were not so remarkable; (3) there were significant degrees of correlation between heavy metal fractions and changes of some selected parameters (for example, pH, composting temperature, and OM content). Only the content of the total mobile fractions for Cu could be predictable from its total content. For the prediction of the total mobile fractions of Zn, Ni, Cd and Cr, the R(2) value was significantly increased by the inclusion of other variables such as pH, temperature and OM content.     

Investigation of potentially bioavailable and sequestrated forms of polycyclic aromatic hydrocarbons during sewage sludge composting

The present study focuses on the influence of the composting process on the formation of potentially bioavailable and sequestrated PAH fractions. The potentially bioavailable fraction was determined by means of a mild-solvent extraction (with n-butanol). The total and potentially bioavailable PAH content was evaluated in the consecutive composting stages, i.e. at the onset of the experiment, after the stabilization phase (on the 35th day), and after the maturation phase (on the 76th day). Four municipal sewage sludges with differentiated PAH content were selected for the present experiment. Eleven PAHs from the US EPA list (with exception of naphthalene, acenaphthylene, acenaphtene, fluorene and benz[ah]anthracene) were determined for the purpose of this experiment. The content of the total PAHs ranged from 3052 to 10352microg kg(-1). The share of the potentially bioavailable fraction was at a similar level in the sludge samples tested and ranged from 75% to 81%. Greater differences were noted in the share of the bioavailable fraction in the case of individual PAH groups. The influence of the composting process on the contribution of the potentially bioavailable fraction of the PAH clearly depended on the stage of the experiment and sewage sludge type. However, in the case of all sludges, a lowering of the bioavailable fraction by 19-52% as compared to the level at the outset of the experiment was observed. During the first phase (stabilization) of the sewage sludge composting process, a reduction of the PAH content took place mainly at the expense of potentially bioavailable fraction, whereas in the second phase (maturation), sequestration processes predominated. The above phenomenon was most clearly visible for the 6-rings PAHs.     

污水处理厂污泥干化焚烧处理可行性分析

以绍兴污水处理厂脱水污泥为研究对象,通过实验分析了污泥进行干化焚烧处理的可行性。对污泥泥质进行分析,采用桨叶式污泥干化机对污泥的热干化特性、干化过程污染排放特性进行研究,使用流化床污泥焚烧试验装置对污泥焚烧工况及焚烧过程中污染物的排放特征进行研究,结果表明,绍兴污水处理厂脱水污泥的泥质特征与大多数污水污泥类似,灰分较高、发热量较低,需干化后才可实现稳定燃烧;污泥在小型桨叶式污泥干化机内的干化速率最高达到0.6kg/(m2·min),并随污泥干化的进行而逐渐降低;干化过程产生的常规污染气体中氨气浓度最高,可达170 mg/Nm3;污泥干化冷凝水的COD高达820 mg/L,氨氮等指标也很高。污泥干化系统的设计需充分考虑污泥热干化过程中气体和液体污染物的排放,设置相应的处理设施。污泥干化至含水率30%时,可在不投加辅助燃料的情况下实现流化床焚烧炉内的焚烧处理,干化污泥焚烧时需关注烟气中常规污染气体和重金属的控制,焚烧灰渣浸出毒性未超过国标限值。     

城市污泥桨叶式干化优化实验研究

桨叶式干化是一种高效的污泥干化处理技术，为了降低污泥含水率达到污泥减量减容效果，同时为后期的工程化应用提供依据和参考，实验采用倾斜盘式桨叶干燥机，以北京市污水处理厂污泥为研究对象，研究了不同滞留时间、污泥供给量、干燥机换热面积等因素对桨叶式干化处理后蒸发速度和污泥含水率的影响，并从处理效率以及与工程化应用数据对比分析等多方面考核，确定最佳工艺运行条件：使用0．5—0．8MPa的蒸气，蒸发速率达到14～21．8kg／（m^2·h）时，干化处理后污泥含水率〈40％。     

城市污泥微波干化工艺及干化特性研究

采用微波和烘箱结合及全程烘箱2种方式对城市污泥干化进行对比研究,考察了不同粒径、微波干化预处理、预处理时间及烘箱温度对污泥干燥特性的影响。结果表明,同一温度条件下,微波预处理时间越长,污泥干化速率越快。最优条件下,全程烘箱污泥达到最大干化速率的含水率为77%。微波干燥污泥具有时间短、干燥速率大的特点,微波和烘箱结合对比全程烘箱干化速率高且能耗低。     

Phosphorus release from ash, dried sludge and sludge residue from supercritical water oxidation by acid or base

Leaching of ash and dried sewage sludge were investigated and compared with the leaching results of sludge residue from supercritical water oxidation (SCWO). This article focuses on how the composition of ash and sludge residues influences the extraction of phosphate and heavy metals and if different treatment temperatures of the sludge effect the leachability. Results showed that acid leaching gave a higher release of phosphate than alkaline leaching for all ash and sludge residue samples. Also, alkaline leaching dissolved phosphate with a lower metal contamination than acid leaching. Furthermore, it was found that iron had a low release at both alkaline and acid leaching from ash and from SCWO residue. The difference in composition of ash and sludge residue samples had no significant influence on release of phosphate at high concentrations of acid. Phosphate release from ash, dried sludge at 300 degrees C and SCWO residue showed similar results at 1M acid leaching. However, it seems to be easier to release phosphate from the SCWO residue than from the ash at low acid concentrations. SCWO residue showed higher release than the other ashes at 0.5M HCl. Results for alkaline leaching showed higher release from ash at 1M NaOH than from SCWO residue or from dried sludge at 300 degrees C. The leaching of phosphate from dried sludge seems to be temperature dependent, as the dried sludge treated at higher temperature showed less release of phosphate. It was found that the pre-treatment of the ash may be important for better release of phosphate.