Organic Contaminants from Sewage Sludge Applied to Agricultural Soils. False Alarm Regarding Possible Problems for Food Safety? (8 pp)

Goal, Scope and Background Sewage sludge produced in wastewater treatment contains large amounts of organic matter and nutrients and could, therefore, be suitable as fertiliser. However, with the sludge, besides heavy metals and pathogenic bacteria, a variety of organic contaminants can be added to agricultural fields. Whether the organic contaminants from the sludge can have adverse effects on human health and wildlife if these compounds enter the food chain or groundwater still remains a point of controversial discussion. Main Features This paper presents an overview on the present situation in Europe and a summary of some recent results on the possible uptake of organic contaminants by crops after addition to agricultural fields by sewage sludge. Results Greenhouse experiments and field trials were performed to study the degradation and uptake of organic micro-contaminants in sludge-amended agricultural soil in crops, such as barley and carrots grown in agricultural soil amended with anaerobically-treated sewage sludge from a wastewater treatment plant, but studies hitherto have revealed no immediate risks. Common sludge contaminants such as linear alkylbenzene sulphonates (LAS), nonylphenol ethoxylates (NPE), polycyclic aromatic hydrocarbons (PAH), bis(diethylhexyl) phthalate (DEHP), showed neither accumulation in soil nor uptake in plants. Discussion It is assumed that the annual amount of sewage sludge produced in Europe will increase in the future, mainly due to larger amounts of high quality drinking water needed by an increasing population and due to increasing demands for cleaner sewage water. Application of sewage sludge to agricultural soils is sustainable and economical due to nutrient cycling and disposal of sewage sludge. However, this solution also involves risks with respect to the occurrence of organic contaminants and other potentially harmful contents such as pathogens and heavy metals present in the sludge. There have been concerns that organic contaminants may accumulate in the soil, be taken up by plants and thereby transferred to humans via the food chain. Results obtained so far revealed, however, no immediate risk of accumulation of common organic sludge contaminants in soil or uptake in plants when applying sewage sludge to agricultural soil. With very high dosages of sewage sludge, there may be a risk for accumulation of very apolar contaminants, such as DEHP, to the soil. Conclusions Any conclusions on the safe use of sewage sludge in agriculture have to be drawn carefully, as the studies performed until now have been limited. Further studies are required, and before final statements can be drawn, it is imminent to study a larger variety of common crops and the effect sewage sludge application may have on a possible accumulation of organic contaminants in the crops. Furthermore, a larger variety of organic contaminants need to be studied and special focus should be given to contaminants newly introduced into the environment. Besides investigating possible plant uptake of organic contaminants, the fate of these compounds in soil after sludge application need to be monitored too. Here, special attention has to begiven to studies on degradation and the formation of degradation products, to weathering and to leaching effects on groundwater, to the application of different crops on the same field (crop rotation), to the use of full-width tillage and strip tillage, and to long term application of sewage sludge on the soil. Recommendations and Perspectives There are environmental, political as well as economical incentives to increase the agricultural application of sludge. However, such usage should be performed with care as there are also ways in which sludge fertilisation could harm the environment and human health. Recently, a new European COST Action (859) has been established covering the field of food safety and improved food quality. Part of the Action is dealing with the application of sewage sludge in agriculture. Before any political and economical measures can be taken, the pros and cons have to be sufficiently investigated on a scientific level first. ESS-Submission Editor: Prof. Elena Maestri (elena.maestri@unipr.it)     

The importance of pathogenic organisms in sewage and sewage sludge.

Deficient sanitation poses a serious threat to human and animal health, involving complex relationships between environments, animals, refuse, food, pathogens, parasites, and man. However, by sanitizing and stabilizing the organic matter of sewage sludge, agriculture can utilize it to maintain soil, water, and air quality. As ingredients in soil amendments, such bioresidues are a source of nutrients for plants. Stabilization and sanitation of sewage sludge safely couple its recycling and disposal. This coupling becomes increasingly important as economic and environmental constraints make strategies for waste disposal more difficult to apply. The occurrence of viruses, bacteria, yeasts, fungi, and zooparasites in sewage sludge is reviewed in this article, and consequential epidemiologic concerns that arise from sewage sludge recycling is also addressed.     

城市污水污泥固结体重金属浸出毒性及路用性能研究

城市污水污泥的重金属离子Pb、Zn超过国家固体废弃物排放最高允许值,属于危险废物。污水污泥的最佳出路是无害化处理,资源化利用,产业化发展。研究了以上海市污水污泥为原料,加入一定比例的固化剂和矿物掺合料使之固结,经养护满足路用强度性能,测试其固结体重金属离子浸出质量浓度亦满足国家固体废弃物排放标准,即污泥中的重金属离子得到有效的束缚和稳定固化,既解决了环境问题,又为污泥产业化发展开辟了新的途径。     

Revegetation of lagoon ash using the legume species Acacia auriculiformis and Leucaena leucocephala

A greenhouse study was conducted to evaluate the potential use of two legume species, Acacia auriculiformis and Leucaena leucocephala for growth on ameliorated lagoon ash with or without nitrogen (N(2))-fixing bacteria inoculation. Even though amendments of 30% (w/w) vermiculite or with sewage sludge compost were added to improve the chemical and physical limitations of lagoon ash, significant suppressions in biomass and plant nutrient content were found with ameliorated lagoon ash in comparison to an agricultural soil. The high proportion of clay-sized (<53 microm) ash particles limited root growth. In addition, heavy metal toxicity was a possible factor contributing to poor seedling growth. Higher plant productivity resulted from the sewage sludge compost-amended lagoon ash than with vermiculite due to a greater contribution of plant nutrients in the compost. Nodulation was inhibited in ameliorated lagoon ash but not in agricultural soil. High pH and electrical conductivity and elevated toxic metals may be important parameters that limit bacterial activity. Both species showed potential to establish on amended lagoon ash, with Acacia auriculiformis being the best adapted.     

Examining farmland applications of composted biosolid wastes depending on nutrient balance in soils

This study emphasizes nutrient balance of soils in the farmland application of composted biosolid wastes. The loading rates of plant nutrients following the compost application to farmland in Japan were estimated and compared with the nutrient uptake of agricultural plants. Results show that the current compost application in Japan can meet the requirements of agricultural plants for plant nutrient Ca, except for K, Mg, P, Fe, Mn, Cu, and Zn. The compost application could realize the safe disposal of biosolid wastes and the effective recycling of plant nutrients in composts to soils without causing heavy metal accumulation. The application manner of composts affects the heavy metal accumulation in farmlands. Field examination indicates that the excessive compost application has led to the heavy metal accumulation in compost-amended farmlands. Measuring the nutrient balance in compost-amended farmlands is well suitable for explaining the accumulation of heavy metals, such as Cu and Zn.     

典型危险废物的工程力学特性

掌握填埋废物的工程力学特性是确保危险废物填埋堆体稳定性的重要前提条件,因此,针对6种典型危险废物的工程力学特性开展了调查研究.研究结果表明,污泥类危险废物的含水率和有机质含量远高于非污泥类危险废物,而前者的比重则显著低于后者.污泥类危险废物的渗透系数相对较小,比污染土壤和飞灰炉渣混合物的渗透系数小1个数量级,比滤池填料的渗透系数小2个数量级.不同危险废物的无侧限抗压强度排序为:飞灰炉渣混合物(314.3 kPa)和滤池填料(278.9 kPa)＞污染土壤(124.9 kPa)＞杭州氧气厂污泥(68.6 kPa)、锌铬污泥(71.4 kPa)、油泥(58.4 kPa).不同危险废物的粘聚力排序为:飞灰炉渣混合物(40.8 kPa)、滤池填料(31.1 kPa)＞污染土壤(20.9 kPa)＞杭州氧气厂污泥(1.94kPa)、锌铬污泥(3.10 kPa)、油泥(1.81 kPa).此外,不同危险废物的内摩擦角差异相对较小,其变化范围在18.8°～35.0°之间.综合分析可知,飞灰炉渣混合物和滤池填料的工程力学特性较好,而污泥类危险废物的工程力学特性则较差.     

几种模拟处理方式污泥淋出液重金属与养分特征

为了减少城市污泥重金属对农田的污染,更好地实现污泥农业资源化利用,通过盆栽实验研究不同处理(对照、黑网、附Fe黑网、附Fe黑网+K2SO4及附Fe黑网+玉米)对城市污泥淋出液重金属和养分含量等的影响。结果表明,黑网可降低污泥淋出液的Zn﹑Cd总量,且没有减少污泥淋出液中氮、磷和钾的总量。Fe(OH)3可使淋出液中Zn总量降低,但同时也显著减少了淋出液中的磷总量。K2SO4可降低淋出液中的Cu总量,且促进Fe结合磷的释放。玉米的种植可使污泥的总重降低,同时玉米籽粒和茎叶重金属含量达到饲料标准。综合来看,任何处理每次淋出液的Cu、Zn、Pb、Cd浓度均符合农田灌溉水标准,淋出液氮、磷、钾量占原污泥中氮、磷、钾总量的比例(0.98%～9.88%)远远大于重金属元素(Cu,Zn,Pb,Cd)占原污泥对应重金属总量的比例(0.04%～0.41%),污泥淋出液作为农田灌溉水进行肥水利用将是污泥农业资源化利用的适合途径,同时黑网+玉米处理可能是较理想的污泥综合处理利用方式。     

Phytoavailability and Fractions of Iron and Manganese in Calcareous Soil Amended with Composted Urban Wastes

Little is known about the effects of applying composted urban wastes on the phytoavailability and distribution of iron (Fe) and manganese (Mn) among chemical fractions in soil. In order to study this concern several experiments in pots containing calcareous soil were carried out. The received treatments by adding separately two rates (20 and 80 Mg ha^?1) of municipal solid waste (MSW) compost and/or municipal solid waste and sewage sludge (MSW-SS) co-compost. The cropping sequence was a lettuce crop followed by a barley crop. It was observed that treatments amended with composted urban wastes tended to promote slight increases in lettuce yield compared to the control. The highest Fe levels in lettuce were found when higher rates of MSW-SS co-compost were applied; these values were significant compared to those obtained in the other treatments. In all cases, the application of organic materials increased the concentration and uptake of Mn in lettuce compared to the control; however, these increases were significant only when higher rates of MSW compost were applied. The organic amendments had beneficial delayed effects on barley yields, showing, in most cases, significant increases compared to the control. In this context, treatments with MSW compost were found to be more effective than the equivalent treatments amended with MSW-SS co-compost. Compared to the control, composted urban wastes increased Fe concentration in straw and rachis, and decreased Fe concentration in barley grain. Similarly, a decreased concentration of Mn in the dry matter of barley crop grown in soils treated with composted urban wastes was observed.     

Cumulative and Residual Effects of Repeated Sewage Sludge Applications: Forage Productivity and Soil Quality Implications in South Florida,USA (9 pp)

Background, Aim and Scope The cow-calf (Bos taurus) industry in subtropical United States and other parts of the world depends almost totally on grazed pastures. Establishment of complete, uniform stand of bahiagrass (BG) in a short time period is important economically. Failure to obtain a good BG stand early means increased encroachment of weeds and the loss of not only the initial investment costs, but production and its cash value. Forage production often requires significant inputs of lime, N fertilizer, and less frequently of P and K fertilizers. Domestic sewage sludge or biosolids, composted urban plant debris, waste lime, phosphogypsum, and dredged materials are examples of materials that can be used for fertilizing and liming pastures. Perennial grass can be a good choice for repeated applications of sewage sludge. Although sewage sludge supply some essential plant nutrients and provide soil property-enhancing organic matter, land-application programs still generate some concerns because of possible health and environmental risks involved. The objectives of this study were to evaluate the cumulative and residual effects of repeated applications of sewage sludge on (i) bahiagrass (BG, Paspalum notatum Flügge) production over years with (1997–2000) and without (2001–2002) sewage sludge applications during a 5-yr period, and (ii) on nutrients status of soil that received annual application of sewage sludge from 1997 to 2000 compared with test values of soils in 2002 (with no sewage sludge application) in South Florida.Methods The field experiment was conducted at the University of Florida Agricultural Research and Education Center, Ona, FL (27o26’N, 82o55’W) on a Pomona fine sandy soil. With the exception of the control, BG plots received annual sewage sludge and chemical fertilizers applications to supply 90 or 180 kg total N ha–1 yr–1 from 1997 to 2000. Land application of sewage sludge and fertilizer ceased in 2001 season. In early April 1998, 1999, and 2000, plots were mowed to 5-cm stubble and treated with the respective N source amendments. The experimental design was three randomized complete blocks with nine N-source treatments: ammonium nitrate (AMN), slurry biosolids of pH 7 (SBS7), slurry biosolids of pH 11 (SBS11), lime-stabilized cake biosolids (CBS), each applied to supply 90 or 180 kg N ha–1, and a nonfertilized control (Control). Application rates of sewage sludge were calculated based on the concentration of total solids in materials as determined by the American Public Health Association SM 2540G method and N in solids. The actual amount of sewage sludge applications was based on the amount required to supply 90 and 180 kg N ha–1. Sewage sludge materials were weighed in buckets and uniformly applied to respective BG plots. Soil samples were collected in June 1997, June 1999, and in June 2002 from 27 treatment plots. In 1997 and 1999, soil samples were collected using a steel bucket type auger from the 0- to 20-, 20- to 40-, 40- to 60-, and 60- to 100-cm soil depths. Forage was harvested on 139, 203, 257, and 307 day of year (DOY) in 1998; 125, 202, 257, and 286 DOY in 1999; 179, 209, 270, and 301 DOY in 2000; and on 156 and 230 DOY in 2002 (no sewage sludge applications) to determine the residual effect of applied sewage sludge following repeated application. Forage yield and soils data were analyzed using analysis of variance (PROC ANOVA) procedures with year and treatment as the main plot and sub-plot, respectively. As a result of significant year effects on forage yield, data were reanalyzed annually (i.e., 1998, 1999, 2000, and 2002).Results and Discussion All sewage sludges used in this study were of class B in terms of USEPA’s pathogens and pollutant concentration limit. Pathogen and chemical composition of the class B sewage sludge that were used in the study were all in compliance with the USEPA guidelines. The liquid sludge (SBS11) had the lowest fecal coliform counts (0.2 x 106 CFU kg–1) while the cake sewage sludge (CBS) had the greatest coliform counts of 178 x 106 CFU kg–1. The fecal coliform counts for SBS7 was about 33 x 106 CFU kg–1. Average soil test values in June 2002 exhibited: i) decrease in TIN (NO3-N + NH4-N), TP, K, Ca, Mg, Mn, and Fe; and ii) slight increase in Zn and Cu when compared with the June 1997 soil test results. The overall decrease in soil test values in 2002 might be associated with nutrient cycling and plant consumption. Although the average BG forage yield in 2002 (2.3 ± 0.7 Mg ha–1) was slightly lower than in 2000 (3.5 ± 1.2 Mg ha–1), yield differences in 2002 between the control (1.2 + 0.2 Mg ha–1) and treated plots (2.3 ± 0.5 Mg ha–1 to 3.3 ± 0.6 Mg ha–1) were indicative of a positive residual effect of applied sewage sludge. This study has shown that excessive build up of plant nutrients may not occur in beef cattle pastures that repeatedly received sewage sludge while favoring long-term increased forage yield of BG. All sources of N (sewage sludge and AMN) gave better forage production than the unfertilized control during years with sewage sludge application (1997–2000) and also during years with no sewage sludge application (2001–2002). The favorable residual effects of applied sewage sludge in 2002 may have had received additional boost from the amount of rainfall in the area.Conclusions Repeated applications of sewage sludge indicate no harmful effects on soil quality and forage quality. Our results support our hypothesis that repeated land application of sewage sludge to supply 90 and 180 kg N ha–1 would not increase soil sorption for nutrients and trace metals. Results have indicated that the concentrations of soil TIN and TP declined by almost 50% in plots with different nitrogen sources from June 1997 to June 2002 suggesting that enrichment of nitrogen and phosphorus is insignificant. The concentrations of soil nitrogen and phosphorus in 2002 following repeated application of sewage sludge were far below the contamination risk in the environment. The residual effect of these sewage sludge over the long term can be especially significant in many areas of Florida where only 50% of the 1 million ha of BG pastures are given inorganic nitrogen yearly.Recommendation and Outlook Successive land application of sewage sludge for at least three years followed by no sewage sludge application for at least two years may well be a good practice economically because it will boost and/or maintain sustainable forage productivity and at the same time minimize probable accumulation of nutrients, especially trace metals. Consecutive applications of sewage sludge may result in build up of some trace metals in some other states with initial high metallic content, but in this study, no detrimental effects on soil chemical properties were detected. The possibilities for economically sound application strategies are encouraging, but more and additional research is required to find optimal timing and rates that minimizes negative impacts on soil quality in particular or the environment in general. For proper utilization of sewage sludge, knowledge of the sewage sludges’ composition, the crop receiving it, are absolutely crucial, so that satisfactory types and rates are applied in an environmentally safe manner. There is still much to be learned from this study and this investigation needs to continue to determine whether the agricultural and ecological objectives are satisfied over the longer term.     

Phytoavailability and fractions of iron and manganese in calcareous soil amended with composted urban wastes

Little is known about the effects of applying composted urban wastes on the phytoavailability and distribution of iron (Fe) and manganese (Mn) among chemical fractions in soil. In order to study this concern several experiments in pots containing calcareous soil were carried out. The received treatments by adding separately two rates (20 and 80 Mg ha-1) of municipal solid waste (MSW) compost and/or municipal solid waste and sewage sludge (MSW-SS) co-compost. The cropping sequence was a lettuce crop followed by a barley crop. It was observed that treatments amended with composted urban wastes tended to promote slight increases in lettuce yield compared to the control. The highest Fe levels in lettuce were found when higher rates of MSW-SS co-compost were applied; these values were significant compared to those obtained in the other treatments. In all cases, the application of organic materials increased the concentration and uptake of Mn in lettuce compared to the control; however, these increases were significant only when higher rates of MSW compost were applied. The organic amendments had beneficial delayed effects on barley yields, showing, in most cases, significant increases compared to the control. In this context, treatments with MSW compost were found to be more effective than the equivalent treatments amended with MSW-SS co-compost. Compared to the control, composted urban wastes increased Fe concentration in straw and rachis, and decreased Fe concentration in barley grain. Similarly, a decreased concentration of Mn in the dry matter of barley crop grown in soils treated with composted urban wastes was observed.     

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.     

Fecal sludge management in developing urban centers: a review on the collection,treatment, and composting

The problems posed by fecal sludge (FS) are multidimensional because most cities rapidly urbanize, which results in the increase in population, urban settlement, and waste generation. Issues concerning health and waste treatment have continued to create alarming situations. These issues had indeed interfered with the proper steps in managing FS, which contaminates the environment. FS can be used in agriculture as fertilizer because it is an excellent source of nutrients. The recent decline in crop production due to loss of soil organic component, erosion, and nutrient runoff has generated interest in the recycling of FS into soil nutrients through stabilization and composting. However, human feces are considerably liable to spread microorganisms to other persons. Thus, sanitation, stabilization, and composting should be the main objectives of FS treatment to minimize the risk to public and environmental health. This review presents an improved FS management (FSM) and technology option for soil amendment that is grouped into three headings, namely, (1) collection, (2) treatment, and (3) composting. On the basis of the literature review, the main problems associated with the collection and treatment of FS, such as inadequate tools and improper treatment processes, are summarized, and the trends and challenges that concern the applicability of each of the technologies in developing urban centers are critically reviewed. Stabilization during pretreatment before composting is suggested as the best method to reduce pathogens in FS. Results are precisely intended to be used as a support for decisions on policies and strategies for FSM and investments for improved treatment facilities.     

Emission characteristics for co-combustion of leather wastes,sewage sludge,and coal in a laboratory-scale entrained flow tube furnace

Four different mixed fuels consisted of leather waste, coal, and sewage sludge were combusted in a lab-scale entrained flow fluidized bed furnace. The influence of blending ratio on emission characteristics of SO₂, NO_x, HCl, particulate matter (PM), heavy metals, and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied. Results showed that the mixing of coal with sewage sludge had a complex effect on the emission characteristics. On the one hand, with more sewage sludge blending in the mixed fuel, the acid gas pollutant (SO₂, NO_x) decreased a lot, and the recovery of volatile heavy metals (Cd, Pb) increased at the same time. Furthermore, the leaching toxicity of Cr in the fly ash and bottom ash went down below the national standard with the adding of sewage sludge. On the other hand, the mixing of sewage sludge which consisted of more ash content resulted in the increase of the PM emission. Moreover, the high content of Cu and chlorine in the sewage sludge can promote the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) when the fuel 3 and 4 were combusted. Most importantly, the concentration of toxic PCDD/Fs in the flue gas produced from fuel 3 and fuel 4 was successfully controlled down below 0.20 ng I-TEQ/Nm³ by the active carbon.

     

Long-term study of palladium in road tunnel dust and sewage sludge ash

The present work summarizes data about palladium contents of road tunnel dust from 1994 to 2007 and sewage sludge ash from 1972 to 2006. Since palladium is emitted from automotive catalytic converters as elemental particles, road dust is quiet useful to study traffic-related Pd emissions. Very high Pd values of up to 516 μg Pd kg⁻¹ were found in the road dust samples collected in 2007. Heavy metals of all urban emissions, also dental practice effluent, are enriched in sewage sludge ash and thus this matrix is useful for the documentation of palladium emission caused by the use of Pd alloys in dental medicine. In sewage sludge ash highest Pd contents of maximum 460 μg Pd kg⁻¹ were found in the years 1986-1997. In both matrices correlations of Pd content to Pd demand of industry are discussed.     

矿区炼金废渣的固化/稳定化处理

通过对金矿矿区炼金废渣的酸中和能力、净产酸量及浸出毒性实验,测定了废渣的产酸潜力及重金属砷、镉、铅、锌的总量和它们的浸出量。为了合理处置矿区炼金废渣,并为矿区重金属污染土壤的修复提供技术支持,采用石灰、粉煤灰、堆肥化污泥作为添加剂对废渣进行固化/稳定化处理;通过浸出毒性实验对固化/稳定化处理效果进行综合分析,试图寻求一种最佳的稳定剂。结果表明,无论是单独添加石灰、粉煤灰或者堆肥化污泥还是两两组合混合添加,样品浸出液的pH都有升高,As、Cd的浸出浓度都有明显下降,而且两两组合添加比单独添加的固化/稳定化处理效果更好。在两两组合添加中,粉煤灰混合堆肥化污泥的处理效果最好,浸出液的pH值达到7.82,As、Cd的浸出率分别下降72.0%和72.2%。说明粉煤灰混合堆肥化污泥处理炼金废渣效果最佳,同时具有以废治污的资源化生态效能。     

不同改性剂改善污泥土工性质的比较研究

选择了泥土、矿化垃圾、粉煤灰和建筑垃圾4种改性剂改性城市污水处理厂污泥(以下简称污泥)。结果表明:(1)随着4种改性剂与污泥的混合比增大,混合物含水率降低。(2)当混合比为0.7(质量比)时,各种混合物的抗压强度都达到50kPa的填埋要求;当混合比为0.3～1.0时,混合物的抗压强度随着混合比的增大呈指数形式增大;比较4种改性剂对抗压强度的增大能力,粉煤灰最强,建筑垃圾次之,泥土和矿化垃圾较弱。(3)在50kPa预压力下,混合物要达到不小于25kPa的抗剪强度,泥土与污泥最小混合比为1.0,矿化垃圾与污泥最小混合比为1.0,粉煤灰与污泥最小混合比为0.7,建筑垃圾与污泥最小混合比为0.7。(4)除加泥土的混合物外,混合物压缩系数随着混合比的增大呈总体下降趋势。(5)粉煤灰除臭效果最好,矿化垃圾次之,建筑垃圾较差,泥土最差。     

Extraction of raw sewage sludge containing iron phosphate for phosphorus recovery

The objective of the present study was to establish an alkali extraction technology for FePO₄-containing sewage sludge obtained from a wastewater treatment system that includes phosphorous removal by iron electrolysis. By clarifying the extraction properties of phosphorous, organic matter, and inorganic matter, conditions for alkali extraction were optimized. As a result, it was suggested that unheated phosphorous extraction would be superior for FePO₄-containing sewage sludge. And, extraction methods and sewage sludge properties were also compared, and the noteworthy result that extraction of metals can be suppressed to extremely low amounts with alkali extraction as compared with acid extraction was obtained. A new insight was also gained that, as compared with the use of incinerated ash reported in previous studies, alkali extraction was more efficient when raw sewage sludge was used.     

Ecotoxicity, phytotoxicity and extractability of heavy metals from different stabilised sewage sludges

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study compares different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) in order to assess the extractability of heavy metals using simple extraction, water and DTPA. The stabilisation treatment undergone by the sludges influenced the heavy metals extractability. The least mineralised sludges (unstabilised and aerobic) showed higher metal extractability. The sewage sludges were subjected to chemical characterisation and toxicity testing (ecotoxicity and phytotoxicity assays) in absence of substrate, to provide a preliminary assessment of their suitability for land application. The ecotoxicity assays confirmed that no sludge constituted a hazardous waste. The sludge extracts had significant adverse effect on the germination index (GI) of barley (Hordeum vulgare L.) and cress (Lepidium sativum L.), a fact which indicates that some characteristics affected root growth.     

Remediation of metal contaminated soil with mineral-amended composts

This study examined the use of two composts derived from green waste and sewage sludge, amended with minerals (clinoptilolite or bentonite), for the remediation of metal-contaminated brownfield sites to transform them into greenspace. Soils contaminated with high or low levels of metals were mixed with the mineral-enhanced composts at different ratios and assessed by leaching tests, biomass production and metal accumulation of ryegrass (Lolium perenne L.). The results showed that the green waste compost reduced the leaching of Cd and Zn up to 48% whereas the composted sewage sludge doubled the leachate concentration of Zn. However, the same soil amended with composted sewage sludge showed an efficient reduction in plant concentrations of Cd, Cu, Pb or Zn by up to 80%. The results suggest that metal immobilisation and bioavailability are governed by the formation of complexes between the metals and organic matter. The amendment with minerals had only limited effects.     

Anaerobic codigestion of municipal, farm, and industrial organic wastes: a survey of recent literature.

Codigestion of organic wastes is a technology that is increasingly being applied for simultaneous treatment of several solid and liquid organic wastes. The main advantages of this technology are improved methane yield because of the supply of additional nutrients from the codigestates and more efficient use of equipment and cost-sharing by processing multiple waste streams in a single facility. Many municipal wastewater treatment plants (WWTPs) in industrialized countries currently process wastewater sludge in large digesters. Codigestion of organic wastes with municipal wastewater sludge can increase digester gas production and provide savings in the overall energy costs of plant operations. Methane recovery also helps to reduce the emission of greenhouse gases to the atmosphere. The goal of this literature survey was to summarize the research conducted in the last four years on anaerobic codigestion to identify applications of codigestion at WWTPs. Because the solids content in municipal wastewater sludge is low, this survey only focuses on codigestion processes operated at relative low solids content (slurry mode). Semi-solid or solid codigestion processes were not included. Municipal wastewater sludge, the organic fraction of municipal solid waste, and cattle manure (CAM) are the main wastes most often used in codigestion processes. Wastes that are codigested with these main wastes are wood wastes, industrial organic wastes, and farm wastes. These are referred to in this survey as codigestates. The literature provides many laboratory studies (batch assays and bench-scale digesters) that assess the digestibility of codigestates and evaluate the performance and monitoring of codigestion, inhibition of digestion by codigestates, the design of the process (e.g., single-stage or two-stage processes), and the operation temperature (e.g., mesophilic or thermophilic). Only a few reports on pilot- and full-scale studies were found. These evaluate general process performance and pretreatment of codigestates, energy production, and treatment costs.