Sources of Cd, Cu, Pb and Zn in biowaste

Co-composting of sewage sludge as an effective technology for the production of substrates with reduced content of pharmaceutical residues

Sewage sludge is a valuable source of elements such as phosphorus and nitrogen. At the same time, heavy metals, emerging organic compounds, micropollutants (pharmaceuticals, pesticides, PCPs, microplastics), or some potentially dangerous bacteria can be present. In this study, the sewage sludge was aerobically treated by composting with other materials (co-composted), and the resulting substrate was tested for suitability of its use in agriculture. Closer attention was focused on the pharmaceuticals (non-steroidal antiphlogistics, sartanes, antiepileptics, caffeine, and nicotine metabolites) content and ecotoxicity of the resulting substrates in the individual phases of sludge co-composting. It has been verified that during co-composting there is a potential for reduction of the content of pharmaceutical in the substrates up to 90 %. The course of the temperature in the thermophilic phase is decisive. Growth and ecotoxicity experiments demonstrated that with a suitable co-composting procedure, the resulting stabilized matter is suitable as a substrate for use in plant production, and the risk of using sewage sludge on agricultural land is substantially reduced.

Spatial distribution and ecological risk assessment of soil heavy metals in a typical volcanic area: Influence of parent materials

To understand the distribution characteristics and potential ecological risks of heavy metals in soils in the typical volcanic area, 2,592 soil samples were collected from the surface layer (0-20 cm) and 269 samples were collected from the middle (80-100 cm) and deep layers (180-200 cm) in northeast of Hainan province, China. Accordingly, eight heavy metals (Cu, Pb, Zn, Cr, Ni, Cd, As, and Hg) were analyzed and determined. The effects of different parent materials and land use types on the accumulation of heavy metals in soils were compared, and the primary heavy metal sources were analyzed. The pollution level and ecological risk of heavy metals in soils in the study area were evaluated using the geo-accumulation index (Igeo) and potential ecological risk indices (E _i & RI). The results showed that, except that of Pb, the median concentrations of the analyzed heavy metals in the surface soils were higher than the background concentrations in the Hainan Island soils, indicating varying degrees of accumulation. The influence of land use type on the accumulation of heavy metals in surface soils varied from that of the parent materials. Anthropogenic activities highly influenced As, Cd, Hg, and Pb concentrations, whereas geological conditions primarily influenced Cr, Cu, Ni, and Zn concentrations. The Igeo results showed that the mean value of the eight metal elements were greater than zero, except for Pb. In the surface soils, the Igeo values of As, Cd, Hg, and Zn mostly fell into the light to moderate pollution class, and those of Cr, Cu, and Ni fell into the medium and heavy pollution class. The RI of the study area showed a high to significantly high ecological risk because of the Cd, Hg, and Ni concentrations. The results give a new insight in the parent material's geochemical control on the heavy metal elements in soils, and it can serve as a reference for the background value of local soil heavy metals and provide a scientific basis for controlling the potential ecological risk of heavy metals and reasonable land use plans.

Transport of toxic metals in the bottom sediments and health risk assessment of Corbicula fluminea (Asiatic clam) collected from Laguna de Bay, Philippines

Laguna de Bay, the 3rd largest lake in Southeast Asia, is the most significant source of freshwater fish in the Philippines. With decades of unregulated discharge of industrial, domestic, and agricultural wastewaters into the lake, this study investigates the apportionment of heavy metals from the bottom sediments and its impact on the toxicity of Corbicula fluminea (Asiatic clam), a popular food item in the markets. The sediment samples from the western part of the lake contained higher Cd, Cu, Pb, and Zn and lower As and Cr concentrations compared to the eastern part. There were positive correlations for As, Cr, Cu, Pb, and Zn and negative correlations for Cd and Ni concentrations noted between sediments and C. fluminea. Human health risk associated with the consumption of C. fluminea collected from Laguna de Bay was attributed to the following heavy metals: Cu > As > Zn > Cd > Pb > Cr > Ni. Interestingly, the observed trend in toxicities of the shellfish was consistent with the transport phenomenon of heavy metals facilitated by the counterclockwise direction of the bottom current. This study strongly suggests the re-evaluation of the waste management plan in the industrial zones and policies regulating the sale of the shellfish harvest.

Home and community composts in Nantes city (France): quality and safety regarding trace metals and metalloids

Home and community composting are key strategies for local organic waste management. The quality and safety of industrial composts are controlled, but those of home and community composts are not, and this could make them unsafe for use in kitchen gardens. Home (n = 20) and community (n = 41) composts, from urban and suburban areas including mildly Pb-contaminated allotment gardens, were analyzed for quality and safety regarding trace metals and metalloids (TMM) using mid-infrared Fourier transform spectrometry (FT-MIR) and portable X-ray fluorescence spectrometry, respectively. Home composts had a significantly higher Pb content (98 mg.kg^-1 ± 10 mg.kg^-1) than community composts (21 mg.kg^-1 ± 2 mg.kg^-1). Numerous home composts (85%) and a few community composts (17%) exceeded the organic farming thresholds for Pb (45 mg.kg^-1) and Zn (100 mg.kg^-1). The high mineral matter content and the relative abundance of chemical functions attributable to silicates (up to 35%) highly paralleled with TMM contents, mostly concentrated in the fine fraction. Co-inertia analysis highlighted strong and significant links between TMM contents and the whole chemical signature delivered by FT-MIR spectrometry. Pb-contaminated soil could be carried into home compost by green waste or by voluntary addition. Covariance analyses indicated that mineral matter and chemical functions only partly explained the variability in Pb content, suggesting a more complex combination of drivers. Community composting appears as a suitable local solution resulting in high-quality compost that complies with European organic farming regulations, while home composting from allotment gardens should be seriously evaluated to comply with such safety requirements.

Composition and contamination of source separated food waste from different sources and regulatory environments

Food waste recycling is needed to create a more sustainable, circular food system; however, the process must be carefully managed to avoid the introduction and build-up of contaminants. We collected and screened source-separated food waste for five classes of contaminants (physical contaminants, heavy metals, halogenated organics, pathogens and antibiotic resistance genes) from two regulatory environments (voluntary vs mandated food separation) to quantify contamination. Physical contamination was frequently found; 57% of samples contained non-compostable waste. Most heavy metals were not detected, and although copper and zinc were present in most samples, they were always below the most stringent global standards for compost. Some samples had detectable halogenated organics, including perfluoroalkyl substances (PFAS), which is cause for concern because some of these accumulate in the food chain. PFBA was detected in 60%, PFHxS in 8% and PFNA in 4% of samples tested. The pathogen Salmonella was present in 3% (2/71) and L. monocytogenes in 11% (8/71) of samples. Shiga toxin-producing E. coli was not detected. Next generation sequencing showed the presence of several genera that contain foodborne pathogens, most commonly Yersinia. Antibiotic resistance genes tet(M) and bla_TEM were present in 96% and 97% of samples respectively, however the last-resort colistin resistance gene mcr-1 was not detected. Overall contamination in our source-separated samples was low, with the exception of some antibiotic resistance genes, however our processing method might have underestimated packaging-associated contamination. Regulatory environment did not affect contamination, but carbon, nitrogen phosphorus, calcium, copper, tet (M), and physical contamination varied by source type.

Ecological risk assessment and source identification of heavy metal pollution in vegetable bases of Urumqi, China, using the positive matrix factorization (PMF) method

Heavy metal pollution is a widespread problem and strongly affects human health through the food chain. In this study, the overall pollution situation and source apportionment of heavy metals in soil (Hg, Cd, As, Pb, Ni, Zn, Cu and Cr) were evaluated using various methods including geo-accumulation index (Igeo), potential ecological risk index (RI) and positive matrix factorization combined with Geographical Information System (GIS) to quantify and identify the possible sources to these heavy metals in soils. The results of Igeo showed that this farmland top soil moderate contaminated by Hg, other selected elements with noncontamination level. And the average RI in the top soil was 259.89, indicating a moderate ecological risk, of which Hg and Cd attributed 88.87% of the RI. The results of the PMF model showed that the relative contributions of heavy metals due to atmospheric depositions (18.70%), sewage irrigations (21.17%), soil parent materials (19.11%), industrial and residential coal combustions (17.43%) and agricultural and lithogenic sources (23.59%), respectively. Of these elements, Pb and Cd were came from atmospheric deposition. Cr was attributed to sewage irrigations. As was mainly derived from the soil parent materials. Hg originated from industrial and residential coal combustions, and most of the Cu, Zn and Ni, except for Pb, were predominantly derived from agricultural and lithogenic sources. These results are important in considering management plans to control the aggravation of heavy metal pollution and ultimately to protect soil resources in this region. In addition, this study enhances the understanding of heavy metal contamination occurrence in agroecosystem that helps predicting and limiting the potential of heavy metal exposure to people and ecosystem.

Quantitative evaluation of heavy metals' pollution hazards and estimation of heavy metals' environmental costs in leachate during food waste composting

Heavy metals in leachate during food waste composting may produce different degrees of pollution hazards and further induce environment costs, when the concentrations of heavy metals exceed the discharging quality standards. Quantitative evaluation of heavy metals' pollution hazards and estimation of such environmental costs are under-represented in the existing literature. This paper uses a logistic function approach to evaluate the extent of pollution hazards of heavy metals such as cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb) and arsenic (As) and to estimate heavy metals' environmental costs in leachate during food waste composting from Minhang food waste treatment plant located in northern Shanghai, China. Major findings of this study are: (1) The pollution hazards rate of Cd amounts to 94.03%, probably because Cd-containing materials such as plastics are mixed with food waste; (2) With the comprehensive pollution hazards rate estimated as 94.48%, the environmental costs caused by heavy metals in leachate during food waste composting amount to US$0.52 per tonne. This magnitude of environmental costs is meaningful and significant, considering that it is equivalent to 2.97% of Shanghai's food waste treatment charges.

Effect of drying, composting and subsequent impurity removal by sieving on the properties of digestates from municipal organic waste

The application of organic soil amendments is a common measure to prevent structural degradation of agricultural soils and to maintain and improve long-term soil fertility. Solid residues from anaerobic digestion of municipal organic waste (MOW) are rich in nutrients and organic matter and have a promising potential to be used as soil amendment. However, no study has related amendment properties of MOW digestate of one origin to different treatment procedures. We therefore investigated the impact of drying, composting and sieving on final digestate properties and specifically nutrient availability and heavy metal and carbon elution. Samples were provided by a semi-industrial two-stage biogas plant with dry fermentation of MOW. Results confirm that in comparison to drying, composting of MOW digestates leads to a significant increase of K, P, Mg, Ca, Cd and Cr in the digestates. Sieving of composted digestates showed that heavy metals are not evenly distributed and that heavy metal concentration in the digestate increases with decreasing mesh sizes (highest concentrations in the fractions <1 mm). Although the element concentration is higher in composted batches, the water-extractability of nutrients, heavy metals and carbon is significantly lower from composted over dried digestates. A significant correlation was found between the dissolution of Zn, Ni, Ca and Mg and pH of eluate as well as dissolved organic carbon (DOC) release (R > 0.7, p<0.05). Results confirm that the extent of carbon elution depends on the degradation rate of digestates. DOC may therefore be a good measure to evaluate digestate stability and to decide on treatment measures.

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.

Nutrient and heavy metal accumulation in municipal organic waste from separate collection during anaerobic digestion in a two-stage laboratory biogas plant

Municipal organic waste (MOW) is a promising feedstock for biogas plants and separate collection will increase available quantities. To close nutrient circles digestates shall be redistributed to arable land. However, less is known about digestate properties and how they are influenced during digestion. Therefore, changes in nutrient and heavy metal concentration in the solid digestate were investigated during anaerobic treatment of MOW in a two-stage laboratory biogas plant. Results show that the solid digestate is exposed to element accumulation, except for N, P and Mg. The loss of initial N, P and Mg load accounts up to 45%, which must be redistributed elsewhere in the digester system. K load of feedstock was completely rediscovered in the solid digestate. Heavy metal concentration in the digestate increases by factor 1.6 at average. The results emphasize that element retention in the digester system has a decisive impact on nutrient content of digestates.

Exploring social dimensions of municipal solid waste management around the globe - A systematic literature review

Currently, municipal solid waste (MSW) is experiencing a massive increase in both the amount and composition throughout the world. Effective and efficient MSW management has been widely accepted as an emergent factor for future social development, which requires not only technical innovation, but also the involvement of all stakeholders as well as social, economic, and psychological components. On account of this reality, there is an urgent need for research related to the social dimensions of MSW management. In this paper, a systematic literature review was carried out to characterize and critically evaluate the published literature on the social dimensions of MSW management from 1980 to 2014 in terms of vulnerability, public participation, public attitude and behavior, and policy. A keyword search was first performed by using the Institute for Scientific Information (ISI) Web of Science, which retrieves 1843 documents. After removing the papers that were not closely related to the topic, 200 articles were retained for an in-depth review. In each category, major research issues and observations were summarized, and important insights were obtained. Besides compiling a related list of key references, the analysis results indicate that the global distribution of social dimensions reports on MSW management is inequitable and the research on the social dimensions of MSW management is insufficient, which may attract increased research interest and attention.

Physico-chemical characterisation of material fractions in residual and source-segregated household waste in Denmark

Physico-chemical waste composition data are paramount for the assessment and planning of waste management systems. However, the applicability of data is limited by the regional, temporal and technical scope of waste characterisation studies. As Danish and European legislation aims for higher recycling rates evaluation of source-segregation and recycling chains gain importance. This paper provides a consistent up-to-date dataset for 74 physico-chemical parameters in 49 material fractions from residual and 24 material fractions from source-segregated Danish household waste. Significant differences in the physico-chemical properties of residual and source-segregated waste fractions were found for many parameters related to organic matter, but also for elements of environmental concern. Considerable differences in potentially toxic metal concentrations between the individual recyclable fractions within one material type were observed. This indicates that careful planning and performance evaluation of recycling schemes are important to ensure a high quality of collected recyclables. Rare earth elements (REE) were quantified in all waste fractions analysed, with the highest concentrations of REE found in fractions with high content of mineral raw materials, soil materials and dust. The observed REE concentrations represent the background concentration level in non-hazardous waste materials that may serve as a reference point for future investigations related to hazardous waste management. The detailed dataset provided here can be used for assessments of waste management solutions in Denmark and for the evaluation of the quality of recyclable materials in waste.

ATSDR evaluation of potential for human exposure to zinc

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the toxicological profile for zinc. The primary purpose of this article is to provide interested individuals with environmental information on zinc that includes production data, environmental fate, potential for human exposure, analytical methods and a listing of regulations and advisories. Toxicology and Industrial Health 2007; 23: 247—308

Assessment of cadmium (Cd) concentration in arable soil in China

Cadmium (Cd) concentration in arable soil has drawn broad public attention due to its direct effect on Cd concentration in food. However, there have been few studies of surveying Cd accumulation on the national scale in China. This paper collected 486 studies of Cd concentrations in Chinese arable soil. The results showed that the average Cd concentration was 0.27 mg/kg, higher than its background value, indicating that Cd had been introduced into arable soil by human activity. The Cd concentrations in areas of mining and smelting, urban areas, and areas irrigated by wastewater were obviously higher than that in remote areas. Spatially, Cd concentrations were lower in the north than those in the south, and many hotspots existed throughout China due to mining and smelting activities. Most Cd in the arable soil were accumulated from external sources in all investigated provinces except Ningxia Hui Autonomous Region.

Assessment of a particle size fractionation as a technology for reducing heavy metal, salinity and impurities from compost produced by municipal solid waste

A physical fractionation of a compost obtained by municipal solid wastes (MSW) was conducted by dry-sieving process, to quantify coarse impurities and assess the distribution of nutrients, heavy metals and salinity values in particle size fractions of 2, 1.2-2, 0.8-1.2, 0.4-0.8, 0.2-0.4, 0.1-0.2 and <0.1mm diameter. The whole unfractionated compost and all physical fractions were analyzed for the same chemical parameters. The results showed that the studied compost was of a low grade due to high salinity and heavy metal concentrations, and the presence of coarse impurities, mainly glass. The physical fractionation analysis showed that heavy metal and base cations concentrations, and salinity values significantly increased with decreasing of particle size, whereas macro nutrients such as C, N and P were more evenly distributed among the different particle size fractions. Overall, our results showed that the removal of selected particle size fractions <0.8mm and coarse impurities (e.g. glass impurity >2mm) could significantly improve the compost quality without reduce its fertilization potential. We concluded that particle size fractionation is a feasible and sustainable approach to improve composted MSW materials for their safe recycle in agriculture.

Insights into metals in individual fine particles from municipal solid waste using synchrotron radiation-based micro-analytical techniques

Excessive inter-contamination with heavy metals hampers the application of biological treatment products derived from mixed or mechanically-sorted municipal solid waste (MSW). In this study, we investigated fine particles of <2mm, which are small fractions in MSW but constitute a significant component of the total heavy metal content, using bulk detection techniques. A total of 17 individual fine particles were evaluated using synchrotron radiation-based micro-X-ray fluorescence and micro-X-ray diffraction. We also discussed the association, speciation and source apportionment of heavy metals. Metals were found to exist in a diffuse distribution with heterogeneous intensities and intense hot-spots of <10 μm within the fine particles. Zn-Cu, Pb-Fe and Fe-Mn-Cr had significant correlations in terms of spatial distribution. The overlapped enrichment, spatial association, and the mineral phases of metals revealed the potential sources of fine particles from size-reduced waste fractions (such as scraps of organic wastes or ceramics) or from the importation of other particles. The diverse sources of heavy metal pollutants within the fine particles suggested that separate collection and treatment of the biodegradable waste fraction (such as food waste) is a preferable means of facilitating the beneficial utilization of the stabilized products.

Heavy metal leaching and environmental risk from the use of compost-like output as an energy crop growth substrate

Conversion of productive agricultural land towards growth of energy crops has become increasingly controversial. Closed landfill sites represent significant areas of brownfield land, which have potential for the establishment of energy crops. Increasingly composts are now being produced from the degradable fraction of mixed municipal solid waste (MSW) and are commonly referred to as Compost-Like-Output (CLO). However, leaching of heavy metal and other elements due to the use of CLO as soil amendment has the potential to pose a risk to the wider environment as a diffuse pollution source if not managed correctly. Salix viminalis and Eucalyptus nitens were grown at 5 different CLO application rates (equivalent to 250, 1000, 3000, 6000, 1,0000 kg N/Ha) with weekly leachate analysis to assess the solubility of heavy metals and the potential release into the environment. The change in plant total dry mass suggested 3,000 kgN/Ha as the optimum application rate for both species. Weekly leachate analysis identified excess soluble ions within the first 4 weeks, with heavy metals concentrations exceeding water quality limits at the higher application rates (>3,000 kg N/Ha). Heavy metal uptake and accumulation within each species was also investigated; S. viminalis accumulated greater levels of heavy metals than E. nitens with a general trend of metal accumulation in root>stem>leaf material. Heavy metal leaching from soils amended with CLO has the potential to occur at neutral and slightly alkaline pH levels as a result of the high buffering capacity of CLO. The use of CLO at application rates of greater than 250 kg N/Ha may be limited to sites with leachate collection and containment systems, not solely for the heavy metal leaching but also excess nitrogen leaching. Alternatively lower application rates are required but will also limit biomass production.

Black water sludge reuse in agriculture: are heavy metals a problem?

Heavy metal content of sewage sludge is currently the most significant factor limiting its reuse in agriculture within the European Union. In the Netherlands most of the produced sewage sludge is incinerated, mineralizing the organic carbon into the atmosphere rather than returning it back to the soil. Source-separation of black water (toilet water) excludes external heavy metal inputs, such as industrial effluents and surface run-offs, producing sludge with reduced heavy metal content that is a more favorable source for resource recovery. The results presented in this paper show that feces is the main contributor to the heavy metal loading of vacuum collected black water (52-84%), while in sewage the contribution of feces is less than 10%. To distinguish black water from sewage in the sludge reuse regulation, a control parameter should be implemented, such as the Hg and Pb content that is significantly higher in sewage sludge compared to black water sludge (from 50- to 200-fold). The heavy metals in feces and urine are primarily from dietary sources, and promotion of the soil application of black water sludge over livestock manure and artificial fertilizers could further reduce the heavy metal content in the soil/food cycle.

Heavy metals in source-separated compost and digestates

The production of compost and digestate from source-separated organic residues is well established in Europe. However, these products may be a source of pollutants when applied to soils. In order to assess this issue, composts, solid and liquid digestates from Switzerland were analyzed for heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) addressing factors which may influence the concentration levels: the treatment process, the composition, origin, particle size and impurity content of input materials, the season of input materials collection or the degree of organic matter degradation. Composts (n=81) showed mean contents being at 60% or less of the legal threshold values. Solid digestates (n=20) had 20-50% lower values for Cd, Co, Pb and Zn but similar values for Cr, Cu and Ni. Liquid digestates (n=5) exhibited mean concentrations which were approximately twice the values measured in compost for most elements. Statistical analyses did not reveal clear relationships between influencing factors and heavy metal contents. This suggests that the contamination was rather driven by factors not addressed in the present study. According to mass balance calculations related to Switzerland, the annual loads to agricultural soils resulting from the application of compost and digestates ranged between 2% (Cd) and 22% (Pb) of total heavy metal loads. At regional scale, composts and digestates are therefore minor sources of pollution compared to manure (Co, Cu, Ni, Zn), mineral fertilizer (Cd, Cr) and aerial deposition (Pb). However, for individual fields, fertilization with compost or digestates results in higher heavy metal loads than application of equivalent nutrient inputs through manure or mineral fertilizer.

Characteristics of Food Residue in Accordance with Catering Habits

Food residue is receiving increasing attention because of its large quantity of production, wide generation and potential environmental hazards. The characteristics of food residue vary greatly with catering habits. In order to study the composition characteristics of food residue, and to determine the reasonable treatment technologies, ten types of catering habits in Shanghai were sampled, and experimental research was conducted by means of analyzing the variation of moisture content, volatile solid, C/N ratio, salt content and metal elements. The results showed that moisture content varied greatly in accordance with catering habits, while VS/TS ratio was comparatively stable, ranging from 90.60% to 96.17%. The C/N ratio and salt content fluctuated with the change of catering habits, and the highest value was from Sichuan cuisine restaurants and local cuisine restaurants, respectively. Among the four metal elements, Mg had the highest content, followed by Al, and both Fe and Zn accounted for little content in food residue.

Occurrence and distribution of heavy metals and tetracyclines in agricultural soils after typical land use change in east China

Land use in east China tends to change from paddy rice to vegetables or other high-value cash crops, resulting in high input rates of organic manures and increased risk of contamination with both heavy metals (HMs) and antibiotics. This investigation was conducted to determine the accumulation, distribution and risks of HMs and tetracyclines (TCs) in surface soils and profiles receiving different amounts of farmyard manure. Soil samples collected from suburbs of Hangzhou city, Zhejiang province were introduced to represent three types of land use change from paddy rice to asparagus production, vineyards and field mustard cultivation, and divided into two portions, one of which was air-dried and sieved through 2-, 0.3- and 0.149-mm nylon mesh for determination of pH and heavy metals. The other portion was frozen at -20 °C, freeze-dried and sieved through a 0.3-mm nylon mesh for tetracyline determination. HM and TC concentrations in surface soils of 14-year-old mustard fields were the highest with total Cu, Zn, Cd and ∑TCs of 50.5, 196, 1.03 mg kg(-1) and 22.9 μg kg(-1), respectively, on average. The total Cu sequence was field mustard>vineyards>asparagus when duration of land use change was considered; oxytetracycline (OTC) and doxycycline were dominant in soils used for asparagus production; OTC was dominant in vineyards and chlortetracycline (CTC) was dominant in mustard soils. There were positive pollution relationships among Cu, Zn and ∑TCs, especially between Cu and Zn or Cu and ∑TCs. Repeated and excessive application of manures from intensive farming systems may produce combined contamination with HMs and TCs which were found in the top 20 cm of the arable soil profiles and also extended to 20-40 cm depth. Increasing manure application rate and cultivation time led to continuing increases in residue concentrations and movement down the soil profile.

Determining factors for the presence of impurities in selectively collected biowaste

The presence of impurities in biodegradable waste (biowaste) causes problems with the management of waste, among which are additional costs derived from the need to improve pre-treatment of biowaste, loss of treatment capacity and the difficulty selling treated biowaste as compost owing to its low quality. When treated biowaste is used for soil conditioning it can also cause soil pollution. Understanding the reasons why impurities are in biowaste and the factors affecting the percentage of impurities present can be used to determine ways to minimise these negative effects. This article attempts to identify the main causes for the presence of impurities in biowaste. In order to do so, it carries out an empirical analysis of the level of impurities in biowaste from municipal waste collection in two steps. First, a bivariate analysis focuses on significant correlations between the presence of impurities and several variables. Second, the construction of an explanatory model based on the significant relations obtained in the first step, and on literature research, are used to check the stated hypothesis. The estimates demonstrate that the collection system, the global levels of separate collection, the urban density of the municipality and the requirement to use compostable bags may be the main drivers of impurity levels in biowaste.

Nondestructive characterization of the contaminated biodegradable fraction of municipal solid waste using synchrotron radiation-induced micro-X-ray fluorescence

Synchrotron radiation-induced micro-X-ray fluorescence (SR-μXRF) was employed to elucidate the elemental characteristics of contaminated biodegradable fraction of municipal solid waste (BFMSW). Six sectioned BFMSW samples were selected for SR-μXRF mapping and 50 individual fine particles sorbed onto BFMSW were analyzed using SR-μXRF point scanning. The results showed that heavy metals tended to be concentrated on the surface of BFMSW and highly localized to some "hot-spots". Marked differences in heavy metal sequestering potentials among various kinds of BFMSW, and the significant role of heavy metal "hot-spots" in BFMSW contamination were identified. The lower heavy metal levels in the simulated samples compared to field samples (with longer and more intense mixing) indicated that inter-contamination during waste handling contributed significantly to heavy metal accumulation in BFMSW. Furthermore, additional information regarding elemental characteristics of individual particles could be acquired using SR-μXRF.

Monitoring of total metal concentration in sludge samples: case study for the mechanical-biological wastewater treatment plant in Velika Gorica, Croatia

In this paper, monitoring of total metal concentration in sludge samples from wastewater treatment process is elaborated. The presented results summarize the analyses of sludge samples in a period from 2008 to 2012. Possible sources of pollutions are given. Primarily, waste solid samples were collected from different pretreatment steps: (A) coarse grid, (B) fine grid and (C) aerated sand grease grid. Samples of A and B followed a repeatable pattern in 2008 and 2010. According to the results from 2008, samples of C contained measurable concentration of the following metals (mg/kg dry matter): Zn (21), Ni (1.05) and Ba (14.9). Several types of sludge samples were analyzed: fresh raw sludge (PS; 6-12 hour old), the sludge from the digester for anaerobic sludge treatment (DS; 48-72 hour old), samples from lagoons where the sludge is temporarily deposited (DOS and DOSold; 30-120 days) and sludge samples from agricultural areas (AA; aged over 180 days). Additionally, samples of dehydrated sludge (DEHS and DEHSold; 90-180 days) were collected upon construction of equipment for sludge dehydration in 2011. An analysis of total metal concentrations for Cu, Zn, Cr, Pb, Ni, Hg, Cd, Ba, As, Se, Sb, Co, Mo, Fe and Mn was performed by flame atomic absorption spectrometry (FAAS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). The most recent results (year 2011) indicated a high concentration of heavy metals in PS samples, exceeding the MCLs (mg/kg dry matter): Cu (2122), Zn (5945), Hg (13.67) and Cd (6.29). In 2012 (until July), only a concentration of Cu exceeded MCL (928.75 and 1230.5 in DS and DEHS, respectively). A composition of sludge was variable through time, offering the limited possibility for future prediction. The sludge is being considered as a hazardous waste and a subject of discussion regarding disposal.

Investigation of potentially toxic heavy metals in different organic wastes used to fertilize market garden crops

The benefits of using organic waste as fertilizer and soil amendment should be assessed together with the environmental impacts due to the possible presence of heavy metals (HMs). This study involved analysing major element and HM contents in raw and size-fractionated organic wastes (17 sewage sludges and composts) from developed and developing countries. The overall HM concentration pattern showed an asymmetric distribution due to the presence of some wastes with extremely high concentrations. HM concentrations were correlated with the size of cities or farms where the wastes had been produced, and HM were differentiated with respect to their origins (geogenic: Cr-Ni; anthropogenic agricultural and urban: Cu-Zn; anthropogenic urban: Cd-Pb). Size fractionation highlighted Cd, Cu, Zn and Pb accumulation in fine size fractions, while Cr and Ni were accumulated in the coarsest. HM associations with major elements revealed inorganic (Al, Fe, etc.) bearing phases for Cr and Ni, and sulfur or phosphorus species for Cd, Cu Pb and Zn.

Effect of composting on the mobility of arsenic, chromium and nickel contained in kitchen and garden waste

The study was focused on evaluation of possible changes in As, Cr, and Ni mobility and fractionation during composting of kitchen and garden waste. Fresh bio-waste taken up seasonally was thoroughly mixed with woodchips in the wet weight portion of 3:1 and the mixture was put into batch-wise aerated fermenters under 3 air flow rates. An increased drop in exchangeable Cr and Ni was found in kitchen and garden waste after 12 weeks of composting, respectively. The exchangeable content of As decreased only during kitchen waste composting. The order of fractions in the final compost was as follows: residual>oxidizable>exchangeable>reducible. The proportion of Cr and Ni in exchangeable fraction decreased after composting more than 3- and 4-fold, respectively. Results proved that an intensive composting process is a suitable method for immobilization of Cr and Ni, and for decreasing total As contained in household bio-waste.

Performance of a commercial-scale DiCOM demonstration facility treating mixed municipal solid waste in comparison with laboratory-scale data

The current paper describes the performance of a commercial-scale (20,000 tpa) demonstration facility of the DiCOM process, a biological treatment for the organic fraction of municipal solid waste (OFMSW). The 21-d process combines aerobic composting and high-solids (30%DM), thermophilic (55 °C) anaerobic digestion (AD), within a single vessel. Mechanically sorted OFMSW, derived from mixed household MSW (324 t), was exposed to sequential aerobic/anaerobic/aerobic treatment. The AD, initiated by adding anaerobic inoculum from a previous trial, was stable (without pH intervention) and the onset of methanogenesis, rapid (<3 h). Volatile fatty acids formed during AD (including propionate) were exhausted prior to reuse of the inoculum. As measured by an electron flux from solids to gaseous end-products, AD accounted for the greatest portion of solids degradation (86%=160 m(3)CH(4)/drytOFMSW). However, unlike laboratory trials, limited degradation occurred during initial aerobic treatment. The discharged solids were classified as a composted soil conditioner.

Use of organic acids in the composting of municipal solid waste: a pilot-scale study

Compost made from municipal solid waste (MSW) contains heavy metals that can interfere with the use of organic amendment in soil. In order to find effective ways to reduce the potential risk of heavy metals, we have investigated a novel approach by use of organic acid during MSW composting. Citric and oxalic acid dissolutions (0.25 mol x (-1)) were used at determined ratios (kg dried MSW: cm(3) acid). Cr and Ni concentrations were similar in compost, independent of acid contribution. By contrast, Cu concentrations decreased by 63% (at citric acid ratio 1:15), 65% (at citric acid ratios 1:20 and 1:40) and 83% (at oxalic acid ratio 1:40); furthermore, Pb concentrations reduced by 71% (at citric acid ratios 1:20 and 1:40 and at oxalic acid ratio 1:40) and Zn concentrations reduced by 67% (at citric acid ratios 1:10 and 1:20) and 70% (at oxalic acid ratio 1:40). The total metal mass decreased by an average of 12% in the compost fraction, whereas the total percentage of the residual fraction increased by an average of 20%. The acid addition in the studied ratios improved compost quality without negatively influencing biostabilization.

Composition and parameters of household bio-waste in four seasons

Bio-waste makes up almost half portion of municipal solid waste. The characterization of household bio-waste is important in determining the most appropriate treatment method. The differences in composition and parameters of bio-waste derived from urban settlement (U-bio-waste) and family houses (F-bio-waste) during the four climate seasons are described in this paper. Twelve components and 20 parameters for bio-waste were evaluated. The composition of U-bio-waste was almost steady over those seasons, unlike F-bio-waste. U-bio-waste was comprised mainly (58.2%) of fruit and vegetable debris. F-bio-waste was primarily made up of seasonal garden components. The amount of variation among seasons in both type of bio-waste increased in sequence: basic parameters<macro-elements<potentially toxic elements. Spearman's correlations among proportions of individual components and parameters of bio-waste were found out. Results of this research could be utilized to support another composition and parameters of bio-waste and be suitable for establishing bio-waste processing.

Trace elements in compost regulation: the case of Spain

We use the example of the Spanish Decree on Fertilizers (2005) to discuss the need of new horizontal regulations for assessing the quality of all the materials reaching the soil as amendments of fertilizers, in particular in what concerns potentially toxic trace elements in compost. Here it is proposed that the new regulations take into account the following: establishing maximum legal limits for the total loads for each element when compost is added to agricultural soils; establishing the maximum total concentration and bioavailability of each element in the final compost; and that they take into account the soil characteristics for establishing those limits.

Bacterial composting of animal fleshing generated from tannery industries

Animal fleshing (ANFL) is the major proteinaceous solid waste generated during the manufacture of leather, which requires to be disposed of by environmentally sound manner. This study reports about the treatment of ANFL into an organic compost and its effects on physiological parameters of different crops in a laboratory study. The ANFL was hydrolysed using Selenomonas ruminantium HM000123 and then the hydrolysed ANFL was mixed with cow dung and leaf litter for producing composted organic fertilizer (COF). The COF was characterized for pH, electrical conductivity (EC), total Kjeldhal nitrogen (TKN), and total organic carbon (TOC). The composting resulted in a significant reduction in pH, TOC and C:N ratio and an increase in TKN after 49 days in a compost reactor. Scanning electron microscope and FT-IR were used to analyse the hydrolysis of intra structural ANFL matrix and changes in the functional groups, respectively, in initial and final day COF. Thermogravimetry (TG) analysis was carried out for the raw mixture and COF samples to identify the weight loss under the nitrogen environment. The relative seed germination was found to be 94% in tomato (Lycopersicon esculentum), 92% in green gram (Vigna radiata), 86% in bottle gourd (Lagenaria siceraria (Mol.) Standl.) and 84% in cucumber (Cucumis sativus L.) using the extracts of COF. The results indicate that the combination of both hydrolysis and bacterial composting reduced the overall time required for composting and producing a nutrient-enriched compost product.

Domestic waste composting facilities: a review of human health risks

In the management of municipal solid waste (MSW), the sorting-composting approach presents many advantages. However, since MSW contains a number of chemical and biological agents, the compost should not be necessarily a harmless product. These contaminants may expose different populations to health hazards, ranging from the composting plant workers to the consumers of vegetable products grown in soils treated with compost. Recent information concerning health risks derived from occupational exposure to organic dusts, bioaerosols and microorganisms in MSW composting plants is here reviewed. An evaluation of the potential health risks of volatile organic compounds (VOCs) released during composting is also included. Taking into account the potential biological and chemical risks, an exhaustive control of the workers employed in MSW composting facilities is clearly recommendable. Moreover, because the compost derived from the organic fraction of MSW can contain a number of metals and persistent organic pollutants, as well as microbial and fungi toxins, any compost that may mean a health risk for the population should not be commercialized.

Municipal solid waste characteristics and management in Gümüşhane, Turkey

This paper presents a general overview of the current municipal solid waste (MSW) management in Gümüşhane Province, Turkey. In order to characterize the solid waste stream in the Municipality of Gümüşhane, a long-term study was conducted over a 52-week period between the spring of 2004 and the winter of 2005. In this study, percentage of components and specific weight of the MSW, the composting parameters (moisture content, total organic carbon, total nitrogen and pH), organic matter content, calorific value and the heavy metal concentrations (Cd, Cr, Cu, Ni, Pb, Zn, Fe, Mn, Co) of the compostable wastes sorted from the mixed MSW were determined and evaluated. In Gümüşhane, a mean of 70 tons of MSW are generated each day or 1 kg/day/capita. Approximately 4,500 kg of the MSW were collected and sorted in a year, and the mean specific weight of these is 308 kg/m(3). Approximately 30% of the MSW generated is compostable wastes and the yearly mean moisture content, organic matter content, C/N ratio and pH of these are 78%, 92.1%, 21.6/1 and 4.73, respectively, and approximately 24% of the MSW consists of recyclable materials. The recommended system deals with maximizing recycling and minimizing landfilling of the MSW, and consists of separation at source, collection, sorting, recycling, composting and sanitary landfilling. Heavy metal concentrations of the compostable wastes from the open dump were determined to decrease in the following order: Fe>Mn>Zn>Cr>Cu>Pb>Ni>Cd>Co.

Evolution of non-dissolved particulate organic matter during composting of sludge with straw

Long term composting induces loss of C and organic matter stabilisation. These two processes may have opposite effects on long term carbon storage in soils. To check whether raw materials should be composted or not before being spread on the soil, changes in particle size fractions were quantified during composting of 9 tons of sewage sludge and straw. Both the mass of the fine fraction (<2 microm) and the amount of carbon contained in it increased after seven months, respectively, +37% and +43%. The fine fraction contributes to carbon sequestration. A literature review supported the assumption that composting should increase long term C storage. Nevertheless, soil texture or agricultural practices modify the behaviour of this fraction. Thus, the fractionation method used for soils is relevant to predict the effect of composting as a mitigation option in greenhouse gas reduction strategies, but is not sufficient in itself.

Source analysis of heavy metals and arsenic in organic fractions of municipal solid waste in a mega-city (Shanghai)

Heavy metals and arsenic contamination in municipal solid waste (MSW) and its treatment products has garnered increasing attention. This study investigated the heavy metals and arsenic flows in organic fractions of MSW (OFMSW) in Shanghai, China, through a one-year monitoring program. The OFMSW separated directly from the source (source-separated, pure organic waste), obtained from the treatment facilities were sampled and compared with pure foodstuffs. The heavy metals and arsenic contents in the source-separated OFMSW resembled those in foodstuffs, whereas the OFMSW from the treatment facilities was significantly contaminated with heavy metals and arsenic and failed to meet the government standards for land use. Using flow analysis, > 80% of heavy metals and arsenic were from extrinsic inorganic waste with high ash content that was combined with OFMSW during MSW collection, transfer, transportation, and storage stages. Based on source analysis of heavy metals and arsenic, suggestions for reducing heavy metals and arsenic contents in the current MSW management system in Shanghai are presented.

Variations of metal distribution in sewage sludge composting

In the study, the variations of heavy metal distributions (of Cu, Mn, Pb, and Zn) during the sewage sludge composting process were investigated by sequential extraction procedures. The total content of Cu and Zn in the composted mixture increased after the composting process. Mn and Zn were mainly found in mobile fractions (exchangeable fraction (F1), carbonate fraction (F2), and Fe/Mn oxide fraction (F3)). Cu and Pb were strongly associated with the stable fractions (organic matter/sulfides fraction (F4) and residual fraction (F5)). These five metal fractions were used to calculate the metal mobility (bioavailability) in the sewage sludge and composted mixture. The mobility (bioavailability) of Mn, Pb, and Zn (but not Cu) increased during the composting process. The metal mobility in the composted mixture ranked in the following order: Mn>Zn>Pb>Cu.

Maturity assessment of compost from municipal solid waste through the study of enzyme activities and water-soluble fractions

In this work the dynamics of biochemical (enzymatic activities) and chemical (water-soluble fraction) parameters during 100 days of municipal solid wastes composting were studied to evaluate their suitability as tools for compost characterization. The hydrolase (protease, urease, cellulase, beta-glucosidase) and dehydrogenase activities were characterized by significant changes during the first 2 weeks of composting, because of the increase of easily decomposable organic compounds. After the 4th week a "maturation phase" was identified in which the enzymatic activities tended to gently decrease, suggesting the stabilisation of organic matter. Also the water-soluble fractions (water-soluble carbon, nitrogen, carbohydrates and phenols), which are involved in many degradation processes, showed major fluctuations during the first month of composting. The results obtained showed that the hydrolytic activities and the water-soluble fractions did not vary statistically during the last month of composting. Significant correlations between the enzymatic activities, as well as between enzyme activities and water-soluble fractions, were also highlighted. These results highlight the suitability of both enzymatic activities and water soluble fractions as suitable indicators of the state and evolution of the organic matter during composting. However, since in the literature the amount of each activity or fraction at the end of composting depends on the raw material used for composting, single point determinations appear inadequate for compost characterization. This emphasizes the importance of the characterization of the dynamics of enzymatic activities and water-soluble fractions during the process.

Stabilization of nickel and chromium in sewage sludge during aerobic composting

The speciation of heavy metals can play a major role in the toxicity of those metals in sewage sludge following land application. Tessier sequential extraction was used to investigate the changes in Ni and Cr speciation in sewage sludge treated by forced-aeration composting. Ni and Cr concentrations increased 30.4% and 36.0%, respectively, during the composting process, with H(2)O and CO(2) volatilization being a major contributor to the change. It was found that the exchangeable, carbonate-bound, Fe-Mn oxide-bound, and organic matter-bound Ni and Cr were transformed to residual fractions. For Cr, the carbonate-bound, Fe-Mn oxide-bound, and organic matter-bound fractions were major contributors, while organic matter-bound Ni was a major contributor to the residual fraction. Composting appeared to reduce Ni and Cr availability by stabilizing the two metals and making them more stable and less mobile.

Fluorescence characterization of metal ion–humic acid interactions in soils amended with composted municipal solid wastes

Fluorescence spectroscopy has been used to probe the structural properties and Cu(II), Zn(II), Cd(II), and Pb(II)-binding behavior of humic acid (HA)-like fractions isolated from a municipal solid waste compost (MSWC) and HAs from unamended and MSWC-amended soils. The main feature of the fluorescence spectra, in the form of emission-excitation matrix (EEM) plots, was a broad peak with the maximum centered at an excitation/emission wavelength pair that was much shorter (340/437 nm) for MSWC-HA than for unamended and MSWC-amended soil HAs (455/513 and 455/512 nm, respectively). Fluorescence intensity for MSWC-amended soil HA was less than that for unamended soil HA. These results were indicative of more aromatic ring polycondensation and humification of soil HAs, and of partial incorporation of simple and low-humified components of MSWC-HA into native soil HA, as a result of MSWC amendment. Titrations of HAs with Cu(II), Zn(II), Cd(II), and Pb(II) ions at pH 6 and ionic strength 0.1 mol L(-1) resulted in a marked decrease of the fluorescence intensities of untreated HAs. By successfully fitting a single-site fluorescence-quenching model to titration data, the metal ion complexing capacities of each HA and the stability constants of metal ion-HA complexes were obtained. The binding capacities and stability constants of MSWC-HA were smaller than those of the unamended soil HA. Application of MSWC to soil slightly reduced the metal-ion-binding capacities and affinities of soil HAs.

Effects of scrubber by-product-stabilized dairy lagoon sludge on growth and physiological responses of sunflower (Helianthus annuus L.)

Brick manufacturing industries are challenged to comply with clean air mandates. Dry air scrubbers have been used to remove acid gases from the exhaust air from brick manufacturing plants. The use of dry air scrubbers results in the production of large quantities of an alkaline powder by-product. A greenhouse experiment was conducted to evaluate the potential of using dairy lagoon sludge stabilized with the scrubber by-product as a soil amendment. Lagoon sludge was stabilized with scrubber by-product at an application rate of 20 gl(-1). The sludge-scrubber by-product mixture was applied to a sandy loam soil to provide amendments ranging between 28 and 168 kg of plant available nitrogen (PAN)/ha for the growth of Helianthus annuus (sunflower). Use of the sludge-scrubber by-product mixture as a nitrogen fertilizer did not adversely affect sunflower seedling emergence; however, significantly higher (p<0.05) plant volume indices, leaf area, dry shoot and root masses, and seed yields were obtained for mature plants grown in sludge-treated soil relative to the control or fertilizer treatment. The sludge amendment did not severely impact gas exchange or chlorophyll a fluorescence of the plants and nutrient content of the sunflower tissues was generally within a sufficient range. The increased growth and yield of sunflower plants indicated the potential of the sludge-scrubber by-product mixture as a soil amendment in agricultural crop production.

Heavy Metal Contamination in Compost. A Possible Solution

With the objective of improving qualitative characteristics of compost, an analytical survey was carried out in a composting plant in Lombardy (Italy) in all process of production, with particular reference to heavy metals (HM) Zn and Pb. The investigation was principally aimed to study the contents and the accumulation of HM during composting process and to identify a technological solution for reducing HM content in the final product. A merceological analysis of Municipal Solid Waste (MSW) input to the composting plant, a chemical analysis of the organic fraction of MSW after mechanical separation, and a comparison with values reported by some authors, showed that Zn and Pb are significant contaminants, even though concentrations have recently decreased in comparison to previous years. On the basis of Zn and Pb content in raw material input to the plant, an estimate of the theoretical value of Zn and Pb in produced compost was made. The comparison of theoretical values with the real ones, experimentally determined, confirmed that at the end of composting process the concentration is 2.6 times the initial value for Zn and 1.6 times the initial value for Pb, as suggested by some authors. Finally, the analytical investigation of Zn and Pb contents in the compost refining line, carried out by means of sieving tests, showed that by eliminating a fraction of compost < 1 mm, both Zn and Pb, which is the more critical one, can be largely removed, without a substantial yield loss (only 10% of the final product is eliminated).

Biodegradable municipal solid waste: characterization and potential use as animal feedstuffs

Five different fractions of the biodegradable municipal solid waste (BMSW) were evaluated as potential animal feedstuffs. For each source of waste (meat waste (MW), fish waste (FW), fruit and vegetables waste (FVW), restaurant waste (RW), household waste (HW)), samples were obtained from small shops (butchers, fishmongers, fruit and vegetable shops), restaurants and a MSW treatment plant (household waste). The chemical composition, microbiological characterization, dioxins, furans, PCB's and mineral content were determined for every type of waste fraction. The analysed biodegradable waste presented high moisture content (from 60% to 90%). Some fractions were dense in one nutrient: meat waste in ether extract, fish waste in crude protein, fruit and vegetable waste in nitrogen free extract. The other studied fractions (restaurant fraction and household fraction) presented a more balanced composition, but the presence of toxic concentrations of contaminants such as metals was higher than European legislation permitted values in animal feeding. From a microbiological standpoint, a heat treatment at 65 degrees C for 20 min was sufficient to ensure microbiological quality of the samples. This treatment was also advisable to reduce the moisture content: a lower moisture content facilitates the waste handling and processing and, therefore, the inclusion of these waste fractions in commercial animal diets. This paper presents a potential alternative for the recovery of organic matter content in municipal solid waste. The results obtained in this research and the feedstuffs legislation in force related to animal feed, indicated that some of the studied biodegradable waste fractions (meat waste, fruit and vegetable waste and fish waste) could be considered as alternatives to typical raw materials used in animal feeds.

Advanced bioconversion of biowaste for production of a peat substitute and renewable energy

Traditional composting systems for biowaste generally produce low quality composts that may endanger recycling. A pilot-scale bioconversion process yielding quality compost and renewable energy was designed and tested. The process consisted of a set of wet physical separation units, composting and anaerobic digestion. Biowaste was divided in four streams by physical separation: (1) organic fraction >2 mm, (2) inorganic fraction 0.05-2 mm, (3) residual fraction composed of organics 0.05-2 mm and the fraction <0.05 mm and (4) a fraction solubilised in the washing water. The organic fraction >2 mm was composted and the compost, high in organic matter and low in EC and heavy metals, aimed at replacing peat in horticulture. The inorganic fraction 0.05-2 mm was completely made up of sand and can be used as a construction material. Solubilised organic matter in the washing water was converted to CH(4) by anaerobic digestion. The residual fraction can be used as landfill cover material.

Assessment of heavy metal removal technologies for biowaste by physico-chemical fractionation

In the Netherlands, the heavy metal content of biowaste-compost frequently exceeds the legal standards for heavy metals. In order to assess heavy metal removal technologies a physico-chemical fractionation scheme was developed to gain insight into the distribution of heavy metals (Cd, Cu, Pb and Zn) over the physical entities of biowaste and to determine the binding strength of heavy metals to these physical entities. The scheme was based on a particle fractionation on size and density followed by sequential chemical extraction of the fractions. The organic fraction >1 mm contributed to 40% of the mass of biowaste and this fraction met the legal standards for compost after composting. About 28% of biowaste was composed of sand, which can be reused in road and building construction as the heavy metal content is very low. The heavy metals were concentrated in the organic particles from 0.05-1 mm and the organo-mineral fraction <0.05 mm. The heavy metal content has to be reduced to reach the legal standards for compost. The extractability from the inorganic organic and organo-mineral fractions showed the order Cd>>Zn>Pb>Cu. The order of extractability for Pb and that for Zn were sometimes reversed most probably because the extraction is not only determined by the adsorption strength but also by the accessibility of adsorbed metals. The results of sequential chemical extraction showed that the amount of heavy medals available for extraction was sufficient. Citric acid turned out to be the best option for the removal of heavy metals from solid organic waste streams.