Spectroscopic and Thermal Investigation Of Hydrophobic and Hydrophilic Fractions Of Dissolved Organic Matter

Hydrophobic (HO) and hydrophilic (HI) fractions of dissolved organic matter (DOM) isolated from several substrates including a source separated urban waste compost, a mechanically separated urban waste compost, an anaerobically digested municipal sewage sludge, a composted sewage sludge and a cow slurry were characterised by Fourier transform infrared spectroscopy (FT-IR), monodimensional fluorescence spectroscopy in the emission, excitation and synchronous scan modes, tridimensional excitation emission matrix (EEM) fluorescence spectroscopy, ¹H nuclear magnetic resonance (¹H-NMR) spectroscopy, and differential scanning calorimetry (DSC). The FT-IR spectra indicated that the HI fractions were rich in both aromatic and aliphatic structures, whereas the HO fractions were rich in carboxylic groups and polysaccharides. The synchronous scan spectra of HO fractions showed the main peak at a wavelength much longer than that of the HI fractions, which indicated a greater molecular complexity of the HO fractions with respect to HI fractions. The ¹H-NMR data indicated a great percentage of aliphatic structures in all samples, whereas the HO samples were also characterised by the presence of aromatic structures. The DSC curves confirmed the more distinct aromatic nature of HO fractions, as compared to the corresponding HI fractions.     

Influence of origin and properties of dissolved organic matter on the partition of polycyclic aromatic hydrocarbons (PAHs)

We investigated dissolved organic matter (DOM) from soil, sewage sludges, water from waste disposal sites, and composts as sorbents and potential carriers for hydrophobic polycyclic aromatic hydrocarbons (PAHs) in soil. Partition coefficients (expressed log K_DOC) for two 5-ring compounds were 4·8–4·9 for DOM from soil, 4·5–47 from composts, and 4·3–4·4 from sewage sludges. The DOM from compost and sewage sludge can influence the transport of non-ionic organic contaminants because of the large concentrations of dissolved organic carbon (DOC) released from these materials. Leachates from waste disposal sites did not sorb PAHs. The DOM from compost contained a large percentage of organic molecules > 14 000 Da (32–46%), whereas DOM from waste disposal leachates contained only 7-lo%, and so bound less PAHs. The percentage of total hydrophobic components, as characterized by XAD-8 chromatography, was 50 ± 9% for most of the DOM solutions and did not express the differences in affinity of the organic sorbents to PAHs in the same way as the K_DOC values. Isolated molecular-weight fractions of DOM from composts sorbed benzo(k)fluoranthene in each fraction. The log K_DOC values were 4·1–4·3 for both fractions, < 1000 and 1000–14 000 Da, and 4·8–5·0 for the fraction > 14 000 Da. The interaction of PAHs with DOM < 1000 Da cannot be explained by partitioning within intramolecular nonpolar environments of dissolved macromolecules; rather it seems to be due to the amphoteric properties of DOM. This type of interaction of PAHs with small DOM molecules might affect the mobility of hydrophobic organic chemicals in soils.     

Comparison of dissolved organic matter from sewage sludge and sludge compost as electron shuttles for enhancing Fe(III) bioreduction

Purpose  

Land utilization of sewage sludge and sludge compost is a common practice in many countries. Soils amended with sewage sludge and sludge compost display different physicochemical properties, especially in terms of dissolved organic matter (DOM) composition that affects the electron-donating capacity (EDC) of DOM in soils. The aim of this paper was to compare the EDC of DOM derived from sewage sludge and sludge compost for enhancing Fe(III) bioreduction. It is expected that this research could be helpful for further understanding of soil remediation in the future.     

Zur Dynamik gelöster organischer Substanzen (DOM) in Fichtenökosystemen - Ergebnisse analytischer DOM-Fraktionierung

Dissolved organic matter (DOM) dynamics in spruce forested sites - examinations by analytical DOM fractionation Dissolved organic matter from two spruce forested sites in the Fichtelgebirge (Germany) was divided into different chemical and functional fractions, and the budgets of the fractions obtained were calculated. For both sites hydrophobic acids (HoS), hydrophilic acids (HiS), hydrophobic neutrals (HoN), hydrophilic neutrals (HiN), and hydrophilic bases (HiB) are discriminated concerning their dynamics in the compartments. Most of the HiN and HoN are mobilized by leaching from the forest canopy. Both neutral fractions are netto retained in the forest floor as well as in the mineral soil. In contrast, HoS and HiS are mainly released in the organic layers with a total input of organic acids from the forest floor into the mineral soil of ca 100 kg C (HoS) ha^?1 a^?1, and 50 kg C (HiS) ha^?1 a^?1, respectively. HoS are selectively better retained in the mineral horizons, leading to a mineral soil output of 2.4 – 4.4 kg C (HoS) ha^?1 a^?1, and 2.7 – 6.5 kg C (HiS) ha^?1 a^?1, respectively. It is concluded that the different mobility of the DOM fractions has implications for the mobilization and transport of organic pollutants and heavy metals.     

Magnetic Separation of Ferrite Sludge from a Wastewater Purification Process

The purpose of this research was to evaluate the apparent molecular weight distribution of dissolved organic matter (DOM) from pig slurry and the binding ability of its fractions toward copper (Cu²⁺) ions. In addition, the binding ability (maximum complexing capacity – MCC) of the DOM was compared with that of humic (HA) and fulvic (FA) acids from a clay-loam soil. The study was performed using Cu²⁺ ions since this metal is widely used as a supplement in pig diets and, consequently, is present in pig slurry. The techniques adopted were gel filtration chromatography (GFC) and dialysis. GFC showed that the DOM from pig slurry is mainly composed of a fraction with an apparent molecular weight higher than 5000 Da and the copper naturally present in the slurry is completely complexed by this fraction. The dialysis procedure enabled MCC to be determined. The MCC of pig slurry DOM and soil HA, which contained a similar concentration of carboxylic groups, were analogous, while MCC of soil FA, which contained double the concentration of carboxylic groups, was higher.     

Changes in the microbial activity of an arid soil amended with urban organic wastes

Changes produced in the biological characteristics of an arid soil by the addition of various urban wastes (municipal solid waste, sewage sludge and compost) at different doses, were evaluated during a 360-day incubation experiment. The addition of organic materials to the soil increased the values of biomass carbon, basal respiration, biomass C/total organic C ratio and metabolic quotient (qCO₂), indicating the activation of soil microorganisms. These biological parameters showed a decreasing tendency with time. Nevertheless, their values in amended soils were higher than in control soil, which clearly indicates the improvement of soil biological quality brought about by the organic amendment. This favorable effect on soil biological activity was more noticeable with the addition of fresh wastes (municipal solid waste or sewage sludge) than with compost. In turn, this effect was more permanent when the soil was amended with municipal solid waste than when it was amended with sewage sludge. Received: 28 May 1996     

Long-term effects of compost amendment of soil on functional and structural diversity and microbial activity

We studied the effects of applying different composts (urban organic waste, green waste, manure and sewage sludge), mineral fertilizer and compost plus mineral fertilizer on chemical, biological and soil microbiological parameters over a 12‐year period. The organic C and total N levels in soils were increased by all compost and compost + N treatments. Microbial biomass C was significantly (P ≤ 0.05) increased for some compost treatments. In addition, basal respiration and the metabolic quotient (qCO₂) were significantly higher in all soils that had received sewage sludge compost. The Shannon diversity index (H), based on community level physiological profiling, showed a higher consumption of carbon sources in soils treated with compost and compost + N compared with the control. The utilization of different guilds of carbon sources varied amongst the treatments (compost, compost + N or mineral fertilizer). Cluster analysis of polymerase chain reaction‐denaturing gradient gel electrophoresis patterns showed two major clusters, the first containing the mineral fertilization and compost treatments, and the second, the composts + N treatments. No differences in bacterial community structure could be determined between the different types of compost. However, the results suggest that long‐term compost treatments do have effects on the soil biota. The results indicate that the effects on the qCO₂ may be due to shifts in community composition. In this study, it was not possible to distinguish with certainty between the effects of different composts except for compost derived from sewage sludge.     

Carbon and nitrogen transformation during composting of sweet sorghum bagasse

Two types of compost, consisting of sweet sorghum bagasse with either sewage sludge or a mixture of pig slurry and poultry manure, were studied in a pilot plant using the Rutgers system. The total degradation of the piles as determined by the weight loss of organic matter during the bio-oxidative and maturation phases accounted for 64% of the organic matter applied and followed a first-order kinetic function. Concentrations of total and organic N increased during the composting process as the degradation of organic C compounds reduced the compost weight. Losses of N through NH₃ volatilization were low, particularly in the compost with sewage sludge due to pH values of <7.0 and the low temperatures reached in the compost during the first 2 weeks. The C:N ratio in the two composts decreased from 24.0 and 15.4 to values between 12 and 10. Increases in cation exchange capacity and in fulvic and humic acid-like C revealed that the organic matter had been humified during composting. The humification index, the C:N ratio, fulvic:humic acid-like C, and cation exchange capacity proved to be the most suitable parameters for assessing the maturity of these composts.     

Comparison of Sewage Sludge and Yard Waste Compost As Biofilter Material for Ammonia Removal

Sewage sludge compost and yard waste compost were compared with respect to their efficiency as biofilter material for removing ammonia from air. Ammonia removal efficiency was investigated using both small-scale filter columns in the laboratory and large-scale filter columns operated at a pig farm. The laboratory experiments were carried out using 30 cm high columns with a volume of 250 cm³ supplied with an artificially produced ammonia-air mixture, whereas 1 m columns with a volume of 27 liters supplied with the ambient air from the pig stable were used in the large-scale experiments. All filter columns were able to remove more than 95% of the ammonia in the inlet regardless of compost type and applied air flow rate. Ammonia concentration profiles inside the compost columns measured at the end of the experiments indicated that sewage sludge compost removes ammonia at significantly higher specific rates than yard waste compost. The likely explanation is that sewage sludge compost contains higher numbers of nitrifying bacteria originating from the wastewater treatment process.     

Dynamics of Organic C Mineralization and the Mobile Fraction of Heavy Metals in a Calcareous Soil Incubated with Organic Wastes

Organic wastes such as sewage sludge and compost increase the input of carbon and nutrients to the soil. However, sewage sludge-applied heavy metals, and organic pollutants adversely affect soil biochemical properties. Therefore, an incubation experiment lasting 90 days was carried out to evaluate the effect of the addition of two sources of organic C: sewage sludge or composted turf and plant residues to a calcareous soil at three rates (15, 45, and 90 t of dry matter ha^–1) on pH, EC, dissolved organic C, humic substances C, organic matter mineralization, microbial biomass C, and metabolic quotient. The mobile fraction of heavy metals (Zn, Cd, Cu, Ni, and Pb) extracted by NH₄NO₃ was also investigated.The addition of sewage sludge decreased soil pH and increased soil salinity to a greater extent than the addition of compost. Both sewage sludge and compost increased significantly the values of the cumulative C mineralized, dissolved organic C, humic and fulvic acid C, microbial biomass C, and metabolic quotient (qCO₂), especially with increasing application rate. Compared to compost, the addition of sewage sludge caused higher increases in the values of these parameters. The values of dissolved organic C, fulvic acid C, microbial biomass C, metabolic quotient, and C/N ratio tended to decrease with time. The soil treated with sewage sludge showed a significant increase in the mobile fractions of Zn, Cd, Cu, and Ni and a significant decrease in the mobile fraction of Pb compared to control. The high application rate of compost resulted in the lowest mobility of Cu, Ni, and Pb. The results suggest that biochemical properties of calcareous soil can be enhanced by both organic wastes. But, the high salinity and extractability of heavy metals, due to the addition of sewage sludge, may limit the application of sewage sludge.     

不同有机废弃物对土壤磷吸附能力及有效性的影响

城郊农地是循环有机废弃物的重要场所,但长期施用畜禽粪和城市污泥可引起土壤磷素积累、磷饱和度提高,增加土壤向环境流失磷的风险。为了解施用不同来源的有机废弃物对城郊耕地土壤磷素化学行为的影响,选择4种不同磷含量的土壤,探讨在等量磷素情况下,施用KH2PO4、猪粪/稻草秸秆堆肥、沼渣、猪粪、鸡粪、生活垃圾堆肥和2种污泥等不同磷源时,土壤有效磷含量及磷吸附能力的差异。结果表明,施用有机废弃物增加了土壤有效磷和水溶性磷含量,降低了土壤对磷的吸附能力,但影响程度因有机废弃物来源而异。施用猪粪/稻草秸秆堆肥和猪粪降低土壤磷最大吸附量比例(9.03%~15.60%)与施KH2PO4(10.59%~16.63%)相当,但施用沼渣、鸡粪和生活垃圾堆肥降低土壤磷最大吸附量的比例(5.09%~9.84%)明显低于施KH2PO4;施用2种污泥降低土壤磷最大吸附量的比例(4.32%~6.77%)最小。不同有机废弃物对土壤有效磷的影响差异较小,但对水溶性磷的影响较大。施用有机废弃物后,土壤磷最大吸附量的下降值与施用有机废弃物中铁、铝、钙含量呈负相关;土壤水溶性磷的变化量与施用有机废弃物后土壤交换性钙的增加量呈负相关,表明有机废弃物中铁、铝和钙等矿质成分的增加,可在一定程度上减少有机废弃物在土壤循环处理时磷对环境的负影响。在农田施用有机废弃物时,不仅要考虑有机废弃物磷素状况,也应适当考虑其他矿质成分的组成特点。该研究可为城郊农地科学施用有机废弃物提供依据。     

Ecotoxicological assessment of organic wastes using the soil collembolan Folsomia candida

The reproduction test with the collembolan Folsomia candida is used as a tool to evaluate the ecotoxicological potential of organic wastes currently applied to soil. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. F. candida showed varied sensitivity depending on the waste, but also depending on the endpoint assessed. Reproduction was more sensitive than survival, although no correlations between reproduction and physico-chemical parameters and pollutant burden could be found. On the other hand, mortality was directly related to the lack of stability of wastes, probably reflecting the toxicity of end-products such as ammonium. Body length was not shown to be a sensitive endpoint for waste testing, as it was neither affected nor even stimulated by waste concentrations.Organic matter, pH, and electrical conductivity varied with waste concentration in soil-waste mixtures, although their effect on collembolan performance was expected to be low and part of the complex effect exerted by wastes when applied to real soils. Selection of the water content is the most problematic aspect in waste testing, as it may affect the performance of test organisms. In this study, a qualitative approach for water content selection in waste testing was considered to be the most suitable.Treatment of wastes affected composition and toxicity. Composting of sewage sludge increased its stability, compared to the initial sludge, but decreased its non-persistent organic pollutant burden and toxicity. On the other hand, thermally dried wastes from sludge and pig slurry displayed high toxicity, mainly attributable to their low stability. The results from the study indicate the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays, but also the need for stabilization treatments of organic wastes prior to their reuse in soils.     

Molecular weight-dependent electron transfer capacities of dissolved organic matter derived from sewage sludge compost

Purpose

Dissolved organic matter (DOM) has been shown to be an efficient electron transfer facilitator in biogeochemical reactions due to its ability to mediate redox reactions. It has been known that various fractions of DOM differed in their chemical and biogeochemical behaviors in environment. However, there has been relatively little work directed at predicting the dependence of redox properties of DOM on its fractions.

Materials and methods

DOM was extracted from sewage sludge compost. Freeze-dried DOM was grouped into three fractions of different molecular sizes (<3,500, 3,500–14,000, and >14,000 Da) using dialysis bags (Spectra/Por 3 and 4, Spectrum Industries, California, US). Cycle voltammetry was used to investigate the redox behavior of the fractions. Chronoamperometry was employed to study their electron accepting capacities and electron donating capacities by applying fixed positive or negative potential to the working electrode in a conventional three-electrode cell. Fourier-transform infrared and three-dimensional excitation/emission matrix fluorescence spectroscopies were used to determine the functional groups in the fractions. Shewanella putrefaciens 200 (SP200) and Klebsiella pneumoniae L17 (L17) were used for all microbial iron(III) reduction experiments.

Results and discussion

Electrochemical methods show that the electron transfer capacity (ETC) of DOM depends on its molecular weight, and ETC is in the order of high-molecular weight DOM (H-DOM) > moderate-molecular weight DOM > low-molecular weight DOM. The same trend is discovered in the DOM-stimulated iron(III) oxide bioreduction where DOM fractions act as electron shuttles transferring electrons from the Fe(III)-reducing bacteria to the iron oxide. Both spectroscopic and cyclic voltammogram assays show the highest abundance of redox moieties associated to H-DOM, which is possibly responsible for its strongest electron-shuttling ability.

Conclusions

DOM has a wide molecular weight (MW) distribution due to the complexity of its chemical composition and structure. In addition to structural variations, DOM fractions with different MW have different redox properties and electron-shuttling capacities in microbial Fe(III) reduction. The results are of great significance for further studies on DOM geochemical behavior in environment.     

The use of urban organic wastes in the control of erosion in a semiarid Mediterranean soil

Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%.     

Sorption of dissolved organic nitrogen by acid subsoil horizons and individual mineral phases

Dissolved organic matter is important in translocation and export of nutrients from forest ecosystems. Its mobility in soil is restricted by sorption to mineral surfaces which depends on its chemical properties. Carboxyl and hydroxyl groups form strong bondings to mineral surfaces, whereas the role of N‐containing functional groups in the sorption process is less well understood. We examined in laboratory experiments the binding of dissolved organic matter from the forest floor to amorphous Al(OH)₃, goethite, kaolinite, and illite and to subsoils in order to compare the sorption and desorption of dissolved organic C with that of dissolved organic N. The mineral samples were equilibrated with acidic solutions of organic matter at pH 4. In the equilibrium solutions organic C and N and their contribution to two operationally defined fractions, namely the so‐called hydrophilic and hydrophobic fractions, were determined. We measured neutral and acidic amino sugars to discover the nature of the binding of organic N. Within the hydrophilic and hydrophobic fractions, the sorption and desorption of organic C and N did not differ, indicating that there was no preferential binding of N‐containing compounds. The hydrophilic fraction contained more N and sorbed less than the hydrophobic fraction, and so the overall retention of organic N by the mineral phases and subsoils was smaller than that of organic C. Among the amino sugar compounds, muramic acid was preferentially removed from the solution, whereas the neutral amino sugars were sorbed similar to organic C. The results suggest that the sorption of N‐containing compounds is favoured by acidic groups and not by amino groups.     

Long-term amendment of four different compost types on a loamy silt Cambisol: impact on soil organic matter,nutrients and yields

This study investigated the long-term effects of different composts (urban organic waste compost (OWC), green waste compost (GWC), cattle manure compost (MC) and sewage sludge compost (SSC)) compared to mineral fertilisation on a loamy silt Cambisol, after a 7-year start-up period. The compost application rate was 175 kg N ha^?1, with 80 kg mineral N ha^?1 and without. Soil characteristics (soil organic carbon (SOC), carbon-to-nitrogen (C/N) ratio and soil pH), nutrients (nitrogen (N), phosphorous (P) and potassium (K)) and crop yields were investigated between 1998 and 2012. SOC concentrations were increased by compost applications, being highest in the SSC treatments, as for soil pH. N contents were significantly higher with compost amendments compared to mineral fertilisation. The highest calcium-acetate-lactate (CAL)-extractable P concentrations were measured in the SSC treatments, and the highest CAL-extractable K concentrations in the MC treatments. Yields after compost amendment for winter barley and spring wheat were similar to 40 kg mineral N ha^?1 alone, whereas maize had comparable yields to 80 kg mineral N ha^?1 alone. We conclude that compost amendment improves soil quality, but that the overall carbon (C) and N cycling merits more detailed investigation.     

Modelling long‐term carbon dynamics in soils reconstituted with large quantities of organic matter

In urban conditions, the widescale availability of organic matter to be recycled and the necessity for soil reconstitution (Technosol) has led to the input of very large quantities of organic matter (up to 50% v/v). The long‐term degradation of these large quantities of organic matter in the soil is not well known. We monitored, over a 60‐month period, the total carbon (C) content and the particulate and biochemical fractions of reconstituted soils placed in 600‐litre boxes under natural conditions. The top layer was a sandy loam amended with 20 or 40% of sphagnum peat or organic compost (sewage sludge, wood chip compost or green waste compost) lying on a layer of sandy loam. We measured C mineralization over time under controlled conditions and built a long‐term model to simulate carbon dynamics where exogenous organic carbon (EOC) was divided into two biodegradable compartments. The model yielded the proportions of EOC that either resisted degradation or contributed to soil organic C storage by mineralization and/or humification. Organic matter degradation was linked to its maturity and to its contents in certain particulate and biochemical fractions but was independent of how much of a given organic matter was introduced. We found a good correlation between the degradable organic compartment and the lignin and cutin‐like, hemicellulose and cellulose‐like fractions larger than 1 mm. The model showed that a large part of initial EOC was still present in the soil after 5 years in a potentially biodegradable but resistant compartment. The degradation of that compartment by mineralization or humification is therefore expected to take longer.     

Phosphorus fractions and phosphorus delivery potential of a luvisol derived from loess amended with organic materials

In a long-term field experiment, started in 1962, the fate of P applied with different organic materials [farmyard manure (FYM), compost and sewage sludge] in comparison to mineral fertilizer was investigated. Soil samples were collected after 38 years' continuous addition of these amendments to a luvisol derived from loess and cultivated to a cereal-root crop sequence. The total P (P_t) content of all treatments increased compared with the original soil; NaOH-inorganic P (NaOH-P_i) representing Fe- and Al-bound P was the dominant inorganic fraction. At the beginning of the experiment the various P pools could be quantitatively ranked in the following order: NaOH-P_i>residual P~NaHCO₃-P_i>H₂O-P>HCl-P. The order changed as follows: NaOH-P_i>NaHCO₃-P_i>residual P~H₂O-P>HCl-P, with transformations of non-labile residual P to the labile NaHCO₃-P_i pool with continued P fertilization and cropping. In addition, the content of organic P (P_o) forms (NaOH-P_o and NaHCO₃-P_o) increased. P_t delivery potential (desorbable P pool) increased between 35% and 185% compared to the P delivery potential in 1962. Compared to mineral fertilizer application, the application of organics resulted in a significantly higher, and FYM in a lower, P adsorption capacity of soils. The calcium lactate-extractable P (plant-available P) increased from 43.1 mg kg^-1 soil in 1962 to 175.9 mg kg^-1 soil in the treatment with 49 t compost ha^-1. The increase in the citrate-dithionate Fe-O ranged between 44% and 154% in the different treatments compared to the Fe-O content in 1962. In a pot experiment with soil from the field experiment, P removal by ryegrass was in the following sequence: FYM>compost=sewage sludge>mineral fertilizer.     

Improvement of earthworm (Lumbricidae) community and activity in mine soils from open-cast coal mining by the application of different organic waste materials

Earthworms are important members of the decomposer food web in a wide range of sites. Previous field investigations on the development of earthworm populations of mine soils in the Lusatian coal mining region, Germany, have shown quite small population densities in quaternary sands and less or even no earthworms present in sandy soils derived from tertiary deposits. The aim of the present investigation was to improve the development of earthworm populations in mine soils from tertiary deposits by applying various types and amounts of organic waste residues, such as sewage sludge, composted sewage sludge, and green waste derived compost. Additionally, we were interested in the stimulation effect of organic waste materials on parameters of earthworm activity, such as food consumption and burrowing activity. The investigations were carried out in field mesocosms and laboratory experiments (microcosms; observation cages). In general, the population density, fresh biomass, food consumption, and the burrowing activity of earthworms were significantly improved by the application of the various organic waste materials compared with mineral fertilizers. Fresh sewage sludge in addition to composted sewage sludge were found to be the most favourable organic waste residues compared with green waste derived composts. The addition of brown coal sludge to sewage sludge did not reduced the stimulation effect. There was considerable variation in the population structure of a defined earthworm community which was exposed in the mesocosms during a two year period in relation to the types and amounts of the organic waste materials applied.     

Effects of fertilization with urban and agricultural organic wastes in a field trial – Waste imprint on soil microbial activity

In the past decades a significant change in composition of urban organic waste products has occurred in many first world countries, due to cleaner technologies as well as outsourcing of heavy industries. However, the societal perception of organic urban waste has become increasingly negative, leading to widespread advocacy of incineration. Therefore we established the ‘CRUCIAL’ long-term field trial in 2003, with the rationale that by approaching the known limits for a number of heavy metals below which no profound disturbance should be observed on key soil ecological functions, it should be possible to discern if some of the many unknown components in the composite urban waste as well as agriculturally based fertilizers have measurable impacts. The following treatments were established: human urine, sewage sludge (normal N-level and accelerated level aiming at three times normal N-level), degassed and subsequently composted organic municipal waste (normal and accelerated level), deep litter, cattle slurry, cattle manure (accelerated level), NPK fertilizer, unfertilized but with clover undersown and an unfertilized control. After 4 years the soil organic matter (SOM) C content, basal CO₂ respiration and soil microbial biomass (SMB) C was significantly affected by treatments. All soils having received organic fertilizer had higher SMB C than those with no added fertilizer (unfertilized and unfertilized with clover undersown) and inorganic fertilizer. The treatment effect on qCO2 (CO₂/SMB C) was not significant, but the unfertilized treatments showed the highest values. Treatments with accelerated levels of composted household waste and sewage sludge had the highest number of colony forming heterotrophic bacteria. Sole carbon source utilization in EcoPlates indicated a very robust microbial community in the treatments. Cumulative input of heavy metals was less than that required for reaching the heavy metal ecotoxicological limits, even after accelerated loading with sewage sludge corresponding to approximately 55 years of normal application. This could indicate that it is possible use organic urban waste for an extended period on a given site, without compromising soil functioning as long as ecotoxicological guidelines for heavy metal content are observed.