Trace metal analysis of sewage sludge and soils in Bahrain

Trace metals such as Pb, Zn, Cu, Ni, Cd and Fe were determined in sewage sludge produced at a sewage treatment plant in Bahrain (Tubli) and soils. The soils, both untreated and treated with the sludge, are used for agricultural purposes in Bahrain. The Trace-metals level showed the following range (μg g^?1 dry weight); Pb, 242 to 609; Zn, 704 to 836, Cu, 329 to 512; Ni, 23 to 41; Cd, 1.8 to 3.9 and Fe, 1867 to 4284. The data show the degree to which untreated soils have already been contaminated with trace elements. The level of trace-elements found in sludge showed the following range (μg g^?1 dry weight); Pb, 140 to 186; Zn, 597 to 836; Cu, 348 to 449; Ni, 47 to 53; Cd 5.7 to 9.2 and Fe, 5950 to 8520. Mean levels were generally close or lower than mean concentration reported in the United Kingdom and the United States for sludge. They were also lower than the suggested concentration limits for application of sludge on agricultural land, which is one of the most cost effective and attractive techniques for sludge disposal. Soils treated with this sludge (after 1 yr) were also analyzed and showed substantial enhancement of the available level of trace elements in the soil. This eventually will lead to an increase in the trace-element level in plants grown for human or animal consumption. This could have phytotoxic effects, and the possibility of toxic effects on live-stocks and human beings.     

Tillage effects on the accumulation of polychlorinated biphenyls in biosolid‐amended soils

Soil tillage along with the application of organic waste probably affects the concentrations of organic carbon and the enrichment of introduced polychlorinated biphenyls (PCBs). In a three‐year experiment the PCB status of soils from three different field sites (silty clay loam, silt loam, sandy loam) which were long‐term differently tilled (NT = no‐tillage, CT = conventional plough tillage) and amended with two different organic wastes such as sewage sludge and compost (biosolids) was examined. No significant alteration in soil‐PCB quality and quantity with biosolid application could be proven within the course of the experiments. This indicates soil‐air exchange of PCBs dominates their concentrations in soil. Organic carbon in soil was significantly tillage‐dependent and determined the fate of PCBs resulting in a generally elevated PCB‐level in the non tilled soils. Linear regression of PCB load and organic matter content of all investigated untreated soils was highly significant (R² = 0.73). Due to already elevated PCB levels in non tilled soils with a maximum of 65 μg kg^—1 in the superficial layer of the silt loam control plot, any additional potential input, i. e. through the amendment with organic wastes, should therefore be avoided.     

Urease activity in sewage sludge-amended soils

Three diverse field-moist soil samples were treated with five sewage sludges (applied at five loading rates) containing high concentrations of heavy metals. Urease activity was assayed after 0, 3, 7, 14 and 30 days of incubation. Results showed that when soils were treated with the sewage sludges, urease activity was often inhibited at the lower loading rates (2.2 and 8.9mg sludge g^?1 soil), but was enhanced substantially with the higher application rates (22.2, 44.4 and 100 mg sludge g^?1 soil). Inhibition of urease activity in the sewage sludge amended-soils ranged from 4 to 37% (Domino soil), 8–27% (Hesperia soil), and 3–49% (Ramona soil) at various times of incubation. Inhibition of the enzyme activity was attributed to the presence of heavy metals in the sludges. The increased activity of urease in the sludge-amended soils at the highest application rate (100 mg sludge g^?1 soil) ranged from 1.13 to 5.00-fold (Domino soil), 1.20–4.04-fold (Hesperia soil), and 1.13–5.40-fold (Ramona soil). Enhanced urease activity was believed to be due to the additional source of organic matter and nutrients supplied by the sludge which stimulated microbial activity and subsequent urease synthesis.     

Possibilities of using sewage sludge as nitrogen fertilizer for maize

Abstract

The objective of this study was to determine the effects of nitrogen fertilizer sources of ammonium sulphate and municipal sewage sludge on yield, N content and uptake of the maize (Zea mays L.). Nutrient and heavy metals were determined in soil and plant. The experiment with three sludge rates (256, 513 and 1026 kg total N ha^?1 or 9.5, 18.0 and 38.1 t ha^?1 sludge), two nitrogen rates (80 and 160 kg N ha^?1) and zero-N control were conducted on a clay loam soils under irrigated conditions in Eastern Anatolia region in Turkey. Treatments were arranged in a randomized complete block design with four replications. Yield, N content and total N uptake of maize increased significantly with sludge application. 9.5 t and 19.0 t ha^?1 sewage sludge applications did not significantly affect heavy metal content of leaf and grain. However, 38.1 t ha^?1 sludge applications increased leaf Pb and Zn. DTPA-extractable Cd, Cu, Fe, Pb and Zn concentrations of the soil increased at applications of 38.1 t ha^?1 sewage sludge, whereas applications of 9.5 t and 19.0 t ha^?1 sludge only resulted in elevated levels of Cu and Zn, We conclude that if sewage sludge is to be used in production of maize, applications rate up to 19 t ha^?1 could be accepted. However, this means also that the N requirement of maize crop is not covered by the sludge; therefore, the rest of nitrogen could be supplied as inorganic N.     

Survival of Rhizobium japonicum in soil-sludge environment

The usage of sewage sludge on agricultural lands is an effective and inexpensive practice that provides nutrients for crops. A successful legume crop also depends on the survival of Rhizobium in the soil environment. The number of R. japonicum (USDA 110) in treatment groups containing various soil-to-sludge ratios (control, 13:1, 9:1 and 5:1) during incubation for 1, 21 and 42 days was investigated. The control group contained soil without sludge. Mecklenburg clay and Enon sandy loam soils (both are fine, mixed, thermic, ultic Hapludalfs) were used. All treatments were adjusted to pH 6.7 and brought to 75% of field capacity with 1 ml inoculum (9 × 10⁸ cells ml^? 1) and distilled water. Samples were incubated at 25 C and monitored periodically for the number of surviving R. japonicum (USDA 110) organism by the plant infcction-MPN method. Strains were identified by gel-immunodiffusion. Recovery of rhizobia from both soils was < 1% in all treatment groups after 42 days. However, for control, 13:1, 9:1 and 5:1 groups, the percentage recovery was higher in Enon sandy loams (7.9, 2.3, 2.3 and 2.3%, respectively) at 21 days. Recovery of rhizobia in the 5:1 group from both soils was 7.9% after 1 day, whereas control values were 92%. A decline in rhizobial populations in higher sludge soils may be due to the heavy metals present and available during mineralization of sludge in soils. However, the number of R. japonicum that survived to 21 days was 1.7 × 10₅g^?1 and 1.7 x 10⁶g^?1 for Mecklenburg clay and Enon sandy loam soils with highest sludge, respectively.     

Growth of apple seedlings on sludge‐amended soils in the greenhouse

Abstract

Open pollinated ‘York Imperial’ apple (Malus domestica Borkh.) seeds were germinated and grown for a period of 7 months in: (1) sand with complete nutrient solutions added; (2) limed and unlimed soil, (3) limed and unlimed soil amended with two different sewage sludges at rates of 25, 50 or 100 dry kg ha^‐1. A third composted, lime stabilized sludge was added either sieved or non‐sieved (to remove wood chips) at the same rates. The sludge materials used were: (1) a high metal, composted sludge from Baltimore, MD (BALT); (2) a high Cd sewage sludge (CITY) and (3) a low metal, composted sewage sludge from Washington, D.C. (DC).

Germination was unaffected by treatments. After 7 months, the best growth was obtained from the sand plus nutrient solution media. Two of the three sludge materials increased seedling growth over that of the soil, either limed or unlimed. The BALT compost treated soils produced the lowest growth, particularly when unlimed. Elevated tissue metal levels indicated that Mn, Zn, Cu and Ni were the probable causes of reduced growth noted from the BALT compost treatment. The use of soil with or without low metal sludges as media for early apple seedling growth when compared to standard sand culture is not recommended.     

Effect of Chloride and Sulfate Salinity on Micronutrients Release and Uptake from Different Composts Applied on Total Phosphorus Basis

Generation of different biowastes is increasing day by day, and ultimate load on agricultural lands has increased. Concerns over increased phosphorus (P) application with nitrogen (N)–based compost application shifted the trend to P‐based applications. But focus on only one or two nutritional elements will not serve the goals of sustainable agriculture. Full insight into nutrient availability from different composts is necessary. The need to understand the nutrient release and uptake from different composts has increased because of the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, current greenhouse studies were designed to evaluate the bioavailability and leachability of some micronutrients [calcium (Ca), magnesium (Mg), and zinc (Zn)] from different biocomposts under chloride (Cl^?) and sulfate (SO₄ ^?2) saline environment. In the first pot experiment, soil was amended with livestock compost (AC), poultry compost (PC), and composted sludge (SC) at the rate of 200 kg P ha^?1 equivalent bases. Pots were irrigated with artificial saline water of sodium chloride (NaCl) or sodium sulfate (Na₂SO₄; 60 mmol_c L^?1), and leachates were collected for Ca and Mg analysis. As composts were applied on total P bases, which left varying amounts of nutrients in each treatment, it was observed that nutrient uptake and release differed greatly regardless of the total amount applied with each compost type. Amount of Ca applied with PC (3.9 g pot^?1) was greater, but Ca concentration in leachate was greater under AC‐amended treatments. Magnesium concentration also varied greatly under compost types. Among the saline irrigation, Ca and Mg concentration in leachate increased under both saline irrigations compared to nonsaline treatment, and SO₄ ^?2 had relatively greater ionic strength to replace cations than Cl^?. Calcium, Mg, and Zn uptake by maize stem and leaves were greater from SC‐amended pots followed by PC, SC, and control. Irrespective of the salt types, Ca and Mg uptake reduced under both saline irrigations, whereas Zn uptake increased as compared to nonsaline treatment. Among the salt types, it was observed that plant growth and nutrient uptake was more influenced by Cl^? than SO₄ ^?2 saline irrigation. In the second experiment, soil was saturated with NaCl and NaSO₄ (75 mmol_c L^?1) and amended with AC. The trend of nutrient uptake under both salt types was similar to first experiment, and the results of AC amendments have been discussed. It can be inferred from the results that regardless of the total amount applied, nutrient uptake greatly varies under different composts and their availability depends upon the source rather than total amount applied. Analogously, sulfate‐dominated irrigation water can increase the leaching of Ca and Mg from root zone more than chloride.     

Rice yield nutrient uptake as affected by cyanobacteria soil amendments—a pot experiment

Rice production and cyanobacterial N in acid soil can be improved by liming. There is evidence that the organic amendments can increase the soil pH. The aim of this study was to find appropriate combination of soil amendments and cyanobacteria capable for enhancing nutrient uptake and improving rice yield in acidic paddy soil. Three soil amendments (rice straw, sewage‐sludge composts, NPK) with and without inoculation of cyanobacteria were studied for rice plants (Oryza sativa L.) in a pot experiment. The sludge compost had significantly reduced soil acidity from 5.44 to 6.67. The plant N and K uptake increased significantly with sludge and cyanobacteria application. The yield components increased significantly with sludge, but decreased thereafter, an exception was the number of panicles, with straw compost. These characters were also significantly affected by inoculation with cyanobacteria except 100‐grain weight, filled‐grain percentage, and harvest index. The combination of sludge compost and cyanobacteria improved the yield components and consequently grain yield (138 g pot^–1) compared with sludge treatment only (132 g pot^–1). The amount of cyanobacterial N absorbed (N‐difference method) by rice plant under sludge compost was higher than that of soils amended with either rice straw or NPK treatments. Therefore, the addition of sewage sludge to acid paddy soil not only amended the soil properties but also activated the cyanobacteria and consequently improved rice plant nutrition and grain yield.     

Spatial,seasonal and ecological risk assessment of organohalogenated contaminants in sediments of Swartkops and Sundays Estuaries,Eastern Cape province,South Africa

Purpose

Run-off from industrial and agricultural activities has continued to be a major source of organohalogenated contaminants (OHCs) in the environment. Swartkops (SWE) and Sundays Estuaries (SDE) located in the city of Port Elizabeth, South Africa, were selected for this study because of their proximity to industrial and agricultural activities.

Materials and methods

In this study, we determined the levels, seasonal occurrence as well as the ecological risk monitoring of 18 organochlorine pesticides (OCPs), 17 polychlorinated biphenyls (PCBs) and six polybrominated diphenyl ethers (PBDEs) in the sediments of SWE and SDE using a gas chromatograph coupled with a micro electron capture detector.

Results and discussion

HCHs, BDE-17, tri- and tetra-CBs dominated the OHC profiles in sediments of both estuaries. The respective concentration ranges of OCPs, PCBs and PBDEs in SDE sediment were 0.06–0.93 μg g^?1 dw, 0.08–1.71 μg g^?1 dw and 0.08–32.41 ng g^?1 dw while that of SWE in that order were 0.10–4.70 μg g^?1 dw, 0.07–3.80 μg g^?1 dw and 0.11–130.21 ng g^?1 dw. The high concentrations of OHCs in SWE may be due to the high usage of its surrounding area for industrial activities. The concentrations of all OHCs with exception of PCBs were higher in spring for both estuaries probably due to the heavy rain experienced during spring season. Cluster analysis and spatial distribution of OHCs indicated that samples around the Motherwell Canal in the SWE were more polluted. Total organic carbon (TOC) was strongly correlated with most OHCs in SWE revealing that TOC controls the sorption of OHCs in this estuary. Risk analysis showed that most sampling points had PCBs and HCHs concentration greater than their respective sediment quality guideline (SQGL) indicating a high risk to benthic species in SDE and SWE.

Conclusions

Samples collected from the SWE were more polluted than those collected from the SDE probably due to the extensive use of the catchment of SWE for industrial activities. In comparison with SQGL, most sampling points had PCBs and HCHs concentrations greater than their respective ERL and TEL values, indicating the potential risk to biota in SDE and SWE. Thus, an urgent need to manage and mitigate the OHCs concentrations in these estuaries is recommended.

     

Growth and Heavy-Metal Uptake by Lettuce Grown in Soils Applied with Sewage Sludge Compost

A pot experiment was conducted to investigate the effect of sewage sludge compost (SSC) alone and applied with chemical fertilizer on growth and heavy-metal accumulations in lettuce grown on two soils, a Xanthi-Udic Ferralosol and a Typic Purpli-Udic Cambosol. The treatments included control; nitrogen–phosphorus–potassium (NPK) fertilizer; sewage sludge compost applied at the rates of 27.54 (SSC), 82.62 (3SSC), 165.24 (6SSC) t hm^–2; and coapplication treatment (1/2 SSC + 1/2 NPK), where the N, P, and K inputs from NPK fertilizer, SSC, and coapplication treatments were normalized to the local recommend rates. The SSC application increased the biomass; copper, zinc, and lead contents in lettuce; and soil total and diethylenetriaminepentaacetic acid (DTPA)–extractable metals. However, SSC alone at the recommended rate caused less plant biomass than NPK fertilizer alone. Coapplication treatment obtained greater or similar biomass to NPK fertilizer alone and did not increase heavy-metal accumulation in soils and plants. The results demonstrated that SSC should be applied to soils with chemical fertilizers.     

Effect of sewage sludge on nodulation and N2−fixation in alfalfa grown on calcareous loamy soils

The influence of different rates of sludge applications to calcareous loamy soils of Saudi Arabia, on nodulation and symbiotic N₂?fixation in alfalfa plants (Medicago sativa L.) was studied in a pot experiment. The effect of heavy metals accumulation in soil due to continuous irrigation of the test soil with sewage water was also investigated. Application of up to 80 g sludge per pot enhanced nodulation, nitrogenase activity, dry matter yield and N-contents of alfalfa plants growing in loamy soils either previously irrigated with sewage water or well water. However, sludge applied at the rate of 160–200 g pot^?1 inhibited the nodulation, N accumulation and dry matter yield of alfalfa. The response of alfalfa to sludge was dependent on the rhizobial strain used. Our results also showed that accumulation of heavy metals due to continuous irrigation of a calcareous sandy loam soil with sewage water, for more than 10 years, didn't inhibit N₂?fixation in alfalfa plants, but enhanced it. Microelements in alfalfa plants increased with increase in the rate of sludge application. Although high rates of sludge application affected nodulation and N₂?fixation of alfalfa, dry matter and the nitrogen contents of the plants were not highly affected. Therefore, the inhibitory effect of high rates of sludge was most probably due to the toxic effect of heavy metals on the microsymbiont rather than on the plants.     

Selected persistent organic pollutants (POPs) in the rhizosphere of sewage sludge-treated soil: implications for the biodegradability of POPs

The impact of regular application of sewage sludge or farmyard manure on the organic contaminant loads in soil was assessed in a model rhizobox experiment. Two soils originating from a long-term field crop rotation and fertilizer experiment running since 1996 were used. The total polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorinated pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS) contents were determined in the rhizosphere and bulk soil. The results showed low but still detectable contents of PCBs and OCPs in the soil, substances which were banned a few decades ago. Among the OCPs, dichlorodiphenyltrichloroethane (DDT) and its metabolites reaching up to 18.2 µg kg^?1 of the soil even exceeded the preventive levels for these compounds in agricultural soils, i.e. 7.5 µg kg^?1 of soil. For PBDEs, PFOA, and PFOS, their contents in the soil significantly increased with sewage sludge application. The enhancement of the potential biodegradability of the POPs in the rhizosphere was confirmed only for hexachlorocyclohexane (γ-HCH), where, the level of γ-HCH increased significantly in the rhizosphere soil compared to bulk soil. Thus, natural attenuation of POPs in the soil-plant system seems to be insufficient for most of the investigated compounds.     

Impact of anthropogenic activity on the Hg concentrations in the Piracicaba river basin (São Paulo State, Brazil)

A sampling and analysis program has been completed between 1995 and 1998 in order to determine mercury concentrations in water, sediments, soils and fish in the Piracicaba river basin, one of the most populated and industrialized regions in Brazil. In sediment, the average Hg concentrations varied between 33 ± 17 ng g^?1 and 106 ± 78 ng g^?1, in samples collected during the rainy and dry season, respectively. The same averages were also found for soil samples (35 ± 14 and 109 ± 61 ng g^?1). In water, the total Hg concentration varied between < 1.1 and 24.0 ng L^?1. In piscivore fish, up to 943 μ g Hg kg^?1 was found. Our results show that all compartments undergo Hg contamination, in view of the levels found in pristine environments. Water contamination seems to be due mainly to diffuse processes of soil erosion and suspension of river bed sediment during the rainy season. Also untreated wastewaters generated by industrial activities and from domestic sewage appear to be potential non-point sources in the most industrialized and populated part of the basin. On the other hand, atmospheric transport of mercury originating from the Campinas Metropolitan Region could be another source of mercury contamination, especially in the basin headwaters.     

Comparative availability to wheat of metals from sewage sludge and inorganic salts

A greenhouse experiment was conducted to evaluate the availability of metals from sewage sludge and inorganic salts, and the effect of pH and soil type on yield and metal (Zn, Cu, Cd and Ni) uptake by wheat (Triticum aestivum L. var. ‘holly’). Soils used in this study were Hartsells sandy loam (fine-loamy, siliceous Thermic Typic Hapludult) and Decatur silty clay loam (Clayey, kaolinitic, Thermic Rhodic Paleudult). Two treatments of sewage sludge containing metals were applied at the rate of 20 and 100 mt ha^?1. Inorganic Salts of Zn, Cu, Cd, and Ni were applied (as sulfate salts) at concentrations equivalent to those found in the 20 and 100 mt ha^?1 sludge. One treatment consisted of inorganic metals plus sewage at the 20 Mg ha^?1 rate. Two soil pH levels, one at field pH (below 6.0) and another pH adjusted between 6.5 and 7.0 were used. Wheat plants were harvested four weeks after germination. Two more subsequent harvests were made at four week intervals. For each harvest, dry matter yield increased as the rate of sludge application increased for both soil types. The soil pH also influenced the dry matter yield. High yield was observed when the pH was adjusted between 6.5 to 7.0 for both soils. An increase in yield was also observed at each subsequent harvest for most of the treatments. Inorganic salt treatments produced lower dry matter yields when compared with the sludge. Both sludge application and metal salts increased plant tissue concentration of Zn, Cu, Cd, and Ni at field pH for both soils. However, increasing the pH of the soil for both sludge and inorganic salt treatments generally decreased the tissue concentration of the above metals.     

Cadmium soil sorption at low concentrations. VII: Effect of stable solid waste leachate complexes

Soil sorption of Cd in solid waste leachates of landfill, sewage sludge, and incinerator residue was studied in the laboratory with emphasis on the behavior of Cd present as stable complexes. A previously developed speciation method was employed to determine free divalent Cd and complexed Cd of various stability. The experiments involved 13 soils covering a wide range of clay contents. Speciation of Cd present in solution after exposure to increasing amounts of soil showed that stable Cd complexes did not sorb onto the soil. This was supported by equilibrium isotherms exhibiting similar solute concentration intercepts and by a leaching study of soil columns which resulted in the same concentration of stable Cd complexes. The stable complexes were of the order of 1 to 10 μg Cd L^?1, the higher values found in landfill and sewage sludge leachate. Very little Cd present in the leachates was free divalent Cd (a few percent), which may explain the low Cd distribution coefficients (3 to 70 L kg^?1).     

Evolution of mercury content in agricultural soils due to the application of organic and mineral fertilizers

Purpose

Mercury pollution in agricultural soils associated to the use of fertilizers and its influence on crops is a cause of major concern. The purpose of this work was to investigate the impact of the application of different organic and mineral fertilizers on the Hg concentration in the agricultural soils and its uptake by barley.

Materials and methods

Hg concentration was studied through a field test in an agricultural land located in the province of Palencia (Spain) over a 5-year period. The impact of irrigation and of four different fertilizers (a mineral one and three different organic waste materials, namely municipal solid waste compost, sewage sludge, and dehydrated sewage sludge) was assessed. The amounts of the mineral and organic fertilizers added to the soil were determined according to agricultural fertilization needs. The experimental crop was barley (Hordeum vulgare L.), planted as an annual crop. Mercury analyses were conducted using a direct mercury analyzer and validated according to EPA Method 7473. BCR-141R was used as a certified reference material.

Results and discussion

After 5 years, whereas the application of the mineral fertilizer did not increase the mercury content in the agricultural soils, the application of the organic residues led to Hg contents 1.7–7.6 times higher than that of the control soil. The treatment with solid municipal waste compost (MSWC) led to the largest increase in Hg content in the soil, followed by composted sewage sludge (CSS) and by dehydrated sewage sludge (DSS). No significant differences were observed in the Hg content in the barley grains, although the highest values were associated to the sludge-treated plots.

Conclusions

The application of organic fertilizers such as sewage sludges and municipal solid wastes led to an increase in the mercury concentration in the agricultural soils, noticeable for soils with low initial Hg concentrations (similar to background levels). This increase differed depending on the type of waste and on the intra-organic matter diffusion mechanisms, as well as on the type of irrigation of the agricultural land. Conversely, no significant differences in the Hg content in grains were found among the soils with the different fertilization treatments, although the highest values were observed for those treated with sewage sludge. The resulting Hg levels in both soils and grains were within legal limits, posing no danger to the environment or to human health.

     

Impact of Sewage Sludge Compost Utilization on Chemical Properties of Olive Grove Soils

Field experiments were conducted for four years, between 1998 and 2002, in two olive grove soils of adult olive orchards (Olea europaea L. cv. Cornicabra) in a clay loam soil in Seseña (Toledo, Spain) and in a sandy loam soil in Aranjuez (Madrid, Spain). There were four treatments, sewage sludge compost (SSC), sewage sludge compost plus urea (SSC+U), urea (U) and control (C). Each treatment was replicated four times and two depths were studied (0-15 and 15-30 cm). Once a year, before spreading sewage sludge compost, soil samples were taken at depths of 0 to 15 cm and 15 to 30 cm. Organic matter, total Kjeldhal nitrogen, phosphorus availability, pH, and electric conductivity were measured. No differences were found between treatment on organic matter and electric conductivity after four years of application of sewage sludge compost to two olive grove soils. In relation to nitrogen content, sewage sludge compost, only in Seseña, produced higher nitrogen soil content than the traditional urea treatment. Sewage sludge compost applied on olive grove soils improved the Phosphorus availability for the olive tree. In Aranjuez, the use of sewage sludge compost increased the pH of the soil with respect to Urea and Control plots. In Seseña, the reverse effect was found.     

Long‐lasting impact of biowaste‐compost application in agriculture on soil‐quality parameters in three different crop‐rotation systems

Soil‐quality parameters, such as soil organic matter (SOM) and plant‐available nutrient contents, microbial properties, aggregate stability, and the amounts of heavy metals were carried out in arable soils of different rotation schedules applied with a total of 50 Mg dry mass ha^–1 biowaste compost relative to an untreated control. This was investigated during a 10 y period from 1994 to 2004. Overall, soil‐quality parameters studied appeared to be promoted by biowaste‐compost application. This was evidenced for example by a remarkable increase of SOM and total N content of ≈ 15%–20% relative to the control. Subsequently, amounts of soil microbial biomass and alkaline phosphatase activity were significantly increased as well. In addition, biowaste‐compost application revealed an increase of plant‐available P and K contents and aggregate stability in soil. There was, however, no treatment effect for net N‐mineralization rates. Moreover, in soils of maize and sugar beet rotation schedule a slight decrease was found. Heavy‐metal contents of Pb and Zn were significantly increased in all compost‐treated soils, whereas no significant increase of Cd and Cu contents was measured. However, the investigated amounts were far below of the limits of the German Biowaste Ordinance. It is finally recommended, that biowaste compost may sustain and improve soil quality in agriculture when N nutrition will be considered.     

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.     

Soil Organic Matter Quality and Zinc and Lead Sorption as Affected by a Sewage Sludge Or a Sewage Sludge Compost Application

Sewage sludge (SS) or sewage sludge compost (SSC) were applied to soil under controlled conditions, at rates of 0 or 200 Mg ha^?1, to investigate changes in dissolved organic matter (DOM), humic acids (HA), and Pb and Zn sorption in the soil. Infrared spectroscopy, visible spectrophotometry, and sorption isotherms (mono-metal and competitive sorption systems) methods were used to assess the changer. The E₄/E₆ ratio (λ at 465 / λ at 665 nm) and the infrared spectra of DOM and HA showed aromatic behaviour in compost-soil (SSC-S); in contrast sewage sludge-soil (SS-S) showed an aliphatic behaviour. Application of either SS or SSC increased the Pb and Zn sorption capacity of soil. The Pb and Zn sorption increased in soil and soil mixtures with a competitive metal system. The metal affinity sequence for soil, SS-S, and SSC-S was compared with the predicted affinity sequences obtained from metal properties. Poor correspondence was observed between the metal affinity sequence and the metal affinity sequence predicted by ionic potential, indicating that metals bonding to soils were not predominantly electrostatic. An affinity sequence based on Pearson's theory agreed with the metal affinity sequences for soils. A statistical analysis showed that the bands assigned to esters (1080 cm^?1) of DOM, phenolic OH (1420 cm^?1), amide I (1650 cm^?1), carboxyl and carbonyl C=O stretches of different nature, C=O stretch of aromatic esters, aliphatic cetone, aldehyde (1720 cm^?1), ethers and esters (1230 cm^?1), aliphatic alcohols (1125 cm^?1), and lignin (1380 cm^?1) of HA were correlated with Zn constants of Langmuir adsorption isotherm (P < 0.05).