Recycling Of Sewage Sludge Research Articles

Chelate-Assisted Heavy Metal Removal by Sunflower to Improve Soil with Sludge

Crops are used to improve land through phytoremediation. When heavy metals are the pollutants, chelates are added to increase their solubility for uptake and removal. The U.S. Environmental Protection Agency recommends recycling of sewage sludge back to land, which results in heavy metal accumulations at sludge farms. However, almost no information is available concerning the efficacy of chelates applied to soil with sludge for heavy-metal removal. The objective of this work was to compare heavy metal uptake by sunflower (Helianthus annuus L.) grown in composted sludge or in soil from a sludge farm, when the chelate ethylenediamine-tetraacetic acid (EDTA) was added to facilitate uptake of the heavy metals. Plants were grown in pots in a greenhouse. Fifty-four days after planting, the tetrasodium salt of EDTA was applied at rates of 0, 1, and 2 g EDTA salt per kg medium (composted sludge or soil with sludge). At harvest, 68 days after planting, three non-essential (Cd, Ni, Pb) and four essential heavy metals (Cu, Fe, Mn, Zn) were measured in roots, stems, and leaves. At 2 g EDTA salt/kg, EDTA increased uptake of Cd, Ni, Pb, Cu, Fe, and Zn by roots of sunflower grown in the composted sludge. The EDTA did not increase concentrations of the heavy metals in any plant part of the sunflowers grown in the soil with sludge or in the aboveground portions of the sunflower grown in the composted sludge. With no EDTA, stems and leaves of plants grown in the composted sludge had higher-than-normal concentrations of Cd, Ni, and Pb. With no EDTA, the bioaccumulation coefficients (concentration of metal in the plant/concentration of metal in the medium) for Cd, Ni, and Pb in leaves of sunflower grown in the composted sludge were 2.0, 1.4, and 0.4, respectively; for stems, the bioaccumulation coefficients were 2.9, 2.2, and 0.7, respectively. With no EDTA, the bioaccumulation coefficients for Cd, Ni, and Pb in leaves of sunflower grown in the soil with sludge were 2.3,0.4, and 0.4, respectively; for stems, they were 0,0, and 0, respectively. (The concentrations of Cd, Ni, and Pb in stems of sunflower grown in the soil with sludge were below detection limits.) The higher-than-one bioaccumulation coefficients for Cd and Ni in the leaves and stems of sunflower grown in the composted sludge with no EDTA indicate that natural chelating agents were solubilizing these non-essential heavy metals and making them bioavailable.

Safe Recycling of Sewage Sludge on Agricultural Land—Biowaste

More than 50 000 wastewater treatment plants are operating in the European Union, producing more than 7.9 million tons of dry solids per year. The amount of sewage sludge will continue to increase as the Urban Wastewater Treatment Directives continues to be implemented in the different member countries. It is now undeniable that various toxic organic compounds, such as surfactants, hydrocarbons and residues derived from plastics are found in sewage sludge. The BIOWASTE project, under the EU 5th framework programme, offers an integrated study of xenobiotics throughout sludge recycling, using a combination of complementary approaches such as biotechnology, eco-toxicology, plant toxicology, analytical chemistry, microbiology, mathematical modelling, life cycle costing and life cycle analysis. This paper presents an overview of the results as well as their implication on the current EU regulatory work in progress concerning sewage sludge application. Particularly, two major findings are here detailed: the isolation, characterization and use of anaerobic xenobiotic-degrading microorganisms, and the modelling of the fate and impact of xenobiotics on anaerobic digestion.

Transition metal rates in latosol twice treated with sewage sludge

Agricultural recycling of sewage sludge has been a source of accumulation of heavy metals in the environment which may reach toxic levels and cause serious damage to the biota. Field experiments were undertaken for two agricultural years (2000 and 2002) and effects of two sewage sludge applications were evaluated through the extraction of (essential and non-essential) transition metals by diethylenetriaminepentaacetic acid (DTPA) extractor in a medium texture dystrophic Dark Red Latosol. Cd, Ni, Co, Pb and Cr were not detected. Application of sewage sludge initially caused a slight pH rise in the soil; later pH lowered and kept itself close to the starting level. It could be concluded that through consecutive sludge application, extractable rates of Fe and Mn in soil samples gradually increased during the two agricultural years in proportion to sewage sludge doses and sampling period. In fact, they were higher than rates of control. Due to low concentrations of soil samples, extractor had a restricted capacity for evaluation of its phytoavailability.

Effect of SiO 2–Al 2O 3–flux ratio change on the bloating characteristics of lightweight aggregate material produced from recycled sewage sludge

This study investigates the characteristics of lightweight aggregates sintered from sewage sludge ash by modifying the proportion of the main components (SiO 2–Al 2O 3–flux). The ash of incinerated sludge from a municipal sewage treatment plant (STP) was used as the tested material and sintering temperature ranged from 1050 to 1100 °C within a time span of 10–30 min. The sludge ash appeared to have a high proportion of SiO 2 (44.89%), Al 2O 3 (11.62%) and Fe 2O 3 (6.81%) resembling the dilatable shale. When the sintering temperature was raised to above 1060 °C, the blowing phenomenon appeared. The aggregates become lighter in weight by prolonging the sintering time and raising the temperature. Cullet powder (amorphous SiO 2), Al 2O 3, and fly ash were added to sludge ash to analyse the characteristic changes of the aggregates. The results showed that amorphous SiO 2 lowered the melting point and increased foaming; Al 2O 3 raised the compression resistance; fly ash lowered the sintering temperature required. However, the composition of fly ash can vary dramatically, resulting in a less predictable characteristic of aggregates.

Digested sewage sludge solidification by converter slag for landfill cover

A new technology for solidification of digested sewage sludge referred to as converter slag solidification (CSS) has been developed using converter slag as the solidifying agent and quick lime as the solidifying aid. The CSS technology was investigated by analyzing the physicochemical properties of solidified sludge and determining its microstructural characteristics. The feasibility of using solidified sludge as a landfill cover material was considered in the context of the economical recycling of waste. Sludge solidified using the CSS technology exhibited geotechnical properties that are appropriate for replacing currently used cover soil. Microscopic analyses using XRD, SEM and EDS revealed that the main hydrated product of solidification was CSH (CaO · SiO 2 · nH 2O), which may play an important role in the effective setting process. Negligible leaching of heavy metals from the solidified sludge was observed. The solidification process of the hydrated sludge, slag and quicklime eliminated the coliform bacteria. Recycled sewage sludge solidified using CCS technology could be used as an effective landfill cover.

Biotechnology of intensive aerobic conversion of sewage sludge and food waste into fertilizer

Biotechnology for intensive aerobic bioconversion of sewage sludge and food waste into fertilizer was developed. The wastes were treated in a closed reactor under controlled aeration, stirring, pH, and temperature at 60 degrees C, after addition of starter bacterial culture Bacillus thermoamylovorans. The biodegradation of sewage sludge was studied by decrease of volatile solids (VS), content of organic carbon and autofluorescence of coenzyme F420. The degradation of anaerobic biomass was faster than biodegradation of total organic matter. The best fertilizer was obtained when sewage sludge was thermally pre-treated, mixed with food waste, chalk, and artificial bulking agent. The content of volatile solid and the content of organic carbon decreased at 24.8% and 13.5% of total solids, respectively, during ten days of bioconversion. The fertilizer was a powder with moisture content of 5%. It was stable, and not toxic for the germination of plant seeds. Addition of 1.0 to 1.5% of this fertilizer to the subsoil increased the growth of different plants tested by 113 to 164%. The biotechnology can be applied in larger scale for the recycling of sewage sludge and food wastes in Singapore.

Potential for increased human foodborne exposure to PCDD/F when recycling sewage sludge on agricultural land.

Sewage sludge from municipal wastewater treatment is used in agriculture as a nutrient source and to aid in moisture retention. To examine the potential impact of sludge-amended soil on exposures to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from plant and animal foods, we conducted a review of published empirical data from international sources. Levels of PCDD/F in municipal sewage sludge ranged from 0.0005 to 8,300 pg toxic equivalents (TEQ)/g. Background levels in soil ranged from 0.003 to 186 pg TEQ/g. In sludge-amended soils, levels of PCDD/F ranged from 1.4 to 15 pg TEQ/g. Studies that measured levels before and after sludge treatment showed an increase in soil concentration after treatment. Relationships between PCDD/F levels in soil and resulting concentrations in plants were very weakly positive for unpeeled root crops, leafy vegetables, tree fruits, hay, and herbs. Somewhat stronger relationships were observed for plants of the cucumber family. In all cases, large increases in soil concentration were required to achieve a measurable increase in plant contamination. A considerably stronger positive relationship was observed between PCDD/F in feed and resulting levels in cattle tissue, suggesting bioaccumulation. Although PCDD/Fs are excreted in milk, no association was found between feed contamination and levels of PCDD/Fs measured in milk. There is a paucity of realistic data describing the potential for entry of PCDD/Fs into the food supply via sewage sludge. Currently available data suggest that sewage sludge application to land used for most crops would not increase human exposure. However, the use of sludge on land used to graze animals appears likely to result in increased human exposure to PCDD/F.

下水汚泥の共ガス化特性(FP2 燃料多様化・環境技術2)

Recently, the amount of sewage sludge in waste is increasing. However, the technology for thermal recycling of sewage sludge is not established yet. The purpose of this study is to develop a co-gasification technology for a mixture of sewage sludge and higher calorific fuel such as plastic waste. Co-gasification experiments have been performed in a lab-scale bubbling fluidized bed. As to the results, gasification gases such as H_2, CO, CH_4, C_2H_4, C_2H_6 and C_3H_6 were produced. Concentration of the gases obtained increase as air ratio is reduced. Heating value of the obtained eas is higher than 1500 kcal/m^3N for an air ratio of 0.3.

Recycling of sewage sludge to grassland: a review of the legislation to control of the localization and accumulation of potential toxic metals in grazing systems

AbstractThe recycling of sewage sludge or biosolids to grassland is strategically important in the European Union (EU) and its use is tightly regulated to control the risk of pathogen transfer to animals and the food chain. Sewage sludges not only contain valuable concentrations of beneficial nutrients, but also elevated concentrations of potentially toxic metals (PTM) compared with average background concentrations in the soil. The EC and UK regulations refer to six PTM, Cd, Pb, Cu, Zn, Ni and Hg, with provisional regulations for Cr, that have to be controlled to prevent detrimental effects on soil and animal health. Despite these regulations, there is still a danger that grazing animals may ingest elevated concentrations of PTM. Biosolids may adhere to herbage after the surface application of sewage sludge to grassland. The repeated surface application of sewage sludge to grassland can lead to elevated concentrations of PTM at the soil surface that may be ingested, together with soil and herbage, by grazing ruminants. This may lead to accumulation of Cd or Pb in liver or kidney. The risk to the human food chain is considered to be low, but the impact on the environment is still unknown. There is little information, for example, on the amount of soil and PTMs that may become incorporated into conserved grass. At present EU and UK legislation and voluntary codes of practice have been developed to protect animal from pathogens in sewage sludge and to minimize any potential risks from accumulation of PTM. The background and implementation of the legislation are examined in this review, and the source and mechanisms of accumulation of PTM by the grazing animal are evaluated.

Recycling of sewage sludge and household compost to arable land: fate and effects of organic contaminants, and impact on soil fertility

Effective use of organic wastes for agricultural production requires that risks and benefits be documented. Two types of sewage sludge, household compost and solid pig manure were studied under field and greenhouse conditions to describe their fertilizer value and effects on soil properties and soil biota, the fate of selected organic contaminants, and their potential for plant uptake. A 3-year field trial on two soil types showed no adverse effects of waste amendment on crop growth, and a significant fertilizer value of one sludge type. Accumulation of N and Pi was indicated, as well as some stimulation of biological activity and micro-arthropod populations, but these effects differed between soil types. There was no detectable accumulation of polycyclic aromatic hydrocarbons (PAH), di(2-ethylhexyl)phthalate (DEHP), nonylphenol and ethoxylates (NP+NPE) or linear alkylbenzene sulfonates (LAS) after three repeated waste applications, and no plant uptake was suggested by analysis of the third crop. A plot experiment with banded sludge was conducted to examine sludge turnover and toxicity in detail. Less than 5% of NP or LAS applied in organic wastes was recovered after 6 months, and less than 6% of DEHP applied was recovered after 12 months. Potential ammonium oxidation (PAO) at 0–1 cm distance from the banded sludge was stimulated despite toxic concentrations in the sludge, which suggested that contaminants were degraded inside sludge particles. Phospholipid fatty acid (PLFA) profiles suggested a gradual shift in the composition of the microbial community within sludge, partly due to a depletion of degradable substrates. A pot experiment with sludge-amended soil and soil spiked with contaminants showed no plant uptake of NP, DEHP or LAS. Degradation of LAS and NP added in sludge was delayed and the degradation of DEHP was faster than when the contaminants were added directly to the soil. In conclusion, adverse effects of organic waste application on soil or crop were not found in this study, and for some waste products positive effects were observed.

Risk evaluation for pathogenic bacteria and viruses in sewage sludge compost

Composting can be regarded as the most available option for recycling of sewage sludge. However, the existence of pathogenic bacteria and viruses in the compost has been scarcely investigated until now. So there is little information on the infectious risk through agricultural activities or gardening in using the compost. In this study, several kinds of composts were investigated for detection of pathogenic bacteria (Salmonella spp. and Escherichia coli O157) and enteric viruses. It was concluded from the result that these bacteria and viruses could not be detected in 1.0 g-wet of any kinds of composts. Infectious risks through agricultural activities or gardening were evaluated by Monte Carlo simulation in the case that the compost was polluted by Salmonella spp., E. coli O157:117 and Poliovirus 1. Criteria satisfying the acceptable risk (less than 10(-4) per year) for these pathogenic bacteria and virus in the compost were determined from the result of simulations. 1.0 [CFU or PFU/g-wet] was available as the criteria for E. coli O157 and Poliovirus 1 in the compost. On the other hand, the criterion for Salmonella spp. in the compost should be established on a lower concentration than 0.001 CFU/g-wet.

Bioavailability of heavy metals in soils amended with sewage sludge

The recycling of sewage sludge to agricultural land results in the slow accumulation of potentially toxic heavy metals in soils. A greenhouse experiment was conducted to determine the bioavailability of Cu, Ni, Pb and Zn applied to soils in urban anaerobically stabilized sewage sludge. The soils were Lithic Haplumbrept (Lh), Calcixerollic Xerochrept (Cx1 and Cx2) and Paralithic Xerorthent (Px). Sunflower plants (Helianthus annuus L) were grown in the soils following amendment with the sludge. The addition of sewage sludge markedly increased the average dry weight of the plants in the soils that had lower yields without sludge addition (Lh, Cx2, and Px). The acid pH of the Lh soil favoured the bioavailability of Zn from sewage sludge. The bioavailability of Cu was greater in the alkaline soils than in the acidic soil (Lh), which can be attributed to the high organic matter content of the Lh soil which complexes Cu and impairs its uptake by the plants. The concentration of metals in the plants increased with the sewage sludge dose. The effect of the soil type on the metal concentration in plants was greater that the effect of the dose. Key words: Soils, sewage sludge, heavy metals, bioavailability, sunflower

The Importance of Pathogenic Organisms in Sewage and Sewage Sludge

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

Pipe material and water quality in a holistic view

The new trends in societies towards sustainable development have necessitated a new way of thinking regarding water treatment, the distribution of drinking water and wastewater treatment. A process of implementing new European water directives is ongoing and the consequences and need for coordination of these changes are discussed. Raw water qualities, water treatment technology and drinking water quality have impacts on water quality deterioration in the distribution networks that negatively affect the possibilities for recycling sewage sludge containing valuable nutrients. Measures for coping with these issues are discussed in general terms and suggestions for future strategies and research activities are given.

Merging nitrogen management and renewable energy needs.

The ARBRE (ARable Biomass Renewable Energy) project, the first large-scale wood-fueled electricity generating plant in the U.K., represents a significant development in realising British and European policy objectives on renewable energy. The plant is fueled by a mix of wood from short rotation coppice (SRC) and forest residues. Where feasible, composted/conditioned sewage sludge is applied to coppice sites to increase yields and improve soil structure. In the Yorkshire Water region, typical total N:P:K composition of composted/conditioned sludge is 2.9:3.8:0.3, respectively. Sludge application is calculated on the basis of total nitrogen (N) content to achieve 750 kg N ha, for 3 years’ requirement. Willow coppice forms a dense, widely spaced, root network, which, with its long growing season, makes it an effective user of nutrients. This, in combination with willow’s use as a nonfood, nonfodder crop, makes it an attractive route for the recycling of sewage sludge in the absence of sea disposal, banned under the EC Urban Waste Water Treatment Directive (UWWTD). Further work is required on the nutritional requirements of SRC in order to understand better the quantities of sludge that can be applied to SRC without having a detrimental impact on the environment. This paper suggests the source of N rerouting under the UWWTD and suggests the likely expansion of SRC as an alternative recycling pathway.

Recycling urban waste on farmland: an actor-network interpretation

The problem of disposing of urban waste has been thrown into prominence by the European Union Urban Wastewater Treatment Directive (91/271/EC) banning member states from dumping sewage sludge at sea from the end of 1998. The paper investigates one of the alternative disposal methods available to UK water companies, namely the recycling of sewage sludge on farmland. An `actor-network' interpretation is developed, which focuses on the human actors and non-human intermediaries in the recycling of sewage sludge in agriculture. `Regulation' and `pricing' are shown to be competing `modes of ordering' within the actor network, with scientific knowledge in its material forms as one of the principal actants. The actor network is used to consider the limits to the spreading of sewage sludge on farmland as a form of `sustainable' resource management.

Pathogen Reduction in Sewage Sludge by Composting and Other Biological Treatments: A Review

ABSTRACT The agricultural utilization of sewage sludge imposes a high level of sanitation and stabilization of organic matter in order to maintain soil, water and air qualities and to effectively use such bioresidues as a soil amendment and as a source of nutrients for plants. Improper sanitation poses a serious threat to human and animal health. Stabilization and sanitation of sewage sludge have the advantage of coupling safe sewage sludge recycling in agriculture with its disposal, as many economic and environmental constraints make discharging strategies more and more difficult to apply. This article reviews the various biological methods to sanitize sewage sludge and the efficiency and efficacy of these methods in eliminating pathogens and parasites. Available monitoring techniques are also discussed. Finally, a conceptual approach is presented on the basis of epidemiological and ecological studies in order to assess the environmental and health impacts of recycling sewage sludge through land application.

BOOK REVIEW

Book reviewed in this article: Agricultural Recycling of Sewage Sludge and the Environment By S. R. Smith.

Sewage Sludge Recycling to Agricultural Land: the Environmental Scientist's Perspective

AbstractDuring the next fifteen years, the recycling of sewage sludge to agricultural land will increase significantly in Scotland as a result of EC regulations. This paper describes how soils and related environmental data around Edinburgh can be interrogated and interpreted to assess (a) the suitability of land for sludge utilization, (b) the risk of water pollution in relation to different soil conditions, (c) the ability of soils to adsorb potentially toxic elements in the sludge to prevent transfer to water or plants, and (d) the operational security and environmental sustainability of sludge recycling. The interpretations can make a valuable contribution to the appraisal of sludge disposal policy and implementation, and provide a framework for technology transfer between engineering, environmental and agricultural interests.

Agricultural Recycling of Sewage Sludge and the Environment

Agricultural Recycling of Sewage Sludge and the Environment