File Name: sludge treatment and disposal .zip
- Sanitary and environmental aspects of sewage sludge management
- Sanitary and environmental aspects of sewage sludge management
- Sewage sludge treatment
EGLE has the responsibility to protect the public health and the environment by ensuring wastewater is properly handled and treated safely.
Sanitary and environmental aspects of sewage sludge management
Currently, sewage sludge management is a huge challenge in the field of environmental engineering. New effective solutions for the treatment of wastewater led to an improvement of the quality of the final effluent but considerably increased the volume of produced sewage sludge, which increases each year. This chapter will focus on these aspects, highlighting the health and ecotoxicological risks associated with the presence of such contaminants in sludge.
The environmental dangers of sludge spreading on soils will be presented as well as their possible treatment scenarios to propose an acceptable reuse of sewage sludge in a circular economy. Failure to treat effluents constitutes a serious threat to the environment, the climate, and human health, but this can also be considered a waste of resources. According to the goals of sustainable development and a circular economy, the wastewater shall be considered primarily as a source of water, then energy, organics, metals, and other resources.
Consequently, sewage sludge is recognized as a source of renewable energy and material recovery Christodoulou and Stamatelatou, Sewage sludge is a reservoir of organic matter and nutrients, so it constitutes a potential substrate for a variety of possible reuse scenarios. Therefore, all potentially applied strategies shall fulfill the requirements of ecoinnovation. Thus, they shall lead to an important reduction of the negative environmental impacts by decreasing the consumption of natural resources or the release of harmful substances Rorat and Kacprzak, Consequently, contemporary trends in organic waste treatment follow the sustainable development strategy in terms of environmental, economic, and social impacts.
The composition of sewage sludge is highly variable and may depend on many various factors such as the seasons, the technology applied in wastewater treatment plants WWTPs , the specificity of the source area of the influent, etc. For instance, extractable resources such as phosphorus P are predicted to become scarce or exhausted in the next 50— years, thus P recovery from wastewater is becoming an increasingly viable alternative Connor et al. Nevertheless, a relatively low content of lignin and cellulose makes the organic matter easy to decompose.
Hence, it degrades fast and can cause a sharp peak in the nitrate and pollutant concentration in the soil if applied without pretreatment. The biggest challenge, though, is seen in the contaminants, 1 organic such as polycyclic aromatic hydrocarbons PAH , polychlorinated biphenyls PCB , adsorbable organohalogens AOX , pesticides, surfactants, hormones, pharmaceuticals and 2 inorganic metals and their nanoparticles , and 3 pathogenic species of living organisms for example, bacteria, viruses, protozoa, and parasitic helminths see review by Fijalkowski et al.
In this context, this chapter focuses on the sanitary and environmental dangers of the presence of the above-mentioned contaminants in sludge. The environmental risks of sludge spreading on soils will be presented as well as their possible treatment scenarios to propose an acceptable reuse of sewage sludge in a circular economy.
Consequently, the substantial and constant increase of wastewater sludge and its disposal are becoming a growing challenge for municipalities in Europe. The annual sludge production in EU will grow from Table 1 shows the more recent data considering the production and disposal of sewage sludge for selected countries, according to OECD. While legislation more or less compels European countries to improve their sewage sludge management policies, many poor and developing countries are still studying possible wastewater treatment practices.
The global population exceeded 7. Urban populations may rise nearly twice as fast as they are projected to nearly double from 3. The composition of sewage sludge is highly changeable during the process and also varies a lot between wastewater treatment facilities. Typically, raw untreated sewage sludge contains 2. The potential danger of using raw sewage sludge not stabilized, only mechanically treated for the sewage-to-matter final disposal strategies is huge due to the presence of pathogenic organisms and other contaminants.
Therefore, some stabilization processes shall be applied at the WWTPs. The choice of applied technology depends strongly on the characteristics of raw sludge. Some parameters are crucial for the processes of stabilization, for example, pH, organic acid content, and alkalinity limit the anaerobic digestion process Metcalf et al. After thickening, sludge stabilization is usually performed. It is crucial for the further applications and aims primarily to reduce the potential risks by lowering the number of pathogens in organic matters.
Two types of stabilization of liquid sewage sludge shall be distinguished:. Biological stabilization, meaning anaerobic or aerobic digestion. After stabilization, the sludge shall be dewatered. Usually, this process is carried out using filter presses or centrifuges.
As proper dewatering is crucial for the further disposal of sewage sludge, often an additional step of conditioning is required. The conditioners, synthetic organic polymers, or metal ions typically iron salts are used in order to coagulate the colloids in sludge and thus fasten the dewatering process Novak, Only an efficient stage of water removal allows applying efficiently the selected techniques of final treatment and disposal of sewage sludge.
Matter recovery sewage-to-matter : use in agriculture directly as a fertilizer and remediation of devastated or degraded lands. Energy recovery sewage-to-energy by incineration and alternate thermal methods as pyrolysis, quasipyrolysis and gasification or coincineration in cement plants.
Wastewater contains a chemical energy that shall be converted to the usable form and thus fulfill a part of the worldwide need for renewable energy sources Puyol et al. Different technologies can be used to transfer the excess sewage sludge into energy.
This strategy has lately been of great interest. Primarily, it allows using the potential of sewage sludge without the environmental risks often discussed for land applications that could introduce contaminants into the soil. Moreover, it responds to a global call for renewable energy sources. Others, such as landfilling or dumping at sea, which are forbidden by most countries but still practiced in some parts of the world, mostly in developing countries.
The produced biogas can be used for the self-purposes of WWTPs that are characterized by a high demand for electricity, up to 0. Ideally, the process of anaerobic digestion shall fulfill this high demand.
In order to increase efficiency and thus biogas yields, it was proposed to introduce the other ingredients in the so-called codigestion. For instance, Grosser used grease trap sludge and an organic fraction of municipal waste as cosubstrates in the process, which enhanced the efficiency of sewage sludge anaerobic digestion.
Similarly, other organic wastes have been tested with success, for example, food waste, cheese whey, and olive mill wastewater Maragkaki et al. Thus, codigestion of sewage sludge can be understood as a method of management of different organic wastes. Nevertheless, it cannot be fully seen as a final disposal of sludge, as it generates another byproduct, digested sludge digestate , that still contains a high quantity of nutrients and contaminants and must be treated.
It was proven that the utilization of digestates may replace or reduce the use of mineral fertilizer in agronomic plant production, as it is rich in plant-available nutrients ammonium, phosphate, and potassium Sogn et al. Yet, in-land use as a biofertilizer is possible only if the product can be qualified according to applicable norms, usually regulated by soil protection legislation, fertilizer, or waste legislation. Otherwise, other options shall be considered. Lately, Peng et al. Digestate was also successfully applied with other organic wastes as the organic fraction of municipal wastes, sawdust, and green wastes in the process of vermicomposting Rorat et al.
As the chemical composition of digestate corresponds to the composition of the used substrates, the long-term effects of its introduction to the soil shall be studied in order to appreciate the impact on soil functions soil biodiversity and microbial cycles.
The existing studies focus mainly on the fertilizer properties of the digestates produced from different substrates. According to Nkoa , the most common risks associated with the application of digestate in land are related to:. Risks of atmospheric pollution ammonia emission and fallout, nitrous oxide emission.
Composting as a method of biological decomposition of biowastes in the presence of oxygen contributes powerfully to the recycling and conservation of several macro- and micronutrients from sewage sludge in the soil.
Its alternative, vermicomposting, is a modern, inexpensive, and eco-friendly biotechnology in which earthworms are employed as natural bioreactors in order to decompose the organic matter Suleiman et al. Although composting can be considered highly beneficial and a low cost sewage-to-matter strategy that allows recycling organic nutrients into the ecosystem, it still causes some important problems from an environmental point of view.
Those effects can be partially reduced by the introduction of different bulking agents, for example, agricultural wastes and alkaline amendments such as lime, zeolite, and bentonite. Although these effects can be partially eliminated, researchers are concerned about the input of potentially toxic metal elements and therefore their possible accumulation for several in the soil horizon Fang et al.
The same type of risk is related to the presence of other chemical compounds and pharmaceuticals as well as some pathogens that can survive the process. All thermal processes are considered sludge-to-energy systems that lead to the complete oxidation of the volatile matter with production of a residue ash.
Generally, the most famous technologies are incineration, gasification, pyrolysis, and plasma gasification. This also allows largely reducing the volume of sewage sludge to destroy the microbiological danger, minimize the odors, and simultaneously recover the renewable energy.
Three main variants of this process are used: incineration in dedicated plants, coincineration with municipal solid wastes, and incineration in cement kilns. The environmental cost related to those systems is mostly related to the high energy consumption and production of harmful gaseous emissions i. Moreover, the ashes coming from the process can be considered a concentrated pollutant that accumulates chemical contaminants.
The interesting alternative for ash disposal is a cement replacement. After incineration, sewage sludge is still rich in silica, alumina, calcium oxide, and iron oxide, so it can be used in the production of building materials. Moreover, in this form, metals are stabilized and solidified, so the potential risk is reduced Samolada and Zabaniotou, Pyrolysis is being recognized as a relatively expensive but highly effective technology.
Thus, pyrolysis allows yielding a major bio-oil fraction potentially useful as a fuel or as a source of chemical products. Generally, pyrolysis and similar processes of combustion of sewage sludge are regarded as endothermic. Thus, improvement of the steps allowing water removal is crucial for the future potential of the process.
Independently, numerous studies have shown many advantages of using biochar for environmental management. In general, biochar can thus be defined as a solid, carbon-rich material obtained in the process of zero or low oxygen pyrolysis from different C-based feedstocks, which, applied to the soils, sustainably sequesters carbon and thus improves soil quality in the long term Verheijen et al.
As far as the process of combustion eliminates the microbiological risk related to the land application of sewage sludge, still some questions considering chemical pollutants are being posed.
These need to be evaluated on a case-by-case basis, not only with concern to the biochar product itself but also to soil type and environmental conditions Verheijen et al. Considering all valuable resources present in sewage sludge organic matter, plant culture available nutrients , many countries recognized this byproduct as a potential substrate for fertilization in agriculture or remediation of polluted areas.
Nevertheless, sewage sludge applications on agricultural land might contribute to the dispersal of a broad range of unwanted constituents on soils possibly used for food production. Such undesirable contaminants potentially toxic elements PTE such as metals, trace organic compounds TrOC , and pathogenic organisms may pose sanitary and environmental risks Andreoli et al. Toxic pollutants in sewage sludge could even, in some cases, increase preexisting environmental problems and lead to secondary environmental contaminants and poisonings if not properly managed.
As a reflection of our chemical-based consumer society, our wastewater and sewage sludge mirror compounds we use, produce, release, and discharge.
Sludge composition, its agronomic interests, and contaminations may so differ greatly. Such parameters depend on the wastewater origins agricultural, industrial areas or urban , the local household and consumer habits, the sewer collection separation or not for wastewater and runoff , the regional environmental regulations, the season and obviously of the size and the process used by the considered WWTP.
The environmental risk of sludge contaminants and their concentrations in soil after land application is dependent on their initial concentrations in both soils and sludge and the application rate cumulative effects , management practices, and losses.
Therefore, volatile and easily degradable contaminants may still pose environmental risks in the case of high initial concentrations and repeated applications Harrison et al. There are two environmental and public health issues involved with the use or disposal of WWTP biosolids: potentially toxic elements PTEs and organic contaminants OCs , chiefly persistent chemicals. Concerns relate to potential trophic transfers via cultivated plants and possible contamination of groundwater.
They classically comprise the following metals and metalloids: arsenic As , cadmium Cd , chromium Cr , copper Cu , lead Pb , mercury Hg , molybdenum Mo , nickel Ni , and zinc Zn. Potential environmental risks associated with these PTEs in the context of sludge land applications have been extensively studied and environmental guidelines and regulations defined.
Sanitary and environmental aspects of sewage sludge management
The residue that accumulates in sewage treatment plants is called sludge or biosolids. Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a by-product of wastewater treatment processes. This residue is commonly classified as primary and secondary sludge. Primary sludge is generated from chemical precipitation , sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems.
The book covers in a clear and informative way the sludge characteristics, production, treatment thickening, dewatering, stabilisation, pathogens removal and disposal land application for agricultural purposes, sanitary landfills, landfarming and other methods. Environmental and public health issues are also fully described. Sign In or Create an Account. Advanced Search. Sign In. Skip Nav Destination. Sludge Treatment and Disposal By.
Sludge Treatment and Disposal is the sixth volume in the series Biological Wastewater Treatment. The book covers in a clear and informative way the sludge chara. Please click on the PDF icon to access. eBooks from IWA Publishing: The.
Sewage sludge treatment
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