Amount Of Municipal Sewage Sludge Research Articles

Life cycle assessment of energy consumption and GHG emission for sewage sludge treatment and disposal: a review

With increasing population and urbanization, the amount of municipal sewage sludge generated is huge and growing rapidly. In order to minimize resource inputs and pollutant emissions in the sludge disposal process, it is crucial to carry out an environmental impact analysis and sustainability assessment of different strategies based on life cycle assessment (LCA). LCA provides a flexible framework for quantifying the consumption and emissions of different processes to determine the energy consumption and environmental impact of sewage sludge treatment and disposal. The aim of this review is to compare the energy consumption and GHG emissions of existing sludge management options for energy and nutrient recovery. At the same time, the characteristics of sewage sludge and the potential to convert sludge from waste to valuable products were assessed. While the excessive moisture content and ash content make sludge unsuitable for use as fuel, and the potential risk of contamination with heavy metals makes it less suitable for use as organic fertilizer, energy and material recovery during disposal can reduce disposal costs and environmental impacts. In the context of the current limitations reviewed, the level of potential GHG emissions of existing sludge treatment and disposal routes is: composting > anaerobic digestion > pyrolysis > incineration. With suitable sludge treatment routes, negative GHG emissions could potentially be achieved by substituting fossil fuels for heat and electricity generation, or as a fertilizer substitute. The development and application of future sludge management strategies should aim at reduction and harmless disposal, thereby reducing the operating costs and environmental burdens through resources.

Life cycle assessment of greenhouse gas emissions of typical sewage sludge incineration treatment route based on two case studies in China

The rapidly increasing amount of municipal sewage sludge generated in China necessitates a thorough examination and evaluation of available treatment options. In recent years, thermal-drying and incineration technology has gained popularity, however, it may lead to significant greenhouse gas (GHG) emissions. Nevertheless, the differences in boundary conditions and technological characteristic across various cases may affect emission levels significantly. Therefore, this study utilizes a life cycle assessment to estimate the GHG emissions associated with two typical sludge incineration routes in China: direct thermal-drying combined with coal co-incineration incinerator in Case 1 and indirect thermal-drying and self-sustain combustion in Case 2. The entire treatment processes, containing different functional units, were comprehensively investigated. The results demonstrate that Case 1 and Case 2 produce 1133.33 and 350.89 kg CO2-eq/tDS (sludge dry solid) of GHG emissions, respectively. In Case 1, coal co-incineration produces 828.63 kg CO2-eq/tDS of GHG emissions, accounting for 73.1% of the total GHG emissions. Moreover, the exhaust gas treatment is a significant GHG emission source, accounting for 9.2% and 16.9% of the total GHG emissions in Case 1 and Case 2, respectively. Additionally, the sludge thickening and dewatering unit in Case 2 produces 213.75 kg CO2-eq/tDS of GHG emissions, accounting for 60.9% of the total GHG emissions. Analysis of energy flow and heat balance characteristics indicate that the indirect heat transfer method used in thermal-drying leads to significant heat loss, which limits heat recovery potential and hinders GHG emission reduction. This study proposed a scenario case based on Case 2, addressing the issues with the improvement of heat transfer process and reduction of electricity consumption, potentially reducing GHG emissions by 8.8%. Additionally, applying an exhaust gas heat recovery system could further offset up to 22.8% of the total GHG emission.

Incorporating hydrothermal liquefaction into wastewater treatment – Part I: Process optimization for energy recovery and evaluation of product distribution

• Hydrothermal liquefaction (HTL) conditions were optimized for max energy recovery. • Energy recovery was linearly and positively correlated to biocrude yield. • HTL byproducts (aqueous and hydrochar) were minimized at the optimal conditions. • High HTL reaction severities improved biocrude quality (more C and less heteroatoms). • Elemental distribution (including metals) among HTL products was evaluated. The treatment of significant amounts of municipal sewage sludge requires novel and efficient technologies. This study evaluated hydrothermal liquefaction as a means to sustainably convert sludge waste into a renewable energy source – biocrude, which can mitigate both environmental and energy-related challenges. Response surface methodology was employed to investigate the effects of reaction temperature (290–360 °C) and residence time (0–30 min) on product yield and biocrude quality. Both the highest and the lowest reaction temperature or residence time had negative effects on biocrude yield and energy recovery (ER), while high reaction severities improved biocrude quality. Under optimized conditions (332 °C for 16.9 min), biocrude yield (48.9%, dry ash-free) and ER (70.8%) were maximized. Biocrude composition followed the order of N-heterocycles > O-heterocycles > hydrocarbons, while nitrogenous compounds reduced, and hydrocarbons increased with reaction temperature. More distillable fractions in biocrude were also produced at higher reaction severities. The possible reaction pathways of biocrude formation were discussed and updated to include catalytic effects on inherent metals and Brønsted (acidic and basic) sites. The high content of O (7.8–13.1%), N (4.4–4.9%), and TAN (48.6–63.6 mg KOH/g) suggested the necessity of biocrude upgrading. Separating and recycling trace metals (e.g., 497–656 mg/kg Fe) from biocrude are necessary to relieve upgrading challenges. C, N, and P were mostly distributed into HTL biocrude, aqueous, and hydrochar, respectively, allowing their recovery. Most metals were concentrated in hydrochar. The results contribute to the advancement of the state of the art in biorefinery, which will guide the design of full-scale HTL sludge treatment systems combining resource recovery.

Evolution and Prospects in Managing Sewage Sludge Resulting from Municipal Wastewater Purification

Municipal sewage sludge is the residual material produced as a waste of municipal wastewater purification. It is a sophisticated multi-component material, hard to handle. For many years, it has been landfilled, incinerated, and widely used in agriculture practice. When unproperly discharged, it is very polluting and unhealthy. The rapidly increasing global amount of municipal sewage sludge produced annually depends on urbanization, degree of development, and lifestyle. Some diffused traditional practices were banned or became economically unfeasible or unacceptable by the communities. In contrast, it has been established that MSS contains valuable resources, which can be utilized as energy and fertilizer. The objective of the review was to prove that resource recovery is beneficially affordable using modern approaches and proper technologies and to estimate the required resources and time. The open sources of information were deeply mined, critically examined, and selected to derive the necessary information regarding each network segment, from the source to the final point, where the municipal sewage sludge is produced and disposed of. We found that developed and some developing countries are involved with ambitious and costly plans for remediation, the modernization of regulations, collecting and purification systems, and beneficial waste management using a modern approach. We also found that the activated sludge process is the leading technology for wastewater purification, and anaerobic digestion is the leading technology for downstream waste. However, biological technologies appear inadequate and hydrothermal carbonization, already applicable at full scale, is the best candidate for playing a significant role in managing municipal sewage sludge produced by big towns and small villages.

Energy Properties and Biomass Yield of Miscanthus x Giganteus Fertilized by Municipal Sewage Sludge.

The application of municipal sewage sludge as fertilizer in the production of non-food energy crops is an environmentally and economically sustainable approach to sewage sludge management. In addition, the application of municipal sewage sludge to energy crops such as Miscanthus x giganteus is an alternative form of recycling nutrients and organic material from waste. Municipal sewage sludge is a potential source of heavy metals in the soil, some of which can be removed by growing energy crops that are also remediation agents. Therefore, the objective of the research was to investigate the effect of municipal sewage sludge applied at three different rates of 1.66, 3.22 and 6.44 t/ha on the production of Miscanthus. Based on the analyses conducted on the biomass of Miscanthus fertilized with sludge from the wastewater treatment plant in three fertilization treatments, it can be concluded that the biomass of Miscanthus is a good feedstock for the process of direct combustion. Moreover, the application of the largest amount of municipal sewage sludge during cultivation had no negative effect on the properties of Miscanthus biomass. Moreover, the cellulose and hemicellulose content of Miscanthus is ideal for the production of second-generation liquid biofuels. Fertilizer treatments had no effect on the content of cellulose and lignin, while a significant statistical difference was found for hemicellulose.

Comparative evaluation on municipal sewage sludge utilization processes for sustainable management in Tibet

In recent years, a sharp increase in the amount of municipal sewage sludge (MSS) in Tibet has posed serious threats to the fragile ecological environment. Tibetan sludge, with a high content of volatile and low heavy metals, has re-utilization advantages, and thus, the selection of appropriate utilization processes for Tibetan MSS is of great importance. In this study, not only the processes themselves, but also other factors including legislations and environmental pollution were investigated. This study introduced the current waste management legislation situation (especially for MSS) in China and Tibet, China. Moreover, a series of SWOT (strength & weakness and opportunity & threats) analyses were conducted to compare anaerobic digestion (AD), incineration, pyrolysis (PY), gasification, and anaerobic digestion coupled with pyrolysis. The results showed that anaerobic digestion coupled with pyrolysis was the optimal treatment option, because anaerobic digestion was suitable for the low oxygen content in Tibet. Although only 50–60% of the organic matter in MSS could be degraded by anaerobic digestion, the residual organic matter (energy) could be further decomposed by pyrolysis, converting it into pyrolytic gas, bio-oil, and biochar, as valuable products. Sludge digestate pyrolysis could reduce environmental risks, save energy, recover materials, and produce high value-added materials. Moreover, it provides a “zero waste” solution for sludge disposal and promotes a “Circular Economy.” The challenges and obstacles of MSS anaerobic digestion coupled with pyrolysis in Tibet were also investigated. This study provides an important technical reference for the comprehensive utilization of Tibetan MSS.

Using convolutional neural networks to classify the maturity of compost based on sewage sludge and rapeseed straw

Large amounts of municipal sewage sludge are generated every year. Composting is one of the most popular and cost-effective methods of handling this waste. It is particularly important to carry out the composting of sewage sludge in an efficient way. The identification of the stage of early maturity of composted material is crucial. The objective of this study was to check the possibility of using convolutional neural networks to classify the early maturity of compost made from sewage sludge and rapeseed straw. The literature review showed that this specific and modern type of neural network had not been investigated for this purpose before. A mixture of these two substrates, composted for 25 days in 7 experiments, was the research material. Images of the material samples were acquired in a dedicated photo station illuminated with: visible light, ultraviolet light, and mixed visible and ultraviolet light. For each acquisition variant 1312 images were obtained. On the basis of the acquired images, 25 convolutional neural networks with one convolutional layer and a varied number of convolution filters were developed to determine the stage of early maturity of the material. Their classification error ranged from 0.51% to 17.77%. The best classification result was obtained for the model containing 16 convolution filters and based on images of the material acquired in mixed visible and ultraviolet light. The results presented in this paper have shown that convolutional neural networks are an adequate tool to assess compost maturity. Such models may provide a simplified and cost-effective approach to the approximate evaluation of the early maturity of compost.

Pyrolyzed municipal sewage sludge ensured safe grain production while reduced C emissions in a paddy soil under rice and wheat rotation.

Safe recycling of the growing amounts of municipal sewage sludge containing toxic metals had been critically challenged with the fast urbanization. In this study, we investigated soil amendment of municipal wastewater treatment (MSS) converted biochar for its recycling in agricultural soils. In a field experiment, unpyrolyzed (USS) and pyrolyzed municipal sewage sludge (PSS) was amended at 20tha-1 on dry base to a rice paddy before rice plantation, with a control without amendment. Grain yield and emission of non-CO2 potent greenhouse gases were examined as well as topsoil metal mobility and plant uptake determined throughout a rice-wheat rotation year. Compared to USS treatment, addition of PSS caused a significantly increased grain yield of rice by 35% but no change in grain yield of wheat following the rice season. No distinct difference was observed in grain concentration of major nutrients of N, P, and K between USS and PSS treatments. Compared to USS treatment, PSS treatment reduced CH4 emissions by 91.6% from soil and by 78.5% from ecosystem during rice-growing season. Whereas, PSS treatment led to a reduction of ecosystem N2O emissions by 70.8% relative to USS treatment during wheat-growing season. While both USS and PSS treatments slightly but insignificantly increased soil total content of heavy metals, PSS treatment reduced CaCl2-extractable Cd pool by 33~40% over USS treatment. Grain contents of Cd and Pb and Cd/Zn were markedly reduced under PSS over USS, without exceeding the Chinese state guideline limit. Carbon emission intensity was considerably (by over 20%) reduced for soil and ecosystem but unchanged for wheat soil, under PSS over USS. Thus, soil amendment of pyrolyzed sewage sludge could be a measure for climate smart soil and for safe grain production in rice agriculture. It deserves further study if repeated amendment could exert sustainable impacts on soil health and food security in the paddy.

The influence of selected factors on leaching of metals from sewage sludge

In Poland, the amount of municipal sewage sludge that contains both organic and inorganic pollutants increases steadily. As a result of penetration of atmospheric precipitations through sludge layers, products of biochemical decomposition of organic matter and soluble mineral compounds are washed away and form contaminated leachates (Arain, J. Hazard. Mater. 154:998–1006, 2008; Fang, J. Hazard. Mater. 310:1–10, 2016; Ignatowicz, Environ. Res. 156:19–22, 2017). Metals contained in these leachates may be particularly burdensome and dangerous, which is due to the toxic nature that disturbs the natural biological balance (Fytili and Zabaniotou, Renew. Sust. Energy Rev. 12 (1): 116–140, 2008). In order to check bio-availability of metals in sewage sludge and find out resulting risks to the environment and human health, apart from the determination of total metal content, speciation analysis is often used. It makes possible a quantitative determination of various chemical forms of metals which are bound in the sewage sludge and finding which of them poses the greatest threat to the environment (Amir, Chemosphere 59:801–810, 2005; Ciba, Waste Manage. 23:897–905, 2003; Hei, Procedia Environ Sci 31:232–240, 2016; Liu, Chemosphere 67(5):1025–1032, 2007).The degree of immobilization of selected metals in sewage sludge has been determined using one of the sequential extraction methods designed to identify groups of compounds with which the metal is bound. Such a method is the Tessier procedure (Janas, Pol J Environ Stud 26(5A):37–41, 2017). Results of this research were used to assess the threat resulting from the increase in the amount of sewage sludge; the management of which is subject to constant restrictions (storage of sewage sludge has been prohibited since January 1, 2016).As a result of the conducted research, it was found that metals in sewage sludge, which undergo various transformations, are very difficult to immobilize. The addition of calcium oxide and an agent supporting the composting process to the sludge does not affect radically the increase of leaching of the analyzed elements from the sludge.Graphical abstractThe schema of proceedings in leaching of heavy metals from sewage sludge after various modifications.

Addition of large amount of municipal sewage sludge as raw material in cement clinker production.

Two addition modes were used to explore the maximum addition of municipal sewage sludge as a raw material in cement clinker production. The clinker and cement product quality were determined by chemical analysis, cement quality testing, characterization of the clinker crystalline phases, and leaching tests. Municipal sewage sludge addition in the raw mix could be up to 30% based on the cement clinker moduli, and the cement quality met the P.O 42.5 cement standard (GB 175-2007). The amount of municipal sewage sludge added based on the direct addition mode should be less than 15% because of an insufficient early-term cement strength (third day). The leaching concentrations of heavy metals in all cements were below the threshold (GB 30760-2014) using the latest leaching procedure (GB 30810-2014). The municipal sewage sludge could be used with a high addition (30%) in the raw mix as a raw material in cement clinker production.

Optimizing the formulation of external-soil spray seeding with sludge using the orthogonal test method for slope ecological protection

External-soil spray seeding has gradually become a widely used technology for slope ecological rehabilitation in China in the 21st century. Meanwhile, with ever-increasing amounts of municipal sewage sludge being produced, sewage sludge has become a new source of solid waste pollution in the environment. Therefore, the goal of this study was to utilize sludge as a new kind of spray seeding component to replace non-renewable turfy soil. Orthogonal experiments were conducted to optimize the substrate formulation regarding the four factors of soil-to-sludge ratio, fiber content, soil additive concentration, and bioorganic fertilizer concentration. The results showed that sludge improved the physical and chemical properties of the substrate, increased plant growth, and within a certain range of dosage, reduced runoff and soil loss. The improvements of soil bulk density, total porosity and soil nutrients were particularly notable (P<0.01). Plant growth in experimental groups was better than that of control groups (P<0.05), and Festuca arundinace performed best among the three plants (P<0.01). In addition, besides the physical and chemical properties, fiber content mainly affected plant growth, and soil additive reduced runoff and soil loss, whereas bioorganic fertilizer showed no obvious effect. After the experiments, a simple model was used to integrate the effects of the four factors on 28 parameters and thus to get the optimum component proportions, which were a soil-to-sludge ratio of 6:4 (v/v), fiber content of 15% (v/v), and soil additive concentration of 0.6kgm−3.

Fuel design in co-combustion of demolition wood chips and municipal sewage sludge

Municipal sewage sludge (MSS) is a waste stream resource which contains both energy and elements such as phosphorus which could be recycled. If these two aspects of this waste stream resource are to be used to their full potential the sludge should not be used in landfills or road construction. There is some use of sludge in agriculture today but not all MSS produced is suitable for direct use on arable land due to its content of potentially harmful elements, pathogens or anthropogenic chemicals. By combusting sludge that is not used directly in agriculture the problematic organic content could be destroyed. The combustion process also produces an ash that possibly could be used either directly in agriculture or as a raw material for recovering phosphorus and energy could be recovered. Building mono-combustion plants for sewage sludge is not economically feasible in all parts of the world so it is of interest to investigate how MSS can be introduced together with other fuels in existing infrastructure which already have extensive cleaning systems for potentially harmful elements.To investigate this possible path, demolition wood chips (DWC) were co-combusted with municipal sewage sludge (MSS) in a grate-fired combined heat and power plant running at 50% capacity producing 25MWth and 9MWel. The amount of MSS that was suitable to introduce in blends was determined using a “fuel fingerprint” based on the composition of the raw materials. Thermodynamic equilibrium calculations were made to evaluate potential problems with slagging based on the ash content prior to the combustion experiments. The fuels were introduced as a reference case with only demolition wood and pre-blended fuel mixtures in two ratios; 65w/w-% DWC/35w/w-% MSS and 55w/w-% DWC/45w/w-% MSS and were fired for 12h. The high water content of the MSS affected how much MSS that could be introduced without compromising the heat and power production.The fuel blends worked nicely for 12h of continuous combustion with small adjustments where the primarily the air inlet configuration was changed. The main problems encountered related to cleaning of the flue gases and to some extent ash removal. The bed ash and fly ash produced was analysed both using ICP-AES (elemental) and XRD (speciation) and the bottom ash was subjected to ash melting tests. The major nutrient phosphorus was mainly found in bottom ash (80w/w-%) as whitlockites with some hydroxyapatite whereas fly ash (20w/w-%) contained larger amounts of hydroxyapatite, especially for the reference fuel. The amount of alkali chloride in the fly ash was reduced in favour of alkali sulphate formation.

Soil amendment with municipal sewage sludge affects the immune system of earthworms Dendrobaena veneta

Dendrobaena veneta is an earthworm species capable of consuming a wide range of organic wastes which may be used as a field indicator of municipal sewage sludge applied to land. The aim of the present 8-week laboratory experiment was to check viability, reproduction and the immune system of D. veneta maintained in soil without food additions (control 0s group) or in soil amended with 25% or 50% municipal sewage sludge (25s and 50s groups, respectively). Reproduction and immunity are important physiological functions whose detailed study can provide information on the effects of pollutants. After the 8-week exposure period, earthworm mortality (2 out 20 individuals) was recorded only in the 50s group. Reproduction was high in the 25s group (44 cocoons and 41 juveniles) whereas reproduction was almost completely inhibited both in the food-deprived control 0s group (1 cocoon, 3 juveniles) and in the 50s group containing a high amount of sludge (2 cocoons). Significantly increased numbers of non-invasively extruded coelomocytes were recorded 3 weeks after the start of the experiment in the 50s group, but they dropped to the food-deprived control level by the end of 8 weeks likely due to exhaustion of the immune system coping with sludge-derived microbes and/or toxins. In contrast, numbers of coelomocytes in the 25s group increased gradually reaching the maximum at the end of the experiments. In conclusion, high amounts of municipal sewage sludge are detrimental to worms, inhibiting reproduction and inflicting mortality. A moderate amount of municipal sewage sludge provides a good source of nutrients for D. veneta, supporting their growth and reproduction for at least 8 weeks. Immunological parameters might serve as useful indicators of earthworm exposure to sewage sludge.