Sewage Sludge Management Research Articles

Life cycle assessment of sewage sludge management options including long-term impacts after land application

A life cycle assessment (LCA) was performed on five commonly applied sewage sludge treatment practices: dewatering of mixed sludge (DMS), lime stabilisation of dewatered sludge (LIMS), anaerobic digestion of mixed sludge (ADS), dewatering of anaerobically-digested sludge (DADS) and incineration of dewatered anaerobically-digested sludge (INC). In the first four scenarios, the sludge residues were applied on agricultural land, while in the fifth scenario ash from sludge incineration was landfilled. It was found that the sludge treatment technology influenced in which processes carbon (C) and nitrogen (N) emissions happened. In general, the INC scenario performed better than or comparably to the scenarios with land application of the sludge. Human toxicity (non-carcinogenic) and eco-toxicity showed the highest normalised impact potentials for all the scenarios with land application. In both categories, impacts were dominated by the application of zinc and copper to agricultural soil. For the eutrophication potentials, different scenarios appeared beneficial depending on the receiving compartment in focus. The fate of phosphorus (P) dominated freshwater eutrophication, while the fate of N had a profound effect on all non-toxic impact categories other than freshwater eutrophication. The sensitivity analysis showed that the results were sensitive to soil and precipitation conditions. The ranking of scenarios was affected by local conditions for marine eutrophication. Overall, the present study highlighted the importance of including all sludge treatment stages and conducting a detailed N flow analysis, since the emission of reactive N into the environment is the major driver for almost all non-toxic impact categories.

Evaluation and comparison of product yields and bio-methane potential in sewage digestate following hydrothermal treatment

In recent years, sewage sludge management has been considered one of the biggest concerns in the wastewater industry for the environmental impacts linked to its high content of pollutants. Hydrothermal Treatments are a good option for converting wet biomass such as sewage sludge into high-value products. The digestate following anaerobic treatment of sewage sludge has high organic matter content despite initial conversion into biogas and is normally spread on land or composted; however, this does not fully harness its full potential. In fact, the digestate is a potential feedstock for hydrothermal processing and this route may produce higher value products. In this study, the potential of hydrothermal processing as a novel alternative to treat the digestate has been be evaluated. The effect of temperatures is evaluated with respect to product yields, biomethane potential and solubilisation of organic carbon. Three different temperatures were evaluated: 160, 220 and 250°C at 30min reaction time. The hydrochar yields obtained were 73.42% at 220°C, 68.79% at 250°C and 56.75% at 160°C treatment. The solubilisation of carbon was increased from 4.62% in the raw feedstock to 31.68%, 32.56% and 30.48% after thermal treatments at 160, 220 and 250°C, respectively. The thermal treatment enhanced the potential methane production in all products up to 58% for both, the whole fraction (hydrochar+processed water) and processed waters. The Boyle’s and Buswell’s equation were used to calculate theoretical methane yields for all hydrothermal products. Theoretical methane yields were compare with experimental data from biomethane potential (BMP) tests and it was found that the Boyle’s equation had closer agreement to BMP values.

Effect of microwave pretreatment on semi-continuous anaerobic digestion of sewage sludge

Sewage sludge is a waste produced worldwide in wastewater treatment plants (WWTP) that constitutes a major environmental and health problem. Although anaerobic digestion has become a widely used method for the management and treatment of sewage sludge, the biomethanization of this waste leads to low biodegradability and low methane production. Microwave pretreatment under fixed conditions of 20 × 106 J/kg TS (Total Solids) and 700 J/s has been described as an interesting alternative in order to improve the feasibility of the anaerobic digestion of sewage sludge. In this study at laboratory scale, the semi-continuous anaerobic digestion of raw sewage sludge and pretreated sewage sludge were compared in terms of organic loading rate (OLR), biodegradability and methane production. The main results were found to be OLR up to 2.80 × 10−5 kg TVS (Total Volatile Solids)/m3·s, 70% biodegradability and a 20% improvement in methane yield compared to sewage sludge without pretreatment. Higher loads led to free ammonia accumulation, increase of pH values and system destabilization.

Sustainable Management of Sewage Sludge for the Production of Organo-Mineral Fertilizers

Circular Economy (CE) package accepted by the European Union (EU) in December 2015 promotes close-loop flows of materials. The main targets provided in the documents refer to the prevention of waste landfilling, efficient use of resources and energy, as well as re-use waste and by-products. Sewage sludge—residue from Waste Water Treatment Plant (WWTP)—has a great fertilizer potential and should be recycled in line with the CE strategy. Sewage sludge usage for agricultural purposes seems to be the best sustainable option of its disposal. New EU regulations related to fertilizers derived from bio-waste and by-products assume the uniformity of legislation in Member States and simplification of procedures for introducing innovative fertilizers into the internal market. The characteristic of organo-mineral fertilizers obtained from dried sewage sludge is presented in the paper. In order to obtain balanced NPK fertilizers straight mineral fertilizers, poultry litter ash and phosphoric/nitric acids or a mixture of these were added. As a result organo-mineral fertilizers with N + P2O5 + K2O > 20% were produced. It was found that the largest contribution of contaminants in products comes from Wet Process Phosphoric Acid.

Zalety i wady kompostowania osadów ściekowych w porównaniu z termicznym ich spalaniem – studium przypadku

New challenges for the territorial government in the field of urban sewage sludge oblige to limit it storage. Sewage sludge management is one of the most difficult environmental and economic problems. Therefore, it is important to choose the right technology for the sewage sludge disposal. The purpose of this article is an evaluation of applied disposal methods on sewage treatment sludge plant and comparison of this method (sewage sludge composting) with thermal transformation of sewage sludge. Study confi rms that, in the present case, the composting of sewage sludge is the most advantageous solution.

Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts

Content of heavy metals, including mercury, determines the method of management and disposal of sewage sludge. Excessive concentration of mercury in composts used as organic fertilizer may lead to accumulation of this element in soil and plant material. Fractionation of mercury in sewage sludge and composts provides a better understanding of the extent of mobility and bioavailability of the different mercury species and helps in more informed decision making on the application of sludge for agricultural purposes. The experimental setup comprises the composing process of the sewage sludge containing 13.1mgkg−1 of the total mercury, performed in static reactors with forced aeration. In order to evaluate the bioavailability of mercury, its fractionation was performed in sewage sludge and composts during the process. An analytical procedure based on four-stage sequential extraction was applied to determine the mercury content in the ion exchange (water soluble and exchangeable Hg), base soluble (Hg bound to humic and fulvic acid), acid soluble (Hg bound to Fe/Mn oxides and carbonates) and oxidizable (Hg bound to organic matter and sulphide) fractions. The results showed that from 50.09% to 64.55% of the total mercury was strongly bound to organo-sulphur and inorganic sulphide; that during composting, increase of concentrations of mercury compounds strongly bound with organic matter and sulphides; and that mercury content in the base soluble and oxidizable fractions was strongly correlated with concentration of dissolved organic carbon in those fractions.

Eco-innovations in the functioning of companies

The development of entrepreneurships in the 21st century cannot occur without taking care of the natural environment. The article presents issues related to eco-innovation.Despite the opportunities offered by eco-innovations, implementation of such initiatives remains to lead to various difficulties. They vary across countries and sectors. The insufficient number of enterprises in Poland and other European countries implement adequate level of eco-innovations. The main aim of this paper is to indicate the causes of this status and activities aimed to develop eco-innovativeness. The benefits and risks connected with implementation of innovative products and technologies were also discussed.Furthermore, the advantages of and barriers to their implementation into companies were analysed. The entrepreneurs from the least eco-innovative countries emphasize serious barriers, including uncertain demand from the market, uncertain return on investment or too long a payback period for eco-innovation, lack of funds within the enterprise, insufficient access to existing subsidies and fiscal incentive. They are especially afraid of the financial risks, which raises uncertainty and leads to refraining from innovative initiatives. The possibilities were indicated for the entrepreneurs who face problems with the implementation of innovative solutions. Particular attention was paid to the European Union activities for the development of eco-innovations. Numerous programs supporting their implementation were indicated. The article also presents examples of eco-innovation in water and sewage enterprises. It was emphasized that planning of eco-innovative solutions should be based on comprehensive information about actual benefits and possibility of threats to the environment which can be caused by implementation of eco-innovations. The study presents the example of threats resulting from different methods of sewage sludge management.

Centralized management of sewage sludge and agro-industrial waste through co-composting

In this research study, the co-composting process of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent (SEFW, 190:1:22:90 ratio) was carried out in a dynamic-solid respirometer at pilot scale. The aerobic biodegradability of the mixture was previously ensured in a static-liquid respirometer. The advantages and drawbacks of the SEFW co-composting process were subsequently identified through the determination of respirometric activity and the physical-chemical characterization of the waste, as well as the monitoring of odor emissions. The evolution of the physical-chemical variables showed that pH increased slightly and that the organic matter concentration, expressed as volatile solids (VS, %) or oxidable organic carbon (COXC, %), decreased by around 15% in both cases and by approximately 56% in its biodegradable form (total organic carbon, TOC, %). The low odor emission rate (OER) in the least favorable scenario (the maximum odor generation) during SEFW composting was 1.59 ouE/s, whereas this figure reached 3.52 ouE/s when only the organic fraction of municipal solid waste (OFMSW) was composted. Consequently, the co-composting of SEFW is more favorable in terms of odor emission and permits the simultaneous treatment of different types of waste.

The impact of sewage sludge treatment on the content of selected heavy metals and their fractions

The aim of the study was to assess the physicochemical properties of compost made of municipal sewage sludge from selected Municipal Sewage Treatment Plant. Content of basic macroelements and heavy metals (Zn, Cu, Cr, Cd, Ni, Pb, Hg, Mg, Ca, N, P, K, Na) and their fractions was determined by means of BCR method. Based on the analyzes, it was found that the content of heavy metals in compost did not exceed the limits set by natural land management of sewage sludge; the compost is very abundant in biogenic elements - nitrogen and phosphorus – and it can be also considered a significant source of calcium and magnesium. The analysis of results obtained from the three-stage chemical extraction revealed that deposits subjected to aerobic stabilization and composting accumulate metals (in descending sequence) in fractions III and II, i.e. fractions virtually inaccessible to the ecosystem in optimal conditions of use.

Sewage sludge disposal strategies for sustainable development

The main objective of the present review is to compare the existing sewage sludge management solutions in terms of their environmental sustainability. The most commonly used strategies, that include treatment and disposal has been favored within the present state-of-art, considering existing legislation (at European and national level), characterization, ecotoxicology, waste management and actual routs used currently in particular European countries. Selected decision making tools, namely End-of-waste criteria and Life Cycle Assessment has been proposed in order to appropriately assess the possible environmental, economic and technical evaluation of different systems. Therefore, some basic criteria for the best suitable option selection has been described, in the circular economy “from waste to resources” sense. The importance of sewage sludge as a valuable source of matter and energy has been appreciated, as well as a potential risk related to the application of those strategies.

Life cycle assessment of sludge management with phosphorus utilisation and improved hygienisation in Sweden.

To provide input to sewage sludge management strategies that address expected new regulations in terms of hygienisation and phosphorus recovery in Sweden, an environmental life cycle assessment (LCA) was made. The LCA identified environmental hot spots for methods that may permit sludge or phosphorus from sludge to be applied on agricultural land. In particular, thermophilic digestion, pasteurisation, thermal hydrolysis, urea treatment and mono-incineration with phosphorus recovery were compared. In addition, a sludge management system involving drying of sludge before use in forestry was investigated. The results showed that some major impacts are related to large uncertainties, such as those related to emissions from sludge storage. It also showed that large gains can be achieved when products from the systems replace other products, in particular when biogas is used to replace natural gas in vehicles, but also when sludge is used in agriculture and forestry. In general, there are small differences between the sludge management methods. Retaining the sludge matrix to allow for its utilisation in agriculture may conflict with keeping emissions to air and water from the sludge matrix low. It is recommended that any sludge management option minimises emissions from sludge to air and water and that resources are recovered and used, in line with the principles of a circular economy.

Modeling and cost estimation of energy production from sludge

Energy recovery from sewage sludge offers an opportunity for sustainable management of sewage sludge and energy. Anaerobic digestion and pyrolysis are among the most promising processes applicable for sewage sludge-to-energy conversion. Anaerobic digestion of sewage sludge forms methane-rich biogas, which can be utilized as fuel to offset heat and electricity consumption of the wastewater treatment sector. However, the digestion process has the efficiency limitation since it cannot sufficiently extract the energy from sewage sludge. The digested sludge is still energy profitable and it contains considerable organic matter, but poor in biodegradability. This paper presents a brief overview of anaerobic digestion, pyrolysis, and the combination of other processes with anaerobic digestion in the application to bio energy production from sewage sludge. An assessment of energy conversion of five sludge to energy pathways is also presented. The pathways via pyrolysis and the combination of anaerobic digestion, thermal hydrolysis, and thermal drying could achieve higher energy efficiency compared to other pathways.

Environmental assessment of the Sibiu County, Romania: proposal for sewage sludge and OFMSW management

The aim of the work is to assess current solid waste management (SWM) and wastewater treatment (WWT) in the county of Sibiu, Romania. Sibiu is a region where industrialization and tourism are spreading constantly, while pollution monitoring and the introduction of circular economy (CE) principles are still lacking. The environmental issues are mostly due to the absence of reliable sanitation systems, in particular for what concerns sewage sludge treatment. Moreover, Organic fraction from selective collection of municipal solid waste is still missing, since it is disposed of directly to landfill, increasing environmental pollution and contributing considerably to global warming. As a result, SWM and WWT should be improved at the same time, as sludge requires specific handlings in order to be safety disposed. The objective of the study is to investigate the introduction of affordable technological facilities able to treat sludge and the organic fraction of municipal solid waste, recovering, at least, the energy required for the working phase of the treatment plants. Anaerobic digestion resulted viable, but the organic fraction full stream collection seems to be the only way to have a significant energy recovery. From the financial point of view, the feasibility of this co-treatment option could count on specific opportunities that Romania has in the frame of the European Union context.

Co-digestion of sewage sludge from external small WWTP’s in a large plant

Improving energy efficiency of WWTPs (Waste Water Treatment Plants) is crucial action of modern wastewater treatment technology. Technological treatment process optimization is important but the main goal will not be achieved without increasing production of renewable energy from sewage sludge in anaerobic digestion process which is most often used as sludge stabilization method on large WWTP's. Usually, anaerobic digestion reactors used for sludge digestion were designed with reserve and most of them is oversized. In many cases that reserve is unused. On the other hand, smaller WWTPs have problem with management of sewage sludge due to lack of adequately developed infrastructure for sludge stabilization. Paper shows an analysis of using a technological reserve of anaerobic digestion reactors at large WWTP (1 million P.E.) for sludge stabilization collected from smaller WWTP in a co-digestion process. Over 30 small WWTPs from the same region as the large WWTP were considered in this study. Furthermore, performed analysis included also evaluation of potential sludge disintegration pre-treatment for co-digestion efficiency improvement.

Wastewater and sludge management and research in Oman: An overview

ABSTRACTIt is well recognized that management of wastewater and sludge is a critical environmental issue in many countries. Wastewater treatment and sludge production take place under different technical, economic, and social contexts, thus requiring different approaches and involving different solutions. In most cases, a regular and environmentally safe wastewater treatment and associated sludge management requires the development of realistic and enforceable regulations, as well as treatment systems appropriate to local circumstances. The main objective of this paper is to provide useful information about the current wastewater and sludge treatment, management, regulations, and research in Oman. Based on the review and discussion, the wastewater treatment and sludge management in Oman has been evolving over the years. Further, the land application of sewage sludge should encourage revision of existing standards, regulations, and policies for the management and beneficial use of sewage sludge in Oman.Implications: Wastewater treatment and sludge management in Oman have been evolving over the years. Sludge utilization has been a challenge due to its association with human waste. Therefore, composting of sewage sludge is the best option in agriculture activities. Sludge and wastewater utilization can add up positively in the economic aspects of the country in terms of creating jobs and improving annual income rate. The number of research projects done on wastewater reuse and other ongoing ones related to the land application of sewage sludge should encourage revision of existing standards, regulations, and policies for the management and beneficial use of sewage sludge in Oman.

Integrated dewatering and stabilization system as an environmentally friendly technology in sewage sludge management in Poland

Sludge treatment reed beds (STRBs) are an environmentally friendly technology which provides integrated dewatering and stabilization of sewage sludge. STRBs do not require the use of chemicals to improve the dewatering process. STRB is both, a low-emission and a low-energy-consuming method. After the stabilization process, sludge is characterized by the chemical composition similar to that of humus. The aim of the paper is to present the comprehensive data from Waste Water Treatment Plant (WWTP) in Gniewino (Poland) where the sewage sludge is dewatered and stabilized in a STRB.Research and literature reports indicate that sewage sludge treated in STRB is dewatered, which results in an increase in the dry matter (dm) (from 1.1% to 15.5%) and stabilization due to the decrease in the content of the organic matter (from 71.2% of the dm to 52.4% of the dm). Likewise, thanks to the high concentration of nutrients (TKN concentration − 3.64% of the dm and P concentration − 3.54% of the dm) and the low concentration of heavy metals (below permissible values for the agricultural use) after the time of stabilization, safe and valuable product can be recycled to the environment. Reject water (RW) generated during this process has relatively stable and much better properties in comparison to these which are generated in high technologies for sludge treatment. Thus, recycling the RW from the slugde dewatering in STRB represents a very low internal pollution and should not alert the treatment proceses of wastewater.

Influence of maize straw content with sewage sludge on composting process

Abstract After entrance to EU in 2004, the management of sewage sludge has become more and more important problem for the new members. In Poland, one of the most promising technologies is composting process of sewage sludge with carbonaceous materials. However, the high price of typically used cereal straw forces the specialists to look for new and cheap materials used as donor of carbon and substrates creating good, porous structure of composted heap. This work presents the results of sewage sludge composting mixed with sawdust and maize straw used to create structure favorable for air exchange. The results show dynamic thermophilic phase of composting process in all cases where maize straw was used.

Estimating human toxicity potential of land application of sewage sludge: the effect of modelling choices

PurposeMany municipalities are facing increasing pressure to adapt solid waste and wastewater management infrastructures in order to better close nutrient cycles. The focus of this study is on the estimation of the human toxicity potential associated with chemical contaminants released upon the application of sewage sludge to agricultural land. More specifically, this study investigated the effect of modelling choices regarding fate and exposure assessment.MethodsMonitoring data were collected for contaminants present in the sewage sludge from the wastewater treatment plant in Gothenburg and from other municipal wastewater treatment plants in Sweden. Based on these monitoring data, an overall burden of disease was estimated using characterisation factors taken from the USEtox models (versions 1.01 and 2.0). For the exposure through vegetables, an alternative life cycle impact assessment (LCIA) model was developed. The intake fractions thus obtained were used in combination with human health effect factors taken from the USEtox 2.0 database. The model results were compared with the USEtox models, and whether these two versions of the USEtox model provide significantly different results was also examined. The potential relevance of accidental ingestion of sludge was also considered.Results and discussionThe different LCIA models provided burden of disease estimates that differed from one another for individual contaminants (up to five orders of magnitude). The aggregated burdens of disease (i.e. sum for all contaminants considered in this study) estimated through different model variants, however, were of the same order of magnitude. For both metals and organic contaminants, only a small set of contaminants was found to make significant contributions to the aggregate burden of disease. However, it is uncertain whether the 15 metals and 106 organic contaminants covered by this study are those of greatest health significance of all contaminants potentially present in sewage sludge.Conclusions and recommendationsThe results of this study indicate that the technical information provided by the various approaches to modelling human toxicity in life cycle assessment (LCA) in the context of land application of sewage sludge management is consistent on the whole. However, given the uncertainties associated with the assessment of human toxicity in LCA, it is important to also contemplate the extent to which LCA in general is capable of informing the sewage sludge debate when it comes to human toxicity and possibly also other indicators. Future research could focus on identifying which types of questions of interest in the context of sewage management can be answered by LCA and which cannot.

Changes in light-textured soil parameters following two successive annual amendments with urban sewage sludge

The generation of considerable amounts of sewage sludge during wastewater treatment is inevitable and should be carefully addressed. Among the various options available for urban sewage sludge management, the agricultural re-use as a fertilizer/soil conditioner has seen a wide acceptance because of the high amount of nutrients and organic matter contained in this biowaste. Accordingly, the aim of this field-scale study was to evaluate the changes in agricultural soil parameters following two successive annual amendments with increasing amounts of urban sludge (0, 40, 80 and 120tha−1year−1). Sludge addition improved the fertility of the topsoil, showing a significant dose-dependent increase of TOC, N, P, and K contents up to the excessive amount of 120tha−1year−1 (1.6%, 0.09, 233 and 21mgkg−1, respectively). Consequently, soil biological parameters such as microbial communities and enzymatic activities (dehydrogenase, phosphatase, protease and cellulase) were all enhanced as well. On the other hand, we noticed also a similar increasing trend of soil salinity (EC and Na+) and phytotoxic heavy metals namely, Cd and Cr (2.4 and 3.8mgkg−1 at 120tha−1year−1). This variation was nonetheless below thresholds; and metal bioavailability to microorganisms and lettuce seeds was likely to be hindered by the non change in soil pH, which varied within a neutral range for all treatments (7.43–7.87). According to the C/N ratio, which reflects organic matter evolution in soil, plots treated at 80tha−1year−1 resulted in C/N values below 15. Therefore, this excessive sludge dose for agricultural reuse is likely to be the best practice that ensures an adequate organic matter mineralization with less contamination after two successive annual amendments.

Kinetics of Sewage Sludge Pyrolysis and Air Gasification of Its Chars

Optimal management and utilization of sewage sludge require innovative technological solutions. One of the prospective and novel concepts for the utilization of this waste, targeted at energy production, is the two-stage process combining pyrolysis and gasification. The paper presents the kinetic analysis of sewage sludge pyrolysis and air gasification of “hot” chars with the application of the thermogravimetric analyzer SDT Q600. The pyrolysis was performed below 1173 K in the inert gas atmosphere and with various heating rates of 1, 10, 50, and 100 K/min. The air gasification of chars was performed at 973, 1073, or 1173 K. The lumped model, which encompasses six first-order parallel reactions, was indicated as the most appropriate for the interpretation of the kinetics of sewage sludge pyrolysis. For the description of the char gasification stage, the Avrami–Erofeev model (A3) was proposed. The kinetic parameters estimated on the basis of the experimental data are the first published for sewage sludge “...