Sewage Sludge Management Research Articles

Sustainable sewage sludge management in Morocco: Constraints and solutions

Sustainable sewage sludge management in Morocco: Constraints and solutions

Microwave treatment of municipal sewage sludge: Evaluation of the drying performance and energy demand of a pilot-scale microwave drying system

Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L−1 (0.74 kWh L−1) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.

Anaerobic co-digestion of hydrolysate from anaerobically digested sludge with raw waste activated sludge: Feasibility assessment of a new sewage sludge management strategy in the context of a local wastewater treatment plant

Sustainable sewage sludge management is a worldwide issue in wastewater treatment plants (WWTPs). This work developed a new strategy for sewage sludge treatment involving the integration of hydrothermal treatment (HT) with anaerobic co-digestion (AcoD), particularly on the feasibility of mesophilic AcoD of anaerobically digested sludge (DS) hydrolysate and waste activated sludge (WAS). Results show that AcoD of DS hydrolysate from HT 170℃ for 30 min with WAS achieved the highest CH4 production of 205.39 mL CH4/g-VSfed. By adopting the new AD-HT170-AcoD strategy, 61.88 mL CH4/g-tVSfed higher CH4 yield and 22.2% more total solids (TS) reduction were obtained in addition to much better sludge settleability and 7.6% wt. less sludge cake production compared to the conventional mono AD. Although negative energy gain was obtained, the proposed AD-HT170-AcoD strategy is promising, economically feasible, and sustainable when the final sludge disposal of WAS is concerned in the context of whole WWTP.

The effect of sewage sludge fertilization on the biomass yield of giant miscanthus and the energy balance of the production process

The application of sewage sludge as fertilizer in the production of non-food crops is an environmentally sustainable approach to sewage sludge management. This article presents the results of a multidirectional analysis (agronomic and energy efficiency analysis) evaluating the effects of sewage sludge applied at rates equivalent to 100 and 160 kg N ha−1 on the production of giant miscanthus (Miscanthus × giganteus Greef and Deuter) in north-eastern Poland in 2013–2018. The optimal fertilizer rate was 160 kg N ha−1 regardless of nitrogen source (mineral fertilizers, sewage sludge), and it contributed to the achievement of the highest biomass yield (19.8 Mg ha−1 dry matter - DM) and the highest energy output (272–275 GJ ha−1). Energy demand was highest (19–24 GJ ha−1) in production technologies involving mineral fertilizers. The replacement of mineral fertilizers with sewage sludge decreased energy inputs in the production of giant miscanthus biomass by 32–34%. Energy gain was highest (259 GJ ha−1) when M. giganteus was supplied with sewage sludge at a rate equivalent to 160 kg N ha−1. The energy efficiency ratio peaked (24.7) in the production technology without fertilization. Energy efficiency was 43–52% higher when giant miscanthus plants were supplied with sewage sludge rather than mineral fertilizers.

Hydrothermal Carbonization as a Strategy for Sewage Sludge Management: Influence of Process Withdrawal Point on Hydrochar Properties

Conventional activated sludge systems, still widely used to treat wastewater, produce large amounts of solid waste that is commonly landfilled or incinerated. This study addresses the potential use of Hydrothermal Carbonization (HTC) to valorize sewage sludge residues examining the properties of hydrochars depending on HTC process conditions and sewage sludge withdrawal point. With increasing HTC severity (process residence time and temperature), solid yield, total Chemical Oxygen Demand (COD) and solid pH decrease while ash content increases. Hydrochars produced from primary (thickened) and secondary (digested and dewatered) sludge show peculiar distinct properties. Hydrochars produced from thickened sludge show good fuel properties in terms of Higher Heating Value (HHV) and reduced ash content. However, relatively high volatile matter and O:C and H:C ratios result in thermal reactivity significantly higher than typical coals. Both series of carbonized secondary sludges show neutral pH, low COD, enhanced phosphorous content and low heavy metals concentration: as a whole, they show properties compatible with their use as soil amendments.

Analiza gospodarki osadowej i biogazowo-energetycznej w oczyszczalni ścieków w Opolu

Analiza gospodarki osadowej i biogazowo-energetycznej w oczyszczalni ścieków w Opolu

Investigating the activation of hydrochar from sewage sludge for the removal of terbuthylazine from aqueous solutions

Hydrothermal carbonization offers the opportunity to reduce the issues related to the management of sewage sludge, enhancing dewaterability and avoiding thermal treatment prior landfill disposal or incineration, as water acts as a subcritical medium which catalyzes the process. The hydrochar obtained can find sustainable application as fuel, sorbent and soil amendment. Here, the effects of activation temperature (550–750 °C), time (1–4 h) and impregnation ratio potassium hydroxide: hydrochar (1–3), as well as their interactions, were investigated by Response Surface Methodology. The carbonaceous sorbent was then applied for the removal of terbuthylazine from aqueous solutions. Solid yields up to 32.31% were obtained, with corresponding ash content ranging from 13.05 to 35.06%. The combined effect of time and temperature significantly affects the ash content. An increase of impregnation ratio or temperature leads to low yields but high terbuthylazine adsorption, while the effect of the activation time on the pollutant removal is negligible. Up to 63.87% of the herbicide was adsorbed by the activated material, at terbuthylazine concentration of 2.5 mg L−1. The developed sorbent well fits the circular economy approach, offering a promising potential for sewage sludge management, as well as for water remediation.

Directions and Challenges in the Management of Municipal Sewage Sludge in Poland in the Context of the Circular Economy

Landfilling was the main method of sewage sludge disposal in Poland for decades. After Poland’s accession to the European Union (EU), many investments have been made into providing better access to tap water as well as to collect and treat municipal sewage. However, sewage sludge treatment has not been treated as an integral part of the implementation of wastewater management obligations. Stricter European Union regulations regarding the management of municipal sewage sludge (MSS) pose new challenges for Poland. The aim of this study was to analyze changes in the direction of the final management of municipal sewage sludge in Poland based on the analysis of strategic documents, regulations, literature, and available statistical data. The aim of the analysis was to search for directions to modify how sewage sludge is managed, given the approach promoted by the circular economy concept. The results prove that investments in wastewater treatment plants according to the EU sewage directive are not applied to the development of infrastructure that would enable the disposal of sewage sludge, which, for many years, has been stored (landfilling) or used directly in agriculture and ground reclamation. The introduction of stricter regulations in the area of sewage sludge usage and better wastewater treatment have increased the level of difficulties concerning sewage sludge management. Poland faces the challenge of defining sewage sludge management directions. The circular economy concept offers an approach that can be the basis for the creation of a new sewage sludge management strategy for Poland. The concept allows the combined goals of sewage sludge disposal and of energy and nutrients recovery to be achieved.

Sewage Sludge Thermal Treatment Technology Selection by Utilizing the Analytical Hierarchy Process

Sewage sludge management has gained significance in the last several years, due to its nutrient and energy content. However, technology selection is one of the greater challenges because it is not possible to implement a technology that covers all the requirements of the considered environments. Consequently, this paper shows an example of the utilization of an analytical hierarchy process, as a decision-making tool in terms of technology selection, for sewage sludge management in Rijeka, Croatia. The criteria structuring and evaluation process with the description of several possible alternatives for thermal treatment technologies are defined within this research. For the case of Rijeka, the best and most suitable technology for sewage sludge treatment is gasification, which coincides with the results obtained from the analysis of the literature review. According to the results in this paper, the possibilities of the use of this scientific method on the national level for the selection of sewage sludge treatment technology should be considered, due to the simplicity of its use and capability of its adaptation to various situations and areas.

Studies on the Gasification Performance of Sludge Cake Pre-Treated by Hydrothermal Carbonization

Proper treatment and careful management of sewage sludge are essential because its disposal can lead to adverse environmental impacts such as public health hazards, as well as air, soil, and water pollution. Several efforts are being made currently not only to safely dispose of sewage sludge but also to utilize it as an energy source. Therefore, in this study, initiatives were taken to valorize sewage sludge cake by reducing the moisture content and increasing the calorific value by applying a hydrothermal treatment technique for efficient energy recovery. The sludge cake treated at 200 °C for 1 h was found to be the optimum condition for hydrothermal carbonization, as, in this condition, the caloric value of the treated sludge increased by 10% and the moisture content removed was 20 wt.%. To recover energy from the hydrothermally treated sludge, a gasification technology was applied at 900 °C. The results showed that the product gas from hydrothermally treated sludge cake had a higher lower heating value (0.98 MJ/Nm3) and higher cold gas efficiency (5.8%). Furthermore, compared with raw sludge cake, less tar was generated during the gasification of hydrothermally treated sludge cake. The removal efficiency was 28.2%. Overall results depict that hydrothermally treated sewage sludge cake could be a good source of energy recovery via the gasification process.

Characterization of the residual sludge from the wastewater treatment plant of JERADA

The wastewater treatment plant of the city of JERADA is an aerated lagoon type, it is located in the west of the city of JERADA, It was put into service in 2016 and it is part of the national Moroccan liquid sanitation program, which requires an increasing of the rate of wastewater treatment. Indeed, said STEP generates on the one hand a clean sanitized water with an average flow of 2500 m3/d, which is discharged into the receiving environment without any environmental damage, and on the other handa huge quantities of residual sludge 1740.24 kg/d.The most suitable technique for the management of sewage sludge of the JERADA STATION is their valorization in agriculture after their composting. Such a process requires beforehand a physico-chemical and biological characterization of the station residual sludge.

Effect of Dried Sewage Sludge on Compressive Strength of Concrete

Sewage sludge is a waste product generated from the wastewater treatment process at the treatment plant. The amount of sewage sludge produced is increases every year as the population increased. Poor management of sewage sludge will give negative impact to the environment. Replacing cement with sewage sludge ash is more significant to reduce the amount of waste material from sewage treatment plants. In this study, the various percentage of dried sewage sludge (DSS) has been added to replace the cement. Sewage sludge was dried in the oven with 100°C for 24 hours, then sieve through the sieve size 300 µm. Then, DSS was used in the concrete instead of cement with the replacement percentage of 0%, 5%, 10%, and 15% by weight. The compressive strength of concrete cube specimens was investigated after 7 and 28 days of curing. The results showed that the compressive strength of concrete specimens increased with the replacement of cement in concrete with 5 % to 10 % DSS, but the achieved maximum strength still lower compared to the control sample. However, the compressive strength of concrete specimens decreased when the DSS replacement of cement is more than 10 % by weight. The result of XRF test also showed that DSS has good potential to replace cement in concrete.

Explorando el potencial de lodos urbanos para la producción de humus líquido

Worldwide, scientists have long been researching municipal sewage sludge management options in the context of the circular economy. In Chile, in particular, there have been a lot of misgivings about the disposal of sewage sludge. Liquid humus is a solution of humic and fulvic acids that can be used to add organic matter to soil via irrigation. The objective of this study was to evaluate the industrial potential of sewage sludge as a source material for the production of liquid humus. The sludges analyzed in the study produced liquid humus with high concentrations of humic and fulvic acids (7.3–7.9 g L-1). In one sludge under study, humic acids constituted the principal ingredient, while in another sludge, humic and fulvic acids were found in similar proportions. Since the results point to the occurrence of sewage sludge humification, such sludge from wastewater treatment plants may potentially be used as a source for the production of liquid humus. However, future studies are needed to evaluate agronomical performance of liquid humus sourced from urban sewage sludge.

The impact of agricultural and green waste treatments on compost quality of dewatered sludge.

Composting is one of the environmentally desirable methods for the management of sewage sludge. In this process, the organic matters were decomposed by microorganisms. However, different treatments can improve their qualities. This study aimed to investigate the effect of two agricultural waste wheat straw (WS) and green waste eucalyptus tree leaves (ETL) treatments on the quality of the compost produced from dewatered sewage sludge. So that, the variation trend of heavy metals, temperature, moisture, PH, and C/N ratio was considered during the composting process. The results showed that the variation of some parameters in WS and ETL such as temperature (24.68 ± 0.26 and 23.41 ± 1.35), moisture (4.5 ± 2.64 and 7.66 ± 2.51), pH (5.66 ± 0.35 and 5.97 ± 0.41), and C/N ratio (250 ± 4.08 and 60 ± 3.21) was suitable in both windrows, respectively. Likewise, trend of mineralization was suitable in both masses, because TVS (43 to 78 mg/g DW for WS and 45 to 69 mg/g DW for ETL) and TDS (21 to 55 mg/g DW for WS and 2.6 to 38 mg/g DW for ETL) decreased and increased, respectively, in the composting process. While fecal coliform (2.72 MPN/g DW) and EC (2.4mmho/cm) at WS was more than Iran's agricultural standard. As a consequence, although the quality of both masses was suitable and similar, there are some limitations for using treated compost by WS in agricultural lands due to higher levels of EC, fecal coliforms, and manganese. Therefore, quality of dewatered sludge treated compared with ETL is higher than WS. Furthermore, improvement process and application of some pretreatments are necessary for decreasing the heavy metals.

Image Analysis of Sewage Sludge and Barley Straw as Biological Materials Composted under Different Conditions.

Composting is one of the most important methods of sewage sludge management. This paper describes the methods of computer image analysis used for objective comparison of the appearance of composted materials under diverse conditions in terms of size and thermal insulation of the composting chambers. The research material was a mixture of sewage sludge and barley straw. The composting process was performed under strictly controlled laboratory conditions, using 10 composting chambers with five different volumes. In half of them additional thermal insulation was used, while in the others no insulation was applied. A proper composting process run was observed only in the three chambers with the largest volume and with additional thermal insulation. The images of the materials were subjected to a wide analysis, wherein the values of 17 parameters regarding color and texture were estimated. Significant differences were observed in the appearances between materials obtained during the properly running composting processes and those obtained in the chambers of insufficient size and thermal insulation. The values of the considered parameters determined for images of the composted material under normal and abnormal conditions were significantly different from each other. Thus, these parameters may be used as indicators of a correctly conducted composting process. In the cases of 15 parameters, the values of these differences exceeded 10%, and in the cases of 10 parameters 50%, while in the cases of three parameters as much as 100%.

Co-pyrolysis of sewage sludge and hydrochar with coals: Pyrolytic behaviors and kinetics analysis using TG-FTIR and a discrete distributed activation energy model

Dewatered sewage sludge (DS) has been upgraded to hydrochar (HC) using hydrothermal conversion because of superior fuel quality and avoidance of energy-intensive dewatering. In order to further develop sustainable energy conversion of HC, co-pyrolysis of DS and HC with three different-rank coals have been comprehensively investigated using thermogravimetric analysis coupled with Fourier transform infrared spectrometer and a discrete distributed activation energy model. Pyrolytic behaviors, kinetics and gas releasing characteristics have been examined. Results suggest that low-rank Coal 2 and moderate-rank Coal 3 blended with DS exhibited the highest synergistic removal of N and S, respectively. Co-pyrolysis of DS with high-rank Coal 1 favored C retention and N or S removal, while N was more likely to be stabilized in co-pyrolysis of HC with lower-rank coals. A less intensive but lasting devolatilization process in higher temperature regime (362–487 °C) was expected for HC. Higher fixed carbon content in HC and coals led to higher abundance of activation energy centralized around 180 kJ/mol for coal/HC blends. At the maximum decomposition rate temperature of 293.5 °C, pyrolysis of HC generated remarkable CH4 and other combustible gases with significantly reduced CO2. High-rank Coal 1 showed the most remarkable synergistic effect on the yield of light hydrocarbons and elevated Coal 1/HC blending ratio favored CO2 and CH4 release. Overall, co-pyrolysis of coals with HC could be a more sustainable technique for sewage sludge management and utilization in terms of stable devolatilization and centralized activation energy, higher yield of combustible syngas, and obviously reduced emissions of CO2 and nitrogen-containing gases.

Life cycle assessment approach to sustainable sewage sludge management for water pollution control

Increase in population growth coupled with industrialization, urbanization and requirements for implementation of stricter effluent discharge standards, sludge from wastewater treatment plants (WWTP) is expected to be produced in a continually increasing amount globally. The management of the huge volume of sludge generation becomes an integral component of environmental sustainability. Therefore, the need for environmentally friendly approach to sludge management strategy couldn’t be overemphasized. This paper proposes a rational and more sustainable approach directed towards devising means to solve the problem of the huge amount of WWTPs sludge by converting it to granular activated carbon (GAC) for utilization in water pollution control via incorporating Life Cycle Assessment (LCA). The paper reviews the various approaches and techniques for drying, pyrolysis and activation techniques and the best operating conditions for sludge based activated carbon (SBAC) for optimal pollution control. Based on that, a holistic decision making tool was recommended which incorporates major production, treatment and disposal options for each stage using Life Cycle Assessment (LCA) approach (from-cradle-to-grave), from which wide range of alternative scenarios will be generated vis-à-vis water pollution control efficacy in relation to environmental, cost as well as energy implications.

Analysis of the comprehensive management of sewage sludge in Poland

The methods of sewage sludge management in Poland have largely been determined by the legal requirements related to the Poland’s membership in the European Union. Since 1st January 2016, sewage sludge landfilling is prohibited. It must be emphasised that legal changes regarding wastewater management, along with the systematic increase in the volume of produced sludge, entail the necessity to change the existing method of sewage sludge management. This paper contains an analysis of solutions for management of sewage sludge produced in Poland over the period of 8 years. The goal of the work was an assessment of comprehensive management of sewage sludge produced in Poland from 2009 to 2016. Despite the decrease in the agricultural use of sewage sludge, their average share of 32% was the highest among other forms of sewage sludge management in Poland. Another form, related with the final stage of sewage sludge management, concerned its thermal processing. It was treated as a promising method, with a 19% increase over the analysed period. An optimal solution should be found to ensure safe management of sewage sludge.

Legislation for the Reuse of Biosolids on Agricultural Land in Europe: Overview

The issues concerning the management of sewage sludge produced in wastewater treatment plants are becoming more important in Europe due to: (i) the modification of sludge quality (biological and chemical sludge are often mixed with negative impacts on sludge management, especially for land application); (ii) the evolution of legislation (landfill disposal is banned in many European countries); and (iii) the technologies for energy and material recovery from sludge not being fully applied in all European Member States. Furthermore, Directive 2018/851/EC introduced the waste hierarchy that involved a new strategy with the prevention in waste production and the minimization of landfill disposal. In this context, biological sewage sludge can be treated in order to produce more stabilized residues: the biosolids. In some European countries, the reuse of biosolids as soil improver/fertilizer in arable crops represents the most used option. In order to control the quality of biosolids used for land application, every Member State has issued a national regulation based on the European directive. The aim of this work is to compare the different approaches provided by European Member States for the reuse of biosolids in agricultural soils. A focus on the regulation of countries that reuse significant amount of biosolids for land application was performed. Finally, a detailed study on Italian legislation both at national and regional levels is reported.

Co-pelletization of Microalgae-Sewage Sludge Blend with Sub-bituminous Coal as Solid Fuel Feedstock

Microalgae have been appeared as excellent source of bioenergy recently in Brunei Darussalam due to the favorable growth conditions, while sewage sludge emerged as major threat to the environment. Therefore, the challenge of sewage sludge management and microalgae utilization has spurred the demand of developing an innovative approach to utilize these sources for commercial applications. Hence, the main objective of this study was to characterize the bioenergy properties of microalgae, sewage sludge, and different blending ratios of microalgae-sewage sludge incorporated with sub-bituminous coal. Among three different blended samples, sample mixture 1 (SM-1) combined with 25% microalgae, 25% sewage sludge, and 50% coal presented the highest calorific value of 16.57 MJ/kg and lowest ash content of 45.61%. Along with this, SM-1 also manifested the highest values for pellet density (1.23 g/cm3) and energy density (20.41 GJ/m3) that can be referred as the most favorable values among all co-pelletized samples for transportation and logistics. Besides the characterization of raw samples, this study also emphasized on elemental analysis of ash content to determine the possibility of fouling and slugging. Ash analysis of all blends represented the major inorganic components aluminum (Al) and silicon (Si). Thermogravimetric analysis of all samples demonstrated the different phases of pyrolysis and combustion within 50 to 900 °C at heating rate of 10 °C/min. It can be concluded that this study recommended SM-1 as a potential feedstock for solid fuel purpose.