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Article

An Analysis of the Physicochemical and Energy Parameters of Briquettes Manufactured from Sewage Sludge Mixtures and Selected Organic Additives

by
Sebastian Kujawiak
1,
Małgorzata Makowska
1,
Damian Janczak
2,
Wojciech Czekała
2,*,
Włodzimierz Krzesiński
3,
Ariel Antonowicz
4 and
Karol Kupryaniuk
2
1
Department of Hydraulic and Sanitary Engineering, Poznań University of Life Sciences, Piątkowska 94A, 60-649 Poznan, Poland
2
Department of Biosystems Engineering, Poznań University of Life Sciences, Wojska Polskiego 50, 60-627 Poznan, Poland
3
Department of Vegetable Crops, Poznań University of Life Sciences, Dąbrowskiego 159, 60-594 Poznan, Poland
4
Institute of Computing Science, Poznan University of Technology, Piotrowo 2, 60-965 Poznan, Poland
*
Author to whom correspondence should be addressed.
Energies 2024, 17(18), 4573; https://doi.org/10.3390/en17184573
Submission received: 22 August 2024 / Revised: 6 September 2024 / Accepted: 10 September 2024 / Published: 12 September 2024
(This article belongs to the Special Issue Biofuel Production and Bio-Waste Management)
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Abstract

:
As a by-product of wastewater treatment, sewage sludge can be used for natural, agricultural, or energy purposes. One method of preparing sludge for management and use is solar drying. To intensify the drying process, natural additives can be used to alter the structure of the sludge and accelerate the evaporation of water. This research aimed to evaluate the influences of different organic additives in sewage sludge mixtures on the physicochemical and energy parameters of briquettes. This research was carried out without thermal boosting in a 4 × 2.5 × 2 m plastic tunnel. The tunnel was equipped with three drying stations and control and measuring equipment. In two test series, sludge additives in the form of straw and lignocellulosic materials, sawdust, bark, woodchips, and walnut shells, were used. Briquettes were made from the resulting mixtures and then subjected to physical and chemical analyses. This research showed high variability in the contents of trace elements, nitrogen, and sulphur in relation to an increase in the amount of sludge in the briquettes, which, for the briquettes made from sewage sludge, was nearly twice as high as for the briquettes made from the mixtures. The results of the flue gas analysis for the briquettes with sawdust and wood chip additives were very similar. The briquettes made from sewage sludge with lignocellulosic materials (bark and wood chips) had fuel properties similar to woody biomass, with a calorific value and heat of combustion of 15–16 MJ/kg. Fibrous additives (straw) significantly increased the strength parameters of the briquettes, by more than 50% of the value. The compositions and properties of the mixtures affected the following briquetting parameters: temperature and compressive force. The briquettes made from sewage sludge and additives can be classified according to ISO 21640 as SRFs (solid recovered fuels). In most of the results, the net calorific value (NCV) was 3 to 4; the chlorine content (CL) was 2 to 1; and the mercury content (Hg) was 1. The sewage sludge mixtures facilitated the agricultural and energy use of the briquettes.

1. Introduction

In recent years, the environmental awareness of societies has significantly increased, which has led to greater respect for the resources provided by our planet and their more rational management [1,2]. As a result, this has increased the use of energy from renewable sources [3]. The widespread use of conventional energy sources based on fossil fuels is having an increasingly strong impact on the greenhouse effect [4]. Therefore, in many countries (particularly in the European Union), there has been an intensive search for cheaper and more ecological solutions for obtaining energy from renewable sources (biomass, sun, wind, hydro, and geothermal energy) over the last two decades [5,6,7,8,9].
One of the promising sources of biomass for energy purposes is sewage sludge [10]. In EU countries, approximately 10 million Mg of sewage sludge (calculated in dry mass) is produced each year. According to estimates by Statistics Poland, as much as 1,012,000 tonnes of dry mass of sewage sludge was generated in Poland in 2023 alone. Sewage sludge is a by-product of wastewater treatment [11]. It can serve as a good fertiliser material or soil improver, enriching the soil [12]. The composition of sewage sludge varies and depends, among other things, on the type of wastewater treated, the method of treatment, or its processing [13,14]. Sewage sludge must be prepared appropriately before use for natural purposes or thermal disposal [15,16]. This is necessary mainly due to the high water content in sewage sludge, the varying content of heavy metals, and the varying degree of sanitary risk (with the highest for raw pre-sludge and the lowest for stabilised and hygienised sludge) [16,17,18,19]. However, a major problem in the management of sewage sludge is its high water content. The theoretical energy requirement to evaporate 1 kg of water at normal pressure is 0.627 kWh. For the complete drying of sludge (to 90–92%), the average thermal energy requirement, depending on the design solutions and installation parameters, ranges from 0.6 to 1.2 kWh/kg of evaporated water. Due to the ever-increasing mass of produced sewage sludge and the difficulties in its direct use, it is advisable to use thermal treatment to reduce its mass, achieve a hygienisation effect, and, consequently, facilitate further management [20,21,22].
The most common method of sewage sludge management is agricultural and natural use [23]. In recent years, using sludge as an energy source has also gained significance; in many European countries, 30 to 50% of sludge is incinerated. Due to transportation costs, sludge drying is becoming increasingly popular. This includes not only thermal drying but also solar drying, which is particularly useful in smaller wastewater treatment plants [24,25,26]. In the case of countries with great insolation, such as France, Turkey, Spain, or Croatia, where climatic conditions favour natural methods, solar dryers are very common. While Poland’s climatic conditions are not as favourable, several dozen facilities of this kind are in operation. Research on the solar-drying process is also increasingly widespread [27]. Solar dryers in temperate climates, also in Poland, can be successfully used to dry sewage sludge from small- and medium-sized wastewater treatment plants [28,29]. Solar sludge dryers that lack an additional heating source in autumn and spring typically store the dried sludge. Solar drying is most effective in summer; unfortunately, Poland’s temperate climate makes it impossible to dry the same amount of sludge each season [30].
A very important element of a solar dryer system is ventilation, which supports the evaporation of water from the sludge [31]; unfortunately, ventilating the dryers lowers their internal average temperature, which reduces the intensity of water loss. The use of an additional component in sewage sludge (e.g., a structural material additive) can improve the drying conditions during unfavourable periods (especially autumn and winter). As a result, the physical and chemical parameters of the resulting mixture can be improved, which can later be used for energy or agricultural purposes [32].
A very interesting trend in sludge management is the production of briquettes that serve as an energy source [33]. At present, there are well-known methods for producing biomass briquettes (e.g., from straw), which can be used to produce biofuel from sewage sludge mixtures [34,35]. The technology of solar drying and sludge management, including for energy purposes, combines issues related to waste management and its agricultural and energy use. It also represents an important contribution to the development of closed-loop management methods [36].
Briquetting studies utilising different types of waste and sludge for energy purposes have been described in numerous publications [34,37,38,39,40]. Authors studying the pelletisation of sewage sludge and biomass described the influence of process parameters on the properties of pellets in the co-pelletisation process of sludge and biomass materials. The results showed that the pellet density increased along with the increase in parameters such as pressure, sludge content, and temperature. A pellet with high hardness could be obtained at a low pressure, temperature, and biomass moisture content. The optimum moisture content for co-pelletisation was 10–15%. The addition of sludge can reduce the variation in pellet hardness caused by biomass heterogeneity [41,42]. Increasing the sludge content in the pellets would slow down the release of volatile substances. The synergistic effect of protein and lignin may be the mechanism determining the efficiency of the co-pelletisation of sludge and biomass.
Olorunnisola [43] briquetted mixtures of municipal solid waste with wastepaper and coconut shells using a piston press, obtaining a good-quality energy source. Wzorek [38], meanwhile, described the characteristics of alternative fuels containing sewage sludge and other waste materials. Three types of sludge-based fuels were subjected to comparative analysis: fuel prepared using sewage sludge and coal slurry (PBS fuel), fuel containing sewage sludge and meat and bone meal (PBM fuel), and fuel containing sewage sludge and sawdust (PBT fuel). The physicochemical properties of these fuels were studied, with particular attention paid to their calorific value and physical properties. The results revealed that the fuels produced from waste raw materials had energy values satisfactory for the cement industry, as required for alternative fuels in this industry. Tests of their physical properties showed that these fuels can be subjected to mechanical processes during transport and storage. Refuse-derived fuel (RDF) is a sorted waste used mainly as a fuel for energy generation [44]. The components of alternative fuels mainly include plastics, rubber waste, paper, textiles, and other combustible waste of municipal and industrial origin [45,46]. In Poland, alternative fuel is thermally processed in ten cement plants, and it accounts for 88% of all fuels burned there. Other waste used in cement plants includes used tyres (5%) and plastics and rubber (4%), as well as sewage sludge, sawdust, wood chips, wood, textiles, packaging waste, and other combustible waste.
Briquettes are a particularly favourable fuel for energy use due to their fairly high energy concentration (reaching 18 MJ/kg), energy value, and ease of transport and storage. Yank and Ngadi [47] described the physical properties of briquettes made from rice husks. Thanks to specific binding properties, the briquettes can be formed using a small compressive force. Rice is very effective in this respect; it was also used in the construction of the Great Wall of China. Meanwhile, Lela et al. [48] analysed the physicochemical properties of briquettes made from cardboard/sawdust biomass. The mixture had a calorific value of 17.41 MJ/kg, a minimum ash content of 6.62%, and a maximum compressive strength of 149.54 N/mm. The tested cardboard/sawdust briquettes showed the potential for use as a cost-effective biomass fuel.
Stolarski et al. [49] compared the quality and cost of producing briquettes from biomass of agricultural and forestry origin. The study covered the production of eight types of briquettes. The highest net calorific value was recorded for sawdust briquettes. The highest H, S, and N contents were found in briquettes made from oil cakes. Production costs ranged from 66.55 to 137.87 €/Mg. The production of briquettes was profitable, with the exception of the straw/oil cake mixture.
Polish legislation [50] defines the emission standards for exhaust gases. The regulations specify the maximum values of oxides, SO2, NO2, and dust for various sizes of fuel combustion facilities, such as solid biomass, diesel, natural gas, and other solid, liquid, and gaseous fuels. The regulations are based on European directives [51,52,53]. Regulations related to solid biofuels are governed by ISO 16559 (terminology) [54] and ISO 17225 (fuel specification and classes) [55].
The aim of this research was to determine the influences of various components of mixtures containing sewage sludge, straw, walnut shells, sawdust, bark, and wood chips, as well as ash, on the contents of trace elements, carbon, and nitrogen, the calorific value, and the heat of combustion of the briquettes made from biomass. In addition, the effect of additives on the mechanical properties of briquettes made from dried biomass was determined, and flue gas analysis was performed.

2. Materials and Methods

The preparation of the sewage sludge mixtures with organic additives such as bark, sawdust, wood chips, walnut shells, and straw consisted of their solar drying in a specially designed foil tunnel. The solar drying of the mixtures was carried out in a 4 × 2.5 × 2 m plastic tunnel (area: 10 m2; volume: ca. 20 m3) at the Experimental Station Marcelin of the Poznań University of Life Sciences. The tunnel structure was covered with white PE 140 g·m−2 foil with a UV4 filter and featured 6 tilting windows and a zipped door. The tunnel was equipped with three stations (thermally insulated) measuring 1.8 × 0.8 × 0.15 m, with a capacity of 216 dm3 each (Figure 1). The tunnel was equipped with a proprietary system for measuring and controlling the following solar drying parameters: isolation, temperature, humidity, and moisture mixtures (Figure 1).
The sewage sludge was obtained from a local sewage treatment plant in the Poznań metropolitan area (Rokietnica WWTP). Natural and commonly available materials were used as sludge additives. The ratio of sewage sludge to additive was always 50%/50% (by volume). A brief characterisation of the additives (in raw condition) used prior to mixing with the sewage sludge is presented in Table 1.
The mixtures had an initial moisture content ranging from 43% to 88%. The preparation (solar drying) continued until the mixtures reached a moisture content of 10% to 30%. The drying time depended on the prevailing atmospheric conditions (insolation, temperature, and humidity). Table 2 outlines the study schedule with the mixture designations.

2.1. Selection of the Most Advantageous Mixture

Based on the results of two drying series, four mixtures were selected for briquetting. The mixture had to possess favourable characteristics: high porosity, compressibility, and water absorption. Therefore, mixtures of sewage sludge with the addition of straw, bark, sawdust, and wood chips were selected. Pure sewage sludge from the CS series was used as a control sample. The mixture containing walnut shells assisted in the gelation process of the sewage sludge but was too hard and incompressible, causing the screw press of the briquetting machine to jam.

2.2. Briquetting

A mobile set manufactured by Asket (Figure 2) was used for the mixture-briquetting process. The set featured the following parameters: a capacity of up to 160 kg/h, a briquette diameter of 8 cm (with a hole), a briquetting process temperature adjustable from 0 to 250 °C, a screw press, and an energy consumption of ~70 kWh per 1 Mg of briquette.

2.3. Physicochemical Analyses

2.3.1. Moisture Content and Organic Dry Matter Content of Mixtures

The tests were based on direct measurements by direct weighing and were carried out at each experimental stage using a dryer (drying temperature: 105 °C), muffle furnace (combustion temperature: 550 °C), and analytical balance with an accuracy of 0.0001 g.

2.3.2. Analysis of the Composition of Briquettes and Exhaust Gases

Table 3 summarises the parameters and measurement methodologies.
The measurement of the exhaust gases was carried out using an A 550L Thermodrucker TD 100 (Wöhler, Wünnenberg, Germany) exhaust gas analyser equipped with the following measurement cells: CO, CO2, NOx, and SO2. The measurement sensor was placed in the flue gas chimney of the experimental boiler. The experimental boiler had a power of 12 kW. The combustion chamber capacity was 200 dm3. The exhaust gas temperature was >160 °C. The measurements were performed in a single cycle with 3 repetitions. The measurement uncertainty range was calculated.
The compositions of the mixtures were analysed using the elemental analysis method for nitrogen, sulphur, and carbon. The trace elements were determined using the ICP-MS technique, and the energy parameters were determined using a bomb calorimeter.

2.4. Strength Tests of Briquettes

A rotating drum with a diameter of 598 mm and a rotational speed of 21 rpm was used to test the strength of the briquettes. The tests were conducted in accordance with ISO 17831-2:2015 [62]. The test results are reported as the durability of the briquettes as the percentage (by mass) of briquettes remaining intact after the test procedure.

3. Results

3.1. Briquetting

The parameters of the briquetting process for each mixture were determined based on the structure and moisture content of the material and the amount of sewage sludge in the mixture. The briquetting temperature varied for each mixture. The maximum temperature during briquetting (240 °C) was used for briquetting sewage sludge without any additives. For the other materials, the temperature was lower and ranged from 150 to 220 °C. The screw press of the briquetting machine operated at a constant pressure. Therefore, the temperature of the briquetting process had to be appropriate for the given material. Too low or too high a temperature can cause problems with material bonding, leading to the immediate disintegration of the briquette. After performing several tests of the briquetting machine with different materials, the optimal briquetting temperatures for the samples were as follows: BSI/I—180 °C, BSI/II—200 °C, CSI/I—240 °C, BSII/I—190 °C, and BSII/II—200 °C. Figure 3 shows the produced briquettes.

3.2. Physical and Chemical Properties

Table 4 presents the results of the physicochemical analyses of the briquettes produced from the mixtures. The values of the energy parameters, heat of combustion, and calorific value depended on the compositions of the mixtures. The heat of combustion and calorific value were proportional to the carbon content. The highest ash content was observed in the mixture containing straw, which may indicate the degradation of the additive during the drying process and the partial mineralisation of the straw. Additives containing wood chips and bark have a low ash content, so the additive does not degrade. The energy parameters of the mixtures with straw and sawdust additives were similar. The energy value of the mixtures with bark and wood chips was 30–50% higher. The content of heavy metals in the briquettes containing only sewage sludge was significantly higher compared with the mixtures with additives.
According to the Annex to the Regulation of the Minister of Environment of 6 February 2015 (item 257) [63] and the EU Directive of 1986 [64], the analysed samples, in terms of their heavy metal content, did not exceed the permissible limits adopted in mg/kg of dry mass for the sewage sludge used in agriculture and for land reclamation for agricultural purposes.
According to the ISO 21640:2021 [65] standard, the tested mixtures can be classified as SRFs (solid recovered fuels). Table 5 outlines their characteristics, as specified in the standard.

3.3. Flue Gas Analysis

The analysis of the flue gases produced during the combustion of the briquette mixtures, previously subjected to chemical composition tests, was used to assess their compositions in terms of harmful substances. The chemical composition of the flue gas was determined by measuring the contents of carbon dioxide, carbon monoxide, nitrogen oxides, and sulphur oxides. Since the mixtures chosen for these studies had similar chemical compositions (sawdust and wood chips containing mainly lignocellulosic materials), the contents of the analysed components in the flue gases from the combustion of both mixtures were comparable (Figure 4). The CO2 value was 5% and the NOX value was 13% higher in the BSI/II sample compared with BSII/II. The carbon monoxide (CO) value in the BSII/II sample was 21% higher than in BSI/II. The test results were compared with the applicable regulations [50,51,52,53], and the oxide emission values did not exceed the limits for power plants.

3.4. Strength Tests

Tests conducted in accordance with ISO 17831-2:2015 [62] on the briquettes produced from the mixtures of sludge and additives made it possible to determine their mechanical strengths (Figure 5). The tests had a significant impact on determining the quality of the briquettes. A higher resistance to changes in its structure will make a briquette a more suitable fuel for transport, during which it will not disintegrate, and its performance will not deteriorate.
The best results in this regard were demonstrated by the BSI/I mixture (with the straw additive), achieving a mechanical strength of approximately 81%. The conducted tests indicated an increase in the mechanical strength of the briquette mixtures with the addition of a material with a rough structure (wood chips) or a soft and fibrous material (straw).

4. Discussion

This paper discussed the procedure for drying and briquetting sewage sludge mixtures with organic additives, as well as their physicochemical parameters and the analysis of the flue gases from the combustion of the produced briquettes. The natural additives consisted of straw, sawdust, bark, and wood chips. The materials were mixed with dewatered sewage sludge and dried together in a solar dryer. The structures and properties of the mixtures were affected by specific conditions. From the two drying series, four mixtures were selected for briquetting. The mixtures had to possess favourable characteristics: high porosity, compressibility, and water absorption. Therefore, the mixtures of sewage sludge with the addition of straw, bark, sawdust, and wood chips were selected. Table 4 presents the results of the physicochemical analyses of the briquettes produced from the mixtures. The values of the energy parameters, heat of combustion, and calorific value depended on the compositions of the mixtures. The heat of combustion and calorific value were proportional to the carbon content. Straw underwent strong decomposition during the drying process, which significantly increased the ash content in the briquettes. Additives containing wood chips and bark reduced the ash content in the briquettes. The energy values of the mixtures with bark and wood chips were 30 to 50% higher than those of the remaining mixtures. The calorific values of the mixtures classified them between municipal waste and firewood. The content of heavy metals in the briquette containing only sewage sludge was significantly higher compared with the mixtures with additives, according to the applicable regulations in Poland and the EU. The mixtures are suitable for agricultural use. The flue gas analysis for the mixtures with the addition of sawdust and wood chips showed similar nitrogen oxide contents. The addition of straw in the form of fibres significantly increased the mechanical strength of the briquettes compared with the other additives in the form of compact particles. According to the ISO 21640 [65] standard, the mixture with the addition of sewage sludge was classified as an SRF, suitable for use in waste incineration plants, even though, according to the applicable directives, the emission values of oxides did not exceed the limits for energy facilities. The results of the published research were included in patent application no. P.445919: “Technology for using natural materials for solar drying of sewage sludge and production of sewage sludge-based briquettes”.
The utilisation of biomass waste and sewage sludge for energy purposes enables the fulfilment of environmental standards regarding the emissions of CO2, SOx, NOx, dust, dioxins, chlorine, mercury, and heavy metals. The combustion of biomass reduces the CO2 emission balance as the amount of CO2 previously absorbed during the process of photosynthesis is re-emitted into the atmosphere. The low nitrogen content in biomass waste reduces the emission of NOx compounds into the atmosphere compared with coal combustion [66,67].
The parameters characterising the drying process of sludge mixtures with components were also investigated and will be included in the next scientific paper. The analysis of the results showed that additives to sewage sludge, depending on their type, changed the structure of the mixture and accelerated the gelation process of the sewage sludge. Additionally, it was found that an additive could change the physicochemical properties of the mixture. On the basis of measurement data obtained from a local solar dryer in the Wielkopolska area, it was calculated that the evaporation of 1 t of water from sewage sludge requires 39.8–42.4 kW of electricity, used for turning the sludge and ventilating the greenhouse. The use of mixtures can reduce the energy intensity of solar dryers and increase their efficiency. In comparison, conventional drum dryers require 1200 kW of electricity to evaporate 1 t of water from sludge [68].

5. Conclusions

As a by-product of wastewater treatment, sewage sludge can be used for natural, agricultural, or energy purposes. One method of preparing sludge for management and use is solar drying. To intensify the drying process, natural additives can be used to alter the structure of the sludge and accelerate the evaporation of water. The co-drying of suitable additives with sewage sludge facilitates its agricultural use (as a soil additive) and energy use as an alternative fuel. The mixtures of sewage sludge with lignocellulosic materials (bark and wood chips) had fuel properties similar to woody biomass, with a calorific value and heat of combustion of 15–16 MJ/kg. As the amount of sewage sludge in the briquettes increased, the contents of trace elements, nitrogen, and sulphur also increased. These contents were nearly 100% higher for the briquettes made from sewage sludge than the briquettes made from the mixtures. The compressibility and absorbability of a material are desirable characteristics when it comes to the production of briquettes. Fibrous materials significantly increased the mechanical strength of the briquettes, especially straw (by more than 50%). The composition and properties of the mixture require suitable briquetting parameters, i.e., temperature and compressive force. The briquettes made from sewage sludge and additives can be classified according to ISO 21640 as SRFs. In most of the results, the net calorific value (NCV) was 3 to 4; the chlorine content (CL) was 2 to 1, and the mercury content (Hg) was 1.

6. Patents

The results of the published research were included in patent application no. P.445919: “Technology for using natural materials for solar drying of sewage sludge and production of sewage sludge-based briquettes”.

Author Contributions

Conceptualisation, S.K. and M.M.; methodology, M.M. and W.C.; validation, S.K. and M.M.; formal analysis, W.K. and K.K.; investigation, S.K.; resources, D.J. and M.M.; data curation, M.M. and W.C.; writing—original draft preparation, S.K. and D.J.; writing—review and editing, M.M. and W.C.; visualisation, A.A.; supervision, W.C.; project administration and funding acquisition, S.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Poznań University of Life Sciences as the research program “First grant”, no. 10/2022.

Data Availability Statement

All data generated or analysed during this study are included in this published article.

Acknowledgments

Thanks to EPS Szelejewski and Nowigo (Pomarzanowice) for their help in developing the research equipment and providing the natural research additives.

Conflicts of Interest

The authors declare no conflicts of interest.

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Energies 17 04573 g001
Figure 1. Measuring automation set for a solar-drying tunnel (to be reproduced in colour on the web and in black-and-white in print).
Figure 1. Measuring automation set for a solar-drying tunnel (to be reproduced in colour on the web and in black-and-white in print).
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Figure 2. The process of briquetting mixes.
Figure 2. The process of briquetting mixes.
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Figure 3. Briquettes produced from mixtures.
Figure 3. Briquettes produced from mixtures.
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Figure 4. Contents of carbon monoxide, sulphur oxides, and nitrogen oxides in flue gases from analysed mixtures.
Figure 4. Contents of carbon monoxide, sulphur oxides, and nitrogen oxides in flue gases from analysed mixtures.
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Figure 5. Mechanical strengths of briquettes according to ISO 17831-2:2015.
Figure 5. Mechanical strengths of briquettes according to ISO 17831-2:2015.
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Table 1. Properties of materials and sewage sludge used in mixtures before mixing.
Table 1. Properties of materials and sewage sludge used in mixtures before mixing.
NameNitrogen
Content
[% DM]		Carbon
Content
[% DM]		Dry Organic Matter Content
[% DM org]		Moisture
[%]
Straw chaff (rye)1.2245.9892.927.97
Tree sawdust (mixture: pine, spruce, and beech)1.5652.8297.837.73
Pine bark (sorted)1.1350.0665.0152.05
Beech–alder wood chips0.7348.1973.748.47
Walnut shells0.8349.8970.1110.67
Sewage sludge (BSI + BSIII)6.5737.0862.2588.13
Table 2. Schedule for the implementation of this study.
Table 2. Schedule for the implementation of this study.
Series NumberPeriod
Start		Period
Completion		Drying Time,
Days		Type of Biomix
I17.05.2229.06.2249BSI/I—straw 50%/sewage sludge 50%
BSI/II—tree sawdust 50%/sewage sludge 50%
II07.09.2226.11.2276BSII/I—wood pine bark 50%/sewage sludge 50%
BSII/II—wood chips 50%/sewage sludge 50%
BSII/III—walnut shells 50%/sewage sludge 50%
CS07.07.2207.09.2363CSI/I—sewage sludge 100%
Table 3. Summary of parameters under study with units of measurement and test methodologies.
Table 3. Summary of parameters under study with units of measurement and test methodologies.
ParameterUnit of
Measure		Survey Methodology
Total chlorine content% s.m.PN-EN ISO 16994:2016 [56]
Total moisture content%PN-EN ISO 18134-1 [57]
Total sulphur content% d.m.PN-EN ISO 21663:2021-06 [58]
Total hydrogen content% d.m.PN-EN ISO 21663:2021-06 [58]
Total carbon content% d.m.PN-EN ISO 21663:2021-06 [58]
Ash% d.m.PN-EN ISO 21656:2021-08 method A [59]
Heat of combustion (dry)kJ/kgPN-EN ISO 21654:2021-12 [60]
Calorific value (from dry calculations)kJ/kgPN-EN ISO 21654:2021-12 [60]
Kjeldahl nitrogen% d.m.PN-EN ISO 21663:2021-06 [58]
Hg, As, Cd, Cr, Cu, Ni, Pb, and Znmg/kg d.m.PN-EN ISO 11885:2009 [61]
Table 4. Chemical and energetic properties of the tested mixtures.
Table 4. Chemical and energetic properties of the tested mixtures.
Trial NameBSI/IBSI/IICSI/IBSII/IBSII/II
Total moisture content%9.6 ± 2.2 *8.9 ± 2.010.1 ± 1.619.8 ± 3.28.5 ± 2.9
Total chlorine content% s.m.0.22 ± 0.040.09 ± 0.0150.16 ± 0.030.089 ± 0.0150.066 ± 0.01
Total sulphur content0.57 ± 0.170.47 ± 0.140.71 ± 0.210.44 ± 0.130.47 ± 0.14
Total hydrogen content4.16 ± 1.084.72 ± 1.235.03 ± 1.314.69 ± 1.225.34 ± 1.39
Total carbon content31.3 ± 6.635.6 ± 7.535.7 ± 7.544.1 ± 9.341.6 ± 8.7
Ash44.37 ± 4.4437.43 ± 3.7436.8 ± 3.6825.78 ± 2.5826.2 ± 2.62
Kjeldahl nitrogen2.86 ± 0.572.39 ± 0.484.5 ± 0.92.37 ± 0.472.67 ± 0.54
Heat of combustionMJ/kg11.2 ± 0.2812.6 ± 0.3114.3 ± 0.3616 ± 0.415.7 ± 0.39
Calorific value10.3 ± 0.8211.6 ± 0.9313.2 ± 1.0615 ± 1.214.6 ± 1.17
Hgmg/kg<0.1<0.10.29 ± 0.060.1 ± 0.02<0.1
As<5 <5 <5<5 <5
Cd0.3 ± 0.050.27 ± 0.040.61 ± 0.090.53 ± 0.080.35 ± 0.05
Cr7.5 ± 1.55.1 ± 1.019 ± 48.5 ± 1.79.4 ± 1.9
Cu190 ± 40120 ± 20400 ± 80150 ± 3 0170 ± 30
Ni53 ± 1136 ± 728 ± 623 ± 526 ± 5
Pb4.7 ± 0.793.7 ± 0.78.8 ± 1.86.6 ± 1.37.1 ± 1.4
Zn310 ± 60200 ± 40630 ± 130280 ± 60280 ± 60
* Measurement uncertainty at α = 0.05.
Table 5. Classification of mixtures according to ISO 21640:2021 [65].
Table 5. Classification of mixtures according to ISO 21640:2021 [65].
Classification CharacteristicClass
BSI/IBSI/IICSI/IBSII/IBSII/II
Net calorific value (NCV)44434
Chlorine (CL)21111
Mercury (Hg)11111
Origin3.3.13.3.13.3.13.3.13.3.1
Trade formBriquettesBriquettesBriquettesBriquettesBriquettes
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Kujawiak, S.; Makowska, M.; Janczak, D.; Czekała, W.; Krzesiński, W.; Antonowicz, A.; Kupryaniuk, K. An Analysis of the Physicochemical and Energy Parameters of Briquettes Manufactured from Sewage Sludge Mixtures and Selected Organic Additives. Energies 2024, 17, 4573. https://doi.org/10.3390/en17184573

AMA Style

Kujawiak S, Makowska M, Janczak D, Czekała W, Krzesiński W, Antonowicz A, Kupryaniuk K. An Analysis of the Physicochemical and Energy Parameters of Briquettes Manufactured from Sewage Sludge Mixtures and Selected Organic Additives. Energies. 2024; 17(18):4573. https://doi.org/10.3390/en17184573

Chicago/Turabian Style

Kujawiak, Sebastian, Małgorzata Makowska, Damian Janczak, Wojciech Czekała, Włodzimierz Krzesiński, Ariel Antonowicz, and Karol Kupryaniuk. 2024. "An Analysis of the Physicochemical and Energy Parameters of Briquettes Manufactured from Sewage Sludge Mixtures and Selected Organic Additives" Energies 17, no. 18: 4573. https://doi.org/10.3390/en17184573

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