Sludge Plant Research Articles

Organic matter degradation and redistribution of sediment associated contaminants by benthic invertebrate activities

The fate of sediment associated compounds is the combined result of chemical properties and biological activities. Yet, studies simultaneously addressing the effects of biota on the redistribution and bioaccumulation of contaminants are scarce. Our aim was therefore to assess the effect of benthic invertebrate activities on organic matter degradation and the redistribution of metals and Polycyclic Aromatic Hydrocarbons (PAHs) in contaminated sediment. To this end, we introduced egg ropes of the non-biting midge Chironomus riparius into wastewater treatment plant sludge and allowed these to either develop until fourth instar larvae or to fully complete their life cycle into terrestrial flying adults. Chironomid larvae enhanced sludge degradation, resulting in increased metal concentrations in the sludge and in a flux of metals into the overlying water. Moreover, they hampered PAH degradation in the sludge. Contaminant transport from aquatic to terrestrial ecosystems with emerging invertebrates as a vector is widely acknowledged, but here we showed that biomanipulation prevailed over bioaccumulation, since due to chironomid activity, the flux of metals from the sludge into the overlying water was larger than into chironomid biomass. It is therefore concluded that contaminant-macroinvertebrate interactions are bilateral relationships driven by the interplay between macroinvertebrate traits and contaminant properties.

High-performance removal of anti-inflammatory using activated carbon from water treatment plant sludge: fixed-bed and batch studies

High-performance removal of anti-inflammatory using activated carbon from water treatment plant sludge: fixed-bed and batch studies

Incorporation of the Sludge of Sewage Treatment Plant on Ceramic Bricks Manufacture

Treatment processes used in most sewage treatment stations generate as by-product a material named sludge. The amount of sludge grows proportionally with the increase in effluent collection and treatment services, which in turn must accompany population growth. The disposition of waste generated in an environmentally correct and economically viable way is one of the biggest challenges faced by companies that operate sanitation services. The ceramic industry presents a great potential for the use of this waste. The goal of this work was to evaluate the effect of the incorporation of the sewage sludge in the ceramic mass for the manufacture of solid bricks. The water absorption was lower for bricks with 10% sludge, but it increased for bricks with 15% sludge, resulting in products that presented water absorption slightly beyond of the limit of the standard NBR 15270. However, the results are promising because they show that additions of 10% or 15% sludge increased the compressive strength markedly.

Anaerobic co-digestion of paper sludge: Feasibility of additional methane generation in mechanical–biological treatment plants

In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical–biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH4 kg−1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates.

DENSE AND POROUS CERAMIC MATERIALS FROM COAL SLUDGE OF THE INTA DEPOSIT

Dense and porous thermal-insulating ceramic materials were obtained from the flotation tailings of coal sludge of the processing plant of Inta town. The thermal behavior, changes in the phase and chemical composition during firing in the temperature range from 800 to 1280 °C were studied. During firing, carbonates dissociated, magnetite oxidized, kaolinite amorphized, layers in layered silicates compressed, at 1100 °C cristobalite and spinel were formed, at 1150 °C – mullite, the content of the amorphous phase increased. Dense ceramic materials were obtained at firing temperatures of 800 – 1150 °C, and porous materials at temperatures 1200 – 1280 °C. The physical, mechanical and technical characteristics of the obtained ceramic materials were studied. Porous ceramics, sintered at 1280 °C, belongs to the class of heat-insulating materials with increased thermal conductivity.

Corrosion monitoring by open circuit potential in steel reinforcements embedded in cementitious composites with industrial wastes

Corrosion is one of the main issues affecting service life of reinforced concrete structures. The Open Circuit Potential (OCP) technique is a non-destructive method used to survey and monitor this problem. This test can also be used in laboratory environment and provide valuable information supporting the selection process of supplementary materials for durable concretes. Although this qualitative technique is commonly used, there is still a lack of consensus on the suitability of specific procedures for experimental analysis, such as type of reference electrode and influence of accelerated aging procedures (adoption of wetting/drying cycles and level of immersion of specimens). Therefore, the present study aims to evaluate the method for prediction of early steel corrosion activity in the accelerated OCP tests. The paper is focused on testing eco-efficient cementitious composites containing industrial wastes, such as sugarcane bagasse ash sand (SBAS) and water treatment plant sludge (WTPS), in replacement of natural sand. The results showed that an adoption of combined wetting/drying cycles, together with a partial (rather than total) immersion of specimens in NaCl solution, leads to earlier appearance of corrosion. This allows to shorten the period of testing by almost 10 weeks. It is due to higher access to oxygen and higher concentration of free chlorides from the saline solution accumulated in a porous system. The type of reference electrode is of lesser importance. Moreover, incorporation of 30% SBAS and 3% WTPS results in higher protection for steel corrosion, confirming wide applicability of the OCP technique to any cementitious matrices with or without industrial wastes.

Advantages of MS/MS/MS (MRM3) vs classic MRM quantification for complex environmental matrices: Analysis of beta-lactams in WWTP sludge

When dealing with complex matrices such as wastewater treatment plant (WWTP) sludge or animal manure, usual MRM quantification may lack enough sensitivity or accuracy due to the presence of numerous interfering compounds co-extracted from the matrix. To circumvent the sensitivity and specificity loss, the method development can be focused on sample extraction, purification or/and optimisation of the detection. In this study, we propose an enhancement of a method for the analysis of five beta-lactams (Amoxicillin, Ampicillin, Cefapirin, Ceftiofur, and Cloxacillin) in WWTP, with the use of a hybrid triple quadrupole-Linear Ion Trap (LIT) spectrometer, enabling triple stage MS acquisition, namely MRM3, in place of the usual MS/MS detection. The adaptation of various parameters such as the secondary fragmentation energy, excitation, and accumulation times of the secondly generated ion are described. The method was then validated and enabled quantification limits between 0.8 and 14.7 ng g−1 associated with accurate quantification (between 98% and 113%). This method is the first to report the use of MRM3 acquisition in an environmental matrix as complex as sludge.

Equilibrium, Kinetic and Thermodynamic Studies of Malachite Green Dye Removal using Activated Sludge from Common Effluent Treatment Plant

Disposal of industrial effluents containing synthetic dyes causes a potential hazard to the land and environment and therefore dyes need to be removed before disposal. In the present study, combined effluent treatment plant (CETP) sludge was activated at 200° C for 1 hour and used as an adsorbent for the removal of malachite green dye from wastewater. The adsorbent was characterized by XRF, SEM, XRD and FTIR. Batch studies were carried out under various experimental conditions by varying contact time, dye concentration, adsorption dose, pH and temperature to assess the potentiality of activated sludge for the removal of malachite green dye from wastewater. The results revealed that the removal of malachite green dye was strongly pH dependent and maximum dye removal was observed at equilibrium pH of 8.0. Optimum adsorbent dose and contact time were found to be 10 g/l and 180 minutes respectively. Thermodynamic studies showed the spontaneous and endothermic nature of the adsorption. Adsorption data have also been correlated with different isotherm models. Hence activated sludge can be used as an effective adsorbent for the removal of malachite green dye from wastewater. It could be considered as good replacement of commercially available adsorbent like zeolites, activated carbon etc. due to its significant low cost and high sorption efficiency.

Mechanochemical dechlorination of petrochemical sludge through a planetary ball mill and using industrial wastes as additives

AbstractMechanochemical treatment causes the formation of mineral Cl compounds during the degradation of polychlorinated compounds by planetary ball mill. In the present study, the three types of industrial waste comprising of sludge from petrochemical wastewater treatment plants as source of pollutants, scrap iron and petrochemical water treatment plant sludge as co‐milling reagents were used. The raw samples and the milled products were analyzed by gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, Raman Spectroscopy, and X‐ray diffraction. Further analyses such as ion chromatography and X‐ray fluorescence were performed. The analysis results confirmed that the milling process degraded persistent organic pollutants and showed that major changes occurred in the organic phases, carbon and chlorine bonds. The yield of chloride ions was investigated using Ion Chromatography. The highest percentage of de‐Cl products (95.6%) was achieved after 6 h in equal proportions of reagents. Furthermore, CaCl2 and FeCl2 were present in the final milling product.

Deep learning model based on urban multi-source data for predicting heavy metals (Cu, Zn, Ni, Cr) in industrial sewer networks

The high concentrations of heavy metals in municipal industrial sewer networks will seriously impact the microorganisms of the activated sludge in the wastewater treatment plant (WWTP), thus deteriorating the effluent quality and destroying the stability of sewage treatment. Therefore, timely prediction and early warning of heavy metal concentrations in industrial sewer networks is crucial. However, due to the complex sources of heavy metals in industrial sewer networks, traditional physical modeling and linear methods cannot establish an accurate prediction model. Herein, we developed a Gated Recurrent Unit (GRU) neural network model based on a deep learning algorithm for predicting the concentrations of heavy metals in industrial sewer networks. To train the GRU model, we used low-cost and easy-to-obtain urban multi-source data, including socio-environmental indicator data, air environmental indicator data, water quantity indicator data, and easily measurable water quality indicator data. The model was applied to predict the concentrations of heavy metals (Cu, Zn, Ni, and Cr) in the sewer networks of an industrial area in southern China. The results are compared with the commonly used Artificial Neural Network (ANN) model. In this study, it was shown that the GRU had better prediction performance for Cu, Zn, Ni, and Cr concentrations, with the average R2 significantly increased by 12.35%, 11.94%, 9.21%, and 8.13%, respectively, compared to ANN predictions. The sensitivity analysis based on Shapley (SHAP) values revealed that conductivity (σ), temperature (T), pH, and sewage flow (Flow) contributed significantly to the prediction results of the model. Furthermore, the three input variables including air pressure (AP), land area (A), and population (Pop.) were removed without affecting the prediction performance of the model, which maximized the modeling efficiency and reduced the operational cost. This study provides an economical and feasible technical method for early warning of abnormal heavy metal concentrations in urban industrial sewer networks.

Hanamia caeni gen. nov., sp. nov., a Member of the Family Chitinophagaceae Isolated from Activated Sludge in Korea.

A novel Gram-stain-negative, aerobic, yellowish-pigmented, non-motile, rod-shaped bacterial strain, designated strain BO-59T, was isolated from the activated sludge of a wastewater treatment plant in Hanam City, South Korea. Phylogenetic study based on the 16S rRNA gene sequence positioned BO-59T in a distinct lineage in the family Chitinophagaceae, sharing less than 92.8% sequence similarity with members of the closely related genera Ferruginibacter, Flavitalea, Pseudoflavitalea, Flavisolibacter, Niastella, and Terrimonas. Phylogenomic- and genomic relatedness analyses revealed that strain BO-59T is clearly distinguished from other genera in the family Chitinophagaceae by average nucleotide identity < 66.9%) and the genome-to-genome distance (< 29.5%) values. The strain BO-59T contained MK-7 as the predominant quinone, and iso-C15:0, iso-C17:0 3OH, and iso-C15:1 G as major fatty acids (> 10%). The DNA G + C content was 39.1mol% based on genome sequence analysis. The polar lipids of strain BO-59T were phosphatidylethanolamine, an unidentified aminophospholipid and three unidentified polar lipids. 16S rRNA gene sequence similarity, physiological, and biochemical characteristics indicated that strain BO-59T represents a novel species of a new genus, for which the name Hanamia caeni gen. nov., sp. nov. is proposed. The type strain is BO-59T (= KACC 19646T = LMG 30865T).

Solubilization of rock phosphate by phosphate solubilizing bacteria isolated from effluent treatment plant sludge of a fertilizer plant.

This study evaluates the efficiency of Phosphate solubilizing bacteria isolated from Effluent Treatment Plant sludge of Paradeep Phosphate Limited, Odisha, India, to solubilize rock phosphate (RP) and the mechanism and structural changes during solubilization investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Out of 13 bacterial isolates, Bacillus cereus S0B4, Solibacillus isronensis S0B8, and Bacillus amyloliquefaciens S0B17 strains were found to be the best RP solubilizers. This is the first report on S. isronensis S0B8 with the ability to solubilize RP. In particular, the potent strain B. cereus S0B4 showed maximum soluble P (338.5mg/L) on the 7th day. Negative correlations (r = -0.70; p ≤ 0.01) were observed between soluble P concentration and pH, whereas positive correlation exists with the growth of B. cereus S0B4 (r = 0.91, p ≤ 0.01), S. isronensis S0B8 (r = 0.75, p ≤ 0.01), and B. amyloliquefaciens S0B17 (r = 0.77, p ≤ 0.01) respectively. The P release kinetics followed the 1st order model well (R2 = 0.8001-0.8503). It seems that H+ ions and organic anions released from the organic acids are major factors responsible for RP solubilization. The SEM observations demonstrate that B. cereus S0B4 corroded the RP surface significantly due to the proton attack. The XRD analysis confirms that the intensity of all mineral peaks decreases after treatment with B. cereus S0B4. The FTIR analysis indicated a significant decrease of calcite and fluorapatite's vibrational bands with the disappearance of quartz.

Hydrothermal Carbonization of Paper Mill ETP Sludge and Assessing its Potential Application in Agriculture

Effluent Treatment Plant Sludge (ETPS) from pulp and paper mill is produced in larger quantities and its disposal has the major problem faced by the industries. The conversion of paper mill sludge into hydrochar through the process of Hydro Thermal Carbonization (HTC) has wider opportunities in agriculture. This study explored the optimization processes which influence the preparation of hydrochar from ETPS through the approaches of Response Surface Methodology (RSM). The optimized temperature and time were 220 °C and 4 hours, respectively for hydrochar production based on higher carbon and nitrogen content. The hydrochar and ETPS was characterized using Scanning Electron Microscopy (SEM), Brunauer Emmett Teller (BET) surface area and Fourier Transform Infra-Red Spectroscopy (FTIR) for its structural morphology. Based on the optimized parameters, the hydrochar was produced and used in the pot culture experiment to study the impact of the hydrochar on bhendi (Abelmoschus esculentus) crop growth. Different concentrations of hydrochar were applied as basal in the pot. The treatment with 4% hydrochar germinated first show the good shoot and root length and 11% increase in germination percentage and 22% increase in vigour index when compared with control due to its higher nutritives which is on par with the results of 5% hydrochar.

Dechlorination of persistent organic pollutants in petrochemical wastewater sludge through a planetary ball mill using synthesized nanocomposite

ABSTRACT Numerous tons of hazardous wastes containing persistent organic pollutants (POPs) are stored in an unsafe manner in the petrochemical industries. The planetary ball mill causes the formation of mineral Cl compounds during the degradation of polychlorinated compounds in the presence of various reagents. In addition, the planetary ball mill has been applied for the synthesis of diverse organic-inorganic hybrid nanomaterials. In the present study, Fe-metal organic framework was prepared using a planetary ball mill, and then Fe@C nanocomposite with core/shell structure was synthesised by carbonisation. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) were utilised to study the synthesised materials. The nanocomposite was used as a reagent to degrade persistent organic pollutants in the sludge of a petrochemical wastewater treatment plant by a planetary ball mill. CaO was also used to compare the effect of nanocomposites on system performance. Ion chromatography (IC) analysis was carried out to determine chlorine mineralisation. Furthermore, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were applied to determine chemical bonds. The results illustrated a zero-valent iron nanoparticle in the core protected by carbon shell in a synthesised nanocomposite with a core/shell structure. Hence, nanocomposite was the most efficient additive, with 97% dechlorination efficiency in the first hour while the efficiency of the planetary ball mill in the presence of CaO was only 76% after 12 hours of milling. Furthermore, major changes occurred in the organic phases, carbon and chlorine bonds. Simultaneously, graphite and amorphous carbon were produced in the final products after milling. This indicates that aromatic structures and C-Cl bonds were broken down into inorganic compounds. Thus, this study presented a practical method of producing materials while degrading hazardous pollutants in petrochemical wastewater sludge through a planetary ball mill.

Application of Extracellular Polymeric Substances Extracted from Wastewater Sludge for Reactive Dye Removal

This study aimed to investigate the adsorption of three commercial reactive dyes using extracellular polymeric substances (EPS) extracted from the waste sludge of a beer wastewater treatment plant in Hanoi, Vietnam. EPS was extracted from sludge by the HCHO-NaOH method and was characterized by measuring kaolin flocculation activity, dry weight, chemical composition, and functional groups. Adsorption of dyes on EPS was conducted by Jartest at different pH values, contact times, and EPS dosages. The EPS was composed of 25% sludge by weight. The FTIR analysis showed the presence of amine and carboxyl groups in the EPS structure. The removal efficiencies of reactive dyes were high at pH values below 6, a contact time of 30 to 60 min, and EPS dosage of 200 – 250 mg/L. At optimum condition, removal efficiencies of 85%, 99%, and 99% were obtained for Reactive Yellow 176 (RY 176), Reactive Blue 21 (RB 21), and Reactive Red 241 (RR 241), respectively. The adsorption process could be described by both Langmuir and Freundlich models. The maximum dye adsorption capacities for RY 176, RB 21, and RR 241 were 0.50 g/g, 0.72 g/g, and 0.95 g/g, respectively. It is concluded that EPS in wastewater sludge could be utilized as an effective adsorbent for dye removal, thereby enhancing the value of sludge in wastewater treatment.

Production of surface‐active sophorolipid biosurfactant and crude oil degradability by novel Rhodotorula mucilaginosa strain SKF2

AbstractBiosurfactants are produced by important types of microorganisms such as bacteria, yeast, and filamentous fungi and have been used in a variety of industries. Among the 15 crude oil‐degrading fungi, the two molds and one yeast were identified by 18S rDNA sequences as Mucor circinelloides strain SKMC, Fusarium fujikuroi strain DB2, and Rhodotorula mucilaginosa strain SKF2. These strains were isolated from crude oil–contaminated soil, diesel oil–contaminated soil, and activated sludge in the Oil Refinery Plant in Isfahan, Iran, respectively. The yeast strain was identified as a novel crude oil–degrading and biosurfactant‐producing fungi in the presence of (1% v/v) Iranian light crude oil in the minimal salt medium (MSM). The highest amount of the dry weight of produced biosurfactant was measured at 6.2 g L−1. Chemical nature of produced biosurfactant was determined as a surface‐active sophorolipid biosurfactant compound by thin‐layer chromatography, Fourier transform infra‐red spectroscopy, and gas chromatography–mass spectrometry (GC–MS) analysis. The residual hydrocarbons in the MSM were analyzed by GC–MS, and it was shown that octadecane and docosane were eliminated by this novel strain completely.

Reuse of water treatment plant sludge mixed with lateritic soil in geotechnical works

This work investigates the possibility of reusing water treatment sludge (WTS) at as-collected water content mixed with lateritic soil in geotechnical works to avoid waste disposal and reduce the exploitation of natural soils. Three mixtures with different proportions of soil to WTS (5:1, 4:1, 3:1) were prepared. Leaching and solubilization tests were conducted for environmental characterization of the WTS. Particle size distribution, consistency limits and specific gravity of solids of the soil and the three mixtures were determined for geotechnical characterization. Compaction, permeability and triaxial compression tests were carried out to investigate the geotechnical behaviour of the materials. The sludge was classified as non-hazardous and non-inert by Brazilian standards. The addition of sludge to the soil did not significantly change its granulometry but led to a reduction in the specific gravity of solids and an increase in the plasticity index. In the compaction tests, the maximum dry unit weight decreased, and the optimum moisture content increased with WTS addition. The hydraulic conductivity of the mixtures was between 10 and 100 times that of the soil. In triaxial compressive tests, there was an increase in strain and a reduction in strength during shear, as well as an increase in the friction angle (between 1º and 4º) and reduction in cohesion (between 9 kPa and 16 kPa). Despite causing changes in soil behaviour, the addition of sludge does not preclude the use of the resulting mixtures in geotechnical works, since the parameters remain as established in the literature and technical. However, a case-by-case analysis must be carried out before using the mixtures.

Study on potential of soil stabilization using concrete sludge of batching plant (CSBP)

More than 8 t of fresh concrete waste may be created and returned to the batching plants throughout Malaysia, where it will degrade into concrete sludge. Most batching plants will dump their concrete sludge on the ground or at a landfill which is not eco-friendly at all. Consequently, this study is to investigate the potential of concrete sludge of batching plant (CSBP) to be used as the stabilized material for organic soil which indirectly can help to recycle CSBP from end up at the landfill. The Atterberg limit test was conducted to identify the characteristic of soil used in this study. Four different percentages of CSBP were used which are 0, 5, 10 and 15%. Then, the standard Proctor test and California bearing ratio test were performed, and it shows that the CBR value remarkably increases from 4.8 to 20.7%, with the rise of CSBP percentages from 0 to 15%. The finding shows that CSBP can be used as the potential material to enhance the trend of strength value of CBR. Thus, using CSBP as a stabilized material for organic soil would alleviate the problem of overflowing landfills with concrete sludge and encourage a more sustainable approach in the construction industry.

Pharmaceutical residues in digested sewage sludge: Occurrence, seasonal variation and risk assessment for soil

The occurrences, temporal variations and ecotoxicological risks of 38 selected pharmaceuticals from 7 therapeutic classes (i.e. antibiotics, analgesics, anti-inflammatories, beta-blockers, lipid regulators, anticancer agents, and psychiatric drugs) have been observed in the anaerobically treated sludge of the urban wastewater treatment plant (WWTP) in Konya, Turkey. Sampling was carried out to assess the seasonal variations in one year. The total daily wastewater flow rate of the WWTP was approximately 200,000 m3/day, and 140 tons/day of treated sludge were produced. The total concentrations of all pharmaceutical compounds ranged from 280 to 4898 μg/kg of dry matter (dm). The dominant therapeutic class was analgesics and anti-inflammatories (49%), which was followed by antibiotics (31%). Clarithromycin and azithromycin were the most abundant compounds, with concentrations of 1496 μg/kg dm. The total daily pharmaceutical load in the treated sludge was as high as 1.002 kg/day in the winter season, while the annual pharmaceutical mass load that was discharged into the environment was estimated to be approximately 71.6 kg. The use of treated sludge as fertilizer in agricultural lands causes continuous contamination of the terrestrial environment by pharmaceuticals. Five antibiotics (i.e., azithromycin, clarithromycin, erythromycin, sulfamethoxazole, and doxycycline), one analgesic (acetylsalicylic acid) and one beta-blocker (atenolol) in the digested sludge pose acute and short chronic high risks to environment. The highest short chronic risk in the digested sludge-amended soils was determined for azithromycin (RQ: 54.9). To reduce the potential environmental impact of pharmaceuticals, digested sludge should be monitored in terms of the pharmaceutical contents before being applied to soil.

Microplastics degradation through hydrothermal liquefaction of wastewater treatment sludge

Wastewater treatment plant sludge contains large quantities of microplastics (MPs), which is a problematic substance that impedes sustainability efforts, such as in land management. MPs are resilient to degradation, but extreme conditions, such as high temperature and pressure, can lead to residues that can be used as fertilizers on farmlands. Hydrothermal liquefaction (HTL) creates such conditions, converting sludge into valuable bio-crude. To this end, the current study examined the resilience of MPs in sewage sludge that were treated by continuous HTL operated at supercritical water conditions (400 °C, 30 MPa). MPs were extracted before and after the HTL process and quantified by Fourier Transformation Infrared Spectroscopy (FTIR). Particles of 10–500 μm were quantified using Focal Plane Array (FPA) based micro-FTIR (FPA-μ-FTIR) imaging combined with an automated analysis of the generated spectral image, while Attenuated Total Reflection (ATR)-FTIR was used for MPs >500 μm. The continuous HTL led to an MP reduction of approximately 76% in terms of MP number and 97% in terms of MP mass. The difference in reduction of the number of MPs versus their accumulated mass was the result of MPs being smaller after the HTL process. A total of 18 polymer types were detected in the sludge and slurry entering the continuous HTL while only 11 types were identified in the residual materials. No MPs were detected in the bio-crude, i.e. the most favorable product of the process. The polymer composition changed considerably as a result of the HTL process. Polyurethane, polypropylene, and polyethylene were the dominant polymers in the feedstock, while polypropylene and polyethylene were the most present in the residual products. The findings indicate that HTL can be efficient in reducing MPs in highly polluted sludge from wastewater treatment plants, leaving the byproducts and residuals significantly less polluted, hereby reducing the movement of MPs to the terrestrial environment. Thus the products are better suited for sustainability efforts than the raw material.