Slaughterhouse Sludge Research Articles

Enhancing agricultural sustainability through optimization of the slaughterhouse sludge compost for elimination of parasites and coliforms

For a sustainable ecology, slaughterhouse sludge must be managed effectively in preview of the parasitic or coliforms’ spill over to the community. In order to determine the effectiveness of a customized biological decomposer solution in lowering the parasitic eggs and coliform bacteria, three composting units (Unit 1, Unit 2, and Unit 3) were treated with its different amounts. Over a period of 60 days, pH, temperature, humidity, number of the parasitic eggs per gram (EPG) of faecal material, viability of eggs, and coliform counts were evaluated. By the fifth day of the composting process, pH had significantly (P < 0.05) increased across all the treatments and then decreased gradually. Also on the 5th day, all three units entered the thermophilic range (> 45 °C), which persisted for 20 days for Unit 3 and 15 days for Units 1 and 2. Humidity levels initially increased significantly (P < 0.05) in all three units (Unit 3 = 71%, Unit 2 = 64%, and Unit 1 = 55%) but then gradually decreased. On day 5, no decrease in EPG in Unit 1 was detected; however, a non-significant (P > 0.05) 12.5% decline in EPG in Unit 2 and Unit 3 was recorded. After that, a significant (P < 0.05) reduction in EPG was observed in all the three treatments until day 25. By day 5, decreased egg viability was significantly (P < 0.05) recorded in Unit 3 (21.43%); in Unit 1 and Unit 2, the decrease was 6.25% and 14.29%, respectively. Additionally, all units showed a significant (P < 0.05) decrease in total coliforms, meeting minimum allowable limit in Unit 2 and 3 on day 10 and on day 15 in Unit 1. The most substantial reduction in faecal coliforms was observed in Unit 3 (from 2.6 log₁₀ to 1.3 log₁₀), followed by Unit 2 (from 2.6 log₁₀ to 1.5 log₁₀), and then Unit 1 (from 2.6 log₁₀ to 1.6 log₁₀). The results of this study support recommendation of advanced composting techniques to eradicate or reduce the abundance of pathogens (parasites and coliforms). Hence, we endorse the value of careful composting procedures in environment-friendly abattoir waste management and agricultural practices through creating pathogen-free, eco-friendly fertilizers to promote both agricultural and environmental sustainability.

Optimization of microwave intensified slaughterhouse sludge pretreatment method to enhance anaerobic digestion process by response surface methodology

Optimization of microwave intensified slaughterhouse sludge pretreatment method to enhance anaerobic digestion process by response surface methodology

Selection and agricultural use of potential phosphate-solubilizing bacteria isolated from poultry slaughterhouse sludge in maize

In the farming, increasing demands for higher yields has put pressure on land resources which eventually increased demand for phosphate fertilizers (non-renewable resource), given that low availability of phosphorus in many soils is often compensated by the application high doses phosphate fertilizers. Complementary, studies have been made with a view to select phosphate-solubilizing bacteria. The purpose of his study was to: (i) isolate and characterization potential phosphate-solubilizing bacteria from sludge from the wastewater treatment plant of a poultry slaughterhouse; (ii) evaluate the ability of bacteria to solubilize phosphate rock and promoting plant growth. The bacteria were isolated in culture medium containing calcium phosphate. Morphological characterization consisted in cell shape, Gram staining and the characteristics of the colonies. To assess natural phosphate (NPh) solubilization, maize seeds were inoculated together with Araxá phosphate. The experiment consisted of 10 treatments: eight bacterial isolates + NPh, NPh and a control. The experiment was carried out in a greenhouse for 45 days, in a randomized block design, with six replications. The variables measured were the growth characteristics of the maize. Eight strains were isolated, all stained gram-positive, and 90% were rod-shaped and 10% coccoid-shaped. Inoculation with isolate LSOF-7 (Sphinghomonas sp.) combined with NPh induced increased maize dry matter by 20% compared to the treatment containing only NPh and by 67% compared to the control. It was concluded that sludge from wastewater treatment plants of poultry slaughterhouses contains bacterial strains with potential to phosphate-solubilizing and them also probably present promoting plant growth and promote maize plant growth.

The conversion and migration behavior of phosphorus speciation during pyrolysis of different sludges

&lt;abstract&gt; &lt;p&gt;The study was enforced to probe the conversion and migration behavior of phosphorus speciation in sludge and the biochar received from pyrolysis of municipal sludge (MS), town sludge (TS), and slaughterhouse sludge (SS). This study creatively used fractionation of soil phosphorus to further differentiate speciation of phosphorus in three sludges (MS, TS, and SS). According to the x-ray diffraction (XRD) analysis and sequential extraction, the study proved the dependence of P speciation conversion on pyrolysis temperature and different types of raw sludge. The results of P-fractionation indicated that Ca-bound IP (Ca-IP) content in all biochars significantly increased at pyrolysis temperature of 350–800 ℃, and the proportion of soluble and loosely bound IP (SL-IP), aluminum-bound IP (Al-IP), and Fe-bound IP (Fe-IP) of MS and SS decreased. The difference is that the Al-IP in the TS increased slightly as the pyrolysis temperature increased. Among the three kinds of sludge, the Olsen-P of TS is the lowest because the content of Olsen-P in sludge will decrease with the decrease of pH in the process of sewage treatment after acidification. In addition, XRD patterns of three sludges and biochar further confirmed the low crystallinity of AlPO&lt;sub&gt;4&lt;/sub&gt; minerals. Through in-depth research on the environmental behavior of phosphorus, this study might additionally provide essential knowledge for the recovery and utilization of phosphorus in sludge.&lt;/p&gt; &lt;/abstract&gt;

Application of a Protein Hydrolysate-Based Biostimulant Obtained from Slaughterhouse Sludge on Pepper Crops

Currently, biostimulants obtained from protein hydrolysates are considered essential agronomic tools to promote sustainable agriculture without the use of chemical fertilizers. This study aimed to investigate the effectiveness of a biostimulant obtained from slaughterhouse sludge via enzymatic hydrolysis processes on green pepper crops in a greenhouse. The biostimulant was administered through both root and foliar applications at two different doses (0.7 and 1.4 g L−1), with a total of four applications made over the 140-day experimental period. Throughout the crop growth period, various parameters were assessed, including plant height, the number of flowers and fruits, macro- and micronutrient content, and photosynthetic pigments in the leaves. Additionally, the nutritional content and vitamin C levels in the harvested fruits were determined. The results obtained indicated higher values of these parameters in the pepper plants when the biostimulant was applied at a higher dose and through root application. These higher values are likely a consequence of the increased plant absorption of the low-molecular-weight amino acids and nutrients derived from the biostimulant.

Enhanced Biogas Production from Thermophilic Anaerobic Digestion of Poultry Slaughterhouse Sludge: Effect of Thermal Pretreatment and Micronutrients Supplementation

Enhanced Biogas Production from Thermophilic Anaerobic Digestion of Poultry Slaughterhouse Sludge: Effect of Thermal Pretreatment and Micronutrients Supplementation

A method to characterize precipitated minerals in organic waste and their transformation by anaerobic digestion: Focus on phosphorus

Unsustainable global phosphorus (P) management has led to the identification of digestate from anaerobic digestion (AD) as a potential source of P recovery. Understanding P interactions during AD is thus crucial for P recovery and modeling can help optimize recovery. Both understanding and modeling require accurate P fractionation into minerals that contain P, e.g., struvite, vivianite, amorphous calcium phosphate (ACP). The aim of this study was to develop a novel P fractionation method based on acidic leachate of P, Ca, Mg, Fe, K, and Al. Nine samples were acidified, three of which were digestate and six substrates used to feed a biogas unit. Acidification curves were obtained for each nutrient in each sample. Nutrient leachate was used to develop a fractionation algorithm based on P, allowing nutrient fractionation of all the samples. Dissolved nutrients during acidification were assumed to be issued from precipitated mineral origin. Precipitated P was found in all digestates, slaughterhouse sludge, and pig and cattle slurry and was originated from struvite, vivianite, and amorphous calcium phosphate (ACP) minerals. Struvite represents up to 70.6% of total P and ACP between 13.8% and 24.8% in digestates whereas vivianite was the main P precipitated form in slaughterhouse sludge (27.4%). Precipitated Mg were mainly found in samples where P was fractionated mainly as struvite. Precipitated Ca was fractionated into calcite and ACP while Fe was fractionated into vivianite and other ferrous minerals. No dissolved Al or K was found. Al was mainly fractioned as inert/organic, and K was mainly fractioned as soluble in all the samples. In conclusion, the acidification protocol and the fractionation algorithm developed in this study represent a useful, rapid and inexpensive P fractionation methodology for environmental samples during anaerobic digestion.

Impact of pH in the first-stage of a two-stage anaerobic digestion on metabolic pathways and methane production

The present study focuses on the use of cow manure, slaughterhouse sludge, cheese whey and green beans in a two-stage batch anaerobic process. The effect of pH regulation (4.5 to 7) on metabolic pathways and microbial community involved was studied in the first-stage of the process under mesophilic condition. At a pH lower than 5, fermentation occurred and led to an accumulation of lactic acid with a dominance of Lactobacillus. A pH >5.5 led to dark fermentation. Temporarily lactic acid production was converted in volatile fatty acids. Streptococcus and Enterococcus were involved in lactic conversion at pH 5.5 and 7, respectively. A weak hydrogen production was monitored at these pH ranges. Regardless of fatty acids produced in the first-stage, dark or lactic fermentation did not lead to higher methane production in the second-stage. However, dark fermentation increased methane concentration in biogas from 63.1 % in a single-stage to 83.6 %.

Use of a Biostimulant Obtained from Slaughterhouse Sludge in a Greenhouse Tomato Crop

Currently, the use of biostimulants is widespread in sustainable agriculture because they represent an alternative to chemical fertilizers. In this manuscript, we investigate the response of a greenhouse tomato crop grown in pots to a biostimulant obtained from slaughterhouse sludge applied continuously to the substrate under which the tomato crop was grown or applied directly via the foliar route. Two doses of biostimulant (0.7 and 1.4 g L−1), applied four times throughout the crop growth period (120 days), were used. During this period, the height of the plants, number of flowers and number of fruits obtained were measured. After 90 days of the growth period, the nutrient contents in leaves as well as the chlorophyll a and b contents were analyzed. For fruits, nutrient and lycopene contents were determined, and the equatorial diameter and average fresh and dry weight were measured. The results indicate a higher content of nutrients and chlorophyll a and b in the leaves of plants treated with the highest dose of biostimulant and applied continuously to the substrate. This higher content of photosynthesis pigments in the plant is possibly responsible for a greater absorption of N by the plant and, consequently, for better growth.

Briquette production from a mixture of biomass: poultry slaughterhouse sludge and sawdust.

This study refers to the development of hybrid briquettes using centrifuged sludge from the wastewater treatment of poultry and sawdust from furniture industry. The aim was to evaluate the performance of briquettes as a source of thermal energy, mitigating the risks of the current elimination and reducing the operational costs of their destination. To know the oxidizing characteristics of the briquettes and their mechanical resistance, superior calorific power, ash content, volatile materials, fixed carbon, and resistance to axial compression were evaluated. Thermogravimetric and differential exploratory calorimetry analyses were performed. Statistical treatments were carried out to verify the most significant factors to produce briquettes, the best proportions of the raw materials, and to evaluate whether there is interference from moisture and glue flour used as a binder. The best condition of the sludge-sawdust mixture was 15% and 85%, respectively, with 6.0% moisture. The best-case treatment had 23.82-MPa mechanical resistance, a calorific value of 17.20MJkg-1, and a density of 1374.15kgm-3.

Toxicity and physicochemical parameters of composts including distinct residues from agribusiness and slaughterhouse sludge.

Composting is useful for treatment of residues from agribusiness, but the potential toxicity of the final compost should be evaluated before its agricultural destination. The objective of this study was to evaluate the physicochemical characteristics and the toxicity of agribusiness residues using onion seeds as bioindicators. All tested treatments were composed by sludge from a swine slaughterhouse and sawdust. Besides the control, which included no additional materials, the other treatments included aviary bedding, rice husk and residue from tobacco industries as structuring materials. After 120days of composting, for all treatments, the temperature inside the composting piles approached the environmental temperature, the physicochemical parameters indicated that the composts were stabilized and, except for the treatment including tobacco residues, that could be used for agriculture without impairing plant germination. Although the treatments including tobacco residues and rice husk showed evidence of cytotoxicity and genotoxicity at the beginning of the composting period, that was not observed for the treatment including aviary bedding. Such potential toxicity was not observed at the end of composting for any of the tested treatments.

Use of Slaughterhouse Sludge in the Bioremediation of an Oxyfluorfen-Polluted Soil

The use of organic matter is a highly accepted environmental practice among scientists for the bioremediation of polluted soils. In this manuscript we study under laboratory conditions the bioremediation capacity of a new biostimulant obtained from slaughterhouse sludge in a soil polluted by the oxyfluorfen at a rate of 4 l ha−1 (manufacturer’s rate recommended) over a 90-day period. We determined its effects on dehydrogenase, urease, β-glucosidase and phosphatase activities, the soil microbial community structure and the evolution of the herbicide in soil. Possibly due to the high content of low molecular weight proteins in the biostimulant, the enzymatic activities were stimulated mainly at the beginning of the experiment. Soil biological parameters were inhibited in oxyfluorfen-polluted soil. At the end of the experiment and compared with the control soil, dehydrogenase, urease, β-glucosidase, and phosphatase activities significantly decreased by 47.8%, 50.5%, 36.4%, and 45.5% in the oxyfluorfen-polluted soil. At 5 days into the experiment, the use of the biostimulant in oxyfluorfen-polluted soils decreased soil enzymatic activities and microbial community inhibition. At the end of the incubation period the oxyfluorfen concentration had decreased by 60% in the polluted soil and amended with biostimulants. These results suggested that the use of this biostimulant with higher amounts of low molecular weight proteins and peptides had a positive effect on the remediating oxyfluorfen-polluted soils. Therefore, this study provides the use of a new biostimulant obtained from slaughterhouse sludge by enzymatic hydrolysis processes used in the bioremediation of a soil polluted by the oxyfluorfen herbicide.

Full-Scale Composting of Different Mixtures with Meal from Dead Pigs: Process Monitoring, Compost Quality and Toxicity.

Abundant by-products of large swine industries, such as slaughterhouse sludge and carcasses, require adequate treatment to prevent negative effects of their direct disposal in the open environment. This study is aimed to evaluate the efficiency of composting using meal from dead pigs through physicochemical analyses and phytotoxic assays. Five treatments were tested, all including 50% sawdust: T1, with 50% slaughterhouse sludge (control); T2, with 20% slaughterhouse sludge and 30% meal from dead pigs; T3, with 10% slaughterhouse sludge and 40% meal from dead pigs; T4, with 20% organic stabilizing compost and 30% meal from dead pigs and T5, with 30% organic stabilizing compost and 20% meal from dead pigs. The phytotoxicity assays used lettuce, cucumber, celia, soybean, rice and wheat as bioindicators. Inclusion of meal from dead pigs was related to reduction in pH, C/N ratio, humidity and temperatures inside the pile, although thermophilic peaks lasted longer than 50 days and the final composts showed high content of nitrogen and phosphorous. The germination of bioindicators was reduced in all tested treatments, compared to the control. The composts from treatments that included meal from dead pigs presented acceptable nutrient content, which may indicate their use as organic fertilizers. However, after 4 months, all bioindicators in contact with such composts presented impaired germination.Graphic Supplementary InformationThe online version contains supplementary material available at 10.1007/s12649-021-01422-0.

Valorization of poultry slaughterhouse sludge oil: a strategy to reduce Brazil’s dependency on soybean oil in the biodiesel industry

ABSTRACT During the poultry industrialization process the so-called sludge oil, a residual chicken fat, is recovered in the wastewater treatment plant and its use presents potential as raw material for biodiesel production. Thus, the aim of the study was to prepare blends of sludge oil with soybean oil to obtain fatty acid methyl esters (FAME) through the homogeneous alkaline transesterification reaction. To perform this study, a simple pre-treatment process – heating and subsequent filtration – was used, allowing sludge oil to be mixed with soybean oil to compose blends, without the need to use more sophisticated pre-treatment processes. After this step, blends ranging from 5% to 90% (m/m) of sludge oil mixed with soybean oil were prepared. The results showed that the molar ratio (1:6 oil blend:methanol), catalyst concentration 0.5% NaOH (mcat/moil), at 65 °C for 60 min yielded FAME above 99.0 and 90.0% (m/m) for blends with up to 5 and 15% sludge oil, respectively. By increasing the temperature to 70 °C, under the same selected parameters, the blend with 10% sludge oil provided yield above 99.0% (m/m), presenting appropriate physicochemical properties, within the parameters required by National Agency of Petroleum, Natural Gas and Biofuels (ANP). These findings show the great potential sludge oil provides to reduce Brazil’s dependency on soybean oil for biodiesel production. Highlights Sludge oil, a waste raw material for biodiesel production, is not yet explored in Brazil. A procedure for biodiesel production using soybean oil and sludge oil blends was proposed. The best reaction condition was 1:6 oil blend:MeOH molar ratio; 0.5% NaOH (mcat/moil), at 70 °C for 60 min. Biodiesel yield was higher than 99% (m/m) under optimal reaction conditions. Sludge oil represents a promising waste raw material for biodiesel production.

Biodiesel Production by Acid Methanolysis of Slaughterhouse Sludge Cake.

Simple SummaryExcessive sludge in the wastewater treatment basins has to be removed periodically to ensure good water quality of the effluent. This study aims to evaluate the feasibility of biodiesel production by acid methanolysis of slaughterhouse sludge cake. Experimental and analytical results showed that acid methanolysis of sludge cake was one of the feasible and practical options to recycle sludge waste and produce renewable energy.Biosludge is a normal form of accumulating microbial populations inside the sewage or wastewater treatment facilities. Excessive sludge in the wastewater treatment basins has to be removed periodically to ensure good water quality of the effluent. This study aims to evaluate the feasibility of biodiesel production by transesterification of slaughterhouse sludge cake. The sludge cake was collected from a selected commercial slaughterhouse and transesterified with methanol, n-hexane, and acids (e.g., sulfuric acid or hydrochloric acid) at 55 °C. Three acid concentrations (2%, 4%, and 8%, v/v) in methanol under four reaction time periods (4, 8, 16, and 24 h) were applied. Results showed that the highest accumulated fatty acid methyl ester (FAME) yields of 2.51 ± 0.08% and 2.27 ± 0.09% were achieved when 8% (v/v) of H2SO4 or HCl were added in a 4 h reaction time, respectively. Methyl esters of palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), and oleic acid (C18:1n9c) were the major components of biodiesel from acid methanolysis of slaughterhouse sludge cake. Experimental and analytical results of acid methanolysis of slaughterhouse sludge cake showed that acid methanolysis of sludge cake was one of the feasible and practical options to recycle sludge waste and produce renewable energy.

Co-digestion of tannery waste activated sludge with slaughterhouse sludge to improve organic biodegradability and biomethane generation

A novel approach was used to overcome inhibition of anaerobic digestion of tannery waste activated sludge by co-digesting with slaughterhouse sludge. The seasonal characteristics of the tannery sludge varied significantly. Macronutrient ratios were typically not ideal for anaerobic digestion, mainly due to an over-abundance of nitrogen. In addition, potentially inhibitory concentrations of metals were present. Optimal co-digestion with 50% (vol./vol.) slaughterhouse sludge achieved a CH4 yield of 215mLCH4/gVS, and biodegradability of 55.7% VS, 45.5% TS and 48.2% COD. This resulted in a synergistic increase of ≥59.4% in biodegradability and 156% in CH4 yield compared to mono-digestion of tannery waste activated sludge. Furthermore, the regression of the cumulative CH4 yield using the Logistic, Cone and modified Gompertz model (adj R2≥0.998) showed an increase of 20.4–21.9%, 58.6–252%, and 164% in the ultimate CH4 yield, maximum CH4 production rate and the specific rate constant respectively, and 59.3% reduction of the lag phase. An alternative cleaner production technique that vertically integrates the value chain improves solid waste management and provides an income stream was demonstrated through this co-digestion strategy.

Biogas Production by Anaerobic Co-Digestion of Dairy Wastewater with the Crude Glycerol from Slaughterhouse Sludge Cake Transesterification.

Simple SummaryIn our previous study, slaughterhouse sludge cake was trans-esterified to produce biofuel and some organic waste, i.e., crude glycerol. The crude glycerol was evaluated for feasibility of using crude glycerol as the feedstock to produce biofuel by anaerobic co-digestion with dairy cattle wastewater. Addition of crude glycerol significantly increased production efficiency of biogas but decreased the removal efficiency of total solids and volatile solids with increased crude glycerol volume. The results showed that the slaughterhouse sludge cake is a feasible feedstock for producing biodiesel and the waste, crude glycerol, can promote biogas production.Excessive sludge in the wastewater treatment basins has to be removed periodically and collected as the form of sludge cake for promising good water quality of the effluent. This study aims to evaluate the feasibility of biogas production by anaerobic co-digestion of dairy cattle wastewater and crude glycerol from transesterification of sludge cake. Different ratios of crude glycerol, i.e., 2, 4, and 8% (v/v), from the previous experiment were mixed with dairy cattle wastewater and inoculated with anaerobic sludge in cap-sealed 1-L serum bottles as anaerobic digesters. Although the 8% crude glycerol set showed the highest total biogas and methane production, low pH from volatile fatty acid accumulation decreased the removal efficiency of chemical oxygen demand, biochemical oxygen demand, and suspended solids after a 14-d incubation period. The experimental sets with 2 and 4% of crude glycerol increased total methane production up to 177 and 226% compared to the control set, respectively. We found that addition of crude glycerol decreased removal efficiency of total solids and volatile solids. In our study, we proved that slaughterhouse sludge cake is a feasible feedstock for producing biogas through transesterification and anaerobic co-digestion.

Fate of pharmaceuticals and antibiotic resistance genes in a full-scale on-farm livestock waste treatment plant.

This study investigated, for the first time, the distribution and fate of 28 multiple-class veterinary pharmaceuticals and antibiotics (PhACs), and their corresponding antibiotic resistance genes (ARGs), in a full-scale on-farm livestock waste treatment plant. The plant relies on several technologies, including: anaerobic digestion (AD), solid-liquid separation, and two stages reverse osmosis (RO) of the liquid digestate. Tetracycline, fluoroquinolone, lincosamide and pleuromutilin antibiotics, together with anti-helmintic (flubendazole) and anti-inflammatory (flunixin) drugs were the most frequently detected compounds in livestock waste and in slaughterhouse sludge. This last fraction is used as co-substrate in the AD process and showed to be an important input source of PhACs and ARGs. In terms of treatment performance, AD exhibited moderate to low PhACs and ARGs reduction, while a large fraction (<50%) of the PhACs present in the digestate were distributed onto the solid fraction, after solid-liquid separation. Both solid and liquid digestates had relatively high copy numbers of ARGs. Finally, RO showed high rejection percentages for all PhACs (<90%), with concentrations in the low ng L-1 range in permeates, for most target PhACs. Nevertheless, moderate copy numbers of ARGs were detected in permeates.

Biodiesel microemulsion upgrading and thermogravimetric study of bio-oil produced by liquefaction of different sludges

Different sludges such as municipal sewage sludge, paper/pulp mill sludge, and slaughterhouse sludge were collected and characterized for energy production. Bio-oils were produced from these sludges by supercritical liquefaction at 300 °C with methanol as the solvent. Carbon-rich and viscous bio-oils with yields about 20–30% were obtained. With methyl esters as the dominant component, these bio-oils were upgraded by blending or microemulsifying with biodiesel (fatty acid methyl esters). The optimum microemulsions were formed at biodiesel/bio-oil ratio of 10, with bio-oil content of more than 8% (which doubled that obtained by blending) and surfactant effectiveness of 0.5–0.6 g rhamnolipid/g bio-oil being obtained. The thermogravimetric studies show that the blending and microemulsifying processes led to the shift of decomposition range and rate to higher levels and the reduction of activation energy of the hybrid fuel systems. There may be synergies of enhancing the combustion or ignition of microemulsions when biodiesel and bio-oil were used in combination in diesel engines, overcoming the disadvantages of using either biodiesel (e.g., long ignition delay, etc.) or bio-oil (e.g., long ignition delay and viscosity, etc.) individually. Microemulsification may be a promising bio-oil upgrading technology.

Energy Recovery Efficiency of Poultry Slaughterhouse Sludge Cake by Hydrothermal Carbonization

Hydrothermal carbonization (HTC) is a promising technology used for bioenergy conversion from bio-wastes such as sewage sludge, livestock manure, and food waste. To determine the optimum HTC reaction temperature in maximizing the gross energy recovery efficiency of poultry slaughterhouse sludge cake, a pilot-scale HTC reactor was designed and operated under reaction temperatures of 170, 180, 190, 200 and 22 °C. During the HTC reaction, the gross energy recovery efficiency was determined based on the calorific value of the HTC-biochar and ultimate methane potential of the HTC-hydrolysate. The poultry slaughterhouse sludge cake was assessed as a useful source for the bioenergy conversion with a high calorific value of approximately 27.7 MJ/kg. The calorific values of the HTC-biochar increased from 29.6 MJ/kg to 31.3 MJ/kg in accordance with the change in the reaction temperature from 170 °C to 220 °C. The ultimate methane potential of the HTC-hydrolysate was 0.222, 0.242, 0.237, 0.228 and 0.197 Nm3/kg-CODadded for the reaction temperatures of 170, 180, 190, 200 and 220 °C, respectively. The potential energy of feedstock was 4.541 MJ/kg. The total gross energy recovery (GERtotal) was 4318 MJ/kg, of which the maximum value in the HTC reaction temperature was attained at 180 °C. Thus, the optimum temperature of the HTC reaction was 180 °C with a maximum GERtotal efficiency of 95.1%.