Slaughterhouse Sludge Research Articles

Composted slaughterhouse sludge as a substitute for chemical fertilizers in the cultures of lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.)

Flotation sludge (FS) is produced in huge amounts at slaughterhouses in western Santa Catarina, Brazil. This waste is rich in plant nutrients and a valuable resource for soil amendments. Five FS composts were tested as a replacement for chemical fertilizers (QF), namely T1 (75% poultry manure (PM) and 25% sawdust (SD)); T2 (50% PM and 50% SD); T3 (25% PM and 75% SD); T4 (100% PM and 0% SD); and T5 (0% PM x 100% SD). For lettuce plants, treatments containing composted FS resulted in an increased number of leaves, leaf area and leaf fresh weight (LFW). T1 presented the best results with increases of 1.4 fold in LFW compared to plants supplemented with QF. T2 was the most effective treatment for radish with the best results of root fresh weight and root diameter. Although T4 had the highest nitrogen content, it did not present the best results in growth performance for lettuce or radish. The presence of higher proportions of SD in composts (25% for lettuce and 50% for radish) improved the physical characteristics of the soil and proved to be a more balanced compost.

Strategies for enhancement of bio-hydrogen production using mixed cultures from starch effluent as substrate

ABSTRACTThe present study focused on the enhancement of hydrogen yield by using mixed culture (sewage sludge and/or slaughterhouse sludge) from starch effluent. The process parameters such as pH, temperature and substrate concentration were studied. The maximum hydrogen yield of 5.5 mol/kg chemical oxygen demand (COD) was obtained in the initial optimization study in the dark fermentation at pH, temperature and substrate concentration of 6.5, 55 °C and 15 g/L, respectively. To enhance the hydrogen production the two different strategies were applied at optimum conditions such as (i) a combination of two mixed cultures (anaerobic sewage sludge and slaughterhouse sludge), and (ii) addition of crude amylase to the hydrogen production reactor while using anaerobic mixed sludge as inoculum and starch effluent as substrate. These two strategies gave the maximum hydrogen yield of 8.1 and 7.1 mol/kg COD, respectively.

Obtención y caracterización de carbón activado obtenido de lodos de plantas de tratamiento de agua residual de una industria avícola

The adsorption capacity of activated carbons, obtained from poultry slaughterhouse sludge was evaluated. The precursor was activated with H3PO4 10, 20, 30 and 35% in a 1: 1 ratio and pyrolyzed at 450°C for 2 h in N2 atmosphere at a flow of 50 mL/min, obtaining the C10, C20, C30 and C35 carbons. The DARCOG60 was used as referential activated carbon. The adsorptive capacity of activated carbons obtained was evaluated, using the technique of methylene blue index (AM). The best adsorbent was characterized in terms of moisture content, ash content, bulk density and pH. Elemental composition (CHNO), infrared spectrophotometry FTIR and SEM scanning electron microscopy was determined. The C35 got higher dye adsorption (88.44% removal and 43.48mg AM /g of C35). The DARG60 presented a 86.43% removal of AM. The carbon content in coal obtained poultry increase over the precursor slurry. The hydrogen content decreased significantly (sludge > carbon). The SEM photomicrographs, showed the appearance of a porous outer structure unlike the precursor carbon. FTIR reported the occurrence of several asymmetric carbon bands corresponding to different functional groups on their surfaces, evidencing an aromatic structure besides OH groups.

The comparison of the migration and transformation behavior of heavy metals during pyrolysis and liquefaction of municipal sewage sludge, paper mill sludge, and slaughterhouse sludge

Municipal sewage sludge, paper mill sludge, and slaughterhouse sludge were pyrolyzed and liquefied for the production of bio-char. The migration and transformation behavior of Cu, Cr, and Zn during pyrolysis and liquefaction of these sludges were studied. Pyrolysis and liquefaction promoted mobile fraction (F1 and F2) to stable fraction (F3 and F4). The results showed that pyrolysis and liquefaction largely affected the redistribution of Cu and Zn in raw materials. The environmental risk assessment results indicated that the environmental risk levels of Cu and Zn were significantly reduced in bio-char, and risk level of Cr was slightly decreased after pyrolysis or liquefaction. Both pyrolysis and liquefaction were promising detoxification technologies for the three sludges in terms of the mitigation of heavy metals toxicity. It was suggested that dewatered sludge could be reduced toxicity/risk before utilization by pyrolysis or liquefaction technology, especially for Cu and Zn in slaughterhouse sludge.

Correlation of chemical composition and odor concentration for emissions from pig slaughterhouse sludge composting and storage

The objective of this study was to correlate the chemical composition and the odor concentration of emissions produced during storage and composting of pig slaughterhouse sludge (PSS). Seven experimental conditions were monitored using composting reactors with forced aeration and cells designed to simulate storage. Sixty-six gas samples were collected and characterized by both GC–MS and olfactometry. Two types of correlation were investigated between the chemical composition and the odor concentration (OC) of every gas sample. The odor activity value for a given emitted compound (OAV) was computed as the ratio of its chemical concentration to its odor detection threshold (ODT). The correlation OAVMAX considered that the OC of a gas sample was equal to its highest OAV whereas the correlation OAVSUM considered that the odor of the gas sample was equal to the sum of the OAV of every compound contained in the gas sample. As per Standard EN 13725, both OAVMAX and OAVSUM were compared using a confidence level for OC defined as [OC/1.65 to 1.65×OC]. Whereas OAVMAX values were within the confidence level of OC for 62% of the 66 gas samples, OAVSUM values were within this confidence level for only 53%. Validating OAVMAX as a satisfying correlation between chemical composition and OC, only three compounds among the 66 identified namely trimethylamine, hydrogen sulfide and methanethiol, accounted for the prediction of OC measured during composting and storage of PSS.

Sewage sludge, compost and other representative organic wastes as agricultural soil amendments: Benefits versus limiting factors

Nine different samples of sewage sludges, composts and other representative organic wastes, with potential interest to be used as agricultural soil amendments, were characterized: municipal sewage sludge (SS1 and SS2), agro industrial sludge (AIS), municipal slaughterhouse sludge (MSS), mixed municipal solid waste compost (MMSWC), agricultural wastes compost (AWC), compost produced from agricultural wastes and sewage sludge (AWSSC), pig slurry digestate (PSD) and paper mill wastes (PMW). The characterization was made considering their: (i) physicochemical parameters, (ii) total and bioavailable heavy metals (Cd, Cr, Cu, Ni, Pb, Zn and Hg), (iii) organic contaminants, (iv) pathogenic microorganisms and (v) stability and phytotoxicity indicators. All the sludges, municipal or other, comply with the requirements of the legislation regarding the possibility of their application to agricultural soil (with the exception of SS2, due to its pathogenic microorganisms content), with a content of organic matter and nutrients that make them interesting to be applied to soil. The composts presented, in general, some constraints regarding their application to soil, and their impairment was due to the existence of heavy metal concentrations exceeding the proposed limit of the draft European legislation. As a consequence, with the exception of AWSSC, most compost samples were not able to meet these quality criteria, which are more conservative for compost than for sewage sludge. From the results, the composting of sewage sludge is recommended as a way to turn a less stabilized waste into a material that is no longer classified as a waste and, judging by the results of this work, with lower heavy metal content than the other composted materials, and without sanitation problems.

Anaerobic digestibility of beef hooves with swine manure or slaughterhouse sludge

Anaerobic digestion is an effective method for treating animal by-products, generating at the same time green energy as methane (CH4). However, the methods and mechanisms involved in anaerobic digestion of α-keratin wastes like hair, nails, horns and hooves are still not clear. In this study we investigated the feasibility of anaerobically co-digesting ground beef hooves in the presence of swine manure or slaughterhouse sludge at 25°C using eight 42-L Plexiglas lab-scale digesters. Our results showed addition of beef hooves statistically significantly increased the rate of CH4 production with swine manure, but only increased it slightly with slaughterhouse sludge. After 90-day digestion, 73% of beef hoof material added to the swine manure-inoculated digesters had been converted into CH4, which was significantly higher than the 45% level achieved in the slaughterhouse sludge inoculated digesters. BODIPY-Fluorescent casein staining detected proteolytic bacteria in all digesters with and without added beef hooves, and their relative abundances corresponded to the rate of methanogenesis of the digesters with the different inocula. Fluorescence in situ hybridization in combination with BODIPY-Fluorescent casein staining identified most proteolytic bacteria as members of genus Alkaliphilus in the subfamily Clostridiaceae 2 of family Clostridiaceae. They thus appear to be the bacteria mainly responsible for digestion of beef hooves.

Odorous gaseous emissions as influence by process condition for the forced aeration composting of pig slaughterhouse sludge

Compost sustainability requires a better control of its gaseous emissions responsible for several impacts including odours. Indeed, composting odours have stopped the operation of many platforms and prevented the installation of others. Accordingly, present technologies collecting and treating gases emitted from composting are not satisfactory and alternative solutions must be found. Thus, the aim of this paper was to study the influence of composting process conditions on gaseous emissions. Pig slaughterhouse sludge mixed with wood chips was composted under forcedaerationin 300L laboratory reactors. The process conditions studied were: aeration rate of 1.68, 4.03, 6.22, 9.80 and 13.44L/h/kg of wet sludge; incorporation ratio of 0.55, 0.83 and 1.1 (kg of wet wood chips/kg of wet sludge), and; bulking agent particles size of <10, 10<20 and 20<30mm. Out-going gases were sampled every 2days and their composition was analysed using gas chromatography coupled with mass spectrometry (GC–MS). Fifty-nine compounds were identified and quantified. Dividing the cumulated mass production over 30days of composting, by odour threshold, 9 compounds were identified as main potential odour contributors: hydrogen sulphide, trimethylamine, ammonia, 2-pentanone, 1-propanol-2-methyl, dimethyl sulphide, dimethyl disulphide, dimethyl trisulphide and acetophenone. Five gaseous compounds were correlated with both aeration rate and bulking agent to waste ratio: hydrogen sulphide, trimethylamine, ammonia, 2-pentanone and 1-propanol-2-methyl. However, dropping the aeration rate and increasing the bulking agent to waste ratio reduced gaseous odour emissions by a factor of 5–10, when the required threshold dilution factor ranged from 105 to 106, to avoid nuisance at peak emission rates. Process influence on emissions of dimethyl sulphide, dimethyl disulphide, dimethyl trisulphide were poorly correlated with both aeration rate and bulking agent to waste ratio as a reaction with hydrogen sulphide was suspected. Acetophenone emissions originated from the wood chips. Olfactory measurements need to be correlated to gaseous emissions for a more accurate odour emission evaluation.

Effect of system optimizing conditions on biohydrogen production from herbal wastewater by slaughterhouse sludge

The study evaluates the biohydrogen production from herbal wastewater as the substrate by the enriched mixed slaughterhouse sludge as the seed source. In the following experiments, batch-fermentations are carried out with the optimum substrate concentrations, fermentation pH and fermentation temperature to observe the effects of H2 production, hydrogen yield and other fermentation end products at different conditions. The hydrogen production is increased as substrate concentration increased up to 8 g COD/L WW, but drastically decreased at 10 g COD/L WW. When the pH of fermentation is controlled to 6.5, a maximum amount of hydrogen yield could be obtained. The hydrogen production is maximum at 50 °C (930 ± 30 mL/L WW) compared to 30 °C (436 ± 16 mL/L WW). Acid-forming pathway with butyric acid as a major metabolite dominated the metabolic flow during the hydrogen production. The experimental results indicated that effective hydrogen production from the herbal wastewater could be obtained by thermophilic acidogenesis at proper operational conditions.

Process Conditions Influence on Pig Slaughter House Compost Quality Under Forced Aeration

The objective of this paper was to study the influence of process conditions (aeration rate, bulking agent (BA) particle size distribution, BA incorporation ratio and process duration) on the quality (moisture, stability, disinfection as per the temperature regime and nitrogen conservation) of mechanically aerated pig slaughterhouse sludge (PSS) compost. The waste and wood chips as BA were composted in 300 L mechanically aerated reactors. The range of process conditions tested were: aeration rate from 1.68 to 13.04 L/h/kg of wet sludge; BA particle size distribution of <10 mm, 10–20 mm and 20–30 mm, and; BA:PSS incorporation ratio of 0.55–1.11 (kg of wet wood chips/kg of wet sludge). The results showed that a high aeration rate and a high BA:PSS ratio produced a faster stabilization whereas BA of small particles size distribution increased the amount of biodegradable matter and slowed down stabilization. The composting temperature regime was positively correlated to O2 consumption with a high BA:PSS ratio and a small BA particles size. A low aeration rate, without being O2 limiting, optimized the composting process since too high or too low an aeration rate favored heat losses through respectively convection and water evaporation. Water loss was positively correlated with temperature regime and a higher BA:PSS ratio as opposed to a small BA particle size distribution. Similarly, medium to high aeration rates favored water removal. The composting process duration was reduced with a high aeration rates of 6.22 or 9.8 L/h/kg of wet sludge and a high BA:PSS ratio of 1.11. Finally, process condition had no influence on compost nitrogen conservation.

Effect of low temperature thermal pre-treatment on the solubilization of organic matter, pathogen inactivation and mesophilic anaerobic digestion of poultry sludge

Treatment of poultry industry effluents produces wastewater sludge with high levels of organic compounds and pathogenic microorganisms. In this research, the thermal pre-treatment of poultry slaughterhouse sludge (PSS) was evaluated for low temperatures in combination with different exposure times as a pre-hydrolysis strategy to improve the anaerobic digestion process. Organic compounds solubilization and inactivation of pathogenic microorganisms were evaluated after treatment at 70, 80 or 90°C for 30, 60 or 90 min. The results showed that 90°C and 90 min were the most efficient conditions for solubilization of the organic compounds (10%). In addition, the bacteria populations and the more resistant structures, such as helminth eggs (HE), were completely inactivated. Finally, the thermal pre-treatment applied to the sludge increased methane yield by 52% and reduced hydraulic retention time (HRT) by 52%.

Identity and diversity of archaeal communities during anaerobic co-digestion of chicken feathers and other animal wastes

Digestion of raw feathers in anaerobic digesters inoculated with adapted swine manure, slaughterhouse sludge or dairy manure was investigated using twelve 42-L anaerobic digesters at 25°C. After 120days 74%, 49% and 40% added feathers were converted to methane in swine manure, dairy manure and slaughterhouse sludge anaerobic digesters respectively. 16S rRNA gene clone library analyses identified twenty-one operational taxonomic units containing clone sequences from 5 genera, 5 families and 2 phyla of members of the Archaea from 158 sequenced clones. Fluorescence insitu hybridization revealed that methanogens from the Methanomicrobiales, Methanosarcinales and Methanobacteriales constituted a major fraction (>78%) of these Archaea. A high correlation was seen between the distribution of functional archaeal groups and the NH3–N levels of digester mixed liquors. The compositions of archaeal communities fed different substrates were statistically significantly different (P<0.05).

Anaerobic digestion of chicken feather with swine manure or slaughterhouse sludge for biogas production

Biogas production from anaerobic digestion of chicken feathers with swine manure or slaughterhouse sludge was assessed in two separate experiments. Ground feathers without any pre-treatment were added to 42-L digesters inoculated with swine manure or slaughterhouse sludge, representing 37% and 23% of total solids, respectively and incubated at 25°C in batch mode. Compared to the control without feather addition, total CH4 production increased by 130% (P<0.001) and 110% (P=0.09) in the swine manure and the slaughterhouse sludge digesters, respectively. Mixed liquor NH4N concentration increased (P<0.001) from 4.8 and 3.1g/L at the beginning of the digestion to 6.9 and 3.5g/L at the end of digestion in the swine manure and the slaughterhouse sludge digesters, respectively. The fraction of proteolytic microorganisms increased (P<0.001) during the digestion from 12.5% to 14.5% and 11.3% to 13.0% in the swine manure and the slaughterhouse sludge digesters with feather addition, respectively, but decreased in the controls. These results are reflective of feather digestion. Feather addition did not affect CH4 yields of the swine manure digesters (P=0.082) and the slaughterhouse sludge digesters (P=0.21), indicating that feathers can be digested together with swine manure or slaughterhouse sludge without negatively affecting the digestion of swine manure and slaughterhouse sludge.

Biohydrogen production from dual digestion pretreatment of poultry slaughterhouse sludge by anaerobic self-fermentation

Poultry slaughterhouse sludge from chicken processing wastewater treatment plant was tested for their suitability as a substrate and inoculum source for fermentation hydrogen production. Dual digestion of poultry slaughterhouse sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-seeds. The sludge (5% TS) was dual digested by aerobic thermophilic digestion at 55 °C with the varying retention time before using as substrate in anaerobic self-fermentation. The best digestion time for enriching hydrogen-producing seeds was 48 h as it completely repressed methanogenic activity and gave the maximum hydrogen yield of 136.9 mL H 2/g TS with a hydrogen production rate of 2.56 mL H 2/L/h. The hydrogen production of treated sludge at 48 h (136.9 mL H 2/g TS) was 15 times higher than that of the raw sludge (8.83 mL H 2/g TS). With this fermentation process, tCOD value in the activated sludge could be reduced up to 30%.

Comparison of five organic wastes regarding their behaviour during composting: Part 1, biodegradability, stabilization kinetics and temperature rise

This paper aims to compare household waste, separated pig solids, food waste, pig slaughterhouse sludge and green algae regarding their biodegradability, their stabilization kinetics and their temperature rise during composting. Three experiments in lab-scale pilots (300 L) were performed for each waste, each one under a constant aeration rate. The aeration rates applied were comprised between 100 and 1100 L/h. The biodegradability of waste was expressed as function of dry matter, organic matter, total carbon and chemical oxygen demand removed, on one hand, and of total oxygen consumption and carbon dioxide production on the other. These different variables were found closely correlated. Time required for stabilization of each waste was determined too. A method to calculate the duration of stabilization in case of limiting oxygen supply was proposed. Carbon and chemical oxygen demand mass balances were established and gaseous emissions as carbon dioxide and methane were given. Finally, the temperature rise was shown to be proportional to the total mass of material biodegraded during composting.

Comparison of five organic wastes regarding their behaviour during composting: Part 2, nitrogen dynamic

This paper aimed to compare household waste, separated pig solids, food waste, pig slaughterhouse sludge and green algae regarding processes ruling nitrogen dynamic during composting. For each waste, three composting simulations were performed in parallel in three similar reactors (300 L), each one under a constant aeration rate. The aeration flows applied were comprised between 100 and 1100 L/h. The initial waste and the compost were characterized through the measurements of their contents in dry matter, total carbon, Kjeldahl and total ammoniacal nitrogen, nitrite and nitrate. Kjeldahl and total ammoniacal nitrogen and nitrite and nitrate were measured in leachates and in condensates too. Ammonia and nitrous oxide emissions were monitored in continue. The cumulated emissions in ammonia and in nitrous oxide were given for each waste and at each aeration rate. The paper focused on process of ammonification and on transformations and transfer of total ammoniacal nitrogen. The parameters of nitrous oxide emissions were not investigated. The removal rate of total Kjeldahl nitrogen was shown being closely tied to the ammonification rate. Ammonification was modelled thanks to the calculation of the ratio of biodegradable carbon to organic nitrogen content of the biodegradable fraction. The wastes were shown to differ significantly regarding their ammonification ability. Nitrogen balances were calculated by subtracting nitrogen losses from nitrogen removed from material. Defaults in nitrogen balances were assumed to correspond to conversion of nitrate even nitrite into molecular nitrogen and then to the previous conversion by nitrification of total ammoniacal nitrogen. The pool of total ammoniacal nitrogen, i.e. total ammoniacal nitrogen initially contained in waste plus total ammoniacal nitrogen released by ammonification, was calculated for each experiment. Then, this pool was used as the referring amount in the calculation of the rates of accumulation, stripping and nitrification of total ammoniacal nitrogen. Separated pig solids were characterised by a high ability to accumulate total ammoniacal nitrogen. Whatever the waste, the striping rate depended mostly on the aeration rate and on the pool concentration in biofilm. The nitrification rate was observed as all the higher as the concentration in total ammoniacal nitrogen in the initial waste was low. Thus, household waste and green algae exhibited the highest nitrification rates. This result could mean that in case of low concentrations in total ammoniacal nitrogen, a nitrifying biomass was already developed and that this biomass consumed it. In contrast, in case of high concentrations, this could traduce some difficulties for nitrifying microorganisms to develop.

Hepatitis E virus genotype 3 and sporadically also genotype 1 circulate in the population of Catalonia, Spain

Autochthonous hepatitis E virus (HEV) strains have been described infecting populations of industrialized countries, previously considered as non-endemic areas. The HEV strains circulating in one of those areas in south-western Europe (Barcelona, Spain) have been studied by analysing amplicons obtained from HEV genomes identified in wastewater, biosolids and sludge. Six sewage and two biosolid HEV positive samples from urban wastewater treatment plants and two positive HEV sludge samples with animal contamination were analysed by cloning and sequencing of 10-12 clones per sample. The results proved the presence of HEV strains belonging to genotype 3 and also sporadically to genotype 1 in urban sewage and biosolids, showing the simultaneous circulation of diverse HEV strains in the human population of the studied area. Only HEV genotype 3 was identified in slaughterhouse sludge samples. The circulation of genotype 1 in industrialized areas may have further health implications since this genotype has been associated with important epidemics in developing areas. Contamination of food and water through their contact with sewage not properly treated and biosolids presenting HEV may represent a significant risk for human populations in relation to HEV even in industrialized areas.

Evaluation of Bovine Spongiform Encephalopathy (BSE) Infection Risk of Cattle via Sewage Sludge from Wastewater Treatment Facilities in Slaughterhouses in Japan

Scattered SRM residues from BSE-infected cattle are possible to contaminate sewage during the slaughtering process in slaughterhouses. A proportion of the sludge discharged from wastewater treatment facilities at slaughterhouses has historically been processed into fertilizer. We therefore investigated the associated risk of BSE infection to cattle via sludge-derived fertilizer. Each stage of the process associated with BSE exposure was qualitatively evaluated and quantitative evaluations were subsequently performed using infectious dose as a unit of concern. Results of these qualitative evaluations indicated that installation of filter(s) at the drains to the wastewater treatment facilities has been undertaken by many slaughterhouses and has decreased the likelihood of SRM contamination of sewage. The level of sludge-derived fertilizer ingested by cattle was considered to be very low since the fertilizer is mixed with the ground soil, and the amount of soil ingested by cattle is likely to be small. Results from the quantitative analysis indicated the total infectious dose ingested by cattle in Japan from an infected cow has been estimated to be 5.5 x 10(-3) ID(50). Preventing scattering of SRM during the slaughtering process, installing filters to the drains with the removal of residues from the drain water and preventing the application of sludge-derived fertilizer to pasturelands would be effective to reduce the risk. Although the limited extent of available information, this study should provide useful indication for the development of an inclusive risk assessment for slaughterhouse sludge in the future.

Irradiation of Ascaris ova in sludge using an electron beam accelerator

The efficiency of sludge disinfection by irradiation was investigated using an electron beam accelerator, with the Ascaris ovum as a model. Ova suspensions prepared by worm dissection, immediately after preparation and after storage at 4°C for 2 months were tested. Suspensions of ova extracted from slaughterhouse sludge were also tested. The ova were irradiated in sludge to determine, by probit analysis, the dose that inactivated 90% of viable ova. The D 10 values obtained for irradiation of residual sludge contaminated with ova depended on the source of the ova, the D 10 values were 788±172 Gy for suspensions of ova extracted from slaughterhouse sludge and 1125±145 Gy for suspensions freshly prepared by dissection. Ova suspensions freshly prepared by dissection were more proof against irradiation. Similarly, the D 10 value was affected by storage: 1125±145 Gy for freshly produced ova suspensions and 661±45 Gy for suspensions of ova stored for 2 months at 4°C in deionized water. The medium in which the ova were irradiated (deionized water or sludge) also affected D 10 values, the indirect effects were smaller in samples of contaminated sludge, which were rich in organic matter, with the action of the radiation being mostly direct.

Fermentation of aerobically activated pig slaughterhouse sludge for animal feed purposes

Aerobically activated sludge from a pig slaughterhouse wastewater-treatment plant was mixed with 0.35 or 0.5% (wt/wt) dextrose, with 0.5% (wt/wt) dextrose and 0.05 or 0.2% (v/v) formic acid, or with 2.5% (wt/wt) molasses and 0.1% (v/v) formic acid, and was pasteurized at 95°C for 5 min. After cooling to approximately 20°C the sludge was inoculated with 10 6–10 7 cfu Lactobacillus plantarum/g sludge. Fermentation was performed at 20°C for 21 days. When 0.05% (v/v) formic acid or less was added, the initial pH of the sludge was favourable for the germination and outgrowth of clostridia spores and resulted in amino acid breakdown. In the case of the addition of 0.2% (v/v) formic acid and 0.5% (wt/wt) dextrose the initial pH was below 4 and the number of lactobacilli did not substantially increase. No amino acid breakdown was observed. Concerning the safety of the fermented product, it was concluded that pasteurized activated sludge from a pig slaughterhouse can be effectively fermented into a stable product, suitable for animal feed purposes, with 2.5% (wt/wt) molasses, 0.1% (v/v) formic acid and L. plantarum as the inoculum.