Laboratory-scale Composting Research Articles

Evaluation of ammonia emission reducing effect by adding waste cooking oil in pilot-scale composting of dairy cattle manure.

In our previous study, we observed that the addition of waste cooking oil (WCO) reduced ammonia (NH3) emissions during laboratory-scale composting of dairy cattle manure under low-aeration condition. Therefore, this study aimed to evaluate the effect of addition of WCO on NH3 emissions reduction during pilot-scale composting of dairy cattle manure, which is close to the conditions of practical composting treatment. Composting tests were conducted using pilot-scale composting facilities (1.8 m3 of capacity). The composting mixtures were prepared from manure, sawdust, and WCO. Two treatments were set: without WCO (Control) and with WCO added to 3 wt% of manure (WCO3). Composting was conducted under continuous aeration at 40 L/min, corresponding to 22.2 L/(min‧m3) of the mixture at the start of composting. The changes in temperatures, NH3 concentrations in the exhaust gases, and contents of the composted mixtures were analyzed. Based on these analysis results, the effect of WCO addition on NH3 emissions and nitrogen loss during composting was evaluated. During composting, the temperature increase of the composting mixture became higher, and the decreases of weight and water content of the mixture became larger in WCO3 than in Control. In the decrease of weight, and the residual weight and water content of the mixture, significant differences (p<0.05) were detected between the two treatments at the end of composting. The NH3 concentrations in the exhaust gases tended to be lower in WCO3 than in Control. Nitrogen loss was 21.5% lower in WCO3 than in Control. Reduction of NH3 emissions by the addition of WCO under low aeration condition was observed in pilot-scale composting, as well as in laboratory-scale composting. This result suggests that this method is effective in reducing NH3 emissions in practicalscale composting.

Optimization of vegetable waste composting and the exploration of microbial mechanisms related to fungal communities during composting

The application of additives to regulate the microbial functional composition during composting has attracted much research attention. However, little is known about the succession and role of the fungal community in the laboratory-scale composting of vegetable waste supplemented with pig manure and microbial agents. The purpose of this study was to identify effective additives for improving vegetable waste composting performance and product quality, and to analyze the microbial community succession during composting. The results showed that the combined addition of pig manure and microbial agents (T2 treatment) accelerated the pile temperature increase, enhanced total organic carbon degradation (23.36%), and promoted the maturation of the compost. Furthermore, the T2 treatment increased the activities of most enzymes, reshaped the microbial community, and reduced the relative abundance of potential animal (1.60%) and plant (0.095%) pathogens. The relative abundance of Firmicutes (71.23%) increased with the combined addition of pig manure and microbial agents in the thermophilic stage. In the middle and late stages, Saccharomonospora, Aspergillus, and Thermomyces, which were related to C/N and total phosphorus, were enriched in the T2 treatment. Network analysis demonstrated that the complexity and stability of the fungal network were more evidently increased in the T2 treatment, and Saccharomonospora, Aspergillus, and Microascus were identified as keystone taxa. The keystone taxa associated with extracellular enzymes contributed significantly to compost maturation. These results provide a reference for the application of additives to improve compost safety in pilot-scale composting.

Effect of seeding materials on organic matter degradation and microbial community succession during model organic waste composting

The positive effect of seeding inoculation on the enhancement of organic matter decomposition has been reported only for specific substrates (lignocellulose and organic acids). However, in most cases (food waste or sludge), no effect has been reported. This study aimed to clarify the effect of seeding materials by quantitatively analyzing the relationship between organic matter degradation and microbial community succession during composting. Three seeding materials (one commercial seeding material and two commercial compost products) were compared in laboratory-scale composting of model organic waste. The results showed that the rates and degrees of organic matter degradation were similar irrespective of the seeding material. However, the microbial communities were different in each run, thereby indicating that the seeding materials greatly affected microbial community succession. The enzyme genes of the microorganisms were predicted by phylogenetic investigation of the communities via reconstruction of unobserved states. The abundance of most enzyme genes became similar as composting proceeded with different seeding materials. Therefore, the microorganisms present during composting may have similar enzymatic potential, even if they are in different microbial communities. • Effect of seeds was clarified by organic matter degradation and microbial community. • Degrees of organic matter degradation were similar regardless of seeding types. • Seeding materials influenced succession of microbial communities during composting. • Bacteria in seeds proliferated in thermophilic phase and contribute to degradation. • Predicted functions of the community became similar in all seeds.

Effects of the C/N ratio and moisture content on the survival of ESBL-producing Escherichia coli during chicken manure composting

Antibiotic-resistant bacteria are a threat to human and animal health. In recent years, the presence of extended-spectrum-β-lactamase (ESBL)-producing Escherichia (E.) coli in chicken manure, which is used as organic fertilizer, is a concern. The aim of the present study was to determine the effects of the carbon/nitrogen (C/N) ratio and moisture content (MC) on the survival of ESBL-producing E. coli during laboratory-scale composting of chicken manure. Nine different compost mixtures were enriched with an ESBL-producing E. coli strain to an initial concentration of 7 log10 CFU/g, and the number of E. coli, temperature, and chemical conditions during composting were determined. The fastest decrease in E. coli occurred for all mixtures with a C/N ratio of 10:1. Additionally, dry mixtures with an MC of 20% and a C/N ratio of either 10:1 or 40:1 exhibited faster reductions in E. coli than the moist mixtures did, despite having lower maximum temperatures within the bioreactors. The decimal reduction times ranged from 0.27 days in a mixture with a C/N ratio of 10:1 and 40% MC to 4.82 days in a mixture with a C/N ratio of 40:1 and 40% MC. Both the C/N ratio and MC had a significant effect on the number of ESBL-producing E. coli and on temperature development; the C/N ratio additionally affected the pH value and content of ammoniacal nitrogen during chicken manure composting. The results of this study demonstrate a considerable range of mechanisms involved in the inactivation of E. coli during chicken manure composting.

The Evaluation of Hazards to Man and the Environment during the Composting of Sewage Sludge

Composting is considered an effective treatment option to eliminate or substantially reduce potential hazards relating to the recycling of sewage sludge (SS) on land. The variation of four major types of hazards (heavy metals, instability, pathogenic potential and antibiotic resistance) was studied during laboratory-scale composting of two mixtures of sludge and green waste (1:1 and 1:2 v/v). The heavy metal content of the final compost was governed by the initial contamination of SS, with the bulking agent ratio having practically no effect. The composts would meet the heavy metal standards of the United States of America (USA) and the European Union member states, but would fail the most stringent of them. A higher ratio of bulking agent led to a higher stabilisation rate, nitrogen retention and final degree of stability. A good level of sanitisation was achieved for both mixtures, despite the relatively low temperatures attained in the laboratory system. The antibiotic resistance was limited among the E. coli strains examined, but its occurrence was more frequent among the Enterococcus spp. strains. The type of antibiotics against which resistance was mainly detected indicates that this might not be acquired, thus, not posing a serious epidemiological risk through the land application of the SS derived composts.

Identification of microbial populations contributing to nitrification-associated nitrous oxide emission during cattle manure composting process with forced aeration

This study was conducted to clarify the fates of whole nitrogen cycle-associated microorganisms during laboratory-scale composting of cattle manure with continuous forced aeration, with the primary goal of identifying microbial populations that contributed greatly to high nitrous oxide (N2O) emissions triggered by nitrification. DNA microarray analysis targeting functional genes associated with the entire microbial nitrogen cycle was applied for the first time to investigate the fates of entire nitrogen cycle-associated microbial community during composting, and revealed increased diversity of nitrogen cycle-associated microorganisms, including ammonia-oxidizing populations, during active nitrification and N2O emission periods. Further analyses of the compositions of ammonia-oxidizing populations by DNA microarray, PCR-denaturing gradient gel electrophoresis and clone library methods revealed that Nitrosomonas europaea, Nitrosomonas eutropha, and their relatives were the dominant ammonia-oxidizing populations. Overall, the analyses of entire nitrogen cycle-associated microbial community and specific functional groups by a combination of different molecular biological methods in this study could confirm that N. europaea/eutropha and their relatives contributed greatly to high N2O emissions via active nitrification during cattle manure composting with forced aeration.

Inactivation of Bacillus anthracis Spores during Laboratory-Scale Composting of Feedlot Cattle Manure.

Anthrax outbreaks in livestock have social, economic and health implications, altering farmer’s livelihoods, impacting trade and posing a zoonotic risk. Our study investigated the survival of Bacillus thuringiensis and B. anthracis spores sporulated at 15, 20, or 37°C, over 33 days of composting. Spores (∼7.5 log10 CFU g-1) were mixed with manure and composted in laboratory scale composters. After 15 days, the compost was mixed and returned to the composter for a second cycle. Temperatures peaked at 71°C on day 2 and remained ≥55°C for an average of 7 days in the first cycle, but did not exceed 55°C in the second. For B. thuringiensis, spores generated at 15 and 21°C exhibited reduced (P < 0.05) viability of 2.7 and 2.6 log10 CFU g-1 respectively, as compared to a 0.6 log10 CFU g-1 reduction for those generated at 37°C. For B. anthracis, sporulation temperature did not impact spore survival as there was a 2.5, 2.2, and 2.8 log10 CFU g-1 reduction after composting for spores generated at 15, 21, and 37°C, respectively. For both species, spore viability declined more rapidly (P < 0.05) in the first as compared to the second composting cycle. Our findings suggest that the duration of thermophilic exposure (≥55°C) is the main factor influencing survival of B. anthracis spores in compost. As sporulation temperature did not influence survival of B. anthracis, composting may lower the viability of spores associated with carcasses infected with B. anthracis over a range of sporulation temperatures.

Effects of sucrose amendment on ammonia assimilation during sewage sludge composting

The aim of this study was to evaluate the laboratory-scale composting of sewage sludge and pumice mixtures that were amended with sucrose. The variation in temperature, pH, NH4+-N, ammonia emission, bacterial community, ammonia assimilating bacteria (AAB) populations and enzymatic activity related to ammonia assimilation were detected. The addition of sucrose increased the AAB population by 2.5–3.5 times, reduced ammonia emission by 24.7–31.1% compared with the control treatment, and promoted the growth of Bacillus and Wautersiella. The activities of glutamate dehydrogenase (GDH), glutamate synthase (GS) and glutamine synthetase (GOGAT), were enhanced by the addition of sucrose. GDH made a substantial contribution to ammonia assimilation when the ammonia concentration was high (⩾1.5g/kg) in the thermophilic phase. The GS/GOGAT cycle played an important role at low ammonia concentrations (⩽1.1g/kg) in the cooling phase. These results suggested that adding sucrose to sludge compost could promote ammonia assimilation and reduce ammonia emission.

Effects of biochar amendment on ammonia emission during composting of sewage sludge

The presented research included laboratory scale composting of sewage sludge and woodchips mixtures amended with biochar in 45L reactor system conducted for 16 days. The effect of biochar amendment on ammonia emission was investigated. The addition of biochar reduced significantly volatilization of ammonia during the first week of the process. Also, the addition of biochar increased temperature and organic matter decomposition.

Reduction of foodborne pathogens during cattle manure composting with addition of calcium cyanamide

Abstract Inactivation of four species of foodborne pathogens (E. coli, Salmonella, E. faecalis, and S. aureus) was investigated during laboratory-scale composting of fresh cow manure with addition of calcium cyanamide (CaCN2) at constant temperature conditions, and the effects of temperature and additive content of CaCN2 on the efficacy of inactivation were evaluated. At different composting temperatures (20, 30, 37 and 50 °C), a significant inhibition or quick inactivation of pathogens were observed during 10 d composting with addition of 2.0% CaCN2, and the effect was more obvious at mesophilic temperatures compared to thermophilic temperature. Therefore, the ideal additive content of CaCN2 was determined at 30 °C through mixing 2.0%, 2.5%, and 3.0% CaCN2 with manure. With increase in additive content of CaCN2, the efficacies of pathogen inactivation also increased. However, the result indicates that, no less than 2.5% CaCN2 should be mixed with the manure to entirely eliminate the pathogens during comp...

Effect of matured compost as an inoculating agent on odour removal and maturation of vegetable and fruit waste compost

The use of matured compost as an inoculation agent to improve the composting of vegetable and fruit wastes in a laboratory-scale composter was evaluated, and the commercial feasibility of this approach in a pilot-scale (1.8×104 L) composter was subsequently confirmed. The effect of aeration rate on the physico-chemical and biological properties of compost was also studied. Aeration rate affected the fermentation temperature, moisture content, pH, O2 consumption rate, CO2 production rate and the formation of odour. The optimal aeration rate was 2.5 L air/kg dry solid/min. The CO2 production rate approached the theoretical value during composting and was linearly dependent on temperature, indicating that the compost system had good operating characteristics. The inoculation of cellulolytic bacteria and deodorizing bacteria to compost in the pilot-scale composter led to an 18.2% volatile solids loss and a 64.3% volume reduction ratio in 52 h; only 1.5 ppmv odour was detected. This is the first study to focus on both operating performance and odour removal in a pilot-scale composter.

Biodegradation of specified risk material and fate of scrapie prions in compost

Composting may be a viable alternative to rendering and land filling for the disposal of specified risk material (SRM) provided that infectious prion proteins (PrPTSE) are inactivated. This study investigated the degradation of SRM and the fate of scrapie prions (PrPSc) over 28 days in laboratory-scale composters, with and without feathers in the compost matrices. Compost was mixed at day 14 to generate a second heating cycle, with temperatures exceeding 65°C in the first cycle and 50°C in the second cycle. Approximately 63% and 77% of SRM was degraded after the first and second cycles, respectively. Inclusion of feathers in the compost matrices did not alter compost properties during composting other than increasing (P < 0.05) total nitrogen and reducing (P < 0.05) the C/N ratio. However, addition of feathers enhanced (P < 0.05) SRM degradation by 10% upon completion of experiment. Scrapie brain homogenates were spiked into manure at the start of composting and extracted using sodium dodecyl sulphate followed by detection using Western blotting (WB). Prior to composting, PrPSc was detectable in manure with 1–2 log10 sensitivity, but was not observable after 14 or 28 days of composting. This may have been due to either biological degradation of PrPSc or the formation of complexes with compost components that precluded its detection.

Biodegradation of specified risk material and characterization of actinobacterial communities in laboratory-scale composters

As a result of bovine spongiform encephalopathy in Canada, specific tissues at risk of harbouring prions are not allowed to enter the food chain. Composting may be a viable alternative to rendering and land filling for the disposal of specified risk material (SRM). Two types of laboratory-scale composters, actively-heated and ambient systems were constructed to assess the biodegradation of SRM over 30days. A second heating cycle was generated by mixing the compost after 15days. Compared to ambient composters, temperature profiles in actively-heated composters were above 50°C for 5 and 4days longer in the first and second composting cycles, respectively. Degradation of SRM was similar between two composter types during two composting cycles, averaging 52.2% in the first cycle and 43.9% in second cycle. Denaturing gradient gel electrophoresis (DGGE) revealed that changes in the actinobacteria populations in the first composting cycle were of a temporal nature, whereas alterations in populations in the second composting cycle were more related to active heating of compost. Sequencing of the dominant DGGE bands showed the predominance of Corynebacterium, Promicromonospora, Pseudonocardia, and Thermobifida in the first composting cycle and Corynebacterium, Mycobacterium, Nocardia, Saccharomonospora, and Streptomyces in the second composting cycle. Active heating can alter the nature of actinobacteria populations in compost, but does not appear to have a major impact on the extent of degradation of SRM.

Assessment of Microbial Communities In Decomposition of Specified Risk Material Using a Passively Aerated Laboratory-Scale Composter

The occurrence of bovine spongiform encephalopathy (BSE) in Canada has resulted in the implementation of regulations to remove specified risk material (SRM) from the food chain. SRM includes the distal ileum of all cattle, and the skull, brain, trigeminal ganglia, eyes, palatine tonsils, and spinal cord and dorsal root ganglia of cattle ≥30 months of age. Composting may be a viable alternative to rendering for SRM disposal. In our study, two bulking agents, barley straw and wood shavings, were composted with beef manure along with SRM in passively aerated, laboratory-scale composters. Both composts heated rapidly, exceeding 55°C after 3 days with oxygen declining in the early composting stage with wood-shaving compost, but returning to near-original levels after 5 days. During composting the two matrices differed (P <0.05) only in water content, TC and bulk density. In the final compost, water content, TC and C/N ratio were higher (P < 0.05), while EC was lower (P < 0.05) in the wood shavings as compared to the straw compost. Approximately 50% of SRM was decomposed after 15 days of composting, with 30% of SRM being decomposed within the first 5 days. Phospholipid fatty acid (PLFA) profiles were used to characterize the microbial communities and showed that Gram positive bacteria were predominant in compost at day 5, a point that coincided with a rapid increase in temperature. Gram negative bacteria and anaerobes declined at day 5 but populations recovered by day 15. Fungi appeared to be suppressed as temperatures exceeded 55°C and did not appear to recover over the remainder of the composting period, with the exception of the straw compost at day 15. On day 5, Actinomycetes increased in the straw compost, but declined in the wood shavings compost, with this group increasing in both types of compost at day 15. Although temporal changes were evident, compost matrices or depth within the composter did not obviously influence microbial communities. Decomposition of SRM also did not differ between compost matrices or with depth in the composters. These results suggest that SRM decompose rapidly during composting and that both mesophilic and thermophilic microbial communities play a role in its decomposition.

Effect of Flow Rate, Concentration and Transient—State Operations on the Performance of a Biofilter Treating Xylene Vapors

Biological treatment systems such as biofilters offer a potential alternative to the existing physicochemical techniques for the removal of volatile organic compounds from gaseous emissions. In this experimental work, continuous phase biofiltration of xylene vapors were performed in a laboratory scale compost biofilter that was inoculated with a xylene-acclimatized consortium. The performance was assessed by continuously monitoring the removal efficiency (RE) and elimination capacity (EC) of the biofilter at loading rates varying between 2–220 g m−3 h−1. The steady-state removal efficiencies were maintained between 60% and 90% up to a loading rate of 80 g m−3 h−1. The removal efficiency decreased significantly at loading rates higher than 100 g m−3 h−1. The pressure drop values were consistently less and insignificant in affecting the performance of the system. The present study also focuses in evaluating the stability of biofilter during shut down, restart, and shock-loading operations. An immediate restoration of biological activity after few days of starvation indicated their capability to handle discontinuous treatment situations which is more common to industrial biofilters. The sensitiveness of the biofilm to withstand shock loads was tested by abruptly increasing/decreasing the loading rates between 9–55 g m−3 h−1, where, removal efficiencies between 60–90% were achieved. These results prove the resilience of the biomass and the stability of the compost biofilter. Anew, results from kinetic analysis reveal that, steady-state xylene removal in the biofilter can be adequately represented by Michaelis–Menten type kinetics, and the kinetic constants namely, ECmax (120.4 g m−3 h−1) and K s (2.21 g m−3) were obtained.

Treatment of benzene vapors from contaminated air stream in a laboratory-scale compost biofilter

Biofiltration of process waste–gas streams using microorganisms attached to porous support matrix, at low concentrations and high gas flow rates, has gained importance as a versatile treatment technology ever since the Clean Air Act Amendments (1990), by the US – EPA came into existence. In this study, we evaluated the potential of a laboratory–scale biofilter, inoculated with mixed culture, to remove gas–phase benzene from a synthetic waste gas stream. Experiments were conducted in three different phases, after the acclimatization step, corresponding to empty bed residence times (EBRT) varying between 0.81–2.45 min and benzene concentrations up to 1.7 g/m3. At high concentrations, significant reduction in removal efficiency was observed, which may be due to insufficient biomass in the filter bed to utilize the substrate, or due to substrate inhibition at high concentrations. Removal efficiencies higher than 90% were achieved for inlet benzene loading rates lesser than 40 g/m3hr.

Biomass reduction and arsenic transformation during composting of arsenic-rich hyperaccumulator Pteris vittata L.

Composting is being proposed as a pretreatment step before disposal of metal-rich biomass after phytoextraction process. This study determined the biomass reduction and arsenic transformation during composting As-rich biomass of hyperaccumulator Chinese brake fern (Pteris vittata L.). High-As fern biomass containing approximately 4,600 mg As kg(-1) was composted for 120 days in a laboratory-scale composter under aerated condition. Solid As speciation was determined using X-ray diffraction (XRD) and scanning electron microscopy equipped with X-ray energy dispersive elemental spectroscopy (SEM-EDS), while liquid As speciation was evaluated by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry. Composting reduced the fern biomass by 38%, comparable to 35% reduction of the low-As fern biomass containing approximately 12 mg As kg(-1), indicating that the high As concentration in P. vittata had little detrimental effect on microorganisms involved in composting. Total As on a per composter basis and water-soluble As in composted biomass were lowered by 25% and 32%, respectively. Arsenic loss from the biomass resulted mainly from generation of compost leachate, with less from the As volatilization; whereas As immobilization was due to oxidation of As(III) to As(V), followed by precipitation of hoernesite [Mg(3)(AsO(4))(2).8H(2)O] which was evidenced by XRD and SEM-EDS analysis. Results from this study indicate that composting As-rich fern significantly reduced its biomass, As content, and water-soluble As. It seems that composting can be an effective step for treating As-rich biomass before disposal in landfill.

Involvement and interaction of microbial communities in the transformation and stabilization of chromium during the composting of tannery effluent treated biomass of Vallisneria spiralis L.

Tannery effluent treated with aquatic macrophyte Vallisneria spiralis L. for 14 d showed significant improvement in physico-chemical properties and reduction in Cr concentration. Accumulation of Cr was found maximum in roots (358 μg g −1dw) as compared to shoot (62 μg g −1dw) of the plant. A laboratory scale composter was designed with the objectives to investigate the physico-chemical changes and role of microbes in stabilization and transformation of Cr in the composting material. Results revealed that the composting process was quick within 7–21 d as indicated by peak time for various physico-chemical parameters and drop in C/N ratio up to acceptable limit. The profile of microbial communities indicated that population of anaerobic, aerobic and nitrifying bacteria increased quickly at the initial phase, and reached a peak level of 4.2 × 10 6, 9.78 × 10 8 and 9.32 × 10 9 CFU g −1, respectively at 21 d; while population of actinomycetes and fungi was found maximum i.e. 3.29 × 10 7 and 9.7 × 10 6 CFU g −1, respectively, after 35 d of composting. Overall bacterial population dominated over the actinomycetes and fungi during the composting process. Cr (VI) was transformed to Cr (III) due to the microbial activity during the process. Sequential extraction of Cr fractionation showed its stabilization via changing into organic matter-bound and residual fractions during the composting.

Ammonia emissions from the composting of different organic wastes. Dependency on process temperature

Ammonia emissions were quantified for the laboratory-scale composting of three typical organic wastes with medium nitrogen content: organic fraction of municipal solid wastes, raw sludge and anaerobically digested sludge; and the composting of two wastes with high nitrogen content: animal by-products from slaughterhouses and partially hydrolysed hair from the leather industry. All the wastes were mixed with the proper amount of bulking agent. Ammonia emitted in the composting of the five wastes investigated revealed a strong dependence on temperature, with a distinct pattern found in ammonia emissions for each waste in the thermophilic first stage of composting (exponential increase of ammonia emitted when increasing temperature) than that of the mesophilic final stage (linear increase of ammonia emissions when increasing temperature). As composting needs high temperatures to ensure the sanitisation of compost and ammonia emissions are one of the main environmental impacts associated to composting and responsible for obtaining compost with a low agronomical quality, it is proposed that sanitisation is conducted after the first stage in large-scale composting facilities by a proper temperature control. Capsule Ammonia emission pattern and correlation with process temperature are presented for the composting process of different organic wastes.

Changes in Physical Properties of a Compost Biofilter Treating Hydrogen Sulfide

A technique is presented that can be used to estimate the changes in physical structure in a natural biofilter packing medium, such as compost, over time. The technique applies information from tracer studies, grain size distribution, and pressure drop analysis to a model that estimates the number of channels, average channel diameter, number of particles, and specific surface area of the medium. Important operational factors, such as moisture content, pressure drop, and sulfate accumulation also were evaluated both in a conventionally operated biofilter and in one operated with periodic compost mixing. In the conventionally operated laboratory-scale compost biofilter, hydrogen sulfide (H2S) removal efficiency decreased from 100% to ∼ 90% over 206 days of operation. In a similar system, operated with compost mixing, the H2S removal efficiency was maintained near 100%. Variations in media moisture conditions and specific surface area can explain the results observed in this study. Under conventional operation, drying near the inlet disintegrated the compost particles, producing a large number of particles and flow channels and increasing the specific surface area. At the top of the column, where moisture was added, particle size increased and specific surface area decreased. In the column with media mixing, moisture content, particle size, and specific surface area remained homogeneous.