Fed-batch Composting Research Articles

Effect of reactor temperature and feeding ratio on fed-batch composting of household food waste and green wastes

Currently, most regions of China still treat household food waste (HFW) in a centralized way, which increases the cost of collection and transportation. Therefore, it is necessary to develop a novel technology to treat HFW on site. In this study, a fed-batch reactor was designed to investigate the effect of reactor temperature and feeding ratio on the co-composting of HFW and green wastes (GW). The results showed that an increase in reactor temperature could promote composting efficiency and compost end-product maturity. When the reactor temperature was 50 °C, the moisture (4.1%), weight loss rate (87.3%), organic matter (OM) content (66.1%), and seed germination index (74.1%) of the compost reached the optimum. When the feeding ratio was 2:1, the decomposition rate of OM was the fastest, and the weight loss rate, OM content, and C/N ratio of the compost were 89.3%, 63.1%, and 12.6, respectively. According to the first-order kinetics, it was found that the reactor temperature had a greater impact on fed-batch composting than the feeding ratio. This study suggested that fed-batch composting is a promising technique for the utilization of HFW and GW and provided guidance for the scale-up application of bed-batch reactors.

Cultural, Transcriptomic, and Proteomic Analyses of Water-Stressed Cells of Actinobacterial Strains Isolated from Compost: Ecological Implications in the Fed-Batch Composting Process.

This study was undertaken to examine the effects of water activity (aw) on the viability of actinobacterial isolates from a fed-batch composting (FBC) process by comparing culturability and stainability with 5-cyano-2,3-ditoryl tetrazolium chloride (CTC). The FBC reactor as the source of these bacteria was operated with the daily loading of household biowaste for 70 d. During this period of composting, aw in the reactor decreased linearly with time and reached approximately 0.95 at the end of operation. The plate counts of aerobic chemoorganotrophic bacteria were 3.2-fold higher than CTC-positive (CTC+) counts on average at the fully acclimated stage (after 7 weeks of operation), in which Actinobacteria predominated, as shown by lipoquinone profiling and cultivation methods. When the actinobacterial isolates from the FBC process were grown under aw stress, no significant differences were observed in culturability among the cultures, whereas CTC stainability decreased with reductions in aw levels. A cDNA microarray-based transcriptomic analysis of a representative isolate showed that many of the genes involved in cellular metabolism and genetic information processing were down-regulated by aw stress. This result was fully supported by a proteomic analysis. The results of the present study suggest that, in low aw mature compost, the metabolic activity of the community with Actinobacteria predominating is temporarily reduced to a level that hardly reacts with CTC; however, these bacteria are easily recoverable by exposure to a high aw culture medium. This may be a plausible reason why acclimated FBC reactors in which Actinobacteria predominate yields higher plate counts than CTC+ counts.

Removal of polychlorinated dioxins by semi-aerobic fed-batch composting with biostimulation of “Dehalococcoides”

A semi-aerobic, mesophilic, fed-batch composting (FBC) reactor loaded with household garbage was used to remove polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs). The reactor was packed with woodchips as the solid matrix and PCDD/F-contaminated soil or flyash and then operated at a waste-loading rate of 0.5 kg (wet wt) day(-1). All congeners of PCDD/Fs (initial concentration, 200-830 pmol g(-1) [dry wt]) were totally reduced during the over period of operation, with a half reduction time of 4 months. Direct cell counting and respiratory quinone profiling showed that the reactors at the fully acclimated stage harbored a high population density of bacteria (10(11) g(-1) [dry wt]) with members of the Actinobacteria predominating. Real-time quantitative PCR showed that the population of "Dehalococcoides" and its phylogenetic relatives of Chloroflexi as the possible dechlorinators varied between at the order of 10(7) to 10(8) g(-1) (dry wt). A "Dehalococcoides"-containing dechlorinating culture from the soil-treating reactor was successfully enriched with a model PCDD/F compound, fthalide. 16S rRNA gene-targeted PCR-denaturated gradient gel electrophoresis and clone library analyses showed that this culture comprised at least three major phylogenetic groups of bacteria, Acidaminobacter, "Dehalococcoides," and Rhizobium. These results suggest that the semi-aerobic FBC process is applicable for the bioremediation of PCDD/Fs and possibly other haloorganic compounds with the biostimulation of "Dehalococcoides" and its relatives as the potent dechlorinators.

Combined Use of Cyanoditolyl Tetrazolium Staining and Flow Cytometry for Detection of Metabolically Active Bacteria in a Fed-batch Composting Process

Microbial community dynamics with metabolically active bacteria during the start-up operation of a personal fed-batch composting (FBC) reactor were studied. The FBC reactor was loaded daily with household garbage for 2 months. Metabolically active bacteria were monitored by the redox-dye-staining method using 5-cyano-2,3-ditoryl tetrazolium chloride (CTC), and the fluorescent formazans thus produced were detected by epifluorescence microscopy and flow cytometry (FCM). Microscopic CTC-positive (CTC+) counts accounted for 75-84% of the direct total count during the first week of operation and 19-35% thereafter. Slightly higher CTC+ counts were obtained by FCM. Culture-independent approaches by quinone profiling and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA genes showed that a drastic population change from ubiquinone-containing members of the Proteobacteria to the Actinobacteria took place during the overall period of operation. The PCR-DGGE analysis of FCM-sorted CTC+ cells supported this observation but gave different major clones from those detected in the total community in some cases. These results suggest that metabolically active bacteria as measured by CTC staining are not always predominant in the FBC process.

Aeration improvement in fed batch composting of vegetable and fruit wastes

AbstractVegetable and fruit wastes amended with sawdust and urea were composted in a laboratory scale reactor by controlling a waste feeding rate of 21 g L−1 day−1 under proper conditions of composting. Effects of aeration, agitation, and initial waste‐to‐sawdust ratio on enhancing organic matter degradation and process performance in fed batch composting were investigated. During the feeding stage, rapid increase in moisture content and lowest removal of dry mass (0.28–0.30 g g−1 day−1) were observed at all aeration rates without agitation at a waste‐to‐sawdust ratio of 1:1.5. As the amount of sawdust was doubled, the water released was not only absorbed by waste matrix efficiently, resulted in the highest dry mass removal and total amount of new waste addition, but also demonstrated the substantial N loss (54–71%). The results revealed that the initial waste‐to‐sawdust ratio and agitation mode indeed influenced the performance of the fed batch composting (feeding stage) as indicated by a higher percentage of dry mass removal (34–59%) and larger free air space in compost matrix were determined. Adoption of a large amount of sawdust and agitation mode is recommended for maintaining stable degradation and enhancing fed batch composting under continuous aeration at a rate of 10.62–21.24 L m−3 min−1. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Changes in Bacterial Communities Accompanied by Aggregation in a Fed-Batch Composting Reactor

The contents of fed-batch composting (FBC) reactors often aggregate after prolonged operation. This process leads to irreversible breakdown of the decomposition reaction and possible alteration of the bacterial communities. We compared the structures of bacterial communities in reactors under aggregate and optimal conditions. The results of 16S rRNA gene clone analysis showed that populations of the family Bacillaceae (such as Bacillus spp., Cerasibacillus spp., Gracilibacillus spp.), which dominate (98%) under optimal condition, were significantly decreased under aggregate condition. In contrast, populations of the family Staphylococcaceae considerably increased after aggregation and accounted for 53% of the total. Phylogenetic analysis also showed that anaerobes or facultative anaerobes related to Tetragenococcus halophilus, Atopostipes suicloacalis, Jeotgalicoccus pinnipedialis, and Staphylococcus spp. were dominant in the aggregates. These results suggested that aerobic Gram-positive bacteria mainly contributed to organic degradation and that aggregation created some anaerobic environment, which promoted the growth of bacterial communities usually not found in well-functioning FBC reactors.

Profiling of a microbial community under confined conditions in a fed-batch garbage decomposer by denaturing gradient gel electrophoresis

In order to determine the conditions for the maximum performance of a fed-batch composting (FBC) reactor, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to analyze the microbial communities established under the confined conditions of moisture content and environmental temperature. To evaluate the effects of microbial community structures on the performance of FBC reactors, degradation experiments using small-scale reactors and model waste were conducted under confined environmental conditions. A high degradation rate was observed under a wide range of MC conditions (30–60%) and at higher than usual temperatures (30–50 °C). The microbial communities that formed in the experimental FBC reactors were analyzed by DGGE of PCR-amplified 16S rRNA genes. The DGGE banding patterns at the same level as the degradation rates were similar even if the environmental conditions were different. Sequence analysis of the DGGE bands revealed the primary microbes which act in the reactor.

Water Availability Is a Critical Determinant of a Population Shift from Proteobacteria to Actinobacteria during Start-Up Operation of Mesophilic Fed-Batch Composting

The effects of water availability defined as water activity (aw) or matric water potential (ψm) on microbial community dynamics during the start-up operation of mesophilic fed-batch composting (FBC) of household biowaste were studied using commercially available personal composters. The community changes were monitored for 2 months by direct cell counting, quinone profiling, and 16S rRNA gene sequencing of culturable predominant bacteria. The aw level lowered linearly with operation time and reached around 0.95 at the end of operation. During the steady-state period, aw or ψm had a strong positive correlation with moisture content and ubiquinone content and negative correlation with pH, electric conductivity, and partially saturated menaquinone content. Results of 16S rRNA gene-based phylogenetic identification of the predominant isolates as well as of culture-independent quinone profiling indicated that a drastic population change from ubiquinone-containing members of Proteobacteria to Actinobacteria took place during the overall period of operation. Most of the actinobacterial isolates grew on nutrient agar with an aw of less than 0.98, whereas none of the proteobacterial isolates did. These results suggest that water availability is an important determinant of the population shift from the Proteobacteria to Actinobacteria during the start-up operation of mesophilic fed-batch garbage composting.

Process inhibition due to organic acids in fed-batch composting of food waste ? influence of starting culture

Inhibition of the degradation during low pH conditions has been observed in fed-batch composting systems. To analyse this phenomenon, fed-batch composting of food waste with different amounts of starting culture was examined in laboratory reactor experiments. Changes in temperature, carbon dioxide evolution, pH, solids, ash and short chain organic acids were measured. In reactors with a daily feed rate of 24% or less of the starting culture, thermophilic temperatures occurred and the pH and carbon dioxide evolution were high and stable after a starting period of 4-5 days. In reactors with a daily feed rate of 48% or more of the starting culture the composting process failed, as the pH dropped below 6 and remained there and the temperature and carbon dioxide evolution were low. It was concluded that the use of adequate amounts of starting culture consisting of active compost can efficiently prevent low pH conditions and process inhibition in fed-batch composting of food waste.

Effect of Moisture Content on Fed Batch Composting Reactor of Vegetable and Fruit Wastes

Vegetable and fruit wastes mixed with sawdust were composted in a laboratory scale reactor by controlling the waste feeding rate at 21 kg m−3 day−1 and aeration rate at 10.6 l m−3 min−1. The effects of initial moisture content on organic matter degradation and process performance of fed batch composting were investigated. The absolute amount of removal, removal percentage, and removal rate of dry mass obtained were substantially different among the initial moisture contents. The rapid rise of moisture content and the lowest absolute amount of removal observed were achieved in the 50% condition. The initial moisture content yielding the largest absolute amount of removal in both feeding and curing stage was 30% whereas the removal percentage and rate constant of waste decomposition were highest in the 50% condition. Examined by traditional soil physics method, the moisture content at 50-55% was suitable for satisfying the degree of free air space (65-70%) of compost during the fed batch composting. Most degradable organic matter was mainly consumed in the feeding stage as indicated by a higher removal rate of dry mass in all cases. It is recommended that the initial moisture content of 30% and mode of aeration and agitation should be adopted for achieving practical fed batch composting of vegetable and fruit wastes. The study also demonstrated that the composting kinetics of vegetable and fruit wastes mixed with sawdust can be described by a first order model.

Microbiology of Fed-batch Composting

Microbiology of Fed-batch Composting

Activity and Phylogenetic Composition of Proteolytic Bacteria in Mesophilic Fed-batch Garbage Composters

Crude extracts of extracellular enzymes were prepared from a solid waste-compost mixture (SCM) taken from two mesophilic fed-batch composting (FBC) reactors for garbage treatment, and were tested for protease activity with azocasein as the substrate. The protease activity was highest at a reaction temperature of 70°C and remained relatively high even at 90°C. The optimum pH for the activity was 7 to 10. There were a significant negative correlation between the protease activity and the moisture content in the FBC reactors when the extracts were prepared. Seventy-six strains of proteolytic bacteria were isolated quantitatively by the agar-plating method and identified phylogenetically by 16S rRNA gene sequencing. Most of the isolates were assigned to members of the phyla Actinobacteria, Bacteroidetes, and Firmicutes, especially those of the genera Bacillus, Cellulosimicrobium, and Ornithinococcus and an unaffiliated Cytophaga-like group. Inhibitor and zymography experiments showed that the proteolytic activities of the isolates belonging to the above-noted Gram-positive genera as well as of the SCM sample were inhibited by phenylmethylsulfonyl fluoride and that the isolates of Bacillus, Cellulosimicrobium, and the Cytophaga-like group excreted a protease similar to those from the SCM sample in electrophoretic mobility. The results of this study suggest that bacteria belonging to the phyla Actinobacteria and Firmicutes and producing alkaline serine protease play primary roles in protein digestion in the mesophilic FBC process.

Evaluation of Korean food waste composting with fed-batch operations II: using properties of exhaust gas condensate

Abstract An evaluation of Korean food waste composting, with a fed-batch operation, was conducted using the properties of the exhaust gas condensate. The traditional indices, as well as condensate properties, showed the same patterns of variation over each reaction time in the batch cycles during fed-batch composting. Trends for the variation in the pH of the condensate (pHcn) corresponded to those of the traditional indices, such as pH of the compost (pHcm) and CO2 evolution in the exhaust gas. In addition, the carbon chemical forms in the condensate would indirectly represent the gaseous metabolites, such as CO2, NH3, and VFA, which are generally emitted from aerobic composting processes. The patterns and quantities of NH3 gas evolution in the exhaust gas, especially, could be effectively estimated by their correlations with the NH4 and NH3 concentrations in the condensate or the pHcn in each cycle of fed-batch composting. Therefore, it was considered that the measurement of the condensate properties might serve as more useful and convenient operating indices than the analysis of solid and gas samples, during the composting process.