Effect of enforced aeration on in-vessel food waste composting

Effects of carbon-based additives and ventilation rate on nitrogen loss and microbial community during chicken manure composting

Aerobic composting is a sustainable method for chicken manure recycling, while its unsuitable porosity and carbon to nitrogen ratio (C/N) may result in high nitrogen loss and incomplete composting. With the aim to investigate the effects of carbon-based additives and two ventilation rates on chicken manure composting and microbial community, two series of treatments were set up for chicken manure composting, in order to investigate their effects on the biodegradation process, ammonia (NH₃) emission, nitrogen loss, physiochemical properties and microbial community. The results showed that additives and ventilation rates set in the current study influenced the carbon dioxide (CO₂) production from the 2^nd week and also the physiochemical parameters during the entire process, while no inhibitory effect on the maturity were observed. With woody peat as additive, the NH₃ emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02%, less than those in other treatments, 31.08–80.13 mg and 24.26–34.24%, respectively. The high aeration rate increased the NH₃ emission and nitrogen loss, which were varied when the additives were different. The terminal restriction fragment length polymorphism (T-RFLP) results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. It was concluded that woody peat could improve chicken manure composting more than other additives, especially on reducing nitrogen loss, meanwhile 0.18 L‧min^-1‧kg^-1 DM was suitable for various additives. Therefore, suitable additive and aeration rate could be used in practical application, which could significantly reduce nitrogen loss without influence on the compos maturity process.

Influence of aeration rate and reactor shape on the composting of poultry manure and sawdust

To achieve successful composting, all the biological, chemical, and physical characteristics need to be considered. The investigation of our study was based on various physicochemical properties, i.e., temperature, ammonia concentration, carbon dioxide concentration, pH, electrical conductivity (EC), carbon/nitrogen (C/N) ratio, organic matter (OM) content, moisture content, bacterial population, and seed germination index (GI), during the composting of poultry manure and sawdust for different aeration rates and reactor shapes. Three cylindrical-shaped and three rectangular-shaped pilot-scale 60-L composting reactors were used in this study, with aeration rates of 0.3 (low), 0.6 (medium), and 0.9 (high) L min^-1 kg^-1 DM (dry matter). All parameters were monitored over 21 days of composting. Results showed that the low aeration rate (0.3 L min^-1 kg^-1 DM) corresponded to a higher and longer thermophilic phase than did the high aeration rate (0.9 L min^-1 kg^-1 DM). Ammonia and carbon dioxide volatilization were directly related to the temperature profile of the substrate, with significant differences between the low and high aeration rates during weeks 2 and 3 of composting but no significant difference observed during week 1. At the end of our study, the final values of pH, EC, moisture content, C/N ratio, and organic matter in all compost reactors were lower than those at the start. The growth rates of mesophilic and thermophilic bacteria were directly correlated with mesophilic and thermophilic conditions of the compost. The final GI of the cylindrical reactor with an airflow rate of 0.3 L min^-1 kg^-1 DM was 82.3%, whereas the GIs of the other compost reactors were below 80%. In this study, compost of a cylindrical reactor with a low aeration rate (0.3 L min^-1 kg^-1 DM) was more stable and mature than the other reactors. Implications: The poultry industry is growing in South Korea, but there are problems associated with the management of poultry manure, and composting is one solution that could be valuable for crops and forage if managed properly. For high-quality composting, the aeration rate in different reactor shapes must be considered. The objective of this study was to investigate various physicochemical properties with different aeration rates and rector shapes. Results showed that aeration rate of 0.3 L min^-1 kg^-1 DM in a cylindrical reactor provides better condition for maturation of compost.

The Effect of Co-Additives (Biochar and FGD Gypsum) on Ammonia Volatilization during the Composting of Livestock Waste

The effectiveness of co-additives for improving livestock waste composting (reduction of air pollution and conservation of nutrients) was investigated. Biochar and Flue gas desulphurization gypsum (FGD gypsum) were used to supplement the composting of a mixture of slaughter waste, swine slurry, and sawdust. Different compositions of additives (0% or 5% each, 10% biochar or FGD gypsum) were tested in triplicate on the laboratory scale. In addition, the effects of two different aeration schemes (continuous and intermittent) were also investigated. Ammonia volatilization, physicochemical characteristics, and compost maturity indices were investigated. The results indicated that the use of the co-additive (Biochar and FGD gypsum) during composting of livestock waste led to a reduction of ammonia volatilization by 26–59% and to a 6.7–7.9-fold increase of nitrate accumulation. The total ammonia volatilization of intermittent aeration treatment was lower than that of continuous aeration using co-additives treatment. It was concluded that co-additives (biochar and FGD gypsum) might be utilized in livestock waste composting to reduce ammonia volatilization and improve nutrient conservation.

Assessment of co-composting process with high load of an inorganic industrial waste

This study aims to investigate the co-composting of an inorganic industrial waste (eggshell - ES) in very high levels (up to 60% w/w). Since composting is a process in which solid, liquid and gaseous phases interact in a very complex way, there is a need to shed light on statistical tools that can unravel the main relationships structuring the variability associated to this process. In this study, PCA and data visualisation were used with that purpose. The co-composting tests were designed with increasing quantities of ES (0, 10, 20, 30 and 60%ES w/w) mixed with industrial potato peel and rice husks. Principal component analysis showed that physical properties like free air space, bulk density and moisture are the most relevant variables for explaining the variability due to ES content. On the other hand, variability in time dynamics is mostly driven by some chemical and phytoxicological parameters, such as organic matter decay and nitrate content. Higher ES incorporation (60% ES) enhanced the initial biological activity of the mixture, but the higher bulk density and lower water holding capacity had a negative effect on the aerobic biological activity as the process evolved. Nevertheless, pathogen-killing temperatures (>70°C for 11h) were attained. All the final products obtained after 90days were stable and non-phytotoxic. This work proved that valorisation of high amounts of eggshell by co-composting is feasible, but prone to be influenced by the physical properties of the mixtures.

Influence of N-rich material in valorization of industrial eggshell by co-composting

Industrial eggshell (ES) is an animal by-product (ABP) involving some risk if not properly managed. Composting is a possible treatment approved for its safe use. This study aims to assess the influence of using N-rich material (grass clippings (GC)) to improve co-composting of ES mixtures for reaching sanitizing temperatures imposed by the ABP regulation from the European Union. Two sets of mixtures (M1 and M2) were investigated, each containing industrial potato peel waste, GC and rice husks at 3:1.9:1 and 3:0:1 ratios by wet weight. In each set, ES composition ranged from 0% to 30% (w/w). Co-composting trials were performed in self-heating reactors for 25 days, followed by maturation in piles. Results showed that only M1 trials attained temperatures higher than 70°C for nine consecutive hours, but N-losses by stripping on average were four- to five-fold higher than M2. In the absence of N-rich material, biodegradability of mixtures was 'low' to 'moderate' and organic matter conversion was impaired. Physical, chemical and phytotoxic properties of finished composts were suitable for soil improvement, but M1 took 54 more days to achieve maturity. In conclusion, co-composting ES with N-rich materials is important to assure the fulfilment of sanitizing requirements, avoiding any additional thermal treatment.

Composting of wastewater treatment sludge with different bulking agents

The main objectives of this study were to investigate the compostability of wastewater treatment sludge (WTS) containing different bulking agents (BAs) and to determine the most efficient BA. Four different compost trials consisting of mixtures of wheat straw (WS), plane leaf (PL), corncob (CC) and sunflower stalk (SS) with WTS were performed in laboratory reactors. In all experiments, a mixture of 60% WTS and 40% BA (wet basis) was used. The temperature, dry matter (DM), organic matter (OM), pH, electrical conductivity (EC) and C/N ratio were monitored during the composting process. Evaluation of the operational parameters showed that the highest organic matter degradation (i.e. 37.6%), loss of dry matter (i.e. 29.6%) and temperature (i.e. 64 °C) were achieved for the WTS-CC mixtures. Results also showed that the WTS-SS mixture was also successful in terms of these operational parameters. Use of bulking agents for the treatment of wastewater treatment sludge in composting process is an important issue with regards to process efficiency, economy and disposal of agricultural waste. Corncob and sunflower stalk that were previously not used for the composting of WTS from food industry were shown to be highly successful BA materials in this study.

IMPLICATIONS

The compostability of wastewater treatment sludge from the food industry with different bulking agents was studied. Wheat straw, plane leaf, corncob, and sunflower stalk were used as bulking agents. The required microbial stabilization and degree of mineralization were achieved with corncobs and sunflower stalks.

Turned windrow composting of cow manure as appropriate technology for zero discharge of mulberry pulp wastewater

Turned windrow composting was investigated as appropriate technology for recycling the wastewater (excluding black liquor) from mulberry pulp and paper handicrafts. Two exterior turned windrows (1.5 m width x 1.5 m height x 2.0 m length) with dry leaves/cow manure/sawdust wet weight ratios of 60:40:0 (Pile A) and 55:40:5 (Pile B) were used for the investigation. Changes in the physical and chemical properties of the compost were examined and a phytotoxicity analysis was performed. A soil incubation test and an informal focus group discussion were also conducted. The results revealed that while both piles met the regulatory processing requirements for further reduced pathogens (>or= 55 degrees C for 15 days or longer), the operation without sawdust (Pile A) not only significantly enhanced the thermophilic temperature regime (P < 0.05) but also yielded the highest amount (1.4 m3 ton-1 pile) of wastewater elimination during the first 2 months of composting. It was found that the constant rates of degradation were 0.006 day- 1 (Pile A) and 0.003 day-1 (Pile B), and no pronounced statistically significant difference in N losses was found (P > 0.05). The germination index of two plant species in both piles varied between 126% and 230% throughout the experiment, and no pronounced differences (P > 0.05) among the samples were found. Addition of the compost significantly improved soil organic matter and pH (7-8), as well as reduced the loss of NO3-N. Local discussion groups were initiated to evaluate the cost-benefits, the potential of wastewater removal, the cooperation of community users and supporters, the compost quality and the potential compost market.

Prediction of changes in important physical parameters during composting of separated animal slurry solid fractions

Solid-liquid separation of animal slurry, with solid fractions used for composting, has gained interest recently. However, efficient composting of separated animal slurry solid fractions (SSFs) requires a better understanding of the process dynamics in terms of important physical parameters and their interacting physical relationships in the composting matrix. Here we monitored moisture content, bulk density, particle density and air-filled porosity (AFP) during composting of SSF collected from four commercially available solid-liquid separators. Composting was performed in laboratory-scale reactors for 30 days (d) under forced aeration and measurements were conducted on the solid samples at the beginning of composting and at 10-d intervals during composting. The results suggest that differences in initial physical properties of SSF influence the development of compost maximum temperatures (40-70 degreeC). Depending on SSF, total wet mass and volume losses (expressed as % of initial value) were up to 37% and 34%, respectively. After 30 d of composting, relative losses of total solids varied from 17.9% to 21.7% and of volatile solids (VS) from 21.3% to 27.5%, depending on SSF. VS losses in all composts showed different dynamics as described by the first-order kinetic equation. The estimated component particle density of 1441 kg m-3 for VS and 2625 kg m-3 for fixed solids can be used to improve estimates of AFP for SSF within the range tested. The linear relationship between wet bulk density and AFP reported by previous researchers held true for SSF.

Experimental and modeling approaches for food waste composting: a review

Composting has been used as a method to dispose food waste (FW) and recycle organic matter to improve soil structure and fertility. Considering the significance of composting in FW treatment, many researchers have paid their attention on how to improve FW composting efficiency, reduce operating cost, and mitigate the associated environmental damage. This review focuses on the overall studies of FW composting, not only various parameters significantly affecting the processes and final results, but also a number of simulation approaches that are greatly instrumental in well understanding the process mechanism and/or results prediction. Implications of many key ingredients on FW composting performance are also discussed. Perspects of effective laboratory experiments and computer-based simulation are finally investigated, demonstrating many demanding areas for enhanced research efforts, which include the screening of multi-functional additives, volatile organiccompound emission control, necessity of modeling and post-modeling analysis, and usefulness of developing more conjunctive AI-based process control techniques.

Novel bulking agent from clay residue for food waste composting

New granular material from clay residue was investigated as a bulking agent for food waste composting. Five mixing ratios of granule were conducted in a laboratory scale reactor at the desired low rate of air (0.05 l min(-1)). The evolution of temperature and the accumulative CO(2) emissions were monitored. Physical and chemical changes, N loss, and organic matter degradation of compost were also examined. Adoption of granules of 15% V/V (FAS 31.6%) enhanced the thermophilic composting and CO(2) emissions; thus satisfying the Process to Further Reduce Pathogens (PFRP, USEPA) as well as obtaining the highest rate constant of organic matter degradation (k=0.005 day(-1)). As the amount of granules was doubled (35% V/V), the temperature was not only cooled, but also promoted the substantial N loss (54%). It was suggested that bulking agent from clay residue can be used beneficially as reusable media for microbial inoculation as analyzed by SEM.

The effect of aeration rate on forced-aeration composting of chicken manure and sawdust

The composting of chicken manure and sawdust has been investigated in forced-aeration composting systems at aeration rates of 0.3, 0.5, and 0.7 l min(-1)kg(-1) organic matter (OM), corresponding to pile A, pile B, and pile C. The temperature exceeding 55 degrees C in pile A and pile B remained more than three consecutive days, but only 2 days were above 55 degrees C in pile C. The final electrical conductivity (EC) did not exceed the limit content of 3000 micros cm(-1) in the three piles, and the cation exchange capacity (CEC) met the requirement maturity degree of over 60 c mol kg(-1). The OM loss contents in pile A, pile B, and pile C were 14%, 15.4%, and 12.8%, respectively, corresponding to the final C/N ratio of 17.1, 16.2, and 18.3. The final NH(4)(+)-N content in pile A did not meet the limit value of 400 mg kg(-1), respectively, and the NO(3)(-)-N was 1942, 2190, and 1638 mg kg(-1) in pile A, pile B, and pile C. The final germination index (GI) for pile A, pile B, and pile C was 90.2%, 95.2%, and 79.4%.