Effect of the composting substrate on biodegradation of solid materials under controlled composting conditions

Biodegradability under composting conditions is assessed by test methods, such as ASTM D 5338-92, based on the measurement of CO₂ released by test materials when mixed with mature compost and maintained in a controlled composting environment. However, in real composting, biodegradation occurs in fresh waste. To clarify this point, the biodegradation of paper and of a starch-based biodegradable thermoplastic material, Mater-Bi ZI01U, was followed by measuring the weight loss of samples introduced either into a mature compost or into a synthetic waste. The weight loss in mature compost was higher at the beginning but tended to decrease; in synthetic waste a first lag phase was followed by an exponential phase. Complete degradation of paper was noticed simultaneously in the two substrates (after 25 days). The bulkier Mater-Bi samples were fully degraded after 20 days in fresh waste, but after 45 days in mature compost. Therefore, the test methods using mature compost as a substrate can possibly underestimate the biodegradation rate occurring in fresh waste, i.e., in real composting plants, and have to be considered as conservative test methods. The test procedure described in this paper seems very suitable as a screening method to verify the compostability of plastic materials in a composting environment.     

Study on the quality and stability of compost through a Demo Compost Plant

This study is concerned with the performance of a Demo Compost Plant for the development of acceptable composting technology in Bangladesh. The Demo Compost Plant was setup at the adjacent area of an existing compost plant located at Khulna city in Bangladesh. Four different composting technologies were considered, where Municipal Solid Waste (MSW) were used as a raw material for composting, collected from the adjacent areas of the plant. Initially the whole composting system was conducted through two experimental setups. In the 1st setup three different types of aerators (horizontal and vertical passively aerator and forced aerator) were selected. For a necessary observation four piles, using only MSW as the input materials in the first three compost pile, the fourth one was the existing Samadhan’s compost pile. Based on the analysis of the experimental findings, the horizontal passively aerated composting technique is suitable for Bangladesh as it had better performance for reducing composting period than that of the others. It was being observed from the quality parameters of compost in the both 1st and 2nd setup that as the waste directly come from kitchen, degradation rate of waste shows a positive result for reducing this waste and there is no possibility of toxic contamination, when it would be used as a soil conditioner. Though there is no significant improvement in the quality of the final product in the 2nd setup as comparing with the 1st setup but it fulfills one of the main objectives of this study is to reduce the whole composting period as well as immediate management of the increasing amount of waste and reducing load on landfill. Selfheating tests reveal that degree of stability of compost with respect to maturation period was remained in the acceptable level, which was further accelerated due to the use of organic additives.     

Changes in the microbial communities during co-composting of digestates

Anaerobic digestion is a waste treatment method which is of increasing interest worldwide. At the end of the process, a digestate remains, which can gain added value by being composted. A study was conducted in order to investigate microbial community dynamics during the composting process of a mixture of anaerobic digestate (derived from the anaerobic digestion of municipal food waste), green wastes and a screened compost (green waste/kitchen waste compost), using the COMPOCHIP microarray. The composting process showed a typical temperature development, and the highest degradation rates occurred during the first 14 days of composting, as seen from the elevated CO₂ content in the exhaust air. With an exception of elevated nitrite and nitrate levels in the day 34 samples, physical–chemical parameters for all compost samples collected during the 63 day process indicated typical composting conditions. The microbial communities changed over the 63 days of composting. According to principal component analysis of the COMPOCHIP microarray results, compost samples from the start of the experiment were found to cluster most closely with the digestate and screened compost samples. The green waste samples were found to group separately. All starting materials investigated were found to yield fewer and lower signals when compared to the samples collected during the composting experiment.     

Effect of vermiculite addition on compost produced from Korean food wastes

To evaluate the effect of vermiculite addition on composting food wastes from Korean households, food wastes were composted in three small bins to which different additives were added. The following three bins were employed: in Case I, only recycled compost was composted; in Case II, food wastes with recycled compost; and in Case III, food wastes with recycled compost and vermiculite. In the experiment performed for 30 days, it was confirmed that the supplementary addition of vermiculite to the composting mixture did not significantly improve the weight loss rate and the decomposition rate of food wastes. Due to dilution through the use of inorganic vermiculite, the vermiculite addition reduced the organic matter concentration of the composting mixtures. Vermiculite addition did not raise the pH value. Weight losses of roughly 70% were observed based on calculating moisture loss as well as dry food waste loss and not considering additives, while dry food waste loss was 29.4% and 35.8% with and without the addition of vermiculite, respectively. For these experiments, the major portion of the weight loss was the loss of water. The results indicate a need to differentiate between weight loss percentages and decomposition percentages, and a need to indicate if either of these percentages includes or excludes the mass of additives.     

Aerobic composting of waste activated sludge: kinetic analysis for microbiological reaction and oxygen consumption

In order to examine the optimal design and operating parameters, kinetics for microbiological reaction and oxygen consumption in composting of waste activated sludge were quantitatively examined. A series of experiments was conducted to discuss the optimal operating parameters for aerobic composting of waste activated sludge obtained from Kawagoe City Wastewater Treatment Plant (Saitama, Japan) using 4 and 20 L laboratory scale bioreactors. Aeration rate, compositions of compost mixture and height of compost pile were investigated as main design and operating parameters. The optimal aerobic composting of waste activated sludge was found at the aeration rate of 2.0 L/min/kg (initial composting mixture dry weight). A compost pile up to 0.5 m could be operated effectively. A simple model for composting of waste activated sludge in a composting reactor was developed by assuming that a solid phase of compost mixture is well mixed and the kinetics for microbiological reaction is represented by a Monod-type equation. The model predictions could fit the experimental data for decomposition of waste activated sludge with an average deviation of 2.14%. Oxygen consumption during composting was also examined using a simplified model in which the oxygen consumption was represented by a Monod-type equation and the axial distribution of oxygen concentration in the composting pile was described by a plug-flow model. The predictions could satisfactorily simulate the experiment results for the average maximum oxygen consumption rate during aerobic composting with an average deviation of 7.4%.     

Degradation of Starch–Calcium Carbonate Disposable Packaging in a Solid Waste Composting Facility

The compostability of starch–CaCO₃ disposable packaging was examined in a source-separated municipal solid waste (MSW) composting facility located in East Hampton, NY. Source-separated MSW:starch–CaCO₃ container mixtures of 0 (control), 5, and 20% (by volume) were prepared as feedstock for composting. Compost samples were collected weekly or biweekly during the composting process and examined for fragments of the starch–CaCO₃ containers. Changes in compost quality due to the presence of starch–CaCO₃ containers were assessed by measuring the nutrient and metal content of the three resultant MSW:starch–CaCO₃ composts. Finally, plant growth studies were conducted to examine the composts for possible plant growth inhibition due to the deterioration of the starch–CaCO₃ containers. Results showed that portions of the starch–CaCO₃ containers were not identified in any of the 5 and 20% sieved and characterized compost fractions > 1.3 cm following 1–3 weeks of composting. Mechanical agitation of the waste along with optimum composting conditions were sufficient to initiate the rapid degradation of the starch–CaCO₃ composites. Degradation of starch–CaCO₃ containers did not affect compost nutrient and trace element content. Grass biomass measurements were performed once weekly over 28 days for grass grown in control (0%), 5%, and 20% starch–CaCO₃-containing compost:soil mixtures. Significant differences in grass biomass for these compost:soil mixtures were measured only for the 0 and 20% starch–CaCO₃-containing compost:soil mixtures at 28 days (9.07 vs 11.05 g, respectively; P = 0.046).     

Composting of waste algae: A review

Although composting has been successfully used at pilot scale to manage waste algae removed from eutrophied water environments and the compost product applied as a fertiliser, clear guidelines are not available for full scale algae composting. The review reports on the application of composting to stabilize waste algae, which to date has mainly been macro-algae, and identifies the peculiarities of algae as a composting feedstock, these being: relatively low carbon to nitrogen (C/N) ratio, which can result in nitrogen loss as NH₃ and even N₂O; high moisture content and low porosity, which together make aeration challenging; potentially high salinity, which can have adverse consequence for composting; and potentially have high metals and toxin content, which can affect application of the product as a fertiliser. To overcome the challenges that these peculiarities impose co-compost materials can be employed.     

Recycling of waste biomass and mineral powder for preparation of potassium-enriched compost

An attempt was made to recycle waste biomass and mineral powder (waste mica) as an alternative source of potassium (K) through composting technology. Two different waste biomass, isabgol straw and palmarosa distillation waste along with two levels of waste mica (2 and 4% as K) were used for preparation of enriched composts. A notable decrease of C:N ratio was observed at the end of the composting (150 days) as an indicator of compost maturity. The mature composts were evaluated for K-supplying capacity through laboratory leaching and soil incubation study. Significantly higher water-soluble K released initially followed by a sharp decrease up to 21 days of leaching thereafter gradually decreased up to 35 days of leaching. Water-soluble K was released from K-enriched (mica charged) compost significantly higher than the ordinary compost throughout the leaching period. Soil incubation study also revealed that application of K-enriched compost greatly improved the available K (water soluble and exchangeable) pools in K-deficient soil which indicated that a considerable amount of K releases during composting. Therefore, K-enriched compost could be an effective alternative of costly commercial K fertilizer and eco-friendly approach to utilize low-cost waste mineral powder and plant residue.     

Effect of the mixing ratio on the composting of OFMSW digestate: assessment of compost quality

This study presents the results obtained in compostability tests of organic fraction of municipal solid waste (OFMSW) digestate. The final aim was to obtain mature compost without phytotoxic effects. For the evaluation of the composting process, a novel parameter describing the performance of the composting process, the relative heat generation standardized with the initial volatile solid content (RHGVS₀), was defined and evaluated at laboratory-scale. From these laboratory-scale test, the optimum operational conditions were obtained, a mixing ratio (v/v) of 1:1:0 (bulking agent:digestate:co-substrate) and with 15% of mature compost as inoculum. Subsequently, these optimum operational conditions were applied in the active phase of the composting pilot-scale reactor. The active composting stage took 7 days, subsequently a curing phase of 60 days was carried out at ambient conditions. After 30 days of curing, the mature compost showed a specific oxygen uptake rate (SOUR) of 0.14 mg O₂/g VS·h, a germination index (GI) of 99.63% and a low volatile fatty acids (VFA) concentration (41.3 AcH mg/kg_dm), being indicative of the good compost stability and maturity of the compost. The very good quality of the final compost obtained indicated that the RHGVS₀ accurately describes the performance of the composting process.

     

Mass and element balance in food waste composting facilities

The mass and element balance in municipal solid waste composting facilities that handle food waste was studied. Material samples from the facilities were analyzed for moisture, ash, carbon, nitrogen, and the oxygen consumption of compost and bulking material was determined.Three different processes were used in the food waste composting facilities: standard in-vessel composting, drying, and stand-alone composting machine. Satisfactory results were obtained for the input/output ash balance despite several assumptions made concerning the quantities involved. The carbon/nitrogen ratio and oxygen consumption values for compost derived only from food waste were estimated by excluding the contribution of the bulking material remaining in the compost product. These estimates seemed to be suitable indices for the biological stability of compost because there was a good correlation between them, and because the values seemed logical given the operating conditions at the facilities.     

Open windrow composting of polymers: an investigation into the operational issues of composting polyethylene (PE)

This paper investigates the operational issues surrounding the open windrow composting of degradable polyethylene sacks. Areas for consideration were the impact of degradable polyethylene sacks on the composting process, the quality of the finished compost product, and how the use of sacks influenced the on-site processing. These factors were investigated through determining the amount of polymer residue and chemical contaminants in the finished compost product and the daily monitoring of windrow temperature profiles. Site and practical handling considerations of accepting an organic waste contained within PE sacks are also discussed. Statistical analysis of the windrow temperature profiles has led to the development of a model that can help to predict the expected trends in the temperature profiles of open compost windrows where the organic waste is kerbside collected using a degradable PE sack.     

Composting clam processing wastes in a laboratory- and pilot-scale in-vessel system

Waste materials from the clam processing industry (offal, shells) have several special characteristics such as a high salinity level, a high nitrogen content, and a low C/N ratio. The traditional disposal of clam waste through landfilling is facing the challenges of limited land available, increasing tipping fees, and strict environmental and regulatory scrutiny. The aim of this work is to investigate the performance of in-vessel composting as an alternative for landfill application of these materials. Experiments were performed in both laboratory-scale (5L) and pilot-scale (120L) reactors, with woodchips as the bulking agent. In the laboratory-scale composting test, the clam waste and woodchips were mixed in ratios from 1:0.5 to 1:3 (w/w, wet weight). The high ratios resulted in a better temperature performance, a higher electrical conductivity, and a higher ash content than the low-ratio composting. The C/N ratio of the composts was in the range of 9:1-18:1. In the pilot-scale composting test, a 1:1 ratio of clam waste to woodchips was used. The temperature profile during the composting process met the US Environmental Protection Agency sanitary requirement. The final cured compost had a C/N ratio of 14.6, with an ash content of 167.0+/-14.1g/kg dry matter. In addition to the major nutrients (carbon, nitrogen, calcium, magnesium, phosphorus, potassium, sulfur, and sodium), the compost also contained trace amounts of zinc, manganese, copper, and boron, indicating that the material can be used as a good resource for plant nutrients.     

Kinetic Study Of The Composting Of Evergreen Oak Forestry Waste

The successive stages in the composting process of forestry waste from evergreen oak (Quercus ilx sbsp. ballota) were studied under controlled conditions (initial) carbon to nitrogen ratio = 30, T = 27°C). The original material was composted for 6 months and sampled every 15 days. The variables measured on the oak biomass in the course of the experiment showed different kinetics: the weight loss and germination index underwent a monotonic increase whereas the reducing sugars, phenols and E₄₆₅/E₆₆₅ extinction ratio of the water-soluble fraction stabilized at their lowest values after the first 2 weeks. Other variables, such as alkali solubility, water repellency, pH and particle size, showed maximum or minimum values at intermediate stages of the experiment. In contrast to the adverse agrobiological effects of the direct application to soil of the original waste, germination biotests and greenhouse experiments showed that plant response improved from the 2 first weeks of composting. The kinetics observed for the parameters studied suggested that the less favourable effect on plant yield may come from phytotoxic substances in compost but also from the microbial use of soil N required for the transformation of the most biodegradable compost fractions in special hemicelluloses.     

Composting in small laboratory pilots: performance and reproducibility

Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed the performance of composting considering the transformations of organic matter. Moreover, composting at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and the reproducibility of composting has rarely been reported. The objectives of this study are to design an innovative small-scale composting device safeguarding self-heating to drive the composting process and to assess the performance and reproducibility of composting in small-scale pilots. The experimental setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The performance of the process was assessed by monitoring the temperature, O₂ consumption and CO₂ emissions, and characterising the biochemical evolution of organic matter. A good reproducibility was found for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments, excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility of the process and the quality of the final compost make it possible to propose the use of this experimental device for research requiring a mass reduction of the initial composted waste mixtures.     

Proposal for the integration of decentralised composting of the organic fraction of municipal solid waste into the waste management system of Cuba

Municipal solid waste (MSW) generation and management in Cuba was studied with a view to integrating composting of the organic fractions of MSW into the system. Composting is already included as part of the environmental strategy of the country as an appropriate waste management solution. However, no programme for area-wide implementation yet exists. The evaluation of studies carried out by some Cuban and international organisations showed that organic matter comprises approximately 60-70% of the MSW, with households being the main source. If all organic waste fractions were considered, the theoretical amount of organic waste produced would be approximately 1 Mio. Mg/a, leading to the production of approximately 0.5 Mio. Mg/a of compost. Composting could, therefore, be a suitable solution for treating the organic waste fractions of the MSW. Composting would best be carried out in decentralised systems, since transportation is a problem in Cuba. Furthermore, low technology and low budget composting options should be considered due to the problematic local economic situation. The location for such decentralised composting units would optimally be located at urban agricultural farms, which can be found all over Cuba. These farms are a unique model for sustainable farming in the world, and have a high demand for organic fertiliser. In this paper, options for the collection and impurity-separation in urban areas are discussed, and a stepwise introduction of source-separation, starting with hotel and restaurant waste, is suggested. For rural areas, the implementation of home composting is recommended.     

Change of the chemical composition and biodegradability of the Van Soest soluble fraction during composting: A study using a novel extraction method

Van Soest fractionation is widely employed to characterize exogenous organic matter. The soluble fraction of Van Soest fractionation (SOL, extracted using hot water and then neutral detergent) often increases in line with compost maturity, although it is generally considered as labile. We have developed an alternative extraction method that comprises four successive steps (extraction using hot water, sodium tetraborate, dichloromethane/methanol and chelating resin) in order to clarify the chemical nature of the SOL fraction and explain its biodegradability. This method was tested on municipal solid waste compost sampled during the thermophilic phase (MSWi) and after 8 months of composting (MSWm). Both methods extracted similar proportions of organic matter. The composition of the residues was similar in MSWm although differences were noted for the extraction of polysaccharides and lipids in the case of MSWi. The hot water extractable fraction decreased during composting. Its high biodegradability in MSWi was linked to the high polysaccharide content revealed by pyrolysis–GC/MS and FTIR spectroscopy. The increase in the sodium tetraborate extractable fraction mainly explained the increase in the SOL fraction during composting. This was made up of N-containing compounds, polysaccharides and lipids in the immature compost, and a majority of N-containing compounds in the mature compost. During composting, the stabilization of organic matter in the SOL fraction extractable by sodium tetraborate and EDTA might principally involve N-containing structures through the formation of complexes of organic matter with metal ions, especially Ca²⁺, which may be broken down during extraction of the Van Soest soluble fraction. These mechanisms still need to be investigated.     

Biodegradation of paper waste under controlled composting conditions

The presence of paper in municipal solid waste (MSW) interferes with the efficiency of composting plants. The compost feedstock to these plants is between 12% and 27% paper on a dry weight basis, with an initial C:N ratio ranging from 32:1 to 57:1. Tests of the last aerobic biodegradability (LAB) of the type of paper present in paper and cardboard packaging were carried out, following UNE-EN 14046 standards. The results obtained, measured through the quantity of CO₂ generated over 45 days, compared with the maximum that could be produced (ThCO₂), showed that the presence of paper retards, to a great degree, the biodegradation of organic material in general. Specifically, the presence of papers with a degradation D (%) >60% at 45 days (white (W) and recycled paper (R)) could be allowed, but always in proportions that did not exceed 27% in dry weight. These results can be achieved with an industrial level process, pre-treated by trituration.     

CIELAB color variables as indicators of compost stability

The composting process of different organic wastes both in laboratory and on a large-scale was characterized using CIELAB color variables to evaluate compost stability for the better application in agriculture. The time courses of the CIELAB variables of composting materials were determined directly from the bottom of a glass petri dish filled with dried and ground samples using a Minolta Color Reader (CR-13) calibrated with clean empty petri dishes placed on a white tile. To compare the proposed method with conventional methods, the same materials were also evaluated using commonly used compost stability evaluation indices. Most of the CIELAB variables of a compost made from a mixture of green tea waste and rice bran reached a plateau after 84 days of composting and showed strong relationships with the commonly used compost stability evaluation indices. The time needed for CIELAB variables, especially the L*and b* values, to stabilize at large-scale composting plants of cattle litter, farmyard manure, kitchen garbage and bark compost, were more or less similar to the times of maturation evaluated by the respective compost producers. The CIELAB color variable offers a new, simple, rapid and inexpensive means of evaluating compost stability and its quality prior to agricultural use.     

Questionnaire and onsite survey on municipal solid waste composting in Sri Lanka

This study was conducted to evaluate the composting processes in Sri Lanka and to identify essential improvements. The study consisted of a questionnaire survey, field observations, and interviews. The main shortcomings identified by this study were: no source separation at origin, and no monitoring for temperature, moisture, stability, or maturity during processes of composting. These problems hinder the smooth operation of the composting processes and lead to low demand for compost. Based on the findings, the recommendations for increasing the demand for compost are performing source separation during waste collections, improvement of processes by monitoring the temperature and moisture, and marketing compost so as to improve the popularity of the compost among farmers.     

Investigation and optimization of composting processes-test systems and practical examples

To determine the optimal course of composting it is useful to carry out experiments. The selection of the right experimental set-up depends on the question of concern. Each set-up is useful for a particular application and has its limits. Two test systems of different scales (up to 1500 ml; up to 100 l) are introduced. The purpose and importance of each system design shall be highlighted by application examples: (1). Suitability of a liquid industrial residue as composting accelerator; (2). Determination of the compost maturity; (3). Behaviour of odor-reducing additives during waste collection and composting; (4). Production of tailor-made compost with respect to Nitrogen (5). Suitability of O(2)-enriched air for acceleration of composting. Small-scale respiration experiments are useful to optimize parameters which have to be adjusted during substrate pre-treatment and composting, with the exception of particle size and temperature, and to reduce the number of variants which have to be investigated in greater detail in larger scale experiments. As all regulation possibilities such as aeration, moistening, turning can be simulated with the technical scale set-up, their complex cooperation can be taken into consideration. Encouraging composting variants can be tested, compared and optimized.