Microbial succession associated with organic matter decomposition during thermophilic composting of organic waste.

Using dog food as a model of the organic waste, thermophilic composting was carried out for 14 days at a fixed temperature of 60 degrees C. The relationship between organic matter decomposition measured by CO2 evolution during the bio-stabilization process and microbial succession expressed as the changes over time in the restriction fragment length polymorphism (RFLP) patterns of 16S rDNA sequences, of micro-organisms associated with the composting material was also examined. The CO2 evolution rate peaked on day 3 and gradually decreased until it became extremely small after day 9 of composting, indicating that vigorous organic matter decomposition ceased around this time. On the other hand, the RFLP pattern changed drastically from day 0 to day 4 or 5, then remained stable until day 7 or 8, reaching its final configuration, with little variations, after day 9 of composting. RFLP analysis therefore indicates that microbial succession continued into the later stage of composting. Nevertheless, by day 9, the rate of organic matter decomposition was so low that its influence on microbial populations could be hardly recognized by conventional methods of dilution plating. Moreover, the compost produced by day 9 showed no inhibitory effect on the growth of Komatsuna (Brassica campestris L. var. rapiferafroug), indicating that the maturity of compost is sufficient for plant growth when the rate of organic matter decomposition has become extremely low and the RFLP patterns become stable.     

A novel model of organic waste composting in Taiwan military community

The relatively large quantities of waste generated daily in military barracks pose a significant impact on environments in this small island of Taiwan due to limited land and crowded populations. In order to find a suitable handling method to the barracks' characteristics in Taiwan, a comprehensive selection model for various barracks carrying out waste composting was established through personal interviews and questionnaire data analyses on the military barracks. From this, the basic data for this research was also built, to evaluate the experiences and management practices in these facilities. This study found that environmental responsibility and expertise are the primary concerns and considerations among all of the military units when doing waste composting. Support of the commander, organizational image and human resource/facilities are also concerns. To offer the military barracks a selection model and policy guidelines for the waste composting treatment, an itemized score evaluation standard and a selecting chart of composting recycling methods were designed by combining the practical experimental results with economic considerations, waste classification, and Delphi expert technique.     

Mass balances and life cycle inventory of home composting of organic waste

A comprehensive experimental setup with six single-family home composting units was monitored during 1 year. The composting units were fed with 2.6-3.5 kg organic household waste (OHW) per unit per week. All relevant consumptions and emissions of environmental relevance were addressed and a full life-cycle inventory (LCI) was established for the six home composting units. No water, electricity or fuel was used during composting, so the major environmental burdens were gaseous emissions to air and emissions via leachate. The loss of carbon (C) during composting was 63-77% in the six composting units. The carbon dioxide (CO(2)) and methane (CH(4)) emissions made up 51-95% and 0.3-3.9% respectively of the lost C. The total loss of nitrogen (N) during composting was 51-68% and the nitrous oxide (N(2)O) made up 2.8-6.3% of this loss. The NH(3) losses were very uncertain but small. The amount of leachate was 130 L Mg(-1) wet waste (ww) and the composition was similar to other leachate compositions from home composting (and centralised composting) reported in literature. The loss of heavy metals via leachate was negligible and the loss of C and N via leachate was very low (0.3-0.6% of the total loss of C and 1.3-3.0% of the total emitted N). Also the compost composition was within the typical ranges reported previously for home composting. The level of heavy metals in the compost produced was below all threshold values and the compost was thus suitable for use in private gardens.     

Modelling of organic matter dynamics during the composting process

Composting urban organic wastes enables the recycling of their organic fraction in agriculture. The objective of this new composting model was to gain a clearer understanding of the dynamics of organic fractions during composting and to predict the final quality of composts. Organic matter was split into different compartments according to its degradability. The nature and size of these compartments were studied using a biochemical fractionation method. The evolution of each compartment and the microbial biomass were simulated, as was the total organic carbon loss corresponding to organic carbon mineralisation into CO₂. Twelve composting experiments from different feedstocks were used to calibrate and validate our model. We obtained a unique set of estimated parameters. Good agreement was achieved between the simulated and experimental results that described the evolution of different organic fractions, with the exception of some compost because of a poor simulation of the cellulosic and soluble pools. The degradation rate of the cellulosic fraction appeared to be highly variable and dependent on the origin of the feedstocks. The initial soluble fraction could contain some degradable and recalcitrant elements that are not easily accessible experimentally.     

Environmental impact of organic fraction of municipal solid waste treatment by composting in Sri Lanka

Journal of Material Cycles and Waste Management - In Sri Lanka, the management of the organic fraction of municipal solid waste (OFMSW) is a challenge. Composting is an environmentally and...     

Study of the organic matter evolution during municipal solid waste composting aimed at identifying suitable parameters for the evaluation of compost maturity

In this work the composting process of municipal solid wastes was studied in order to characterize the transformations of organic matter, particularly humic acid (HA). A composting process, lasting three months, was monitored by chemical methods; the following parameters were measured: water-soluble carbon concentration (WSC) and humic substances content (humic and fulvic acid (FA)). The effects of humification on the molecular structure of humic acid (HA) were also evaluated by Fourier transform infrared (FT-IR) and (13)C NMR spectroscopy. WSC concentration rapidly increased reaching a maximum at day-14 of the composting process and then declined. The humic and fulvic acid content (HA and FA, respectively) slightly increased during the process. The FT-IR and (13)C NMR spectra of HA indicate a high rate of change in structure during composting. The groups containing aromatic and carboxylic C increased, while polysaccharides and other aliphatic structures degraded during composting, resulting in HA structures of higher aromaticity. Therefore, spectrometric measurements could provide information significantly correlated to conventional chemical parameters of compost maturity.     

Fuzzy control for the process of heat removal during the composting of agricultural waste

This paper shows the concept and preliminary test of the composting process control with fuzzy logic. The temperature in the compost heap during the process is greater than 80 °C. Because wastes of agricultural origin do not require hygienization, part of the heat can by retrieved, which lowers the temperature in the heap to 55 °C (this is also the optimum temperature for the composting process). The heat retrieved from a compost heap can be used in another place. Therefore, a composting system was developed in which the aeration rate and heat removal rate can be adjusted. There are two goals of this system: maximising the amount of the heat retrieved from the heap and minimising the duration of the composting process. In the preliminary experiments freshly mown grass with 50 % cabbage was used as the compost material. The results show that the fuzzy logic control system functions correctly with respect to calculations. During the study, a median 90 MJ of heat was produced by the bioreactor; the thermophilic phase was shortened to 12 days. There was also a reduction in the emission of ammonia.     

Emission of volatile sulfur compounds during composting of municipal solid waste (MSW)

Volatile sulfur compounds (VSCs) are the main source for malodor from composting plants. In this study, the VSCs generated from composting of 15–80 mm municipal solid waste (T0), kitchen waste (T1) and kitchen waste mixed dry cornstalks (T2) were measured in 60 L reactors with forced aeration for a period of 30 days. The VSCs detected in all treatments were hydrogen sulfide (H₂S), methyl mercaptan (MM), dimethyl sulfide (DMS), carbon bisulfide (CS₂) and dimethyl disulfide (DMDS). Over 90% of the VSCs emissions occurred during the first 15 days, and reached their peak values at days 4–7. The emission profiles of five VSCs species were significantly correlated with internal materials temperature and outlet O₂ concentration (p < 0.05). Total emissions of the VSCs were 216.1, 379.3 and 126.0 mg kg^?1 (dry matter) for T0, T1 and T2, respectively. Among the five VSCs, H₂S was the most abundant compound with 39.0–43.0% of total VSCs released. Composting of kitchen waste from separate collection posed a negative influence on the VSC and leachate production because of its high moisture content. An addition of dry cornstalks at a mixing ratio of 4:1 (wet weight) could significantly reduce the VSCs emissions and avoid leachate. Compared to pure kitchen waste, VSCs were reduced 66.8%.     

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.     

Comparison of mass balance, energy consumption and cost of composting facilities for different types of organic waste

Mass balance, energy consumption and cost are basic pieces of information necessary for selecting a waste management technology. In this study, composting facilities that treat different types of organic waste were studied by questionnaire survey and via a chemical analysis of material collected at the facilities.The mass balance was calculated on a dry weight basis because the moisture content of organic waste was very high. Even though the ratio of bulking material to total input varied in the range 0-65% on a dry basis, the carbon and ash content, carbon/nitrogen ratio, heavy metal content and inorganic nutrients in the compost were clearly influenced by the different characteristics of the input waste. The use of bulking material was not correlated with ash or elemental content in the compost. The operating costs were categorised into two groups. There was some economy of scale for wages and maintenance cost, but the costs for electricity and fuel were proportional to the amount of waste. Differences in operating costs can be explained by differences in the process characteristics.     

Performance of compostable baby used diapers in the composting process with the organic fraction of municipal solid waste

In modern societies, disposable diapers constitute a significant percentage of municipal solid wastes. They have been traditionally landfilled or incinerated as only limited recycling processes are being implemented in some parts of Europe. With the implementation of separated collection systems for the organic fraction of municipal solid wastes (OFMSWs) and the need to preserve the environment, compostable diapers have appeared in the market to avoid the main environmental impacts associated to non-biodegradable disposable diapers. In this study, a full-scale composting of door-to-door collected OFMSW with a 3% (w/w) of compostable diapers has also been carried out. Previously, lab-scale experiments confirmed that almost 50% of carbon of compostable diapers is emitted as CO₂ under aerobic controlled conditions. The results obtained at full-scale demonstrate that both the composting process and the final end product (compost) are not altered by the presence of compostable diapers in crucial aspects such as pathogenic content, stability and elemental composition (including nutrients and heavy metals). The main conclusion of this study is that the collection of the OFMSW with compostable diapers can be a new way to transform this waste into high-quality compost.     

Hydrolysis of organic matter during autoclaving of commingled household waste

Commingled household waste (HW) that had a controlled composition was autoclaved at elevated pressures in the presence of saturated steam for one hour at the nominal temperature levels of 130 °C, 160 °C and 200 °C. The focus of this study was the impact of temperature/pressure on hydrolysis of organic matter during autoclaving and the extent of its hydrolysis. The pH decreased with autoclaving temperature with which it had a linear relationship, and ranged from 7.4 and 6 in floc, and 6.7 and 3.6 in steam condensate. Overall, organic matter solubilisation, as indicated by dissolved organic carbon, biological and chemical oxygen demands, and total dissolved solids, increased with temperature. Lignin did not appear to hydrolyse. Hemicellulose hydrolysed and degraded the most, followed by cellulose. The highest recoveries of hemicellulose and cellulose in solution were achieved at 160 °C, although the latter could be due to experimental error. The largest losses of hemicellulose and cellulose were recorded at 200 °C. The performance of the system in respect to hydrolysis was inferior compared to other hydrothermal systems, particularly those employing wet oxidation.     

Cost effective waste management through composting in Africa

Greenhouse gas (GHG) emissions per person from urban waste management activities are greater in sub-Saharan African countries than in other developing countries, and are increasing as the population becomes more urbanised. Waste from urban areas across Africa is essentially dumped on the ground and there is little control over the resulting gas emissions. The clean development mechanism (CDM), from the 1997 Kyoto Protocol has been the vehicle to initiate projects to control GHG emissions in Africa. However, very few of these projects have been implemented and properly registered. A much more efficient and cost effective way to control GHG emissions from waste is to stabilise the waste via composting and to use the composted material as a soil improver/organic fertiliser or as a component of growing media. Compost can be produced by open windrow or in-vessel composting plants. This paper shows that passively aerated open windrows constitute an appropriate low-cost option for African countries. However, to provide an usable compost material it is recommended that waste is processed through a materials recovery facility (MRF) before being composted. The paper demonstrates that material and biological treatment (MBT) are viable in Africa where they are funded, e.g. CDM. However, they are unlikely to be instigated unless there is a replacement to the Kyoto Protocol, which ceases for Registration in December 2012.     

Effectiveness of three bulking agents for food waste composting

Rather than landfilling, composting the organic fraction of municipal solid wastes recycles the waste as a safe and nutrient enriched soil amendment, reduces emissions of greenhouse gases and generates less leachate. The objective of this project was to investigate the composting effectiveness of three bulking agents, namely chopped wheat (Triticum) straw, chopped mature hay consisting of 80% timothy (milium) and 20% clover (triphullum) and pine (pinus) wood shavings. These bulking agents were each mixed in duplicates at three different ratios with food waste (FW) and composted for 10 days using prototype in-vessel composters to observe their temperature and pH trends. Then, each mixture was matured in vertical barrels for 56 days to measure their mass loss and final nutrient content and to visually evaluate their level of decomposition. Chopped wheat straw (CWS) and chopped hay (CH) were the only two formulas that reached thermophilic temperatures during the 10 days of active composting when mixed with FW at a wet mass ratio of 8.9 and 8.6:1 (FW:CWS and FW:CH), respectively. After 56 days of maturation, these two formulas were well decomposed with no or very few recognizable substrate particles, and offered a final TN exceeding the original. Wood shavings (WS) produced the least decomposed compost at maturation, with wood particles still visible in the final product, and with a TN lower than the initial. Nevertheless, all bulking agents produced compost with an organic matter, TN, TP and TK content suitable for use as soil amendment.     

Characterization of food waste and bulking agents for composting

The characterization of food waste (FW) and locally available bulking agents (BA) are a prerequisite to optimizing compost recipes. This study measured the variation in FW characteristics (pH, dry matter (DM), carbon (C), wet bulk density and Total Kjeldahl Nitrogen (TKN)) produced by a restaurant and a community kitchen in downtown Montreal, Canada from May to August 2004. The project also measured the mass of FW produced by another restaurant and a group of 20-48 households, from June to August 2004. Locally available BA (hay, straw, pine wood shavings, cardboard, left over cattle feed and wheat residue pellets) were also characterized to formulate composting recipes based on the FW characteristics observed during a period representative of winter and summer conditions. Residential and restaurant FW characteristics varied significantly over the summer months, although the mass produced remained constant at 0.61 and 0.56 kg capita(-1)day(-1), respectively. In addition, the number of customers served by the restaurant increased by nearly 50% from June to August. The BA with the highest moisture adsorption capacity was found to be the wheat residue pellets, followed by chopped straw. Wheat residue pellets, chopped hay and left over cattle feed all presented a balanced C/N ratio. Wheat residue pellets and wheat straw, chopped hay and cardboard demonstrated neutral pH values. Based on the variable FW characteristics and monthly production rates, the formulation of recipes indicates that compost facilities must be flexible enough to handle seasonal variations of as much as 50% by volume.     

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.     

A kinetic analysis of solid waste composting at optimal conditions

This discussion explores the possibility of having a measure of the biodegradable organic carbon content in solid wastes. Currently, indirect measures for determining the concentration of biodegradable organic matter are being used and most of them are based on respiration indices (oxygen consumption or carbon dioxide production) or chemical parameters (volatile solids or total organic carbon). The results obtained for the cumulative carbon dioxide production in composting experiments can be expressed as "aerobic biodegradable carbon" for the wastes that were studied. The calculation of a useful biodegradable C/N can also be obtained from the aerobic biodegradable carbon content. A comparison with some results obtained in measuring the concentration of "anaerobic biodegradable carbon" also is presented.     

Selective organic compounds degradation under controlling composting conditions

Organic matter stabilization resulted from the decrease of cellulose, xylan, arabinan, acetyl groups, glucuronic acids, galacturonic acids (easily biodegradable fractions) and the increase of lignin (resistant compound) and humic substances coming from the initial wastes have been studied. A central composite experimental design was used to investigate the influence of environmental composting parameters (moisture, aeration and particle size) on organic matter evolution. The organic matter evolution was clearly influenced by the studied composting parameters. All results were concordant, with an increase of humic substances and lignin and a decrease of the rest of the cellulose and hemicellulose compounds. Lower cellulose, xylan, acetyl groups and glucuronic acids contents (higher degradation) have been observed under low particle size (1 cm) and higher moisture content (70%). However lower lignin and higher humic substances under medium (3 cm) to low particle size and low moisture content (40%) have been found.     

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

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