Microbial biomass in a soil amended with different types of organic wastes.

Application of different types of organic wastes may have a marked effect on soil microbial biomass and its activity. The objective of this study was to quantify the amount of microbial biomass in a loamy-clayey soil, amended with different types of organic waste residues (composts of municipal solid waste of different ages, sewage sludge and farmyard manure) and incubated for 8 weeks at 25 degrees C and two-thirds of field capacity, using the fumigation-extraction method. Both microbial biomass-C and -N (BC and BN, respectively) appeared to be dependent on the type of organic waste residues, on their degree of stability, and on their chemical characteristics. In general, organic wastes increased the microbial biomass-C content in the soil and the microbial BC was positively correlated with the organic C content, the C/N, neutral detergent fibre/N (NDF/N) and acid detergent fibre/N (ADF/ N) ratios. The microbial biomass content decreased according to the period of incubation, especially when the compost used was immature. The microbial biomass-N was positively correlated with the total N and percentage of hemicellulose. The microbial biomass-C was linearly related with the microbial biomass-N and the ratio BC/BN was exponentially related with the BC.     

Effects of municipal solid waste compost application on the microbial biomass of cultivated and non-cultivated soil in a semi-arid zone.

The aim of this study was to assess whether soil microbial biomass could be used as an indicator of environmental changes following the application of organic residue (compost of municipal solid waste and farmyard manure) or mineral fertilizers (N and P) into cultivated or uncultivated loam-clayey soil, for three consecutive years. The carbon and nitrogen of the microbial biomass (B(C) and B(N) were studied using the fumigation-extraction method. For the two cultivated and uncultivated plots, B(N) and B(C) were more important in the superficial profile (0-20 cm) than in the deep one (20-40 cm). In the uncultivated soil, we observed a good linear relation between B(C) and B(N) at the level of upper soil horizon during the wet season with r coefficients of 0.95, 0.71 and 0.80 for the consecutive years 2000, 2001 and 2002, respectively. Microbial biomasses C and N increased during the rainy season and decreased during the dry season. Microbial biomass C and N showed the higher content with compost and farmyard manure at 40 tonnes ha(-1). Moreover, the results showed that at the beginning of the experiment, the microbial biomass was higher in the ploughed wheat-cultivated plot than in the uncultivated one. Microbial biomass C and N in the cultivated plot amended with compost at 40 tonnes ha(-1) were significantly different in comparison with the soil microbial biomass amended with farmyard manure. The combining of chemical fertilizer with the organic fertilizer, such as compost at 40 or 80 tonnes ha(-1) and farmyard manure, increased the microbial biomasses C and N after 1 and 2 years. In the cultivated or uncultivated plots the results revealed that the best application rate of the compost was 40 tonnes ha(-1) and when the compost rate was increased from 40 to 80 tonnes ha(-1) both B(C) and B(N) decreased significantly.     

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.     

Estimating the demand for municipal waste compost via farmers' willingness-to-pay in Ghana

This paper has its primary focus on the analysis of perceptions and willingness-to-pay (WTP) for composted municipal solid and faecal waste among urban and peri-urban farmers and other potential compost users in Ghana. Participatory rural appraisal and contingent valuation methods (CVM) were used for the demand analysis. Most respondents were clear and firm in their responses to the principal question about WTP for compost, as well as in giving their views and perceptions about issues involved in demand for compost. The probit analysis proved valuable in highlighting variables, which explain variations in the WTP. The WTP analysis allowed the quantification of the compost demand under different scenarios of subsidized and non-subsidized compost production, with due allowance for a local reference price to cover compost station operating costs. The analysis revealed that the effective demand for compost for agricultural purposes is marginal and limited by farmers' transport costs. Only through the additional consideration of the demand of the construction sector can about 25% of the organic waste produced in Ghana's capital, Accra, be transformed and utilized. Public subsidies appear necessary and could be generated through savings in transport and disposal. Without subsidies, the challenge for an increased agricultural use is how to produce a low-cost but nutrient-rich compost, which can compete with abundant and cheap poultry manure and still achieve the price to maintain a compost station. The experience in Ghana shows that this is hardly possible except through private-public partnerships.     

Enzymatic hydrolysis of organic waste materials in a solid-liquid system

In the current climate of increasing emphasis on environmental protection and efficient waste management, regional management bodies and environmental agencies are striving to achieve an economical and environmentally acceptable system for the recycling of biodegradable organic wastes. Composting would appear to be a cost effective solution to this problem, but in its entirety, composting is an inherently lengthy and variable process and is restrictive in terms of the demand on resources and space in composting plants. The aim of this study was to compare a biological composting process of solid residues with an enzymatic hydrolysis process of residues. The length of time required to naturally compost three organic materials, spent mushroom compost (SMC), farmyard manure (FYM) and dairy wastewater sludge (DWS) under optimal conditions was 42 days, 98 days and 84 days, respectively. In an attempt to accelerate this process, commercial enzymes were added to the waste products in a heterogeneous solid-liquid system. The enzymes utilised included a range of proteases, cellulases, ligninases, lipases and pectinases, which are responsible for the hydrolysis of protein, cellulose, lignin, lipids and carbohydrates, respectively. Preliminary results indicate that all of the organic materials were stabilised within 9h and that the enzymes used would, therefore, improve the efficiency of a waste management plant, if such a system were employed. Spent mushroom compost has a mean N/P/K ratio of 20:10:10 recorded for composted SMC, while a similar ratio of 20:10:20 was obtained for hydrolysed SMC. In contrast, composted farmyard manure has a N/P/K ratio of 30:0:30 and a ratio of 10:1:10 for hydrolysed FYM. Finally, composted DWS has a N/P/K ratio of 20:1:30 while DWS hydrolysate has a N/P/K ratio of 40:1:20, with the decrease in nitrogen in the composted DWS attributed to the addition of wood chippings and sawdust as a bulking agent. While all three materials have a considerable supply of plant nutrients, the variability in nutrients could be overlooked when employed as a soil amendment.     

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.     

Effect of organic matter and moisture on the calorific value of solid wastes: An update of the Tanner diagram

Objective of the work was to experimentally determine the effect of the organic matter and moisture contents on the calorific value of organic solid wastes. Nine substrates (i.e. newsprint, biodried municipal solid wastes, municipal solid waste derived composts, wastewater sludges, and sea weed derived compost), with organic matter contents that ranged from 12% to 91% (dry weight) were used in the experiments. All substrates were dried and ground and deionized water was artificially added in order to achieve certain target moisture contents per substrate. The higher heating value (HHV) was, then, determined experimentally for each sample using a bomb calorimeter. Best reduced models were developed to describe the higher and lower heating values as a function of organic matter, ash and moisture contents. A triangular plot was constructed and the self-sustained combustion area was determined and compared to that of the Tanner diagram. Response surfaces were drawn to visually assess the effect of organic matter and moisture contents on the calorific value of the wastes.     

Wet explosion of wheat straw and codigestion with swine manure: Effect on the methane productivity

The continuously increasing demand for renewable energy sources renders anaerobic digestion to one of the most promising technologies for renewable energy production. Twenty-two (22) large-scale biogas plants are currently under operation in Denmark. Most of these plants use manure as the primary feedstock but their economical profitable operation relies on the addition of other biomass products with a high biogas yield. Wheat straw is the major crop residue in Europe and the second largest agricultural residue in the world. So far it has been used in several applications, i.e. pulp and paper making, production of regenerated cellulose fibers as an alternative to wood for cellulose-based materials and ethanol production. The advantage of exploiting wheat straw for various applications is that it is available in considerable quantity and at low-cost. In the present study, the codigestion of swine manure with wheat straw in a continuous operated system was investigated, as a method to increase the efficiency of biogas plants that are based on anaerobic digestion of swine manure. Also, the pretreatment of wheat straw with the wet explosion method was studied and the efficiency of the wet explosion process was evaluated based on (a) the sugars release and (b) the methane potential of the pretreated wheat straw compared to that of the raw biomass. It was found that, although a high release of soluble sugars was observed after wet explosion, the methane obtained from the wet-exploded wheat straw was slightly lower compared to that from the raw biomas s. On the other hand, the results from the codigestion of raw (non-pretreated) wheat straw with swine manure were very promising, suggesting that 4.6 kg of straw added to 1 t of manure increase the methane production by 10%. Thus, wheat straw can be considered as a promising, low-cost biomass for increasing the methane productivity of biogas plants that are based mainly on swine manure.     

Assessment of municipal solid waste compost quality using standardized methods before preparation of plant growth media.

The quality of compost and its suitability for agricultural application depend upon physical and chemical parameters such as water-holding capacity, porosity, pH, electrical conductivity, C/N ratio, available nutrients and the absence of toxic substances. In the present study a complete characterization of an industrial municipal solid waste compost (MSWC) based on standardized European methods (CEN) for soil improvers and growing media was obtained, and compared with the quality of other Spanish composted biowaste and conventional substrates such as peat and pine bark. The MSWC was obtained from the main composting plant in Galicia (Spain), which processes organic waste that has been separated at origin and collected from more than 100 000 inhabitants. The MSWC presented a lower C/N ratio (15) than peat (84) and composted pine bark (CPB) (211), but had a similar ratio to other marketed MSWC. The nutrients and heavy metals were extracted using different recommended solvents (water, CaCl2 + diethylen triamin pentaacetic acid, and aqua regia). The nutrient concentrations of composted urban waste or manure were much higher than those of peat, CPB or pine bark. On the basis of the results of the plant tolerance test, the MSWC could be employed directly as a soil improver, but would need to be diluted with other low-salt components such as peat or CPB before being used as a growing media.     

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.     

Evaluation of an organic soil amendment generated from municipal solid waste seeded with activated sewage sludge

This study investigated the feasibility of using fresh activated sewage sludge as inoculum for the microbial valorization of segregated municipal solid waste and evaluated the quality of organic soil amendment generated. Organic fraction of municipal solid waste, which consisted of vegetative (vegetable, fruit and flower) wastes was seeded with activated sewage sludge and processed by rapid aerobic microbial treatment. Efficacy of microbial valorization process and quality of final product were assessed by physico-chemical analysis. Suitability of final product was assessed with regard to heavy metal content, pesticide residues, microbiological quality and phytotoxicity. Quality of the soil amendment generated was compared with the control product generated with a commercial microbial inoculum. Phytotoxicity experiments indicated the stimulatory effect of sewage sludge seeded soil amendment on plant growth but inhibition was observed in closed growth test due to the evolution of gaseous phytotoxic agents. The study suggests that segregated municipal solid waste can be effectively valorized with activated non-dewatered sewage sludge as inoculum and the quality of soil amendment generated was comparable to compost intended for unrestricted applications.     

Effect of granular porous media on the composting of swine manure

This study investigated the feasibility of a bulking agent of granular porous media (GPM) for the composting of swine manure. Two lab-scale composting reactors were operated to evaluate the general performances and maturity parameters using GPM made of wastes from the Portland cement manufacturing processes as an alternative bulking agent. The overall volatile solid (VS) removal was 38.5% (dry basis). During the experiments, moisture content ranged between 41% and 53%, ensuring feasibility of microbial activity in composting. Cured compost showed proper maturity and low phytotoxicity, despite the slight decreases of CO(2) production and VS removal at the second batch operation. Various physico-chemical parameters of the cured compost met the regulatory standards reported elsewhere. The pH, carbon-to-nitrogen ratio, ammonia nitrogen and soluble organic carbon (SOC) of the cured compost were significantly correlated to the germination index (GI) using the seeds of Chinese cabbage and lettuce, indicating the progressive biodegradation of phytotoxins as well as organic matter. Consequently, the results obtained in this study demonstrate that GPM could contribute to the environmentally friendly and economical composting of problematic swine manure as a recyclable bulking agent.     

Home composting versus industrial composting: Influence of composting system on compost quality with focus on compost stability

Stability is one of the most important properties of compost obtained from the organic fraction of municipal solid wastes. This property is essential for the application of compost to land to avoid further field degradation and emissions of odors, among others. In this study, a massive characterization of compost samples from both home producers and industrial facilities is presented. Results are analyzed in terms of chemical and respiration characterizations, the latter representing the stability of the compost. Results are also analyzed in terms of statistical validation. The main conclusion from this work is that home composting, when properly conducted, can achieve excellent levels of stability, whereas industrial compost produced in the studied facilities can also present a high stability, although an important dispersion is found in these composts. The study also highlights the importance of respiration techniques to have a reliable characterization of compost quality, while the chemical characterization does not provide enough information to have a complete picture of a compost sample.     

Removal of batteries from solid waste using trommel separation

This paper describes the design and testing of a trommel for separation of batteries from solid waste. A trommel is a cylindrical separation device that rotates and performs size separation. It has also been used in areas such as municipal solid waste (MSW) processing, classifying construction and demolition debris, screening mass-burn incinerator ash and compost processing. A trommel has been designed based on size separation to separate household batteries from solid waste, which can then be used as feedstock for alternative applications of solid waste combustion, particularly where the metal content of the product is also a critical parameter, such as the Co-Co process for integrated cement and power production. This trommel has been tested with batches of university office and restaurant wastes against various factors. The recovery efficiency of batteries increases with decreasing inclination angle of the trommel and decreasing rotational speed. A physical characterization of the university solid waste has been performed with a 20-kg sample of the tested waste. It was found that there is a trend of decreasing recovery of batteries with increasing paper composition, and a trend of increasing recovery of batteries with increasing organic materials composition.     

A statistical analysis to assess the maturity and stability of six composts

Despite the long-time application of organic waste derived composts to crops, there is still no universally accepted index to assess compost maturity and stability. The research presented in this article investigated the suitability of seven types of seeds for use in germination bioassays to assess the maturity and phytotoxicity of six composts. The composts used in the study were derived from cow manure, sea weeds, olive pulp, poultry manure and municipal solid waste. The seeds used in the germination bioassays were radish, pepper, spinach, tomato, cress, cucumber and lettuce. Data were analyzed with an analysis of variance at two levels and with pair-wise comparisons. The analysis revealed that composts rendered as phytotoxic to one type of seed could enhance the growth of another type of seed. Therefore, germination indices, which ranged from 0% to 262%, were highly dependent on the type of seed used in the germination bioassay. The poultry manure compost was highly phytotoxic to all seeds. At the 99% confidence level, the type of seed and the interaction between the seeds and the composts were found to significantly affect germination. In addition, the stability of composts was assessed by their microbial respiration, which ranged from approximately 4 to 16 g O₂/kg organic matter and from 2.6 to approximately 11 g CO₂–C/kg C, after seven days. Initial average oxygen uptake rates were all less than approximately 0.35 g O₂/kg organic matter/h for all six composts. A high statistically significant correlation coefficient was calculated between the cumulative carbon dioxide production, over a 7-day period, and the radish seed germination index. It appears that a germination bioassay with radish can be a valid test to assess both compost stability and compost phytotoxicity.     

Pelleted organo-mineral fertilisers from composted pig slurry solids, animal wastes and spent mushroom compost for amenity grasslands

In Ireland, conversion of biodegradable farm wastes such as pig manure spent mushroom compost and poultry litter wastes to pelletised fertilisers is a desirable option for farmers. In this paper, results obtained from the composting of pig waste solids (20% w/w) blended with other locally available biodegradable wastes comprising poultry litter (26% w/w), spent mushroom compost (26% w/w), cocoa husks (18% w/w) and moistened shredded paper (10% w/w) are presented. The resulting 6-mo old 'mature' composts had a nutrient content of 2.3% total N, 1.6% P and 3.1% K, too 'low' for direct use as an agricultural fertiliser. Formulations incorporating dried blood or feather meal amendments enriched the organic N-content, reduced the moisture in mature compost mixtures and aided the granulation process. Inclusion of mineral supplements viz., sulphate of ammonia, rock phosphate and sulphate of potash, yielded slow release fertilisers with nutrient N:P:K ratios of 10:3:6 and 3:5:10 that were suited for amenity grasslands such as golf courses for spring or summer application and autumn dressing, respectively. Rigorous microbiological tests carried out throughout the composting, processing and pelletising phases indicated that the formulated organo-mineral fertilisers were free of vegetative bacterial pathogens.     

Revisiting the elemental composition and the calorific value of the organic fraction of municipal solid wastes

In this work, the elemental content (C, N, H, S, O), the organic matter content and the calorific value of various organic components that are commonly found in the municipal solid waste stream were measured. The objective of this work was to develop an empirical equation to describe the calorific value of the organic fraction of municipal solid waste as a function of its elemental composition. The MSW components were grouped into paper wastes, food wastes, yard wastes and plastics. Sample sizes ranged from 0.2 to 0.5 kg. In addition to the above individual components, commingled municipal solid wastes were sampled from a bio-drying facility located in Crete (sample sizes ranged from 8 to 15 kg) and were analyzed for the same parameters. Based on the results of this work, an improved empirical model was developed that revealed that carbon, hydrogen and oxygen were the only statistically significant predictors of calorific value. Total organic carbon was statistically similar to total carbon for most materials in this work. The carbon to organic matter ratio of 26 municipal solid waste substrates and of 18 organic composts varied from 0.40 to 0.99. An approximate chemical empirical formula calculated for the organic fraction of commingled municipal solid wastes was C₃₂NH₅₅O₁₆.     

Use of thermal analysis techniques (TG-DSC) for the characterization of diverse organic municipal waste streams to predict biological stability prior to land application

The use of organic municipal wastes as soil amendments is an increasing practice that can divert significant amounts of waste from landfill, and provides a potential source of nutrients and organic matter to ameliorate degraded soils. Due to the high heterogeneity of organic municipal waste streams, it is difficult to rapidly and cost-effectively establish their suitability as soil amendments using a single method. Thermal analysis has been proposed as an evolving technique to assess the stability and composition of the organic matter present in these wastes. In this study, three different organic municipal waste streams (i.e., a municipal waste compost (MC), a composted sewage sludge (CS) and a thermally dried sewage sludge (TS)) were characterized using conventional and thermal methods. The conventional methods used to test organic matter stability included laboratory incubation with measurement of respired C, and spectroscopic methods to characterize chemical composition. Carbon mineralization was measured during a 90-day incubation, and samples before and after incubation were analyzed by chemical (elemental analysis) and spectroscopic (infrared and nuclear magnetic resonance) methods. Results were compared with those obtained by thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Total amounts of CO₂ respired indicated that the organic matter in the TS was the least stable, while that in the CS was the most stable. This was confirmed by changes detected with the spectroscopic methods in the composition of the organic wastes due to C mineralization. Differences were especially pronounced for TS, which showed a remarkable loss of aliphatic and proteinaceous compounds during the incubation process. TG, and especially DSC analysis, clearly reflected these differences between the three organic wastes before and after the incubation. Furthermore, the calculated energy density, which represents the energy available per unit of organic matter, showed a strong correlation with cumulative respiration. Results obtained support the hypothesis of a potential link between the thermal and biological stability of the studied organic materials, and consequently the ability of thermal analysis to characterize the maturity of municipal organic wastes and composts.     

In-vessel composting of household wastes

The process of composting has been studied using five different types of reactors, each simulating a different condition for the formation of compost; one of which was designed as a dynamic complete-mix type household compost reactor. A lab-scale study was conducted first using the compost accelerators culture (Trichoderma viridae, Trichoderma harzianum, Trichorus spirallis, Aspergillus sp., Paecilomyces fusisporus, Chaetomium globosum) grown on jowar (Sorghum vulgare) grains as the inoculum mixed with cow-dung slurry, and then by using the mulch/compost formed in the respective reactors as the inoculum. The reactors were loaded with raw as well as cooked vegetable waste for a period of 4 weeks and then the mulch formed was allowed to maturate. The mulch was analysed at various stages for the compost and other environmental parameters. The compost from the designed aerobic reactor provides good humus to build up a poor physical soil and some basic plant nutrients. This proves to be an efficient, eco-friendly, cost-effective, and nuisance-free solution for the management of household solid wastes.     

Effect of C/N ratio on the in-vessel composting under air pressure of organic fraction of municipal solid waste in Morocco

The goal of this research was to investigate the effect of the C/N ratio on the in-vessel composting, under air pressure, of organic fraction of municipal solid waste in Morocco. Firstly, an in-vessel bioreactor was designed and used to evaluate the appropriate initial pressure for the composting process. Secondly, five bioreactors were run with C/N ratios of 26 (control; no C supplement), 32.2, 38.4, 44.6, and 50.8. Parameters monitored included internal air pressure, C/N ratio, temperature, volatile solids reduction, and maturity of the obtained composts. The relative microbial activity was observed indirectly using volatile solids removal and the relative heat generation data. The experimental results showed that organic waste could be composted within 10?days and the operating initial parameters that converted the most volatile solids and carbons in the feedstock were as follows: 0.6?×?10⁵ Pa for the initial air pressure and 26 for the C/N ratio. Maturity tests, in optimal conditions, showed that the final compost has characteristics of stable compost and can be used as a soil conditioner. In addition, compost obtained from the experiment that considered a C/N ratio of 32.2 showed good maturity levels and may also be used for agricultural applications.