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.     

Improvement of digestibility of sunflower and corn residues by some saprophytic fungi

The in vitro degradation of fiber from two agricultural residues (Helianthus annuus and Zea mays) was studied using four saprophytic fungi. The changes in cellulolytic enzyme and phosphatase activities, the C/N ratio, the dry weight, the crude fiber (CF) content, and the protein and fiber digestibility coefficients were investigated in solid-state culture during a 45-day period of biodegradation. The FPase activity of Phanerochaete chrysosporium and the endoglucanase activities of P. chrysosporium and Trichoderma reesei compared to those of the other fungi were significantly (P < 0.05) high on both crop resides. Both acid and alkaline phosphatases were produced in greater amounts by P. chrysosporium than by the other fungi. The organic carbon contents of both residues were reduced more by T. reesei than by the other fungi. The fiber digestibility coefficient of untreated corn residue was higher than that of sunflower residue, but after treatment with fungi, the sunflower fiber digestibility increased more than that of corn did. Although the CF contents of both residues were decreased more by P. chrysosporium than by T. reesei, the fiber digestibility coefficients of both residues were increased more by T. reesei than by P. chrysosporium. The treatment of both crop residues increased their protein digestibility coefficients significantly compared to the control. The protein digestibility coefficients of both residues were increased more by T. reesei and P. chrysosporium than by the other fungi. In all treatments, the protein digestibility coefficient of sunflower residue was higher than that of corn residue.     

Assessment of compost quality for its environmentally safe use by means of an ecotoxicological test on a soil organism

A research project was carried out to evaluate toxicological effects of compost addition to agricultural soil using the earthworm Eisenia foetida (Annellida) as a representative organism of the soil fauna. Moreover, the correlation between compost biochemical stabilization and toxicity at different phases of the composting process was assessed. Samples were collected from three composting plants at three different maturation levels (beginning of the composting process, intermediate compost after bio-oxidation, and mature refined compost). Two tests were performed: a standard chronic solid-phase test and an acute solid-phase test (developed originally by the authors). In the first test, the measured end-points were mortality, growth and reproduction; while in the second test earthworms’ behavior was evaluated. The chosen compost concentrations in soil ranged from 2.5 to 100 %, with the aim of obtaining the toxicological parameters (LC50) and to mimic real agricultural dosages for the lower concentrations. Results indicated an increase in compost toxicity with greater compost concentrations; in particular, agricultural compost dosage below 10 % showed no toxicity. Moreover, toxicity did not decrease during composting; intermediate compost showed the highest LC50 values. As a consequence, no correlation was ascertained between the results of ecotoxicological analysis and waste biochemical stability parameters during the composting process.     

Low energy comsumption management of agricultural residues

In this paper, a mechanical filtering system to treat pig slurry is proposed. The filter was made from the aerobic decomposition product of the organic fraction of municipal wastes and wheat straw was used as the support.Using a pilot plant to treat 2100 liters of swine slurry, an adequate reduction in BOD₅; COD, and other parameters was obtained. The organic matter content of the material trapped in the filter was similar to that of compost and farmyard manure, but the nitrogen and phosphorous levels and the C/N ratio were more similar to farmyard manure. After passing through a filtering system, the treated liquid can be used for fertirrigation and as a feed for algae ponds. After a period of stabilization, the solid material can be mixed to produce manure. Although wheat straw was used as the support in this experiment, other agricultural wastes such as rice straw, corn stalks, millet stems, banana, cotton, and coconut trash can be used. Rather than municipal solid waste compost, other kinds of compost obtained from agricultural wastes such as leaves, bark, husks, etc., can be used as the filter.     

Fluorescence excitation-emission spectroscopy with regional integration analysis for assessment of compost maturity

Composting of animal manures is believed as an alternative way for directly recycling them in farms, and therefore assessment of compost maturity is crucial for achieving high quality compost. Fluorescence excitation-emission matrices (EEMs) combined with regional integration analysis is presented to assess compost maturity. The results showed that the EEM contours of water-extract organic matter (WEOM) from immature composts exhibited four peaks at excitation/emission (Ex/Em) of 220/340 nm, 280/340 nm, 220/410 nm, and 330/410 nm, whereas EEM contour of WEOM from mature composts had only two peaks at Ex/Em of 230/420 nm and 330/420 nm. Pearson correlation demonstrated that peaks intensity rather than their ratios had a significantly correlation with the common indices assessing compost maturity, whereas the normalized excitation-emission area volumes (Φ_i,ns) from regional integration analysis had a stronger correlation with the common indices assessing compost maturity than peaks intensity. It is concluded that the Φ_i,ns from regional integration analysis are more suitable to assess the maturity of compost than the intensities of peaks. Therefore, the fluorescence spectroscopy combined with regional integration analysis can be used as a valuable industrial and research tool for assessing compost maturity, given its high sensitivity and selectivity.     

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.     

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.     

Behavior of bromine on the thermal decomposition of paper-based phenolic laminate wastes

We investigated the thermal properties and behavior of bromine on the thermal decomposition of paper-based phenolic laminate wastes containing polybrominated flame retardants. The thermal properties of the phenolic laminate wastes were measured with a thermogravimeter and a conduction-type scanning calorimeter (TG-CSC). The weight loss of the wastes on thermal decomposition was mainly in three phases between 40°C and 600°C. The enthalpy (ΔH) of the thermal decomposition was 104 cal/g. The material balance of the decomposition components was measured with batch-type thermal decomposition equipment. The ratios of carbon residue, liquid, and gas on decomposition at 800°C in a vacuum were 37 wt. %, 48 wt. %, and 15 wt. %, respectively. The bromine contents in the carbon residue and liquid were less than 0.02 wt. % and 10 wt. %, respectively. These results are useful both in the carbonization process of these wastes and in the application of carbon residue as carbon materials. Received: August 11, 2000 / Accepted: March 7, 2001     

Assessment of compost dosage in farmland through ecotoxicological tests

A research project was carried out to evaluate ecotoxicological effects of mature compost addition to agricultural soil, using a battery of ecotoxicological tests. The following species were selected: plant of Lepidium sativum, earthworm Eisenia foetida, aquatic crustacean Daphnia magna and bacteria Vibrio fischeri. The tests were classified as “direct tests” using solid compost samples and “indirect tests” using compost leaching test eluate. The direct bioassays were performed using compost added to artificial soil in concentrations ranging from 2.5 to 100 % (w/w); the indirect ones considered compost eluate, added to a standard solution in the same concentrations used in the direct tests. Both tests aimed at obtaining the ecotoxicological parameters (LC₅₀ and EC₅₀). These values were then utilized to implement the Species Sensitivity Distribution (SSD) analysis and extrapolate the Hazard Concentration (HC), a useful threshold to preserve the biodiversity of agricultural ecosystems. Results indicated an increase in compost toxicity with greater compost concentrations; in particular, for direct tests compost dosage below 10 % showed low toxicity, while for indirect ones the toxicity was higher. Furthermore, SSD analysis showed a Hazardous Concentration (HC₅) for direct bioassays of 3.5 % and for indirect of 14 %.     

Quality assessment of composts prepared with olive mill wastewater and agricultural wastes

The co-composting of solid residue from olive oil production process, exhausted olive cake (EOC), with poultry manure (PM) watered with olive mill wastewater (OMW) was considered as an efficient method for the treatment of olive oil extraction effluent having high organic content including phenolic polluting compounds. The process was carried out by using three aerated windrows of variable compositions. OMW was used continuously during the bio-oxidative period, which lasted three months, to replace water for windrow moistening. The main process parameters (temperature, pH, humidity and C/N) were monitored over four months to ascertain the maturity of the compost. The composting process lasted four months during which 26 moistenings of the mixtures were performed with OMW or water to keep moisture within the ideal range of 45-60% (w/w). At the maturity stage, the C/N ratios were less than 16, pH of the resulting products were slightly alkaline (pH=8) and electrical conductivity was relatively high in the OMW mixtures (5.46-5.48 Sm(-1)) when compared with water application. Nitrates increased (0.16-0.42%) and phenol contents were reduced by more than 49%. Mature composts were then used as an amendment for potato production in a field where no inhibitory effect was observed. Potato productivity increased 10-23% as a result of compost application. No noticeable negative impact of OMW on the soil system was observed. Phenolic compound concentrations in the stabilised composts were comparable in the three studied mixtures (different sites) and averaged 0.24%. Considering previous results and this three year study, it has been observed that the benefit of these composts demonstrated the potential sustainable agronomic production of potato while using locally available recycled organic materials.     

Indicator organisms for assessing sanitization during composting of plant wastes

The potential for using plant pathogens and seeds as indicator organisms for assessing sanitization of plant wastes during composting was tested in bench-scale flask and large-scale systems. Plasmodiophora brassicae was unsuitable due to high temperature tolerance in dry to moist composts, and detection of viable inoculum post-composting using bioassay plants not corresponding with that using TaqMan® PCR, possibly due to preservation of nucleic acids at elevated temperatures. Several other plant pathogens (Sclerotinia sclerotiorum, Microdochium nivale, Phytophthora cinnamomi and Phytophthora nicotianae) were unsuitable due their low temperature tolerance. Fusarium oxysporum f.sp. cepae and f.sp. radicis-lycopersici chlamydospores and tomato seeds were suitable indicators due to their moderate temperature tolerance and ease of viability testing post-composting. Abutilon seeds were more tolerant than tomato seeds of compost temperatures ?52 °C but more prone to degradation at lower temperatures and therefore less suitable as indicators. Relationships between compost temperature during exposures of 2-10 days and subsequent viability of the above chlamydospores or seeds enabled the sanitizing effect of composting processes to be predicted within 2-6 days. Plant waste type (woody or vegetable) had a small but significant effect on the relationship for tomato seeds but not for F. oxysporum chlamydospores.     

Techniques for the evaluation of maturity for composts of industrially contaminated lake sediments

Composting was applied as a bioremediation methodology for the reclamation of dredged sediments of Isnapur, Khazipally and Gandigudem lakes polluted with industrial wastes. The present study is an attempt to elaborate upon organic matter transformations and define the parameters for product maturity adapting chemical and spectroscopic methods during composting. The stability and maturity of sediments were evaluated by assessing parameters like C/N ratio, nitrification index (NH(4)-N/NO(3)-N), water-soluble organic carbon concentration, CO(2) evolution rate, cation exchange capacity and indices such as humification index, E4/E6 ratio, compost mineralization index (ash content/oxidizable carbon), germination index, dehydrogenase, polyphenoloxidase activities and FTIR spectroscopy. The results showed that the changes in the above chemical and biological parameters can be employed as reliable indicators of stability and maturity. The FTIR spectra revealed enrichment in the aromatic groups and a degradation of the aliphatic groups indicating stabilization of the final compost.     

Evaluating compost maturity with a newly proposed index based on a germination test using Komatsuna (Brassica rapa var. peruviridis) seeds

A new index for evaluating compost maturity was developed based on a germination test of Komatsuna seeds using water extract from compost. Several compost samples were collected from a kitchen-garbage composting plant to determine an index to evaluate compost maturity. Firstly, some extraction conditions for extracting compost ingredients with water were evaluated using the time course of total organic carbon concentration in water extract. The water temperature of 60?°C, periodic mixing, and extraction period >1 were selected. Secondly, applying these conditions, the germination test was performed using the water extract solutions at several dilution ratios. The relationship between the germination rate and the dilution ratio was expressed using a logistic regression curve. The dilution ratio to give a germination rate of 0.5, defined as DG₅₀, was calculated with the parameters of the curve. Compared with other maturity indices, DG₅₀ was the most effective. Moreover, it has a unique feature in that maturity is quantified even for the compost from which water extract results in a germination rate of 0. This feature can be used to compare the maturity of different kinds of composts and quantify the change in the levels of inhibitory substances in a composting process.     

Continuous-feeding vermicomposting as a recycling management method to revalue tomato-fruit wastes from greenhouse crops

Huge quantities of discarded fruits generated from greenhouse crops represent a worldwide environmental problem. The aim of this work was to assess the efficiency of vermicomposting as a recycling management option for biotransforming tomato-fruit wastes from greenhouses into an organic nutrient-rich product available for agricultural purposes. A pilot vermireactor was constructed. It was provided with a manure layer, where an initial population of Eisenia fetida was introduced and fed continuously at a high organic loading rate (13.6 kg TOC m^?3 wk^?1) for 150 days. Vermicompost chemical and enzymatic parameters as well as the bacterial and fungal community structure were determined for 210 days (vermicomposting plus a maturation period). Earthworm biomass increased after 90 days, and then declined due to increasing pH, electrical conductivity and ammonium concentration. The temporal patterns of dehydrogenase, β-glucosidase, protease and urease were related to earthworm growth and the stabilization of organic matter. Bacterial DGGE profiles differed between the period of degradation of labile substrates and the maturation step. Fungal communities at the stage of maximum earthworm biomass differed most, suggesting a gut passage effect. The end product was chemically stable and enriched in nutrients, demonstrating that tomato-fruit wastes can be successfully vermicomposted into a valuable soil amendment. We suggest continuous-feeding vermicomposting as an environmentally sound management option for greenhouse wastes.     

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.

     

Heavy metals fractionation before, during and after composting of sewage sludge with natural zeolite

The main limiting factor, in order to use compost in agriculture, is the total concentration of heavy metals. Natural zeolites, such as clinoptilolite, have the ability to take up and remove those metals by utilizing ion exchange. However, it is important to know about the fractionation of the heavy metals during the thermophilic phase and the maturation phase. The purpose of this work was to determine the changes in the fraction of heavy metals in sewage sludge compost in which clinoptilolite is used as a bulking agent to remove metals. The final result indicates that a significant (p < 0.05) percentage of the metals, which is not removed by the zeolite, is associated with the residual fraction which is considered as an inert form.     

Comparison of several maturity indicators for estimating phytotoxicity in compost-amended soil

Compost can provide a rich organic nutrient source and soil conditioner for agricultural and horticultural applications. Ideal compost amendment rates, however, vary based on starting material and compost maturity or their interaction, and there is little consensus on appropriate methods to gauge maturity. In this study, electrical conductivity, carbon-to-nitrogen ratio, and carbon mineralization measurements were made on compost-amended soils and compared to phytotoxicity measured as cress (Lepidium sativum) germination. Cress germination in soil and compost mixtures incubated for 8-10 days significantly decreased with increasing electrical conductivity and carbon mineralization rate of the mixture and with carbon mineralization rate and mineralizable carbon associated with the compost. Cress germination was not related to carbon-to-nitrogen ratio or pH of soil and compost mixtures. The electrical conductivity of the soil and compost mixtures significantly decreased with decreasing mineralizable carbon suggesting that compounds contributing to electrical conductivity were present in the compost and decomposed upon soil amendment. The results of this study indicate that measurements of mineralizable carbon and mineralization rate of composts in soil, and electrical conductivity and mineralization rate of soil and compost mixtures, can be used as indicators of compost maturity.     

Dynamic of functional microbial groups during mesophilic composting of agro-industrial wastes and free-living (N2)-fixing bacteria application

Although several reports are available concerning the composition and dynamics of the microflora during the composting of municipal solid wastes, little is known about the microbial diversity during the composting of agro-industrial refuse. For this reason, the first parts of this study included the quantification of microbial generic groups and of the main functional groups of C and N cycle during composting of agro-industrial refuse. After a generalized decrease observed during the initial phases, a new bacterial growth was observed in the final phase of the process. Ammonifiers and (N₂)-fixing aerobic groups predominated outside of the piles whereas, nitrate-reducing group increased inside the piles during the first 23 days of composting. Ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), showed an opposite trend of growth since ammonia oxidation decreased with the increase of the nitrite oxidation activity. Pectinolytics, amylolytics and aerobic cellulolytic were present in greater quantities and showed an upward trend in both the internal and external part of the heaps.Several free-living (N₂)-fixing bacteria were molecularly identify as belonging especially to uncommon genera of nitrogen-fixing bacteria as Stenotrophomonas, Xanthomonas, Pseudomonas, Klebsiella, Alcaligenes, Achromobacter and Caulobacter. They were investigated for their ability to fix atmospheric nitrogen to employ as improvers of quality of compost. Some strains of Azotobacter chrococcum and Azotobacter salinestris were also tested. When different diazotrophic bacterial species were added in compost, the increase of total N ranged from 16% to 27% depending on the selected microbial strain being used. Such microorganisms may be used alone or in mixtures to provide an allocation of plant growth promoting rhizobacteria in soil.     

Germination test on Komatsuna (Brassica rapa var. peruviridis) seed using water extract from compost for evaluating compost maturity: evaluating criteria for germination and effects of cultivars on germination rate

Germination tests on the Komatsuna (Brassica rapa var. peruviridis) seed using water extract from compost has often been performed in Japan to evaluate compost maturity; however, most of the germination tests have been carried out without using any rationally defined experimental criteria to determine germination and to explain the influence of cultivars. Here, we performed a series of germination tests to examine the applicability of the experimental criteria for germination and the influence of cultivars on germination rate. Germination rate varied according to the criteria introduced in this paper, and two criteria, "seed size (3)" and "5?mm (2)", were selected for testing. In addition, two types of inhibitory influence, stop and slowness, were observed and compared with the criteria. The logistic regression curve of Logit, a function of germination rate to logarithmic value of the dilution ratio of the water extract was parameterized to compare the effects of the cultivars on germination rate. The statistical analysis of the parameters showed that dilution ratio greatly influenced germination rate, and the cultivar itself also influenced the rate. Consequently, the specific experimental criteria for germination and determining the influence of cultivars were proven to be indispensable for evaluating compost maturity using the germination test.     

Evaluation of maturity parameters and heavy metal contents in composts made from animal manure

The objective of this study was to evaluate a variety of maturity indices and heavy metal concentrations in the composting process. A full-scale study was performed on animal manures (dairy:beef:swine = 50%:30%:20%, w/w) mixed with sawdust using a self-screwed turner over a time period of 63 days. Several chemical compost characteristics and germination indices were monitored on samples collected weekly at a prototype composting facility. NH(4)-N concentrations decreased during the composting time, on the contrary NO(3)-N concentrations increased sharply after 30 days. As composting proceeded, the humic acids content increased from 1.45% to 2.70% of the organic carbon content, whereas the fulvic acids content decreased gradually. Temperature in the compost pile and concentration of NH(3) averaged 32.4 degrees C and 12.9 ppm at the initial composting phase and 69.5 degrees C and 47.3 ppm at the active bio-oxidation composting phase, respectively. Seed germination and germination index (GI) increased during the composting process, and the compost samples at the end of composting phase had GI values greater than 120. Among the composting processes, there were significant differences (p<0.05) in concentration of Zn, Cu and Pb in the compost. In conclusion, the suggested maturity parameter values and metal concentrations of composted animal manures can provide better understanding of maturation process of animal manure compost.