Influence of green waste, biowaste and paper-cardboard initial ratios on organic matter transformations during composting

The influence of green waste, biowaste and paper-cardboard proportions in initial mixtures on organic matter (OM) evolution during composting in pilot-scale reactors was studied using respirometric procedure, humic substance extraction, crude fiber analysis and Fourier transform infrared spectroscopy. The stabilisation of OM during composting resulted from the degradation of easily biodegradable organic fraction as cellulose and hemicellulose, the relative increase of resistant compounds as lignin, the microbial synthesis of resistant biomolecules, and from humification processes. Little stabilisation of green waste OM during composting was observed, in relation with their large lignin content. With moderate contents of paper-cardboard in initial mixtures (20-40%), cellulose proportion remained favorable to fast OM stabilisation. Larger proportions of paper-cardboard (more than 50%) affected OM stabilisation, probably due to a lack of nitrogen. The influence of biowastes only appeared at the very beginning of composting, because of their large proportions of easily biodegradable OM.     

Characterization of organic matter degradation during composting of manure-straw mixtures spiked with tetracyclines

The objective of this study was to investigate humification and mineralization of manure-straw mixtures contaminated by tetracyclines during composting. Hen manure, pig manure and rice straw were used as the raw materials. The manure-straw mixtures were spiked with tetracycline, chlortetracycline, and oxytetracycline at the concentration of 60 mg/kg dry matter. The results show that tetracyclines had no obvious influence on the composting process and more than 93% of the tetracyclines was decreased during a 45-day composting. The Fourier transform infrared (FTIR) spectra indicated that easily biodegradable components such as aliphatic substrates, carbohydrates and polysaccharides were decomposed and the contents of aromatic components relatively rose during the composting. The X-ray diffraction (XRD) spectra confirmed the natural formation of struvite, the degradation of easily biodegradable components, and the mineralization of organic matter during the composting. Therefore, FTIR and XRD analysis can be useful tools for monitoring the composting process.     

Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater--batch experiments. Part II: influence of the hydrophobic chain length

The mineralisation and the humification of organic matter (OM) in sterile horticultural plant wastes inoculated with Coriolus versicolor or Phanerochaete flavido-alba was investigated under different aeration rates in order to determine their efficacy as potential inoculants for composting. The change in elemental composition, lignin content and OM fractions was analysed during a 90-day incubation. Both fungi degraded 30% of lignin at low aeration rates. Different aeration rates led to significant changes in OM mineralisation induced by C. versicolor, but did not have noticeable effect on P. flavido-alba activity. The mineralisation was more effectively carried out by P. flavido-alba than by C. versicolor. Lignin degradation and the linked humification process were equally achieved by the two fungi and were enhanced in aerated conditions. The fungi analysed may facilitate the composting of lignocellulosic wastes by means of an increase in substrate bioavailability and OM humification.     

Evaluation of “alperujo” composting based on organic matter degradation, humification and compost quality

The main by-product generated by the Spanish olive oil industry, a wet solid lignocellulosic material called "alperujo" (AL), was evaluated as a composting substrate by using different aeration strategies and bulking agents. The experiments showed that composting performance was mainly influenced by the type of bulking agent added, and by the number of mechanical turnings. The bulking agents tested in this study were cotton waste, grape stalk, a fresh cow bedding and olive leaf; the latter showed the worse performance. Forced ventilation alone was revealed to work inadequately in most of the experiments. The composting process involved a substantial degradation of the organic substrate with average losses of 48.4, 28.6, 53.7 and 57.0% for total organic matter, lignin, cellulose and hemicellulose, respectively. Both organic matter biodegradation and humification were greatly influenced by the lignocellulosic nature of the starting material, which led to low organic matter and nitrogen loss rates and a progressive increase in more humified substances, as revealed by the end-values of the humification indices. The resulting composts were of good quality in terms of nutrient content, stabilised and non-phytotoxic organic matter and low heavy metal content. This demonstrates that composting technology can be used as an alternative treatment method to turn AL into compost that can be used as organic amendments or fertilisers for agricultural systems.     

Humic substances change during the co-composting process of municipal solid wastes and sewage sludge

The change of the degree of stability of compost during the composting process was a kind of guideline for our study. This stability was estimated by monitoring the chemical fractionation (extraction of humic and fulvic acids, and humin) during two cycles of composting. Change of humin (H), humic-like acid carbon (CHA) and fulvic-like acid carbon (CFA) fractions during the composting process of municipal solid wastes were investigated using two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge). Humin and fulvic acid fractions in the two windrows decreased since the start of composting process and tend to stabilize. At the end of composting process, humic acid fraction is more important in the windrow without sludge (W1) than the one with sludge (W2). The humification indexes used in this study showed that the humic-like acid carbon fraction production takes place largely during the phase of temperature increase (thermophilic phase), and it appeared very active in the windrow W2. At the end of composting process, the E₄/E₆ ratio value indicated that the compost of W1 is more mature than the compost of W2. The humification ratio (HR) allowed a correct estimation of compost organic matter stabilization level.     

Effects of olive mill wastewater addition in composting of agroindustrial and urban wastes

In order to study the suitability of olive mill wastewater (OMW) for composting, thisliquid waste was added to two different mixtures of agroindustrial and urban wastesand the composting process was compared with two other piles of similar composition,but without OMW. These four piles were studied in a pilot plant using the Rutgers staticpile system. The addition of OMW produced a greater proportion of degradable organic matter or a higher degradation rate, higher electrical conductivity values, greater losses of total N and lower nitrification than in piles without OMW. Its addition also restricted the increase of the cation exchange capacity and provoked the appearance of phytotoxicity or a longer persistence of phytotoxicity. However, in general, all the composts showed increases in the cation exchange capacity, the percentage of humic acid-like carbon, the polymerisation ratio of these humic substances (which revealed that the organic matter had been humified during composting) and the germination index, the latter indicating the reduction of phytotoxicity during the process.     

Evolution of the fulvic acid fractions during co-composting of olive oil mill wastewater sludge and tree cuttings

Fulvic acids (FAs) were isolated by a conventional procedure from two mixtures of the sludge residue obtained from olive oil mill wastewater (OMW) evaporated in open-air pond and tree cuttings (TC) at different stages of the co-composting process. The FAs were analyzed for elemental (C, H, N, S, O) and acidic functional group (carboxylic and phenolic) composition, and by ultraviolet/visible, Fourier transform infrared and fluorescence spectroscopies. At the initial stage of composting, FAs from the OMW sludge-TC mixtures were characterized by a prevalent aliphatic character, large contents of C, S-containing groups, proteinaceous materials and polysaccharide components, extended molecular heterogeneity, small O and acidic functional group contents, and small degrees of aromatic ring polycondensation, polymerization and humification. As composting proceeded, C, H and S contents, C/N ratio, and aliphaticity decreased, whereas N, O, COOH and phenolic OH contents, C/H and O/C ratios, and aromaticity increased. These results suggested that, with increasing the composting time, the chemical and structural properties of the FA components of the two OMW sludge-TC mixtures approached the characteristics typical of native soil FAs. Thus, co-composting of OMW sludge mixed with TC may represent a suitable treatment for enhancing the quality of organic matter in these materials when used as soil amendments.     

In vitro Studies on lignocellulose degradation by microbial strains isolated from composting processes

An in vitro study of different strains isolated from composting piles in relation to their capacity to biodegrade lignocellulose was achieved. Thirteen microorganisms (five bacteria, one actinomycete, and seven fungi) isolated from compost windrows were grown on agricultural wastes and analyzed for cellulose, hemicellulose, and lignin degradation. Hemicellulose fraction was degraded to a lesser extent because only two of the isolates, B122 and B541, identified as Bacillus licheniformis and Brevibacillus parabrevis, respectively, were able to decrease the concentration of this polymer. On the contrary, most of the isolates were capable of reducing cellulose and lignin concentrations; strain B541 was the most active cellulose degrader (51%), while isolate B122 showed higher lignin degradation activity (68%). Consequently, an increase in humification indices was detected, especially with respect to humification index (HI) for both bacteria and CAH/AF in the case of strain B122. According to these data, the use of microbial inoculants as a tool to improve organic matter biodegradation processes (i.e., composting) may become important if microorganisms’ capabilities are in accordance with the final characteristics required in the product (high humic content, lignin content decrease, cellulose concentration decrease, etc.).     

Enhancement of dry anaerobic batch digestion of the organic fraction of municipal solid waste by an aerobic pretreatment step

The start-up of the dry anaerobic batch digestion by the BIOCEL-concept of the organic fraction of municipal solid waste (MSW) is unbalanced when a methanogenic inoculum (digested sewage sludge) is added to a total solids concentration of 35%. The unbalanced conditions are the result of the rapid degradation of easily-degradable compounds which are present in the organic fraction. Enhancement of the first start-up of the dry batch digestion was tried by applying an aerobic partial-composting step. By this aerobic treatment the easily degradable compounds are removed. After the composting step the anaerobic digestion will be limited by the conversion of the ligno-cellulose part of the organic fraction. It appeared that at least 19·5% of the volatile solids (VS) should be converted during the aerobic composting period before acid formation in the digestion was in balance with the methane formation. This amount of aerobically degraded VS means a 40% loss of potential biogas. The loss of a part of the biogas is a major drawback to the partial composting as a method for enhancing the start-up of the dry anaerobic digestion. A shorter composting period which is combined with another start-up method might be a feasible method to decrease the energy input of the dry digestion process.     

Two-phase olive mill waste composting: enhancement of the composting rate and compost quality by grape stalks addition

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated by the olive oil industry. Its recycling as a soil amendment, either unprocessed or composted, is being promoted as a beneficial agricultural practice in the Mediterranean area. One of the major difficulties when composting TPOMW is the compaction of the material due to its dough-like texture, which leads to an inadequate aeration. For this reason, the addition of bulking agents is particularly important to attain a proper composting process. In this study we followed the evolution of two composting mixtures (A and B) prepared by mixing equal amounts of TPOMW and sheep litter (SL) (in a dry weight basis). In pile B grape stalks (GS) were added (10% dry weight) as bulking agent to study their effect on the development of the composting process and the final compost quality. The incorporation of grape stalks to the composting mixture changed the organic matter (OM) degradation dynamics and notably reduced the total amount of lixiviates. The evolution of several maturation indices (C/N, germination index, water soluble carbon, humification indices, C/N in the leachates) showed a faster and improved composting process when GS were added. Moreover, chemical (NH₄ ⁺, NO₃ ⁻, cation exchange capacity, macro and micronutrients, heavy metals) and physical properties (bulk and real densities, air content, total water holding capacity, porosity) of the final composts were analysed and confirmed the superior quality of the compost where GS were added.     

Bio-degradation of olive mill wastewater sludge by its co-composting with agricultural wastes

The use of maize straw (MS) or cotton waste (CW) as bulking agents in the composting of olive mill wastewater (OMW) sludge was compared by studying the organic matter (OM) mineralisation and humification processes during composting and the characteristics of the end products. Both composts were prepared in a pilot-plant using the Rutgers static-pile system. The use of CW instead of MS to compost OMW sludge extended both the thermophilic and bio-oxidative phases of the process, with higher degradation of polymers (mainly lignin and cellulose), a greater formation of nitrates, higher total nitrogen losses and a lower biological nitrogen fixation. The CW produced a compost with a more stabilised OM and more highly polymerised humic-like substances. In the pile with CW and OMW sludge, OM losses followed a first-order kinetic equation, due to OM degradation being greater at the beginning of the composting and remaining almost constant until the end of the process. However, in the pile with MS and OMW sludge this parameter followed a zero-order kinetic equation, since OM degraded throughout the process. The germination index indicated the reduction of phytotoxicity during composting.     

翻堆频率对堆肥减量化、腐殖化和稳定化的影响

好氧堆肥是有机固体废弃物处理处置的有效手段之一,堆肥还田也是贫瘠土壤改良的常用措施。但好氧堆肥是一个典型的CO_2等温室气体的释放过程。如何减少堆肥过程中的CO_2释放,强化堆肥的腐殖化过程对于实现有机固体废弃物的低碳化堆肥、提高作为优良土壤改良剂的腐殖质产量具有重要意义。本文选取农林秸秆和餐厨垃圾作为堆肥原料,研究不同翻堆频率对堆肥过程中的物料减量化、腐殖化和稳定化的影响,以期发现一个较低碳的堆肥工艺,并从微生物角度初步探索了其影响机制。研究结果显示,不同的翻堆频率(分别为每2 d、4 d和6 d翻堆一次),堆料的减量化和腐殖化程度有一定差异,翻堆频率为4 d的堆肥工艺物料减量率最高为50.5%,但碳减量率最低为77.4%;而翻堆频率为2 d的堆肥工艺腐殖质产量最高;3种堆肥工艺经62 d堆肥都达到了腐熟程度,翻堆频率为4 d的堆肥工艺腐熟化程度最高。不同的翻堆频率可能通过影响堆肥过程中堆料的温度、含氧量等因素从而改变堆料中活性微生物量、种类和生物酶活性,进而影响堆料的矿化和腐殖化进程。     

Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 1: chemical and spectroscopic properties

In this study changes in the properties of natural organic matter (NOM) were studied during composting of sewage sludge in a laboratory experiment using the pile method. Typical physicochemical parameters were measured during 53 days of composting including humic fractions. The effects of humification on the molecular properties of humic acids (HA) were investigated by 13C CP/MAS NMR spectroscopy. On the basis of chemical analyses, 53 days of composting sewage sludge with structural material can be divided into three phases: (i) domination of rapid decomposition of non-humic, easily biodegradable organic matter (two to three weeks), (ii) domination of organic matter humification and formation of polycondensed, humic-like substances (the next two weeks), (iii) stabilization of transformed organic material and weak microbial activity. Spectroscopic characterization (13C NMR) of compost humic acids reveals changes in their structures during maturation. The changes are highly correlated with the processes taking place in bulk compost.     

Evolution of organic matter from sewage sludge and garden trimming during composting

To use compost appropriately in agriculture it is extremely important to estimate the stabilization level of the organic matter. In this work, two different piles of compost were studied by means of (i) humification parameters (degree of humification--DH, humification rate--HR, humification index--HI) prior to and after enzymatic hydrolysis of the extracted organic carbon, (ii) water-soluble organic carbon (WSOC) and (iii) water-soluble nitrogen. A significant relationship between composting time, WSOC and humification parameters after enzymatic hydrolysis (DHenz; HRenz; HIenz) was found.     

Microbial degradation and humification of the lawn care pesticide 2,4-dichlorophenoxyacetic acid during the composting of yard trimmings.

The fate of the widely used lawn care herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) during the composting of yard trimmings consisting of primarily leaves and grass is an important unexplored question. In this study, we determined the extent of 2,4-D mineralization, incorporation into humic matter, volatilization, and sorption during the composting of yard trimmings. Yard trimmings (2:1 [wt/wt] leaves-grass) were amended with 14C-ring-labeled 2,4-D (17 mg/kg of dry weight) and composted in a temperature-controlled laboratory scale compost system. During composting, thermophilic microbes were numerically dominant, reaching a maximum of 2 x 10(11)/g. At the end of composting, 46% of the organic matter (OM) present in the yard trimmings was lost and the compost was stable, with an oxygen uptake rate of 0.09 mg of O2 per g of OM per h, and was well humified (humification index, 0.39). Mineralization of the OM temporally paralleled mineralization of 2,4-D. In the final compost, 47% of the added 2,4-D carbon was mineralized, about 23% was complexed with high-molecular-weight humic acids, and about 20% was not extractable (humin fraction). Less than 1% of the added 14C was present in water expressed from the finished compost, suggesting a low potential for leaching of 2,4-D. Very little volatilization of 2,4-D occurred during composting. It is of interest that our results indicate active mineralization of 2,4-D at composting temperatures of 60 degrees C because microbial 2,4-D degradation at thermophilic temperatures has not been previously documented.     

Comparison of bacterial community structure and dynamics during the thermophilic composting of different types of solid wastes: anaerobic digestion residue,pig manure and chicken manure

This study investigated the impact of composting substrate types on the bacterial community structure and dynamics during composting processes. To this end, pig manure (PM), chicken manure (CM), a mixture of PM and CM (PM + CM), and a mixture of PM, CM and anaerobic digestion residue (ADR) (PM + CM + ADR) were selected for thermophilic composting. The bacterial community structure and dynamics during the composting process were detected and analysed by polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) coupled with a statistic analysis. The physical-chemical analyses indicated that compared to single-material composting (PM, CM), co-composting (PM + CM, PM + CM + ADR) could promote the degradation of organic matter and strengthen the ability of conserving nitrogen. A DGGE profile and statistical analysis demonstrated that co-composting, especially PM + CM + ADR, could improve the bacterial community structure and functional diversity, even in the thermophilic stage. Therefore, co-composting could weaken the screening effect of high temperature on bacterial communities. Dominant sequencing analyses indicated a dramatic shift in the dominant bacterial communities from single-material composting to co-composting. Notably, compared with PM, PM + CM increased the quantity of xylan-degrading bacteria and reduced the quantity of human pathogens.     

Advanced bioconversion of biowaste for production of a peat substitute and renewable energy

Traditional composting systems for biowaste generally produce low quality composts that may endanger recycling. A pilot-scale bioconversion process yielding quality compost and renewable energy was designed and tested. The process consisted of a set of wet physical separation units, composting and anaerobic digestion. Biowaste was divided in four streams by physical separation: (1) organic fraction >2 mm, (2) inorganic fraction 0.05-2 mm, (3) residual fraction composed of organics 0.05-2 mm and the fraction <0.05 mm and (4) a fraction solubilised in the washing water. The organic fraction >2 mm was composted and the compost, high in organic matter and low in EC and heavy metals, aimed at replacing peat in horticulture. The inorganic fraction 0.05-2 mm was completely made up of sand and can be used as a construction material. Solubilised organic matter in the washing water was converted to CH(4) by anaerobic digestion. The residual fraction can be used as landfill cover material.     

The contribution of water soluble and water insoluble organic fractions to oxygen uptake rate during high rate composting

This study aims to establish the contribution of the water soluble and water insoluble organic fractions to total oxygen uptake rate during high rate composting process of a mixture of organic fraction of municipal solid waste and lignocellulosic material. This mixture was composted using a 20 l self-heating pilot scale composter for 250 h. The composter was fully equipped to record both the biomass-temperature and oxygen uptake rate. Representative compost samples were taken at 0, 70, 100, 110, 160, and 250 h from starting time. Compost samples were fractionated in water soluble and water insoluble fractions. The water soluble fraction was then fractionated in hydrophilic, hydrophobic, and neutral hydrophobic fractions. Each fraction was then studied using quantitative (total organic carbon) and qualitative analysis (diffuse reflectance infrared spectroscopy and biodegradability test). Oxygen uptake rates were high during the initial stages of the process due to rapid degradation of the soluble degradable organic fraction (hydrophilic plus hydrophobic fractions). Once this fraction was depleted, polymer hydrolysis accounted for most of the oxygen uptake rate. Finally, oxygen uptake rate could be modeled using a two term kinetic. The first term provides the oxygen uptake rate resulting from the microbial growth kinetic type on easily available, no-limiting substrate (soluble fraction), while the second term considers the oxygen uptake rate caused by the degradation of substrate produced by polymer hydrolysis.     

Composting of the solid fraction of olive mill wastewater with olive leaves: organic matter degradation and biological activity

The flocculated solid fraction of olive mill wastewaters, obtained from two different olive oil extraction systems (FOMW1 and FOMW2) was composted, with olive leaves (OL) as bulking agent, by the static pile system (Rutgers). The dynamic of organic matter (OM) degradation during composting and its relationship with the basal respiration and fluorescein diacetate (FDA) hydrolytic activity, as indicators of biological activity, were studied. Two mixtures were prepared: C1, from 65% FOMW1 plus 35% OL; and C2, from 74% FOMW2 plus 25% OL and 1% urea. The biooxidative phase of composting in C1, which had a high initial C/N ratio, was long, leading to a high OM degradation, mainly of the lignocellulosic compounds. The water-soluble organic carbon content, C/N ratio and the urea supplied as a N source for the C2 compost make this mixture more adequate for composting, as it had a shorter composting time than C1, and developed a microbial population with a high metabolic activity. The results for basal respiration in C1 and C2 were correlated at a high probability level with those of FDA hydrolysis, and both parameters can be used for establishing the degree of biological stability of the composting material.     

Two-phase olive mill waste composting: community dynamics and functional role of the resident microbiota

In this study, physico-chemical modifications and community dynamics and functional role of the resident microbiota during composting of humid husk from a two-phase extraction system (TPOMW) were investigated. High mineralization and humification of carbon, low loss of nitrogen and complete degradation of polyphenols led to the waste biotransformation into a high-quality compost. Viable cell counts and denaturing gradient gel electrophoresis (DGGE) profiling of the 16S rRNA genes showed that the thermophilic phase was characterized by the strongest variations of cell number, the highest biodiversity and the most variable community profiles. The isolation of tannin-degrading bacteria (e.g. Lysinibacillus fusiformis, Kocuria palustris, Tetrathiobacter kashmirensis and Rhodococcus rhodochrous) suggested a role of this enzymatic activity during the process. Taken together, the results indicated that the composting process, particularly the thermophilic phase, was characterized by a rapid succession of specialized bacterial populations with key roles in the organic matter biotransformation.