13C solid-state NMR assessment of decomposition pattern during co-composting of sewage sludge and green wastes

The fate of organic matter during composting is poorly understood. Therefore, we analysed composts of sewage sludges and green wastes (44 samples representative of 11 stages of biodegradation) by conventional chemical methods: pH, humic (HA) and fulvic acid (FA) content, C, N and organic matter (OM) content, and by ¹³C CPMAS NMR to assess the decomposition process of the organic matter. Chemical changes clearly occurred in two phases: first, decomposition of OM during the first 2 months was characterized by decreased C/N ratios, OM content and increased pH; and second, a humification process with increased HA/FA ratios. NMR spectrum changes confirmed this pattern, with an increase in aromaticity and a decrease in alkyl C. A decrease of syringyl to guaiacyl ratio (S/G), a sign of lignin transformation, also indicated humification during composting. NMR spectroscopic properties of composts were also studied by means of principal components analysis (PCA) and revealed changes according to the degree of compost maturation. The factorial map presents a chronological distribution of composts on the two first principal components. The influences of eight chemical factors on the PCA ordination of composts as monitored by their evolution by NMR were also studied by multivariate analyses. PCA clearly indicated two phases: the rapid decomposition of organic matter followed by the formation of humic‐like substances. The first phase, that is ‘new’ composts, was strongly correlated with OM contents, pH and C/N ratios whereas the second phase, corresponding to ‘old’ compost, was correlated with pH, HA content and HA/FA ratio. These results confirm that knowledge of the formation of humic substances is indispensable to suitable monitoring of the composting process.     

Characterization of Organic Matter in Compost Produced with Municipal Solid Wastes: An Italian Approach

Stabilization of the organic matter of a static pile of compost from municipal solid wastes (MSW) under a forced-pressure ventilation composting system was followed for 55 days during winter season. The materials were analyzed according to the official methodologies required by Italian regulations regarding the quality of composts from MSW. The stabilization process of the organic matter was monitored using both the degree of humification (DH), i.e. the ratio between the humified fractions (HA + FA) and the total extractable carbon (TEC), and the electrofocusing technique (EF). The DH increased steadily in compost during stabilization process and converged asymptotically at the end of the period of composting. The EF analyses of the organic extracts of compost from MSW showed a definite trend in the humification process and confirmed the actual evolution of the organic matter composted.     

粉煤灰和钢渣处理多种金属污染的酸性土壤，金属有效性的衰减研究

The objectives of this work were to determine the potential mineralization of various organic pollutants that are likely found in compostable materials during composting, and to evaluate the participation of the microflora of the thermophilic and maturation composting phases in pollutant mineralization. Four composts were used: a biowaste compost (BioW), a municipal solid waste compost (MSW), a green waste compost (GW) and a co-compost of green waste and sludge (GW+S). In each composting plant, two samples were withdrawn: one in the thermophilic phase (fresh compost) and one in the maturation phase (mature compost) to have the microflora of thermophilic and maturation phases active, respectively. The mineralization of 5 organic pollutants, 3 polycyclic aromatic hydrocarbons (PAHs) (i.e., phenanthrene, fluoranthene and benzo(a)pyrene), 1 herbicide (dicamba) and 1 polychlorinated biphenyl (PCB, congener 52), was measured in a laboratory setting during incubations at 60 ℃ in fresh composts and at 28 ℃ in mature composts. All molecules were 14 C-labeled, which allowed the mineralization of the molecules to be measured by trapping of produced 14CO2 in NaOH. Their volatilization was also measured by trapping molecules on glass wool impregnated with paraffin oil. Mineralization of the organic molecules was only observed when the maturation microflora was present in the mature composts or when it was inoculated into the fresh compost. Phenanthrene mineralization of up to 60% in the fresh GW+S compost was the only exception. Mineralization of PAH decreased when the complexity of the PAH molecules increased. Mineralization of phenanthrene and fluoranthene reached 50%-70% in all mature composts. Benzo(a)pyrene was mineralized (30%) only in the MSW mature compost. Dicamba was moderately mineralized (30%-40%). Finally, no PCB mineralization was detected, but 20% of the PCB had volatilized after 12 d at 60 ℃. No clear difference was observed in the degrading capacity of the different composts, and the major difference was the larger mineralizing capacity of the maturation microflora compared with the thermophilic microflora.     

Characterization of humic substances derived from swine manure-based compost and correlation of their characteristics with reactivities with heavy metals

Various composts contain a significant amount of humic substances including humic acid (HA) and fulvic acids (FAs). The FA fraction in soils is considered to be sensitive to agronomic and environmental factors. In this study, three fractions of humic substances, HA (MW > 1000 Da), FA (MW > 1000 Da), and FA (MW < 1000 Da) were extracted from swine manure-based compost and characterized, and then, their reactivities were correlated with heavy metals. Compositions of the three fractions of humic substances were characterized by elemental and total acidity analyses and electron spin resonance (ESR), Fourier transform infrared (FTIR), and 13C nuclear magnetic resonance with cross-polarization and magic-angle spinning spectroscopic techniques. Elemental analyses indicated that HA has higher contents of C, H, N, and S than those of FAs. However, FA (MW > 1000) and especially FA (MW < 1000) have higher contents of O than that of HA (MW > 1000). The g values of the ESR spectra of the three fractions showed that the organic free radical characteristics and the widths of the spectra and free radical concentrations of the three fractions are significantly different. The FTIR spectra indicated that HA (MW > 1000) is abundant in C=C bonds while FA (MW > 1000), especially FA (MW < 1000), are abundant in C=O bonds. In addition, 13C NMR spectra indicate that carboxyl contents of FA (MW > 1000), especially FA (MW < 1000), are higher than that of HA (MW > 1000). The sequence of the reactivity in terms of acidic functional groups was FA (MW < 1000) > FA (MW > 1000) > HA (MW > 1000). Elemental and functional group compositions of the three fractions significantly correlated with reported reactivities with heavy metals. The application of swine manure-based compost containing HA and FAs fractions to soil and associated environments may thus significantly affect the concerned reactions with organic and inorganic compounds including pollutants.     

母质对新形成腐殖质的影响

本文研究了在旱地和水田条件下,母质对新形成腐殖质的影响.供试物料为紫云英、绿萍、稻草和水葫芦.结果表明:1.除绿萍外,各物料腐解三年后均已分解较完全.腐解产物的C/有机N值和腐殖质组成均随原始物料而异.2.当植物物料和母质相同时,与水田条件下的相比,旱地条件下的腐解产物的C/有机N值大多较窄,中性糖量较高,六碳糖/五碳糖值较宽,腐殖酸的提取率较高.3.当水分条件和植物物料相同时,与第四纪红色粘土中的相比,下蜀黄土中腐解产物的胡敏酸的C/N值大多较窄,六碳糖/五碳糖值和胡敏酸/富里酸值大多较宽.作者认为,二者中腐殖质组成的差别在一定程度上系由于粘土矿物的组成不同所致.     

Changes in maturity indicators during the degradation of organic wastes subjected to simple composting procedures

Selected maturity indicators were monitored over a period of 335 days during the degradation of organic wastes subjected to four simple composting procedures, which varied in raw material (garden refuse with and without market refuse) and turning frequency (0×, 6×). All procedures produced mature composts. The inclusion of market refuse and frequent turning generally increased the cation exchange capacity of compost on an ash-free basis. Until day 118 of the composting process, compost samples which contained market refuse in their raw material mixture had the lowest redox potentials after anaerobic incubation. Cress grown on these composts also produced the lowest fresh mass. At a later stage of the composting process, the same composts displayed increased cellulolytic activity. Frequent turning of the compost heaps resulted in greater fluorescein diacetate hydrolysis, a greater occurrence of low-molecular-weight humic compounds and, occasionally, an inhibition of cellulolytic activity. The arginine ammonification assay gave information on the N-status of the composts, rather than on the compost maturity, and suggested that all the composts could be safely applied to soil with no risk of microbial immobilisation of soil N.     

Improving quality of composted biowaste to enhance disease suppressiveness of compost-amended, peat-based potting mixes

Biowaste can be converted into compost by composting or by a combination of anaerobic digestion and composting. Currently, waste management systems are primarily focused on the increase of the turnover rate of waste streams whereas optimisation of product quality receives less attention. This results in low quality composts that can only be sold on bulk markets at low prices. A new market for quality compost could be potting mixes for horticultural container-grown crops to partially replace non-renewable peat and increase the disease suppressiveness of potting mixes. We report here on the effect of wetsieving biowaste prior to composting on compost quality and on disease suppressiveness against the plant pathogen Pythium ultimum of peat mixes amended with this compost. The increased organic matter and decreased salt content of the compost allow for significantly higher substitution rates of peat by compost. In this study up to 60% v/v compost peat replacement did not affect cucumber growth. However, disease suppressiveness of the potting mixes strongly increased from 31 to 94% when the compost amendment rate was increased from 20 to 60%. It was shown that general disease suppression for P. ultimum can only be effective when the basal respiration rate is sufficiently high to support microbial activity. In addition, organic matter of the compost should reach a sufficient stability level to turn from disease conducive to disease suppressive. Increasing the compost addition from 20 to 60% did not significantly affect plant yield, yield variation were due to differences in nutrient levels. It can be concluded that compost from wetsieved biowaste has high potential to replace peat in growing media for the professional market.     

Chemical Evaluation of Compost Produced at a Large Greek Mechanical Biological Treatment Plant: Metal Availability and Phytotoxicity

ABSTRACT

The present work investigates the impact of municipal solid waste mechanical separation and industrial composting on the metal content of composts and assesses the availability of Cu, Cd, Cr, Pb, and Zn at different maturation stages of compost produced at the largest mechanical biological treatment plant in Greece. Substantial metal contamination of composts was found to take place within the industrial facility, attributed to segmentation and sorption mechanisms during composting. In fresh compost, Zn is present in mobile fractions (41%), Cu is mostly held on the less mobile organic phases (57%), Cd is mostly present in bioavailable forms (51%), whereas Pb and Cr are associated with less mobile phases, such as Fe-Mn oxides and organic molecules. Cd, Cu, and Zn migrate to more inert phases during compost maturation, paralleled by the decrease of overall metal leachability. Cu and Pb concentrations (mg kg^?1) exceeded the permissible limits in both composts (Fresh: Cu: 213 ± 48, Pb: 128 ± 69; Mature: Cu: 263 ± 1, Pb: 158 ± 29) and water leachates (Fresh: Cu: 106 ± 4, Zn: 126 ± 13; Mature: Cu: 50 ± 0.50, Zn: 118 ± 20). Nevertheless, toxic effects were not observed in monocot, dicot, or aquatic biosensor plants as indicated by radicle and shoot growth and visual quality ratings. Since metal availability in composts is related to their leaching potential, metal speciation studies should be conducted in leachates for the appropriate characterization of industrial composts.     

Evolution of composition and content of soil carbohydrates following forest wildfires

The time evolution of the content and composition of carbohydrates was studied in the surface layer of forest soils non-affected and affected by wildfires. The low- and high-severity fires caused an immediate reduction of the C present as carbohydrates of 34% and 47–55%, respectively, which was due to the decrease of both hexoses and pentoses in two hydrolysis fractions (hydrolysate-A, non-cellulosic polysaccharides; hydrolysate-B, cellulosic polysaccharides). Carbohydrates tended to recover with time; however, values had still not reached the amounts found in the corresponding unburnt samples after 12–15 months. No difference between the unburnt and burnt samples was observed in the distribution of the neutral sugars in the hydrolysates over time. On a percentage basis, 72–92% of the total neutral sugars was extracted in hydrolysate-A (59 ± 7% hexoses; 24 ± 7% pentoses) and the rest, 8–28%, in hydrolysate-B (15 ± 5% hexoses; 2 ± 1% pentoses). The contribution of hexoses and pentoses to the neutral sugar pool was different between the two hydrolysis fractions being the hexoses/pentoses ratio higher for hydrolysate-B than for hydrolysate-A. The results also showed that the proportion of soil C present as carbohydrates-C rather than the total carbohydrates content should be used for monitoring short- and medium-term changes induced by fire in soil organic matter quality.     

Effective cation exchange capacity of manure compost of varying maturity stages determined by the saturation‐displacement method

Abstract

The effective cation exchange capacity (ECEC) of manure composts, at the start and during the composting process, were determined. During this study we developed a new saturation‐displacement principle based method for compost samples. It was clearly demonstrated that ECEC of manure compost, as analyzed from three successive composting series, profoundly increased as compost matured. In addition, the ECEC values were highly repeatable, due to the proper mixing of the matrix with the saturation, washing, and displacement solutions, as well as to the preventing of any matrix losses with the separation of the matrix from those solutions with careful centrifugation‐filtration procedure.     

Maturity Tests for Composts — Verification Of a Test Scheme for Assessing Maturity

Increased recycling of organic wastes has raised concern about the quality of compost end products. In addition to the limit values for heavy metals and impurities including weeds and pathogens, the quality criteria for compost products should also include criteria for maturity. There is a tremendous number of maturity assays, developed earlier by several authors, and recommended to be used to evaluate maturity of composts. Because no such single test alone reliably demonstrates the complex properties occurring during maturization of compost, we developed a fast and easy-to-use two-phase test scheme for the assessment of maturity. In the first phase the degradation phase e.g. stability of compost samples is evaluated by using a carbon dioxide evolution test and/or determination of the NO₃-N/NH₄-N ratio by simple test strips. In the second phase, the toxicity of the compost is evaluated by a plant growth test, germination tests and/or the Flash bioluminescence test. Eleven plants composting sewage sludge, source-separated biowaste, manure or a combination of these raw materials were sampled after 1-3 weeks of composting and when the compost was considered “ready for use”. Chemical and physical analyses were considered useful as additional information when evaluating maturity especially when the results were not conclusively clear. This fast and easy-to-use test scheme was designed especially for the composting plant operators and official laboratories responsible for evaluating compost quality.     

Maize and pea germination and seedling growth responses to compost generated from biowaste of selected invasive alien plant species

Plant biowaste of alien species represents a potential resource for compost production. This study investigated the seed and seedling responses of maize and pea to composts generated from the biowaste of four invasive species in eThekwini, South Africa: Acacia podalyriifolia, Hedychium gardnerianum, Litsea glutinosa, and Tithonia diversifolia. Except for a 40% concentration of T. diversifolia, leachates of the biowaste from the four species had no marked effects on germination. In seedling growth studies, Berea Red soil (control) was supplemented with composts produced using combinations of the four species (A. podalyriifolia + T. diversifolia [T1], A. podalyriifolia + H. gardnerianum [T2], L. glutinosa + T. diversifolia [T3], and L. glutinosa + H. gardnerianum [T4]), and a commercial compost (T5). Carbon and nitrogen levels of the biowaste composts were higher than the control, while their associated C/N ratios were low enough to encourage microbial growth, facilitate rapid decomposition, and support plant growth. A comparison of percentage seedling production, growth rate, and biomass production between the commercial compost and alien biowaste treatments revealed all parameters to be statistically comparable among T5, T1, and T3 for maize, and between T5 and T1 for pea. These superior biowaste composts did not enhance growth relative to the commercial compost, but supported growth to the same extent. However, N and P levels in T1 and T3 were lower than the commercial compost and appear to have altered biomass allocation patterns in both species relative to the commercial compost. The results suggest that there is potential to use invasive alien plant biowaste to improve soil for agricultural purposes.     

Compositional Changes in Composts During Composting and Mushroom Growth: Comparison of Conventional and Environmentally Controlled Composts from Commercial Farms

Samples from conventional and environmentally controlled (EC) composts taken at various stages of composting and mushroom (Agaricus bisporus) growth were analyzed for changes in 80 percent ethanol and water extracts, monosaccharides in acid hydrolysates of polysaccharides, lignin concentrations and lignin structural features. The relative lignin content of all composts as measured by the acetyl bromide procedure increased, both during composting and mushroom growth. On the assumption that the absolute amount of lignin remains unaltered during composting and mushroom growth, the relative changes to the polysaccharide concentrations were calculated. Thus, during composting, 70, 53 and 58 percent of the initial wall polysaccharides for conventional, “cold” and “hot” EC, respectively, were consumed by compost microorganisms. During spawn running and fruiting, about 15 percent of wall polysaccharides were utilized from all types of composts. Thus, considerable amounts (17–31 percent) of polysaccharide remained at the end of mushroom production. During composting, there were changes in the degree of condensation and in the extent of oxidation of the lignins in all cases, but the rate and extent of these changes was dependent on the different composting regimes. During mushroom growth, further changes occurred, again with different patterns for the different compost types.     

Abstracts of nippon Dojyohiryogaku Zasshi

Color change of city refuse during composting process was investigated according to the methods of measurement for color of materials based on the CIE 1931 Standard Colorimetric System. Stimulus value Y (the degree of lightness) and chromaticity coordinates (x, y) were determined with Color Analyzer by measuring relative spectral reflectance. Stimulus value Y of city refuse decreased during composting process, but chromaticity coordinates (x, y) scarcely changed.

Color of various composts, which were produced from city refuse, straw, hog fecal wastes, tree bark, and tree bark mixed with activated sludge, were also investigated by measuring relative spectral reflectance. The shapes of the reflection spectra of city refuse were different from those of the other composts. Colors of the various composts were similar to each other when specified according to their three attributes: value, hue, and chroma (Munsell renotation).

While city refuse was rotting and maturing, stimulus value Yand C/N ratio equally decreased. A positive correlation was found between stimulus value Y and C/N ratio. It was concluded that stimulus value Y can be used as a criterion for determining the degree of maturity of city refuse compost.

The correlation between stimulus value Y and C/N ratio of various composts was also investigated. According to the position on the two coordinates having stimulus value Y and C/N ratio as axe s, various composts were classified into three groups: (i) city refuse compost group, (ii) straw compost group, and (iii) tree bark compost group.     

Evaluation of maturity and stability parameters of composts prepared from farm wastes

A composting experiment was carried out to study changes in physical [color, odor, temperature, organic matter (OM) loss], chemical [C:N ratio, water-soluble organic carbon (C_w):organic N (N_org) ratio, NH₄ ⁺-N and NO₃ ^?-N, humic acid (HA):fulvic acid (FA) ratio, humification index (HI) and cation-exchange capacity (CEC):total organic carbon (TOC) ratio)] and biological [seed germination index (GI)] parameters to assess compost maturity and stability over a period of 150 days. Five composts were prepared using a mixture of different farm wastes with or without enrichment of N, rock phosphate (RP) and microorganism (MO) inoculation. All the composts appeared to change to a granular and dark grey color without foul odor, and attained a constant temperature with no measurable changes (ambient level) at 120 days of composting. Correlation analysis showed that the optimal values of the selected parameters for our experimental conditions are as follows: organic matter loss > 42%, C:N ratio < 15, HA:FA ratio > 1.9, HI > 30%, CEC:TOC ratio > 1.7 and C_w:N_org ratio < 0.55. Composts enriched with N + RP or N + RP + MO matured at 150 and 120 days, respectively, whereas composts without any enrichment or enrichment with N or RP + MO did not mature even at 150 days of composting.     

Evolution of Humic Acid Molecular Weight As an Index of Compost Stability

This paper proposes an index for the evaluation of compost maturity based on the evolution of molecular weights of humic acids (HA) during composting. The evolution of HA molecular weight was followed during the composting of both olive mill wastewater (OMW) and olive mill pomace (OMP). The wastes were composted in forced aeration static piles. Samples of the compost were collected at different times during composting. The elution profiles of HA obtained by gel filtration (Sephadex G-150) showed the disappearance of fractions with molecular weights ≤ 50 KDa and the contemporary increase of fraction with molecular weights ≥ 10² KDa. In this range, two fractions can be separated: the first one (A1) with molecular weights greater than 10² KDa and below 2 10² KDa, and the second one (A2) with molecular weight greater than 2 10² KDa. During composting, the ratio A2/A1 tends to reach a constant value which indicates the evolution toward the polymerization of HA. The ratio A2/A1 was named HAEI (Humic Acid Evolution Index). It varies with the material composted and the composting process and represents the maximum possible degree of HA polymerization. A comparison between HAEI and the usually used maturity indexes is also presented.     

Windrow Composting Of Biodegradable Packaging Materials

The disintegration of Biopol-coated cardboard, polylactide fabric and film was studied using three different procedures: adding the samples directly to the compost pile, and placing them in the pile in nylon bags as well as in steel frames. Cellulose-based sausage casing, polyethylene and Mater-Bi ZF03U were also tested in steel frames as reference samples. Direct addition of the samples to the compost pile had no detrimental effect on the decomposition of compost biowaste. The use of steel frames proved to be good a method for testing samples like packaging materials. Both polylactide samples and Biopol-coated cardboard degraded completely in the steel frames. The results showed that composting activity parameters should be followed during composting before any conclusions can be made about the compostability of the samples. The compost produced from the polymer samples showed no toxicity in the plant growth test with barley and radish seeds performed at the end of the experiment.     

Evaluation of the maturity of municipal waste compost using simple chemical parameters

Abstract

Changes in different chemical parameters of the mixtures of several organic residues during composting were studied in order to establish simple parameters that can be useful as indices of compost maturity. Circular chromatography test and the study of the colour in solid samples of compost cannot be considered sufficiently reliable for determining the degree of maturity in composts. Similarly, parameters such as ash, C/N ratio, CEC, total organic carbon (TOC), and total nitrogen (TN) must be ruled out. Other parameters such as water soluble carbon (WSC), water soluble carbohydrates, the C/N ratio of the water soluble extract, and the ratios WSC/TN and CEC/TOC, can be used as indices of compost maturity.     

Total soil heavy‐metal concentrations and mobile fractions after 10 years of biowaste‐compost fertilization

The accumulation of heavy metals (HMs) in soils is the most often cited potential risk of compost application. As the ecological effects of metals are related to mobile fractions rather than to total concentrations in the soil, we measured the total (aqua regia–extractable) HM concentrations, the readily available water‐soluble and the potentially bioavailable LiCl‐extractable fraction of soil HMs in a field experiment after 10 y with total applications of 95, 175, and 255 t ha^–1 biowaste compost (fresh matter). Total soil concentrations of Cd, Cr, Cu, Ni, and Pb in the compost treatments were not significantly higher than in the unfertilized control. Total Zn concentrations increased in the treatment with the highest application rate, as expected from the calculation of the Zn load in the composts. In the mobile fractions, as measured in soil saturation extract and LiCl extract, Cd and Pb were not detectable. Concentrations of Cr, Ni, and Zn were in the range published for unpolluted soils in other studies and did not show any differences according to treatment. Easily exchangeable Cu (in LiCl extract) was increased with compost fertilization, most probably due to complexation with low‐molecular organic complexants. Except for Cd and Zn, the results of the mobile HM fractions in the soil were in good agreement with plant HM concentrations. In conclusion, fertilization with high‐quality biowaste compost at such rates and after 10 y of application gives no cause for concern with regard to both total HM concentrations and available HM fractions.     

Comparative Study on Biowaste Definition: Effects on Biowaste Collection,Composting Process and Compost Quality

A comparative study was run during 13 months on two biowaste definitions involving both lab tests and field surveys. A narrow biowaste definition, allowing only biogenic wastes (kitchen and garden waste) and referred to as ‘Biowaste,’ was compared to a broad biowaste definition, referred to as ‘Biowaste Plus’ and including man-made products, such as nonrecyclable wastepaper and diapers. Two similar test areas, each with about 425 inhabitants, were defined in a semiurban area north of Antwerp. During the entire test period, the amount of curbside waste (i.e., biowaste and restwaste or ‘grey waste’), was continuously measured and analyzed regularly (twice per season) for composition. At the start, middle and end of the test, the population of each test area was surveyed. Bench-scale aerobic composting experiments were run to evaluate the influence of both biowaste definitions on the composting process and the compost end product.

The introduction of source separated waste collection resulted in an overall landfill diversion rate of 43 percent for the (narrow) ‘Biowaste’ definition and 46 percent for the (broad) ‘Biowaste Plus’ definition. The contamination of biowaste with restwaste was low for both definitions (about three percent). Assuming that the collection and the appropriate disposal of organics could be improved to 95 percent efficiency (compared to about 60 percent currently), the landfill diversion rate could be increased to 59 percent for the ‘Biowaste’ and 74 percent for the ‘Biowaste Plus’ definition. Whereas the average sorting efficiency of separately collected organics was about 61 percent; 49 percent for nonrecyclable paper; and as low as 20 percent for certain categories of nonrecyclable paper (e.g., nonrecyclable cardboard packages). Apparently more education or a better systém of recognition and identification is needed to improve the collection efficiency of man-made compostables. Indeed, for easily recognizable products such as diapers, the sorting efficiency was as high as 70 percent.

The acceptance and goodwill of the population was significantly higher for the ‘Biowaste Plus’ definition, especially in the summer months. The yearly, overall composition of the total curbside waste (biowaste and restwaste combined) was 17 percent kitchen organics, 47 percent yard waste, four percent recyclable paper, 13 percent nonrecyclable paper and 19 percent noncompostables. It must be mentioned that glass, paper and large yard waste were collected separately by a voluntary bring-system. Biowaste Plus typically contained 16.0 percent paper (of which 2.9 percent was recyclable) versus 2.0 percent for Biowaste (0.3 percent recyclable).

The ‘Biowaste Plus’ definition resulted in improvements for the aerobic composting process due to easier moisture control, better aeration and a more tempered pH evolution. A significant difference was seen for NH₃ and corresponding odor emission, both being much lower with ‘Biowaste Plus.’ The quality of the compost produced was similar and acceptable for both biowaste definitions, according to existing standards (VLACO in Flanders and RAL in Germany).