Stability Evaluation of Mixed Food Waste Composts

As interest in food waste composting grows, so does the need for proven composting methods. Stability testing has been proposed as a compost quality assurance tool. We conducted this study to: (i) to evaluate the efficacy of simple outdoor composting methods in producing a compost with a low, stable decomposition rate, and (ii) to determine the reliability of simple, 4-h compost stability evaluation methods. Composting was conducted outdoors in winter and spring in Eugene, Oregon without moisture addition. Mixed food waste was combined with screened dairy solids and ground yard trimmings. Sawdust was used to cover windrows for the first 27 d of composting. Compost windrow temperatures remained above 55°C for 30+ d. Carbon dioxide evolved with several 4-h test methods was strongly correlated (r² > 0.7) with CO₂ evolved using a 48-h test. A limited-turn windrow (LTW) composting system produced compost with slightly greater stability than a passively aerated windrow (PAW) composting system. Food waste compost samples had a low CO₂ evolution rate after 71 to 99 d using either composting system. Compost CO₂ evolution rate at 25°C decreased with composting time, reaching approximately 1 to 4 mg CO₂-C g compost C^?1 d^?1 for the PAW method and 0.5 to 2 mg CO₂-C g compost C^?1 d^?1 for the LTW method. Putrescible organic matter in food waste was effectively decomposed in outdoor windrows using composting methods that did not employ forced aeration, self-propelled windrow turners, or manufactured composting vessels. Several 4-h stability tests showed promise for implementation as quality assurance tools.     

Chemical and microbiological parameters for the characterisation of the stability and maturity of pruning waste compost

Composting of pruning waste, leaves and grass clippings was monitored by different parameters. A windrow composting pile, having the dimensions 2.5 m (height) x 30 m (length) was establish. The maturation of pruning waste compost was accompanied by a decline in NH₄ ⁺-N concentration, water soluble C (WSC) and an increase in NO₃ ^–-N content. Both organic matter (OM) content and total N (TN) losses during composting followed a first-order kinetic equation. These results were in agreement with the microbiological activity measured either by the CO₂ respiration or dehydrogenase (DH-ase) activity during the process. Statistically significant correlations were found between DH-ase activity, easily biodegradable organic C forms, NH₄ ⁺-N and NO₃ ^–-N concentrations and organic matter content and N losses. For this reason, DH-ase activity and the CO₂ evolution could be used as good indicators of pruning waste compost maturity. In contrast, humification parameters data from the organic matter fractionation did not agree with the initially expected values and did not contribute to the assessment of compost maturity. Neither the cation exchange capacity nor the germination index showed a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.     

Relating Compost Measures of Stability And Maturity to Plant Growth

Assessment of compost maturity is important for successful use of composts in agricultural and horticultural production. We assessed the “maturity” of four different sawdust-based composts. We composted sawdust with either cannery waste (CW), duck manure (DM), dairy (heifer) manure (HM) or potato culls (PC) for approximately one year. Windrows were turned weekly for the first 60 days of composting, covered for four winter months and then turned monthly for six more months. We measured compost microbial respiration (CO₂ loss), total C and N, C:N ratio, water soluble NO₃-N and NH₄-N, dissolved organic carbon (DOC), pH and electrical conductivity at selected dates over 370 days. Compost effects on ryegrass biomass and N uptake were evaluated in a greenhouse study. We related compost variables to ryegrass growth and N uptake using regression analysis. All composts maintained high respiration rates during the first 60 days of composting. Ammonium-N concentrations declined within the first 60 days of composting, while NO₃-N concentrations did not increase until 200+ days. After 250+ days, DM and PC composts produced significantly more ryegrass biomass than either CW or HM composts. Total C, microbial respiration and water-extractable NO₃-N were good predictors of compost stability/maturity, or compost resistance to change, while dissolved organic carbon, C:N ratio and EC were not. The compost NO₃-N/CO₂-C ratio was calculated as a parameter reflecting the increase in net N mineralization and the decrease in respiration rate. At ratio values >8 mg NO₃-N/mg CO₂-C/day, ryegrass growth and N uptake were at their maximum for three of the four composts, suggesting the ratio has potential as a useful index of compost maturity.     

Feedstock Carbon Influence on Compost Biochemical Stability and Maturity

Quantity and quality of readily degradable carbon influences the composting process especially for compost mixture high in lignocellulotic material. Effects of carbon source on stability and maturity of compost from in-vessel systems are poorly understood. Research was conducted to investigate the effects of carbon composition of feedstock on the evolution of stability indices and reliability of maturity tests for accelerated vessel composting systems. Rice straw, sugarcane bagasse, and coffee hulls were composted in a modified rotary in-vessel composter amended with either cattle or sheep manure. Distinct evolution patterns were observed across carbon sources for temperature, with the sugarcane compost never attaining thermophilic temperatures. Time to peak temperature and return to ambient were significantly different between the rice and coffee compost. Comparatively, organic matter degradation followed a similar pattern for all carbon sources, although rice straw showed the faster degradative rate and coffee hulls the greatest overall loss. Both pH and electrical conductivity were inappropriate stability indices across carbon sources, while the NH₄⁺/NO₃^? ratio was lower than the threshold from week 1. The Solvita® maturity test was the best suited quality indicator and was related to compost respiration. The rice compost at week 12 was the only mature compost with an index value of 7. However, the coffee compost was in the curing stage with a value of 6. In vitro phytotoxicity assays on hot pepper contrasted the Sovita® interpretation for rice compost, which showed the lowest germination index. All compost had a stimulatory effect on cucumber seeds. In vivo seeding assays corroborated in vitro results with rice compost showing the greatest negative effect, augmented at 100% compost inclusion. Carbon source significantly influenced compost stability and maturity indices, which suggests that greater attention should be directed to quality indices in relation to feedstock composition.     

Comparison of a gas detection tubes test with the traditional alkaline trap method to evaluate compost stability

Compost stability is an important parameter of compost quality. Among tests proposed to evaluate compost stability, microbial respiration is one of the better accepted tests. Variations in rates of CO₂ evolution during composting were studied in two pilot pruning waste piles using a windrow composting system. To measure the CO₂ production rate, two methods were compared: the alkaline trap test and gas detection tubes. Both respiration tests indicated increasing compost stability with processing time, but CO₂ evolution rates from the alkaline trap method were higher than values from the gas detection tube method. A first-order kinetic equation was used to describe CO₂ evolution over time. A linear relationship (r=0.81, p<0.01) was found between the two methods. Although both methods could distinguish unstable compost from stable compost, CO₂ detection tubes were easier to use and gave results in a shorter period of time.     

Microbial Population Dynamics and Enzyme Activities During Composting

The changes in population size of different microbial groups (total aerobic heterotrophs, actinomycetes, fungi, fecal coliforms, ammonium- and nitrite-oxidizing bacteria, and denitrifying bacteria) and the activities of 19 different enzymes (three phosphatases, three esterases, two proteases, three amino-peptidases, and eight glycosyl-hydrolases) were examined during cocomposting of poultry litter (a mixture of poultry manure, waste feed, feathers, and wood shavings) and yard trimmings (a mixture of grass clippings, leaves, and wood barks). Three piles with forced aeration were established by mixing 2:1 (v/v) ratio of poultry litter and yard trimmings. During composting, samples were taken at three different locations (top, middle, and bottom) of the forced aeration piles for microbial and enzyme analyses. Results demonstrated that population size of different microbial groups was not a limiting factor in this composting process as the microorganisms in the poultry litter + yard trimmings compost are in great abundance. Although the numbers of these microbial groups were reduced by high temperature, their populations multiplied rapidly as composting progressed. Fecal coliforms were eliminated by day 49, suggesting that the poultry litter + yard trimmings compost showed an overall increase in diversity and relative abundance of extracellular enzymes present as composting progressed. The population of fungi and actinomycetes (microorganisms active in degradation of cellulose, hemicellulose, and lignin) were positively correlated with esterase, valine amino-peptidase, α-galactosidase, β-glucosidase, and lipase. Of all 19 enzymes examined, ß-galactosidase (enzyme involved in the hydrolysis of lactose) had the most significant positive correlation with microbial populations, such as total aerobic heterotrophs, ammonium- and nitrite-oxidizing bacteria, denitrifying bacteria, and fecal coliforms. Cystine amino peptidase, chymotrypsin, and trypsin showed no evidence of activity during the entire period of composting. This composting process represented a combined activity of a wide succession of environments in the compost pile as one microbial group/enzyme overlapped the other and each emerged gradually as a result of the continual change in temperature as well as moisture content, O₂ and CO₂ level, and progressive breakdown of complex compounds to simpler ones.     

The Maturity and CH4, N2O,NH3 Emissions from Vermicomposting with Agricultural Waste

This study investigated the maturity and gaseous emissions from vermicomposing with agricultural waste. A vermicomposting treatment (inoculated Eisenia fetida) was conducted over a 50-day period, taking tomato stems as the processing object and using cow dung as the nutrient substrate. A thermophilic composting treatment without earthworm inoculation was operated as a control treatment. During the experiment, maturity indexes such as temperature, pH, C/N ratio, and germination index (GI) were determined and continuous measurements of earthworm biomass and CH₄, N₂O, and NH₃ emissions were carried out. The results showed that the temperature during vermicomposting was suitable for earthworm survival, and the earthworm biomass increased from 10.0 to 63.1 kg m^?3. Vermicomposting took less time on average to reach the compost maturity standard (GI 80%), and reached a higher GI (132%) in the compost product compared with the thermophilic composting treatment. Moreover, the decrease of the C/N ratio in vermicompost indicated stabilization of the waste. The activities of earthworms played a positive role in reducing gaseous emissions in vermicompost, resulting in less emissions of NH₃ (12.3% NH₃-N of initial nitrogen) and total greenhouse gases (8.1 kg CO₂-eq/t DM) than those from thermophilic compost (24.9% NH₃-N of initial nitrogen, 22.8 kg CO₂-eq/t DM). Therefore, it can be concluded that vermicomposting can shorten the period required to reach compost maturity, can obtain better maturity compost, and at the same time reduce gaseous emissions. As an added advantage, the earthworms after processing could have commercial uses.     

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.     

Biological,Chemical and Physical Properties of Composted Yard Trimmings as Indicators of Maturity and Plant Disease Suppression

A full scale system for composting of fermented, odiferous yardwaste trimmings was developed that produced a stabilized compost, minimized odor generation and prevented leachate formation. Characteristics of the compost highly significantly correlated with composting time included availability of the plant nutrients K, P, Ca and Mg, electrical conductivity, total carbon to nitrogen ratio, cation exchange capacity, stability based on O₂ respirometry, and finally, nitrate-nitrogen concentration. Radish was a good indicator of compost maturity. As the compost matured, suppressiveness to Pythium damping-off increased but it remained conducive to Rhizoctonia damping-off.     

Effects of Turning Frequency,Leaves to Grass Mix Ratio and Windrow vs. Pile Configuration on the Composting of Yard Trimmings

Because of proposed bans on the landfilling and incineration of leaves, grass and brush, large-scale composting is fast becoming the primary disposal option for yard trimmings in many states. Few systematic studies have been done to compare the effects of turning regime, feedstock mix ratio, or windrow vs. pile configuration on composting and the characteristics of finished compost. In this study, various ratios of leaves, grass and brush were mixed and composted in two series of windrows; and one set of static piles. One windrow series (#1) was turned seven times every four weeks, while the other windrow series (#2), and the piles, were turned once every four weeks. The effects of the different treatments were examined by measuring compost temperature, oxygen concentration, pH, organic matter and moisture content, volatile fatty acid content, bulk density, stability, humification and seed germination indices, total and available nutrient levels, and particle size distribution. Results showed that turning frequency had little impact on oxygen concentrations, VFA content and temperatures during the composting of yard trimmings in windrows, however, in piles temperatures were substantially higher and oxygen concentrations fluctuated greatly. The composts from all the treatments were stable, (oxygen uptake rates < 0.1 mg O₂/g OM/hr) after 60 days of composting regardless of the turning frequency, mix ratio or configuration. The bulk density inereased much more rapidly in frequently turned windrows than in the other treatments and particle sizes were smaller in these windrows. In most respects however, the final composts (day 136) were remarkably similar and none inhibited Cress seed germination or root elongation. The pH of all the composts, and the soluble salts and nitrate levels in composts made with high levels of grass, exceeded guidelines for greenhouse growth media.     

Chemical,Physical and Biological Criteria for Maturity in Composts for Organic Farming

Properties of organic farming composts were examined during the composting process: pH, electrical conductivity, C/N ratio, total N content, NH₄₊ content, NO_3?content, ash content, and organic matter content. In addition to these properties the respiration rate, microbial population counts, hydrolysis of Fluorescein Diacetate (FDA) and the activity of the enzyme amidase were studied. Composts at several stages of maturity were incubated in soil, and their N mineralization rates were measured. The end of the thermophilic stage was characterized by irreversible decrease in pile temperature to under 55°C, followed by stabilization of the chemical properties. This stage in the composting process is also characterized by decrease in CO₂ evolution rate, changes in microbial populations and specific patterns in FDA hydrolysis and amidase activity. Based on this evidence, we suggest that biological parameters can be considered as indicators for compost maturity.     

Evaluation of Parameters During Composting of Two Contrasting Raw Materials

The aims of this work were: i) to evaluate, during a composting process, some parameters in two contrasting raw materials: one a ligneous material (C1) and the other (C2) a mixture of horse and poultry manure with a low straw percentage and ii) to compare results from microbiological and chemical analyses of both composting material during the process. Total carbon, total nitrogen, C: N ratio, ash, organic matter, organic matter destroyed, CEC, soluble organic carbon, soluble ammonium and nitrate, ammonium: nitrate ratio and respiration rate were evaluated during 18 weeks. C1 material showed a lower rate of organic matter mineralization probably due to the high proportion of ligneous material. This material reached a greater CEC during the experiment. Increase in CEC during composting is due to conversion of the remaining organic material into humic substances. These results would imply that C1 presented a greater humification level and consequently, a better quality. On the other hand, the greater decrease in soluble organic carbon and NH₄⁺-N values in C2 is in accordance with greater organic matter mineralization. A high decrease in soluble fractions, especially the more degradable ones (water soluble components) indicates a high mineralization of the organic matter during composting and a lower humification level. According to the data obtained in our experiment, some parameters such as CEC, soluble organic carbon and soluble NH₄⁺-N seem to achieve the stability level for both studied materials, while those parameters or indices such as C: N ratio, NH₄⁺-N: NO₃^?-N ratio indicated stability/maturity only in C2 material during the experimental time.     

Nitrogen Availability Seven Years After a High-Rate Food Waste Compost Application

Long-term effects of compost application are expected, but rarely measured. A 7-yr growth trial was conducted to determine nitrogen availability following a one-time compost application. Six food waste composts were produced in a pilot-scale project using two composting methods (aerated static pile and aerated, turned windrow), and three bulking agents (yard trimmings, yard trimmings + mixed paper waste, and wood waste + sawdust). For the growth trial, composts were incorporated into the top 8 to 10 cm of a sandy loam soil at application rates of approximately 155 Mg ha^?1 (about 7 yd³ 1000 ft²). Tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’) was seeded after compost incorporation, and was harvested 40 times over a 7-yr period. Grass yield and grass N uptake for the compost treatments was greater than that produced without compost at the same fertilizer N rate. The one-time compost application increased grass N uptake by a total of 294 to 527 kg ha^?1 during the 7-yr. field experiment. The greatest grass yield response to compost application occurred during the second and third years after compost application, when annual grass N uptake was increased by 93 to 114 kg ha^?1 yr^?1. Grass yield response to the one-time compost application continued at about the same level for Years 4 through 7, increasing grass N uptake by 42 to 62 kg ha^?1 yr^?1. Soil mineralizable N tests done at 3 and 6 yr. after application also demonstrated higher N availability with compost. The increase in grass N uptake accounted for 15 to 20% of compost N applied after 7-yr. for food waste composts produced with any of the bulking agents. After 7-yr, increased soil organic matter (total soil C and N) in the compost-amended soil accounted for approximately 18% of compost-C and 33% of compost-N applied. This study confirmed the long-term value of compost amendment for supplying slow-release N for crop growth.     

Spectroscopic and thermal investigations on compost improved by iron salt addition

A quality compost obtained from sewage sludge (one part in weight) and yard trimmings and sawdust (two parts) has been investigated as a potential carrier of iron to plants. At the end of the thermophilic phase, the composting materials were added with crystalline FeSO4.7H2O (97%). Chemical properties, respiratory indices, and seed germination tests proved the compost to be suitable as an iron carrier in agriculture. Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy provided evidence of the effective linking of the iron ion to the organic molecule functional groups, thus preventing the loss of iron ion by leaching and precipitation phenomena and allowing the metal ion to be available to plants as both mineral and organic species. The thermogram obtained on compost without iron was similar to that previously obtained for composted materials of different origins, whereas samples with added iron ion exhibited in addition an exotherm in the medium-temperature region. FT-IR spectra carried out on samples heated at different temperatures indicated a loss of iron ion linked to carboxyl groups.     

Compost Maturity Effects on Nitrogen and Carbon Mineralization and Plant Growth

Improved predictive relationships between compost maturity and nitrogen (N) availability are needed. A total of 13 compost samples were collected from a single windrow over a 91 d period. Compost stability and maturity were assessed using both standard chemical analyses (total C and N, mineral N, total volatile solids) and other methods (CO₂ evolution, commercial maturity kits, and neutral detergent fiber, and lignin). Compost N and carbon (C) were evaluated during a 130 d aerobic incubation in a sandy loam soil after each compost was applied at 200 mg total kg^?1 soil. The effect of compost maturity on plant growth was evaluated by growing two ryegrass (Lolium perenne L.) crops and one barley (Hordeum vulgare L.) crop in succession in compost-amended soil under greenhouse conditions. Potential phytotoxicity from compost was assessed by growing tomato (Lypersicum esculentum L.) seedlings in compost-amended soil. Regression and correlation analyses were used to evaluate the relationship between compost maturity parameters, the rate and extent of net N and C mineralization, plant yield and N uptake, and phytotoxicity. Commonly used maturity parameters like total C, total N, and C:N ratio were poorly correlated with the rate and extent of mineralization, and with plant growth parameters. The N mineralization rate during the first 48 d of aerobic incubation was strongly correlated (r= ?0.82 to ?0.86) to compost fiber and lignin concentration, and to the Maturity Index (r=0.85). Trends in C mineralization were similar. There were few differences in C mineralization between composts after 48 d of aerobic incubation in soil. Ryegrass harvested 35 and 70 d after compost application was not strongly affected by compost maturity, and relatively immature composts were phytotoxic to tomato seedlings. Methods of characterizing compost maturity and stability that more realistically reflect the composting process are better predictors of N release and potential plant inhibition after incorporation into soil.     

Effect of Adding Flue Gas Desulphurization Gypsum on the Transformation and Fate of Nitrogen during Composting

The objective of this study was to investigate the effect of adding flue gas desulphurization gypsum (FGDG) on the transformation and fate of nitrogen during co-composting of dairy manure and pressmud of a sugar refinery. The ammonia absorption of FGDG was investigated. The changes in compost temperature, pH, electrical conductivity (EC), moisture, organic matter, the C/N ratio, Kjeldahl N, NH₄⁺-N, NO₂^?-N, NO₃^?-N were assessed. The addition of FGDG did not significantly affect compost temperature, pH, EC, moisture, and organic matter degradation. However, the addition of FGDG significantly increased the NH₄⁺-N content in the compost during the thermophilic phase, and the NH₄⁺-N maximal content in the compost with FGDG (CP+G) was 59.9% more than that in the compost without FGDG (CP–G). FGDG was thought to create the formation of (NH₄)₂SO₄ and the cation exchange between NH₄⁺ and Ca²⁺. The NO₂^?-N content in the CP+G peaked on day 15, and was not observed in the CP–G. In the final compost products, the NO₃^?-N concentration in the CP–G was more than that in the CP+G, which was 1451 (CP–G) and 1109 mg·kg^?1 (CP+G) dry material. This might be due to the NO₂^? accumulation in the CP+G, which accelerated N loss in the form of N₂O. There is a strong correlation between N₂O emission and NO₂^?-N accumulation in the composting process. Compared with the original N content in the compost mixture, the N loss in CP–G and CP+G were 15.0 and 10.8%, respectively. These results revealed that NH₄⁺-N conservation effect was improved during the thermophilic phase and the total N loss was mitigated by adding FGDG into composting materials. FGDG could be utilized as a potential amendment to conserve nitrogen during composting.     

Effect of Feeding Regime on Composting in Bins

Composting in bins is one of the most practical home composting methods. There is currently a need for greater information to improve the management of the composting process and to create home composting programs, which ensure sustainable production of high quality compost. This study investigates how two aspects of the bin feeding regime—the feeding frequency and the amount of waste applied at each feed—influence the process's evolution and the quality of the compost. Compost bins were assayed after introducing the same amount of kitchen and garden waste according to three different frequencies: in a single batch, weekly, or every 3 weeks. A fourth treatment was applied to calculate the potential waste reduction achieved by the composting process, filling the bins to the brim on a weekly basis. Temperature, mass, and volume changes; the microbial diversity (by Biolog); and gas emissions (CO₂, CH₄, N₂O, and NH₃) were all determined during the process. At the end of the experiment, all of the composts were weighed and characterized. Results show that the main differences were very dependent on the quantity of waste provided. Large amounts of waste were added increasing the compost's temperature and maturity during the process, while slightly affecting the salinity and phytotoxicity of the final compost but without any clear effects on microbial diversity and gas emission. Therefore, from a technical point of view, the shared use of compost bins among several households (community composting) is preferable to individual use.     

Maturity indices for composted dairy and pig manures

Bulking agents and bedding materials used on farms for composting manures affect the time required for composts to mature. The effects of these materials on guidelines for the use of composted manures in potting mixes are not fully known. Several chemical and biological compost characteristics were mentioned and a cucumber plant growth greenhouse bioassay was performed on samples removed from windrows during composting of: (i) dairy manure amended with wheat straw; (ii) dairy manure amended with sawdust (mostly Quercus spp.); and (iii) pig manure amended with sawdust and shredded wood (mostly Quercus spp.). Dry weights of cucumber seedlings grown in fertilized and unfertilized potting mixes amended with composts (30%, v/v) having stability values of <1 mg CO₂-C g^-1 dw d⁻¹, did not differ significantly from those in a control peat mix. Only the most mature dairy manure-wheat straw compost samples consistently established sufficient N concentrations in cucumber shoots in unfertilized treatments. For the dairy manure-wheat straw compost, all possible subset regression analyses of compost characteristics versus cucumber plant dry weight revealed that any of several compost characteristics (electrical conductivity-EC, compost age, total N, organic C, C-to-N ratio, ash content, CO₂ respirometry, Solvita CO₂ index and the Solvita^® Compost Maturity Index) predicted growth of cucumber in the unfertilized treatments, and thus maturity. In contrast, at least two characteristics of the dairy manure-sawdust compost were required to predict growth of cucumber in the unfertilized treatments. Effective combinations were EC with compost age and the Solvita^® maturity index with total N. Even five compost characteristics did not satisfactorily predict growth of cucumber in the non-fertilized pig manure-wood compost. Nutrient analysis of cucumber shoots indicated N availability was the principal factor limiting growth in potting mixes amended with the dairy manure-sawdust compost, and even more so in the pig manure-wood compost even though the compost had been stabilized to a high degree (<1 mg CO₂-C g⁻¹ dw d⁻¹). Maturity of the composted manures, which implies a positive initial plant growth response of plants grown without fertilization, could not be predicted by compost characteristics alone unless the bulking agent or bedding type used for the production of the composts was also considered.     

Evaluation of maturity of poultry manure compost by phospholipid fatty acids analysis

To study the influence of the physical properties of compost feedstock on some characteristics associated with maturity, two types of compost were made from poultry manure, rice husk, and rice bran. The bulk density of one type (PMC) was always higher than that of another type (NMC) during composting. In the case of PMC, the change in temperature, decrease in NH₄⁺, appearance of NO₃^–, and increase in germination indices (GI) with Japanese Komatsuna (Brassica campestris cv. Osome) were all more delayed than in NMC. As the composting process progressed, the proportion of branched (iso-, anteiso-, 10Me-) and saturated phospholipid fatty acids (PLFA) [BRANCHED FAMES (fatty acid methyl esters), biomarkers for gram-positive bacteria] gradually increased, then reached plateau. The high proportion of BRANCHED FAMES was maintained over a long storage period. The straight hydroxyl and saturated PLFAs (SOH-FAMES) initially increased, then disappeared with the progress of composting. The increase in BRANCHED FAMES and the decrease in SOH-FAMES were more delayed in PMC than NMC. The day on which the proportion of BRANCHED FAMES reached plateau and the proportion of SOH-FAMES dipped below 2 mol% coincided with the maturity stage based on the changes of physicochemical characteristics and GI. The composition of BRANCHED FAMES showed highly positive and negative correlation with GI and NH₄⁺, respectively. In the case of SOH-FAMES, inverse correlations were observed. This indicates that the proportion of BRANCHED FAMES and/or SOH-FAMES can be used as a tool for evaluating the maturity of poultry manure compost.     

Treatment of Source-Separated Human Feces via Lactic Acid Fermentation Combined with Thermophilic Composting

Human feces from urine diverting dry toilets can serve as valuable soil conditioners. For a successful agricultural application, an efficient pathogen reduction needs to be ensured, with no negative effects on plants. This study assessed the efficiency of lacto-fermentation combined with thermophilic composting on pathogen removal from human feces and the post-treatment effects on germination and growth of radish (Raphanus sativus) and tomatoes (Lycopersicum esculentum) compared to lacto-fermentation combined with vermi-composting and the control. The NH₄⁺-N/NO₃^?-N ratio of 3.0 and 3.6, respectively, suggested the obtained compost and vermi-compost was not yet mature. A complete reduction in the concentration of all investigated bacterial indicators (i.e., coliforms, Escherichia coli, Enterococcus faecalis, and Clostridium perfringens) from 5–7 log CFU g^?1 to below detection limit (<3 log CFU g^?1) was achieved after lacto-fermentation combined with thermophilic composting. Lacto-fermentation combined with vermi-composting also contributed to pathogen die-off, but coliform bacteria were reduced to only 5 log CFU g^?1. Fertilization of seeds of radish by compost obtained after lacto-fermentation combined with thermophilic composting led to a higher germination index than by the vermicast obtained by lacto-fermentation and vermi-composting (90% versus 84%). Moreover, significantly bigger average fruit weight and total biomass per tomato plant (p < 0.05) were obtained after compost amendment compared to vermicast or the control.