• Feedstocks Analysed at Celignis
    Spent Mushroom Compost

Background on Spent Mushroom Compost

Spent mushroom compost (SMC) is the substrate remaining after mushroom production, with approximately 5 kg of SMC produced for each kg of mushrooms. Mushroom compost is a mixture of 60 to 70% straw, 28 to 34% poultry litter, and 2 to 4.5% gypsum. It is made in a series of stages, termed phases. In the first phase the components (e.g. straw, litter, gypsum) are mixed and then placed in long windrows for a period of up to 2 weeks with the resulting product being termed Phase I compost. The second phase takes up to 18 days and takes place indoors in plastic tunnels that allow for the environment to be controlled so that any unwanted organisms or diseases in the compost can be controlled. Once the compost is of a quality suitable for mushroom production the compost is mixed with spawn, a monoculture of mushroom mycelium on grain. This compost is termed Phase II. Phase III involves the spawning and growth of the mycelium and takes place under controlled conditions. It is considered complete when the mycelia have fully colonised the compost.

Mushroom producers either receive Phase II or Phase III composts. Once the compost is fully colonised mushroom production involves placing a casing layer of peat on top of the compost. This layer promotes the formation of promordia; mushroom pins. Approximately three weeks after this point the first crop (first flush) of mushrooms can be harvested. The compost can then be rewet allowing for the harvesting of subsequent flushes at approximately 7 day intervals. Typically up to three flushes are harvested from each compost shipment. The remaining material is known as SMC and can sometimes be sterilised (cooked out) by heating for 12 hours at 70 degrees Celsius.

The overall composition of SMC will vary according to the time of year, the amount of peat casing put on by the grower, the compost manufacturers, and the amount of water added to the mushroom by the grower. The chemical composition of the ultimate spent material will be significantly different from the composite of the materials that make up the mushroom compost and casing layer, however, due to the effects of the composting process and mushroom growth.

Analysis of Spent Mushroom Compost at Celignis



Celignis Analytical can determine the following properties of Spent Mushroom Compost samples:



Lignocellulosic Properties of Spent Mushroom Compost

Cellulose Content of Spent Mushroom Compost

Celignis founder Daniel Hayes has extensive experience in the collection, preparation, and chemical/infrared analysis of mushroom composts and spent mushroom composts. He has carried out a research project, funded by the Irish Environmental Protection Agency, that involved the analysis of a number of samples. These samples covered the various stages of production of mushroom compost as well as spent mushroom composts produced in different greenhouses under different numbers of flushes.

Typically the cellulose content of spent mushroom compost is higher than the hemicellulose content but lower than the lignin content.

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Hemicellulose Content of Spent Mushroom Compost

Xylose is the principal hemicellulose sugar in most spent mushroom composts. However the ratios of the different sugars can vary substantially according to the stage of mushroom production. Therefore, specific analysis of the sample in question is recommended.

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Lignin Content of Spent Mushroom Compost

The lignin content of spent mushroom composts can be significant and can also vary greatly depending on the biomass that was used to make the compost and on the conditions used for mushroom growth.

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Starch Content of Spent Mushroom Compost

The starch content of spent mushroom compost is typically low as starch will have been utilised by the mushrooms.

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Uronic Acid Content of Spent Mushroom Compost

Uronic acids are present in the straws that are typically used to generate mushroom compost, however we are not aware of any studies to date on the fate of these uronic acids during the composting process and post mushroom production.

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Enzymatic Hydrolysis of Spent Mushroom Compost

We can undertake tests involving the enzymatic hydrolysis of Spent Mushroom Compost. In these experiments we can either use a commercial enzyme mix or you can supply your own enzymes. We also offer analysis packages that compare the enzymatic hydrolysis of a pre-treated sample with that of the native original material.

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Bioenergy Properties of Spent Mushroom Compost

Ash Content of Spent Mushroom Compost

Ash content of spent mushroom compost can be high and can also vary significantly.

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Heating (Calorific) Value of Spent Mushroom Compost

The heating value of spent mushroom compost is often quite low due to the high moisture and ash contents of the feedstock. Despite this, however, there has been commercial interest in the utilisation of spent mushroom compost in energy/power generation facilities. This is primarily due to its very low cost. Indeed spent mushroom compost can often be obtained for a gate fee.

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Ash Melting Behaviour of Spent Mushroom Compost

Ash melting, also known as ash fusion and ash softening, can lead to slagging, fouling and corrosion in boilers which may reduce conversion efficiency. We can determine the ash melting behaviour of Spent Mushroom Compost using our Carbolite CAF G5 BIO ash melting furnace. It can record the following temperatures:

Ash Shrinkage Starting Temperature (SST) - This occurs when the area of the test piece of Spent Mushroom Compost ash falls below 95% of the original test piece area.

Ash Deformation Temperature (DT) - The temperature at which the first signs of rounding of the edges of the test piece occurs due to melting.

Ash Hemisphere Temperature (HT) - When the test piece of Spent Mushroom Compost ash forms a hemisphere (i.e. the height becomes equal to half the base diameter).

Ash Flow Temperature (FT) - The temperature at which the Spent Mushroom Compost ash is spread out over the supporting tile in a layer, the height of which is half of the test piece at the hemisphere temperature.



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Major and Minor Elements in Spent Mushroom Compost

Examples of major elements that may be present in Spent Mushroom Compost include potassium and sodium which are present in biomass ash in the forms of oxides. These can lead to fouling, ash deposition in the convective section of the boiler. Alkali chlorides can also lead to slagging, the fusion and sintering of ash particles which can lead to deposits on boiler tubes and walls.

We can also determine the levels of 13 different minor elements (such as arsenic, copper, and zinc) that may be present in Spent Mushroom Compost.

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Analysis of Spent Mushroom Compost for Anaerobic Digestion



Biomethane potential (BMP) of Spent Mushroom Compost

Given that spent mushroom compost has high ash and lignin contents, it is not considered to be a good feedstock for anaerobic digestion. The matter is made worse by the low contents of labile sugars (e.g. water soluble carbohydrates) and relatively small amounts of cellulose and hemicellulose in the feedstock. Hence, even when expressed on a non-lignin volatile solids basis, the biochemical methane potential (BMP) is likely to be low.

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Physical Properties of Spent Mushroom Compost



Bulk Density of Spent Mushroom Compost

At Celignis we can determine the bulk density of biomass samples, including Spent Mushroom Compost, according to ISO standard 17828 (2015). This method requires the biomass to be in an appropriate form (chips or powder) for density determination.



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Particle Size of Spent Mushroom Compost

Given that spent mushroom compost has high ash and lignin contents, it is not considered to be a good feedstock for anaerobic digestion. The matter is made worse by the low contents of labile sugars (e.g. water soluble carbohydrates) and relatively small amounts of cellulose and hemicellulose in the feedstock. Hence, even when expressed on a non-lignin volatile solids basis, the biochemical methane potential (BMP) is likely to be low.

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Publications on Spent Mushroom Compost By The Celignis Team

Hayes, D. J. M. (2011) Analysis of Lignocellulosic Feedstocks for Biorefineries with a Focus on The Development of Near Infrared Spectroscopy as a Primary Analytical Tool, PhD Thesis832 pages (over 2 volumes)

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The processing of lignocellulosic materials in modern biorefineries will allow for the production of transport fuels and platform chemicals that could replace petroleum-derived products. However, there is a critical lack of relevant detailed compositional information regarding feedstocks relevant to Ireland and Irish conditions. This research has involved the collection, preparation, and the analysis, with a high level of precision and accuracy, of a large number of biomass samples from the waste and agricultural sectors. Not all of the waste materials analysed are considered suitable for biorefining; for example the total sugar contents of spent mushroom composts are too low. However, the waste paper/cardboard that is currently exported from Ireland has a chemical composition that could result in high biorefinery yields and so could make a significant contribution to Irelandís biofuel demands.

Miscanthus was focussed on as a major agricultural feedstock. A large number of plants have been sampled over the course of the harvest window (October to April) from several sites. These have been separated into their anatomical fractions and analysed. This has allowed observations to be made regarding the compositional trends observed within plants, between plants, and between harvest dates. Projections are made regarding the extents to which potential chemical yields may vary. For the DIBANET hydrolysis process that is being developed at the University of Limerick, per hectare yields of levulinic acid from Miscanthus could be 20% greater when harvested early compared with a late harvest.

The wet-chemical analysis of biomass is time-consuming. Near infrared spectroscopy (NIRS) has been developed as a rapid primary analytical tool with separate quantitative models developed for the important constituents of Miscanthus, peat, and (Australian) sugarcane bagasse. The work has demonstrated that accurate models are possible, not only for dry homogenous samples, but also for wet heterogeneous samples. For glucose (cellulose) the root mean square error of prediction (RMSEP) for wet samples is 1.24% and the R2 for the validation set ( ) is 0.931. High accuracies are even possible for minor analytes; e.g. for the rhamnose content of wet Miscanthus samples the RMSEP is 0.03% and the is 0.845. Accurate models have also been developed for pre-treated Miscanthus samples and are discussed. In addition, qualitative models have been developed. These allow for samples to be discriminated for on the basis of plant fraction, plant variety (giganteus/non-giganteus), harvest-period (early/late), and stand-age (one-year/older).

Quantitative NIRS models have also been developed for peat, although the heterogeneity of this feedstock means that the accuracies tend to be lower than for Miscanthus. The development of models for sugarcane bagasse has been hindered, in some cases, by the limited chemical variability between the samples in the calibration set. Good models are possible for the glucose and total sugars content, but the accuracy of other models is poorer. NIRS spectra of Brazilian bagasse samples have been projected onto these models, and onto those developed for Miscanthus, and the Miscanthus models appear to provide a better fit than the Australian bagasse models.





Examples of Other Feedstocks Analysed at Celignis



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