Feasibility of Processing spent mushroom substrate to recover additional value.
Composting is the breakdown of organic matter in the presence of oxygen. This is not new to mushroom producers, as a high percentage of the substrate is partially composted material. This substrate material is not "mature" compost when it is removed from the mushroom facility, however. It is possible that a more "sale"-able product may be obtained by allowing this SMS to complete the compost process. Active composting involves mixing the SMS and storing it in piles or windrows, which are periodically turned or agitated. This provides faster decomposition, prevents compaction and disperses gases (Hardy et al., 2000). This composting should be done on a concrete or compacted low-permeability surface, collecting waste liquids for storage and treatment. Piles need to be managed to maintain aerobic conditions, and storm water runoff should be diverted (Hardy et al., 2000). Heinemann et al. (2003) found that aeration significantly reduced the intensity and offensiveness of odors.
Anaerobic digestion is the breakdown of organic matter in the absence of oxygen. A typical system involves adding heat to maintain a specific temperature. The input material is in liquid form (usually between 1 and 15% dry matter) and at least 60% of the solids are volatile solids. This process usually takes between 15 and 40 days (20 days is typical). It yields biogas and a liquid digestate. The biogas consists mainly of methane and carbon dioxide. It is the methane that has the highest value, as it may either be burned directly or used to fuel a generator, thus producing electricity. The production of gas and electricity from a digester depends on the efficiency of the digester. Estimates of efficiency range from 16 to 50% (Hardy et al., 2000).
There is relatively little information on using anaerobic digestion to further process SMS. While there is some information on composting, there remain gaps in the knowledge. This study was initiated with the following objectives:
1. Assess the feasibility of using anaerobic digestion to further process spent mushroom substrate. A focus of this part of the study is the value of the recovered methane gas.
2. Assess the feasibility of using composting to further process and add value to spent mushroom substrate.
All tests were carried out at the Ridgetown Campus of the University of Guelph, located in Ridgetown, Ontario, Canada. A compost system and an anaerobic digester were both available for testing. The source of SMS was Rol-Land Farms, a major Ontario mushroom producer, located nearby. The compost trial began in December, 2005. The anaerobic digester trials began in January, 2006.
The composter was an in-vessel system consisting of three concrete channels-each 15.2 m long, 2.2 m wide and 1.8 m deep. The channels were covered (housed in a building), to give protection from the weather. The mechanical turner was the MARVEL (Global Earth Products). It was hydraulically operated, with an adjustable apron, so that the turner could move both directions in the channel. This allowed for batch composting.
Each channel was equipped with an aeration system installed below the floor. One aeration fan (Model # ILC-318, 2.25 kW electric) was provided for each of the three channels.
Compost temperatures in the channels were measured continuously using six thermocouples, connected to a data-logger (Campbell Scientific CR10). There were also thermocouples set up to measure outside air temperatures and the temperature of air inside the building.
The data logger read the temperatures and operated the aeration fans. A base level of aeration was maintained (3 minutes on in each hour) until any one of the six thermocouples in a channel exceeded 66[degrees]C. Then a second level of aeration was initiated--three minutes on for every 10 minutes, until the temperature dropped below 60[degrees]C.
The study was run as a single batch using all three channels. Composting measurements started on December 13, 2005. The SMS was weighed and evenly distributed among the three compost channels. A total of 72,670 kg of SMS was delivered and each channel received 24,223 kg (divided based on equal volumes). The resulting volume in each channel was 48 [m.sup.3], and the average depth was 1.5 m. Based on the earlier nutrient and moisture testing, no additions were needed to the composting mix (e.g. C:N ratio was 17 and moisture level was 58%). The test procedure was set up to compare turning frequency and its impact on how rapidly the SMS composted.
The material in each channel was mechanically turned on December 14, to break up any dense areas and to help level out the channels. This was the only turning for Channel 1. Channel 2 was turned monthly and the material in Channel 3 was turned weekly. The exception was a 20-day period between Day 8 and Day 28, when no turning was done. All compost sat undisturbed in the channels from February 8 until it was removed, starting May 10. Monitoring continued for 12 weeks when the composting process was expected to be finished.
The initial volume in the composting vessel and volumes throughout the study period were measured to track the reduction in compost volume. Measurements were made of the mass and bulk density of the SMS-at the start of the study, partway through the study and again at the end of the study period. The volume and mass of the finished compost (in each channel) were measured at the completion of the study.
Temperatures were measured constantly during the in-vessel treatment (December 14, 2005 to March 15, 2006) using up to 6 thermocouples per channel, connected to the data logger. Ventilation rates, static pressure and times of fan operation were also recorded. Odors were assessed subjectively during each visit to the compost building.
Two preliminary samples of SMS were collected to determine if additional carbon or nitrogen had to be added for composting. When the study was initiated, seven nutrient samples were taken to get a representation of the nutrient content of the SMS as delivered. Throughout the study period, two representative composite samples were taken monthly from each channel.
Samples for pathogen analysis were delivered within 24 hours of sampling to the Laboratory Services Division, University of Guelph. Pathogen samples were tested for Total Coliform and E. coli. Nutrient samples refrigerated until delivery to the Laboratory Services Division, University of Guelph. All nutrient samples were tested for N, P, K, N[H.sub.4]-N, N[O.sub.3]-N, Total Carbon, Organic Carbon, Inorganic Carbon, Ash, Dry Matter and pH.
In addition, several samples were taken to A & L Canada Laboratories Inc., London, Ontario for heavy metals analysis, maturity (C[O.sub.2]) and germination tests using cucumber.
The pilot scale digester is 2.6 m wide, 8.5 m long and 3.6m high. It is designed to operate in the mesophilic temperature range (around 37[degrees]C). It consists of two main tanks, both insulated and heated and all related piping, pumps, heating system and controls. The first tank is a mixing/preheat tank, with a capacity of 3200L. The main digestion tank (stainless steel) holds 7900 L. Each tank is cylindrical and has a mechanical mixer with several paddles that rotate based on preset times. Mixers are set to one hour cycles six times per day in the digester and three times per day in the mix tank.
The temperature of liquid in each tank is maintained using hot water. This water is heated in a water heater and circulated with a pump.
Normal operation involves adding a well-mixed liquid (target DM content of around six to 10%) to the mixing/preheat tank. If needed, extra liquid may be added in a nearby tank and the mixture stirred and pumped with a chopper pump. This tank is normally filled weekly. The liquid is temporarily stored in the mixing/preheat tank until it is added to the digester tank, at a rate of about 450 L per day (i.e. the normal rate of addition of fresh material). This addition of material is cycled manually and usually takes place only five days per week, so the average hydraulic retention time is in the range of 20 to 28 days. Once a new material is added, the system should reach a steady-state condition within a few weeks. As digestate is removed from the system it is directed to a nearby underground storage.
Biogas is stored in a bag beneath the digester. The biogas may be flared off or used to produce hot water for the digester or to run a small generator. During the fall of 2005, before SMS was added, the digester produced up to 10 [m.sup.3] of biogas per day using liquid swine manure.
The digester has thermocouples in the mixing/preheat tank and in the digester tank to measure temperatures. The level of digestate in the mixing/preheat tank and digester tank are measured by an electronic device connected to floats. An electric power meter measures all electricity used in the digester. The volume of all biogas produced in the anaerobic digester is measured with a gas meter. Finally, pH is measured using a portable meter.
The test ran from January 12 to March 31, 2006 (88 days). The recipe was based on the nutrient content of the SMS plus added water so that only the contribution of SMS to the biogas production would be evaluated. The mixture consisted of 180 L of SMS gradually added to 600 L of water--giving a final volume of 675 to 690 L. Only the volume of SMS added was measured--mass was not measured each time (the bulk density of fresh material averaged 505 kg/[m.sup.3], so it was assumed that 90 kg of SMS was added each time). The SMS was mixed using a shredder pump in a portable tank. This step was designed to raise the moisture level from around 70% (of the SMS) to about 94%. This moisture content was similar to the liquid swine manure previously tested in the system. During mixing, the solids had a tendency to float. These were mixed in using a fork or shovel. The pump was run for about an hour to ensure all coarse material was chopped up.
Approximately 1350 L of the SMS/water blend was added to the mixing/preheat tank. Typically this volume of material was added to the system twice per week. Material was prepared and added to the mixing/preheat tank to ensure that the blend of SMS and water could be added to the digester tank at a rate of about 450 L per day, for five days a week (i.e. the target rate of addition of fresh material).
During the study period, daily gas production was recorded, along with electrical power used, biogas pressure in the system, the temperature of the mix tank and the digester tank, as well as the heating system water pressure, pH of the SMS and water, mix tank and digester tank. Other operational notes were taken documenting how the digester was working and technical issues involved in operations. Samples of biogas, SMS and water, SMS, mix tank liquids, and digested SMS were collected throughout this time period.
A total of 42 biogas samples were collected using a 20 mL syringe. The gas was then injected into a pre-evacuated sealed vial (10 mL). The vials were refrigerated until shipping to the lab. The following samples were collected for nutrient analysis: the fresh SMS, the SMS/water mixture before entry into the digester, liquid from the mix tank and the digested SMS. Samples for the bacteria analysis were taken from fresh SMS (solid) being added to the digester and from the digestate draining from the digester.
The gas analysis was done using Gas Chromatography by the Department of Soil Science, University of Manitoba. These tests included methane, carbon dioxide and nitrous oxide. The remainder of the samples were delivered to the Laboratory Services Division of the University of Guelph. All nutrient samples were tested for Total N, P, and K, N[H.sub.4]-N, N[O.sub.3]-N, Total Carbon, Organic Carbon, Inorganic Carbon, Ash, Dry Matter, E.C. and pH. Pathogen samples were tested for Total Coliform and E. coli.
Results & Discussion--Composting
The SMS was brown to dark brown in color, with visible straw. The odor was slightly offensive, with an organic smell. Over time, the straw broke down and disappeared and the material became darker. On Day 28, the color was almost black. When Channels 2 and 3 were turned, the compost appeared to have a consistency similar to an organic soil. This was not the case on the surface of Channel 1, which had not been turned. The surface material had not been exposed to the high temperatures of the inside of the mass, and the straw had not broken down at all. By Day 57 (final turning date for Channels 2 and 3), the material appeared to be finished compost, especially in Channel 3. In color and consistency, it appeared to be at least as good as the bagged compost available at garden supply outlets.
Odor levels were generally low throughout the compost process, decreasing as time went on. By January 11, the building was odor free. When digging into the compost, any odors detected were best described as "earthy."
Within a day of adding the SMS to the channels, the internal temperatures in the channels had risen to the range of 40 to 60[degrees]C. Outside air temperatures were around 0[degrees]C throughout the study. Temperatures of the three channels and the ambient air are shown in Figure 1.
Generally, the temperatures followed the expected pattern: fairly high for several weeks, then dropping off and gradually approaching ambient air temperatures. These temperatures are consistent with a material that contains a good deal of compostable organic material. The temperatures in Channel 1 remained the highest during the study period, presumably because this channel was never turned. The temperatures represent averages of four to six thermocouples, but all were installed inside the compost mass. What they do not show is the fact that the surface material in Channel 1 was never exposed to the high temperatures, and therefore did not break down over time. In each case, the maximum temperature in the three channels was around 60[degrees]C for at least the first month in the channels. The locations in the channels of these maximum readings were not always the same.
[FIGURE 1 OMITTED]
Mass & Volume
The initial bulk density was 505 kg/[m.sup.3] and at Day 150, the values ranged from 626 to 725 kg/[m.sup.3]. The decrease in mass over time is shown in Table 1. These reductions ranged from 38 to 54% of the initial mass. Similarly, volumes reduced by 30 to 44% of initial values. Using Channel 3 as a design guide, we would expect the volume to decrease by about 2/3, the bulk density to increase from about 505 to 725 kg/[m.sup.3] and the mass to decrease to 1/2 of the initial mass.
Table 2 gives a summary of the main chemical constituents measured--for the initial SMS and for the compost in the three channels on Day 56. Considering the fact that the appearance of the material changed dramatically over the period of time and there was such a quantity of heat and moisture given off, the concentrations of the parameters in Table 2 changed surprisingly little.
The Conservation of Ash approach (assuming that ash remains constant) was used to create Figures 2 and 3. These graphs show the changes in the total mass of Dry Matter and N over the first 56 days of the study, when the most active composting was going on. The graphs demonstrate that the three channels performed similarly when considering these constituents, despite the turning frequency. As expected, the total dry matter decreased in all three channels. The amount of N lost from each channel ranged from 25 to 32%, with the lowest loss from Channel 1.
All Electrical Conductivity (EC) values are considered to be "high." Seeds should not be placed directly into this material without diluting with other soils having a lower salt content. None of the material used in these trials had been exposed to any rainwater--which would have helped lower salt content by leaching it out (and perhaps causing other environmental concerns). Samples of compost and fresh SMS were collected on March 15 for germination testing, using cucumber seeds. Germination results for Channels 1, 2 and 3 and the fresh SMS were: 86, 89, 97 and 97%, respectively. These relatively high values suggest that plant growth may be better than the EC test would indicate.
Samples collected on January 11 and March 15 were submitted for Compost Stability Index testing. This test measures the respiration of C[O.sub.2]-C, expressed as a percentage of both the total organic matter and also the total solids content of the compost. A Compost Stability Index value of 7 denotes compost that is "Well matured, aged compost, cured." A value of 8 is interpreted as "Inactive, highly matured compost." The sample from Channel 3 (turned weekly) collected on January 11 was scored 7, as was the SMS sample (collected December 13 and frozen until January 11). All other samples were scored 8. Given that the fresh SMS had such a high score, having undergone a considerable amount of composting activity before arriving as SMS, it was somewhat surprising to see the amount of heat produced when it was initially added to the channels. It obviously still contained significant amounts of compostable material.
The samples from March 15 (Day 92) were also submitted for an analysis of heavy metal concentrations. There are Canadian Guidelines for metals contents in compost that is marketed as finished compost (CCME & AAFC, 1995). The metals of concern were copper and molybdenum, where the compost concentrations were somewhat higher than the allowable concentrations. Copper levels ranged from 117 to 123 :g/g (Dry Matter basis) and the guideline is 100 :g/g. Molybdenum levels ranged from 5.4 to 7.7 :g/g and the guideline is 5 :g/g. It may be possible to reduce these concentrations at the source, but it is more likely that the compost could be mixed with a material such as sand, to dilute these metals to acceptable levels (and bring down salt concentrations also).
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Total Coliform and E. coli were detected in the fresh SMS and in composted SMS. Though the densities dropped as time went on, more samples should be taken to better document the survival (or re-establishment) of bacteria in the composting SMS.
An analysis was preformed based on current Ontario (Canada) costs. A summary is presented here. Based on a mushroom facility producing 750 t/week and composting in a covered in-vessel system for two weeks with a further two weeks of curing, the following are possible expenses and revenues (in $Can.--multiply by 0.9 to convert to $US):
* initial capital cost of the system = $2,628,000
* annual costs to own and operate = $702,000
* finished compost produced per year = 15,600 t
* annual revenue @ $30/t ("average" compost) = $468,000
* annual revenue @ $60/t (premium compost) = $936,000
* there are economies of scale so larger operations have an economic advantage
It appears that composting can be an economically feasible alternative method of handling SMS, as long as the compost can be sold at a premium price. Market development and market research is vital to ensure that the estimated value of the composted SMS can be realized. Of course, there is the potential to oversupply the marketplace, even if it is high quality compost.
Even though the composting SMS was left in the channels for 150 days, there would be no advantage to taking so long for this composting process to finish. Judging by the appearance of the compost, the material that was turned weekly (i.e. in Channel 3) could have been removed in three weeks or less. Certainly by the four-week period at the latest, the compost had an appearance similar to an organic soil. The material inside the mass of Channel 1 also had this appearance, but the surface material (which had never been mixed in) looked very similar to the fresh SMS. Based strictly on appearance, the desirable strategy would be to turn the SMS regularly (e.g. once a week or more often), to ensure good mixing and uniform breakdown of organic matter.
The biggest issues with the finished compost relate to salt and heavy metal levels. The nutrient tests showed relatively high salt levels--at levels, which would not support the germination of seeds without mixing with other soils. The germination tests were in conflict with these results. Cucumber seeds had relatively high germination levels.
Labor inputs were fairly low. Most of the labor with this system is in the moving of material in and out of the channels. Much of the rest of the process could be automated.
Results & Discussion--Anaerobic Digestion
The requirement to mix the SMS with water was somewhat cumbersome. This step required that a chopper pump be used for long periods of mixing. Even with all the mixing, settled solids created concerns. Figure 4 shows the cumulative loading of the system. The rate of loading remained relatively even from start to finish, although the loading rate for the first third of the study was somewhat higher than during the second two thirds.
The preheat tank maintained temperatures between 30 and 35[degrees]C for almost the entire study. The mean preheat tank temperature was 32.7[degrees]C. More important, the main digester tank temperature averaged 38[degrees]C and stayed between 35 and 40[degrees]C for almost the entire study (the lowest temperature was 33[degrees]C). There was no evidence to suggest that the variations in temperature caused any decrease in performance of the system.
[FIGURE 4 OMITTED]
The cumulative production of biogas between January 12 and March 31, 2006 is shown in Figure 5. During this 78 day period, biogas production averaged 0.99 [m.sup.3]/day. However, swine manure was used in the system prior to the start of this study and it took several days to move it out of the system. Assuming that the period between February 10 and March 31 represents a steady-state condition where only SMS and water are present in the system, the gas production from the SMS averaged 0.720 [m.sup.3]/day.
[FIGURE 5 OMITTED]
Overall, 18,950 L of the SMS/water mix were added to the system, at an average rate of 252.7 L/day. The average hydraulic retention time (HRT) was 31.3 days, longer than planned. However, during the first 28 days, the average rate of liquid addition was 299 L/day (HRT = 26.4 days). During the remaining 50 days, liquid additions averaged 212 L/day (HRT = 37.4 days).
During anaerobic digestion, it is the volatile solids that are broken down by bacteria to produce biogas. The SMS contained 65.4% (DM basis) Organic Matter--or Volatile Solids (VS). Another way of expressing this is that for the period of interest between February 10 and March 31, the loading rate of VS was 6.7 kg/day.
It is the methane portion that has the greatest value as an energy source, and the methane concentration of biogas (e.g. for livestock manure) is often in the range of 60 to 65% of total volume. This number varies based on the properties of the raw material, but the higher the percentage the better. For the 36 useable samples of biogas, the average concentration of carbon dioxide was 48.0% (range from 44.2 to 51.1%). The average concentration of methane was 49.3% (range from 47.6 to 50.6%). Only trace amounts of nitrous oxide were measured and no other gases were analyzed.
These concentrations of methane were low but not surprising considering the nature of the input material. The average biogas production from February 10 to March 31 was 0.720 [m.sup.3]/day. Therefore, the average production of methane was 355 L/day. If the loading rate of VS was 6.7 kg/day, then the SMS yielded only 53.0 L C[H.sub.4]/kg VS. To put this into perspective, it is useful to look at methane yields for livestock manure. A number of researchers have reported yields of between 288 and 562 L C[H.sub.4]/kg VS, depending on whether the manure was from swine, dairy, poultry or beef (e.g. Fulhage et al., 1993; Barker, 2001). The Ridgetown system yielded methane from swine manure at a rate of 410 L C[H.sub.4]/kg VS in November, 2005. It seems safe to conclude that the methane production for SMS is less than 20% of what might be achieved for fresh livestock manure.
Based on 355 L/day of methane, a heat boiler might typically produce 3.0 kWh of heat energy per day. Similarly an engine (e.g. 20% efficient at producing electricity and 40% thermally efficient) might recover 2.1 kWh/day (as electricity and heat). Compare this with the electricity needed to run the study. The demand was fairly steady throughout the time period. The main users of power were the water heater (needed to maintain tank temperatures) and the agitators. During the period from February 10 and March 31, electrical inputs averaged 89.8 kWh/day. It is likely that the electrical efficiency of the test setup could be improved by adding more insulation to the tanks and by converting to a gas water heater. However, the fact remains that the system generated methane having an energy value of about 2.1 kWh/day, while using 89.8 kWh/day. This fact should be enough to discourage anyone from considering this treatment option if the main benefit is recovery of energy.
General Discussion of Anaerobic Digestion
This portion of the study showed that SMS can be successfully digested using a mesophilic digester. The biogas yield was far below that which would be considered feasible. The energy inputs far exceeded the energy outputs (i.e. using methane gas as a fuel).
Anaerobic digestion was quite effective in reducing the levels of the indicator bacteria measured. Also, anaerobic digestion of SMS was effective in controlling odors. Odor emissions were minimal, and were only present in the raw materials (i.e. before entering the digester).
The digestate is a liquid, which contains nearly all of the nutrients that entered the digester. As such, it should be land-applied. There is a large volume of liquid that will require storage before land application, and trucking costs will be higher than for the original SMS due to the large amount of water that is needed. This consideration alone would be enough to discourage most producers from considering the treatment technology.
More water was added during this study than would theoretically be necessary, mainly to accommodate the equipment at hand. It was felt that this extra water would not hurt the process. However, a commercial setup would be designed to use less water. Reducing the volume of water would reduce the heat needed, would raise the throughput (and resulting gas production) and would reduce the volume of liquid digestate that must be stored and spread. It may however require several design changes to handle the thicker material. While most digesters are designed as liquid systems, there are anaerobic digesters designed to handle materials with lower moisture contents (e.g. source separated municipal organic waste). Perhaps these should be considered, though the gas output values will not improve.
This study confirmed that both composting and anaerobic digestion can be used to further break down the organic matter in Spent Mushroom Substrate (SMS). For composting, the SMS was added as-is to the channels of a covered in-vessel system having mechanical turning and forced aeration. Anaerobic digestion was carried out by first mixing the SMS with tap water to create a slurry. Specifically:
* The composting process resulted in finished compost having an excellent feel and appearance. It contained salt levels high enough to potentially limit the range of applications.
* Based on the final appearance of the compost, a marketable product could be removed from the system in as little as four weeks. Also, based on the final appearance of the compost, turning at least weekly was better than not turning at all or turning on a monthly basis. Weekly turning ensured a homogeneous end product with no sign of the straw present in the other channels.
* The final mass of the compost was 38 to 54% of the original, depending on the channel. A design value in the range of 40 to 50% appears reasonable.
* The biogas production (steady state period) averaged 0.72 [m.sup.3]/day, and methane represented 49.3% of the total gas yield (i.e. lower than desired).
* Both composting and anaerobic digestion were effective at reducing or eliminating odors and at greatly reducing numbers of indicator bacteria.
* In the original SMS, 65.4% of the dry matter was in the form of volatile solids.
* The methane yield from the steady state system averaged 53 L C[H.sub.4]/kg VS. This value is considerably less that what would be expected if livestock manure were the digested material (i.e. between 288 and 562 L C[H.sub.4]/kg VS, depending on manure type).
* Based on recovering 20% of the theoretical energy yield from methane in the production of electricity and a further 40% in the recovery of heat energy, the SMS biogas production was equivalent to 2.1 kWh/day. Unfortunately, electrical energy inputs to the system (for heating and agitation) averaged 90 kWh/day. Recovering energy from SMS in the form of methane using an anaerobic digester does not appear to be practical, since the energy inputs are so much higher than the outputs.
This study was made possible thanks to support from the Canadian Mushroom Growers Association and the Ontario Ministry of Agriculture, Food and Rural Affairs, through its partnership with the University of Guelph. Geoffrey Van Heeswijk provided invaluable technical assistance and Hank Vander Pol and Rol-Land Farms supplied the SMS and assisted in many other ways with the project.
Barker, J.C. 2001. Methane Fuel Gas from Livestock Wastes: A Summary. Publication No. EBAE 071-80, North Carolina Cooperative Extension Service.
Fulhage, C., Sievers, D., and Fischer, I. 1993. Generating Methane Gas from Manure. Department of Agricultural Engineering, University of Missouri Extension.
Hardy, C., Hedges, S., and Simonds, D. 2000. Integrated Bio-Systems: Mushrooming Possibilities. Yale Forestry & Environmental Studies Bulletin, Connecticut, USA.
Heinemann, P.H., Pretia, G., Wysocki, C.J., Graves, R.E, Walker, S.P., Beyer, D.M., Holcomb, E.J., Heuser, C.W., and Miller, F.C. 2003. In-Vessel Processing of Spent Mushroom Substrate for Odor Control. Applied Engineering in Agriculture, 19(4):461-471.
University of Guelph
Presented at the 2nd SMS Symposium
Table 1: Changes in Mass from start to study completion Channel 1* Channel 2 Channel 3 Mass (kg) Mass (kg) Mass (kg) Start (Day 0) 24,223 24,223 24,223 Final Day 150 13,175 9313 11,788 Final as % of Initial 54 38 49 * Channel 1 -- no turning; Channel 2 -- turned monthly; Channel 3 -- turned weekly Table 2: Chemical characteristics of fresh SMS on Dec. 13, 2005 and compost from the three channels on Feb. 7, 2006 (Day 56)--reported on an "As is" basis (i.e. wet weight) and on a "Dry Matter" Basis, as appropriate Units SMS Ch 1* Ch 2 Ch 3 N[H.sub.4]-N mg/kg (as is) 341 732 69.8 62 N[O.sub.3]-N mg/kg (as is) 14.1 71.3 116 128 Total N % (as is) 0.95 0.84 0.81 0.85 Total N % (DM) 2.66 2.65 2.38 2.38 Total P % (as is) 0.49 0.59 0.54 0.58 Total P % (DM) 1.37 1.86 1.59 1.62 Total K % (as is) 0.81 0.74 0.85 0.89 Total K % (DM) 2.28 2.32 2.51 2.50 pH pH units 6.5 7.8 7.3 7.4 Dry Matter % (as is) 35.7 31.8 34.0 35.7 Ash % (DM) 35.4 46.8 46.6 44.5 EC mS/cm 5.6 6.2 6.5 6.4 Total C % (DM) 30.7 28.1 28.4 29.1 Organic C % (DM) 29.7 26.4 26.5 27.5 C:N ratio 11.6 10.6 11.9 12.2 * Ch1 -- no turning; Ch2 -- turned monthly; Ch3 -- turned weekly