BioCycle July 2007, Vol. 48, No. 7, p. 26
From tip fee invoice tracking to process control to compost product sampling, information gathering, analysis and reporting are key to successful facility operations.
COMPOSTING is a highly regulated component of the waste management industry. It also manufactures a product that in many cases lacks an inherent demand by the buying public (unlike, say, shoes). These two distinguishing characteristics require careful attention to information management if a composting facility is to be successful. Information is what regulators need to do their job. Information is what answers neighbors’ questions, and it is the best compost sales tool in the producer’s toolbox.
Information management in composting requires monitoring, data collection, analysis, and reporting. Gathered information is needed for process and product quality control, regulatory compliance, good neighbor relationships and market education. Questions that need to be asked (and answered) about monitoring are: What should be monitored? How should it be monitored? How should the monitoring data be recorded and stored? How should it be organized, analyzed and reported? Deciding what to monitor can be answered with one word – everything (within the boundaries of reasonable cost). It is far easier to discard unneeded or unwanted information than to deal with problematic data gaps (i.e. lack of wind speed and direction data during an odor event that causes complaints).
Monitoring incoming wastes is a regulatory requirement in most cases, as well as the primary source of customer invoicing information for tipping fee materials. Monitoring composition of incoming wastes not only protects product quality, it can prevent unauthorized wastes from entering the facility, avoiding significant long-term headaches and costs in the case of hazardous materials. Incoming tonnages are weighed with either an on-site truck scale or through commercially-available off-site scales (like those at a truck stop). The weigh tickets a driver receives about the load are the backup proof behind the customer’s tip fee invoice.
Before a composting facility accepts a new waste for composting, potential customers should be requested to provide detailed chemical characterization data about the waste (total metals and Toxicity Characteristic Leaching Procedure (TCLP) data at a minimum, depending on the nature of the waste). Equally important, composters need to know about any changes to the waste composition as soon as they occur.
Understanding the physical and chemical characteristics of compostable feedstocks is paramount to good compost mix recipe development. Get a representative sample from the generator and send it to a qualified laboratory. At a minimum, analytical parameters to monitor are the percentages of total carbon, total nitrogen and moisture in the waste. Optional parameters would include bulk densities and soluble salts (electrical conductivity).
If your facility takes in wastes from multiple sources, be sure to get current heavy metals data on each incoming feedstock, as appropriate to the waste. (There is little need to monitor waste produce from a farmers’ market for metals.) You can use a spreadsheet program like Excel to array that data by element, then sum across all the feedstocks. Depending on bulking agent volume ratios and biodegradability over a three to four month period, heavy metal concentrations can increase during the composting process due to the loss of mass associated with volatile solids reduction. One rule of thumb is that the total amount of heavy metals in your feedstocks prior to compost should be less than 50 percent of the 40 CFR Part 503 limits (or 50 percent of your state’s limits, if they are more restrictive).
MONITORING THE PROCESS
Monitoring the composting process is required for effective process quality control, and in the case of temperature data, to verify the compost has met obligatory time-temperature standards (i.e. Process to Further Reduce Pathogens and/or Vector Attraction Reduction, or PFRP/VAR). The main process control elements to monitor are temperature, moisture and either oxygen or carbon dioxide levels (one is the inverse of the other). Measuring this data is traditionally done with manual methods and specialized monitoring equipment (moisture, of course, is often monitored with the rather nontechnical “squeeze” test). With the advent of computers and wireless networks, a whole new generation of compost process monitoring equipment and compost management computer software is now on the market. The advantages of these technologies are to reduce labor costs and to automate data monitoring and collection, which reduces the potential for error. Much of this was explored in a June, 2006 BioCycle article (see “Knowledge is Power in Compost Process Control” on p. 36 of that issue).
Systems that control operations or equipment in a plant are known as Supervisory Control and Data Acquisition Systems (SCADA). SCADA systems have been around since the 1960s and are widely used in wastewater treatment facilities to monitor the treatment process remotely and convey that information back to a central process control area. A SCADA system gathers information (such as where a leak on a pipeline has occurred), transfers the information back to a central site, then alerts the home station that a leak has occurred, carrying out necessary analysis and control, such as determining if the leak is critical, and displaying the information in a logical and organized fashion. These systems can be relatively simple, such as one that monitors environmental conditions of a small office building, or very complex, such as a system that monitors all the activity in a nuclear power plant or the activity of a municipal water system.
A simple SCADA system for composting facilities uses thermocouples to monitor pile temperature and then transmits that data back to a central process control computer, where the data can be analyzed to let the operator know if a pile has reached PFRP/VAR or if temperatures have declined to the point where the material can be moved to curing. In aerated static pile composting facilities, this same type of SCADA system can be used to adjust fan speeds (provided blowers are equipped with variable frequency drive units) as a function of pile temperature. SCADA systems can be either hard-wired or wireless.
The advantages of wireless monitoring systems are obvious – reduced labor cost for manual monitoring, instant (relatively) data transfer to a process control computer, and no need to deal with wired (cabled) systems, which are fraught with potential for damage from the moving equipment and the harsh environment of a composting facility. Wireless systems are not without their own challenges, however, as they rely on radio frequency (RF) waves for communication. RF waves require line-of-sight between transmitter and receiver. Signal repeaters are used to double the line of site distance when the range of the device is exceeded, such as at large windrow facilities. RF waves also are subject to interferences from other sources of electromagnetic radiation.
“These types of wireless systems are not really subject to much interference, as they do not broadcast continuously, unlike a cell phone,” says Michael Bryan-Brown of Green Mountain Technologies (GMT). “It wakes up for a couple of milliseconds every fifteen minutes and broadcasts data to a receiver.” Periodic transmission is fine for monitoring data (a temperature reading every three minutes is still far more information than what is needed for regulatory reporting), but not for real-time control, such as increasing fan speed in response to a climb in pile temperature, which needs monitoring frequencies of several reliable data points per minute.
One alternative to RF transmissions is remote data storage. This is the approach behind the PocketPC component of GMT’s Windrow Manager™ system, where a technician takes a small hand-held minicomputer out to record the temperature and oxygen data being captured (and stored in the remote probe). The PocketPC data then is downloaded to a central computer.
Another advantage to the remote data storage approach is cost, according to Nathan O’Connor of Reotemp (makers of the EcoProbe wireless compost monitoring system). “We’ve found that smaller composting facilities can’t justify the higher costs of wireless systems and are better off with one of various other collection methods, like our compost data logger which stores temperature readings within the probe,” he explains. “We’ve found that larger compost facilities either have the ability to create the control software in house or are hiring an outside engineering/design firm to create the software.”
Compost SCADA systems normally monitor temperatures, as this data is relatively easy to get and is most representative of the quality of the compost process. Monitoring oxygen (or carbon dioxide) and/or moisture is more often used to troubleshoot a potential problem flagged by temperature monitoring. GMT has developed a new wireless combination moisture and temperature sensor where the data is transmitted back to a receiving station every 15 minutes; Windrow Manager™ retrieves the data every 12 hours. Bryan-Brown notes this sensor is a capacitance-type moisture meter (like those used to monitor the moisture content of kiln-dried wood in furniture building) as opposed to the conductance-type moisture meter many are familiar with and that it is accurate provided compost salinity levels are below 8 mmhos/cm.
Conductance- and capacitance-type meters rely on the relationships between an electrical property and the moisture in a material. Conductance type meters measure the resistance to the flow of direct current, or low frequency alternating current, and capacitance-type meters measure some function of the dielectric constant. In principle, the dielectric constant is a measure of how much electric potential energy (dipole moment per unit volume) is stored in the material when it is placed in a given electric field.
Others are less convinced of the need for automated collection of oxygen and moisture data. “We have not seen an inherent value in automating that monitoring,” says Tim O’Neill of Engineered Compost Systems (ECS), which offers the TeleProbe Monitoring System and the CompTroller automated compost control system, “The main problem in our minds is how to keep the equipment properly calibrated.” O’Neill notes that oxygen sensors are subject to interferences from various compounds in the gas stream being monitored, and that they depend on permeability, which can be compromised by probe fouling: “The mushroom composting industry has used in-line oxygen sensors for years, but they have to calibrate those sensors weekly.” Bryan-Brown adds that its software recalibrates the oxygen sensor to 21 percent at the start of every sampling day.
Similarly, moisture meters are affected by the dielectric properties (electrical resistance) of the surrounding medium, which, in turn, are affected by density, moisture and composition of the material. Given the relative ease of a squeeze test and the finely-tuned accuracy of a quick microwave oven drying test, it’s not yet clear that automated monitoring and data transmission is cost-effective in every application.
Software systems available to monitor the composting process are based on graphical user interfaces that allow the operator to see at a glance how the composting process is doing. For example, the graphical depiction of a compost pile may be colored green if PFRP/VAR have been met, but grey if they have not been met. The software is capable of distilling the vast amounts of data acquired with these monitoring systems down to quickly understandable and useable formats.
How often should you monitor the composting process? Obviously, in the initial phases of composting, the answer is more frequently. Table 1 suggests manual (i.e. old-fashioned) monitoring frequencies for various parameters and at various points in the process.
Some compost process control parameters (as well as some feedstock characteristics) can be monitored in a small on-site field laboratory. These include moisture content (using a microwave and a scale), stability/maturity (with either a Solvita™ test kit or with a germination test), pH, bulk density, percentage of man-made inerts (regulated in final product quality in some states), and particle size (sieve analyses). Detailed physical and chemical characterizations of feedstocks and product quality should be done by a qualified outside lab.
SITE ENVIRONMENTAL CONDITIONS
Monitoring site environmental conditions is becoming increasingly important. There are a number of good quality, affordable weather stations on the market now, with the ability to interface with computers inside the composter’s office. For example, GMT’s Windrow Manager has the capability of weather data monitoring, which is very helpful for understanding ambient conditions at the site. This allows operators to make decisions about when to turn or tear down a pile, and also provides recorded histories of environmental conditions (useful in correlating a claim of an odor problem to actual wind speed and direction at the time of the complaint).
Future environmental monitoring needs will be related to storm water quantity and quality and to ambient air quality. Many states are now regulating compost facility storm water and requiring “no discharge” systems, where storm water is recycled into the compost process for moisture control, spray-applied to cropland, treated and released into nearby surface waters, or some combination of these options.
One of the advantages of an accurate remote moisture meter is to alert operators when windrow moisture levels drop so that a water tank and hose reel can be set up to irrigate. Ultimately, it may be possible for software to integrate monitoring systems with real-time equipment control systems, for example, to activate a pump to fill a windrow irrigation tank based on monitored windrow moisture levels, monitored storm pond water levels, and recent rainfall data.
Monitoring product quality is needed both for regulatory compliance and in support of compost marketing and sales efforts. Regulatory compliance parameters include biologicals (fecal coliform, salmonella, and Ascaris ova), heavy metal concentrations (usually the 40 CFR Part 503 list of metals), and, in some states, stability and/or percentage of man-made inerts (glass, metal, plastic, etc.). Market driven monitoring parameters are nutrients (both macro and micro), soluble salts (electrical conductivity), and horticultural characteristics such as water holding capacity, cation exchange capacity, etc. It is also possible to monitor final product for nonpathogenic biologicals (essentially the abundance and diversity of various micro and higher-order organisms), but the relationships between these biologicals, compost quality and the market’s willingness to pay are poorly defined at present.
A great challenge in analyzing product quality is ensuring that the sample going to the laboratory is representative of the product going to market. While materials handling procedures during the composting process can mix and combine compost so that variations from pile to pile (or batch to batch) are minimized, it’s a good management practice to develop a sampling plan (see sidebar).
Sampling frequencies are normally specified in a facility’s operating permit or in a state’s composting regulations, and are usually monthly or quarterly (small facilities may be able to test annually). Sample analytes (the parameters the lab tests for) are similarly specified in permits and in regulations. Compost quality certification programs, such as the U.S. Composting Council’s Seal of Testing Assurance (STA) and The Composting Council of Canada’s Compost Quality Assurance, are designed so that the most important regulatory and market-driven parameters are tested periodically by participants. In both initiatives, composters must use laboratories approved by the programs for compost product testing.
If you wish to make compost-based specialty soils (like U.S. Golf Association rootzone mix, bioretention pond growth media, green roof growth media, etc.), you will also need to sample and test those products for compliance with the appropriate specification. These specifications are primarily horticultural in nature, and include analytes like percentage of organic matter, pH, soil texture analysis, particle size analysis, infiltration rate, water holding capacity, and both macro and micronutrients. Remember, few construction specifications are written around compost-based materials, thus, lab data is essential to get a compost-based product approved by an architect or engineer as “equal” to the specified material.
In summary, the 21st Century has been called, by some, the Information Age. We clearly live in a world where vast amounts of information are being created and processed daily. Smart, deliberate and informed decision-making using an information management system and the application of computer-based monitoring and control programs – while challenging to learn – are becoming critically important aspects of successful composting operations.
Craig Coker is a Contributing Editor to BioCycle and a Principal in the firm of Coker Composting & Consulting in Roanoke, Virginia. He can be reached at (540) 904-2698 or by email at firstname.lastname@example.org.
COMPOST SAMPLING PLAN
KEY to compost product sampling is ensuring that a representative sample of the pile is collected for laboratory analysis. The sampling plan should specify who is doing the sampling, where the samples will be taken and how often samples will be taken. The following is a suggested sampling protocol:
1. Locations should be about 25 feet apart and depths should be at least two feet into the pile or windrow.
2. Tools must be clean and disinfected (be sure not to pick up that shovel used earlier to clean up some minor waste spillage) so as to avoid cross-contamination.
3. At each location, take a small subsample and transfer it to a mixing bucket or box, which will hold all the subsamples collected in that sampling event.
4. When collection is completed, mix all the subsamples together very thoroughly in the mixing bucket or box, then fill a one-gallon plastic bag nearly full with the mixed subsamples. If testing for biologicals, put the bagged composite sample on ice or in the freezer immediately.
5. The sampling technician needs to complete a Chain-of-Custody form when sending the sample to the lab. Ship samples with an overnight delivery service.