BioCycle December 2008, Vol. 49, No. 12, p. 47
New technology measures four key composting parameters – temperature, oxygen, moisture and CO2 – and provides pile management instructions to operators.
Eric Crouch

IN recent years, the composting industry in the United Kingdom (UK) has increased considerably in size highlighting the need for a thorough management procedure throughout the composting process. In order to succeed, such a system should be capable of reducing production costs, increasing production volumes, improving product quality and demonstrating compliance with relevant and what may become future legislation.
The nature and complexity of monitoring and control systems currently in use in the UK vary enormously and are dependent on the size and type of composting method being used. The majority of open windrow sites routinely monitor temperature; some also monitor other parameters such as oxygen and moisture. Until recently, this recorded data have played a very small part in the management of most composting sites. Instead, day-to-day operation is based primarily on the movement of material through the site (from feedstock to finished product) rather than the creation of favorable microbiological and physical environments required for optimum composting. Sites operated with this limited level of control over the process are susceptible to problems with odor and poor quality end product, as well as increased costs associated with unnecessary fuel and plant usage.
Process Management Tool
Several years ago, the need for a comprehensive management process was identified by soil scientist George Longmuir of Freeland Horticulture. Freeland is one of the largest users of compost in the UK, currently supplying over 250,000 cubic meters/year of green waste compost for horticultural end uses including growing media and topsoil manufacture. To ensure a reliable supply of ever increasing volumes of high quality compost, Longmuir enlisted the author, with Soil and Land Consultants, Ltd., to develop a management and analytical system.
A monitoring instrument with a single probe and a software package that takes care of processing, storing, and interpreting all of the collected data was developed. The probe length, hole diameters, and spacings have all been optimized for windrow composting of green waste. The probe has integral moisture measuring electrodes, thermocouple, and gas sampling holes; the main instrument contains a simple user interface coupled to a gas sampling pump and sensors for CO2 and O2. There is also a Bluetooth-enabled cordless barcode scanner to provide traceable and reliable data.
The software is based on an algorithm developed from detailed analysis of data collected from extensive field trials, both on isolated windrows and full-scale operational sites. Parameters measured are temperature, oxygen, carbon dioxide and moisture. The role of the algorithm is to convert data collected from the instrument into meaningful and specific instructions for site operators. Data is forwarded via the Internet to a central unit.
The data can be viewed in a variety of ways. In its most simple form, the details of each windrow on the site are listed, together with the relevant instruction generated from the algorithm such as “Turn Row 3” or “Irrigate Row 6” (Figure 1). All four recorded parameters can be viewed for the entire site on any given day; historical data can be retrieved for any given row. Each row is identified by its own bar code. The instrument ensures that the correct barcode is scanned prior to a reading being taken.
Case Study
The Rainham composting facility is located to the east of London and is operated by Veolia Environmental Services PLC. The site processes about 75,000 (US) tons/year of green waste from curbside collections and recycling centers throughout London and South East England. The waste is shredded and formed into trapezoidal windrows about 15 feet wide by 10 feet high by 350 feet long. There are on average 25 to 30 windrows on the site at any one time. The windrows are periodically turned by front-end loader; temperatures are routinely monitored in order to demonstrate compliance with the UK standard for compost production (PAS 100).
An initial visit by SLC to the Rainham composting facility found that the moisture content of the material being composted was below optimum for the majority of the site. Correlation of gas levels to moisture content with the Composting System Analyzer showed that the low moisture levels directly resulted in a low rate of composting. Site operators improved the irrigation system and began applying a much greater volume of water when the compost was being turned.
The monitoring system was used regularly to monitor the rows. Figure 2 is an example of all four data parameters collected at the Veolia site. It was possible to demonstrate that by maintaining adequate moisture, the rate of composting increased significantly. This led to a noticeably superior end product with a lower proportion of oversized materials. The collected data and concise instructions generated enable Veolia to optimize operation of their site; consistently high quality compost can be produced with fewer turns and therefore at lower cost.
Dr. Eric Crouch is the principal research scientist with Soil and Land Consultants (ericcrouch@soil-land.com).