Fundamentals and Application of Windrow Composting

The conventional windrow and aerated windrow processes are viable sludge-disposal options that produce marketable end products. Both methods entail constructing long parallel rows containing a mixture of sludge cake and amendment and turning the rows frequently with mobile equipment. The conventional process relies on natural ventilation whereas the aerated method uses forced mechanical aeration in addition to natural ventilation. Major drawbacks of the conventional process include excess odor generation and susceptibility to upset from adverse weather. Odor control is a major advantage of aerated windrow composting; these systems, however, are more capital intensive than the simpler conventional systems. The Sanitation Districts of Los Angeles County, California, operate a state-of-the-art conventional windrow facility at the Joint Water Pollution Control Plant in Carson, California. The operation uses two composting steps and two different composting machines. Quality-control monitoring has shown that the two-step method provides excellent disinfection and produces a dry product during most of the year. Rainy weather and cool air temperature reduce the drying rate, resulting in the production of a wetter compost during the winter.