DYNAMICS OF COMPOSTING BIOSOLIDS WITH GREEN WASTE MATERIALS

Biosolids with green waste material composting has recently gained significance as an essential beneficial reuse strategy, especially in southern California. This is due to a convergence of several factors, including new road impact fees in land application host counties, new Class A requirements for land application, new setbacks and prohibitions on acreage that has been used for land application, and a desire for more local solutions among biosolids managers. This paper cites examples from projects (in southern California and elsewhere) that demonstrate the impact of these changes on biosolids composting strategies. The southern California market has changed in a number of ways recently. Namely, all conditions mentioned above have converged on this single geographic area. Consequently the cost of trucking and land application has risen from 20 to 30 per wet ton to 35 to 50 per wet ton. This rise in unit costs, together with the uncertainty of future restrictions and regulations has brought composting forward as an economically feasible alternative for biosolids disposal.As managers have looked to composting, they are faced with new challenges. These include, effectively controlling odors during composting, producing a quality product, and developing sustainable and cost effective compost marketing strategy. Southern California also has some unique complications in addition to these issues. Specifically, some proposed air quality regulations would require enclosed composting with emission control devices, as well as enclosed curing and product storage.The dynamics of odor control, product quality, and controlling cost, are the three most significant challenges facing the future of biosolids composting. They must all be executed successfully, and they are inter-related. The industry has some ambitious plans that must balance the three to be sustainable over the long term. The alternatives to composting appear to be exportation to remote land application, thermal technologies to create Class A biosolids for less remote land application, and new digestion technologies to increase the solids destruction while minimizing biosolids production. At this point in time, composting appears to be one of the most attractive alternatives. However, due to the number and size of facilities now being planned compost markets must be viewed as a dynamic situation.