EVALUATIONS OF ALTERNATIVES FOR PRODUCING CLASS A BIOSOLIDS AT A REGIONAL UTILITY WITH MULTIPLE WASTEWATER TREATMENT PLANTS

The Washington Suburban Sanitary Commission's (WSSC) Prince George's County Biosolids Management Facilities Plan was produced in 1994. Since then, biosolids processing and disposal practices at the WSSC have remained relatively the same, despite the developments of numerous local and national issues in the biosolids industry. During this period, existing WSSC biosolids processing facilities have aged an additional 10 years, which makes most of the major equipment more than 15 years old, and some over 40 years old. Thus, significant investments in biosolids processing facilities are likely in the near future. It is predicted that in the year 2025, on average, approximately 58 DT of biosolids will be generated every day at all three plants.This paper summarizes a portion of a study that developed and evaluated different biosolids management alternatives for the three wastewater treatment plants in Prince George's County. Four basic biosolids management technologies and three sites combined to form thirteen specific management strategies. The management strategies included a variety of stabilization and disposal methods for the biosolids generated at the wastewater treatment plants that WSSC operates in Prince George's County. One of the options evaluated was to continue the existing Class B biosolids operations and determine its implications.The stabilization technologies considered were:

lLime/Heat Stabilization
Heat Drying/Pelletization
Incineration

The management strategies combined various forms of these technologies that ranged from building and operating a regional heat drying/pelletization facility at one of the three plants that treats all the biosolids generated at all plants, to building/operating three individual lime/heat stabilization at each plant.For each of the 13 management strategies, advantages/disadvantages were identified along with a present worth analysis that included both the capital and the operation and maintenance costs.Costs per DT biosolids generated were developed for each site under each management strategy for the following cost items:

Dewatering O&M
Stabilization O&M
Transportation
Disposal
Annualized Dewatering Capital Cost
Annualized Stabilization Capital Cost