District of Columbia Water and Sewer Authority is currently constructing new solids processing facilities at Blue Plains, based on thermal hydrolysis, anaerobic digestion, and belt filter presses. The filtrate, which will have high concentrations of ammonia and carbon in the form of volatile fatty acids, will be treated in a sidestream facility before being returned to the plant. Sidestream treatment is needed to minimize recycle of ammonia to the mainstream process where it would exert significant oxygen and chemical demands. The DEMON ® deammonification process was selected as the most cost-effective treatment mode. The DEMON ® process will be applied in six sequencing batch reactors operating in parallel. The DC Water DEMON ® will be the largest facility of its type in the world. Scale-up and numerous detailed design features were incorporated during detailed design. Lessons learned in taking Concept Design through preparation of detailed Final Design will be presented.

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The biosolids management program being developed by DC Water is distinguished by the use of innovative technology (thermal hydrolysis for enhanced digestion kinetics), dedication to sustainability (energy recovery and Class A residual solids), implementation on a massive scale ($407M investment), and employment of multiple delivery formats for component projects (traditional design-bid-build for site preparation and final dewatering, alternative design build for the main process train, and alternative design-build-operate for combined heat and power). The biosolids program management team assembled by DC Water faced significant challenges to adapt the traditional project delivery mechanisms that have been used in the past for procurement, negotiation, design, and construction using two different alternative project delivery approaches on major elements of the biosolids program.Contract documents including drawings and specifications for traditional design-bid-build projects recognize that the design engineer and construction contractor have separate contractual relationships with DC Water but no direct relationship with each other. In alternative delivery type projects, the design engineer and construction contractor are integral components of the design-build team and individually may have no direct relationship with DC Water. The subtle differences in roles and relationships of various participants in the delivery process have a significant impact upon the development of drawings and specifications used in procurement for alternative project delivery.The development of the procurement package faced two conflicting needs, i.e. the need for ample review time versus the need for rapid program development. In an effort to address both needs, the biosolids program team established a series of discipline oriented workshops to allow technical input from DC Water engineering, operations and maintenance personnel without adverse impact on project schedule. Although equipment were not pre-selected or pre-qualified due to schedule constraints (exception being the Thermal Hydrolysis Process and Distributed Control System vendor), the request for proposal procurement documents do include prescriptive requirements for design aspects, process choices, sizing, controls, and equipment reflecting lessons learned in the construction, operation, and maintenance of existing facilities at Blue Plains. This paper presents the development after alternative project delivery selection of procedures and documents to achieve a balance between maintaining established DC Water quality standards and allowing innovative design-build proposals.

A decrease in the nitrogen discharge from wastewater effluent has been mandated by the U.S. Environment Protection Agency (EPA) under the National Pollutant Discharge Elimination System (NPDES) program to minimize the nitrogen loading into the Chesapeake Bay. Meeting this regional objective requires increasing the denitrification treatment capacity at the District of Columbia Water and Sewer Authority's (DC Water) wastewater treatment plant by constructing a new Enhance Nitrogen Removal Facilities (ENRF). This will increase methanol usage during denitrification, requiring regulated air permitting prior to construction and facility operation. It also requires implementation of O&M practices that mitigate methanol emissions, and periodic compliance filing to regulatory agencies. This paper discusses design, construction, and operating considerations including: a) implications on equipment and process design and operation b) integration of permit conditions into design and operation of ENRF system, and c) emissions mitigation and management through monitoring, O&M programs and software tools.

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