69th Street WWTP Facility Rehabilitation
Phases I - IV
The 69th Street Complex is located on Buffalo Bayou, east of Downtown Houston near the IH 10/IH610 interchange. The plant was originally constructed in the late seventies and early eighties and consisted of two basic sections: the Wastewater Treatment Plant and the Sludge Handling Facility. S&B Infrastructure, Ltd. (S&BI) was called upon to manage a five-year program for the City of Houston to upgrade the facility in order to meet changing regulations and to enhance operations and maintenance. S&BI provided Preliminary Engineering Reports (PERs) for approximately 150 individual improvements. These documents enabled the city to prioritize budgeted funds and allocate resources to the most needed areas. S&BI was also responsible for preliminary and final design, cost estimating, and construction management. Projects included solutions to the grit problem, process projects, architectural work, instrumentation and control improvements, upgrade of existing mechanical equipment, and purchasing improved tools for plant operations and maintenance, such as:
Projects completed include administration building remodeling, renovation of four buildings, two new buildings, new roof sections, American Disabilities Act (ADA) upgrades, library upgrades, carpeting, fire sprinkler systems, elevator upgrades, pavement and parking upgrades, landscaping, area lighting, security, and fiber optic transmission cable systems.
Design of new pumps, centrifuges, and mixers, as well as rehabilitation of existing blowers, cranes, pumps, and mixers.
Modifications and upgrades to MCCs, a power substation, lighting, power factor correction network, building modifications, and an electrical security network (over 10,000 lf of fiber optics were used to tie the various system components together).
Digester improvements and new lines. Hydraulic analysis of treatment plant, analysis of bottlenecks, recommendations for piping solutions, analysis of grit removal system, plant operations, and repair of corrosive storage structure. Upgraded the wastewater process to improve its performance. This included improvements to the reactors, clarifiers, and screening facility and evaluated the non-potable/ potable water usage at the plant.
Instrumentation & Control Improvements
More than $5 million in upgrades to the Honeywell TDC systems from 2000’s to 3000’s;10 new PLCs; DCS graphics and programming; increased efficiency by adding new graphics to system; wrote several program conversions to preserve existing data; mapped entire system (city was unable to provide instrumentation or as-builts) and provided the city with a copy for their future use.
To meet increased need for capacity as a result of the city’s Infiltration/ Inflow program, S&BI identified hydraulic bottlenecks within the facility. By changing elbow size in the piping, the total capacity of the plant was raised to accommodate additional storm run-off. The required upgrades were accomplished with a total cost of less than $500,000 in piping upgrades.
The 69th Street Wastewater Treatment Plant (wet end) was designed for a 200-mgd capacity with a peak flow capacity of 400 mgd. It was the City of Houston’s largest wastewater treatment facility and consisted of a pre-treatment headworks, pure oxygen activated sludge system, filtration, chlorination and dechlorination.
The raw waste is collected in a wet well where it is discharged into a headwork entrance basin by four constant speed (52,000 gpm) and four variable speed (36,000 gpm) pumps. The headworks consist of four climbing bar screens and eight aerated grit chambers.The grit chamber effluent is discharged into a splitter box where the flow is divided between eight two-stage, activated sludge trains. The carbonaceous BOD removal first stage is followed by a nitrification second stage with each stage having its own individual clarifier. The activated sludge system employs the UNOX pure oxygen process with oxygen being generated on site with a 300-ton- per-day cryogenic oxygen plant.
The second stage clarifier effluents discharge into a common inlet channel feeding 22 automatic backwash, low head filters. The filter effluent is chlorinated, flows through three chlorine contact chambers, and is then dechlorinated, and discharged into Buffalo Bayou through an outfall structure upstream from the Houston Ship Channel Turning Basin.
The 69th Street Sludge Disposal Plant (dry end) was designed to process 112 tons of dry sludge per day with a short duration peak capacity of 140 tons per day. The sludge is extracted from the wastewater treatment plant process and concentrated by gravity in thickener basins. It is then pumped into aerobic digesters and later to the Sludge Plant, where it is dewatered by 21 centrifuges oriented in seven independent process trains.The sludge cake is dried by hot gases (1300° Fahrenheit) in seven gas-fired dryers and reduced to a combination of pellets and fine powder or dust. The dryer system contains specialized equipment to process the sludge. This includes belt conveyors, paddle mixers, screw conveyors, shakers, cage mills, cyclones, process fans, heat exchangers, scrubbers and stacks. The pelletized product from this sludge drying process is sold as fertilizer. The unsold sludge powder is loaded into trucks and hauled to approved landfills.