Brazoria County MUD No. 5 Wastewater Treatment Plant

The Brazoria County MUD No. 5 WWTP was originally designed using the Rotating Biological Contactor (RBC) process for biological treatment.  Unfortunately, the plant process was sized too small based on the manufacturer’s claims that the undersized designs would perform properly (such claims were common in the 1980’s).  In addition, the plant operators were having plugging problems in the RBC’s due to rapid growth of snails.

WaterEngineers recommended a design that would convert the RBC’s to provide primary treatment, followed by conventional activated sludge using coarse bubble aeration.  The project was designed and constructed in a 700,000 gpd first phase, followed by the 950,000 gpd final phase, to allow matching capital spending to the requirements for new home lots as they were developed.

Two rotating drum fine screens were installed at the head of the plant to remove influent debris.  An existing digester was converted to an aeration basin and a new aeration basin was constructed.  A second 40-foot square clarifier was added, as well as a new two-stage aerobic digester.  The air supply to the plant was expanded and upgraded by replacing noisy positive displacement blowers with four 1200-scfm multistage centrifugal blowers in a new blower building.  A new one-ton cylinder chlorine storage, handling and feeding facility was constructed to replace an existing pressure chlorine manifold using multiple 150-lb. cylinders of chlorine.

A hydraulic evaluation of the existing effluent sand filter indicated that it could handle normal flows but its capacity would be exceeded during peak flows. Since the effluent permit allowed for higher daily and weekly concentrations of the effluent parameters, an overflow weir was installed that would bypass a portion of the flow to the filters directly to the chlorine contact chamber during high flow periods. This allowed the facility to meet its effluent requirements without expanding the filter.