Napoleon Waste Water Treatment Plant

   
Overview | Old and New Waste Water Treatment Plants | Treatment Process Stages
Plan Design Data

   Wastewater generated in Napoleon is collected by a combined collection system on the West and South sides of town and a separated system in the North, Central, and West sides of town. The wastewater is transported into the treatment plant through a 35 inch by 45 inch brick combined sewer and a 12 inch force main under the river from the south side lift station.

   The Napoleon Wastewater Plant is a trickling filter plant which includes phosphorus and grit removal facilities, primary sedimentation, nitrification, reaeration basin, final settling, chlorination,  dechlorination and sludge disposal.

   The sludge disposal equipment consists of a primary digester, two secondary digesters, two belt filter presses and a 258,000 gallon sludge lagoon.  Digested sludge is land applied for use as a soil conditioner.

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   The original plant was constructed in 1958 and was basically half the size of the current plant which was completed in 1982.  The 1982 plant expansion updated plant equipment and doubled the plants capacity with the addition of a new barminutor, one primary tank, a new chlorination tank, with building and a new primary and secondary digester.

  In order to meet new NPDES permit requirements, a $3.8 million expansion and rehabilitation project was started in the summer of 1997 and finished in November of 1998. The project increased the hydraulic capacity of the plant from 6.0 MGD to 7.5 MGD to provide more capacity for wet weather flows.

   The rehabilitated plant also provides for ammonia removal and dechlorination of plant effluent. The project also included the replacement of mechanical screens with two new traveling screens; the replacement of sludge collection equipment in the two existing primary tanks; and the addition of a third final settling tank and sludge pump, reaeration tanks and a blower building. Facilities for feeding chlorine gas, alum and sodium bisulfate in the process stream were also added.

   In order to cut costs, the rock media trickling filters were increased in height from 6 foot side walls to 32 foot and converted to biotowers with plastic media for ammonia removal and aluminum dome covers were also installed to protect the media.

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   The treatment process used at the Napoleon Wastewater Plant consist of the following basic stages:

SCREENING
   On entering the plant, the sewage is channeled through one of two traveling screens. The screens remove large solids and trash that could otherwise interfere with the operation of the plant. At appropriate intervals, the debris accumulated on the screens is removed for disposal to the sanitary landfill.   The screens are located in the new screen room at  the northeast corner of the Main Building.

DEGRITOR

   Sewage is then pumped to one of the two grit removal channels in front of the Main Building.  The mechanism is essentially a large mechanical rake, which drags the grit that settles out in the bottom of the channel, out of the channel and down the length of the basin and up the sloping end into a storage bin.  The motion of the mechanism washes the grit as it is worked up the incline.  If the grit was not removed from the sewage at this point, it would finally build up a solid cake in the bottom of  the tanks and digesters, thus seriously reducing the capacity of the basins and digesters, making it necessary to clean the units on a frequent basis. 

Primary Settling
   From the Degritor the sewage passes through the end of the channels to the Primary Settling Tanks.  In the primary settling tanks, solid particles in the sewage settle to the bottom and are swept into a sump by the tanks sweeps on the revolving mechanism.  From there they are pumped to the digester by the sludge pumps in the Main Building.  The sewage enters the settling tank at the center of the tank and flows through the v-notch weirs at the perimeter of the tank.  The floating material is collected by the surface sweep mechanism and disposed of.  Settled sewage from the primary tanks then flows into the recirculation chamber were sewage is continuously pumped to the high rate trickling filters.  The primary treatment stage of wastewater treatment removes 45 to 50 percent of the pollutants in the raw sewage.

Biotowers
  After primary treatment wastewater still contains solid materials either floating on the surface, or dissolved in the water, or both.  Under natural conditions these substances would provide food for such organisms as fungi, algae and bacteria  that live in a river or lake.  In our biotowers the sewage is distributed over plastic media in the towers that provide a medium for the growth of certain bacteria which feed on the dissolved solids in the settled sewage.  The organisms which develop within the towers  provide BOD removal and Nitrification for ammonia nitrogen removal. This stage of treatment can remove up to 85 to 90 percent of the pollutants found in the settled sewage.

Aeration Basin
   The aeration basin consists of  two channels which provide aeration detention time of 15 minutes at 2.5 MGD.  The basin also provides additional soluble BOD reduction, provides a feed point for alum,  phosphorus removal and conditions the floc from the biotowers.

Secondary Settling
  The final settling tanks clarify the effluent from the trickling filters by removing the solids formed by the biological process of the biotowers.  The effluent from  the settling tanks then flows into the chlorine contact chamber.

Chlorination
  In the chlorine contact chamber at average flow, a 45 minute detention time is provided for sterilization of harmful bacteria that may have survived the treatment process.  The flow through the tank is in a snake-like flow to maximize the contact between chlorine and the effluent.  The chlorine is provided from two gas chlorinators, which are connected to a bank of 150 lb. cylinders.

Dechlorination Chamber
   At the end of the chlorine contact basin, the chlorinated water flows into a baffled basin were Sodium Thiosulfate is added, to remove any chlorine still remaining in the plant effluent. The effluent then flows to the regulation chamber located to the east of the plant, just outside of the dike and then through the outfall sewer into the river.

Sludge Digesters
  The solids that are removed as sludge are pumped to the primary digester where they are heated and kept in circulation at a temperature of 95 degrees Fahrenheit.  At this temperature the volatile portion of the sludge is broken down efficiently by anaerobic bacteria.  During this process methane gas and carbon dioxide are formed, along with the reduction of the sludge volume.  The secondary digester is equipped with a gas tight floating cover which floats on a cushion of gas collected above the liquid surface.  The cover holds a normal day's gas production and its weight regulates the gas pressure.  The gas produced is used to heat the main building and heat the sludge.  The sludge is stored for a time in the secondary digester and as it stratifies, the remaining liquid is drawn of near the top and is pumped back to the plant influent.  The digested sludge is then pumped to the Belt Filter Press Building.

Belt Filter Press
  The digested sludge is then processed through the two 1.5 meter belt filter presses. As the sludge flows into the belt filter press, a polymer is mixed with the sludge to coagulate the solids and the remaining water is then removed as the sludge continues through the press. The sludge enters the press at 5 - 6% solids and comes off the press at 18 - 23% dry solids. After dewatering, the sludge has no objectionable odor. The sludge is then loaded on trucks and disposed of either as fertilizer or land filled.

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 Plan Design Data  

   All Units in Service

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