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News: Plant Spotlight

Smithfield – Tar Heel Facility Wastewater Treatment Plant

Thursday, May 3, 2018  
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Smithfield – Tar Heel Facility WWTP. Note the
90,000,000-gallon effluent storage basin to
the right.

 

Aeration basins and anaerobic lagoon
in background

 

Routine maintenance and repairs made to Aeration Basin 1 during Labor Day Weekend 2017.


 

Waste solids being dewatered on a two-meter belt press.

 

 

Clarifier effluent polishing/utilizing a DAF Unit.

 

 

Tim Weaver with Fuzzy Filter media.

 

 

Jacob Davis performing a bug count in the Lab.

 

The Tar Heel Facility WWTP next to the small package WWTP – the Sanitary Waste Package Plant.

Originally published in theWinter 2017-2018 issue of NC Currents magazine.

General

In 1992, Virginia-based Smithfield Foods extended its operations into Bladen County in the southeastern section of North Carolina. Since that time, the Tar Heel facility has expanded into the largest pork processing facility in the world, currently employing about 4,600 associates in the daily production of Smithfield’s line of quality pork products. The production facility typically works five days a week, harvests 34,000 heads of hog per day, and is ISO 14001 certified. The Environmental Department of Smithfield – Tar Heel currently has 24 staff members, with three management and clerical staff, six operating the pretreatment unit and solids handling facilities, six operating the wastewater plant (WWTP), three operating the reuse and potable well water system, three operating the potable surface water plant, one dedicated maintenance mechanic (with production plant maintenance assistance, when required), and two lab personnel. This allows for 24/7/365 monitoring of all environmental operations within the facility. The WWTP has a “flow equalized” design flow of 3.0-mgd (monthly average) and the plant’s effluent discharges into the Cape Fear River Basin. 

 

Key Treatment Processes Include: Pretreatment:

 

 • Three rotating drum screens

• One 250,000-gallon dissolved air flotation (DAF) unit

• Two three-phase centrifuges (solids, grease, centrate)

 

WWTP:

 

 • One 90-MG effluent storage basin

• Two 13-MG anaerobic lagoons (26-MG capacity)

• One biogas system (biogas sent to feed three boilers for steam to the production facility)

• Three anoxic basins

• Three 1-MG aeration basins and one 2-MG aeration basin (5-MG of aeration capacity)

• Four clarifiers

• One clarifier effluent polishing DAF unit

• Four Schrieber Fuzzy Filters

• Dual disinfection - chlorination (sodium hypochlorite)/dichlorination (sodium bisulfite), and ultraviolet (UV) light

 

Solids Handling:

  • One 500,000-gallon WAS sludge holding tank

• One two-meter belt press

 

Water Reuse:

 • Two flocculators

• Two lamella plate clarifiers

• One Schrieber Fuzzy Filter

• One chlorine contact chamber

 

Treatment Processes

 The WWTP operates in concert with the main facility’s production schedule. During an average production day, the WWTP can expect to receive a flow of up to 4.6-mgd of production water, with flow decreasing on the weekends to around 600,000 gallons per day.

 

 The recovered processing water first flows to our pretreatment unit, where it is screened to remove any bits of meat or other solids. Next, chemicals (typically an alum-based coagulant and polymer) are added and the water is passed to a DAF system.

 

The system acts as a reverse clarifier, causing the solids and grease to rise to the top, where they are skimmed off. The skimmings are sent to a three-phase centrifuge, which spins the skimmings and separates out solids, grease, and the leftover centrate. The solids and grease that are recovered are then sent to the rendering facility and sold as a product, and the centrate is recycled back to the raw water for another pass. Next, the DAF effluent is pumped to the WWTP, where it is equitably split between two covered anaerobic lagoons. These lagoons process the wastewater using anaerobic bacteria and convert a portion of the remaining ‘food’ into methane gas. We typically experience a 65 to 70% drop in chemical oxygen demand (COD) through this process. The methane is utilized to fire three boilers that supply steam to the production facility, displacing the equivalent of $30,000 of natural gas monthly, on average. These lagoons also serve as flow equalization for downstream processes.

 

During the production week, we utilize a flow control valve and allow water to accumulate in the anaerobic basins. During the weekend when we have lower influent flows, the water level decreases. This allows a more steady state flow throughout the downstream treatment processes. As the water moves forward, we go into our aerobic biological treatment and biological nutrient removal processes. The anaerobic effluent is distributed to the anoxic basins and is mixed in with aerobic bacteria by way of return activated sludge (RAS) from the clarifiers and mixed-liquor return (MLR) from the aeration basin effluent. The anoxic effluent is then distributed to the aeration basins, which utilize aerobic bacteria to remove the remaining ‘food’ via biochemical oxygen demand (BOD) and COD.

 

 Excess solids are sent to a 500,000-gallon aerated storage tank and are dewatered using a two-meter belt press. The solids are sent to a landfill as a bacterial supplement to enhance methane production. The methane is then used by the landfill to generate power.

 The WWTP has limits on both ammonia and total nitrogen in our discharge. In order to satisfy both requirements, we go through the process of nitrification and denitrification. Nitrification occurs in the aeration basins at the same time the ‘food’ (BOD, COD) is being removed. A special group of aerobic bacteria (most notably nitrosomonas and nitrobacter) work to convert ammonia (NH3) to nitrite NO2 and finally to nitrate NO3. In the aeration effluent  there is little to no ammonia present, as it has been converted to nitrate. Nitrate is a nitrogenous compound, however, and contributes to the amount of total nitrogen in the discharge.

 

 In order to decrease the total nitrogen, high nitrate aeration effluent is recirculated (mixed liquor return) back to the anoxic basins. The anoxic basins have mixers that mix these solids with the anaerobic effluent in basins that have a low dissolved oxygen (DO). The bacteria look for air to breathe and when they find none, they start stripping the oxygen molecules off the nitrate NO3, thereby causing nitrogen to be released as a gas and dissipated to the atmosphere. For this reaction to occur, there also needs to be a carbon source applied to the anoxic basins. Although this is an extremely simplified version of the denitrification process, when the anaerobic effluent doesn’t have enough carbon, it can supplement with methanol.

 

From there, sedimentation occurs in four round clarifiers. The solids that settle are pumped back to the aeration basin to allow the bacteria to continue to do their work. The clarifier effluent can run either to tertiary processes that help polish and disinfect the effluent prior to discharge, or it can be pumped to a small-footprint reuse system. The tertiary processes include an additional DAF unit to remove any solids that might still be present. DAF effluent is then filtered with four Fuzzy Filters, which utilize small proprietary media resembling small cotton balls.

 

 Disinfection is accomplished using a sodium hypochlorite feed just prior to using the Fuzzy Filters in order to maximize  time and to prevent bacteria buildup in the filters. The chlorinated filter effluent goes to a re-aeration basin to boost DO levels prior to discharge, and then sodium bisulfite is added to the reaeration basin effluent to dechlorinate. The last stage of treatment is UV disinfection – we have three banks of 10 modules with eight bulbs each, for a total of 240 UV bulbs – and treated water is then discharged to the Cape Fear River. If for any reason the effluent does not meet our permit requirements, we can divert the entire effluent flow to the effluent storage basin. This flow is then filtered and reintroduced to the WWTP for further treatment.

 

 We are also fortunate to have a reuse system that is capable of additional polishing up to 2 mgd of clarifier effluent for reuse in the WWTP in non-product contact areas. The system is designed after a small footprint surface water plant and is comprised of two flocculation tanks, to which alum and polymer are added; two lamella plate clarifiers; fuzzy filtration; and chlorine disinfection in a chlorine contact basin that allows for at least 30 minutes of detention time at design flow. This system also has the ability to polish up plant effluent for discharge into the receiving stream, when needed, to help meet treatment objectives.

 

 Due to the requirement for the reuse system to separate out sanitary streams, we have a small package WWTP that treats all of our sanitary (bathroom and cafeteria) waste, located next to the Tar Heel Facility WWTP. The waste solids from this unit are transported to a municipal facility to maintain this requirement, and the effluent is blended into our main plant final effluent just prior to disinfection. This unit was just replaced last year. We also have a state-certified lab that handles most of our lab needs.

 

Challenges and Unique Features

 With so many loops and further treatment options, any upset within the production facility or any upstream process effects everything downstream of that process, usually by applying more ‘food’ than the system is designed to handle. Sometimes this is a real balancing act, facilitated by many features that are unique to this plant. The effluent storage basin allows for us to send the entire plant flow to storage and further treatment in case of plant upset or issues. We recently acquired a DAF unit to polish clarifier effluent and decrease loading on our Fuzzy Filters. We also have the ability to utilize the reuse system to polish the effluent, if needed.

 

 Although not typically considered during a discussion of WWTP operations, we have found that our potable water supply can have a very large impact on wastewater operations – mainly due to temperature variances. The original deep-well system is comprised of eight source wells and provides water that is fairly consistent in temperature. In 2013, when the Bladen Bluffs Surface WTP was added as an additional water source, it was discovered that the significant seasonal temperature changes had the ability to impact wastewater treatment. If the water gets too cold or too hot, anaerobic activity becomes inconsistent and leaves the potential for ‘food’ to not get processed optimally.

 

 Additionally, ammonia conversion within the aeration system can be negatively affected. To mitigate potential issues, the temperatures are carefully monitored, sometimes with favor given to the well system water to buffer out these temperature variations.

 

Personnel

 Smithfield has been very proactive in training, certification, and cross training within all areas. Currently there are: 13 Grade IV Operators, three Grade II Operators, three Grade I Operators, six Land Application Operators, two Maintenance 2 Operators, two Collection 1 Operators, three A Well Operators, two B Well Operators, five C Well Operators, three A Surface Operators, five C Surface Operators, seven Physical Chemical 1 Operators, and two Collection System Operators.

 

Training

 Annually, Smithfield sponsors and participates in holding state-approved continuing education training classes in both water and wastewater subjects. Usually there are four classes per year, and these training events are open to outside participants for free. Three of the staff also actively participate in teaching at NC Water and Wastewater CE Training Classes and NC Water and Wastewater Certification Classes.

 

Awards

 • Timothy L. Weaver – Wilbur E. Long Industrial WWTP Operator of the Year 2010

• Robert “Buddy” Harris – Wilbur E. Long Industrial WWTP Operator of the Year 2013

• Ronald Mains – NCWOA C Well Operator of the Year 2013

• Dwayne Russ – NC AWWA-WEA Industrial WWTP Operator of the Year 2014

 

Contact Information

 Tim Weaver

Wastewater Superintendent

Tel: (910) 862-5248

tweaver@smithfield.com   


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