© BUILDING FRAC TANK TREATMENT SYSTEMS

FRACair and Frac Tank Configurations for Treatment Systems

This section illustrates the many ways frac tanks, FRACair and appurtenances can be configured to create treatment systems. Frac tanks can be used to build treatment systems for landfill leachates, domestic and industrial wastewater, groundwater remediation, and water treatment. FRACair provides an economical and efficient means of providing aeration and mixing.

Frac tank rentals are available through a variety of rental entities including United Rentals, Rain for Rent, Adler, Evergreen, Ironclad, and other rental companies. Tank sizes range from 5,000 to 20,000 gallons with closed or open tops or weirs. Frac tanks are more accessible on short notice than complete mobile treatment systems.

RET can assist with bench-scale testing, design, and operational plans.

Step One

Determine the duration of treatment in months or years. Is the system going to be temporary or permanent? Temporary FRACair systems that operate for less than 1 year with the appropriate wastewater characterizations can be constructed out of less expensive parts than stainless steel used for permanent systems.

Step Two

Determine wastewater flowrates (average and maximum), variation of wastewater characteristics, and space available for frac tanks.

Step Three

Determine if continuous or batch treatment is appropriate.

Step Four

Determine Treatment Process Required: single unit operation treatment, plant pre-treatment for discharge to sanitary sewers, or complete treatment for discharge under a NPDES permit.

Single unit operations are situations when you only need one treatment process such as solids mixing, flow and concentration equalization, chemical addition, or biological treatment.  

Examples are: one operation is being renovated, upgraded, or cleaned in a wastewater treatment plant and a temporary system is required; additional capacity is required for flow increases or concentration equalization.  

Step Five

Can treatment be performed under an existing permit or is a new one required? Can existing plant operators operate or are additional ones required?

Temporary treatment systems generally require approved designs, sometimes pilot tests to demonstrate performance, regulatory and local approvals, and treatment plant operational plans. Emergency permits can be issued by regulatory authorities. Treatment permits need to be completed first as this the critical path in brining your system on line.

Step Six

Conduct Bench-Scale Treatability Tests to Confirm Treatment Selection & Design.

The order of testing depends on the matrix to be treated and past experience with similar waste streams. The objective is to develop a treatment process that requires the minimal number of unit operations and simplist/economical treatment process.  

Tests to be considered include:

▶ Select representative samples to conduct tests that includes worst case concentrations and flowrates

▶ Determine if pH adjustment is required.

▶ Test if air stripping will remove volatiles

▶ Conduct gravitational setting and clarification tests using gravity setting. If unsuccessful, then go to next step

▶ Conduct non-shear coagulant clarification tests that can be added during aeration mixing that won't break apart floc formation during clarification such as FeCL3, CaCl2, powdered activated carbon, bentonite, lime, polyaluminum chloride/polyaluminum hydroxychloride, and other additives. If additional clarification is required then go to next step.  

▶ Conduct shear prone coagulant additives that require controlled mixing by post aeration inline or serpentine addition to prevent breaking floc appart during clarification. These coagulants include; alum, super floc cationic polymers, and others.

▶ Determine if post clarification treatment is required to further reduce target contaminants which include, filtration, granular activated carbon, ion exchange, dissolved air floatation, or additional coagulant treatment.

▶ Dissolved Air Floatation (DAF) can be simulated (frequently 65% effective) by using fine bubble aeration using FRACair and may be pilot tested.

▶ Determine if biological treatment such as activated sludge, PACT, alone or in combination with physical chemical treatment is required. Note that this type of testing takes considerable longer, requires seeding of biological media, and time to consider the efficacy of biological treatment.

▶ Specialized Treatment for Difficult to Treat Waste streams

PACT Treatment (Powdered Activated Carbon Treatment) sometime with the addition on non-shear coagulants can treat difficult wastewater and can be mixed by aeration.

Advantages

▶ Improves removal of refractory and toxic organic compounds

▶ Reduces shock loads and toxic influent spikes

▶ Enhances COD and BOD removal

▶ Improves color and odor removal

▶ Improves sludge settling characteristics

▶ Adsorbs compounds for microorganisms to biodegrade

How It Works

▶ Wastewater enters the aeration basin.

▶ PAC is added to the mixed liquor.

▶ Organic contaminants adsorb onto the PAC.

▶ Microorganisms biodegrade adsorbed and dissolved organics.

▶ PAC reduces biomass toxicity.

▶ PAC and biological solids are removed in the secondary clarifier.

For landfill leachate applications, PACT systems have often been used where ammonia has already been addressed or where difficult-to-treat COD, color, and trace organics require additional treatment beyond conventional biological processes.

PAC serves as a bacterial attachment surface for microbial attachment for nitrification similar to fixed bed biological reactors without filling the entire reactor with film forming media. The PACT process was is widely used for difficult industrial wastewater such as:

▶ Petrochemical wastewater

▶ Landfill leachate

▶ Coke plant wastewater

▶ Textile wastewater

▶ Pharmaceutical wastewater

Step Seven

Based on treatability tests design the frac tank treatment system.  

Step Eight

1. Determine Tank Configurations

1a. Manifolding Tanks

Connecting multiple frac tanks together provides larger volumes for treatment. Tanks need to be on level ground to ensure liquid levels remain the same in each tank.

Connection options include: manifolding tank outlets in the fromt or rear of each frac. A valve should be placed on each outlet prior to connections to a common pipe to provide even flows to the next treatment module.

1b. Connecting Tanks in Series

Tanks can be connected with gravity overflow connections or by pump transfers. Transfer rates between tanks requires determination of flow rates and retention times to achieve the desired treatment efficacy.

1c. Tank Wastewater Inlets

Tank inlets can be through the 22" open top manifolds or the 4" inlet valves located on the front of the frac tank.

1d. Tank Wastewater Discharges

Wastewater Discharges can be through the 4" drain line located behing the rear wheels of the frac tank or through a suction line placed through the top manhole. Removal via the 4" drain line is typically for complete mixed wastewater or sludge removal.  

Removal through the top manhole is for removal of clarified liquids. Use of a floating skimmer is sometimes used to remove floating matrices. Floating decanters with a 18" drop tube facilitates removal of clarified liquids while minimizing sludge removal.

Positioned drop hoses through the top manhole with a check valve can be use to withdraw clarified liquids but is prone to pick up more settled solids than a floating decanter. Both the floating decanter and drop hoses require pumps that can pull the required suction lifts and stay primed. Diaphragm pumps are ideal for this purpose since they can run dry and wet.

2. Type of Tank Connections

2a. Air & Wastewater

2a.1 Open top Manole Connections - adjustable manhole bridges, grating mounts for open top fracs, lifting lugs for open fracs without top gratings.

2a.2 Closed Tank Connections - flange mounted top or front side connections.

2b. Piping Supports - Tank, overhead, and ground pipe supports are illustrated below.

3. Liquid Level Monitoring (Sight Gages) - manual sight gages can be attached to full size or mini frac tanks as illustrated below.

4. Pump Types - transfer pumps and chemical feed pumps.

4.1 Pump & Feed Controls - level switches, pH controllers, dissolved oxygen controllers, chemical feed controllers.

5. Flow Monitoring - manual read flow meters or digital recording flow meters.

6. Blower Selection - plant air (usually not cost or supply effective as may reduce plant air demand), rotary lobe or two stage regenerative blowers (depends on amount and pressure of air to be delivered to FRACair system (see Design Criteria) ➡.

7. FRACair Magnetic Aeration System - (see FRACair Magnetic Aeration Treatment Section) ➡