3.5 Root, Grease & Debris Management

Root, Grease & Debris Management

Quick Answer: Root intrusion and Fats, Oils, and Grease (FOG) are the two leading causes of collection system stoppages and SSOs. Mechanical root saws provide immediate clearance, while chemical foaming herbicides provide 2- to 3-year residual control. Grease blockages require high-velocity hydro-jetting and source enforcement; chemical degreasers and enzymes are prohibited because they transfer grease downstream.

Maintaining free-flowing collection systems requires proactive management of tree roots, grease, mineral encrustation, and solid debris. Operators must understand the biological mechanisms of root intrusion, the chemical properties of grease saponification, and the regulatory limitations governing chemical additives.

---

1. Root Intrusion Mechanisms & Biology

Tree and shrub roots do not break healthy, sound pipes directly. Instead, microscopic hair roots (<0.1 mm diameter) enter through existing vulnerabilities:

• Unsealed or deteriorated mortar joints in vitrified clay or concrete pipe
• Displaced or deteriorated rubber compression gaskets
• Defective, cracked, or improperly tapped service lateral connections
• Structural stress fractures and abandoned connections

                  ROOT INTRUSION & REGROWTH CYCLE

   (1) HAIR ROOT ENTRY          (2) PROLIFERATION            (3) PIPE RUPTURE
   Vapor / Nutrients            Dense Root Tail             Girth Expansion / Fracture
   +-----+  +-----+             +-----+  +-----+            +--+       +--+
   |     |  |     |             |     |  |     |            |  |       |  |
   |     |\ |     |             |    {}} |     |            |  |  {}   |  |
   |     | \|     |             |   {{}}}|     |            |  | {{{{}}|  |
   |     |  |     |             |    {}} |     |            |  |  {}   |  |
   +-----+  +-----+             +-----+  +-----+            +--+       +--+
   (Follows moisture)          (Traps solids/FOG)          (Hoop stress splits pipe)

Once inside the moist, nutrient-rich sewer atmosphere, the root thrives. It develops a fine root "tail" or curtain that catches passing toilet paper, sanitary products, and grease. As the root expands in diameter, it exerts immense circumferential hoop stress, widening joints, shearing pipe bells, and eventually collapsing the pipe wall.

---

2. Mechanical vs. Chemical Root Management

+-------------------------------------------------------------------------+
|                 ROOT CONTROL METHODOLOGY COMPARISON                     |
+-----------------------+---------------------+---------------------------+
| Parameter             | Mechanical Cutting  | Chemical Foaming          |
+-----------------------+---------------------+---------------------------+
| Tooling               | Hydraulic root saw, | High-expansion foam       |
|                       | chain flail         | applicator (14:1 to 20:1) |
| Active Agent          | Physical steel blade| Metam-sodium + Dichlobenil|
|                       |                     | or Diquat dibromide       |
| Immediate Flow Relief | Immediate (100%)    | Delayed (roots decay over |
|                       |                     | several weeks)            |
| Regrowth Window       | Rapid (dense regrowth| Extended residual control |
|                       | in 6 to 9 months)   | (2 to 3 years)            |
| Labor Requirement     | High; frequent cycle| Moderate; multi-year cycle|
+-----------------------+---------------------+---------------------------+

The Pruning Paradox of Mechanical Cutting

Mechanical root cutting is essential for emergency stoppage relief. However, cutting a root inside a pipe acts like pruning a hedge: it stimulates plant growth hormones (auxins), causing the root stump to branch aggressively into a denser, thicker root mass within 6 to 9 months. Mechanical cutting alone is a short-term holding action, not a long-term solution.

Chemical Herbicide Foaming Mechanism

To prevent rapid regrowth, utilities apply EPA-registered chemical herbicides formulated specifically for sewer mains:

1. Active Ingredients:
   • Metam-Sodium: A fast-acting contact herbicide that destroys root cellular structure within hours.
   • Dichlobenil: A systemic residual growth inhibitor that binds to organic material and pipe joints, preventing root cell division for 2 to 3 years.
   • Diquat Dibromide: A non-volatile contact desiccant used as an alternative contact killer.
2. Foaming Application: The liquid herbicide is mixed with a foaming surfactant and compressed air. The generated foam expands 14:1 to 20:1, completely filling the pipe barrel from invert to crown. This ensures the chemical coats roots hanging from the top and sides of the pipe that liquid spraying would miss.
3. Environmental Protection: Properly applied chemical foam kills only the root tissue inside and immediately adjacent to the pipe joint without translocating to damage the tree above ground or disrupting biological treatment processes at the downstream wastewater treatment plant.

---

3. Fats, Oils, and Grease (FOG) Management

FOG is discharged into collection systems from food service establishments (FSEs) and residential kitchens. When warm grease enters sewer mains, it cools and undergoes a complex chemical transformation:

$\text{Fats/Grease (Triglycerides)} + \text{Calcium Ions (from concrete/water)} \longrightarrow \text{Calcium Soap ("Fatbergs")}$

                       FOG DEPOSITION IN GRAVITY SEWER

            Pipe Crown
      +-------------------------------------------------------------+
      |   Air Headspace (H2S Gas Corrosion Zone)                    |
      |                                                             |
      |   +-----------------------------------------------------+   |
      |   | Hardened Calcium Soap Collar (Fatberg Encrustation) |   |
      |   +-----------------------------------------------------+   |
      |                                                             |
      | ~ ~ ~ ~ ~ ~ ~ ~ ~ Normal Wastewater Flow ~ ~ ~ ~ ~ ~ ~ ~ ~ ~|
      |                                                             |
      |=============================================================|
      | Settled Silt, Sand, and Grit Bed                            |
      +-------------------------------------------------------------+
            Pipe Invert

Saponification and "Fatbergs"

Free fatty acids react with calcium ions (leached from concrete sewer pipe or hard water) through saponification, creating insoluble, rock-hard calcium soap deposits. These deposits adhere firmly to pipe walls, reducing hydraulic capacity until total blockage occurs.

The Prohibited Use of Degreasers, Solvents, and Enzymes

Exam Key Point: Most municipal sewer ordinances and state regulations strictly prohibit the addition of chemical emulsifiers, solvent degreasers, or biological enzyme additives to collection systems to clear grease.

Why are enzymes and degreasers prohibited?

• Enzymes and solvents do not destroy grease molecules; they merely break the grease into a temporary liquid emulsion.
• As the emulsified grease travels downstream, the chemical dilutes, the temperature drops, and the grease re-solidifies in downstream interceptors, pump station wet wells, and pump impellers.
• It shifts a localized problem into a catastrophic system-wide failure at lift stations and treatment plants.

Correct FOG Remediation

• Physical Jetting: High-velocity hydraulic jetters equipped with spinning rotary nozzles (e.g., Warthog nozzles) to cut and peel grease collars from the pipe wall.
• Source Control (FOG Ordinances): Mandating indoor grease traps and outdoor gravity grease interceptors (minimum 750–1,500 gallon capacity) at food service establishments, enforced through regular pumping inspections (the "25% Rule": interceptors must be pumped when combined grease and solids exceed 25% of total liquid depth).

---

4. Chemical Foam Volume Calculation

Operators must calculate the volume of chemical foam required to treat a sewer pipe segment based on pipe diameter and length:

$\text{Pipe Volume (gal)} = \frac{\pi \times D^2 \times L}{4} \times 7.48$

Where $D$ is pipe diameter in feet, and $L$ is length in feet. Simplified formula:

$\text{Pipe Volume (gal)} = D^2\text{ (inches)} \times 0.0408 \times L\text{ (feet)}$

Worked Example: Calculate the volume of chemical foam required to treat a 300-foot section of 8-inch vitrified clay sewer line.

$\text{Volume} = (8)^2 \times 0.0408 \times 300$ $\text{Volume} = 64 \times 0.0408 \times 300 = 783.4\text{ gallons of foam}$

If the foaming machine generates a 20:1 foam expansion ratio, the required liquid chemical concentrate mixture is:

$\text{Liquid Mixture Needed} = \frac{783.4\text{ gal}}{20} = 39.2\text{ gallons of liquid solution}$