Septage, the liquid waste from septic systems, poses a very real problem: What do you do with it?
Many wastewater treatment plants have set up Septage Receiving Stations that accept and process septage. Septage is collected by liquid waste haulers that empty the septic systems and bring it to the septage receiving station for processing. The job of the receiving station is to remove the inorganic solids from the septage before passing the remainder as wastewater.
Septage receiving stations offer many benefits: to the plant, to the community, and to the environment.
- They are a revenue source for the plant.
- They offer a service to the community by offering a safe disposal alternative for waste that could pose a serious health hazard.
- They are good for the environment because the septage is screened, treated, and regulated.
However, septage requires special handling before it can be passed to wastewater treatment plants. This blog discusses the unique challenges for septage receiving stations.
Challenges with Septage
Septage poses a real challenge for wastewater plants because it is not the same as typical wastewater and can be the most difficult waste stream to a wastewater treatment plant. Concentrations of rocks, rags, grit, and FOG (fats, oils, and grease)can be as much as 30-100 times greater than those found in typical wastewater.
As a result, septage presents several unique requirements for the equipment used at septage receiving stations, such as:
- Variability of its contents between loads, from high rag content to large rocks to heavy concentrations of FOG, the equipment must be capable of handling the worst case in each category to ensure continued operation.
- When waste haulers pump out the contents of wastewater lift stations, the septage can have high concentrations of grit and FOG. This grit can contain anything from small grains of sand to large rocks. Large rocks can pose a hazard to equipment if they get caught in the system or damage equipment that was not designed to handle them.
- Waste haulers use gravity to empty their tanks. This means that, at the beginning of the tanker offloading process, there is a high flow and a high concentration of suspended solids, which can blind the screen and overload the compactor if the equipment is not properly sized to handle the sudden influx of material.
- Towards the end of the offloading process, the flow rate and the velocity are markedly decreased. This can result in grit accumulating in the dead spaces, which can cause damage to equipment.
- The high concentrations of fat, oil, and grease (FOG) can solidify and collect in pipes, resulting in blocked drains and equipment malfunctions.
- The high concentrations of nutrients can cause corrosion in the pipes and processing equipment that is not designed to handle them.
- Rags, the fibrous material that do not break down once they enter the wastewater system, can damage pumping equipment at wastewater treatment facilities and must often be removed manually.
- System components should also be resistant to grit, abrasives, and corrosion.
- Septage receiving equipment should be resistant to wear and tear, with replacement items such as brushes and screen elements minimized.
- Control systems should have interlocks to prevent tank overflow, automatic flushing, and system recovery. This will help automate the process and minimize human interaction with the septage.
- It is critical that large debris, such as trash, rags, and plastic cartons, are removed before they have a chance to clog or damage pumps, valves, and other downstream equipment. These items are removed by screens with openings of 6 mm (~0.25 in) or larger.
- The system should have the ability to grind up rocks, remove solid debris, and automatically flush tanks and screens to avoid damage to system components downstream. Removing solids from the influent removes most of the inorganic solids, making it possible for the remaining organic material to be broken down through microorganisms.
These challenges can cause reduced throughput, damaged screening, increased equipment wear, manual cleaning, equipment failure, and less revenue to the treatment facility.