Sludge removal is a key part of wastewater treatment. A by-product coming from the various treatment processes needed to maintain a treatment plant, sludge management is one of the most expensive burdens many plants will have.
Sludge removal is not as easy as it may sound. Management of this by-product commonly requires multiple steps including thickening, treatment, hauling, and disposal, all of which need labor and other expenses to complete.
The costs of sludge management easily account for a large portion of the total WWTP operating cost and can be as much as 35% of the capital costs of new plants and plant upgrades. When it comes to sludge reuse, the numbers aren’t too promising either. Less than 1/3 of all sludge produced in the United States is used for some beneficial purpose (e.g., land application for crops, energy generation, etc) – the rest is carted off to landfill or incinerated.
You can imagine that the carbon footprint of dealing with all of this sludge is enormous - there are an estimated 15,000 US wastewater treatment plants and all of them have to treat and deal with sludge.
Due to high sludge management costs and the availability of disposal sites, we believe it is vital to find new ways to reduce sludge production. Here are some of the best ways to tackle sludge in wastewater treatment today:
Understanding The Role Of The Sewer Network
You can picture the sewer collection system as being a smaller version of a treatment plant itself, even offering the same biological opportunities. As wastewater travels through the sewer, small amounts of the organic material (as measured by Chemical Oxygen Demand or COD) are made more soluble by certain types of beneficial bacteria present in the waste stream.
Part of the organic material they feed off of is readily biodegradable, (rbCOD), some of it can be biodegraded relatively quickly (fhCOD), and some of it takes a great deal of time to solubilize (sbCOD).
When normal sewer conditions are present, the bacteria present are not enough to make a difference in these ratios, especially when dealing with the changing environment they find on the way.
How The Sludge Forms
The sludge formed from sewage is a by-product of wastewater treatment. When waste and stormwater go into the sewage collection system, the solid wastes are separated from the liquid ones.
At this point of the process, the materials are digested and processed by the bacteria that naturally form part of the system.
The processed solids are what make up sewage sludge as we know it, and will usually contain hazardous materials that include household, medical, and other industrial waste.
Sludge Treatment Methods
As mentioned earlier, the treatment of sludge will make use of thickening, digestion, and other processes before being ready for disposal. Here is a closer look at each step and what it does:
Step 1: Thickening
The first step the sludge will undergo is thickening. This is because it can be more impractical to deal with sludge if it’s too thin in consistency.
Thickening helps suspend any remaining solids in the wastewater sludge and happens in a special piece of equipment known as a gravity thickener. This tank-like machine reduces the volume of the sludge to less than half, effectively thickening it.
Another approach makes use of a process known as dissolved air flotation. This step sees air bubbles injected into the mixture, which carries the solids to the surface of the wastewater where the thickened sludge then forms.
Once thickened, the sludge can move on to the next step: digestion.
Step 2: Digestion
The next step is the biological process known as digestion. Sludge digestion sees the solids in the mixture be decomposed into more stable materials. Digestion effectively decreases the size of the solids while also targeting pathogens and other hazardous materials.
Digestion also preps the sludge for dewatering or drying. By this point of the process, the digested sludge takes on the appearance of potting soil.
The majority of bigger sewage treatment plants make use of a two-stage system when it comes to digesting sludge. The first part of the process has the sludge, now thickened and dried, is heated and enclosed in a special container for several days.
Special bacterias and enzymes within the heated mixture break down larger molecules like proteins into smaller molecules that are easier to process such as fatty acids. Once complete, the sludge is directed to a second tank where there is a conversion into biogas. The biogas, a mixture of carbon dioxide and methane, can then be used as fuel to heat the digestion tank or even generate power for the treatment plant.
The bacterial digestion taking place during this step is sensitive to temperature changes and acidity, as well as other environmental circumstances. This means this process needs careful control and monitoring to stay consistent.
Step 3: Dewatering
The digested sludge goes into step three where it is completely dewatered. The term ‘dewatered’ can be slightly misleading - the mixture will still contain some water after this process, but it has reduced enough for the sludge to act as a solid material.
The most common method of dewatering is known as a sludge-drying bed. The digested sludge mix is spread evenly over open sand beds where they stay until considered dry. The actual drying takes place through a combination of gravity and evaporation powered by the sand.
After about six weeks of drying, the sludge mixture can then easily be removed with a front–end loader.
In wastewater treatment plants where space constraints are a concern, a rotary drum vacuum filter may be used in conjunction with other machines.
Step 4: Disposal
After undergoing all the steps above, the sludge is then safely disposed of in a sanitary landfill site. The sludge may also be reused in certain agricultural situations as a soil fertilizer. The caveat is that the sludge may still contain some remnants of risky chemicals, and so it is typically not spread on land used for crops aimed at human consumption.
If soil disposal isn’t an available option, incineration might be used. Here the dried sludge mixture is reduced to ash which is easier to dispose of. The disadvantage of this approach is that it can contribute to air pollution if not carefully managed and monitored.
The In-Pipe Approach
In-Pipe Technology custom engineers the right treatment solution for each customer.
Strategic dosing locations are chosen at the outset of the project by our engineering staff. During installation and subsequent microbe reloads, each dosing location is evaluated and its state is documented (i.e., accumulation of FOG, excessive odor, etc.). Taking this information into consideration, the engineering and microbiology teams at IPT can make adjustments to the microbe blend at any location during the project in order to more effectively treat the specific situation at that location. Additionally, we provide reports highlighting potential problems observed during our field service so that we can proactively address potential problems.
In short, our solution changes the game. Some of the most adaptable and efficient bacteria on earth come from the soil.
Just think about it: billions of years of evolution of one of the most basic life forms, in an environment that is changing all the time. Our specialized blend of the most efficient types of these bacteria thrives in any environment found in the sewer, going to work on the nutrients in the waste stream with or without oxygen, using nitrogen if that’s available – and under a wide range of temperature and pH conditions.
We continuously (24/7/365) dose high concentrations of these non-pathogenic, facultative, spore-forming bacteria throughout the entire sewer network with small, self-contained, and battery-powered dosing units, using the time it takes for the waste to travel to the plant to make much more of it soluble and biodegradable.
Our service is specifically tailored to each collection system, taking into account the size and complexity of the collection system, and the detailed operating profile of the treatment plant. We supply equipment and bacteria, and service and refill the installed dosing system – completely turnkey - for a flat monthly fee. In many cases, the cost savings generated from a reduction in sludge pays for our service in 12 months or less.
It doesn’t have to cost more either. You already the infrastructure to start doing this today – with zero additional capital costs. In fact, IPT’s approach can likely help you reduce the costs of managing sludge by as much as 30%!
Contact us today to find out how our custom solutions can transform your treatment plant’s sludge solution - it’s better for the environment, the budget, and you.